Pharmacological Research 55 (2007) 560–569

Review

The aging brain, a key target for the future:The protein kinase C involvement

Alessia Pascale a,∗, Marialaura Amadio a,Stefano Govoni a, Fiorenzo Battaini b

a Department of Experimental and Applied Pharmacology, University of Pavia, Pavia, Italyb Department of Neurosciences, University of Roma “Tor Vergata”, Roma, Italy

Accepted 16 April 2007

Abstract

The brain represents the primary centre for the regulation and control of all our body activities, receiving and interpreting sensory impulses andtransmitting information to the periphery. Most importantly, it is also the seat of consciousness, thought, emotion and especially memory, being infact able to encode, store and recall any information. Memory is really what makes possible so many of our complex cognitive functions, includingcommunication and learning, and surely without memory, life would lose all of its glamour and purpose. Age-associated mental impairment canrange in severity from forgetfulness at the border with pathology to dementia, such as in Alzheimer’s disease. In recent years, one of the mostrelevant observations of research on brain aging relates to data indicating that age-related cognitive decline is not only due to neuronal loss, aspreviously thought; instead, scientists now believe that age-associated functional changes have more to do with the dysfunctions occurring overtime. Within this context a prominent role is certainly played by signal transduction cascades which guarantee neuronal cell to elaborate coordinatedresponses to the multiple signals coming from the outside and to adapt itself to the environmental changes and requests. This review will focusthe attention on protein kinase C pathway, with a particular interest on its activation process, and on the role of protein–lipid and protein–proteininteractions to selectively localize the cellular responses. Furthermore, information is emerging and will be discussed on the possibility of mRNAstabilization through PKC activation. This review will also approach the issue on how alterations of these molecular cascades may have implicationsin physiological and pathological brain aging, such as Alzheimer’s disease.

© 2007 Elsevier Ltd. All rights reserved.

Keywords: Aging; Brain; PKC; RACK; ELAV; Signal transduction; Memory and Alzheimer’s disease

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5612. PKC: structure information and regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561

2.1. Diversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5612.2. Phosphorylation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5612.3. Pseudosubstrate interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5622.4. Subcellular localization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 562

3. Aspects within the PKC activation pathway: anchoring proteins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5634. Emerging aspects within the PKC activation pathway: ELAV proteins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563

5. PKC and neuronal rescue/survival . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5646. The aging-associated memory impairment: PKC as a key actor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5647. Pathological aging and PKC: the example of Alzheimer’s disease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5658. Interventions on PKC signalling in physiological and pathological aging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 566

∗ Corresponding author. Tel.: +39 0382 987 963; fax: +39 0382 987 405.E-mail addresses: alessia.pascale@unipv.it (A. Pascale),

battaini@med.uniroma2.it (F. Battaini).

1043-6618/$ – see front matter © 2007 Elsevier Ltd. All rights reserved.doi:10.1016/j.phrs.2007.04.013

A. Pascale et al. / Pharmacological Research 55 (2007) 560–569 561

9. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 566. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567. . .

1

aagvtoocsrstdinorttgdfmwtn[imcgrkfaa(

2

2

speir

eaC

ammpbtCtanap

plP

2

a(fstiPmirtp“oioitn“(cb

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. Introduction

In recent years science and technology have made big steps,llowing us to greatly improve knowledge in basically everyspect of biology, culminating in the mapping of the humanenome. However, although the brain is considered our mostital organ, the essence of personality and memory, much abouthe human brain still remains a mystery. Up to the second halff the 80s, neuroscientists thought that the brain was inex-rably losing neurons with age, ultimately leading to seriousognitive deficits. In fact, morphological analyses seemed toupport the idea that senescence was accompanied by neu-onal loss, particularly evident in the cortical and hippocampaltructures [1]. The remaining neurons compensated this deficithrough an increased dendritic sprouting, at least until theegeneration did not exceed a certain threshold [2]. However,nvestigations based on stereological techniques, suggested thateuronal loss was much less important than what was previ-usly believed [3]. Within this context, the finding that oldats, showing a reduced performance in the Morris maze spa-ial task, do not present any hippocampal (the hippocampus ishe brain area mainly implicated in spatial orientation) neurode-eneration [4] further supports the concept that the cognitiveecline that occurs with normal aging may be rather due tounctional changes, such as those involving cell-to-cell com-unication and signal transduction mechanisms [5,6]. Alongith this idea, a growing number of observations indicates

hat age-associated alterations involve a broad spectrum ofeurotransmitter systems and their related signalling pathways7–10]. Overall, these changes are responsible for an alterednterneuronal communication that can represent, rather than

orphological modifications, the primum movens leading toognitive decline. Considering that protein kinases play a strate-ic role aimed to convert the extracellular signals into biologicalesponses, it is logic to hypothesize that functional alterations oninases may directly contribute to age-dependent neuronal dys-unctions. At brain level, among the different protein kinases,nd especially for its key involvement in memory processes,great interest has always been addressed to protein kinase C

PKC).

. PKC: structure information and regulation

.1. Diversity

Several specific extracellular signals target selected cellurface receptors leading to the hydrolysis of membrane

hospholipids via Phospholipase C activation with the gen-ration of two second messengers: diacylglycerol (DAG) andnositol 1,4,5-trisphosphate (IP3). IP3 triggers the subsequentelease of calcium (Ca2+) from the intracellular store—the

Ptfr

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567

ndoplasmic reticulum. Ca2+ and DAG are implicated in thectivation of a specific family of kinases named protein kinases.

The serine/threonine PKC family is ubiquitously expressednd involved in multiple neuronal functions able toodulate short—(neurotransmitter release and ion fluxes),id—(receptor regulation), as well as long-term processes (cell

roliferation, synaptic remodelling and gene expression). So far,ased on the selective sensitivity to the second messenger activa-ors Ca2+ and DAG, at least 10 isoenzymes have been described.a2+ and DAG are in fact required to fully activate the conven-

ional or calcium-dependent cPKCs (�, �I, �II, and �); DAGlone completely stimulates the calcium-independent or novelPKCs (�, �, �, and �); finally, the atypical aPKCs ( and /�)re both Ca2+- and DAG-independent [11] but sensitive to otherhospholipids [12].

Correct PKC signalling requires three consecutive steps:hosphorylation, pseudosubstrate exposure, and subcellularocalization. Interference in any of these steps results in derangedKC signalling.

