In vitro differentiation of muscle-derived stem cells and their potential role in attenuation of abdominal aortic aneurysm formation

Abstract

Introduction: Abdominal aortic aneurysms (AAA) are a growing problem worldwide, yet there is no known medical therapy. The pathogenesis involves degradation of the elastic lamina by two combined mechanisms: increased degradation of elastin by matrix metalloproteinases (MMP) and decreased formation of elastin due to apoptosis of vascular smooth muscle cells (VSMC). In this study, we set out to examine the ability of muscle-derived stem cells (MDSC) to differentiate to VSMCs in vitro, and their potential role in the attenuation of AAA formation by inhibition of these pathogenetic mechanisms.

Methods: Muscle-derived stem cells were isolated from murine skeletal muscles using a modified preplate technique. These cells were stimulated with PDGF-BB in vitro for differentiation to VSMC-like progenitor cells (VSMC-PC) and were subsequently implanted into elastase-induced AAAs in rats. After 6 weeks, the aortas were harvested and the formation of AAA was investigated. Immunohistochemical staining, RT-PCR, western blot and gel zymography for MMPs were performed and compared to a control group.

Results: Isolated MDSCs showed characteristic expression of markers Sca-1 and CD34. When stimulated in vitro with PDGF-BB, the cells showed expression of α-SMA, a specific marker for smooth muscle cells. In vivo studies of elastase-perfused AAAs showed that the cell therapy group had decreased rate of aneurysm formation compared to control (83% vs. 50%), and MMP expressions at the genetic, protein and enzymatic levels were significantly decreased in the cell therapy group. Furthermore, direct implantation of VSMC-PCs in the intima of harvested aortas was visualized under immunofluorescent staining, suggesting that these cells were responsible for the inhibition of MMPs and consequent attenuation of AAA formation.

Conclusions: These results show a promising role of stem cell therapy for the treatment of AAAs, and with further studies, may be able to reach clinical significance.