MTG16 Plays a Critical Role in Intestinal Stem Cell Differentiation and Injury Responses

as a transcription factor, Signal Transducer and Activator of Transcription 3 (STAT3) resides in the mitochondria of cells where phosphorylation at serine 727 (S727), but not tyrosine 705 (Y705), is required for optimal ETC activity and protects against stress-induced mitochondrial dysfunction.In this study, we explored whether PHB protects against mitochondrial dysfunction and apoptosis induced by pro-inflammatory cytokines via mitochondrial pS727-Stat3.Methods: Mitochondrial dysfunction, as indicated by increased mitochondrial reactive oxygen species (ROS) production, decreased ATP concentration, and reduced activity of ETC complexes, was induced in Caco2-BBE and IEC-6 intestinal epithelial cell lines by treatment with tumor necrosis factor α (TNFα), a pro-inflammatory cytokine involved in IBD that promotes cellular injury via mitochondrial damage.The effect of PHB overexpression on mitochondrial dysfunction and apoptosis was determined during TNFα treatment.The interaction of PHB with STAT3 was assessed by co-immunoprecipitation and immunofluorescent staining.To determine whether mitochondrial STAT3 is necessary for the protective effect of PHB on mitochondrial function, cells overexpressing PHB were transfected with a mitochondrial targeted pS727-STAT3 dominant negative (MLS-S727-STAT3dn) during TNFα treatment.Results: PHB overexpression protects against TNFα-induced mitochondrial dysfunction and apoptosis in cultured IECs.This protection was eliminated by expression of MLS-S727-STAT3dn.PHB co-immunoprecipitates and co-localizes with pS727-STAT3, but not pY705-STAT3, in the mitochondria of cultured IECs and in vivo in colonic epithelium from wild-type mice.PHB/pS727-STAT3 interaction is decreased in IECs during TNFαinduced mitochondrial stress due at least in part to decreased PHB expression.PHB overexpression maintains PHB/pS727-STAT3 interaction during TNFα treatment.Conclusions: Our data demonstrate a potential mechanistic link between PHB and mitochondrial STAT3 in the intestinal epithelium to prevent mitochondrial dysfunction, which is thought to participate in the pathogenesis of IBD.Reduced levels of PHB during IBD may be an underlying factor promoting mitochondrial dysfunction and apoptosis of the intestinal epithelium.