Abstract 1705: Arginase Stimulates Cell Cycle Progression and Neointima Formation in Rat Injured Carotid Arteries
Arginase is the central enzyme of the urea cycle hydrolyzing L-arginine to L-ornithine which is subsequently metabolized to growth-stimulatory polyamines. Although arginase has been demonstrated to stimulate the proliferation of cultured vascular smooth muscle cells (VSMCs), the underlying mechanisms have not been fully characterized. Moreover, the involvement of arginase in governing vascular growth in vivo is not known. Accordingly, the present study investigated the role of arginase on cell cycle progression and neointima formation in a rat carotid artery injury model. Balloon injury resulted in an increase in vessel arginase activity that was first detected 2 days after injury, peaked after 7 days, and persisted for 14 days. The induction of arginase activity correlated with a 2-fold increase in arginase I protein which was observed in both the media and intima of injured vessels. Perivascular application of the potent and selective arginase inhibitors S-(2-boronoethyl)-L-cysteine (BEC; 1mg) or N-hydroxy-nor-L-arginine (L-OHNA; 1mg) via a pluronic gel immediately following injury markedly attenuated neointima formation after 2 weeks by ~65%. Furthermore, PCNA-staining indicated that BEC or L-OHNA inhibited both medial and neointimal DNA synthesis by ~80%. In contrast, arginase inhibition had no effect on VSMC apoptosis or endothelial regrowth after injury. Finally, cultured rat aortic VSMCs selectively expressed arginase I protein, and inhibition of arginase activity with BEC or L-OHNA blocked polyamines synthesis. BEC and L-OHNA also inhibited VSMC proliferation in vitro and arrested these cells in the G0/G1 phase of the cell cycle. This antiproliferative effect did not involve alterations in cell viability or p27, cyclin D1, E or A protein expression but was associated with a 2-fold increase in p21 and p53 expression, and was reversed by the exogenous administration of the polyamine, putrescine. In conclusion, this study demonstrates that arginase is essential for VSMCs to enter the cell cycle and that arginase contributes to the remodeling response following arterial injury. Arginase I represents a potentially novel therapeutic target for the treatment of occlusive vascular disorders.