Histone deacetylase 9 (HDAC9) is implicated in ischemic stroke by genome-wide association studies. We conducted a series of experiments using a mouse model of ischemic stroke (middle cerebral artery occlusion followed by reperfusion) to examine the potential role of HDAC9. Briefly, HDAC9 was upregulated in the penumbra. Deletion of HDAC9 from neurons reduced infarction volume, inhibited neuronal apoptosis in the penumbra, and improved neurological outcomes. HDAC9 knockout from neurons in the penumbra upregulated cGMP-dependent kinase II (cGK II), blocking which abrogated the protective effects of HDAC9 deletion. Mechanistically, HDAC9 interacts with the transcription factor MEF2, thereby inhibiting MEF2\'s binding to the promoter region of the cGK II gene, which results in the suppression of cGK II expression. Inhibiting the interaction between HDAC9 and MEF2 by BML210 upregulated cGK II and attenuated ischemic injury in mice. These results encourage targeting the HDAC9-MEF2 interaction in developing novel therapy against ischemic stroke.

Aortic aneurysm/dissection (AAD) is a serious cardiovascular condition characterized by rapid onset and high mortality rates. Currently, no effective drug treatment options are known for AAD. AAD pathogenesis is associated with the phenotypic transformation and abnormal proliferation of vascular smooth muscle cells (VSMCs). However, endogenous factors that contribute to AAD progression remain unclear. We aimed to investigate the role of histone deacetylase 9 (HDAC9) in AAD pathogenesis. HDAC9 expression was considerably increased in human thoracic aortic dissection specimens. Using RNA-sequencing (RNA-seq) and chromatin immunoprecipitation, we demonstrated that HDAC9 transcriptionally inhibited the expression of superoxide dismutase 2 and insulin-like growth factor-binding protein-3, which are critically involved in various signaling pathways. Furthermore, HDAC9 triggered the transformation of VSMCs from a systolic to synthetic phenotype, increasing their proliferation and migration abilities and suppressing their apoptosis. Consistent with these results, in vivo experiments revealed that TMP195, a pharmacological inhibitor of HDAC9, suppressed the formation of the β-aminopropionitrile-induced AAD phenotype in mice. Our findings indicate that HDAC9 may be a novel endogenous risk factor that promotes the onset of AAD by mediating the phenotypic transformation of VSMCs. Therefore, HDAC9 may serve as a potential therapeutic target for drug-based AAD treatment. Furthermore, TMP195 holds potential as a therapeutic agent for AAD treatment.

Major depressive disorder (MDD) is a pervasive and devastating mental disease. Broad spectrum histone deacetylase (HDAC) inhibitors are considered to have potential for the treatment of depressive phenotype in mice. However, due to its non-specific inhibition, it has extensive side effects and can not be used in clinical treatment of MDD. Therefore, finding specific HDAC subtypes that play a major role in the etiology of MDD is the key to develop corresponding specific inhibitors as antidepressants in the future. Copy number variation in HDAC9 gene is thought to be associated with the etiology of some psychiatric disorders. Herein, we found that HDAC9 was highly expressed in the hippocampus of chronic restraint stress (CRS) mouse model of depression. Upregulation of HDAC9 expression in hippocampal neurons of mice induced depression-like phenotypes, including anhedonia, helplessness, decreased dendritic spine density, and neuronal hypoexcitability. Moreover, knockdown or knockout of HDAC9 in hippocampal neurons alleviated depression-like phenotypes caused by chronic restraint stress (CRS) in WT mice. Importantly, using immunoprecipitation-mass spectrometry (IP-MS), we further found that Annexin A2 (ANXA2) was coupled to and deacetylated by HDAC9. This coupling resulted in the inhibition of ubiquitinated ANXA2 degradation and then mediates depression-like behavior. Overall, we discovered a previously unrecognized role for HDAC9 in hippocampal neurons in the pathogenesis of depression, indicating that inhibition of HDAC9 might be a promising clinical strategy for the treatment of depressive disorders.

Postoperative cognitive decline (POCD) is a common and serious complication following anesthesia and surgery; however, the precise mechanisms of POCD remain unclear. Our previous research showed that sevoflurane impairs adult hippocampal neurogenesis (AHN) and thus cognitive function in the aged brain by affecting neurotrophin-3 (NT-3) expression; however, the signaling mechanism involved remains unexplored. In this study, we found a dramatic decrease in the proportion of differentiated neurons with increasing concentrations of sevoflurane, and the inhibition of neural stem cell differentiation was partially reversed after the administration of exogenous NT-3. Understanding the molecular underpinnings by which sevoflurane affects NT-3 is key to counteracting cognitive dysfunction. Here, we report that sevoflurane administration for 2 days resulted in upregulation of histone deacetylase 9 (HDAC9) expression, which led to transcriptional inactivation of cAMP-response element binding protein (CREB). Due to the colocalization of HDAC9 and CREB within cells, this may be related to the interaction between HDAC9 and CREB. Anyway, this ultimately led to reduced NT-3 expression and inhibition of neural stem cell differentiation. Furthermore, knockdown of HDAC9 rescued the transcriptional activation of CREB after sevoflurane exposure, while reversing the downregulation of NT-3 expression and inhibition of neural stem cell differentiation. In summary, this study identifies a unique mechanism by which sevoflurane can inhibit CREB transcription through HDAC9, and this process reduces NT-3 levels and ultimately inhibits neuronal differentiation. This finding may reveal a new strategy to prevent sevoflurane-induced neuronal dysfunction.

