Vitamin D promotes autophagy to inhibit LPS-induced lung injury via targeting cathepsin D

Pneumonia is a frequent-occurring event in children death. Vitamin D (VD) can alleviate inflammatory response and it might be a promising adjunct to antibiotics for the treatment of acute childhood pneumonia. This study intended to uncover the relevant mechanism of VD in pneumonia. For simulating inflammatory condition, BEAS-2B cells were induced using lipopolysaccharide (LPS). Cell viability was detected using cell counting kit-8 (CCK-8) method, and cell apoptosis was detected using flow cytometry and western blot. Inflammatory cytokines as well as oxidative stress markers were detected using enzyme-linked immunosorbent assay (ELISA) and corresponding assays. Western blot evaluated the contents of cathepsin D (CTSD), apoptosis- and autophagy-related proteins. Through real-time reverse transcriptase-polymerase chain reaction (RT-qPCR) and western blot, the transfection efficiency of overexpression (OV)-CTSD was detected. Immunofluorescence assay detected light chain 3 (LC3II) level. Through SuperPred database analysis, VD can target CTSD. VD was revealed to suppress viability damage, inflammatory response, oxidative stress, and autophagy injury in BEAS-2B cells induced by LPS via targeting CTSD. However, the protective effects exhibited by VD against LPS-induced viability damage, inflammatory response, and oxidative stress in BEAS-2B cells were all counteracted by autophagy inhibitor 3-methyladenine (3-MA). Collectively, VD alleviated the severity of LPS-induced lung injury by promoting autophagy through targeting CTSD.