Abstract 19312: Endothelial Specific erbB2 Deletion Enhances Ischemia Induced Angiogenesis
Neuregulins (NRG) are endothelial derived growth factors that are ligands for erbB receptors. We have previously shown that NRG promotes angiogenesis and that loss of endothelial NRG impairs the angiogenic response to ischemia. However, the erbB receptor(s) involved in this process remains largely unknown. We hypothesized that endothelial erbB2, the erbB receptor with the most potent kinase domain, mediates angiogenesis in response to ischemic injury. To test this hypothesis, a mouse line expressing tamoxifen-inducible Cre -recombinase under the control of the vascular endothelial cadherin promoter with homozygously floxed erbB2 sites (CFF) was generated. CFF or Cre only expressing mice (C) were treated daily with vehicle (V) or tamoxifen (T) beginning three days before femoral artery ligation (1mg, i.p. to knock out endothelial erbB2 expression) and continuing for 28 days after surgery (n=4 per group). To assess angiogenesis in vivo, lower limb blood flow was measured using Doppler. Contrary to our hypothesis, we observed that 4 weeks post surgery, erbB2 deletion resulted in a significant increase in flow in the lower limb compared to control (138±5.1 vs.78±5.8 % PU/ surface area, P<0.05). To further confirm these findings, ischemic and non-ischemic muscle sections were stained with anti-PECAM to quantify capillaries. The ratio of capillary numbers per muscle fiber in the ischemic to non-ischemic leg was higher in the erbB2 endothelial deleted mice compared to control (2.18±0.4 vs.1.38±0.2, P<0.05) confirming an enhanced angiogenic response in the absence of endothelial erbB2 expression. The mechanism for enhanced angiogenesis was investigated by immunoblotting for VEGF in protein extract from muscle isolated from CFF-T and CFF-V treated mice. ErbB2 endothelial specific deletion resulted in a 2-fold increase in VEGF protein expression, which may, in part explain the enhanced angiogenic response. Thus, surprisingly, we found that erbB2 in skeletal muscle endothelium may be a negative regulator of angiogenesis in response to ischemic insult.
- © 2010 by American Heart Association, Inc.