Essential role for autophagy protein ATG7 in the maintenance of intestinal stem cell integrity

Abstract

The intestinal epithelium acts as a barrier between the organism and its microenvironment, including the gut microbiota. It is the most rapidly regenerating tissue in the human body thanks to a pool of intestinal stem cells (ISCs) expressing Lgr5. The intestinal epithelium has to cope with continuous stress linked to its digestive and barrier functions. Epithelial repair is crucial to maintain its integrity, and Lgr5-positive intestinal stem cell (Lgr5+ISC) resilience following cytotoxic stresses is central to this repair stage. We show here that autophagy, a pathway allowing the lysosomal degradation of intracellular components, plays a crucial role in the maintenance and genetic integrity of Lgr5+ISC under physiological and stress conditions. Using conditional mice models lacking the autophagy gene Atg7 specifically in all intestinal epithelial cells or in Lgr5+ISC, we show that loss of Atg7 induces the p53-mediated apoptosis of Lgr5+ISC. Mechanistically, this is due to increasing oxidative stress, alterations to interactions with the microbiota, and defective DNA repair. Following irradiation, we show that Lgr5+ISC repair DNA damage more efficiently than their progenitors and that this protection is Atg7 dependent. Accordingly, we found that the stimulation of autophagy on fasting protects Lgr5+ISC against DNA damage and cell death mediated by oxaliplatin and doxorubicin treatments. Finally, p53 deletion prevents the death of Atg7-deficient Lgr5+ISC but promotes genetic instability and tumor formation. Altogether, our findings provide insights into the mechanisms underlying maintenance and integrity of ISC and highlight the key functions of Atg7 and p53.

Autophagy Compensates for Lkb1 Loss to Maintain Adult Mice Homeostasis and Survival

“…p53 is activated upon autophagy deletion, leading to increased apoptotic rates in mouse liver and brain, impairing the overall mouse homeostasis (36). A recent study shows that Atg7 specific deletion in Lgr5 + epithelium cells promotes p53-induced apoptosis, leading to impaired integrity of intestinal barrier during stress (33). Our data was in line with these recent findings, where we found that whole body deletion of p53 significantly rescued the survival of Atg7 -/-;Lkb1 -/mice.…”

“…Intestinal epithelium cell-specific deletion of Lkb1 results in an increased susceptibility to dextran sodium sulfate-induced colitis and a definitive shift in the composition of the microbial population in the mouse intestine (32), suggesting that Lkb1 plays an important role in maintaining the immune barrier function of the intestinal epithelium. Moreover, it has recently been reported that autophagy is essential for the maintenance of Lgr5 + stem cells and regeneration of epithelium barrier during cytotoxic stress (33). We therefore examined the integrity of intestinal epitheliumbarrier in mice with systemic deletion of Atg7 or Lkb1 alone, or their co-deletion by measuring the Fluorescein Isothiocyanate (FITC)-dextran in-fluxed from the gastrointestinal tract to peripheral circulation.…”

Autophagy compensates for Lkb1 loss to maintain adult mice homeostasis and survival

“…Of the 90 metabolites we examined, we found that acute deletion of Atg7 or p53 is activated upon autophagy deletion, leading to increased apoptotic rates in mouse liver and brain, impairing the overall mouse homeostasis (39). A recent study shows that Atg7 specific deletion in Lgr5 + epithelium cells promotes p53-induced apoptosis, leading to impaired integrity of intestinal barrier during stress (36). Our data was in line with these recent findings,…”

“…Stk11-deficient mice protects the intestinal epithelium-barrier functionIntestinal epithelium cell-specific deletion of Stk11 results in an increased susceptibility to dextran sodium sulfate-induced colitis and a definitive shift in the composition of the microbial population in the mouse intestine(11), suggesting that Lkb1 plays an important role in maintaining the immune barrier function of the intestinal epithelium. Moreover, it has recently been reported that autophagy is essential for the maintenance of Lgr5 + stem cells and regeneration of epithelium barrier during cytotoxic stress(36). We therefore examined the integrity of intestinal epithelium-barrier in mice with systemic deletion of Atg7 or Stk11 alone, or their co-deletion by measuring the Fluorescein Isothiocyanate (FITC)-dextran in-fluxed from the gastrointestinal tract to peripheral circulation.…”

Physical plasma therapy accelerates wound re‐epithelialisation and enhances extracellular matrix formation in cutaneous skin grafts

“…Positive staining for caspase 3 indicates cytotoxic damage and apoptosis, and was evident in both differentiated villi and proliferative crypts of Atg 7 −/− intestinal epithelium (Figure 5D). Irradiated and tamoxifen‐treated Atg 7 −/− mice have been described elsewhere [37], and microscopic sections of the Atg 7 −/− small intestine were kindly provided by the authors of the above‐mentioned work. Microscopic sections of day 7 mouse wounds treated with CAP were negative using TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labelling) staining, an indicator of apoptosis and DNA fragmentation (Figure 5E).…”