Abstract 1359: Only the Catalytic p110alpha Isoform Mediates Class IA PI 3-Kinase-Induced Atherogenic Signals in Vascular Smooth Muscle Cells
Proliferation, migration, and apoptosis of vascular smooth muscle cells (VSMC) are pivotal determinants of the pathogenesis of vascular diseases, which are mainly controlled by growth factor dependent activation of PI 3-Kinase (PI3K). Growth factors like platelet-derived growth factor (PDGF) activate class IA PI3Ks containing one of three p110 catalytic subunits (p110alpha, p110beta, and p110delta). We investigated the specific function of these isoforms for PDGF-controlled proliferation, migration, and apoptosis of VSMC using novel isoform-specific inhibitors. PDGF-dependent proliferation and migration solely depended on p110alpha. Stimulation of VSMC with PDGF-BB (50 ng/ml) mediated a 2.5±0.4 increase (p<0.05) of DNA-synthesis (BrdU incorporation assay) and induced a 3.4+/−0.7 fold increase (p<0.05) of VSMC migration (modified Boyden-chamber). Inhibition of p110alpha with PIK075 (1 μM, Ki=100 nM) completely abrogated PDGF-dependent DNA-synthesis and migration (p<0,05), whereas inhibitors against p110beta (TGX 221, 1 μM) or p110delta (IC87114 1μM) had no influence. Consistently, PDGF-induced DNA-synthesis and migration were suppressed by siRNA-dependent downregulation of p110alpha (p<0,05) whereas p110beta or p110delta knockdown had no effect. Interestingly, stimulation of VSMC with PDGF-BB (50 ng/ml) induced anti- or proapoptotic effects depending on the duration of PDGFR activation. Incubation of VSMC with H2O2 (50 μM, 16h) led to a 2.8±0.7 fold increase (p>0.05) of apoptosis (Cell Death Detection ELISA). Simultanous addition of PDGF-BB (50 ng/ml) significantly diminished the H2O2-induced apoptosis (52±7%, p>0.05). In contrast, prestimulation with PDGF-BB 24h prior to the addition of H2O2 led to an increase of H2O2-induced apoptosis (7.8±1.3, p>0.05). The anti- as well as the proapoptotic effect depended strictly on p110alpha as PIK075 (1 μM, p<0,05) or p110alpha specific siRNA completely abrogated PDGF-BB-mediated pro- as well as antiapoptotic effects. Our results demonstrate that only the catalytical PI3K subunit p110alpha mediates the growth factor-induced atherogenic responses. Therefore, p110alpha represents an interesting therapeutic target for prevention of atherosclerosis and restenosis formation.