Tumor Necrosis Factor-α Accelerates the Resolution of Established Pulmonary Fibrosis in Mice by Targeting Profibrotic Lung Macrophages

Abstract

Idiopathic pulmonary fibrosis (IPF) is a relentless, fibrotic parenchymal lung disease in which alternatively programmed macrophages produce profibrotic molecules that promote myofibroblast survival and collagen synthesis. Effective therapies to treat patients with IPF are lacking, and conventional therapy may be harmful. We tested the hypothesis that therapeutic lung delivery of the proinflammatory cytokine tumor necrosis factor (TNF)-α into wild-type fibrotic mice would reduce the profibrotic milieu and accelerate the resolution of established pulmonary fibrosis. Fibrosis was assessed in bleomycin-instilled wild-type and TNF-α(-/-) mice by measuring hydroxyproline levels, static compliance, and Masson's trichrome staining. Macrophage infiltration and programming status was assessed by flow cytometry of enzymatically digested lung and in situ immunostaining. Pulmonary delivery of TNF-α to wild-type mice with established pulmonary fibrosis was found to reduce their fibrotic burden, to improve lung function and architecture, and to reduce the number and programming status of profibrotic alternatively programmed macrophages. In contrast, fibrosis and alternative macrophage programming were prolonged in bleomycin-instilled TNF-α(-/-) mice. To address the role of the reduced numbers of alternatively programmed macrophages in the TNF-α-induced resolution of established pulmonary fibrosis, we conditionally depleted macrophages in MAFIA (MAcrophage Fas-Induced Apoptosis) mice. Conditional macrophage depletion phenocopied the resolution of established pulmonary fibrosis observed after therapeutic TNF-α delivery. Taken together, our results show for the first time that TNF-α is involved in the resolution of established pulmonary fibrosis via a mechanism involving reduced numbers and programming status of profibrotic macrophages. We speculate that pulmonary delivery of TNF-α or augmenting its signaling pathway represent a novel therapeutic strategy to resolve established pulmonary fibrosis.

Pharmacological In Vivo Inhibition of S-Nitrosoglutathione Reductase Attenuates Bleomycin-Induced Inflammation and Fibrosis

“…3). The importance of the latter finding is in the central contribution of these cytokines to the mechanisms of ILD through their direct effect on fibroblasts and indirect effect through regulation of inflammation (Redente et al, 2014;Luzina et al, 2015).…”

“…The elevations of IL-6, MCP-1, and TGF-b, which are well known for their profibrotic activities (Luzina et al, 2015), were significantly attenuated by SPL-334, whereas the levels of protective cytokines IFN-g and TNF-a (Redente et al, 2014;Luzina et al, 2015) were significantly increased or tended to be elevated, respectively, by SPL-334 (Fig. 3).…”

Mechanisms of Lung Fibrosis Resolution

“…92 The surface markers that differentiate fibrolytic macrophages and the specific precursor from which they develop have yet to be identified. However, the concept that subpopulations of macrophages can be manipulated to enhance lung fibrosis resolution was demonstrated by Redente et al, 99 where pulmonary delivery of tumor necrosis factor-a to mice with established bleomycininduced fibrosis accelerated fibrosis resolution by directly down-regulating and reducing the number of alternatively activated macrophages.…”

A Pneumocyte–Macrophage Paracrine Lipid Axis Drives the Lung toward Fibrosis

“…This epithelial injury hypothesis is supported by multiple lines of evidence, including human genetic studies, which link mutations in epithelial-specific genes to the development of idiopathic and familial forms of pulmonary fibrosis (1, 2). However, opponents of this theory argue that injury to the epithelium does not easily explain the myriad of other pathological features common to the fibrotic lung, such as alveolar macrophage (AM) M2 polarization and oxidant/antioxidant imbalances (3)(4)(5).…”