Impaired Mitochondrial Transcription Factor A Expression Promotes Mitochondrial Damage to Drive Fibroblast Activation and Fibrosis in Systemic Sclerosis

Abstract

Objective Mitochondrial transcription factor A (TFAM) controls the transcription of core proteins required for mitochondrial homeostasis. This study was undertaken to investigate changes in TFAM expression in systemic sclerosis (SSc), to analyze mitochondrial function, and to evaluate the consequences for fibroblast activation. Methods TFAM expression was analyzed by immunofluorescence and Western blotting. The effects of TFAM knockout were investigated in cultured fibroblasts and in murine models of bleomycin‐induced skin fibrosis, bleomycin‐induced lung fibrosis, and skin fibrosis induced by overexpression of constitutively active transforming growth factor β type I receptor (TGFβRΙ). Results TFAM expression was down‐regulated in fibroblasts in SSc skin and in cultured SSc fibroblasts. The down‐regulation of TFAM was associated with decreased mitochondrial number and accumulation of damaged mitochondria with release of mitochondrial DNA (mtDNA), accumulation of deletions in mtDNA, metabolic alterations with impaired oxidative phosphorylation, and release of the mitokine GDF15. Normal fibroblasts subjected to long‐term, but not acute, exposure to TGFβ mimicked SSc fibroblasts, with down‐regulation of TFAM and accumulation of mitochondrial damage. Down‐regulation of TFAM promoted fibroblast activation with up‐regulation of fibrosis‐relevant Gene Ontology terms in RNA‐Seq, partially in a reactive oxygen species–dependent manner. Mice with fibroblast‐specific knockout of Tfam were prone to fibrotic tissue remodeling, with fibrotic responses even to NaCl instillation and enhanced sensitivity to bleomycin injection and overexpression of constitutively active TGFβRI. TFAM knockout fostered Smad3 signaling to promote fibroblast activation. Conclusion Alterations in the key mitochondrial transcription factor TFAM in response to prolonged activation of TGFβ and associated mitochondrial damage induce transcriptional programs that promote fibroblast‐to‐myofibroblast transition and drive tissue fibrosis.

Effect of Anti‐S100A4 Monoclonal Antibody Treatment on Experimental Skin Fibrosis and Systemic Sclerosis–Specific Transcriptional Signatures in Human Skin

“…CASQ1 is a coding gene for CASQ1, a primary calcium ion buffer in the sarcoplasmic reticulum of skeletal muscle and a modulator of ryanodine receptor type 1 activity. Deregulation of CASQ1 has been linked to enhanced oxidative stress and mitochondrial damage, 24 mechanisms that have been implicated in the pathogenesis of SSc and might thus drive disease progression 25 . We and others identified STAT3 signaling as an important downstream regulator of fibroblast and leukocyte activation in SSc, and inhibition of STAT3 signaling has been shown to ameliorate experimental fibrosis 26–31 .…”

“…Deregulation of CASQ1 has been linked to enhanced oxidative stress and mitochondrial damage, 24 mechanisms that have been implicated in the pathogenesis of SSc and might thus drive disease progression. 25 We and others identified STAT3 signaling as an important downstream regulator of fibroblast and leukocyte activation in SSc, and inhibition of STAT3 signaling has been shown to ameliorate experimental fibrosis. [26][27][28][29][30][31] Consistent with the results obtained by RNASeq on the messenger RNA (mRNA) level, we found AMPK and CASQ1 to be up-regulated in response to S100A4, whereas pSTAT3, the active form of the profibrotic transcription factor STAT3, was down-regulated on S100A4 inhibition (Figure 3).…”

Dopamine D2 Receptor Signaling Attenuates Acinar Cell Necroptosis in Acute Pancreatitis through the Cathepsin B/TFAM/ROS Pathway

“…TFAM is a mitochondrial transcription and replication regulator encoded by a nuclear gene [39,40]. TFAM deficiency leads to a reduction in mitochondrial DNA copy number and severe respiratory chain function defects, accompanied by a significant increase in mitochondrial ROS levels [40][41][42]. Mitochondrial ROS are known to promote necrotic apoptosis.…”

Mammary Fibrosis Tendency and Mitochondrial Adaptability in Dairy Cows with Mastitis

“…Mitochondrial transcription factor A (TFAM) plays an important role in maintaining mitochondrial DNA stability [34]. Studies have shown that a significant decrease in the protein level of TFAM represents a malfunction of mitochondrial function [35], and promoting the increase in TFAM protein level is conducive to alleviating the dysfunction caused by mitochondrial damage. VDAC1 and HSP60 have relatively highly conserved DNA sequences, so they are often used as mitochondrial markers.…”