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Aging  as  alteration    Paul-­‐Antoine  Miquel  Université  de  Toulouse  2/  Le  Mirail  Laboratoire  Erraphis    Abstract    Aging   is   a   normative   biological   process,   and  not   simply   a   physical   one.   It   is   not  accurate  to  define  it  by  the  fact  that  life  has  an  entropic  cost,  and  to  characterize  it  as   a   pure   imbalance   between   exergonic   and   endergonic   reaction   in  metabolism  (“the   free   radical   theory   of   aging”)   or   finally   as   an   imbalance   between   the  excessive  formation  of  reactive  oxygen  species  and  limited  antioxidant  defences.  In  connective  tissues,  aging  is  alteration.  And  alteration  is  more  than  destruction  or   degradation.   It   deals   with   self-­‐destruction,   and   with   the   so-­‐called  molecular  vicious  circles  of  aging.   In  worms,   in  yeast,  and   in  other  organisms,  aging   is  also  opposed   to   longevity   that   “counteracts”   this   self-­‐destruction   process,   as   if  longevity  was   something   like   a   developmental   constraint   (delay)   opposed   to   an  evolutionary  one  (alteration).        “L’individualité  loge  donc  son  ennemi  chez  elle”.                                                                                                                      Henri  Bergson,  L’évolution  créatrice,  1907,  p  13.      

Introduction    As  we   live,  we  will   die.   It   seems  obvious   then   that  we  age.  We  are  not  what  we  were  anymore.  It  means  first,   that  we  change.  Aging  is  nothing  but  an  irreversible  biological  process.   It   deals   not   simply   with   regulation,   but   also   with   becoming,   and   with   the  emergence   of   a   “before”   and   “after”   parameter,   into   the   description   of   living  mechanisms.    Yet  aging  is  also  alteration,  unlike  development,  or  evolution.  Thus,  the  first  temptation  is   to  refer  aging   to  “a  wear  and  tear  mechanism”  (1).  Aging   is  very  often  associated   in  biochemistry   with   the   existence   of   free   radicals   produced   during   the   process   of  respiration,  like  the  hydroxyl  radical  (•OH-­‐),  or  the  superoxide  anion  (•O2−  ).  In  genetics  of   populations,   the   Gompertz   equation   seems   to   attest   that   the   deterioration   of   an  organism  growth  exponentially  during  time.  Referring  to  this  first  interpretation,  living  organisms  age  like  entropic  machines.    Yet  there   is  no  obligation  in  biology  to  think   in  this  way,  since   it   is  attested  today   that  biological   systems   are   open   thermodynamic   structures   far   of   equilibrium   (2)   (3)   (4).  Even  a  crystal  can  grow  up  exponentially,  with  persistent  negative  entropy.  And  simply  following  Schrödinger’s  assumption  (5),  a  living  organism  is  more  than  a  crystal.  It  is  not  defined  as  a  mere  autocatalytic  process.  It  is  able  of  reproduction  with  variation  (6).  Look  a  bacterium,  for  instance.  Is  there  some  definitive  proof  that  bacteria  will  age?  Leonard  

