Imbalance of autophagy and apoptosis in intestinal epithelium lacking the vitamin D receptor

Apoptosis and autophagy are dynamic processes that determine the fate of cells. Vitamin D receptor (VDR) deficiency in the intestine leads to abnormal Paneth cells and impaired autophagy function. Here, we will elucidate the mechanisms of the intestinal epithelial VDR regulation of autophagy and apoptosis. We used in vivo VDRlox and VDR Delta IEC mice and ex vivo organoids generated from small intestine and colon tissues. We found that VDR deficiency induced more apoptotic cells and significantly increased cell death in the small intestine and colon of VDR Delta IEC mice. The proapoptotic protein B-cell lymphoma 2 (BCL-2) associated X protein (Bax) was enhanced, whereas autophagy related 16 like 1 (ATG16L1) and Beclin-1 were decreased in the intestines of VDR(Delta IEC)mice. Apoptosis induced by Bax reduced autophagy by decreasing Beclin-1. Physical interactions between Beclin-1 and Bcl-2 were increased in the VDR-deficient epithelia from mice. The growth of VDR Delta IEC organoids was significantly slower with fewer Paneth cells than that of VDR+/+ organoids. The expression levels of Beclin-1 and lysozyme were decreased in VDR Delta IEC organoids. Bacterial endotoxin levels were high in the serum from VDR Delta IEC mice and made mice susceptible to colitis. In the organoids and colitis IL-10(-/-) mice, vitamin D-3 treatment increased VDR and ATG16L1 protein expression levels, which activated autophagic responses. In summary, intestinal epithelial VDR regulates autophagy and apoptosis through ATG16L1 and Beclin-1. Our studies provide fundamental insights into the tissue-specific function of VDR in modulating the balance between autophagy and apoptosis.