Histone Deacetylase 9 Activates IKK to Regulate Atherosclerotic Plaque Vulnerability

Rationale: Arterial inflammation manifested as atherosclerosis is the leading cause of mortality worldwide. Genome-wide association studies have identified a prominent role of HDAC (histone deacetylase)-9 in atherosclerosis and its clinical complications including stroke and myocardial infarction. Objective: To determine the mechanisms linking HDAC9 to these vascular pathologies and explore its therapeutic potential for atheroprotection. Methods and Results: We studied the effects of Hdac9 on features of plaque vulnerability using bone marrow reconstitution experiments and pharmacological targeting with a small molecule inhibitor in hyperlipidemic mice. We further used 2-photon and intravital microscopy to study endothelial activation and leukocyte-endothelial interactions. We show that hematopoietic Hdac9 deficiency reduces lesional macrophage content while increasing fibrous cap thickness thus conferring plaque stability. We demonstrate that HDAC9 binds to IKK (inhibitory kappa B kinase)-α and β, resulting in their deacetylation and subsequent activation, which drives inflammatory responses in both macrophages and endothelial cells. Pharmacological inhibition of HDAC9 with the class IIa HDAC inhibitor TMP195 attenuates lesion formation by reducing endothelial activation and leukocyte recruitment along with limiting proinflammatory responses in macrophages. Transcriptional profiling using RNA sequencing revealed that TMP195 downregulates key inflammatory pathways consistent with inhibitory effects on IKKβ. TMP195 mitigates the progression of established lesions and inhibits the infiltration of inflammatory cells. Moreover, TMP195 diminishes features of plaque vulnerability and thereby enhances plaque stability in advanced lesions. Ex vivo treatment of monocytes from patients with established atherosclerosis reduced the production of inflammatory cytokines including IL (interleukin)-1β and IL-6. Conclusions: Our findings identify HDAC9 as a regulator of atherosclerotic plaque stability and IKK activation thus providing a mechanistic explanation for the prominence of HDAC9 as a vascular risk locus in genome-wide association studies. Its therapeutic inhibition may provide a potent lever to alleviate vascular inflammation. Graphical Abstract: A graphical abstract is available for this article.

The diverse and unanticipated roles of histone deacetylase 9 in coordinating plant development and environmental acclimation

Plants tightly control gene transcription to adapt to environmental conditions and steer growth and development. Different types of epigenetic modifications are instrumental in these processes. In recent years, an important role for the chromatin-modifying RPD3/HDA1 class I HDAC HISTONE DEACETYLASE 9 (HDA9) emerged in the regulation of a multitude of plant traits and responses. HDACs are widely considered transcriptional repressors and are typically part of multiprotein complexes containing co-repressors, DNA, and histone-binding proteins. By catalyzing the removal of acetyl groups from lysine residues of histone protein tails, HDA9 negatively controls gene expression in many cases, in concert with interacting proteins such as POWERDRESS (PWR), HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES 15 (HOS15), WRKY53, ELONGATED HYPOCOTYL 5 (HY5), ABA INSENSITIVE 4 (ABI4), and EARLY FLOWERING 3 (ELF3). However, HDA9 activity has also been directly linked to transcriptional activation. In addition, following the recent breakthrough discovery of mutual negative feedback regulation between HDA9 and its interacting WRKY-domain transcription factor WRKY53, swift progress in gaining understanding of the biology of HDA9 is expected. In this review, we summarize knowledge on this intriguing versatile—and long under-rated—protein and propose novel leads to further unravel HDA9-governed molecular networks underlying plant development and environmental biology.

The Role of Histone Deacetylase 9 in the Therapeutic Effects of Astaxanthin on Non-Alcoholic Steatohepatitis

Objectives The objectives of this study were to determine the role of histone deacetylase 9 (HDAC9) in the development of non-alcoholic steatohepatitis (NASH); and to evaluate the therapeutic effects of astaxanthin (ASTX), a xanthophyll carotenoid, on NASH via the modulation of HDAC9 in vivo. Methods Eight-week-old male and female wild-type (WT) and global Hdac9 knockout (KO) mice (n = 30/sex/genotype) were fed a high-fat/high-sucrose/high-cholesterol (HFHSHC) diet for 20 weeks to induce NASH. Subsequently, subsets of WT (n = 10/sex) and KO (n = 10/sex) mice were sacrificed to examine NASH features and served as baseline controls. The rest of the mice were randomly assigned into two diet groups for another 10 weeks: One continued on the HFHSHC diet, while the other group was fed an HFHSHC containing 0.03% ASTX (w/w). Results After 20 weeks on the HFHSHC diet, male KO mice had lower liver weights and triglycerides than WT, but no genotypic differences were observed in the female. Male KO mice showed less liver steatosis and fibrosis with significant decreases in the hepatic expression of lipogenic genes than male WT mice, but Hdac9 deletion did not inhibit NASH development in female mice. Compared with male KO baseline controls, consumption of control diet for an additional 10 week increased hepatic expression of lipogenic and pro-inflammatory genes in male KO mice, losing the beneficial effect of Hdac9 deletion shown at week 20 on the HFHSHC diet. However, the ASTX diet abrogated the induction. There were no significant differences in hepatic lipid contents and histological features of NASH between any genotypes regardless of ASTX supplementation. Also, additional control diet feeding did not induce any changes in hepatic gene expression in female mice, compared with those on the ASTX diet. Conclusions Hdac9 deletion protected male, but not female, mice from diet-induced hepatic steatosis and fibrosis, which may be attributable to decreased lipogenesis in the liver. However, the protection did not exist when liver damages progressed. Hdac9 deletion or ASTX alone did not alleviate the liver damage progression, but they together inhibited the induction of lipogenic and pro-inflammatory genes in the liver of male mice, indicating that they may have synergistic effects on ameliorating NASH progression. Funding Sources The study was supported by National Institutes of Health.