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Hayflick   discovered   a   telomere’s  molecular  mechanism   acting   in   human   cells   (7).   But  telomerase   can   fit   the   damaged   telomeres.   Thus,   there   is   no  molecular   evidence   that  aging  is  an  entropic  necessity  for  the  organism.  “Alteration”  is  not  simply  destruction,  or  degradation.      Would  it  mean,  that  the  genome  orders  this  alteration’s  process?    Such  a  vision  is  deeply  challenged  in  contemporary  biology  (8).    We   will   insist   first   on   the   presence   of   vicious   circularities   at   the   molecular   levels;  particularly   concerning   the   degradation   of   extra-­‐cellular  matrix   in   connective   tissues,  since   they  attest,   that  aging  cannot  be  understood  only  as  determined  by  genes,  or  by  the  action  of   free   radicals   (9).  As  Kauffman   (10)   spoke  of   “propagative   constraints”   in  development,  we  will  speak  of  “repulsive  organisational  constraints”  in  aging.      Second,   we   will   show   that   such   repulsive   constraints   also   involve   epigenetics  mechanisms   that  counteract   the  action  of   genes,   since   “longevity”   and   “aging”  are   two  different  concepts.  We  will   refer  on   this  point   to   the  Leonard  Guarente  works   (11)  on  life  extension  by  activation  of  Sirtuins.    Third,   we  will   comment   the   last   Rose’s   (12)   results   attesting   that   in   large   cohorts   of  drosophila,   the  process  of   alteration   seems   to   stop  at   a   very   late   age,   in   contradiction  with   the   concept   of   antagonistic   pleiotropy   by   which   some   genes   responsible   for  increased  fitness  in  the  younger,  fertile  organism  contribute  to  decreased  fitness  later  in  life  (13),  and  also  with  the  soma  disposable  theory  proposed  by  Thomas  Kirkwood  (14).  It   can   be   interpreted   for   us,   as   if   longevity   could   be   connected   with   organismic  constraints  that  would  counteract  aging,  and  not  only  with  evolutionary  ones.    Thus,  in  a  way,  aging  is  nothing  but  an  alteration  process  that  can  also  be  delayed.  And  it  seems   to   show  as   such  a   central  property  of   life.   Coming   from  a  French  philosophical  tradition  (15)(16)(17),  we  will  understand  life  as  a  normative  property.  In  other  words,  life  is  polarised,  not  only  in  terms  of  physical  states,  like  electrons  and  protons,  but  also  in  terms  of  biological  values.  Death  is  not  simply  opposed  to  life.  Death  is  in  life,  and  life  is  in  death.   In   a   way,   death   is   in   life,   what   has   to   be   overcome   by   an   adaptive   biological  system.   In   another   way   death,   aging,   monstrosity   and   pathology   are   biological  constraints,  and  not  simple  physical  properties.        

1-­‐  Can  aging  be  reduced  to  an  entropic  cost?                                      «  The  most  injurious  of  these  is  the  identification  of  senescence  with  the  «  wearing  out  »  that  is  shown  in  human  artefacts.  A  moment  of  serious  consideration  should  convince  a   biologist   of   the   fundamental   dissimilarity   between   these   two   processes  »   (Georges  Williams,  Evolution,  1957,  11,  398-­‐411).        As   a   process   of   deterioration,   aging   is   traditionally   referred   to   “a   wear   and   tear  mechanism”   (1),   to   an   imbalance   between   exergonic   and   endergonic   reaction   in  metabolism  (“the  free  radical  theory  of  aging”,  (18),  or  finally  to  an  imbalance  between  the  excessive  formation  of  reactive  oxygen  species  and  limited  antioxidant  defences.      

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Starting  with  the  first  point,  August  Weismann  (1)  proposed  a  comparison  between  “the  strength  of   the   spring”   and   “duration  of   life”,   using   an   image   taken   from   the  world  of  machines  and  mechanics.  Yet  the  “wear  and  tear  mechanism”  that  he  had  in  mind,  was  founded   on   the   distinction   between   germinal   and   somatic   cells1.   Such   a   mechanism  applied  to  somatic  cells  is  a  strategy  that  permits  the  unlimited  reproduction  of  germinal  cells.  One   could   already   see   it,   as   a   biological   constraint,   and  not   simply   as   a  physical  deterioration.    By  extension,  contemporary  biologists  often  use  the  same  expression  to  vaguely  remind  that   biological   systems   also   obey   to   the   physical   principle   of   entropy   in  thermodynamics:   “wear-­‐and-­‐tear   must   affect   all   machines   in   a   world   subject   to   the  second   law   of   Thermodynamics,   and   the   machinery   of   living   things   cannot   be   an  exception”   (19).   One   could   also   find   the   same   topic   in   Hayflick’s   view,   when   the  American   biologist   tries   to   dissociate   longevity,   as   a   biological   process   controlled   by  genes,   and   aging,   as   a   pure   stochastic   one:   “blueprints   contain   no   information  instructing  a  car…  how  to  age,  yet  in  their  absence,  molecules  composing  these  objects  dissipate   energy   producing   structural   and   functional   losses.   Analogously,   the   genome  also   does   not   contain   instructions   for   aging   because,   like   the   car,   instructions   are  unnecessary   to  drive  a   spontaneous  process”   (20).  Aging   is  also  put   in   relation  with  a  characterisation  of  entropy  as  an  irreversible  loss  of  information.  It  vaguely  refers  to  the  statistic   definition   of   entropy   proposed   by   Boltzmann   and   Gibbs,   at   the   end   of   the  nineteenth  Century.   Such   an   interpretation  would  be   strongly   criticized  by  Weismann  itself,   since   a   lot   of   animals,   from   insects   to   salmons   are   dying   immediately   after  reproduction  showing  that  aging  and  longevity  are  controlled  by  biological  processes.      The  “free  radical   theory  ”  proposed  at   first  by  Denham  Harman  (21)   is  a  more  precise  and   interesting   attempt   to   understand   aging.   It   is   based   on   an   imbalance   between  exergonic  and  endergonic  reactions  in  the  metabolic  process  of  cellular  respiration,  and  it  considers   this   imbalance   as   the   main   factor,   that   would   explain   the   degradation   of  organisms,   through   cellular   dysfunction,   genetic   mutations   and   deceases   (Harman,  (21)).   In   another   paper   (22),   Harman   also   insisted   on   the   role   of   mitochondrial  machinery   in   aging,   since   the   mitochondrial   DNA   is   located   close   the   respiration  complex,  and  since  it  is  not  well  repaired.    Cellular   respiration   is   a   metabolic   reaction   that   converts   nutrients   of   an   organism  (C6H1206)  in  ATP  by  the  use  of  an  oxidizing  agent:  the  oxygen  (02).  In  aerobic  reactions,  we  have  the  general  and  schematic  equation:    C6H1206  +  6O2  =>  6CO2  +  6H2O  +  Energy    Mitochondria  convert  the  energy  released  in  adenosine  triphosphate  (ATP).  The  process  through   which   ATP   is   synthesised   by   a   flow   of   H+,   and   by   phosphates   (Pi)   is   called  oxidative  phosphorylation.  During  this  process,  an  exergonic  and  oxidative  reaction  that  releases  energy  (by  the  creation  of  an  electrons  chain)  is  in  balance  with  an  endergonic  one   (synthesis   of   ATP   by   a   flow   of   protons   H+).   Finally   oxidants   and   electrons   are  reduced  in  ATP  and  water.    

