APEX1 and atherosclerosis: However, SIRT1 also activates other components of the BER pathway, including the enzymes thymine DNA glycosylase, apurinic/apyrimidinic endonuclease 1, and poly(ADP-ribose) polymerase 1,48,49 which may partly explain the profound effect of VSMC SIRT1 knockout in atherosclerosis.10