Abstract 16333: S100A1 Deficiency Impairs Post-Ischemic Angiogenesis via Compromised Proangiogenic Endothelial Cell Function and Nitric Oxide Synthase Regulation
Background - Impaired NO homeostasis in endothelial cells (ECs) lacking the EF-hand calcium (Ca2+) sensor protein S100A1 prompted investigation of its pathophysiological role in regenerative angiogenesis in humans and experimentally induced critical limb ischemia (CLI) in mice.
Methods and Results - Patients with chronic CLI showed almost complete loss of S100A1 mRNA expression (decrease to 5%, P<0.05, control n=3 vs. CLI n=5) in ischemic skeletal muscle biopsies. Human arterial ECs were particularly susceptible to hypoxia-induced loss of S100A1. Ensuing studies in S100A1 knockout (SKO) mice with acute limb ischemia due to femoral artery resection (FAR), using clinical scoring, functional, histological and anatomical endpoints, unveiled insufficient perfusion recovery and high rates of autoamputation (0/22 for WT vs. 10/18 for SKO, P<0.01) due to defective angiogenesis compared with wild-type (WT) mice. Cellular studies in SKO ECs demonstrated impaired in vitro and in vivo proangiogenic properties (migration, proliferation, tube and capillary formation), attenuated vascular endothelial growth factor (VEGF)- and hypoxia-stimulated eNOS activity, and reduced nitric oxide (NO) bioavailability. Consistently, NO in ischemic SKO tissue was also reduced (3-fold vs. ischemic WT skeletal muscle tissue, n=4). Molecular assays revealed Ca2+-dependent S100A1/eNOS interaction in ECs and dose-dependent improvement of dysfunctional eNOS from SKOischemic tissue by S100A1. Insufficient angiogenesis and continued ischemia in SKO limbs provoked excessive VEGF accumulation entailing VEGF-receptor-2 degradation and attenuation of the proangiogenic PI3K/Akt/eNOS signaling cascade. NO supplementation strategies rescued defective angiogenesis and salvaged limbs in SKO mice post-FAR.
Conclusions - Our study shows for the first time a downregulation of S100A1 expression in humans with CLI and characterizes S100A1 as an indispensable factor for postischemic regenerative angiogenesis. Loss of S100A1 seems to compromise key aspects of EC-dependent neovascularisation based on abnormal NO bioavailability and eNOS function. Its pathophysiological impact on CLI prompts further investigation of its therapeutic regenerative potency in PAD.
- © 2012 by American Heart Association, Inc.