                                                                                                               1  “I  found  the  essential  reason  for  confining  the  life  of  the  Metazoan  to  a  fixed  and  limited  period,  in  the  wear  and  tear  to  which  an  individual  is  exposed  in  the  course  of  a  life-­‐  time”.  (1891)    

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 Yet  this  equilibrium  has  an  entropic  cost:   the  creation  of   reactive  oxygen  species  as  by-­‐products.   They   are   synthesised   intracellularly   through   multiple   processes.   Oxygen   is  incompletely   reduced   to   give   the   superoxide   radical  (·O2-­‐)   and   other   ones,   like   the  hydroxyl   radical   (•OH-­‐).   There   is   a   lot   of   antioxidant   defences.   For   instance,   the  superoxide   anion   (·O2-­‐)   is   reduced   to   (H202)   by   superoxide   dismutase.   And   (H202)   is  reduced  to  water  (H20)  by  catalase.  However,  this  reduction  is  also  incomplete,  since  a  part  of  (·O2-­‐)  is  converted  to  ONOO-­‐  and  a  part  of    (H202)  is  also  converted  to  •OH-­‐.  One  could   also   argue   that   the   first   imbalance   between   the   endergonic   and   the   exergonic  reaction  in  the  process  of  oxidative  phosphorylation  is  in  a  way  prolonged  or  completed  by   the   second   imbalance   between   the   creation   of   free   radicals   and   the   reaction   of  antioxidant  defences.  Nothing  in  such  biochemical  reactions  seems  to  go  again  a  classical  application  of  the  second  principle  of  thermodynamics,   in  his  stochastic  and  molecular  characterisation.   In   this   way   of   thinking,   one   shall   conclude   that   aging   could   be  completely  reduced  to  a  physical  deterioration  process.    1-­‐  It  is  easy  to  show  that  such  a  way  of  thinking  is  not  working  in  biology.  Let’s  start  with  some   matter   of   fact   arguments.   Blocking   the   production   of   natural   antioxidants   in  organisms   doesn’t   lead   necessary   to   a   shorter   life   span.   On   the   contrary,   it   has   been  shown  recently  (23)  that  a  round  worms  has  a  duration  of  life  extended,  when  the  action  of  hyperoxide  dismutase   is  blocked   in   its  metabolism.  Similar  studies  have  been  made  on  mice  (24).  More  generally,   first,   the  overexpression  of  antioxidant  reactions  doesn’t  lead  automatically   to  an  extended   life  span;  and  second,  when  a  correlation   is  attested  between  both,  it  is  not  a  proof.    