BACKGROUND: Atherosclerosis is a main cause of multiple cardiovascular diseases, and cell damage of human umbilical vein endothelial cells (HUVECs) was reported to participate in the development of atherosclerosis. In this study, we aimed to study the action of Astragaloside IV (ASV) on AS development using in vitro AS cell model.
METHODS: MTT assay, EdU staining assay, and flow cytometry were utilized for detection of cell proliferation and apoptosis, respectively. The protein expression of histone deacetylase 9 (HDAC9), Bax, Bcl-2, p-P65, P65, p-IκBα, and IκBα was gaged using western blot. The angiogenesis was evaluated by tube formation assay. The inflammatory response was evaluated by ELISA kits. SOD activity and MDA level were detected using the matched commercial kits. RT-qPCR was used for HDAC9 mRNA expression measurement.
RESULTS: Oxidized low-density lipoprotein (ox-LDL) significantly repressed cell proliferation, angiogenesis, and enhanced apoptosis, inflammation, and oxidative stress in HUVECs. ASV addition could alleviate ox-LDL-caused cell damage in HUVECs. Moreover, HDAC9 was overexpressed in AS patients and AS cell model. Functionally, HDAC9 knockdown also exhibited the protective role in ox-LDL-treated HUVECs. In addition, ASV treatment protected against ox-LDL-induced damage in HUVECs via targeting HDAC9. ASV could inactivate the NF-κB pathway via regulating HDAC9 in AS cell model.
CONCLUSIONS: ASV exerted the protective effects on ox-LDL-induced damage in HUVECs through the HDAC9/NF-κB axis.

Following the publication of the above paper, it was drawn to the Editors\' attention by a concerned reader that certain of the flow cytometric data featured in Figs. 2D, 4D and 5D, the colony formation assay data shown in Figs. 2C, 4C and 5C, and the tumor images shown in Fig. 7A were strikingly similar to data appearing in different form in other articles by different authors. Owing to the fact that the contentious data in the above article were already under consideration for publication, or had already been published, prior to its submission to Oncology Reports, the Editor has decided that this paper should be retracted from the Journal. The authors were asked for an explanation to account for these concerns, but the Editorial Office did not receive a reply. The Editor apologizes to the readership for any inconvenience caused. [Oncology Reports 43: 635‑645, 2020; DOI: 10.3892/or.2020.7456].

BACKGROUND: The expression of programmed death-ligand 1 (PD-L1) is associated with the response of patients to PD-1/PD-L1 blockade immunotherapy. It has been demonstrated that histone deacetylase (HDAC) inhibitors may alter the expression of PD-L1/PD-L2 and enhance the antitumor immune responses. However, the profile of PD-L1 expression and its association with HDACs in hepatocellular carcinoma (HCC) has not been accurately investigated.
METHODS: The expression of PD-L1 and HDACs were examined by immunohistochemical (IHC) staining using tissue microarray (TMA) of 109 HCC specimens. Expression data from TCGA database and IHC staining of TMA were used for correlation analysis. Survival rates were analyzed based on data from 109 HCC patients.
RESULTS: We found that PD-L1 was upregulated in the majority of HCC samples. Furthermore, correlation analysis revealed that PD-L1 expression was positively correlated with HDAC9 and HDAC2 expression in HCC. Survival analysis showed that high levels of PD-L1 combined with increased expression of HDAC9 decreased overall survival (OS) in patients with HCC. In addition, univariate and multivariate analysis further suggested that the increased PD-L1/HDAC9 expression was an independent prognostic biomarker in HCC. HDAC9 overexpression promoted HCC growth and PD-L1 expression.
CONCLUSIONS: The results of the current study highlighted the strong association between HDACs with immunotherapy, thus providing a rational basis for combining HDAC9 specific inhibitors and PD-1 blockade in a future clinical approach for HCC.

