Atherosclerosis  develops  predominantly  at  regions  of  the  arterial  tree  exposed  to  disturbed   blood   flow,   which   generates   low,   oscillatory   shear   stress   (WSS)   at   the   lumen.   Of   note,   endothelial   cells   (EC)   at   lesion-­‐prone   regions   are   characterised   by   an   increased   rate   of   apoptosis,   thus   providing   a   potential   explanation   for   the   distinct   spatial   localisation   of   atherosclerosis.   To   understand   the   interaction   between   flow   and   apoptosis   we   used   microarray   technology   coupled   to   computational   fluid   dynamics   (CFD)   to   identify   genes   differentially   expressed   at   high   or   low   WSS   regions   of   the   porcine   aorta.   We   examined   whether  putative  regulators  of  apoptosis  can  be  activated  by  flow  in  vitro  and  studied  their   function  using  cultured  EC.  
In  this  study,  we  employed  magnetic  resonance  imaging  and  CFD  to  model  blood  flow   in  the  porcine  aortic  arch  and  generate  WSS  maps  that  served  as  guidelines  for  the  isolation   of   EC   for   subsequent   transcriptional   analysis.   Furthermore   we   characterised   the   flow   in   stenosed   carotid   arteries   where   a   constrictive   extravascular   device   was   surgically   applied.   The   influence   of   WSS   on   the   expression   of   putative   regulators   of   apoptosis   was   studied   using  in  vitro  flow  assays  and  gene  function  was  analysed  using  siRNA-­‐based  approaches.  
Computed   WSS   maps   revealed   great   spatial   heterogeneity   and   challenged   common   assumptions   about   the   mechanical   conditions   at   susceptible   and   protected   regions.   In   addition,   microarray   analysis   of   ECs   isolated   from   the   aortic   arches   of   5   pigs   identified   764   differentially   expressed   genes   that   influence   diverse   physiological   activities.   Functional   annotation  of  these  transcripts  highlighted  the  presence  of  41  molecules  with  an  inferred  or   known   role   in   the   regulation   of   apoptosis.   We   selected   two   candidates   for   functional   screening   in   vitro:   PERP   and   PDCD2L.   Staining   for   active   caspase-­‐3   and   DNA   fragmentation   revealed   that   EC   apoptosis   was   significantly   enhanced   in   EC   exposed   to   oscillatory   shear   stress  compared  to  cells  exposed  to  uniform  flow.  Silencing  of  PERP  reduced  apoptosis  in  EC   exposed  to  oscillatory  shear  stress,  while  silencing  PDCD2L  did  not  have  a  significant  effect.  
We   conclude   that   shear   stress   influences   EC   viability   through   transcriptional   mechanisms   that   might   involve   the   novel   apoptosis   regulator   PERP.   Our   observations   illuminate   the   molecular   mechanisms   that   regulate   the   focal   nature   of   vascular   injury   and   atherosclerosis  and  provide  a  large  genetic  dataset  to  use  in  future  studies.