Systemic lupus erythematosus is an autoimmune disease characterized by excessive inflammation and production of pathogenic Abs. Histone deacetylase 6 (HDAC6) is a class IIb histone deacetylase. It has been reported that selective HDAC6 inhibition decreases inflammation in lupus mouse models. In this study, sex- and age-matched wild-type (WT) and HDAC6-/- mice on the C57BL/6 background were administered 0.5 ml of pristane or PBS i.p. at 8-12 wk of age and were euthanized 10 d later. At sacrifice, body weight and spleen weight were measured, sera were collected, and splenocytes and peritoneal cells were harvested for flow cytometry. We found pristane administration increased the spleen weight with no difference between WT and HDAC6-/- mice. Pristane administration promoted the population of CD11b+Ly6C++ inflammatory monocytes and CD11b+Ly6G+ neutrophils. Peritoneal recruitment of these inflammatory monocytes and neutrophils was significantly decreased in HDAC6-/- mice compared with the WT mice. Flow cytometry results showed that the number of CD69+ T and B cells was increased in HDAC6-/- mice. Pristane administration also induced the IFN signature genes as determined by RT-qPCR. Furthermore, IFN signature genes were not affected in HDAC6-/- mice compared with the WT mice. In vitro studies in J774A.1 cells revealed that the selective HDAC6 inhibitor (ACY-738) increased acetylation of NF-κB while increasing Stat1 phosphorylation, which resulted in inducible NO synthase production in LPS/IFN-γ-stimulated cells. Taken together, these results demonstrate that although HDAC6 inhibition may inhibit some inflammatory pathways, others remain unaffected.

Histone deacetylase 6 (HDAC6) belongs to the class IIb group of the histone deacetylase family, which participates in remodelling of various tissues. Herein, we sought to examine the potential regulation of HDAC6 in cardiac remodelling post-infarction. Experimental myocardial infarction (MI) was created in HDAC6-deficient (HDAC6-/-) mice and wild-type (HADC6+/+) by left coronary artery ligation. At days 0 and 14 post-MI, we evaluated cardiac function, morphology and molecular endpoints of repair and remodelling. At day 14 after surgery, the ischemic myocardium had increased levels of HADC6 gene and protein of post-MI mice compared to the non-ischemic myocardium of control mice. As compared with HDAC6-/--MI mice, HADC6 deletion markedly improved infarct size and cardiac fibrosis as well as impaired left ventricular ejection fraction and left ventricular fraction shortening. At the molecular levels, HDAC6-/- resulted in a significant reduction in the levels of the transforming growth factor-beta 1 (TGF-β1), phosphor-Smad-2/3, collagen I and collagen III proteins and/or in the ischemic cardiac tissues. All of these beneficial effects were reproduced by a pharmacological inhibition of HADC6 in vivo. In vitro, hypoxic stress increased the expressions of HADC6 and collagen I and III gene; these alterations were significantly prevented by the HADC6 silencing and TubA loading. These findings indicated that HADC6 deficiency resists ischemic injury by a reduction of TGF-β1/Smad2/3 signalling activation, leading to decreased extracellular matrix production, which reduces cardiac fibrosis and dysfunction, providing a potential molecular target in the treatment of patients with MI.

BACKGROUND: Mechanical unloading-induced bone loss threatens prolonged spaceflight and human health. Recent studies have confirmed that osteoporosis is associated with a significant reduction in bone microvessels, but the relationship between them and the underlying mechanism under mechanical unloading are still unclear.
METHODS: We established a 2D clinostat and hindlimb-unloaded (HLU) mouse model to simulate unloading in vitro and in vivo. Micro-CT scanning was performed to assess changes in the bone microstructure and mass of the tibia. The levels of CD31, Endomucin (EMCN) and histone deacetylase 6 (HDAC6) in tibial microvessels were detected by immunofluorescence (IF) staining. In addition, we established a coculture system of microvascular endothelial cells (MVECs) and osteoblasts, and qRT‒PCR or western blotting was used to detect RNA and protein expression; cell proliferation was detected by CCK‒8 and EdU assays. ChIP was used to detect whether HDAC6 binds to the miRNA promoter region.
RESULTS: Bone mass and bone microvessels were simultaneously significantly reduced in HLU mice. Furthermore, MVECs effectively promoted the proliferation and differentiation of osteoblasts under coculture conditions in vitro. Mechanistically, we found that the HDAC6 content was significantly reduced in the bone microvessels of HLU mice and that HDAC6 inhibited the expression of miR-375-3p by reducing histone acetylation in the miR-375 promoter region in MVECs. miR-375-3p was upregulated under unloading and it could inhibit MVEC proliferation by directly targeting low-density lipoprotein-related receptor 5 (LRP5) expression. In addition, silencing HDAC6 promoted the miR-375-3p/LRP5 pathway to suppress MVEC proliferation under mechanical unloading, and regulation of HDAC6/miR-375-3p axis in MVECs could affect osteoblast proliferation under coculture conditions.
