Background: Given that cathepsin S (CatS) gained attention due to its enzymatic and non-enzymatic functions in signaling, the role of CatS in ischemia-induced angiogenesis of aged mice was explored.Methods and Results:To study the role of CatS in the decline in aging-related vascular regeneration capacity, a hindlimb ischemia model was applied to aged wild-type (CatS+/+) and CatS-deficient (CatS-/-) mice. CatS-/-mice exhibited impaired blood flow recovery and capillary formation and increased levels of p-insulin receptor substrate-1, Wnt5a, and SC35 proteins and decreased levels of phospho-endothelial nitric oxide synthase (p-eNOS), p-mTOR, p-Akt, p-ERK1/2, p-glycogen synthase kinase-3α/β, and galatin-3 proteins, as well as decreased macrophage infiltration and matrix metalloproteinase-2/-9 activities in the ischemic muscles. In vitro, CatS knockdown altered the levels of these targeted essential molecules for angiogenesis. Together, the results suggested that CatS-/-leads to defective endothelial cell functions and that CatS-/-is associated with decreased circulating endothelial progenitor cell (EPC)-like CD31+/c-Kit+cells. This notion was reinforced by the study finding that pharmacological CatS inhibition led to a declined angiogenic capacity accompanied by increased Wnt5a and SC35 levels and decreased eNOS/Akt-ERK1/2 signaling in response to ischemia.
Conclusions: These findings demonstrated that the impairment of ischemia-induced neovascularization in aged CatS-/-mice is due, at least in part, to the attenuation of endothelial cell/EPC functions and/or mobilization associated with Wnt5a/SC35 activation in advanced age.
Keywords: Aging; Angiogenesis; Cathepsin S; SC35; Wnt5a.