Abstract 15894: STAT3 Inhibits Hypoxia-Induced Apoptosis via Post-Translational Modification of GSK-3β and Bad in Mesenchymal Stem Cells
Introduction: Although STAT3 signaling is known to impact cell death/survival, whether STAT3 plays any specific role in MSC apoptosis remains unclear. Recent studies suggest that phosphorylated STAT3 translocates to mitochondria to regulate apoptosis; however, downstream signaling events remain virtually unknown.
Hypothesis: STAT3 inhibits MSC apoptosis via mitochondrial signaling.
Methods and Results: Treatment of MSCs with interleukin-6 (IL-6)+epidermal growth factor (EGF) for 30 min resulted in marked increase in pTyr-STAT3 (1096±104% vs. control), p-GSK-3β (263±24% vs. control), and p-Bad (474±27% vs. control), and caused mitochondrial translocation of pTyr-STAT3. Further, 2 h of hypoxia followed by 2 h of reoxygenation caused an increase in cleaved (active) caspase-9 (506±96% vs. control) and poly (ADP-ribose) polymerase (PARP-1/89 kDa fragment, 793±53% vs. control) in MSCs. These apoptotic changes were inhibited by pretreatment of MSCs with IL-6+EGF for 30 min prior to hypoxia, suggesting that mitochondria-mediated pathway of apoptosis is inhibited. Also, pretreatment of MSCs with STAT3 inhibitor WP1066 blocked IL-6+EGF-induced mitochondrial translocation of pTyr-STAT3 and reversed the inhibitory effects of IL-6+EGF-on hypoxia-induced caspase-9 activation and PARP-1 cleavage. Immunoprecipitation of IL-6+EGF-treated homogenates with anti-pTyr-STAT3 antibodies followed by immunoblotting showed that pTyr-STAT3 physically interacts (co-precipitated) with p-GSK-3β and p-Bad, but not with p-PI3K/p85α (Figure). Importantly, phosphorylated GSK-3β and Bad are known to inhibit mitochondrial apoptosis.
Conclusions: We conclude that STAT3 functions as a kinase to modulate downstream GSK-3β and Bad that inhibit hypoxia-induced apoptosis in MSCs. These data indicate that pTyr-STAT3 interacts with GSK-3β and Bad, leading to formation of two novel p-STAT3-p-GSK-3β and pSTAT3-p-Bad signaling pathways that regulate cell death.
Author Disclosures: Y. Xuan: None. Y. Zhu: None. O. Wang: None. J. Rajasingh: None. B. Dawn: None.
- © 2014 by American Heart Association, Inc.