REPRESSED MITOCHONDRIAL FUNCTION LIMITS CRYPT FISSIONING IN INFLAMMATORY BOWEL DISEASE

Abstract

Abstract BACKGROUND Mucosal healing in inflammatory bowel disease (IBD) is a predictor of remission. Unfortunately, many IBD patients remain refractory or lose responsiveness to therapies leading to persistent mucosal ulceration. Prospective pediatric studies suggest that reduced mitochondrial gene expression associates with unfavorable clinical outcomes in ulcerative colitis (UC) and Crohn’s disease (CD). In this study, we postulate that in diverticulitis (DvC) patients, moderate-to-severe level of tissue inflammation induces fissioning of crypts with normal level of mitochondria. By comparison, in UC and CD, moderate-to-severe tissue inflammation induces lesser crypt fissioning in part due to lower level of mitochondria in crypt intestinal epithelial cells (IECs). We posit that the inability to restore epithelial mitochondrial respiration attenuates crypt fissioning in IBD compared to DvC. METHODS Surgical resections were collected from patients with colonic DvC (n=39), active Crohn’s disease (CD; n=27), ulcerative colitis (UC; n=21) and uninvolved areas of colorectal cancer patients (normal control, nc). Formalin-fixed paraffin-embedded tissues were H&E-stained to allow examination of crypt architecture, branching and fissioning along with extent of inflammation scored by blinded GI-pathologist. Immunohistochemical (IHC) staining was performed for marker of mitochondrial complex-IV (MTCO1). RESULTS Histological investigations revealed higher number fissioning crypts per 100 crypts in DvC (4.778±2.9) as compared to UC (3.469±1.79) or CD (3.604±1.3) patients. This represents 37.7% and 32.6% higher crypt fissioning in DvC vs UC (**p<0.01) and DvC vs CD (*p<0.05), respectively. Alternate analysis of fissioning crypts per 100μm colonic length showed 83.9±24.8% and 22.8±9.6% more crypt fissioning in DvC compared to UC and CD, respectively. Further, IHC showed higher MTCO1 expression (area %) in DvC (14.32±3.3) compared to UC (6.6±4.85) and CD (9.25±5.9). Interestingly, all three inflammatory conditions (DvC, UC, CD) showed reduction in MTCO1 expression compared to normal control (DvC/nc: 27%; p<0.067, UC/nc: 71%; **p<0.01, CD/nc: 60.3%; **p<0.01), although the MTCO1 suppression in more pronounced in UC and CD. Crypt-specific MTCO1 expression revealed 2.16-fold and 1.55-fold higher MTCO1 levels in DvC compared to UC and CD, respectively. Furthermore, detailed examination of fissioning crypts in DvC, CD and UC patients revealed significantly higher expression of complex-IV protein (MTCO1) compared to non-fissioning crypts. CONCLUSION Overall, our findings suggest that lack of adequate mitochondrial function is associated with perturbed crypt fissioning in IBD patients, in contrast to DvC with comparatively higher mitochondrial complex levels. Thus, mitochondria-targeted therapy may provide an alternative treatment approach for severe chronic IBD patients.