Sirt1 overexpression improves senescence-associated pulmonary fibrosis induced by vitamin D deficiency through downregulating IL-11 transcription

Determining the mechanism of senescence-associated pulmonary fibrosis is crucial for designing more effective treatments for chronic lung diseases. This study aimed to determine the following: whether Sirt1 and serum vitamin D decreased with physiological aging, promoting senescence-associated pulmonary fibrosis by activating TGF-beta 1/IL-11/MEK/ERK signaling, whether Sirt1 overexpression prevented TGF-beta 1/IL-11/MEK/ERK signaling-mediated senescence-associated pulmonary fibrosis in vitamin D-deficient (Cyp27b1(-/-)) mice, and whether Sirt1 downregulated IL-11 expression transcribed by TGF-beta 1/Smad2 signaling through deacetylating histone at the IL-11 promoter in pulmonary fibroblasts. Bioinformatics analysis with RNA sequencing data from pulmonary fibroblasts of physiologically aged mice was conducted for correlation analysis. Lungs from young and physiologically aged wild-type (WT) mice were examined for cell senescence, fibrosis markers, and TGF-beta 1/IL-11/MEK/ERK signaling proteins, and 1,25(OH)(2)D-3 and IL-11 levels were detected in serum. Nine-week-old WT, Sirt1 mesenchymal transgene (Sirt1(Tg)), Cyp27b1(-/-), and Sirt1(Tg)Cyp27b1(-/-) mice were observed the pulmonary function, aging, and senescence-associated secretory phenotype and TGF-beta 1/IL-11/MEK/ERK signaling. We found that pulmonary Sirt1 and serum vitamin D decreased with physiological aging, activating TGF-beta 1/IL-11/MEK/ERK signaling, and promoting senescence-associated pulmonary fibrosis. Sirt1 overexpression improved pulmonary dysfunction, aging, DNA damage, senescence-associated secretory phenotype, and fibrosis through downregulating TGF-beta 1/IL-11/MEK/ERK signaling in Cyp27b1(-/-) mice. Sirt1 negatively regulated IL-11 expression through deacetylating H3K9/14ac mainly at the region from -871 to -724 of IL-11 promoter, also the major binding region of Smad2 which regulated IL-11 expression at the transcriptional level, and subsequently inhibiting TGF-beta 1/IL-11/MEK/ERK signaling in pulmonary fibroblasts. This signaling in aging fibroblasts could be a therapeutic target for preventing senescence-associated pulmonary fibrosis induced by vitamin D deficiency.

Automated summary

This study determined the mechanism of senescence-associated pulmonary fibrosis and revealed the roles of Sirt1 and vitamin D in this process. Sirt1 improved lung function and prevented pulmonary fibrosis by modulating the TGF-beta 1/IL-11/MEK/ERK signaling pathway. This research is of great importance for designing treatments for chronic lung diseases.