PLF‐1 (Proliferin‐1) Modulates Smooth Muscle Cell Proliferation and Development of Experimental Intimal Hyperplasia

BACKGROUND: Although apoptosis and cell proliferation have been extensively investigated in atherosclerosis and restenosis postinjury, the communication between these 2 cellular events has not been evaluated. Here, we report an inextricable communicative link between apoptosis and smooth muscle cell proliferation in the promotion of vascular remodeling postinjury. METHODS AND RESULTS: Cathepsin K–mediated caspase‐8 maturation is a key initial step for oxidative stress–induced smooth muscle cell apoptosis. Apoptotic cells generate a potential growth‐stimulating signal to facilitate cellular mass changes in response to injury. One downstream mediator that cathepsin K regulates is PLF‐1 (proliferin‐1), which can potently stimulate growth of surviving neighboring smooth muscle cells through activation of PI3K/Akt/p38MAPK (phosphatidylinositol 3‐kinase/protein kinase B/p38 mitogen‐activated protein kinase)‐dependent and ‐independent mTOR (mammalian target of rapamycin) signaling cascades. We observed that cathepsin K deficiency substantially mitigated neointimal hyperplasia by reduction of Toll‐like receptor‐2/caspase‐8–mediated PLF‐1 expression. Interestingly, PLF‐1 blocking, with its neutralizing antibody, suppressed neointima formation and remodeling in response to injury in wild‐type mice. Contrarily, administration of recombinant mouse PLF‐1 accelerated injury‐induced vascular actions. CONCLUSIONS: This is the first study detailing PLF‐1 as a communicator between apoptosis and proliferation during injury‐related vascular remodeling and neointimal hyperplasia. These data suggested that apoptosis‐driven expression of PLF‐1 is thus a novel target for treatment of apoptosis‐based hyperproliferative disorders.