Ketogenic diet induces autophagy to alleviate bleomycin-induced pulmonary fibrosis in murine models

Ketogenic diet (KD) has been identified as an effective strategy in treating multiple diseases. KD is capable of inducing autophagy which is an important therapeutic target for pulmonary fibrosis (PF). This study aimed to investigate the effect of KD treatment on PF progression. Materials and Methods: Intratracheal instillation of bleomycin (BLM, 5 mg/kg) to establish PF model in male Kunming mice fed either KD or standard diet. The survival of mice was recorded every day for 3 weeks. The pulmonary tissues were weighed on day 21 and the pulmonary index was calculated. The histopathological changes of pulmonary tissues were analyzed by hematoxylin and eosin staining and Masson staining, and the collagen deposition by hydroxyproline assay. Then the content of proinflammatory factors in pulmonary tissues was measured using enzyme-linked immunosorbent assay, and the expression of profibrogenic cytokines, autophagy markers and PI3K/AKT/mTOR pathway-related proteins in pulmonary tissues using western blotting or immunohistochemistry. Results: KD treatment significantly restored the BLM-induced increase of pulmonary index and had a tendency to increase the survival rate of PF mice. Furthermore, KD treatment restored the BLM-induced damage of alveolar structure, infiltration of inflammatory cells and collagen deposition and decreased hydroxyproline content. In addition, the BLM-induced secretion of tumor necrosis factor-alpha, interleukin-6 and interleukin-1β and expression of transforming growth factor β1, phospho-Smad2/3, connective tissue growth factor, α-smooth muscle actin and collagen type III alpha 1 chain were inhibited by KD. KD treatment also up-regulated the expression of light chain 3 II/I and Beclin1 and down-regulated the expression of p62, phospho-AKT, phospho-mTOR and phospho-p70S6K, suggesting that KD induced autophagy and suppressed the BLM-induced activation of PI3K/AKT/mTOR signaling pathway. Conclusions: These findings indicate that KD can alleviate PF in vivo by regulating autophagy and PI3K/AKT/mTOR signaling pathway, which provides a novel therapeutic strategy for PF.