SIRT3 blocks myofibroblast differentiation and pulmonary fibrosis by preventing mitochondrial DNA damage

Abstract

Myofibroblast differentiation is a key process in the pathogenesis of fibrotic diseases. Transforming growth factor-β (TGF-β) is a powerful inducer of myofibroblast differentiation and is implicated in pathogenesis of tissue fibrosis. This study was undertaken to determine the role of mitochondrial deacetylase SIRT3 in TGF-β-induced myofibroblast differentiation in vitro and lung fibrosis in vivo. Treatment of human lung fibroblasts with TGF-β resulted in increased expression of fibrosis markers, smooth muscle α-actin (α-SMA), collagen-1, and fibronectin. TGF-β treatment also caused depletion of endogenous SIRT3, which paralleled with increased production of reactive oxygen species (ROS), DNA damage, and subsequent reduction in levels of 8-oxoguanine DNA glycosylase (OGG1), an enzyme that hydrolyzes oxidized guanine (8-oxo-dG) and thus protects DNA from oxidative damage. Overexpression of SIRT3 by adenovirus-mediated transduction reversed the effects of TGF-β on ROS production and mitochondrial DNA damage and inhibited TGF-β-induced myofibroblast differentiation. To determine the antifibrotic role of SIRT3 in vivo, we used the bleomycin-induced mouse model of pulmonary fibrosis. Compared with wild-type controls, Sirt3-knockout mice showed exacerbated fibrosis after intratracheal instillation of bleomycin. Increased lung fibrosis was associated with decreased levels of OGG1 and concomitant accumulation of 8-oxo-dG and increased mitochondrial DNA damage. In contrast, the transgenic mice with whole body Sirt3 overexpression were protected from bleomycin-induced mtDNA damage and development of lung fibrosis. These data demonstrate a critical role of SIRT3 in the control of myofibroblast differentiation and lung fibrosis.

Emerging therapies for idiopathic pulmonary fibrosis, a progressive age-related disease

“…Interestingly, OGG1 levels are reduced in SIRT3-deficient mice with a consequent increase in 8-Oxo-dG levels and mtDNA damage. Consistent with these data, mice overexpressing SIRT3 have sustained expression of OGG1, preserved mtDNA integrity and are protected from bleomycin-induced lung fibrosis 203 . As a therapeutic approach, mitochondria-targeted OGG1 has been shown to limit oxidant-induced mtDNA damage and lung injury 205,206 .…”

“…SIRT3 expression decreases with age, and mice deficient in SIRT3 develop spontaneous tissue fibrosis in multiple organs, including the lungs, with age 199,200 . SIRT3 expression is diminished in the skin and lungs of patients with systemic sclerosis 201 , and mice deficient in SIRT3 are more susceptible than wild-type mice to bleomycin-induced lung fibrosis 202,203 . Two main mechanisms have been described as potential SIRT3-mediated protective mechanisms against fibrosis.…”

Sirtuins and Accelerated Aging in Scleroderma

“…Other studies showed similar fibrosis-inhibiting effects mediated by SIRT1 in cultured fibroblasts from patients with hypertrophic scars [103] and transformed human and mouse fibroblast cell lines [99]. Similar to studies on SIRT1, several groups found that SIRT3 inhibited TGF-β-induced profibrotic effects such as increases in collagen, alpha-smooth muscle actin (α-SMA), or plasminogen activator inhibitor-1 (PAI1) in cultured normal human lung or skin fibroblasts [111–113]. Similar effects were seen in vivo with exaggerated profibrotic responses to bleomycin in SIRT3 KO mice [112–114] and decreased bleomycin-induced lung fibrosis in SIRT3 transgenic mice [113].…”

“…Similar to studies on SIRT1, several groups found that SIRT3 inhibited TGF-β-induced profibrotic effects such as increases in collagen, alpha-smooth muscle actin (α-SMA), or plasminogen activator inhibitor-1 (PAI1) in cultured normal human lung or skin fibroblasts [111–113]. Similar effects were seen in vivo with exaggerated profibrotic responses to bleomycin in SIRT3 KO mice [112–114] and decreased bleomycin-induced lung fibrosis in SIRT3 transgenic mice [113]. Intratracheal adenoviral delivery of SIRT6 similarly suppressed bleomycin-induced epithelial to mesenchymal transition (EMT) in murine lung [119].…”

“…The authors found a tendency for all seven SIRTs to be decreased in patients with fibrosis, with a particularly notable decrease in SIRT7. Although the specific mechanism for this decline is unknown, several studies have demonstrated downregulation of SIRT mRNA and protein [101, 111–113, 121] levels by TGF-β in human dermal and lung fibroblasts [101, 111–113, 121] and murine skin and lung tissues [101, 112]. Decreased SIRT expression in SSc may be a marker both of aging, given the known decline of SIRTs with age, and TGF-β-driven fibrosis.…”