Abstract 9629: Cathepsin K-Mediated Noich1 Activation Contributes to Neovascularization in Response to Hypoxia

Background: Cysteine proteases play important roles in human pathobiology. This report shows the participation of cathepsin K (CatK) in ischemia-induced neovascularisation. Methods and Results: Left femoral artery ligation-induced ischemia in mice showed increased CatK expression and activity. CatK-deficient young and aged mice showed impaired functional recovery following hind ischemia. These mice also showed reduced levels of cleaved Notch1 (c-Notch1), vascular endothelial growth factor (VEGF), Flt-1 and phospho-Akt proteins of the ischemic muscles. In vitro , CatK knockdown reduced the levels of c-Notch1, VEGF and Flt1, essential molecules for angiogenesis and vasculogenesis. Together, the effects of CatK knockdown led to defective endothelial cell invasion, proliferation and tube formation. Recombinant human CatK degrades gama-secretase substrate in time- and dose dependent manners, suggesting CatK is involved in Notch1 activation. This was reinforced by the finding that CatK inhibition impairs Notch1 activation in response to hypoxia with no change in known gama-secretase activity.CatK-deficiency decreased circulating EPC-like CD31+/c-Kit+cells in mice of both ages. Transplantation of bone-marrow-derived mononuclear cells from CatK+/+ mice restored neovascularisation in CatK -/- mice. Conclusions: CatK activity controls neovascularisation via partial modulation of Notch1 signaling activation in response to hypoxia. Thus, CatK has a critical role in vascular formation and represents a new therapeutic target for vascular disease.