The maternal-foetal interface is an immune-privileged site where the semi-allogeneic embryo is protected from attacks by the maternal immune system. Uterine macrophages are key players in establishing and maintaining pregnancy, and the dysregulation of the M1-M2 subpopulation balance causes abortion. We separated two distinct mouse uterine macrophage subpopulations during early pregnancy, CD45+ F4/80+ CD206- M1-like (M1) and CD45+ F4/80+ CD206+ M2-like (M2) cells. The M1 preponderance was significantly exaggerated at 6 hours after lipopolysaccharide (LPS) treatment, and adoptive transfer of M2 macrophages partially rescued LPS-induced abortion. RNA sequencing analysis of mouse uterine M2 versus M1 revealed 1837 differentially expressed genes (DEGs), among which 629 was up-regulated and 1208 was down-regulated. Histone deacetylase 9 (Hdac9) was one of the DEGs and validated to be significantly up-regulated in uterine M2 as compared with M1. Remarkably, this differential expression profile between M1 and M2 was also evident in primary splenic macrophages and in vitro polarized murine peritoneal, bone marrow-derived and RAW 264.7 macrophages. In Hdac9/HDAC9 knockout RAW 264.7 and human THP-1-derived macrophages, the expression of M1 differentiation markers was unchanged or decreased whereas M2 markers were increased compared with the wild-type cells, and these effects were unrelated to compromised proliferation. Furthermore, Hdac9/HDAC9 ablation significantly enhanced the phagocytosis of fluorescent microspheres in M2 Raw 264.7 cells yet decreased the capacity of THP-1-derived M1 macrophages. The above results demonstrate that Hdac9/HDAC9 deficiency exaggerates M2 macrophage polarization in mouse and human macrophages, which may provide clues for our understanding of the epigenetic regulation on macrophage M1/M2 polarization in maternal-foetal tolerance.

OBJECTIVE: Myocardial infarction (MI) is the leading cause of death worldwide. Histone deacetylases (HDACs) collectively participate in the initiation and progression of heart diseases, including MI. This study aimed to investigate the roles of histone deacetylase 9 (HDAC9) in the development of MI.
METHODS: In vivo and in vitro assays were conducted to determine the effects of HDAC9 on heart function and MI. qRT-PCR was applied to determine the mRNA level. Western blot was performed for protein expression. Immunofluorescence was applied to detect the fluorescence tensity of Myog and Myod. CCK-8, flow cytometry and transwell assays were carried out for function analysis.
RESULTS: HDAC9 was upregulated in MI models in vivo and in vitro. Downregulated HDAC9 modulated the changes in left ventricle ejection fraction (LVEF), left ventricle fractional shortening (LVFS) and left ventricular end-diastolic diameter (LVEDD) and left ventricular end-systolic diameter (LVESD). Moreover, HDAC9 knockdown activated NFE2-related factor 2 (Nrf2)/Keap1/HO-1 pathways. Additionally, HDAC9/Nrf2 axis modulated the proliferation, apoptosis and myogenesis of cardiomyocytes.
CONCLUSIONS: Taken together, HDAC9 knockout induced the activation of Nrf2 and protected heart from MI injury. Thus, the HDAC9/Nrf2 axis can be a novel marker for the treatment of MI.

A number of studies have verified the vital effects of long non‑coding RNAs on the malignant behaviour of retinoblastoma (RB). The objective of the present study was to examine the specific role and mechanisms of HLA complex P5 (HCP5) in RB. For this purpose, reverse transcription‑quantitative polymerase chain reaction was used to determine the expression of HCP5, microRNA (miRNA/miR)‑3619‑5p and histone deacetylase 9 (HDAC9). A 3‑(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2‑H-tetrazolium bromide assay was conducted to detect cell viability. Transwell assays were used to evaluate the abilities of cell migration and invasion. A mouse tumor model was established to explore the functions of HCP5 in RB in vivo. The interactions between HCP5, miR‑3619‑5p and HDAC9 were confirmed by a dual‑luciferase reporter assay. The protein expression of HDAC9 was determined by western blot analysis. The results revealed that the expression levels of HCP5 and HDAC9 were upregulated, whereas those of miR‑3619‑5p were downregulated in RB tissues and cell lines. The downregulation of HCP5 or the overexpression of miR‑3619‑5p suppressed RB cell proliferation, migration and invasion in vitro. Simultaneously, the knockdown of HCP5 suppressed tumor growth in mice in vivo. In addition, HCP5 was directly bound to miR‑3619‑5p and inversely correlated with miR‑3619‑5p. HDAC9 was found to be a target gene of and negatively regulated by miR‑3619‑5p. HCP5 expression also positively correlated with HDAC9 expression. Rescue experiments revealed that the overexpression of HDAC9 or the inhibition of miR‑3619‑5p reversed the inhibition of RB cell viability, migration and invasion induced by the knockdown of HCP5. On the whole, the present study demonstrates that the silencing of HCP5 exerts an anti‑tumor effect in RB by sponging miR‑3619‑5p to target HDAC9.