Abstract 1393: Targeting of KLF15 Reveals a Critical Role in the Vascular Smooth Muscle Cell Response to Injury
Background: Under physiologic conditions, VSMC contract and relax and thereby regulate vascular tone and blood pressure. In response to injury, these cells proliferate, migrate and contribute to neointima formation in atherosclerosis and restenosis. Here, we identify the Kruppel-like Factor 15 (KLF15) as a novel regulator of the VSMC response to injury.
Methods and Results: KLF15 expression is robust in several tissues including the aorta and is significantly reduced in the rodent carotid artery following balloon injury. Immunohistochem-istry reveals that KLF15 expression is exclusively seen in the smooth muscle layer of blood vessels. In vitro, KLF15 expression is high in quiescent rat aortic smooth muscle cells (0.4% serum for 72 hours; RASMC) and strongly reduced by pro-proliferative stimuli such as serum, platelet-derived growth factor (PDGF-bb), or angiotensin (Ang II). Adenoviral overexpression of KLF15 in cultured RASMC strongly inhibits cell proliferation under both basal and PDGF-bb-stimulated conditions. Conversely, KLF15-deficient (KLF15−/ −) SMCs exhibit enhanced proliferation under both basal and PDGF-bb-stimulated conditions. Mechanistically, KLF15 induced expression of growth inhibitory factors (e.g. p27), and reduced expression of pro-proliferative targets (e.g. KLF5). Targeting of KLF15 by homologous recombination revealed viable and fertile animals. The systolic blood pressure using tail vein cuff method in KLF15−/ − mice is higher than wild-type mice (105±0.002 vs. 88±1.17, p<0.001). Ex vivo vasoreactivity studies using endothelium denuded aortic rings demonstrate that KLF15−/ − aortas are hypercontractile in response to phenylephrine treatment. In addition, vasorelaxation in KLF15−/− aortic rings is reduced in response to nitroprusside. Finally, to investigate the role in the SMCs response to injury, femoral artery wire injury experiments were performed. At 14d, KLF15 (−/−) mice exhibited a significant increase in neointimal area (KO=0.015±0.008 vs. WT=0.009±0.006 mm2 p<0.001) and intima:media area ratio (KO=0.98±0.46 vs. WT=0.66±0.41, p<0.01).
Conclusion: KLF15 is a novel transcriptional regulator of VSMC proliferation, vascular reactivity, and the blood vessel’s response to injury.