Abstract 18017: The Dual Rho-GEF Kalirin Promotes Atherosclerosis by Augmenting Smooth Muscle Cell Rac1 Signaling, Migration, and Proliferation
Integral to atherosclerosis, smooth muscle cell (SMC) migration and proliferation are regulated by RhoA and Rac signaling, activated by GTP exchange factors (GEFs). Both Rac- and RhoA-GEF domains reside in kalirin, a 340 kDa protein associated with human atherosclerosis by genetic epidemiology. We previously showed that kalirin up-regulates in SMCs during atherogenesis and promotes SMC migration and proliferation in vitro. We therefore used congenic mice without (Kalrnflox/+) and with (SM22α-Cre+/Kalrnflox/+) SMC-specific Kalrn haploinsufficiency to test the hypothesis that SMC kalirin promotes SMC migration/proliferation and atherogenesis. In SMC-Kalrn−/+ mice, kalirin protein levels were 60±10% of WT in SMCs, but equal to WT in leukocytes and neurons (by IB). Kalrn−/+ SMCs showed only 40±20% and 50±7% of WT SMC Rac1 activation (PAK1 autophosphorylation) in response to PDGF and endothelin-1, resp., but ∼100% of WT SMC RhoA activation (MYPT1 phosphorylation). SMC-Kalrn−/+, Kalrnflox/+, and WT mice had equivalent systolic BPs and heart rates (tail cuff manometry). To assess SMC migration/proliferation we denuded the common carotid endothelium (0.36-mm wire), a procedure we showed (by bone marrow transplant) produces neointima comprising SMCs from only arterial media. Neointimal area 4 wk post-op was 70±10% less in SMC-Kalrn−/+ than Kalrnflox/+ mice (4±1 vs. 11±3 μm2 × 103, p=0.03). To assess atherosclerosis, we fed a Western diet for 12 wk to Apoe−/−/SMC-Kalrn−/+ and Apoe−/−/Kalrnflox/+ mice (n = 7 each) matched for sex, age, and weight; serum cholesterols were equivalent. Sudanophilic aortic lesion area (%) was equivalent en face in both groups, but brachiocephalic artery cross sections showed 10-fold less neointimal area in Apoe−/−/SMC-Kalrn−/+ than in Apoe−/−/Kalrnflox/+ mice (70±30 vs 700±100 μm2, p=0.02). Further, brachiocephalic plaques evinced SMC-rich fibrous caps only in Apoe−/−/SMC-Kalrnflox/+ mice (100%). Thus, SMC kalirin enhanced atherosclerotic lesion thickness and complexity, but did not affect early foam cell lesion formation. We conclude that kalirin is an important GEF for Rac1, but not RhoA, in SMCs, and that SMC kalirin promotes atherosclerosis, at least in part, by augmenting SMC proliferation and migration in vivo.
- © 2010 by American Heart Association, Inc.