1,25(OH)2D3 promotes the elimination of Klebsiella pneumoniae infection by inducing autophagy through the VDR-ATG16L1 pathway br

Objective: Previous studies have shown that vitamin D has regulatory functions in both innate and adaptive immune responses, indicating that it can perform essential roles in host resistance to pathogen infections. This study aimed to verify its effects on Klebsiella pneumoniae (Kp) infection and explore the underlying mechanisms.Methods: THP-1-derived macrophages were infected with Kp and then incubated with 1,25(OH)2D3. Autophagy induced by 1,25(OH)2D3 was investigated by western blotting and immunofluorescence. Real-time PCR (qPCR) was performed to determine the expression of inflammatory mediators. Baf A1 and 3-MA were used to inhibit autophagy. The intracellular killing of Kp was measured using qPCR and colony-forming unit assays. RNA interference assays were used to silence VDR or ATG16L1. The lungs of C57BL/6 mice were infected with Kp via intratracheal instillation, and the established pneumonia models were used for in vivo validation experiments.Results: Treatment with 1,25(OH)2D3 enhanced the bactericidal activity of macrophages and concomitantly reduced the expression of the pro-inflammatory mediators TNF-alpha and IL-6. Kp infection led to a lower expression level of VDR in macrophages than in the control, whereas co-treatment with 1,25(OH)2D3 up-regulated VDR expression and robustly induced autophagy via the VDR signaling pathway. Silencing ATG16L1 significantly counteracted autophagy induced by 1,25(OH)2D3 in Kp-infected macrophages. Furthermore, we found that when autophagy activity was diminished by ATG16L1 siRNA or blocked by Baf A1, the ability of 1,25(OH)2D3 to promote macrophages to eliminate Kp infection was obviously impaired, as were its anti-inflammatory effects. These protective efficacies of 1,25(OH)2D3 against Kp infection were also validated in vivo using a mouse model of pneumonia.Conclusions: The present study demonstrated the protective features of 1,25(OH)2D3 in macrophages against Kp infection and may provide evidence for further exploration of its potential as an adjunctive therapy agent for the treatment of bacterial infections.