Epithelial NAD+ depletion drives mitochondrial dysfunction and contributes to intestinal inflammation.

Introduction: We have previously demonstrated that a pathologic downregulation of peroxisome proliferator-activated receptor-gamma coactivator 1-alpha (PGC1α) within the intestinal epithelium contributes to the pathogenesis of inflammatory bowel disease (IBD). However, the mechanism underlying downregulation of PGC1α expression and activity during IBD is not yet clear. Methods: Mice (male; C57Bl/6, Villincre/+;Pgc1afl/fl mice, and Pgc1afl/fl) were subjected to experimental colitis and treated with nicotinamide riboside. Western blot, high-resolution respirometry, nicotinamide adenine dinucleotide (NAD+) quantification, and immunoprecipitation were used to in this study. Results: We demonstrate a significant depletion in the NAD+ levels within the intestinal epithelium of mice undergoing experimental colitis, as well as humans with ulcerative colitis. While we found no decrease in the levels of NAD+-synthesizing enzymes within the intestinal epithelium of mice undergoing experimental colitis, we did find an increase in the mRNA level, as well as the enzymatic activity, of the NAD+-consuming enzyme poly(ADP-ribose) polymerase-1 (PARP1). Treatment of mice undergoing experimental colitis with an NAD+ precursor reduced the severity of colitis, restored mitochondrial function, and increased active PGC1α levels; however, NAD+ repletion did not benefit transgenic mice that lack PGC1α within the intestinal epithelium, suggesting that the therapeutic effects require an intact PGC1α axis. Discussion: Our results emphasize the importance of PGC1α expression to both mitochondrial health and homeostasis within the intestinal epithelium and suggest a novel therapeutic approach for disease management. These findings also provide a mechanistic basis for clinical trials of nicotinamide riboside in IBD patients.

Biosimilars for Pediatric Patients With Inflammatory Bowel Disease: Pediatric Gastroenterology Clinical Practice Survey.

BACKGROUND: Biosimilars are biological agents that have been demonstrated to have similar safety and efficacy profiles as the originator. The objective of this study was to evaluate the perspectives of pediatric gastroenterologists in the United States (U.S.) toward biosimilar use and to explore factors that impact their comfort level with prescribing infliximab biosimilars. METHODS: A cross-sectional survey was developed and distributed to pediatric gastroenterology physicians from the U.S. via a listserv (Pediatric gastroenterology Bulletin Board). Respondent's demographics were recorded. Using a 6-point Likert scale, the survey assessed the respondent's perceptions toward biosimilars and initiating switches from the originator to biosimilar agent along with factors impacting provider's comfort level. Fischer exact tests were used to detect statistically significant differences in responses for hypotheses of interest. RESULTS: One hundred thirty-nine pediatric gastroenterologists completed the online survey (response rate 5.4%). Eighty-seven percent of respondents reported being comfortable prescribing infliximab biosimilars to anti-tumor necrosis factor naive patients, and 69% reported being comfortable doing a one-time switch if the patient was in clinical remission. Factors that negatively impacted a respondent's comfort level included respondents not practicing at an ImproveCareNow (ICN) center and managing less than 50 patients with inflammatory bowel diseases (IBD). CONCLUSIONS: Nearly 90% of pediatric gastroenterologists felt comfortable prescribing an infliximab biosimilar, and 70% felt comfortable with a one-time switch to the biosimilar if the patient was in clinical remission. Involvement in ICN a learning health system and caring for higher numbers of patients with IBD was associated with increased provider comfort with biosimilar use.

Cyclic GMP-AMP synthase contributes to epithelial homeostasis in intestinal inflammation via Beclin-1-mediated autophagy.

Inflammatory bowel disease (IBD) represents a set of idiopathic and chronic inflammatory diseases of the gastrointestinal tract. Central to the pathogenesis of IBD is a dysregulation of normal intestinal epithelial homeostasis. cGAS is a DNA-sensing receptor demonstrated to promote autophagy, a mechanism that removes dysfunctional cellular components. Beclin-1 is a crucial protein involved in the initiation of autophagy. We hypothesized that cGAS plays a key role in intestinal homeostasis by upregulating Beclin-1-mediated autophagy. We evaluated intestinal cGAS levels in humans with IBD and in murine colonic tissue after performing a 2% dextran sulfate sodium (DSS) colitis model. Autophagy and cell death mechanisms were studied in cGAS KO and WT mice via qPCR, WB analysis, H&E, IF, and TUNEL staining. Autophagy was measured in stimulated intestinal epithelial cells (IECs) via WB analysis. Our data demonstrates cGAS to be upregulated during human and murine colitis. Furthermore, cGAS deficiency leads to worsened colitis and decreased levels of autophagy proteins including Beclin-1 and LC3-II. Co-IP demonstrates a direct binding between cGAS and Beclin-1 in IECs. Transfection of cGAS in stimulated HCT-116 cells leads to increased autophagy. IECs isolated from cGAS KO have diminished autophagic flux. cGAS KO mice subjected to DSS have increased cell death and cleaved caspase-3. Lastly, treatment of cGAS KO mice with rapamycin decreased the severity of colitis. Our data suggest that cGAS maintains intestinal epithelial homeostasis during human IBD and murine colitis by upregulating Beclin-1-mediated autophagy and preventing IEC death. Rescue of autophagy can attenuate the severity of colitis associated with cGAS deficiency.