P2554Transplantation of adipose tissue mesenchymal cells overexpressing telomerase and myocardin promotes revascularization and tissue repair in a murine model of myocardial infarction

Abstract

Rationale: The success of stem cell therapies for acute myocardial infarction (AMI) has been hampered by poor cellular engraftment and survival, which may be due to the harmful microenvironment within the ischemic myocardium and the senescence of cells derived from older individuals with cardiovascular disease. Inducing the overexpression of myocardin (MYOCD), a promyogenic transcription factor with anti-apoptotic activity, and telomerase reverse transcriptase (TERT), an antisenescence protein, may promote survival and cardiomyogenesis of transplanted adult cells, and rejuvenate senescent cells. Objective(s): We used a murine model of AMI to assess the in vivo efficacy of transplanted adipose tissue-derived mesenchymal stromal cells (AT-MSCs) engineered to overexpress MYOCD and TERT. As the capacity of AT-MSCs overexpressing TERT and MYOCD for cardiac repair does not involve AT-MSC differentiation into cardiac myocytes, we characterized in vitro their paracrine effects and interactions with murine heart biopsy-derived c-kit+ cardiac stem cells (CSCs) isolated in the form of cardiospheres (CSp), as part of their regenerative repertoire. Method(s): Twelve-month-old C57BL/6 mice underwent coronary artery ligation to induce AMI, and were randomized into 4 treatment groups: sham, vehicle (PBS), mock-transduced AT-MSCs (mock), or "rejuvenated" AT-MSCs overexpressing TERT and MYOCD (rTMAT-MSCs). Comparative proteomics, metabolomics and microRNA analyses of the whole conditioned medium (CM) and its exosome fraction (Exo+) from mock or rTMAT-MSCs were carried out. Result(s): When transplanted into the infarcted hearts, rTMAT-MSCs decreased fibrosis, increased arteriogenesis and preserved myocardial fractional shorten- ing, compared with PBS or mock. These effects were accompanied by increased numbers of Ki-67+ and c-kit+ cells, as well as enhanced expression of cardiac actin, GATA4, Nkx2.5, myosin heavy chain and myocardin A within the heart of mice transplanted with rTMAT-MSCs. In vitro, rTMAT-MSCs or its CM and Exo+ stimulated c-kit+ CSCs proliferation and differentiation into contracting CSp expressing the ryanodine receptor, which showed spontaneous intracellular Ca2+ flux. In the simulated ischemia/reperfusion (SI/R) experiments testing the cytoprotective effect of CM and Exo+, c-kit+ CSp-derived cells (CDCs) were incubated with CM or Exo+ from wild-type AT-MSCs, mock or rTMAT-MSCs. Afterwards, ckit+ CDCs were subjected to hypoxia, followed by normoxia. c-kit+ CDCs cultured in the SI/R media had lower survival rates compared with c-kit+ CDCs cultured in the normoxic conditions, while this phenomenon was dramatically rescued when c-kit+ CDCs were pre-treated with CM or Exo+ from wild-type AT-MSCs or mock, and further rescued by CM or Exo+ from rTMAT-MSCs. Conclusion(s): Delivering TERT and MYOCD genes into AT-MSCs before transplantation promotes activation of the cardiomyogenesis, vasculogenesis, and stem cell survival in a murine model of AMI.