Restoration of SIRT3 gene expression by airway delivery resolves age-associated persistent lung fibrosis in mice

Abstract

Aging is a risk factor for progressive fibrotic disorders involving diverse organ systems, including the lung. Idiopathic pulmonary fibrosis, an age-associated degenerative lung disorder, is characterized by persistence of apoptosis-resistant myofibroblasts. Here we demonstrate that sirtuin 3 (SIRT3), a mitochondrial deacetylase, is downregulated in the lungs of humans with idiopathic pulmonary fibrosis and in mice subjected to lung injury. Overexpression of Sirt3 cDNA via airway delivery restored the capacity for fibrosis resolution in aged mice, in association with activation of the forkhead box transcription factor FoxO3a in fibroblasts, upregulation of pro-apoptotic members of the Bcl2 family and recovery of apoptosis susceptibility. While transforming growth factor-β1 reduced levels of SIRT3 and FOXO3A in lung fibroblasts, cell non-autonomous effects involving macrophage-secreted products were necessary for SIRT3-mediated activation of FOXO3A. Together, these findings reveal a novel role of SIRT3 in pro-resolution macrophage functions that restore susceptibility to apoptosis in fibroblasts via a FOXO3A-dependent mechanism.

SIRT3 Overexpression Ameliorates Asbestos-Induced Pulmonary Fibrosis, mt-DNA Damage, and Lung Fibrogenic Monocyte Recruitment

“…SIRT3 may attenuate pro-fibrotic signaling in other cells within these fibrosis-promoting distal lung niches. Consistent with this notion is that SIRT3 deficiency is evident in the AECs and fibroblasts of patients with IPF as well as aged mice [32,33,35]. Notably, a recent study showed that airway delivery of a Sirt3 overexpression cDNA promotes resolution of lung fibrosis in aged mice in part by working along with macrophage-derived paracrine secreted products in activating the forkhead box (FOX) transcription factor FoxO3a in fibroblasts, which subsequently augments fibroblast pro-apoptotic Bcl2 family member expression and apoptosis [35].…”

“…Although the causal role of lung recruitment of Mo-AMs in mediating lung fibrosis is established, the precise molecular mechanisms involved are unclear and an area of ongoing study by our group and others [35,[40][41][42][55][56][57][58]. Using the asbestos lung fibrosis model with a combination of confocal microscopy and single-cell RNA sequencing, our group reported that Mo-AMs are recruited to fibrotic areas of the lungs, engulf asbestos fibers, and provide a connection between injured alveolar epithelium and activated fibroblasts by localizing in spatially restricted pro-fibrotic niches [41].…”

“…Accumulating evidence has firmly implicated a key role for SIRT3 deficiency in the pathobiology of IPF as well as the bleomycin murine model of lung fibrosis, but the detailed molecular mechanisms involved are not fully understood, nor is it known whether augmenting SIRT3 in mice following exposure to asbestos is protective [32][33][34][35][36][37][38][39]. In this study we addressed these two important gaps in our understanding of the role of SIRT3 in modulating pulmonary fibrosis by showing that Sirt3 Tg mice are protected from asbestos-induced pulmonary fibrosis and that lung protection is associated with reduced levels of lung mtDNA damage and fibrogenic Mo-AM recruitment.…”

“…Accumulating evidence firmly implicates SIRT3 deficiency in the development of pulmonary fibrosis. First, SIRT3 function is reduced in the AECs and fibroblasts of patients with IPF as well as the lungs in aged mice [32,34,35]. Additionally, extracellular vesicles (EVs) from IPF lung fibroblasts contain miR-23b-3p and miR-494-3p that can reduce lung epithelial cell SIRT3 expression, resulting in mitochondrial dysfunction and senescence [36].…”

“…Sirt3 −/− mice are also more susceptible to bleomycin-and asbestosinduced lung fibrosis in association with detrimentally impacted mtOGG1 function, resulting in mtDNA damage in AECs [32] and fibroblasts [33]. Third, overexpression of SIRT3 using either genetic or pharmacologic approaches mitigates oxidant-induced fibroblast profibrotic signaling and AEC mtDNA damage and apoptosis in vitro as well as bleomycin-induced lung fibrosis in vivo [32][33][34][35]37,38] and promotes lung fibrosis resolution in aged mice [35]. Mesenchymal stem cells can diminish diabetic lung fibrosis by augmenting SIRT3 protein expression and SIRT3-mediated stress response [39].…”