Abstract 708: Short And Long Term Fate of Preconditioned Skeletal Myoblasts in The Infarcted Heart and The Role of IL11 in Cytoprotection of Preconditioned Cells
Background: We have previously reported that preconditioning (PC) of stem cells imparts cytoprotection. We investigated the short and long term beneficial effects of PC on survival of skeletal myoblasts (SkMs) in an infarcted heart and the possible signaling pathways involved therein.
Methods & Results: SkMs from male Fischer-344 rats were preconditioned (PCSkMs) with 200μM diazoxide (DZ) for 30 minutes and labeled with nuclear localized lacZ reporter gene before transplantation. Acute myocardial infarction model was developed in female Fischer-344 rats and were grouped to receive 70μl basal medium containing 1.5x106 non-preconditioned SkMs (non-PCSkMs) (group 1) or PCSkMs (group 2). The animals were euthanized at 2, 4 and 7 days time-points to assess donor cell survival and engraftment. Real-time PCR for sry gene showed ~2 fold higher survival of cells in group 2 at 4 and 7 days as compared with group 1. Histochemistry for lacZ expression on rat heart tissue confirmed the higher survival of transplanted cells in group 2. Ki67 and PCNA immunostaining revealed higher percentage of proliferating PCSkMs (25.26% p=0.025) as compared with non-PCSkMs. Real-time PCR showed increased IL11 gene expression (1.91 fold) in group 2 animal hearts as compared with group 1. Likewise, 1.78 fold increase in IL11 expression was observed in the PCSkMs in vitro as compared with non-PCSkMs. The cytoprotective effects of PC against oxidant stress (100μM H2O2 for 2 h) were abolished in PCSkMs transfected with IL11 specific siRNA. Moreover, inhibition of ERK1/2 downstream of IL11 by treatment of PCSkMs with 100μmol PD98059 diminished phospho-STAT3 expression and significantly increased cell death upon exposure to 100μM H2O2 thus suggesting IL11/ERK/STAT3 involvement in PC induced cytoprotection. Long term study for 16 weeks post transplantation showed higher myogenesis and capillary density in the peri-infarct region of group 2 (68.19) as compared to group 1 (53.26; p=0.01). Echocardiography showed stably improved left ventricle ejection fraction and fractional shortening in group 2 as compared with group 1 at 6 and 12 weeks which persisted until 16 weeks.
Conclusion: PC of stem cells with DZ enhances grafted cell viability that possibly acts via the IL11/STAT3 survival pathway.