Post-transcriptional regulation of the epithelial cell response to colitis

Aim: RNA binding proteins (RBPs) are emerging as critical regulators of gut homeostasis via post-transcriptional control of key growth and repair pathways. IMP1 (IGF2 mRNA Binding Protein 1) is ubiquitously expressed during embryonic development and Imp1 hypomorphic mice exhibit severe gut growth defects. In the present study, we investigated the mechanistic contribution of intestinal epithelial IMP1 to gut homeostasis and response to injury.Method: We evaluated IMP1 expression in patients with Crohn’s disease followed by unbiased ribosome profiling in IMP1 knockout cells. Concurrently, we measured differences in histology and cytokine expression in mice with intestinal epithelial-specific Imp1 deletion (Imp1ΔIEC) following dextran sodium sulfate (DSS)- colitis. Based on ribosome profiling analysis, we evaluated changes in autophagy in Imp1ΔIEC mice as well as in silico and in vitro approaches to evaluate direct protein:RNA interactions. Finally, we analyzed the consequence of genetic deletion of Atg7 in Imp1ΔIEC mice using colitis and irradiation models.Results: IMP1 was robustly upregulated in Crohn’s disease patients and Imp1 loss lessened DSS-colitis severity. Unbiased ribosome-profiling revealed that IMP1 may coordinate translation of multiple pathways important for intestinal homeostasis, including cell cycle and autophagy, which we verified by Western blotting. Mechanistically, we observed evidence for increased autophagy flux in Imp1ΔIEC mice, reinforced through in silico and biochemical analyses revealing direct binding of IMP1 to autophagy transcripts. Finally, we found genetic deletion of Atg7 reversed the phenotype observed in DSS- or irradiation-challenged Imp1ΔIEC mice.Conclusions: IMP1 acts as a post-transcriptional regulator of gut epithelial repair, in part through modulation of autophagy. This study highlights the need for examining post-transcriptional regulation as a critical mechanism in inflammatory bowel disease.