Abstract 10371: Pre-induction of Hsp70 is Associated with Stem Cell Resistance to Ischemic Stress via Hsf1-mir34a-hsp70 Interaction
Background and objective: We report preferential induction of heat shock protein (HSP)70 in stem cells during heat shock priming with a critical regulatory role for miR-34a which improved stem cell resistance to ischemic stress.
Methods and results: Sca-1+ were heat shocked for 3 h at 42°C HSSca-1+ for induction of HSP70 (peak level 12 fold expression at 14 h in HSSca-1+ vs untreated controls). Akt (ser473; 47.8 fold activation vs control) dependent nuclear translocation of HSF1 was observed in HSSca-1+ which was abrogated by pretreatment with 40uM LY294002. Computational analysis predicted miR34a targeting Hsp70 via 3′UTR binding which was confirmed by luciferase assay. Treatment with miR34a mimic reduced HSP70 expression while miR-34a LNA inhibitor upregulated Hsp70 suggesting that miR34a was a direct repressor of Hsp70. ChIP assay identified enrichment of HSF1 on promoter region of miR34a in HSSca-1+ and low occupancy by H3K4me3 and RNA polymerase II but high occupancy of by H3K27me3 compared to control Sca-1+. HSF1 abrogation with siRNA repressed miR34a by histone modification. Hence, Hsp70 was not only upregulated by direct transactivation of HSF1, but also involved Akt dependent HSF1-miR34a-Hsp70 signaling, resulting in reduced cell death under lethal anoxia as determined by LDH (20.0%±2.7 vs. 42.5%±4.5% in control, p<0.01) and TUNEL assays (15.2%±2.3% vs 38.6%±1.8% in control, p<0.01). Co-immunoprecipitation coupled with LC-MS/MS identified CoxIV as a novel Hsp70 interacting protein. CoxIV significantly increased in HSSca-1+ under lethal anoxia which was abolished by Hsp70 siRNA. Sex-mismatched transplanted HSSca-1+ had higher survival (2.5 fold vs controls; p<0.01) in the infarcted mouse heart (n=4/ group) at 4 days post-transplantation. The long-term (4 weeks) in vivo study showed that transplantation of HSSca-1+ cells reduced infarct size and significantly improved indices of global heart function as compared to the hearts treated native Sca-1+ cells.
Conclusions. Heat shock treatment induced Hsp70 in stem cells due to repression of miR-34a and activation of HSF1 to enhance their resistance to ischemic stress and promote their survival in the infarcted heart.
- © 2011 by American Heart Association, Inc.