Epigenetic regulation of cardiac fibroblast senescence by class I histone deacetylases and ING2

Abstract

Fibrosis is estimated to contribute to 45% of deaths in the western world. A key cellular mediator of fibrosis is the activated myofibroblast, which is characterized by the secretion of extracellular matrix (ECM) proteins. Myofibroblasts are thought to initially have a positive mechanical influence following an injury. However, long-term activation of these cells can lead to excessive ECM accumulation, culminating in fibrosis and organ failure. Cellular senescence is an irreversible form of cell cycle arrest, associated with a senescence-associated secretory phenotype (SASP), which is characterized by production of ECM-degrading enzymes such as matrix metalloproteases. Thus, it has been proposed that induction of the SASP might be a promising strategy for the resolution of organ fibrosis. In this context, histone deacetylase (HDAC) inhibitors might be candidate therapies for senescence modulation, as this class of enzymes is intensely involved in the control of cellular proliferation. Here, adult rat ventricular fibroblasts stimulated with TGF-β were used as a cell-based model of myofibroblast activation, and a panel of isoform-selective HDAC inhibitors was tested. Inhibitors of class I HDACs (especially HDAC1 and HDAC2), but not class IIa or IIb HDACs, potently stimulated cardiac fibroblast senescence, as assessed by upregulation of p16 and p21 gene expression, enhanced b-galactosidase activity, and induction of the classical SASP pathway. The mechanism of stimulation of senescence by class I HDAC inhibitors appears to involve ING2, a methyl-histone reader protein and phosphoinositide receptor. These findings define a chromatin signaling program for cardiac fibroblast senescence that could be could targeted with ‘epigenetic therapies’ such as small molecule HDAC inhibitors to treat fibrosis of the heart.