.2. Phosphorylation

The primary aminoacidic structure of PKC, deduced fromvailable cDNA sequences, comprises four conserved domainsC1–C4) separated by five variable regions (V1–V5). C1–C2orm the regulatory portion of each enzyme, interacting with thepecific activators, while C3–C4 represent the catalytic regionhat is implicated in intrastructure phosphorylation, kinase activ-ty and substrate binding (see Fig. 1). In the native stateKC is considered “immature” and it is associated with theembrane as an unphosphorylated form [12]. The first step

mplicated in the maturation process of each isoenzyme, alsoepresenting the rate-limiting step of the whole process, ishe phosphorylation on threonine residues, mediated by the 3-hosphoinositide-dependent protein kinase-1 (PDK-1), at PKCactivation loop” in the C4 region (see Fig. 1). The importancef PDK-1 for native PKC is underlined by investigations show-ng that the deletion of PDK-1 dramatically decreases the levelsf “mature” PKCs, consistent with the notion of their instabilityn the non-phophorylated form [13]. PKD-1 phosphorylationriggers then the autophosphorylation on serine and/or threo-ine (depending on the isozyme) of the “turn motif” and thehydrophobic motif” of PKCs, always within the C4 regionsee Fig. 1; reviewed in Ref. [12]). Structural studies indi-ate that, following these phosphorylations, each isoenzymeecomes “catalytically” competent and stable. At this point

KC is considered “mature” and can be released in the dis-

inct subcellular compartments or in the cytosol, as inactiveorm, ready to respond to specific activators [12]. Phospho-ylation is thus a rate-limiting step in the PKCs modulation

562 A. Pascale et al. / Pharmacological Research 55 (2007) 560–569

Fig. 1. (A) DAG, Ca2+ and PS are important factors in the activation mechanism of PKC, allowing it to assume its “unfolded active conformation”. The figure showsthe organization of a general conventional PKC as a model (note that RACK1 interacts also with the V5 region of PKC�II-not shown [94]). The activated enzyme canthen translocate to different subcellular compartments taking part to multiple cellular functions, such as neurotransmission, synaptic remodelling, cell proliferation,translation, etc. Anchoring proteins (i.e. RACK1 for PKC�II) have been documented to be also implicated in the translocation process. (B) Alterations/reductions(arrow down) in any of these actors can induce a deregulation of the mentioned pathways leading to some of the changes occurring in physiological or pathological (i.e.Alzheimer’s disease) aging. Ca2+: calcium; DAG: diacylglycerol; PS: phosphatidylserine; SB: substrate; P1: phosphorylation at the “active loop”; P2: phosphorylation

add

2

tibtts[

mltiwHnlm

wao

at the “turn motif”; P3: phosphorylation at the “hydrophobic motif” (see text for

preceding the regulation by lipid physiological activators. Fur-ther phosphorylations on serine/threonine and tyrosine residuescan additionally regulate the function of “mature” PKCs[14].

2.3. Pseudosubstrate interactions

All the different isoforms share a high degree of homologyat the catalytic domain. The C1 region bears the pseudo-substrate sequence followed by one (in atypical) or two (inconventional and novel) cysteine-rich sequences occupying thephosphatidylserine (PS) and DAG/phorbol esters (i.e. PMA)docking-sites. The pseudosubstrate sequence keeps the enzymein the inactive form (“folded conformation”) until the inter-action of PKC with the physiological activators triggers theactivation of the enzyme by opening the “folded conformation”reducing the affinity of the pseudosubstrate for the catalyticdomain, which becomes then free to exert its phosphorylat-ing activity. The C2 region is present in both the cPKCs andnPKCs. In the cPKCs this sequence bears the Ca2+ binding-site, while the nPKCs are not responsive to Ca2+ because ofthe lack of aminoacids essential for the interaction with thision, and for this reason is named C2-like domain: in thiscase, the recruitment to the membrane depends on the C1

region characterized by a higher affinity for phospholipids (incomparison with cPKCs) [15]. Finally, C3 contains the ATPbinding sequence, while C4 bears the substrate docking-site[16].

Pddm

itional details).

.4. Subcellular localization

The activation mechanism is associated with the transloca-ion of PKC from the cytosol (or other locations) to differentntracellular compartments [17,18], and this process is regulatedy anchoring/scaffolding proteins dictating correct spatio-emporal distribution of PKC (see following chapter). Theranslocated enzyme has been related to the phosphorylation ofpecific substrates, ultimately leading to the functional response19,20].

Following PKC activation, phosphatases take part in thisolecular cascade by turning off the signal via dephosphory-

ation. The extinction of the response is in fact guaranteed byhe dephosphorylation of both the substrates and/or the enzymetself. It seems that in the dephosphorylated state PKC interactsith the molecular chaperone Heat Shock Protein 70 (Hsp70).sp70 stabilizes the C kinase that can be recycled back as solubleewly reactivable enzyme; preventing PKC/Hsp70 associationeads, instead, to the interaction of PKC with cytoskeletal ele-

ents and its eventual down-regulation by proteolysis [12,21].The cleavage, via Ca2+-activated proteases (i.e. calpains),

ithin the hinge region (V3) located between the regulatorynd the catalytic domains, generates a constitutively active formf all PKCs lacking the N-terminal regulatory domain named

KMs. To date, only the PKM has been described in someetail, being stably expressed together with PKC indepen-ently on calpains action and having an involvement in memoryolecular mechanisms (i.e. hippocampal long term synaptic

gical

p6

3a

pTsttpo[ddRa

dbfhPvoawpRcts[tiastsfipovcmosiAotRo

i

pafs

dtpaattw

4p

ampttmgbit3eTo[(tocEvnso

sP(iancaPb

A. Pascale et al. / Pharmacolo

otentiation maintenance) [22] (see later discussion in Section).

. Aspects within the PKC activation pathway:nchoring proteins

As previously mentioned, the interaction of PKC with itshysiological stimulators allows the activation of the enzyme.he redistribution/translocation of PKC from one to anotherubcellular compartment was initially thought to reflect onlyhe interaction between PKC and lipids. However, studies onrypsin sensitivity underlined the implication also of anchoringroteins within this process, indicating the additional relevancef protein–protein interactions in the PKC activation cascade23]. In fact, several proteins can bind inactive and active PKCsictating enzyme location in both basal and stimulated con-itions [18,24,25]. In this regard, a special place is taken byeceptors for Activated C Kinase (RACKs) in localizing thectivated PKCs close to the pertinent substrates [26–29].

RACKs are intracellular scaffolding proteins originallyescribed in rat heart by Mochly-Rosen et al. [23]. RACKselong to the tryptophan-aspartate 40 (WD40) motif repeatamily regulating protein–protein interactions and they areomologous to the �-subunit of heterotrimeric G-proteins.KC/RACKs interaction depends on the presence of PKC acti-ators in a specific manner [23,30], suggesting the critical rolef RACK proteins in directing the relocation of PKC after itsctivation. The in vivo implication of RACKs in PKC functionas initially documented by investigations performed on Xeno-us oocytes [31]. The synchronous relocation of PKC�II andACK1, following stimuli known to activate PKC, was furtheronfirmed in cardiac myocytes [32] and in CHO cells [33]. Onhe other hand, in rat astrocytes PKC�II did not redistributeynchronously with RACK1, following phorbol esters treatment34]. Furthermore, the amount of membrane-associated PKC�IIhat co-immunoprecipitated with the membrane-bound RACK1ncreased following phorbol esters exposure, suggesting a post-ctivation binding of the two proteins at membrane level. Thistudy indicates that an intermediate interaction of PKC�II withhe actin-cytoskeleton takes place, suggesting that, at least withinome transduction pathways, PKC may translocate, via actinlaments, to different pools of RACKs located in distinct com-artments [34]. In agreement with these findings, functional datan chromaffin cells show that the interaction of F-actin with acti-ated PKC� and � via RACK1 is crucial for the potentiation ofatecholamine release by phorbol esters [Ohara-Imaizumi et al.,anuscript in preparation]. These data indicate that, depending

n cell type, RACK1 may behave either as a membrane anchor orhuttling protein for activated PKC. It is believed that each PKCsozyme may have its specific RACK or anchoring protein [35].long this line one of the more fascinating and promising aspectsf the studies on RACK proteins is the observation that pep-ides interacting with consensus sequences between PKCs and

ACKs can be utilized to pharmacologically modulate (activater inhibit) in vitro and in vivo specific PKC isozymes [26,27].

