Myocyte-Derived Hsp90 Modulates Collagen Upregulation via Biphasic Activation of STAT-3 in Fibroblasts during Cardiac Hypertrophy

Abstract

Signal transducer and activator of transcription 3 (STAT-3)-mediated signaling in relation to upregulated collagen expression in fibroblasts during cardiac hypertrophy is well defined. Our recent findings have identified heat shock protein 90 (Hsp90) to be a critical modulator of fibrotic signaling in cardiac fibroblasts in this disease milieu. The present study was therefore intended to analyze the role of Hsp90 in the STAT-3-mediated collagen upregulation process. Our data revealed a significant difference between in vivo and in vitro results, pointing to a possible involvement of myocyte-fibroblast cross talk in this process. Cardiomyocyte-targeted knockdown of Hsp90 in rats (Rattus norvegicus) in which the renal artery was ligated showed downregulated collagen synthesis. Furthermore, the results obtained with cardiac fibroblasts conditioned with Hsp90-inhibited hypertrophied myocyte supernatant pointed toward cardiomyocytes' role in the regulation of collagen expression in fibroblasts during hypertrophy. Our study also revealed a novel signaling mechanism where myocyte-derived Hsp90 orchestrates not only p65-mediated interleukin-6 (IL-6) synthesis but also its release in exosomal vesicles. Such myocyte-derived exosomes and myocyte-secreted IL-6 are responsible in unison for the biphasic activation of STAT-3 signaling in cardiac fibroblasts that culminates in excess collagen synthesis, leading to severely compromised cardiac function during cardiac hypertrophy.KEYWORDS cardiac hypertrophy, collagen, Hsp90, myocyte-fibroblast cross talk, STAT-3 M yocardial fibrosis is a hallmark of cardiac hypertrophy and a proposed substrate for heart failure (1, 2). The extracellular space is frequently the site for such abnormal accumulation of fibrillar collagen, accounting for myocardial stiffness and ventricular dysfunction during cardiac hypertrophy (3). The cardiac fibroblast is the principal cell type in the myocardium and synthesizes and secretes collagen in response to pressure-overload hypertrophy (4). A close relationship between angiotensin II (AngII) and profibrotic cytokines has been suggested, and several molecular signaling networks have been implicated in the progression of cardiac fibrosis (5, 6). A few reports have also shown that the role of myocytes in myocardial collagen production is mediated by myocyte-derived paracrine factors (7,8). However, the precise mechanisms involving the role of different signaling intermediates in the regulation of collagen gene expression during cardiac hypertrophy have remained unsolved.In an earlier report, we described the mechanism of interleukin-6 (IL-6)-mediated activation of the signal transducer and activator of transcription 3 (STAT-3) and consequent collagen synthesis in the hypertrophied rat heart (9). STAT-3 activation has also

Reduction of cardiac TGFβ-mediated profibrotic events by inhibition of Hsp90 with engineered protein

“…Hsp90 inhibition was found to reduce collagen I synthesis on hepatic stellate cells (HSCs) in liver fibrosis [8]. Interesting data described by different groups including ours, showed that pharmacological and biological inhibition of Hsp90 effectively blocks the pro-fibrotic effects of TGFβ in different preclinical models of skin fibrosis in systemic sclerosis [6], in cardiac hypertrophy [9] or in cardiac fibrosis [10]. Hsp90 was presented as a novel modulator of TGFβ signaling in lung adenocarcinoma and bronchoalveolar carcinoma cells [5].…”

Examining the Paracrine Effects of Exosomes in Cardiovascular Disease and Repair

“…72 Likewise, exosomes secreted from hypertrophied cardiomyocytes contain HSP90 and IL-6 (interleukin 6) to maintain STAT3 (signal transducer and activator of transcription 3)-fibrotic pathway signaling. 86 This study, however, also showed differential regulation of collagen expression in the cardiac fibroblast in vitro versus in vivo, which points toward the potential paracrine effects resulting from crosstalk among different cell types. It will be important for future studies to compare in vivo findings with in vitro systems to confirm which cell type is releasing exosomes to exert specific effects.…”

“…Cardiac fibroblast–derived exosomes enriched in miR‐21‐3p have been shown to be potential regulators of cardiomyocyte hypertrophy . Likewise, exosomes secreted from hypertrophied cardiomyocytes contain HSP90 and IL‐6 (interleukin 6) to maintain STAT3 (signal transducer and activator of transcription 3)–fibrotic pathway signaling . This study, however, also showed differential regulation of collagen expression in the cardiac fibroblast in vitro versus in vivo, which points toward the potential paracrine effects resulting from crosstalk among different cell types.…”

NanotizedPPARαOverexpression Targeted to Hypertrophied Myocardium Improves Cardiac Function by Attenuating the p53-GSK3β-Mediated Mitochondrial Death Pathway

“…As TRITC and FITC work as a donor/acceptor in FRAP assay, TRITC was subjected to 50% bleaching, and FITC intensity in a single cell was measured. FRET efficiency was calculated from the difference between the postbleaching and prebleaching donor intensities (delta donor) using FV1200 confocal microscope (18).…”

“…Data were analyzed by Student's ttest (comparison of two groups) and one-way analysis of variance followed by Tukey's test (comparison of multiple groups) using GraphPad Prism (Version 6.01; GraphPad Software, La Jolla, CA). Results with p-value <0.05 were considered significant (18,58).…”