Overlapping and Divergent Actions of Structurally Distinct Histone Deacetylase Inhibitors in Cardiac Fibroblasts

Abstract

Inhibitors of zinc-dependent histone deacetylases (HDACs) profoundly affect cellular function by altering gene expression via changes in nucleosomal histone tail acetylation. Historically, investigators have employed pan-HDAC inhibitors, such as the hydroxamate trichostatin A (TSA), which simultaneously targets members of each of the three zinc-dependent HDAC classes (classes I, II, and IV). More recently, class- and isoform-selective HDAC inhibitors have been developed, providing invaluable chemical biology probes for dissecting the roles of distinct HDACs in the control of various physiologic and pathophysiological processes. For example, the benzamide class I HDAC-selective inhibitor, MGCD0103 [-(2-aminophenyl)-4-[[(4-pyridin-3-ylpyrimidin-2-yl)amino]methyl] benzamide], was shown to block cardiac fibrosis, a process involving excess extracellular matrix deposition, which often results in heart dysfunction. Here, we compare the mechanisms of action of structurally distinct HDAC inhibitors in isolated primary cardiac fibroblasts, which are the major extracellular matrix-producing cells of the heart. TSA, MGCD0103, and the cyclic peptide class I HDAC inhibitor, apicidin, exhibited a common ability to enhance histone acetylation, and all potently blocked cardiac fibroblast cell cycle progression. In contrast, MGCD0103, but not TSA or apicidin, paradoxically increased expression of a subset of fibrosis-associated genes. Using the cellular thermal shift assay, we provide evidence that the divergent effects of HDAC inhibitors on cardiac fibroblast gene expression relate to differential engagement of HDAC1- and HDAC2-containing complexes. These findings illustrate the importance of employing multiple compounds when pharmacologically assessing HDAC function in a cellular context and during HDAC inhibitor drug development.

Epigenetics in Cardiac Fibrosis

“…Whether HDAC inhibitors trigger senescence of cardiac fibroblasts has not been determined. However, we recently demonstrated that MGCD0103 and MS-275, but not structurally distinct HDAC inhibitors, potently stimulate expression of the SASP components PAI-1 and MMP-13 in cardiac fibroblasts (100) . Further studies are required to determine whether these Class I HDAC inhibitors are bona fide inducers of cardiac fibroblast replicative senescence, and whether other epigenetic regulators, such as BET proteins, KMTs, and DNMTs, influence the cardiac SASP.…”

“…In mouse models of pressure overload, MI, and isoproterenol-induced cardiac injury, fibroblast proliferation spiked within the first week following induction of cardiac remodeling, and thereafter, it returned to basal levels in a manner that correlated with reduced inflammation (97) . Class I HDAC inhibitors such as mocetinostat (MGCD0103) have been demonstrated to potently suppress cardiac fibroblast proliferation and mitigate fibrotic remodeling in response to cardiac injury 98 , 99 , 100 , 101 . Thus, HDAC inhibitor–mediated suppression of cardiac fibrosis is likely due, at least in part, to the ability of these compounds to squelch expansion of the ECM-producing fibroblast pool in the heart.…”

“…Thus, HDAC inhibitor–mediated suppression of cardiac fibrosis is likely due, at least in part, to the ability of these compounds to squelch expansion of the ECM-producing fibroblast pool in the heart. The mechanism by which HDAC inhibitors block cardiac fibroblast proliferation involves induction of genes encoding the cyclin-dependent kinase inhibitors p15 and p57, which leads to reduced retinoblastoma (Rb) protein phosphorylation and blockade of downstream target genes that promote the G 1 -to-S transition 100 , 101 ( Figure 2A ). MGCD0103 treatment of atrial CD90 + cells was also shown to stimulate the p53/p21 axis, inducing cell cycle arrest and apoptosis (99) .…”

Application of Histone Deacetylase Inhibitors in Renal Interstitial Fibrosis

“…In contrast, HDACs remove the acetyl groups from acetylated histones, increase chromatin condensation, and suppress gene transcription [14]. Aberrant expressions of HDACs and subsequent epigenetic modifications have been extensively observed in various animal models of interstitial fibrosis, and inhibitory effects against tissue fibrosis by HDACs inhibitors have also been demonstrated in multiple organs, such as heart [15,16], liver [17,18], and kidney [19,20], which presents the possibility of using HDACs as targets in the treatment of chronic fibrotic diseases. In this minireview, we will discuss HDACs inhibitors' application and molecular mechanism in renal interstitial fibrosis.…”

Class I HDACs control a JIP1-dependent pathway for kinesin-microtubule binding in cardiomyocytes

“…For example, HDAC inhibitor treatment of cardiomyocytes leads to increased expression of the anti-hypertrophic transcription factor, krüppel-like factor 4 (KLF4) [18] and increased expression of an anti-hypertrophic microRNA (miR-9) [19], with subsequent blunting of cardiomyocyte growth. In cardiac fibroblasts, HDAC inhibitors trigger cyclin-dependent kinase inhibitor gene expression, which limits expansion of fibrogenic myofibroblasts [14,20], and they stimulate expression of miR-133, which suppresses pro-fibrotic gene expression [21]. …”