RACK1 has also other non-PKC-related anchoring functionsn respect to other signalling networks (PLC�, cAMP phos-

maOo

Research 55 (2007) 560–569 563

hodiesterase, src kinase, ras-GAP, excitatory and inhibitoryminoacid receptors, and others) making it a coordinator of dif-erent cellular functions [28] as well as a regulator of neuronalurvival [36,37].

Together with RACKs, other scaffolding proteins have beenocumented to be also implicated in PKCs compartmentaliza-ion: proteins that interact with C kinase (PICKs; PICKs areerinuclear proteins interacting with the catalytic site of PKC)nd substrates that interact with C kinase (STICKs which arelso PKC substrates). Although these anchoring proteins bindo different sites within PKC structure, the common function iso recruit the different PKCs within specific signalling networkshere they can influence selected cellular functions [25,38].

. Emerging aspects within the PKC activationathway: ELAV proteins

Long lasting changes occurring in selected cellular domainsre often the result of protein synthesis reprograms that ulti-ately lead to modifications in the content of a given gene

roduct and the related protein, via events affecting nuclearranscription and/or the fate of the transcribed mRNAs. Withinhis context, post-transcriptional processes, and in particular

RNA decay modulation, are emerging as key controllers ofene expression (reviewed in: [39–41]) and are documented toe crucial for the localized changes in the amount of proteinsmplicated in several cellular functions. More than one out ofwenty human genes bear a characteristic motif found in the′-untranslated region (3′-UTR), called Adenine Uridine-richlement (ARE) that governs the decay rates of these mRNAs.he ARE sequence is responsible for the rapid degradationf these mRNAs that include many early responsive genes42], and represents the docking site for RNA binding proteinsRBPs). Some RBPs act on this determinant and increase, post-ranscriptionally, the cytoplasmic stability and rate of translationf the ARE-bearing mRNAs in response to the environmentalell signals. So far, the best-described ARE-binding RBPs areLAV proteins, or Hu antigens (reviewed in Refs. [43,44]). Inertebrates, HuB, HuC and HuD are selectively expressed ateuronal level (nELAVs), while HuR is ubiquitously diffused;tructurally all four proteins are characterized by a high homol-gy within their sequence (70–85%).

We recently demonstrated that ELAV proteins can also repre-ent one of the final targets of the signalling pathway involvingKC, resulting in the stabilization of ARE-bearing mRNAssee Fig. 2; for a review see also Ref. [45]). In fact, employ-ng SH-SY5Y human neuroblastoma cells as a cellular model,nd focusing our interest on the well described modulation ofELAVs on the ARE-bearing GAP-43 mRNA, a gene impli-ated in synaptic remodelling [46–48], we showed that nELAVsre up-regulated and redistributed following treatment with theKC activators phorbol 12-myristate 13-acetate (PMA) andryostatin-1 (a DAG-mimicking compound). The same experi-

ental conditions promoted the stabilization of GAP-43 mRNA

nd induced an early increase in GAP-43 protein amount [49].verall, these findings allowed us to document the primary rolef PKC in the cascade of nELAVs recruitment, ultimately lead-

564 A. Pascale et al. / Pharmacological Research 55 (2007) 560–569

Fig. 2. All the multiple information targeting the brain is temporarily stored as short-term memories, until they are definitively consolidated in long-term memories.A be rei adingD detec

iF

5

Pttaannfeatoidcibfuo

Ppwatic[oFcmApmp[iR

6k

lthough forgetting is part of the normal memory process, all the information cann these processes (i.e. encoding, consolidation and probably also forgetting) leisturbances in any of these steps are responsible for those memory alterations

ng to the modulation of gene expression in neuronal cells (seeig. 2).

. PKC and neuronal rescue/survival

A variety of neuronal pathologies are described in whichKC or selected isoforms may be involved or being one of

he relevant players, such as in acute (cerebral ischemia andrauma), or chronic (amyotrophic lateral sclerosis, Parkinsonnd Alzheimer’s disease) neurodegeneration (see Ref. [50] forreview). Although, as already discussed, neuronal loss is

ot a prerequisite in physiological aging, in pathological agingeurodegeneration is a central player. Early loss of PKC is aundamental step and a prognostic feature of lethal damage inxcitotoxic neuron death in vitro and in vivo [51]. Can PKCctivation be protective against neuronal death? It depends onhe PKC isoform (both on the cellular model and on the typef insult) because different isozymes may play even oppos-ng roles in modulating for instance oxidative stress-inducedeath. For example, in hippocampal immortalized neuronalells, PMA antagonizes death activating PKC� and � and inhibit-ng isozymes associated with cell death such as PKC� (possibly

y down regulating it very efficiently). The activated PKC iso-orms stimulate multiple members of the MAPK kinase familyltimately leading to neuronal protection [52]. Direct evidencen this scenario derives from studies utilizing isoform-selective

cs

called at any time. At molecular level, the PKC/ELAV cascade may be involvedto synaptic remodelling, a key event in memory trace formation mechanisms.

ted in aging or dementia (see text for additional details).

KC probes. In fact, the specific inhibition of PKC� protects hip-ocampal slices from oxygen glucose deprivation (OGD) evenhen the inhibitor is applied up to the first 3 h of reperfusion

fter the ischemic insult [53]. In neurons and astrocytes in cul-ure, OGD is counteracted by selective PKC� activation (PKC�nhibition worsened injury); the PKC� inhibition is instead asso-iated with selective astrocyte damage (with no effect on neurons54]). Utilizing other cell models of neurodegeneration, vari-us compounds activating PKC can inhibit neurodegeneration.or instance A� toxicity is antagonized by resveratrol (in aoncentration-dependent manner with maximal protection at 25icromolar), possibly through PKC� dephosphorylation [55].nother example is rasagiline, a MAO-B inhibitor, in which theropargylamine moiety has in vivo a neuronal survival action inice hippocampus through activation of � and � PKC and this

rotection is associated with induction of RACK1 protein levels37]. Also in this case PKC is part of a cascade of events involv-ng bcl-2 family proteins, cytochrome c, caspases and PARP (seeefs. [56,57]).