 2-­‐  Let’s  focus  now  on  a  very  ancient  story,  the  story  of  the  god  Teuth  reported  by  Plato  in  Phaedrus   (274e-­‐275a)  and  commented  by   the  French  philosopher   Jacques  Derrida   (la  pharmacie  de  Platon,  in  Dissémination,  (25).  Teuth  will   give  writing  as  a  present   to   the  Egyptians,   since   writing   will   be   a   cure   (pharmakon)   against   oblivion.   Yet   with   the  invention  of  writing,  the  people  will  loose  its  oral  tradition,  and  the  cure  is  converted  in  a   poison.  Derrida   shows   that   the   same  process   is   at  work   in  Plato’s   philosophy,   since  Socrates  uses  very  often  the  language  and  the  rhetoric  tools  of  the  sophists  in  order  to  fight   against   them.   So,   the  pharmakon   is   structurally   ambivalent:   it   is   a   cure  precisely  because  it  is  also  a  poison.      Let’s  come  back  now  to  our  biochemical  example  of  imbalance  between  free  radical  and  antioxidant  defences.  The   super  oxide  anion   is   a  poison   that   can  damage  cell.  Yet   it   is  well  known  by  physicians  (26)  that  it  has  vasodilatative  properties  on  human  tissues.  It  can   also   be   associated   with   another   strong   vasodilatator:   the   nitric   oxide   NO.   The  association   between   (·O2-­‐)   and   (NO)   leads   to   vasoconstriction,   and   to   a   possible  regulation   process   between   vasodilatation   and   vasoconstriction   that   is   nothing   but   a  biological   constraint.   As   a   physical   property   (·O2-­‐)   is   simply   involved   in   an   entropic  process  of  destruction,  but  as  a  biological  one  (·O2-­‐)   is  structurally  ambivalent.   It   is,  at  the  same  time,  and  sometimes  in  the  same  context,  a  cure  and  a  poison.  Thus,  it  cannot  be  reduced  to  its  entropic  characterisation.      3-­‐Finally,   there   is   no   physical   obligation   for   aging   in   living   organisms,   since   they   are  open  thermodynamic  systems  far  of  equilibrium.  Like  simple  dissipative  structures,  they  

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exchange  matter   and   energy   through   the   relation   between   exergonic   and   endergonic  chemical  reactions.    A   dissipative   structure   (27),   like   the   flame,   the   Bénard   convection   is   an   open  thermodynamic  system.  The  physical  states  of  such  system  are  not  completely  defined  by  its  internal  determinative  structure,  because  a  specific  flow  of  energy  (for  instance  a  temperature  gradient)  and  of  matter,  in  far  from  thermodynamic  equilibrium  boundary  conditions,   is   maintained   with   the   environment.   Such   a   system   is   also   constructed,  thanks   to   the   relation   with   environment.   It   is   what   it   does.   Even   a   complete   internal  description   of   such   system  will   not   be   enough   to   characterise   it,   because   the   relation  between  what  it  is  and  what  it  does,  will  always  add  some  new  emergent  properties  to  the   initial   ones.   In   the   case   of   a   dissipative   structure,   one   of   these   properties   is   the  persistence  of  negative  entropy.  As  a  new  global  constraint  emerging,  the  coherence  of  the  flame,  the  Bénard  convection  will  persist  under  certain  external  conditions.      Why  would  it  be  different   for  a  cell?  We  would  add  on  the  contrary  that  a  cell   is  not  a  mere  phase  transition  (crystal)  or  a  mere  dissipative  structure  (flame),  as  well  attested  by  Ervin  Schrödinger  (5).  Look  at  the  argument  of  the  famous  Austrian  physicist:  crystal  

growths   indefinitely  under  certain  physical   conditions.  Negative  entropy  persists.  But  it  is  always  the  same  crystal,  with  the  same  shape,  “like  in  an  ordinary  wall  paper”.  On   the   contrary,   life   deals  with   the   principle   of   proliferation  with   variation,   “like   in   a  Raphael  tapestry,  which  shows  no  dull  repetition,  but  an  elaborate,  coherent  meaningful  design   traced   by   the   great   master  »   (5).   Following   Schrödinger,   the   aperiodic   crystal  embedded  in  the  chromosome  structure  will  play  this  role,  because  such  a  structure  is  able  to  generate  new  constraints  indefinitely,  and  not  simply  the  same  global  one.      

