Restoring natural killer cell activity in lung injury with 1,25-hydroxy vitamin D₃: a promising therapeutic approach

NK cells and NK-cell-derived cytokines were shown to regulate neutrophil activation in acute lung injury (ALI). However, the extent to which ALI regulates lung tissue-resident NK (trNK) activity and their molecular phenotypic alterations are not well defined. We aimed to assess the impact of 1,25-hydroxy-vitamin-D3 [1,125(OH)₂D] on ALI clinical outcome in a mouse model and effects on lung trNK cell activations.

Oleic acid (OA)-induced ALI in C57BL/6J mice and 1,25(OH)₂D treatment 2×/2 weeks were performed. Lung tissue was harvested to assess alveolar I/II cell apoptosis and lung injury marker of Surfactant-Protein-D (SP-D). Pulmonary edema markers of epithelial sodium channel, cystic fibrosis transmembrane conductance regulator, and aquaporin 5 were assessed by RT-PCR. Lung trNK cells were assessed for activation markers of CD107a and NKp46, vitamin D receptor (VDR), and programmed cell death protein-1 (PD-1) via flow cytometry. The bronchoalveolar lavage fluid (BALF) obtained was investigated for soluble receptor for advanced glycation end products (sRAGE), inflammatory cytokines, soluble 1,25(OH)₂D, and PDL-1. Naïve mice treated with DMSO (vehicle) were used as a control.

Flow cytometry analysis displayed a high apoptotic rate in alveolar I/II cells of threefold in ALI mice as compared to naïve mice. These findings were accompanied by elevated markers of pulmonary edema as well as lung injury markers of SP-D. Isolated lung trNK cells of the ALI mice exhibited reduced CD107a and NKp46 markers and cytotoxicity potentials and were correlated through significantly 2.1-fold higher levels of PD-1 and diminished VDR expressions as compared to naïve mice. BALF samples of ALI mice displayed high soluble PDL-1 and reduced soluble 1,25(OH)₂D levels compared to naïve mice. 1,25(OH)₂D treatment alongside OA led to a significant fourfold increase in the CD107a and NKp46 expressions to levels higher than the mice treated with the vehicle. Furthermore, 1,25(OH)₂D ameliorates free radical scavengers of GSH, GPX, CAT, and GPx-1; decreased pro-inflammatory cytokines and soluble PDL-1; and increased soluble 1,25(OH)₂D with amelioration in pulmonary edema markers and alveolar I/II apoptosis.

Our results indicate 1,25(OH)₂D's potential therapeutic effect in preventing clinical outcomes associated with ALI via regulating NK cells through inhibiting inflammatory cytokines and alleviating levels of PDL-1 and 1,25(OH)₂D released by lung tissue.