eP646 - Mitochondrial Flux Is Elevated in the Intestinal Epithelium of Mice Subjected to Chemical Colitis and Is Amenable to Therapeutic Targeting

Purpose/Background: Inflammatory Bowel Disease (IBD) represents a spectrum of idiopathic, chronic, and relapsing inflammatory diseases of the gastrointestinal tract. The pathogenesis is multifactorial, including abnormal innate and adaptive immune responses, epithelial barrier dysfunction, and gut dysbiosis. Maintenance of the epithelial barrier is an energy dependent process that relies on mitochondrial viability. However, IBD patients have demonstrated increased susceptibility to gut mitochondrial damage and dysfunction. Mitophagy is a quality-control mechanism that selectively removes dysfunctional mitochondria. Multiple mitophagy pathways co-exist in the intestine, including the canonical PINK1/PARKIN pathway and NIX. We have previously shown that NIX is upregulated in the intestinal epithelium in IBD. Whether this upregulation translates to a physiologic increase in mitochondrial flux remains unanswered. We hypothesize that mitophagic flux represents a key homeostatic response to intestinal epithelial inflammation and is a potential therapeutic target.Methods/Interventions: We subjected a transgenic mouse model that expresses the pH-dependent fluorescent protein Keima directed to the mitochondrial matrix to 3% dextran sodium sulfate (DSS) for 7 days to induce intestinal inflammation. Mitophagic flux was measured in live tissue via confocal microscopy. To determine the functional importance of PARKIN, Parkin-/- mice were subjected to a 7-day treatment of 2% DSS, and disease progression was assessed by disease activity index and histology. To test the hypothesis that mitophagic flux is a potential therapeutic target, we administered a known mitophagy inducer, Urolithin A, to wild type mice on a 7-day course of DSS. We measured protein levels of NIX, PARKIN, and activated PARKIN (pSer65-PARKIN) in the intestinal epithelium collected from mouse colonic scrapings and human biopsies via western blot analysis. Mitochondrial function was assessed via high-resolution respirometry.Results/Outcomes: Mitophagic flux was increased nearly 4-fold (n=3, p < 0.05) in DSS-treated mice compared to controls. Despite this consistent elevation, NIX expression varied in both human and mouse tissue, suggesting that other mitophagy pathways, like PARKIN, may be involved. Interestingly, pSer65-PARKIN was higher in inflamed tissues of humans and mice as compared to controls, and Parkin-/- mice subjected to DSS developed more severe colitis than wild type mice. NIX expression, however, was significantly higher in Parkin-/- mice subjected to DSS compared to wild type mice subjected to the same. These data not only support that mitophagy is elevated in IBD but that both NIX and PARKIN likely work in parallel to respond to the elevated mitophagic demand. Wild type mice subjected to DSS but treated with Urolithin A had elevated NIX and pSer65-PARKIN expression compared to their DSS controls. This elevation correlated with decreased disease activity and improved mitochondrial respiration, suggesting that mitophagy is protective in the setting of intestinal inflammation and potentially modifiable.Conclusion/

Discussion: We conclude that mitophagic flux is an imperative homeostatic response to remove superfluously damaged mitochondria in IBD. Modulation of mitophagy by Urolithin A may offer therapeutic benefits for the treatment of patients with IBD.