OXPHOS DRIVES CRYPT FISSIONING REQUIRED FOR HEALING OF IBD ULCERS

Abstract INTRODUCTION The failure of ulcers healing is a characteristic feature of IBD. Mitochondrial dysfunction in intestinal epithelial cells (IEC) occurs in IBD and is linked to worse clinical outcomes in pediatric Crohn’s and ulcerative colitis (Kugrathasan et al Lancet 2017, Haberman et al Nat Comm 2019). Cellular polarization and maintenance of cell polarity are energy-dependent and highly regulated by mitochondrial biogenesis (Hardie DG et al Genes Dev 2011). Yet, it is unclear how mitochondria participate in mucosal repair. METHODS To model mitochondrial deficiency, TFAM, a transcriptional factor needed for mitochondrial DNA (mtDNA)-encoded genes was silenced in human colonoids (shTFAM) and VilCre/mTmG/TFAMfl/fl (IEC-TFAM-/-) mice. Levels of crypt branching and intestinal stem cell (ISC) and mitochondrial gene mRNA levels were assessed in colonoids cultured in Wnt-containing (WENR) media. Effects on IEC mitochondrial complex levels and oxygen consumption rates (OCR) were assessed in control IEC-TFAM-/- mice and effects on disease activity and ulcer healing assessed in DSS colitis IEC-TFAM-/- mice (fed DSS x 7d, peak ulcer healing-D13-15). Dual florescence confocal microscopy examined crypt fissioning and IHC in WT (Tom+) and Tfamfl/fl (GFP+) crypts during windows of peak ulcer healing. RESULTS shTFAM-treated colonoids expressed 55-92% lower mitochondrial gene mRNA (Cox6A1, mt-CO1, ATP5A1) levels (p<0.01) {A} and displayed reduced size (35%) and budding (86%) compared to WT cells (p<0.005) {B}. Studies on IEC from IEC-TFAM-/- mice revealed lower mitochondrial complex protein levels {C i-iv}, and >65% lower mtDNA (p<0.01) {D} compared to controls that correlated with 43 and 65% lower IEC OCR (using Oroboros). In DSS mice, levels of ulceration were greater in IEC-TFAM-/- mice (25%) compared to WT (7.5%) (P<0.005). More importantly, levels of crypt fissioning were 85% lower in TFAM-deficient (GFP+) compared to WT (Tom+) crypts {E}. WT fissioning crypt stained for SOX9 {F} and nuclear pβCat552 {G}. CONCLUSION Together, these results suggest that IEC mitochondrial deficiency as seen in IBD patients, impairs crypt fissioning during ulcer healing through a process that impairs cooperation between Wnt and PI3K signaling pathways. The data argue that therapeutic improvement of mitochondrial function may enhance mucosal repair in IBD by promoting crypt fissioning needed to re-establish barrier function.