. The aging-associated memory impairment: PKC as aey actor

Generally speaking, learning and memory mechanisms areomplex and dynamic processes encompassing the encoding,torage, and retrieval of diverse types of information that affect

gical

tslcdiiatbrrdm

mctWtaafttpbfsatoioataatawimaGathwtibtapNi

patpmific

iuPpb([larttcPa

7A

mio(diaafaoaTatciicicppa

A. Pascale et al. / Pharmacolo

he biochemistry and physiology of specific brain regions, thetrength and the morphology of multiple synapses, ultimatelyeading to persistent changes that alter the efficacy of cell-to-ell communication (see Ref. [58]). Several investigations haveocumented the critical role of PKC in memory [59–64] andn particular of the PKC� [65,66] and PKM [67] isozymesn in vivo and in vitro models (for an extensive review seelso [68]). Recently, we also reported an in vivo PKC activa-ion coupled with nELAVs up-regulation in the hippocampal ratrain [49]. Within this context, we previously also showed aegion-specific up-regulation of nELAVs in hippocampal neu-ons of rodents trained in spatial discrimination tasks [47,48],emonstrating the involvement of nELAVs in gene expressionodulation occurring in memory trace formation.cPKC activity under basal conditions (in presence of opti-

al concentrations of exogenous activators) shows age-relatedhanges in brain tissues depending on the strain of rat inves-igated (Sprague Dawley- and Fisher 344-decreased, versus

istar-unchanged) reviewed in Ref. [25]. PKC activation andranslocation strictly depends on membrane lipid compositionnd intracellular free calcium levels. As a consequence age-ssociated alterations in these factors may affect the cellularunctions of this enzymatic family. For this reason, to circumventhese variables and directly evaluate PKC activation, the func-ional response of PKC in terms of enzyme translocation afterhorbol esters can be evaluated as a better indicator of possi-le age-related changes in this transduction system. In the brain,ollowing phorbol esters exposure, cPKCs translocation was pre-erved up to middle age (8 months old), but was impaired in agednimals (>24 months old) in both cortex and hippocampus areas,his effect being independent of the strain employed [69,70]. Webserved that the PKC redistribution process was deficient alson terms of calcium-independent activity in cortical tissues ofld Wistar rats [71]. Phorbol esters challenge bypasses receptorctivation and the following DAG production, suggesting thathe defective translocation process is independent of possiblege-associated alterations in neurotransmitter levels, receptorvailability and second messenger production. On the contrary,he amount of the different isozymes (both calcium-dependentnd –independent) was preserved during senescence [69,71],ith the exception of hippocampal PKC� that was significantly

ncreased at membrane level in aged animals. This observationay be directly associated with learning abilities observed in old

nimals. In fact, in agreement with our findings, Colombo andallagher found that, when assessing learning performance onMorris maze task as a function of PKC� content in aged rats,

he worst performance is coupled to higher levels of PKC� inippocampal CA1 and dentate gyrus regions [72]. Similar dataere reported for PKC� in aging rabbit hippocampus [73]. At

his regard, it should be also remembered that PKC� is specif-cally expressed in the nervous system; consequently, higherasal levels of membrane-bound PKC� may represent an attempto compensate a functional age-related alteration/deregulation

ffecting this specific isoform. We additionally investigated theossibility of age-related modifications at transcriptional level.o changes in the content of the different mRNAs were detected

n aged Wistar rats, besides a reduction in the PKC� and PKC�

eept

Research 55 (2007) 560–569 565

roteins already at 8 months of age in the cortex [69]. To furtherssess any potential alterations in PKC mRNA amount and dis-ribution in discrete hippocampal and cortical regions, we alsoerformed in situ hybridization: senescence did not significantlyodify the relative mRNAs of the three calcium-dependent PKC

soforms in any area and subfield analyzed [69]. Overall, thesendings suggest that the translocation process appears to be theommon component of the Kinase C system sensitive to aging.

Taking into account the postulated implication of RACKsn directing the activated PKCs to relevant targets, we eval-ated whether the age-associated impairment observed inKC translocation could be related to additional changes inrotein–protein interactions. Our findings document that, in therain cortex, old Wistar rats show a reduced content in RACK1roughly 50%) in comparison to adult and middle-aged animals71]. More recent results confirmed decreased cortical RACK1evels, associated with a parallel reduction in the relative mRNAmount, also in aged Sprague-Dawley rats [74]. Data on agedabbit hippocampus confirm that a loss of RACK1 contributeso the dysregulation of PKC [73]. All findings further supporthe involvement of RACK proteins in PKCs translocation pro-ess and suggest that, because of senescence-related changes,KCs may not find the appropriate milieu for their full activation,nchoring and function.

. Pathological aging and PKC: the example oflzheimer’s disease

Dementia can especially be considered as an impairment ofemory and other cognitive abilities, which are sufficient to

nterfere with normal daily activities. Dementia may be inex-rably progressive, such as that caused by Alzheimer’s diseaseAD), the most common form of dementia and also the mostramatic manifestation of cognitive decline in the elderly. Typ-cally, AD leads to an insidious impairment of recent memory,nd progressively affects language, personality, and most otherspects of cognition. The highest risk factor for the sporadicorm of Alzheimer’s pathology is represented by age and its rel-tively recent diffusion is indeed associated with the increasef span-life during these last decades. In fact, AD has becomemong the leading causes of death in the over 65 population.he histopathological observations are basically indistinguish-ble in the familial and sporadic AD forms, suggesting thathe genetic component may accelerate the same molecular andellular dysfunctions [75]. Histopathologically, AD is character-zed by the accumulation of extracellular amyloid plaques andntracellular neurofibrillary tangles in typical patterns. Theseellular alterations are coupled with a marked neuronal death,n fact brain atrophy is a frequent finding in AD. The initialhanges develop in poorly myelinated areas of the medial tem-oral lobe and the destructive process then follows a predictableattern as it extends into other cortical areas (i.e. higher-orderssociation cortices). Accordingly, the neurons belonging to the

ntorhinal cortex that project to the hippocampus degeneratearly in the course of the disease, followed by the hippocam-al neurons and then by cortical neurons receiving inputs fromhe hippocampal ones [76]. The widespread nature of the histo-

5 gical

lsptnrIApbt

awaaaaIosoitpOttKaobaMoftitpbdag

8p

tdvtpc([

pttspepwopaweit[

uPuaaPtwmf(drbicp

9

swllttrdoAtmlvd

66 A. Pascale et al. / Pharmacolo

ogical changes in AD suggests that multiple neurotransmitterystems can be implicated, above all a number of studies sup-orts an impairment of the cholinergic function. Of relevanceo this consideration, ninety per cent of the large multipolareurons in the basal nucleus of Meynert are cholinergic andesponsible for the cholinergic innervation of the cerebral cortex.ndeed, these neurons undergo severe changes in the course oflzheimer pathology [77]. Overall, this anatomic-pathologicalattern results in a profile of cognitive deficits that preservesasic neurological functions and further supports the idea thathe deficit in cell-to-cell communication is critical in AD.

