K. E. Cunningham1,2, G. Vincent1, D. J. Hackam1,2, K. P. Mollen1,2 1Children’s Hospital Of Pittsburgh Of UPMC,Pittsburgh, PA, USA 2University Of Pittsburgh,Pittsburgh, PA, USA
Introduction: Defects in intestinal barrier function are known to be characteristic features of Inflammatory Bowel Disease (IBD). Alterations in epithelial integrity are thought to predispose subjects to translocation of pathogenic bacteria and an activation of host defense mechanisms. We recently demonstrated that Peroxisome Proliferator-activated Receptor γ Coactivator 1α (PGC1α) is decreased in the intestinal epithelium of humans with severe IBD and mice undergoing experimental colitis. Mice lacking PGC1α in the intestinal epithelium develop severe colitis due to a dramatic disruption of mitochondrial biogenesis and function. We now hypothesize that PGC1α suppression leads to a breakdown of the intestinal barrier and an increase in bacterial translocation through alterations in mitochondrial dynamics.
Methods: We created an intestinal epithelial-specific PGC1α knockout mouse, the PGC1αΔIEC mouse, by crossing a PGC1αflox/flox mouse with a villin-cre transgenic mouse. PGC1αΔIEC mice and their wild-type littermates (PGC1αflox/flox) were subjected to DSS colitis for 7 days. Animal weights and Disease Activity Index (DAI) were recorded daily. Intestinal tissue was analyzed for expression of inflammatory cytokines, tight junction proteins, and barrier function. H&E staining was used to evaluate inflammatory changes. Immunofluorescence was used to identify infiltrating bacteria within the intestinal mucosa as well as observe differences in the quantity and localization of tight junction proteins.
Results: Mice deficient in PGC1α within the intestinal epithelium demonstrate a significant decrease in the tight junction protein Occludin as demonstrated by western blot, PCR, and immunofluorescence during experimental colitis. This leads to a dramatic increase in bacterial translocation and a worsening of intestinal inflammation. Induction of PGC1α ameliorated experimental colitis.
Conclusion: We demonstrate for the first time that the suppression of PGC1α that is seen within the intestinal epithelium of humans with severe, surgical IBD and mice undergoing experimental colitis leads to a disruption of the intestinal barrier and an increase in bacterial translocation. Strategies aimed at enhancing PGC1α activity may improve treatment strategies for human IBD.