Vitamin D differentially regulates Salmonella-induced intestine epithelial autophagy and interleukin-1β expression

AIM To investigate the effects of active vitamin D3 on autophagy and interleukin(IL)-1β expression in Salmonella-infected intestinal epithelial cells(IECs).METHODS Caco-2 cells, NOD2 siR NA-, Atg16L1 siR NA- or vitamin D receptor(VDR) siR NA-transfected Caco-2 cells were pretreated with 1,25-dihydroxyvitamin D3(1,25D3), and then infected by wild-type S. typhimurium strain SL1344. The conversion of LC3-I to LC3-II was detected by Western blot analysis and LC3+ autophagosome was analyzed by immunofluorescence. Caco-2 cells or VDR si RNA-transfected cells were pretreated with 1,25D3, and then infected by SL1344. Membrane protein and total RNA were analyzed by Western blot and RT-PCR for VDR and Atg16L1 protein and m RNA expression, respectively. Atg16L1 si RNA-transfected Caco-2 cells were pretreated by 1,25D3 and then infected with SL1344. Total RNA was analyzed by RT-PCR for IL-1β mR NA expression.RESULTS The active form of vitamin D, 1,25D3, showed enhanced VDR-mediated Atg16L1 mR NA expression, membranous Atg16L1 protein expression leading to autophagic LC3 II proteins expression and LC3 punctae in Salmonella-infected Caco-2 cells which was counteracted by Atg16L1 and VDR si RNA, but Atg16L1 mediated suppression of IL-1β expression. Thus, active vitamin D may enhance autophagy but suppress inflammatory IL-1β expression in Salmonella-infected IECs.CONCLUSION Active vitamin D might enhance autophagic clearance of Salmonella infection, while modulation of inflammatory responses prevents the host from detrimental effects of overwhelming inflammation.