2-­‐  Aging  as  a  repulsive  organisational  constraint      In  Investigations  Stuart  Kauffman  (10)  gives  a  definition  of  life  that  is  performed  by  “an  autonomous  agent  able  to  make  one  or  more  thermodynamic  work  cycles”.  It  is  also  able  of   self-­‐reproduction.   Let   us   precise   first   the   definition   of   “an   autonomous   agent”.  Kauffman  uses  a  nice  analogy  to  explain  this  point.   Imagine  a  Carnot’s  thermodynamic  cycle,  characterized  by  a  spontaneous  and  a  non-­‐spontaneous  process.  Through  the  first  one,  energy  is  released.  Through  the  second  one,  the  structure  that  permits  this  release  is  reconfigured.  In  an  engine,  it  would  be  gears,  escapements  and  chains.  One  could  call  this  a  set  of  constraints.  But  in  a  Carnot’s  cycle,  like  in  my  watch,  in  my  car,  or  even  in  my  computer,  the  constraints  are  artificial  ones.    The  human  being  creates  them.  The  perfect  example  is  the  inclined  plane  used  by  Galileo  to  explain  the  properties  of  motion.      We  will   assume   that   in   a  dissipative   structure,   or   in   a   crystallisation  process,   such  an  external  or  artificial  constraint   is  replaced  by  new  internal  conditions.  Such  a  system  is  not  characterized  by  its  determinative  structure.  All   invariants  that  permit  to  define  it,  like  conservation  of  energy,  or  conservation  of  motion,  no  longer  suffice  to  define  what  it  is.  What   it   is  depends   first  on  a  topological  condition  that  is  more  than  a  physical  one.  The  system  (A)   is  defined  by  the  relation  with   its  surrounding  (A*).  Its  surrounding,  is  also  itself,  in  a  way.  And  the  system  is  also  an  open  structure  with  boundaries  conditions.        

A

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                           Let  us  show  it  with  a  diagram:              

                         Legend:  The  system  A  as  characterised  by  the  inside/outside  relation  with  its  surrounding  A*.      It  seems  clear  enough  that  all  properties  of  A,  and  of  A  elements  cannot  give  a  complete  definition  of  A.  It  is  not  A  that  will  characterize  the  open  relation  between  A  and  A*.  On  the  contrary  the  inside/outside  relation  between  A  and  A*  will  characterize  A,  as  a  self-­‐referential  structure.  Such  a  structure  is  also  never  simply  defined  through  “what  it  is”.  It  is  defined  by  a  chronological  condition  (before/after):  the  relation  between  what  it   is  and  what  it  does.  Finally,  the  topo-­‐chronological  relation  (17)  between  the  system  and  its  boundary  conditions  will  create  after  a  new  global  and  emergent  constraint  that  was  not  present  before:  the  convective  structure  of  a  Bénard  system.      *   In   a  physical  dissipative   structure   a   single   global   constraint   appears.   Let  us   assume,  that  a  biological  system  is  characterized  by  a  “propagative”  ability  to  generate  more  and  more   constraints.   This   assumption   is   inspired   by   Stuart   Kauffman:   «  in   addition,   an  

21

A*  

 

A*  

A  

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autonomous  systems  carries  out  one  or  more  real  work  cycles,  linking  spontaneous  and  non   spontaneous   processes.   It   does   in   fact   measure,   detect,   and   record   sources   of  energy,   and  does  work   to   construct   constraints   on   the   release   of   energy,  which  when  released  in  the  constrained  way,  propagates  to  do  more  work,  often  constructing  further  constraints  on  the  release  of  energy  or  doing  work  by  driving  further  non  spontaneous  processes  »  (10).  Let  us  add   first   that  an  organism  that   is  able   to  change   its  own  constraints   is  not  only  from   the   physical   world.   It   is   also   in   its   own  world.   It   is   autonomous.   The   laws   that  govern  its  behaviours  are  also  its  own  laws,  its  norms.  It  acts  on  its  own  behalf.  In  such  an  organism,  causality  is  not  simply  complex,  it  is  internalised.    Second,   such  an  organism  is  not  simply  open   in   its  physical  structure.   It   is  open   in  the  ability  to  produce  constraints,  as  if,  such  “openness  function”  already  present  in  complex  physical  system,  was  recursively  internalised  in  biology.  We  can  understand  development,  or  evolution  as  a  mere  illustration  of  this  assumption.        **  Biologists  have  known  for  a   long   time  that  biochemical  reactions  are  exergonic  and  endergonic   and   that   anabolic   processes   are   opposed   to   catabolic   ones.   Let   us   try   to  specify   now   that   biological   organisation   is   also   characterised   by   the   relation  between   propagative   and   repulsive   constraints.   In   a   repulsive   process,   a   new   self-­‐destruction   function   (or  norm)  emerges,   through  which  constraints  are  destroyed.  Let  us  take  this  as  a  new  definition  of  aging,  aging  as  alteration.  Alteration  has  nothing  to  do  with  stochastic  phenomena,  even  if  stochastic  phenomena  are  obviously  involved  in  alteration.  Alteration  is  a  biological  function.    By  such  a  function,  it  is  specified  that  biological  organisation  can  never  be  closed.  What  is  not  biological  organisation   is  also  a  part  of   it.  Thus   life   is  not  only  an  open  physical  structure,   like   a   crystal.   It   is   a   polarised   normative   one.   Death,   passivity,   aging,  pathology,  monstrosity,  as  biological  norms,  are  present  in  life.  The  logic  of  life  requires  that  an  organism  will  provide  some  work  to  destroy  itself  on  its  own  behalf.    