CONCLUSIONS: Our study revealed that disuse-induced bone loss may be closely related to a reduction in the number of bone microvessels and that the modulation of MVEC function could improve bone loss induced by unloading. Mechanistically, the HDAC6/miR-375-3p/LRP5 pathway in MVECs might be a promising strategy for the clinical treatment of unloading-induced bone loss.

OBJECTIVE: Flotillin-2 (FLOT2) is a prototypical oncogenic and a potential target for cancer therapy. However, strategies for targeting FLOT2 remain undefined. Post-translational modifications are crucial for regulating protein stability, function, and localization. Understanding the mechanisms and roles of post-translational modifications is key to developing targeted therapies. This study aims to investigate the regulation and function of lysine acetylation of FLOT2 in nasopharyngeal carcinoma, providing new insights for targeting FLOT2 in cancer intervention.
METHODS: The PhosphoSitePlus database was used to analyze the lysine acetylation sites of FLOT2, and a lysine acetylation site mutation of FLOT2 [FLOT2 (K211R)] was constructed. Nasopharyngeal carcinoma cells were treated with histone deacetylase (HDAC) inhibitor trichostatin A (TSA) and Sirt family deacetylase inhibitor nicotinamide (NAM). TSA-treated human embryonic kidney (HEK)-293T were transfected with FLOT2 mutant plasmids. Co-immunoprecipitation (Co-IP) was used to detect total acetylation levels of FLOT2 and the effects of specific lysine (K) site mutations on FLOT2 acetylation. Western blotting was used to detect FLOT2/FLAG-FLOT2 protein expression in TSA-treated nasopharyngeal carcinoma cells transfected with FLOT mutant plasmids, and real-time reverse transcription PCR (real-time RT-PCR) was used to detect FLOT2 mRNA expression. Nasopharyngeal carcinoma cells were treated with TSA combined with MG132 or chloroquine (CQ) to analyze FLOT2 protein expression. Cycloheximide (CHX) was used to treat HEK-293T cells transfected with FLAG-FLOT2 (WT) or FLAG-FLOT2(K211R) plasmids to assess protein degradation rates. The BioGrid database was used to identify potential interactions between FLOT2 and HDAC6, which were validated by Co-IP. HEK-293T cells were co-transfected with FLAG-FLOT2 (WT)/FLAG-FLOT2 (K211R) and Vector/HDAC6 plasmids, and grouped into FLAG-FLOT2 (WT)+Vector, FLAG-FLOT2 (WT)+HDAC6, FLAG-FLOT2 (K211R)+Vector, and FLAG-FLOT2 (K211R)+HDAC6 to analyze the impact of K211R mutation on total lysine acetylation levels. In 6-0B cells, overexpression of FLOT2 (WT) and FLOT2 (K211R) was performed, and the biological functions of FLOT2 acetylation site mutants were assessed using cell counting kit-8 (CCK-8), colony formation, and Transwell invasion assays.
RESULTS: The PhosphoSitePlus database indicated that FLOT2 has an acetylation modification at the K211 site. Co-IP confirmed significant acetylation of FLOT2, with TSA significantly increasing overall FLOT2 acetylation levels, while NAM had no effect. Mutation at the K211 site significantly reduced overall FLOT2 acetylation, unaffected by TSA. TSA decreased FLOT2 protein expression in nasopharyngeal carcinoma cells without affecting FLOT2 mRNA levels or FLOT2 (K211R) protein expression in transfected cells. The degradation rate of FLOT2 (K211R) protein was significantly slower than that of FLOT2 (WT). The proteasome inhibitor MG132 prevented TSA-induced FLOT2 degradation, while the lysosome inhibitor CQ did not. BioGrid data suggested a potential interaction between FLOT2 and HDAC6, confirmed by Co-IP. Knockdown of HDAC6 in nasopharyngeal carcinoma cells significantly increased FLOT2 acetylation; co-transfection of HDAC6 and FLAG-FLOT2 (WT) significantly decreased total lysine acetylation levels, whereas co-transfection of HDAC6 and FLAG-FLOT2 (K211R) had no effect. Knockdown of HDAC6 significantly reduced FLOT2 protein levels without affecting mRNA levels. MG132 prevented HDAC6-knockdown-induced FLOT2 degradation. Knockdown of HDAC6 significantly accelerated FLOT2 degradation. Nasopharyngeal carcinoma cells transfected with FLOT2 (K211R) showed significantly higher proliferation and invasion than those transfected with FLOT2 (WT).
