BUTYRATE-INDUCED MITOCHONDRIAL FUNCTION IMPROVES BARRIER FUNCTION IN INFLAMMATORY BOWEL DISEASE (IBD)

Abstract

Abstract BACKGROUND Short-chain fatty acids (SCFAs), end-product of gut microbial metabolism, play an important role in colonic homeostasis. Butyrate is a prime SCFA that fuels intestinal epithelial cells (IECs). However, this energy source is deficient in inflammatory bowel disease (IBD) due to dysbiotic microbiota. In this study, we posit that butyrate supplementation drives mitochondrial respiration induced barrier function in IBD. METHODS Normal human Colon mucosal (NCM460) epithelial cells were treated overnight with different concentration of sodium butyrate (SB; 0.5-5.0mM) with or without TNF (1ng/ml). To model mitochondrial deficiency, TFAM (mitochondrial transcriptional factor A), was silenced (shTFAM) in NCM460 cells. For mitochondrial respiration assessment, NCM cells were maintained and treated with SB (-/+TNF) under glucose-free medium and Oxygen consumption rate (OCR) was measured using high-throughput Seahorse XFe24 Extracellular Flux Analyzer (Agilent Technologies). Gene expression analysis was determined by RT-qPCR from total RNA isolated from untreated and treated NCM cells as well as in mitochondria-deficient shTFAM NCMs compared to shControl cells. All assays were performed in triplicate and fold changes were calculated using the ΔΔCT method. RESULT Seahorse analysis showed significant increase in Maximal respiratory capacity, spare respiratory capacity and ATP production at sub-optimal (2mM) and optimal (5mM) SB concentrations, suggesting a SB induced mitochondrial respiration and capacity to overcome oxidative stress. At molecular level, SB significantly increased the expression of genes associated with mitochondrial biogenesis (TFAM), complex I (Ndufa1, Ndufa4, Ndufa6), complex IV (Cox6A1) and complex V (ATP5E, ATP8), at optimal 5mM concentration. The effect of SB was more pronounced under inflammatory condition when NCM cells were treated in the presence of low dose TNF. Further transcriptomic analysis of TFAM-deficient NCMs demonstrated significant decrease in mRNA of major butyrate transporters (MCT1, MCT4, ABCG2) compared to TFAM-proficient shControl cells, irrespective of any treatment. Similar decreased expression pattern was observed for tight junction genes (ZO1 and Occludin) in shTFAM compared to shControl cells. However, butyrate transporters and ZO1 mRNA increased significantly in both shTFAM and shControl cells after SB treatment at sub-optimal concentration (2mM) in the presence of TNF. Interestingly, only shTFAM cells showed increase in transcript level of Occludin after SB+TNF treatment, with no effect in shControl. CONCLUSION These data suggest that butyrate metabolism is a critical player in promoting oxidative health of mitochondria, which further drives transporter-mediated butyrate utilization and promotes barrier integrity under inflammatory conditions as in IBD.