The Role of Neuregulin/erbB Signaling in Endothelial Progenitor Cell Biology

Abstract

Neuregulin (NRG) is a ligand for the erbB3 and erbB4 members of the EGF family receptors, and is known to activate signaling pathways that mediate proliferation, survival, migration and differentiation in various cell types. Stimuli such as exercise and ischemia‐reperfusion, which induce NRG shedding also induce endothelial progenitor cell (EPC) mobilization and recruitment. We hypothesized that NRG signaling may a play role in EPC mobilization and homing.Using western blot and immunostaining, we found that a murine embryonic endothelial progenitor cell line expresses NRG ligand and the ErbB‐2, 3 and 4 receptors. Treatment with recombinant NRG led to ErbB2/B3 phosphorylation as well as downstream Akt and endothelial nitric oxide synthase phosphorylation. NRG activated signaling was blocked by the ErbB receptor inhibitors AG1478 and Lapatanib. To examine the role of NRG/ErbB signaling in EPC biology we performed a matrigel angiogenesis assay. In contrast to mature rat cardiac microvascular endothelial cells (CMEC), EPC's in 3 dimensional monoculture do not form microvessel networks. However when EPC's are co‐cultured with CMEC's in matrigel, EPC's incorporate into the developing microvessel network within 24 hrs. This effect was completely inhibited by the erbB receptor inhibitor AG1478.These results support a role for Neuregulin/ErbB signaling in EPC recruitment. A clearer understanding of what role NRG signaling may play in EPC biology has important implications for cardiovascular biology, as well as the pathophysiology of cardiac dysfunction seen in the setting of erbB2 targeted cancer therapeutics.