Abstract
The mitochondrial calcium uniporter (MCU) regulates metabolic reprogramming in lung macrophages and the progression of pulmonary fibrosis. Fibrosis progression is associated with apoptosis resistance in lung macrophages; however, the mechanism(s) by which apoptosis resistance occurs is poorly understood. Here, we found a marked increase in mitochondrial B-cell lymphoma-2 (Bcl-2) in lung macrophages from subjects with idiopathic pulmonary fibrosis (IPF). Similar findings were seen in bleomycin-injured wild-type (WT) mice, whereas Bcl-2 was markedly decreased in mice expressing a dominant-negative mitochondrial calcium uniporter (DN-MCU). Carnitine palmitoyltransferase 1a (Cpt1a), the rate-limiting enzyme for fatty acid β-oxidation, directly interacted with Bcl-2 by binding to its BH3 domain, which anchored Bcl-2 in the mitochondria to attenuate apoptosis. This interaction was dependent on Cpt1a activity. Lung macrophages from IPF subjects had a direct correlation between CPT1A and Bcl-2, whereas the absence of binding induced apoptosis. The deletion of Bcl-2 in macrophages protected mice from developing pulmonary fibrosis. Moreover, mice had resolution when Bcl-2 was deleted or was inhibited with ABT-199 after fibrosis was established. These observations implicate an interplay between macrophage fatty acid β-oxidation, apoptosis resistance, and dysregulated fibrotic remodeling.
Highlights
Pulmonary fibrosis is a chronic disease that consists of aberrant remodeling of lung tissue
Macrophage mitochondrial calcium uniporter (MCU) regulates apoptosis resistance in lung macrophages by increasing B-cell lymphoma-2 (Bcl-2) Prior evidence showed that the active caspase-3 was markedly reduced in lung macrophages from Idiopathic pulmonary fibrosis (IPF) subjects [9], but the mechanism(s) by which it is reduced is not known
We found that Bcl-2 expression was nearly fourfold higher in lung macrophage mitochondria from IPF subjects compared to normal subjects
Summary
Pulmonary fibrosis is a chronic disease that consists of aberrant remodeling of lung tissue. Bcl2 was significantly increased in bleomycin-injured WT mice, whereas expression in lung macrophages from DN-MCU-Lyz2-cre mice was less than the saline controls (Fig. 1C, D). B Lung macrophages from WT mice exposed to bleomycin or saline control were subjected to mitochondrial isolation and detection of Bcl-2, Cpt1a, and MCU by immunoblot analysis.
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