Program Director/Principal Investigator (Barrett, Terrence, A): The importance of mucosal healing in inflammatory bowel disease (IBD) derives from clinical data that demonstrate it to be a predictor of remission1. Thus, ulcer healing predicts the capacity for therapies to prevent unwanted clinical sequelae (i.e. surgery). Unfortunately, many IBD patients remain refractory or lose responsiveness to therapies leading to persistent mucosal ulceration. Prospective pediatric studies show that reduced mitochondrial gene expression predict unfavorable outcomes in ulcerative colitis (UC)2. These findings were supported by Kugathasan et al who found that increased expression of mitochondrial respiratory chain genes predicted favorable (B1 protected) Crohn?s disease (CD) outcomes3. Based on these results and our own data, we hypothesize that a critical driver of chronic ulceration in IBD is the failure of intestinal epithelial cells (IEC) to increase mitochondrial respiration with ROS generation. We posit that chronic mucosal inflammation suppresses mitochondrial respiration needed for crypt fissioning (in ulcer healing) in IBD. This hypothesis will be tested in the following studies:
Aim 1. Determine the impact of mitochondrial respiration for mucosal healing. These studies benefit from strikingly novel Prelim. Data using VilCre/mTmG/TFAMfl/fl mice where mitochondrial respiration was shown to be required for crypt fissioning in ulcer healing.
In Aim 2 we will determine the requirement of mitochondrial- derived ROS in IEC crypt division using primary human colonoids.
Aim 3 studies will determine the impact of chronic inflammation on ulcer healing in patients. IEC transcriptomics from ulcer edges from CD and ulcerative colitis will be compared to normal ulcer healing. Normal ulcer healing will be interrogated using a novel biopsy of a biopsy (Bx/Bx) approach (IEC will be isolated from Bx/Bx sites 4-6day after initial biopsies). ScRNAseq results have already shown that mitochondrial biogenesis (PGC1?) increases in Bx/Bx ulcers whereas levels drop in IBD IEC. In summary: Studies will investigate the cause of non-healing ulceration in IBD by interrogating novel murine, human and in vitro colonoid culture models of determining the impact of suppressed mitochondrial respiration on IEC responses (crypt fissioning). The studies will test the notion that chronic mucosal inflammation (as in IBD) suppresses mitochondrial respiration which impedes ROS-induced PI3K signaling and crypt fissioning. Our goal is to identify therapeutic targets to allow for enhanced mitochondrial respiration to aide mucosal repair in IBD. OMB No. 0925-0001/0002 (Rev. 01/18 Approved Through 03/31/2020) Page Continuation Format Page
The importance of understanding the role of mitochondrial respiration in ulcer healing and determining clinical phenotypes in inflammatory bowel disease has been recently strengthened by major prospective clinical studies in pediatric Crohn?s (Kugathasan et al Lancet) and ulcerative colitis (Haberman) patients. Studies proposed here use a novel genetically-engineered mouse model of mitochondrial deficiency in combination with single cell RNAseq analysis of normal and diseased (CD/UC) patients. We posit this work will identify key mechanisms that underlie the cause of nonhealing ulceration in IBD with the goal of identifying targets for new drug development.
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