Objective: Circulating progenitor cells possess vasculogenesis property and participate in repair of vascular injury. Cx (connexin) 43-a transmembrane protein constituting gap junctions-is involved in vascular pathology. However, the role of Cx43 in smooth muscle progenitor cells (SPCs) remained unclear. Approach and Results: Human SPCs cultured from CD34+ peripheral blood mononuclear cells expressed smooth muscle cell markers, such as smooth muscle MHC (myosin heavy chain), nonmuscle MHC, calponin, and CD140B, and Cx43 was the most abundant Cx isoform. To evaluate the role of Cx43 in SPCs, short interference RNA was used to knock down Cx43 expression. Cellular activities of SPCs were reduced by Cx43 downregulation. In addition, Cx43 downregulation attenuated angiogenic potential of SPCs in hind limb ischemia mice. Protein array and ELISA of the supernatant from SPCs showed that IL (interleukin)-6, IL-8, and HGF (hepatocyte growth factor) were reduced by Cx43 downregulation. Simultaneously, Cx43 downregulation reduced the phosphorylation of NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) and Akt (protein kinase B) pathway and reactivation of NF-κB and Akt using betulinic acid, and SC79 could restore the secretion of growth factors and cytokines. Moreover, FAK (focal adhesion kinase)-Src (proto-oncogene tyrosine-protein kinase Src) activation was increased by Cx43 downregulation, and inactivation of Akt-NF-κB could be restored by Src inhibitor (PP2), indicating that Akt-NF-κB inactivated by Cx43 downregulation arose from FAK-Src activation. Finally, the depressed cellular activities and secretion of SPCs after Cx43 downregulation were restored by FAK inhibitor PF-562271 or PP2.
Conclusions: SPCs possess angiogenic potential to repair ischemic tissue mainly through paracrine effects. Gap junction protein Cx43 plays an important role in regulating cellular function and paracrine effects of SPCs through FAK-Src axis.
Keywords: angiogenesis; connexin43; hepatocyte growth factor; interleukin-6; interleukin-8; paracrine; smooth muscle progenitor cells.