Nicholas N. Hoke, Fadi N. Salloum, David A. Kass, Anindita Das, Rakesh C. Kukreja
Enhancing the therapeutic potential of stem cells in ischemic microenvironments by novel preconditioning strategies is critical for improving cellular therapy. We tested the hypothesis that inhibition of phosphodiesterase-5 (PDE-5) with sildenafil (Viagra) or knockdown with a silencing vector in adipose derived stem cells (ASCs) would improve their survival and enhance cardiac function following myocardial implantation in vivo. ASCs were treated with sildenafil or PDE-5 silencing vector shRNA (shRNAPDE-5) and subjected to simulated ischemia/re-oxygenation in vitro. Both sildenafil and shRNAPDE-5 significantly improved viability, decreased necrosis, apoptosis, and enhanced the release of growth factors, VEGF, b-FGF, and IGF. Inhibition of protein kinase G (PKG) reversed these effects. To show the beneficial effect of preconditioned ASCs in vivo, adult male CD-1 mice underwent myocardial infarction. Preconditioned ASCs (4x105) were directly injected intramyocardially. Preconditioned ASCs-treated hearts showed consistently superior cardiac function as compared with non-preconditioned ASCs after 4 weeks of treatment. This was associated with significantly reduced fibrosis, increased vascular density and decreased resident myocyte apoptosis as compared to mice receiving non-preconditioned ASCs. VEGF, b-FGF, and Ang-1 were also significantly elevated 4 weeks after cell therapy with preconditioned ASCs treatment. We conclude that preconditioning by inhibition of PDE-5 can be a powerful novel approach to improve stem cell therapy following myocardial infarction.