Hypoxia-stimulated cardiac fibroblast production of IL-6 promotes myocardial fibrosis via the TGF-β1 signaling pathway

Abstract

Interlukin-6 (IL-6) is a multifunctional cytokine produced by several cell types that has a role in fibrosis. Fibroblasts (FBs) maintain this underlying pathogenic change through regulation of IL-6 production; however, its potential functional role in regulating surrounding cellular structural changes during ischemic myocardial remodeling remains unexplored. Here, we generated FBs, cardiomyocytes (CMs), and blood vascular endothelial cells (ECs) from the ventricles of neonatal rats. IL-6 was then overexpressed in FBs and the cells were treated with IL-6 receptor inhibitor (IL6RI), TGF-β1 receptor inhibitor (TβRI), or MMP2/MMP9 inhibitor (MMPI) using monoculture or coculture models under hypoxic conditions. The results indicate that overexpression of IL-6 is sufficient to induce myofibroblastic proliferation, differentiation, and fibrosis, probably via increased TGF-β1-mediated MMP2/MMP3 signaling. The use of IL6RI, TβRI, or MMPI diminished these effects. In addition, IL-6 activated the apoptosis-associated factors Caspase3 and Smad3, and decreased the expression of anti-apoptotic factor Bcl2, resulting in apoptosis of CMs under hypoxic coculture: IL6RI or TβRI inhibited these effects. Unexpectedly, IL-6-overexpressing FBs significantly increased the angiogenesis of ECs, which involved significant increases in the expression of proangiogenic growth factors. Treatment of FBs with IL6RI or TβRI in coculture with ECs reduced the levels of secreted proangiogenic growth factors, and the angiogenesis of ECs was significantly downregulated. Thus, IL-6 functions in ischemic myocardial remodeling through multifunctional reprogramming of hypoxia-associated FBs towards fibrosis via upregulation of the TGF-β1 signaling pathway.

Bone Marrow-Derived Mesenchymal Stem Cells Expressing Thioredoxin 1 Attenuate Bleomycin-Induced Skin Fibrosis and Oxidative Stress in Scleroderma

“…Trx-1 also has antiapoptotic and growth stimulatory functions through interactions with apoptosis signal regulation kinase-1 (Saitoh et al, 1998) and hypoxia inducible factor-1 alpha (Welsh et al, 2002). In this study, Trx-1 overexpression also increased levels of the apoptosis-associated proteins caspase 3 and decreased expression of the antiapoptosis factor Bcl2, which has previously been described in an in vitro model of hypoxia-induced fibrosis (Wang et al, 2016).…”

“…Here, Trx-1 overexpression prevented thickening of the dermis in an SSc mouse model, suggesting that Trx-1 can also protect against SSc, possibly by inhibiting ROS production. Enhanced TGF-b signaling has been shown to promote fibrosis (Wang et al, 2016); therefore, Trx-1 may exert its antifibrotic effect through TGF-b.…”

TGF-β pathway activation by idiopathic pulmonary fibrosis (IPF) fibroblast derived soluble factors is mediated by IL-6 trans-signaling

“…Moreover, IL-6-deficient (IL-6(−/−)) mice had relatively attenuated fibrotic changes following bleomycin treatment in comparison to the wild type controls [8]. Recent studies showed that the IL-6 can also promote fibrosis by driving chronic inflammation [5] and by activating the TGFβ pathway [9,10], which is the most potent profibrotic cytokine known [11][12][13].…”

CD154 Induces Interleukin-6 Secretion by Kidney Tubular Epithelial Cells under Hypoxic Conditions: Inhibition by Chloroquine

“…The induction of IL-6 secretion by hypoxic stress per se remains debated; lack of or moderate inductions of IL-6 protein secretion by hypoxic stress have been described in other cellular models; a significant IL-6 induction may require prolonged hypoxia or reoxygenation steps. Hypoxic stress was found associated with an increased expression of IL-6 mRNA, as shown in fibroblasts, vascular smooth cells, endothelial cells, astrocytes or cardiac myocytes, and TECs, after a brief or a prolonged hypoxic challenge [40][41][42][43][44]. Mechanisms linking signaling pathways activated by hypoxia to the increased expression of IL-6 mRNA remain to be fully understood; however, some cues may be brought by transcription studies that show increased transcription of the IL-6 gene upon hypoxic stress [40][41][42][43].…”