Abstract BACKGROUND Up to 17% of distal ulcerative colitis (UC) patients have discontinuous (proximal) inflammation referred to as Cecal Patch (CP), associated with greater abdominal pain, bleeding and diarrhea. Despite these known associations, the pathogenesis of CP lesions is poorly understood. Recent data suggest that reduced mitochondrial (Mito) function predicts unfavorable clinical outcomes in active UC (Haberman et al; Nat Comm 2019). We posit that inflammation and tissue injury induced in UC-associated CP involves Mito dysfunction. METHOD UC patients with/without cecal disease and normal controls were biopsied. Tissue from CP lesions or normal caecum were collected in Allprotect® (AP) and formalin. Total RNA from AP-preserved biopsies were used for cDNA synthesis and RT-qPCR for Mito complexes, cytokines, anti-oxidant and calcineurin (CaN) signaling genes and tissue processed for IHC for Mito complexes. RESULT Transcriptomic analysis showed significant downregulation in genes associated with Mito biogenesis (PGC1α, TFAM, NRF2) and Mito complexes (Ndufa1, Ndufa4, Ndufb2, Ndufb6, mtCO1, mtCO2, Cox5B, Cox6A1, ATP5A1, ATP5B, ATP5E) in CP lesions compared to normal caecum from active patients. Major regulators of Mito biogenesis (PGC1α and TFAM) revealed ~39% and ~24% reductions of mRNA respectively, while NRF2 (anti-oxidant regulator) showed ~62% reduced mRNA in CP lesions compared to normal cecum from distal UC patients. Electron transport chain complex mRNAs showed 31%, 47%, and 48% reduction in complex I (Ndufa1, Ndufa4, Ndufb2, Ndufb6), complex IV (mtCO1, mtCO2, Cox5B, Cox6A1), and complex V (ATP5A1, ATP5B, ATP5E) levels, respectively in CP lesions compared to normal controls. Concomitantly, the IHC staining also showed significant reductions in Ndufb6, MTCO1 and Cox5A protein levels in CP lesions compared to normal cecum sections. The CP-related decreased markers of Mito biogenesis and function correlates with increased proinflammatory cytokine mRNA (IL-6: 2-fold; TGFβ1: 1.6-fold; IL-2: 2.6-fold) and decreased anti-inflammatory (IL10: 3.2-fold) gene expression in CP lesions. Further investigation demonstrated that repressed Mito function in CP lesions is associated with downregulation of anti-oxidant genes (SOD1, SOD2, Prdx3, Gpx4, Trx2) compared to normal cecum. Inflammation-induced Mito dysfunction in CP lesions also stimulates CaN signaling as demonstrated by significant increases in mRNA levels of CaN and downstream regulated genes (Cathepsin-L, Rel-A Glut4, CREB-BP and Igf-1r). CONCLUSION These data represent the first indication that Mito dysfunction occurs in CP associated with distal UC. Furthermore, we speculate that Mito dysfunction-induced CaN signaling promotes regional (CP) inflammatory responses. These important findings indicate that targeting Mito metabolism may be an important therapeutic goal of treating UC patients with CP.
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