Structurally, neurofibrillary tangles contain paired helical fil-ments that are forms of abnormally phosphorylated tau protein,hile neuritic plaques, which are largely extracellular lesions,

re mainly composed of a 42 aminoacid peptide referred to as ß-myloid peptide (A�). A� is generated through a quantitativelyberrant proteolytic cleavage, involving � and � secretases, oflarger precursor named APP (Amyloid Precursor Protein).

nstead, in the non-amyloidogenic pathway, APP metabolismccurs via the �-secretase enzyme that cuts within the A�equence, preventing A� production and leading to the secretionf the soluble fragment of APP (sAPP) [78,79]. Several in vitronvestigations reported a direct role of PKC in the modulation ofhe non-amyloidogenic pathway of APP. In fact, phorbol estersotentiate sAPP secretion [80] and decrease A� release [81].f relevance to our previous investigations, it was documented

hat PKC activation is deficient in AD brain in terms of markedranslocation loss in response to phorbol esters challenge and

+ depolarization [82]. In comparison with normal senescence,nchoring protein levels too were found altered as a consequencef Alzheimer’s disease. In fact, RACK1 content was reduced inoth soluble and membrane compartments when compared toge-matched controls in human frontal cortex autopsies [83].oreover, in AD tissues, no pathology-related changes were

bserved in PKC�II basal levels [83], in analogy with the datarom senescent animals (see Ref. [70]). These findings suggesthat, again, it is not the expression of PKCs that is deficientn AD, rather, the mechanism of kinase activation-anchoringhat undergoes pathology-dependent changes. Recent data haveostulated a link between neurofibrillary tangles in sensitiverain areas of AD patients and PKM-aggregation, leading toisruption of glutamatergic neurotransmission [84]. PKC maylso modulate tau hyperphosphorylation through inhibition oflycogen synthase kinase-3 [85].

. Interventions on PKC signalling in physiological andathological aging

Is it possible to counteract the age-related loss of PKC activa-ion? Various conditions known to recover age-related functionaleficits are reported to involve PKC signalling. The first obser-ations reported are indirect data relating PKC activationo age-dependent changes. For instance, exogenous phos-

hatidylserine given chronically (17 days) to aged animals canounteract the impaired hippocampal depolarization-dependentand PKC-mediated) phosphorylation of the GAP-43 protein86]. Moreover, the phorbol 12,13-dibutyrate-induced phos-

cacd

Research 55 (2007) 560–569

horylation of synapsin I (a protein involved in synapticransmission) is impaired in aged rats and conditions knowno ameliorate a variety of deficits associated with aging,uch as caloric restriction and antioxidant (N-tert-butyl-�-henylnitrone) treatment, ameliorate this deficit [87]. Othervidence has been provided by more recent findings on hip-ocampal tissues from aged rats in which a two week treatmentith dehydroepiandrosterone (reported to antagonize a varietyf age-related deficits) can partially recover RACK1 mRNA androtein to levels observed in young animals [88]. In addition, inrat model of young to aged pineal gland transplantation, inhich aged animal survival is increased together with a recov-

ry in immunological and brain parameters, the age-dependentmpaired cortical PKC�II and PKC� translocation is restoredogether with a partial recovery in membrane RACK1 levels70].

As far as pathological aging is concerned, the studies havetilized mouse models of AD with overexpression of APP andresenilin 1 (PS1) or both. Joseph and collaborators have doc-mented in the double transgene that a chronic diet rich inntioxidants (blueberry extracts from 4 through 12 months ofge) can improve spatial memory and increase hippocampalKC� levels [89]. Etcheberrygaray et al. have demonstrated

hat, in both the APP and APP/PS1 transgene, PKC activationith benzolactam and bryostatin reduces A� and improves pre-ature death and behavioural outcomes [90]. More recent data

rom Choi and colleagues have discovered a new target for PKCthe � isozyme in particular) being directly involved in A� degra-ation. In fact in mice models of AD, overexpression of PKC�educes A� levels as a consequence of increased degradationy an enzyme called endothelin converting enzyme (ECE) [91],ndicating that activation of PKC� in the brain may increase A�learance, thus being potentially useful in the treatment of thisathology.

. Conclusions

Brain science is making tremendous progress to better under-tand what happens to memory and other cognitive functions ase age. Signal transduction can be considered the official trans-

ator of the cells, allowing each cell to understand in its ownanguage the stimuli arriving from the external environment andhus becoming able to elaborate the adequate outputs. Withinhis context, it is logical to think that age-related changes occur-ing in cell-to-cell communication may be extremely relevant inetermining alterations in molecular cascades involved in mem-ry processes or making them more susceptible to pathology.mong the different molecular pathways, the PKC cascade cer-

ainly plays a critical role (see Fig. 2). A key step within theechanism of PKC activation is its relocation from one subcel-

ular compartment to another one. On the functional point ofiew, this redistribution mechanism is fundamental since it canirect PKC close to the specific substrates. The PKC translo-

ation process then represents a strategy adopted by the cell tollow selected responses to specific activating signals in distinctellular micro domains. An additional trick used by the cell toirect a specific activated enzyme towards selective subcellu-

gical

lttdtPb(if[Pstpotutfi

cig

ualnPtdoraiAbsisaffmmdp

A

ffwL

R

[

[

[

[

[

[

[

[

[

[[

[

[

[

A. Pascale et al. / Pharmacolo

ar regions, is the involvement of scaffolding/targeting proteins;his observation indicates that not only protein–lipid interac-ions, but also protein–protein interactions play a critical roleuring the PKC relocation mechanism [23]. Within this con-ext, besides the already discussed role of RACK proteins inKC functions (see before), another anchoring protein shoulde taken into consideration: the A-kinase- anchoring protein 79AKAP79). AKAP79 is a multivalent adaptor protein with bind-ng sites for cAMP-dependent protein kinase (PKA) as well asor PKC and the calcium-dependent phosphatase 2B-calcineurin92]. AKAP79 can thus co-localize all the three enzymes, PKA,KC and calcineurin, in specific cellular compartments (post-ynaptic density fractions). This is of relevance consideringhat the coordination of cellular signals often involves phos-horylation/dephosphorylation processes requiring the controlf multiple protein kinases and phosphatases. AKAP79 mayhen integrate distinct signals to control specific events partic-larly occurring during synaptic plasticity. It is worth mentionhat upon binding to AKAP79 PKC activity is inhibited [93] dif-erentiating this from other PKC-anchoring proteins [38], alson terms of isozyme selectivity.

Interestingly, the contribution of PKC in post-transcriptionalontrol mechanisms acting on mRNA stability and translatabil-ty provides an additional opportunity for a local regulation ofene expression in “activated” neuronal micro domains.

