Histone Deacetylase 9 Activates IKK to Regulate Atherosclerotic Plaque Vulnerability

Abstract

Rationale: Arterial inflammation manifested as atherosclerosis is the leading cause of mortality worldwide. Genome-wide association studies have identified a prominent role of histone deacetylase 9 (HDAC9) 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 employed two-photon and intravital microscopy to study endothelial activation and leukocyte-endothelial interactions. We show that hematopoietic Hdac9 deficiency reduces lesional macrophage content whilst increasing fibrous cap thickness thus conferring plaque stability. We demonstrate that HDAC9 binds to IKKα 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 pro-inflammatory responses in macrophages. Transcriptional profiling using RNA-Seq 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-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.

Histone Deacetylases (HDACs) and Atherosclerosis: A Mechanistic and Pharmacological Review

“…Consistently, HDAC9 deficiency in ApoE −/− mice resulted in evidently reduced lesion size in aortas and less advanced lesions (Azghandi et al, 2015). Further studies showed that HDAC9 could activate inhibitory κB kinase and regulate atherosclerotic plaque vulnerability (Asare et al, 2020). Moreover, HDAC9 repressed cholesterol efflux by downregulating ABCA1, ABCG1, and PPARγ and alternatively promoted macrophage activation in AS (Cao et al, 2014).…”

Histone deacetylase 9 deficiency exaggerates uterine M2 macrophage polarization

“…Furthermore, Hdac9 −/− LDLr −/− BMMs have increased expression of M2 markers and decreased expression of M1 inflammatory genes, resulting in macrophage polarization towards an M2‐like phenotype via increased total H3Ac, H4Ac and H3K9Ac at the promoters of Pparg and up‐regulated expression of Pparg 59 . Hdac9 –/– Apoe –/– BMMs have reduced TNF‐α‐induced up‐regulation of pro‐inflammatory gene expression, and during the development of atherosclerosis, HDAC9 binds to, deacetylates and activates inhibitory kappa B kinase (IKK)‐α and β, driving inflammatory responses in macrophages and endothelial cells 53 . Interestingly, DNA methyltransferase Dnmt3a up‐regulates the expression of Hdac9, to deacetylate the key PRR signalling molecule TBK1 and to activate the transcription of type I interferon genes in primary PM during innate antiviral immunity 60 .…”

“… 17 In contrast, Hdac6 KO BMMs show normal LPS‐induced expression of inflammatory genes endothelin‐1 ( Edn‐1 ) and IL12p40 . 52 Notably, Class IIa HDAC inhibitors attenuate inflammation in mouse and human macrophages, 49 , 53 stabilize atherosclerotic plaques in mice and limit the expression of inflammatory factors IL‐1β and IL‐6 in monocytes from patients with atherosclerosis, a chronic arterial inflammatory condition. 53 Therefore, it is reasonable to consider that high‐level expression of HDAC9, a class IIa HDAC member, in M2 is involved in suppressing key genes that drive M2 differentiation.…”

“… 59 Hdac9 –/– Apoe –/– BMMs have reduced TNF‐α‐induced up‐regulation of pro‐inflammatory gene expression, and during the development of atherosclerosis, HDAC9 binds to, deacetylates and activates inhibitory kappa B kinase (IKK)‐α and β, driving inflammatory responses in macrophages and endothelial cells. 53 Interestingly, DNA methyltransferase Dnmt3a up‐regulates the expression of Hdac9, to deacetylate the key PRR signalling molecule TBK1 and to activate the transcription of type I interferon genes in primary PM during innate antiviral immunity. 60 Taken together, these studies inspire us to suspect that Hdac9 plays conservative roles in uterine macrophages and other tissue‐resident macrophages.…”

Targeting non-coding RNAs in unstable atherosclerotic plaques: Mechanism, regulation, possibilities, and limitations

“…The endothelium plays a pivotal role in the progression of AS and its complications, and endothelial dysfunction is widely recognized as one of the early alterations in the vessel wall preceding the development of plaques [24,25]. Emerging evidence has shown that the degree of endothelial cell (EC) apoptosis may be a key factor in the transition of a plaque from a stable state to a fragile state [26,27].…”