Mesenchymal stem cells (MSCs) residing in old humans may respond poorly to tissue attrition or injury. Myocardin-A (McA) acts as a transcription cofactor for cardiomyogenesis while telomerase prevents senescence. This study assessed whether gene delivery to over-express the catalyitic subunit of telomerase TERT and McA impacts survival, growth and myogenic differentiation in aged MSCs.
MSCs from bone marrow of 24 months-old C57BL/6 male mice were efficiently transduced or co-transduced with 3th generation lentiviral vectors carrying cDNAs coding for TERT-yellow fluorescence protein (YFP) or McA-V5 epitope fusion proteins. Evidence for interaction between TERT and McA was obtained by co-immunoprecipitation and by bioluminescence resonance energy transfer assay. Transduction with TERT, and to a less extent, McA, but not empty vectors (mock) elevated cell viability (assessed by flow cytometry), proliferation (by BrdU uptake), and self-renewal (by colony formation). MSCs with TERT and McA transduction showed decreased apoptotic responses to Fas induction (Fig. 1 A). Increased expression of endogenous McA and smooth muscle α-actin occurred in MSCs with TERT overexpressed (n = 3, p < 0.05 by ANOVA vs mock-transduced) (Fig. 1 B). MSCs with co-expression of both TERT and McA showed enhanced expression of cardiac and smooth muscle α-actin expression (Fig. 1 C), Oct-4 and promyogenic genes Nkx2.5, MLC2v, Mef2c and McA. The cells showed increased activity of serum response factor.
Delivery of TERT and McA genes may resuscitate MSCs from aged mice by increasing the cell ability of survival, proliferation and differentiation into cardiomyogenic cells. Detrimental effects of aging on the heart may be reversed by transplantation of MSCs following their rejuvenation in vitro by TERT and McA gene transfer.