Age-related modifications in any of these actors or the dereg-lation of this scenario may then have implications in celllterations, such as those reported in physiological or patho-ogical (i.e. Alzheimer’s disease) aging (see Fig. 2) or in otherervous system-related pathological states [50]. ModulatingKC transduction pathway offers then an interesting novel addi-

ional approach for developing innovative therapeutic tools iniverse physiologic and pathologic conditions. To this aim, onef the most interesting breakthroughs within this field is theecognition that it is possible to interfere with the translocationnd the function of individual PKC isozymes by peptides mim-cking the sites of interaction between PKC and RACK [26].n additional step in this direction is the finding that, in therain, activation of PKC with the non-tumour promoter bryo-tatin reduces beta amyloid accumulation, premature death andmproves behavioural outcomes in AD mice models [90]. Con-idering that bryostatin is also able to up-regulate nELAVs that,s mentioned, are implicated in memory processes, these resultsurther support the concept that a better insight of the differentacets within the PKC molecular cascades may lead to new phar-acological interventions. In particular, new therapeutic toolsay be addressed to improve or modulate those signal trans-

uction pathways, affected during senescence or age-relatedathologies that are responsible for memory disturbances.

cknowledgements

The authors would like to thank Annamaria Pascale-Prokschor carefully reviewing the manuscript and Dr. Miriam Duchenor her precious and constant support. Part of these studiesas supported by a grant from Italian Ministero Sanita/Regioneazio (Progetto Alzheimer) to F.B.

[

[

Research 55 (2007) 560–569 567

eferences

[1] Flood DG, Coleman PD. Neuron numbers and sizes in aging brain: compar-isons of human, monkey, and rodent data. Neurobiol Aging 1988;9:453–6.

[2] Bertoni-Freddari C, Fattoretti P, Paoloni R, Caselli U, Galeazzi L,Meier-Ruge W. Synaptic structural dynamics and aging. Gerontology1996;42(3):170–80.

[3] Wickelgren I. For the cortex, neuron loss may be less than thought. Science1996;273:48–50.

[4] Rapp PR, Gallagher M. Preserved neuron number in the hippocampusof aged rats with spatial learning deficits. Proc Natl Acad Sci USA1996;93:9926–30.

[5] Gallagher M. Aging and hippocampal/cortical circuits in rodents.Alzheimer Dis Assoc Disord 2003;17:S45–7.

[6] Kelly KM, Nadon NL, Morrison JH, Thibault O, Barnes CA, Blalock EM.The neurobiology of aging. Epilepsy Res 2006;68(Suppl 1):S5–20.

[7] Agnati LF, Zoli M, Grimaldi R, Fuxe K, Toffano G, Zini I. Cellular andsynaptic alterations in the aging brain. Aging 1990;2:5–25.

[8] Fulop Jr T, Seres I. Age-related changes in signal transduction. Drugs Aging1994;5:366–90.

[9] Yamada K, Nabeshima T. Changes in NMDA receptor/nitric oxide signal-ing pathway in the brain with aging. Microsc Res Tech 1998;43:68–74.

10] Yamamoto M, Suhara T, Okubo Y, Ichimiya T, Sudo Y, Inoue M, et al. Age-related decline of serotonin transporters in living human brain of healthymales. Life Sci 2002;71:751–7.

11] Nishizuka Y. The protein kinase C family and lipid mediators for trans-membrane signaling and cell regulation. Alcohol Clin Exp Res 2001;25(5Suppl ISBRA):3S–7S.

12] Newton AC. Regulation of the ABC kinases by phosphorylation: PKC asa paradigm. Biochem J 2003;370:361–71.

13] Balendran A, Hare GR, Kieloch A, Williams MR, Alessi DR. Furtherevidence that 3-phosphoinositide-dependent protein kinase-1 (PDK1) isrequired for the stability and phosphorylation of protein kinase C (PKC)isoforms. FEBS Lett 2000;484:217–23.

14] Parker PJ. Protein kinase C phosphorylation: an introduction. Methods MolBiol 2003;233:159–62.

15] Giorgione JR, Lin JH, McCammon JA, Newton AC. Increased membraneaffinity of the C1 domain of protein kinase C delta compensates for the lackof involvement of its C2 domain in membrane recruitment. J Biol Chem2006;28:1660–9.

16] Newton AC, Johnson JE. Protein kinase C: a paradigm for regulation ofprotein function by two membrane-targeting modules. Biochim BiophysActa 1998;1376(2):155–72.

17] Kraft AS, Anderson WB. Phorbol esters increase the amount of Ca2 ,phospholipid-dependent protein kinase associated with plasma membrane.Nature 1983;301:621–3.

18] Mochly-Rosen D, Smith BL, Chen CH, Disatnik MH, Ron D. Interactionof protein kinase C with RACK1, a receptor for activated C-kinase: a rolein beta protein kinase C mediated signal transduction. Biochem Soc Trans1995;23(3):596–600.

19] Stabel S, Parker PJ. Protein kinase C. Pharmacol Ther 1991;51:71–95.20] Tanaka C, Nishizuka Y. The protein kinase C family for neuronal signaling.

Annu Rev Neurosci 1994;17:551–67.21] Gao T, Newton AC. The turn motif is a phosphorylation switch that

regulates the binding of Hsp70 to protein kinase C. J Biol Chem2002;277:31585–92.

22] Hernandez AI, Blace N, Crary JF, Serrano PA, Leitges M, Libien JM,et al. Protein kinase M zeta synthesis from a brain mRNA encoding anindependent protein kinase C zeta catalytic domain. Implications for themolecular mechanism of memory. J Biol Chem 2003;278:40305–16.

23] Mochly-Rosen D, Khaner H, Lopez J. Identification of intracellular recep-tor proteins for activated protein kinase C. Proc Natl Acad Sci USA1991;88:3997–4000.

24] Jaken S. Protein kinase C isozymes and substrates. Curr Opin Cell Biol1996;8:168–73.

25] Battaini F, Pascale A, Paoletti R, Govoni S. The role of anchoring pro-tein RACK1 in PKC activation in the ageing rat brain. Trends Neurosci1997;20:410–5.

5 gical

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

68 A. Pascale et al. / Pharmacolo

26] Csukai M, Mochly-Rosen D. Pharmacologic modulation of protein kinaseC isozymes: the role of RACKs and subcellular localisation. PharmacolRes 1999;39:253–9.

27] Schechtman D, Mochly-Rosen D. Adaptor proteins in protein kinase C-mediated signal transduction. Oncogene 2001;20:6339–47.

28] McCahill A, Warwicker J, Bolger GB, Houslay MD, Yarwood SJ. TheRACK1 scaffold protein: a dynamic cog in cell response mechanisms. MolPharmacol 2002;62:1261–73.

29] Sklan EH, Podoly E, Soreq H. RACK1 has the nerve to act: structuremeets function in the nervous system. Prog Neurobiol 2006;78(2):117–34.