3-­‐  Vicious  circles    What   could   be   a   catabolic   characterisation   of   aging   as   an   emergent   self-­‐destruction  function,  or  norm,  or  constraint  (these  words  have  the  same  meaning)?  It  is  not  easy  to  give   an   answer,   and   to   find   good   examples,   since   it   shows   the   influence   of   a   blind  reductionist   attitude   in   contemporary   experimental   sciences.   As   explained   recently  “biological   organisation”   is   not   information   (28)   and   also   not   only   “genetic  determination”  (29)(8).    For  instance,  it  is  clear  for  me,  that  there  is  no  gene  of  aging,  even  if  genes  are  obviously  involved   in   the   aging   process.   It   doesn’t   have   any   sense   to   assert   as   such   that  inactivation  of   the   insulin/IGF1-­‐   like-­‐   receptor  will  extend   the   longevity  of   the  worms  (30)   and   will   activate   stress-­‐resistance   transcription   factors.   Even   the   concept   of  “signalling   pathways”   is   too   descriptive   and   too   simple.   Proteins   are   synthesised   by  genes,  but  genes  are  activated  and  down  regulated  by  proteins  and  other  epigenetic  or  posttranslational   or   systemic   factors.   What   comes   first   in   biology   is   not   genes,   but  various  entanglements  of  determinative  levels  (28)  (29).      

