Intestinal epithelial autophagy is required for the regenerative benefit of calorie restriction

Abstract

Calorie restriction can enhance the regenerative capacity of the injured intestinal epithelium. Among other metabolic changes, calorie restriction can activate the autophagy pathway. While independent studies have attributed the regenerative benefit of calorie restriction to downregulation of mTORC1, it is not known whether autophagy itself is required for the regenerative benefit of calorie restriction. We used mouse and organoid models with autophagy gene deletion to evaluate the contribution of autophagy to intestinal epithelial regeneration following calorie restriction. In the absence of injury, mice with intestinal epithelial-specific deletion of autophagy gene Atg7 (Atg7ΔIEC) exhibit weight loss and histological changes similar to wildtype mice following calorie restriction. Conversely, calorie restricted Atg7ΔIEC mice displayed a significant reduction in regenerative crypt foci following irradiation compared to calorie restricted wildtype mice. Targeted analyses of tissue metabolites in calorie restricted mice revealed an association between calorie restriction and reduced glycocholic acid (GCA) in wildtype but not Atg7ΔIEC mice. To evaluate whether GCA can directly modulate epithelial stem cell self-renewal, we performed enteroid formation assays with or without GCA. Wildtype enteroids exhibited reduced enteroid formation efficiency in response to GCA treatment, suggesting that reduced availability of GCA during calorie restriction may be one mechanism by which calorie restriction favors epithelial regeneration in a manner dependent upon epithelial autophagy. Taken together, our data support the premise that intestinal epithelial Atg7 is required for the regenerative benefit of calorie restriction, due in part to its role in modulating luminal GCA with direct effects on epithelial stem cell self-renewal.

Caloric restriction and fasting-mimicking diets in the treatment of cancer patients

“…Compared with ad libitum-fed mice, the regenerative capacity of intestinal epithelium after radiation injury is enhanced in long-term 60% calorie-restricted (40% of normal energy intake) mice. This effect was abolished in animals with intestinal epithelial-specific deletion of autophagy gene Atg7 , supporting the assumption that caloric restriction confers a regenerative benefit, which is dependent on functional autophagy [10 ▪ ]. Similarly, regrowth of bone marrow after cellular depletion by irradiation was improved by caloric restriction (50% for 7 days or fasting for 3 days) prior to the injury [11].…”

“…Similarly, regrowth of bone marrow after cellular depletion by irradiation was improved by caloric restriction (50% for 7 days or fasting for 3 days) prior to the injury [11]. Further analyses revealed that intestinal radioprotection was associated with lowering of luminal glycocholic acid [10 ▪ ], while in bone marrow, an increase in H 2 S generation was involved [11].…”