30] Robles-Flores M, Garcia-Sainz JA. Activated protein kinase C bindsto intracellular receptors in rat hepatocytes. Biochem J 1993;296(Pt2):467–72.

31] Smith BL, Mochly-Rosen D. Inhibition of protein kinase C function byinjection of intracellular receptor for the enzyme. Biochem Biophys ResCommun 1992;188:1235–40.

32] Ron D, Luo J, Mochly-Rosen D. C2 region-derived peptides inhibittranslocation and function of beta protein kinase C in vivo. J Biol Chem1995;270(41):24180–7.

33] Ron D, Jiang Z, Yao L, Vagts A, Diamond I, Gordon A. Coordi-nated movement of RACK1 with activated betaII PKC. J Biol Chem1999;274(38):27039–46.

34] Pascale A, Alkon DL, Grimaldi M. Translocation of protein kinase C-betaIIin astrocytes requires organized actin cytoskeleton and is not accompaniedby synchronous RACK1 relocation. Glia 2004;46(2):169–82.

35] Schechtman D, Mochly-Rosen D. Isozyme-specific inhibitors and activa-tors of protein kinase C. Methods Enzymol 2002;345:470–89.

36] Choi DS, Young H, McMahon T, Wang D, Messing RO. The mouse RACK1gene is regulated by nuclear factor-kappa B and contributes to cell survival.Mol Pharmacol 2003;64:1541–8.

37] Bar-Am O, Yogev-Falach M, Amit T, Sagi Y, Youdim MB. Regulation ofprotein kinase C by the anti-Parkinson drug, MAO-B inhibitor, rasagilineand its derivatives, in vivo. J Neurochem 2004;89:1119–25.

38] Jaken S, Parker PJ. Protein kinase C binding partners. Bioessays2000;22:245–54.

39] Osborne HB. An insight into the post-transcriptional control of gene expres-sion in cell function. Biol Cell 2003;95:125–7.

40] Kracht M, Saklatvala J. Transcriptional and post-transcriptional control ofgene expression in inflammation. Cytokine 2002;20:91–106.

41] Shim J, Karin M. The control of mRNA stability in response to extracellularstimuli. Mol Cells 2002;14:323–31.

42] Sachs AB. Messenger RNA degradation in eukaryotes. Cell1993;74:413–21.

43] Keene JD. Why is Hu where? Shuttling of early-response-gene messengerRNA subsets. Proc Natl Acad Sci USA 1999;96:5–7.

44] Brennan CM, Steitz JA. HuR and mRNA stability. Cell Mol Life Sci2001;58:266–77.

45] Amadio M, Battaini F, Pascale A. The different facets of protein kinase C:old and new players in neuronal signal transduction pathways. PharmacolRes 2006;54:317–25.

46] Mobarak CD, Anderson KD, Morin M, Beckel-Mitchener A, Rogers SL,Furneau H, et al. The RNA-binding protein HuD is required for GAP-43 mRNA stability, GAP-43 gene expression, and PKC-dependent neuriteoutgrowth in PC12 cells. Mol Biol Cell 2000;11:3191–203.

47] Quattrone A, Pascale A, Nogues X, Zhao W, Gusev P, Pacini A, et al.Posttranscriptional regulation of gene expression in learning by the neu-ronal ELAV-like mRNA-stabilizing proteins. Proc Natl Acad Sci USA2001;98:11668–73.

48] Pascale A, Gusev PA, Amadio M, Dottorini T, Govoni S, Alkon DL, etal. Increase of the RNA-binding protein HuD and posttranscriptional up-regulation of the GAP-43 gene during spatial memory. Proc Natl Acad SciUSA 2004;101:1217–22.

49] Pascale A, Amadio M, Scapagnini G, Lanni C, Racchi M, Provenzani A,et al. Neuronal ELAV proteins enhance mRNA stability by a PKC alpha-dependent pathway. Proc Natl Acad Sci USA 2005;102(34):12065–70.

50] Battaini F. Protein kinase C isoforms as therapeutic targets in nervoussystem disease states. Pharmacol Res 2001;44:353–61.

[

Research 55 (2007) 560–569

51] Durkin JP, Tremblay R, Chakravarthy B, Mealing G, Morley P, Small D, etal. Evidence that the early loss of membrane protein kinase C is a necessarystep in the excitatory amino acid-induced death of primary cortical neurons.J Neurochem 1997;68:1400–12.

52] Maher P. How protein kinase C activation protects nerve cells from oxida-tive stress-induced cell death. J Neurosci 2001;21:2929–38.

53] Bright R, Raval AP, Dembner JM, Perez-Pinzon MA, Steinberg GK, YenariM, et al. Protein kinase C delta mediates cerebral reperfusion injury in vivo.J Neurosci 2004;4(24):6880–8.

54] Wang J, Bright R, Mochly-Rosen D, Giffard RG. Cell-specific rolefor epsilon- and betaI-protein kinase C isozymes in protecting corticalneurons and astrocytes from ischemia-like injury. Neuropharmacology2004;47:136–45.

55] Han YS, Zheng WH, Bastianetto S, Chabot JG, Quirion R. Neuroprotec-tive effects of resveratrol against beta-amyloid-induced neurotoxicity inrat hippocampal neurons: involvement of protein kinase C. Br J Pharmacol2004;141:997–1005.

56] Mandel S, Weinreb O, Amit T, Youdim MB. Mechanism of neuroprotectiveaction of the anti-Parkinson drug rasagiline and its derivatives. Brain ResBrain Res Rev 2005;48:379–87.

57] Szabo C. Roles of poly(ADP-ribose) polymerase activation in the patho-genesis of diabetes mellitus and its complications. Pharmacol Res2005;52:60–71.

58] Amadio M, Govoni S, Alkon DL, Pascale A. Emerging targets for thepharmacology of learning and memory. Pharmacol Res 2004;50:111–22.

59] Alkon DL, Rasmussen H. A spatial-temporal model of cell activation.Science 1988;239:998–1005.

60] Olds JL, Anderson ML, McPhie DL, Staten LD, Alkon DL. Imaging ofmemory-specific changes in the distribution of protein kinase C in thehippocampus. Science 1989;245:866–9.

61] Wehner JM, Sleight S, Upchurch M. Hippocampal protein kinase C activityis reduced in poor spatial learners. Brain Res 1990;523(2):181–7.

62] Lucchi L, Pascale A, Battaini F, Govoni S, Trabucchi M. Cognition stim-ulating drugs modulate protein kinase C activity in cerebral cortex andhippocampus of adult rats. Life Sci 1993;53:1821–32.

63] Pascale A, Milano S, Corsico N, Lucchi L, Battaini F, Martelli EA, et al.Protein kinase C activation and anti-amnesic effect of acetyl-L-carnitine:in vitro and in vivo studies. Eur J Pharmacol 1994;265:1–7.

64] Nogues X, Micheau J, Jaffard R. Protein kinase C activity in the hippocam-pus following spatial learning tasks in mice. Hippocampus 1994;4(1):71–7.