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Like  Maffini,  Soto  and  Sonnenschein  (31)  analyse  cancer  through  the  relation  between  stroma  and  epithelium,  we  will  analyse  aging  at  the  level  of  connective  tissues,  and  not  simply  at  the  level  of  genes.  We  will  focus  more  specifically  on  the  relation  between  cells  and   extracellular   matrix   in   the   connective   tissues.   We   will   use   for   this   the   work   of  Ladislas  Robert  and  Jacqueline  Labat-­‐Robert  because  they  provide  during  the  eighties  a  non-­‐trivial  example  of  aging’s  vicious  circle.    Other   examples   of   vicious   circles   has   been   analysed   by   many   biologists.   The   most  famous   one   is   the   way   by   which   the   production   of   oxygen   radicals   during   cellular  respiration   enhances   somatic   mutation   of   mitochondrial   DNA   that   will   induce  respiratory   chain   dysfunction,   enhancing   more   mutations.   Finally   such   a   biochemical  vicious  circle  will  lead  exponentially  to  more  ROS  expression,  and  to  more  mitochondrial  damage.   Unfortunately,   such   an   exponential   degradation   is   mostly   blocked   by   cell  apoptosis,  or  other  mechanisms  (32).    Another  interesting  example  concerns  the  relation  between  degraded  proteins  and  the  proteasome,   since   proteasome   dysfunction   can   also   be   induced   by   oxidative   stress  through   interactions   of   protein   aggregates   (33).   However   this   point   needs   to   be  clarified.   For   instance,   what   is   the   exact   role   of   proteins   aggregates   in  neurodegenerative   diseases?   How   the   balance   between   the   action   of   chaperone  molecules  and  of  the  proteasome  can  be  perturbed  during  aging?  Many  questions  have  been  posed,  and  only  limited  replies  are  proposed.      As  often  mentioned  by  Robert,  cells  were  considered  up  to  the  end  of  70’s  as  producing  the  extra  cellular  matrix,  as  if  they  were  functionally  independent  from  it.  In  connective  tissues,   the  extra  cellular  matrix   (ECM)   is  composed  of   two  classes  of  macromolecules  proteoglycans   and   fibrous   proteins,   like   collagen,   elastin,   fibronectin   or   laminin.   Such  proteins  are  transcripted,  translated  and  expressed  in  cells.  But  the  matrix  is  not  inert;  it  interacts  with  cells  and  cytoskeletons,  through  integrin  and  other  receptors  inducing  a  loop  (34)  between  (ECM)  and  the  elements  from  which  (ECM)  is  synthesised.  Yet  using  topologic  language,  this  loop  is  not  cyclically  closed  on  itself.      In   1989   Robert,   Fülop   et   alli   (35)   identified   the   elastin/laminin   receptor.   It   is   well  known   that   more   connective   tissues   are   generated   during   aging,   and   that   they   are  structurally   and   functionally   changed.   One   also   knows   the   influence   of   connective  tissues   in   certain   human   pathologies,   like   cancer   (31).   In   connective   tissues,  degradation   is   controlled.   It   propagates,   as   a   dynamic   post-­‐translational   property  emerging  during  aging.  Thus,  aging   is  not  only  a  degradation  of   constraints.  A  new  global  constraint  emerges  in  this  process  of  degradation.    Going  down,  elastin  molecules  induce  in  mammals  an  increasing  fixation  of  calcium  and  lipid  deposition  that  saturates  elastin   fiber,  degraded  by  elastases  produced   in  an  age-­‐dependent   manner   by   smooth-­‐muscles   cells   and   fibroblasts.   It   is   a   typical   post-­‐translational   process,   in   which   chemical   agents   interacting   with   elastin   are   not  synthesised  by  genes.  Robert  et  alli  have  shown  (35)  that  elastin  degradation  products  interact   with   the   elastin   receptor,   inducing   loss   of   calcium   regulation   and   elastases  productions,  that  will  degrade  more  elastin  proteins  in  a  self-­‐amplifying  process.  Gilles  Faury  (36)  has  also  showed  that  in  addition  with  this  receptor  elastin  peptides  produce  NO-­‐dependent   vasorelaxation   in   rat   aorta   rings.   This   effect   has   efficiency   in   young  adults,  but  declines  with  age.  In  this  case,  another  process  is  involved,  through  which  the  chronic   overload   of   the   elastin   receptor   triggers   a   release   of   elastases   and   of   free  radicals.  The  same  occurs  with  fibronectin  degraded  by  proteases  in  fragments  that  will  

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also  increase  the  proteolytic  activity.  Such  complex  self-­‐amplified  processes  appear  to  have  been  not  fully  clarified  today.  For  instance,  why  are  more  connective  tissues  generated  during  mammalian  aging?  Why  the  rate  of  biosynthesis  fibronectin  (34)  or  of  tropoelastin  RNA  (37)  increases  with  age?  But  the  point  is  not  here  for  us.  The  interactive  loop  between  cells  and  (ECM)  is  altered  by  such  self-­‐amplified  processes,   in  a  dynamical  way.  And   it   is   clearly   in   connection  with  the   formation   of   atheroma,  with   heart’s   loss   of   contractile   efficiency,   decline   of   lungs  respiratory  capacity,  progressive  hardening  of  vascular  walls,  etc…                    

4-­‐  Alteration  and  delay    In  Creative  evolution  (15)  Henri  Bergson  was  already  cautious  with  the  characterization  of   aging   as   a   mere   «  catabolic  »   property.   He   also   understood   aging   not   only   as  “alteration”,  but  also  as  “delay”.      First,  it  seems  interesting  to  connect  this  point  with  some  considerations  on  epigenetic  factors  of  aging.  We  will   focus  on  a   family  of  proteins  studied   in  worms,   in  nematode,  and   in   drosophila:   the   Sirtuins.   Aging   is   studied   by   counting   the   number   of   cell  daughters  produced  by  an  individual  cell  mother  (replicative  life  span)  or  by  measuring  the  survival  time  of  populations  of  non-­‐dividing  cells  (chronological  life  span).    Sirtuins  act  in  yeast  by  removing  histone  acetyls  groups  in  the  presence  of  NAD+.  Thus,  they  are  classified   as   “NAD+-­‐dependent   deacetylases”   (11).   An   extra   copy   of   Sir2  extends   yeast  replicative   longevity   by   40%.   As   a   deacetylase,   it   prevents   sterility,   decreases   the  formation  of  rDNA  circles,  and  plays  a  crucial  role  in  the  formation  of  silent  chromatin.  Starving   of   yeast   cells   also   extends   life   span.   It   increases   cell   respiration   and   the  available  amount  of  NAD+.  It  has  the  potential  to  increase  the  activity  of  Sir2.  One  could  conclude  that  combination  of  starving  with  this  epigenetic  mechanism  mediated  by  Sir2  and  NAD+  could  explain  the  extent  of  replicative  life  span.  Experiments  in  Nematode  and  in  the  fruit  fly  seem  to  support  these  findings.  In  this  way  of  thinking,  Leonard  Guarente  writes:      «  In   our   own   studies,   what   seemed   almost   magical   was   that   yeast   genetics   led   us  something  that  promoted  survival.  The  SIR  troika  works  to  counteract  aging  »  (Ageless  Quest,  2003,  p.  32)  (11).    For  us,   such   a   conclusion  means   simply   that   aging   can  be   regulated   through   systemic  and   epigenetic   factors   in   relation   with   environmental   constraints.   Starvation   is   not  simply  controlled  by  a  stochastic  genetic  mutation,  even   if  a  mutation  of   the  gene  Sir2  seems  to  be  involved  in  this  case.  It  is  induced  by  environmental  constraints.  It  is  a  way  by  which  yeast  can  survive  in  the  absence  of  food.  It   is  a  plastic  norm  that  proves  “the  

