Targeting scleraxis combats cardiac fibrosis and preserves myocardial function in pressure-overloaded myocardium
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Date
2021
Authors
Nagalingam, Raghu Sundaresan
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Abstract
Cardiac fibrosis is a major cause of arrhythmia and sudden death. Fibrotic myocardium loses its ability to contract and relax due to increased tissue stiffness, which leads to heart failure. The severity of heart failure is determined by the amount of fibrosis and its association with other cardiac pathogeneses. Inadequate understanding of the mechanisms and lack of specific therapeutic targets makes cardiac fibrosis a lethal disease. Mechanical stress or injury induces fibroblast-to-myofibroblast activation, which promotes uncontrolled matrix turnover and pathological remodelling. Therefore, limiting fibroblast activation may reduce fibrosis and its associated adverse outcomes. The transcription factor scleraxis is up-regulated in failing human hearts and various heart failure models. Furthermore, scleraxis directly transactivates genes that collectively define the myofibroblast phenotype, including collagens, -smooth muscle actin, and fibronectin. Thus, we hypothesize that scleraxis gene deletion will attenuate fibrosis and improve cardiac function in pressure-overloaded myocardium, and scleraxis transcriptionally regulates matrix proteins periostin and MMP-2. Tamoxifen-induced fibroblast-specific scleraxis knockout (Scx-fKO) attenuated pressure-overload-induced cardiac fibrosis, and significantly improved cardiac function compared to wild-type (WT) transverse aortic constriction (TAC) animals. Wild-type TAC myocardium showed a marked increase in periostin-positive myofibroblasts, which were not present in Scx-fKO TAC mice; knockout cells demonstrated a failure of fibroblast activation and a reduction in fibrosis in response to pressure overload. After 4 weeks of TAC, scleraxis deletion in established cardiac fibrosis prevented the further decline in cardiac function, and cells showed loss of periostin expression concomitant with an improvement in fibrosis. In long-term pre-existing pressure-overloaded hearts, Scx-fKO animals exhibited significant improvement in systolic function and reduction in heart failure-induced mortality than WT controls. Furthermore, scleraxis directly binds and transactivates periostin and MMP-2 gene promoters and regulates their expression in cardiac myofibroblasts. Scleraxis-mediated transactivation was validated using luciferase, electrophoretic mobility shift, and chromatin immunoprecipitation assays. Scleraxis is sufficient and essential for TGF1-mediated induction of periostin and MMP-2 gene expression in cardiac myofibroblasts. Collectively, these results indicate that scleraxis governs fibroblast activation during heart failure, that arresting fibrosis improves cardiac function, that scleraxis transcriptionally regulates profibrotic-responsive genes, such as periostin and MMP-2, and that scleraxis is a viable antifibrotic treatment target.
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Keywords
Fibroblast, myofibroblast, transcription, pressure overload, cardiac fibrosis, heart failure