Adult Mesenchymal Stem Cells and Derivatives in Improved Elastin Homeostasis in a Rat Model of Abdominal Aortic Aneurysms

Abdominal aortic aneurysms (AAAs) are localized rupture-prone expansions of the aorta with limited reversibility that develop due to proteolysis of the elastic matrix. Natural regenerative repair of an elastic matrix is difficult due to the intrinsically poor elastogenicity of adult vascular smooth muscle cells (VSMCs). This justifies the need to provide external, pro-elastin regenerative- and anti-proteolytic stimuli to VSMCs in the AAA wall towards reinstating matrix structure in the aorta wall. Introducing alternative phenotypes of highly elastogenic and contractile cells into the AAA wall capable of providing such cues, proffers attractive prospects for AAA treatment. In this regard, we have previously demonstrated the superior elastogenicity of bone marrow mesenchymal stem cell (BM-MSC)-derived SMCs (cBM-SMCs) and their ability to provide pro-elastogenic and anti-proteolytic stimuli to aneurysmal SMCs in vitro. However, the major issues associated with cell therapy, such as their natural ability to home into the AAA tissue, their in vivo biodistribution and retention in the AAA wall, and possible paracrine effects on AAA tissue repair processes in the event of localization in remote tissues remain uncertain. Therefore, in this study we focused on assessing the fate, safety, and AAA reparative effects of BM-MSC-derived cBM-SMCs in vivo. Our results indicate that the cBM-SMCs (a) possess natural homing abilities similar to the undifferentiated BM-MSCs, (b) exhibit higher retention upon localization in the aneurysmal aorta than BM-MSCs, (c) downregulate the expression of several inflammatory and pro-apoptotic cytokines that are upregulated in the AAA wall contributing to accelerated elastic matrix breakdown and suppression of elastic fiber neo-assembly, repair, and crosslinking, and (d) improve elastic matrix content and structure in the AAA wall toward slowing the growth of AAAs. Our study provides initial evidence of the in vivo elastic matrix reparative benefits of cBM-SMCs and their utility in cell therapy to reverse the pathophysiology of AAAs.