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ability  of  an  organism  to  react  to  internal  or  external  environmental  input  with  a  change  in   form,   state,   movement   or   rate   of   activity   (38).   However,   the   causal   role   of   Sir2   in  aging  process   is  not  very  clear.  Another  study  (39)  concludes   that   the  deletion  of  Sir2  combined  with  caloric  restriction  and  mutations  in  glucose  signalling  pathways  extends  the  chronological  lifespan  even  if  it  reduces  the  replicative  one.      

Conclusion    By   our   first   example,   we   have   shown   that   aging   is   not   simply   physical   degradation.  Aging  is  a  repulsive  constraint  by  which  self-­‐amplification  of  degradation  is  biologically  controlled  in  complex  vicious  circles.  It  means  that  biological  organisation  is  not  only  the  ability  to  generate  new  constraints,  or  norms,  but  also  to  destroy  them.    It  shows  something  concerning  the  logic  of  life  that  refuses  the  principle  of  the  excluded  middle.   Life   is   the   ability   to   construct   constraints   through  work.   But  what   is   not   life_  aging,   pathology;   death_   is   also   a   biological   constraint.   It   expresses   that   life   as   a  biological  normative  activity  and  not  only  as  a  physical  dissipative  structure   is  always  outside  of  itself.  Thus,  the  negation  of  life  is  something  for  life.  It  is  not  a  pure  vacuum.      Of  course,  stochasticity,  genes  and  epigenetic  factors  are  involved  in  aging,  but  in  a  very  complex  manner.  The  so-­‐called  aging  clock  is  not  really  found  for  now.  Let  us  take  one  example.   In  several  papers  Holzenberger   (37)  shows  on  mice   that   the  gene  coding   for  IGF-­‐1   receptor   has   pleiotropic   effects   during   age.   It   promotes   the   secretion   of   GH  hormone  during  childhood,  and  delays  it  after  adult  age.  It  works  in  conformity  with  the  concept  of  antagonist  pleiotropy.    Yet   in  experiments  on  Drosophila  and  by  collecting  eggs   from  the   longest-­‐lived  flies   in  each   generation  Michael  Rose  has  produced  by   artificial   selection   flies   that   quadruple  their  original  life  span.  And  they  lay  more  eggs  at  every  stage  of  life!  He  suggests  today  that  it  could  be  connected  with  “protagonistic  pleiotropy”:  beneficial  effects  in  later  life  as  a  result  of  selection  in  earlier  life.  Who  is  wrong,  Rose  or  Holzenberger?      In   Rose’s   investigations,   a   plateau   in   the   action   of   natural   selection   is   observed   on  Drosophila.  It  means  that  deleterious  effects  of  pleiotropic  genes  on  elder  organisms  are  no  more  observed.  Rose  (40)  tries  to  find  an  explanation  of  this  phenomenon  in  terms  of  classical  genetics  of  populations,  through  the  ageless  action  of  certain  genes.  For  us  the  explanation   is   not   here.   Longevity   could   be   extended,   and   aging   delayed   for  environmental  reasons  that  are  not  governed  as  such  by  natural  selection  and  that  can  be  managed   by   individual   and   organisational   constraints,   and   not   by   reproductive   or  populational  ones.        

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