Sca-1 ⁺ stem cell survival and engraftment in the infarcted heart: Dual role for preconditioning-induced connexin-43

Background - We report that elevated connexin-43 (Cx-43) in stem cells preconditioned with insulin-like growth factor-1 (IGF-1) is cytoprotective and reprograms the cells for cardiomyogenic differentiation. Methods and Results - Sca-1 ⁺ cells were preconditioned with 100 nmol/L IGF-1 for 30 minutes followed by 8 hours of oxygen glucose deprivation to assess the cytoprotective effects of preconditioning. LDH release assay, cytochrome c release, and mitochondrial membrane potential assay showed improved survival of preconditioned Sca-1 ⁺ cells under oxygen glucose deprivation compared with nonpreconditioned Sca-1 ⁺ cells via PI3K/Akt-dependent caspase-3 downregulation. We observed PI3K/Akt-dependent upregulation of cardiac-specific markers including MEF-2c (2.5-fold), GATA4 (3.1-fold), and Cx-43 (3.5-fold). Cx-43 inhibition with specific RNA interference reduced cell survival under oxygen glucose deprivation and after transplantation. In vivo studies were performed in a female rat model of acute myocardial infarction (n=78). Animals were grouped to receive intramyocardially 70 μ, Dulbecco modified Eagles medium without cells (group 1) or containing male 1 × 10 ⁶ nonpreconditioned Sca-1 ⁺ cells (group 2) or preconditioned Sca-1 ⁺ (group 3) cells labeled with PKH26. Survival of the preconditioned Sca-1 ⁺ cells was 5.5-fold higher in group 3 compared with group 2 at 7 days after transplantation. Confocal imaging after actinin and Cx-43 specific immunostaining showed extensive engraftment and myogenic differentiation of preconditioned Sca-1 ⁺ cells. Compared with group 2, group 3 showed increased blood vessel density (22.3 ±1.7 per microscopic field; P<0.0001) and attenuated infarction size (23.3±3.6%; P=0.002). Heart function indices including ejection fraction (56.2±3.5; P=0.029) and fractional shortening (24.3±2.1; P=0.03) were improved in group 3 compared with group 2. Conclusions - Preconditioning with IGF-1 reprograms Sca-1 ⁺ for prosurvival signaling and cardiomyogenic differentiation with an important role for Cx-43 in this process.