65] Van der Zee EA, Compaan JC, de Boer M, Luiten PG. Changes in PKCgamma immunoreactivity in mouse hippocampus induced by spatial dis-crimination learning. J Neurosci 1992;12:4808–15.

66] Angenstein F, Riedel G, Reymann KG, Staak S. Hippocampal long-termpotentiation in vivo induces translocation of protein kinase C�. NeuroRe-port 1994;5:381–4.

67] Sacktor TC, Osten P, Valsamis H, Jiang X, Naik MU, Sublette E. Persistentactivation of the zeta isoform of protein kinase C in the maintenance oflong-term potentiation. Proc Natl Acad Sci USA 1993;90:8342–6.

68] Nogues X, Pascale A, Micheau J, Battaini F, Protein Kinase C. In: RiedelG, Platt B, editors. Memories are made of these: from messengers tomolecules. Georgetown, TX: Landes Bioscience; 2003. p. 383–410.

69] Battaini F, Elkabes S, Bergamaschi S, Ladisa V, Lucchi L, De Graan PN,et al. Protein kinase C activity, translocation and conventional isoforms inaging rat brain. Neurobiol Aging 1995;16:137–48.

70] Battaini F, Pascale A. Protein kinase C signal transduction regu-lation in physiological and pathological aging. Ann NY Acad Sci2005;1057:177–92.

71] Pascale A, Fortino I, Govoni S, Trabucchi M, Wetsel WC, Battaini F. Func-tional impairment in protein kinase C by RACK1 (receptor for activated Ckinase 1) deficiency in aged rat brain cortex. J Neurochem 1996;67:2471–7.

72] Colombo PJ, Gallager M. Individual differences in spatial memory amongaged rats are related to hippocampal PKC gamma immunoreactivity. Hip-

pocampus 2002;12:285–9.

73] Van der Zee EA, Palm IF, O’Connor M, Maizels ET, Hunzicker-Dunn M, Disterhoft JF. Aging-related alterations in the distribution ofCa2+-dependent PKC isoforms in rabbit hippocampus. Hippocampus2004;14:849–60.

gical

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

A. Pascale et al. / Pharmacolo

74] Sanguino E, Roglans N, Alegret M, Sanchez RM, Vazquez-Carrera M,Laguna JC. Prevention of age-related changes in rat cortex transcriptionfactor activator protein-1 by hypolipidemic drugs. Biochem Pharmacol2004;68:1411–21.

75] Mattson MP, Magnus T. Ageing and neuronal vulnerability. Nat Rev Neu-rosci 2006;7:278–94.

76] Braak H, Braak E. Evolution of neuronal changes in the course ofAlzheimer’s disease. J Neural Transm Suppl 1998;53:127–40.

77] Whitehouse PJ, Price DL, Struble RG, Clark AW, Coyle JT, Delon MR.Alzheimer’s disease and senile dementia: loss of neurons in the basalforebrain. Science 1982;215:1237–9.

78] Racchi M, Govoni S. Rationalizing a pharmacological interventionon the amyloid precursor protein metabolism. Trends Pharmacol Sci1999;20:418–23.

79] Gandy S. The role of cerebral amyloid beta accumulation in common formsof Alzheimer disease. J Clin Invest 2005;115:1121–9.

80] Gillespie SL, Golde TE, Younkin SG. Secretory processing of theAlzheimer amyloid beta/A4 protein precursor is increased by protein phos-phorylation. Biochem Biophys Res Commun 1992;187(3):1285–90.

81] Buxbaum JD, Koo EH, Greengard P. Protein phosphorylation inhibits pro-duction of Alzheimer amyloid beta/A4 peptide. Proc Natl Acad Sci USA1993;90(19):9195–8.

82] Wang HY, Pisano MR, Friedman E. Attenuated PKC activity and translo-cation in Alzheimer’s disease brain. Neurobiol Aging 1994;15:293–8.

83] Battaini F, Pascale A, Lucchi L, Pasinetti GM, Govoni S. Protein kinaseC anchoring deficit in postmortem brains of Alzheimer’s disease patients.Exp Neurol 1999;159:559–64.

84] Crary JF, Shao CY, Mirra SS, Hernandez AI, Sacktor TC. Atypical protein

kinase C in neurodegenerative disease I: PKMzeta aggregates with lim-bic neurofibrillary tangles and AMPA receptors in Alzheimer disease. JNeuropathol Exp Neurol 2006;65:319–26.

85] Liu SJ, Zhang AH, Li HL, Wang Q, Deng HM, Netzer WJ, et al. Overacti-vation of glycogen synthase kinase-3 by inhibition of phosphoinositol-3

[

Research 55 (2007) 560–569 569

kinase and protein kinase C leads to hyperphosphorylation of tau andimpairment of spatial memory. J Neurochem 2003;87:1333–44.

86] Gianotti C, Porta A, De Graan PN, Oestreicher AB, Nunzi MG. B-50/GAP43 phosphorylation in hippocampal slices from aged rats: effectsof phosphatidylserine administration. Neurobiol Aging 1993;14:401–6.

87] Eckles KE, Dudek EM, Bickford PC, Browning MD. Amelioration of age-related deficits in the stimulation of synapsin phosphorylation. NeurobiolAging 1997;18:213–7.

88] Racchi M, Govoni S, Solerte SB, Galli CL, Corsini E. Dehydroepiandros-terone and the relationship with aging and memory: a possible linkwith protein kinase C functional machinery. Brain Res Brain Res Rev2001;37:287–93.

89] Joseph JA, Denisova NA, Arendash G, Gordon M, Diamond D, Shukitt-Hale B, et al. Blueberry supplementation enhances signaling and preventsbehavioral deficits in an Alzheimer disease model. Nutr Neurosci2003;6:153–62.

90] Etcheberrigaray R, Tan M, Dewachter I, Kuiperi C, Van der Auwera I,Wera S, et al. Therapeutic effects of PKC activators in Alzheimer’s diseasetransgenic mice. Proc Natl Acad Sci USA 2004;101:11141–6.

91] Choi DS, Wang D, Yu GQ, Zhu G, Kharazia VN, Paredes JP, et al.PKCepsilon increases endothelin converting enzyme activity and reducesamyloid plaque pathology in transgenic mice. Proc Natl Acad Sci USA2006;103:8215–20.

92] Klauck TM, Faux MC, Labudda K, Langeberg LK, Jaken S, Scott JD. Coor-dination of three signaling enzymes by AKAP79, a mammalian scaffoldprotein. Science 1996;271(5255):1589–92.

93] Faux MC, Rollins EN, Edwards AS, Langeberg LK, Newton AC, ScottJD. Mechanism of A-kinase-anchoring protein 79 (AKAP79) and pro-

tein kinase C interaction. Biochem J 1999;343(October (Pt. 2)):443–52.

94] Stebbins EG, Mochly-Rosen D. Binding specificity for RACK1 residesin the V5 region of beta II protein kinase C. J Biol Chem2001;276(32):29644–50.