IGF2BP1/IMP1 Deletion Enhances a Facultative Stem Cell State via Regulation of MAP1LC3B

Abstract

Background & AimsThe intestinal epithelium interfaces with a diverse milieu of luminal contents while maintaining robust digestive and barrier functions. Facultative intestinal stem cells are cells that survive tissue injury and divide to re-establish the epithelium. Prior studies demonstrate autophagic state as functional marker of facultative intestinal stem cells, but regulatory mechanisms are not known. The current study evaluated a post-transcriptional regulation of autophagy as an important factor for facultative stem cell state and tissue regeneration. MethodsWe evaluated stem cell composition, autophagic vesicle content, organoid formation, and in vivo regeneration in mice with intestinal epithelial deletion of the RNA binding protein IMP1. The contribution of autophagy to resulting in vitro and in vivo phenotypes was evaluated via genetic inactivation of Atg7. Molecular analyses of IMP1 modulation of autophagy at the protein and transcript localization levels were performed using IMP1 mutant studies and single molecule fluorescent in situ hybridization (smFISH). ResultsEpithelial Imp1 deletion reduced Lgr5+ cell frequency but enhanced both organoid formation efficiency and in vivo regeneration following irradiation. We confirmed prior studies demonstrating increased autophagy with IMP1 deletion. Deletion of Atg7 reversed the enhanced regeneration observed with Imp1 deletion. IMP1 deletion or mutation of IMP1 phosphorylation sites enhanced expression of essential autophagy protein Microtubule Associated Protein 1 Light Chain 3 Beta (MAP1LC3B). Furthermore, immunofluorescence imaging coupled with smFISH demonstrated IMP1 colocalization with MAP1LC3B transcripts at homeostasis. Stress induction led to decreased co-localization. ConclusionsDepletion of IMP1 enhances autophagy, which promotes intestinal regeneration via expansion of facultative intestinal stem cells.