.....We examined whether the overexpression of myocardin (MYOCD) and telomerase reverse transcriptase (TERT) enhanced the survival, growth, and myogenic differentiation of mesenchymal stromal cells (MSC) isolated from adipose or bone marrow tissues of aged mice. We also examined the therapeutic efficacy of transplanted MSCs overexpressing MYOCD and TERT in a murine model of hindlimb ischemia. Methods and Results: MSCs from adipose or bone marrow tissues of young (1-month-old) and aged (12-month-old) male C57BL/6 and apolipoprotein E-null (ApoE-/-) mice were efficiently transduced with lentiviral vectors encoding TERT and/or MYOCD. Flow cytometry and bromodeoxyuridine cell proliferation assays showed that transduction with TERT and, to a lesser extent, MYOCD, increased MSC viability and proliferation. In colony forming assays, MSCs overexpressing TERT and MYOCD were more clonogenic than mock-transduced MSCs. Fas-induced apoptosis was inhibited in MSCs overexpressing MYOCD or TERT. When compared with aged mock-transduced MSCs, aged MSCs overexpressing TERT and/or MYOCD increased myogenic marker expression, blood flow, and arteriogenesis when transplanted into the ischemic hindlimbs of ApoE -/- mice. Conclusions: The delivery of the TERT and MYOCD genes into MSCs may have therapeutic applications for restoring, or "rejuvenating," aged MSCs from adipose and bone marrow tissues.