CONCLUSIONS: The K211 site of FLOT2 undergoes acetylation modification, and HDAC6 mediates deacetylation at this site, inhibiting proteasomal degradation of FLOT2 and maintaining its stability and tumor-promoting function in nasopharyngeal carcinoma.
目的: 浮舰蛋白(flotillin-2，FLOT2)是典型的致瘤蛋白和潜在的肿瘤治疗靶点，但靶向FLOT2的干预策略仍未确定。翻译后修饰作为表观调控的重要方式，对蛋白质的活性、定位和稳定性等特性具有重要的调控作用，揭示蛋白质翻译后修饰的调控机制和功能是靶向治疗开发的一种有效手段。本研究旨在研究鼻咽癌中FLOT2赖氨酸乙酰化修饰的调控机制及其功能，为靶向FLOT2的肿瘤干预手段提供新思路。方法: 利用PhosphoSitePlus数据库分析FLOT2的赖氨酸乙酰化位点，并构建赖氨酸乙酰化位点突变的FLOT2突变体[FLOT2(K211R)]；用组蛋白去乙酰化酶(histone deacetylases，HDAC)抑制剂曲古菌素A(trichostatin A，TSA)、Sirt家族去乙酰化酶抑制剂烟酰胺(nicotinamide，NAM)处理鼻咽癌细胞，TSA处理转染FLOT2突变体质粒的人胚肾细胞(human embryonic kidney，HEK)-293T细胞；利用免疫共沉淀(co-immunoprecipitation，Co-IP)检测FLOT2的总赖氨酸乙酰化水平以及特定赖氨酸(K)位点突变对FLOT2总赖氨酸乙酰化水平的影响。用蛋白质印迹法检测TSA处理未转染/转染FLOT2突变体质粒后的鼻咽癌细胞中FLOT2/FLAG-FLOT2的蛋白质表达，实时反转录聚合酶链反应(real-time reverse transcription PCR，real-time RT-PCR)检测TSA处理后鼻咽癌细胞中FLOT2 mRNA的表达。用TSA分别联合MG132或氯喹(chloroquine，CQ)处理鼻咽癌细胞后，检测FLOT2的蛋白质表达。用放线菌酮(cycloheximide，CHX)分别处理已转染FLAG-FLOT2(WT)或FLAG-FLOT2(K211R)质粒的HEK-293T细胞，检测FLAG-FLOT2、FLOT2(K211R)的蛋白质表达水平以反映蛋白质的降解速率。通过BioGrid数据库查询FLOT2与HDAC6之间是否可能存在相互作用，并采用Co-IP验证。用FLAG-FLOT2(WT)/FLAG-FLOT2(K211R)质粒分别联合空白对照(Vector)/HDAC6质粒转染HEK-293T细胞，分为FLAG-FLOT2(WT)+Vector、FLAG-FLOT2(WT)+HDAC6、FLAG-FLOT2(K211R)+Vector、FLAG-FLOT2(K211R)+HDAC6共4组，分析K211R突变对FLOT2总赖氨酸乙酰化水平的影响。在6-0B细胞中，分别过表达FLOT2(WT)和FLOT2(K211R)，用细胞计数试剂盒-8(cell counting kit-8，CCK-8)、平板克隆形成和Transwell侵袭检测FLOT2乙酰化位点突变体的生物学功能。结果: PhosphoSitePlus数据库显示FLOT2的K211位点存在乙酰化修饰，Co-IP结果证实FLOT2蛋白存在明显的乙酰化修饰，且TSA可以显著上调FLOT2的总乙酰化修饰水平，而NAM则无此作用；K211位点突变后FLOT2的总赖氨酸乙酰化水平显著下降，且不受TSA影响。TSA下调鼻咽癌细胞中FLOT2的蛋白质表达水平，而不影响FLOT2 mRNA的表达水平，也不影响转染FLAG-FLOT2(K211R)的鼻咽癌细胞中FLOT2(K211R)的蛋白质表达水平。FLOT2(K211R)的蛋白质降解速率显著慢于FLOT2(WT)的降解速率。蛋白酶体抑制剂MG132可以阻止TSA引起的FLOT2降解，溶酶体抑制剂CQ则无此功能。BioGrid数据库数据显示FLOT2与HDAC6可能存在相互作用，Co-IP结果证实FLOT2与HDAC6抗体可以相互共沉淀对方蛋白。在敲减HDAC6表达的鼻咽癌细胞中，FLOT2的总赖氨酸乙酰化水平显著提高；共转染HDAC6和FLAG-FLOT2(WT)可显著降低总赖氨酸乙酰化水平，而共转染HDAC6和FLAG-FLOT2(K211R)不影响总赖氨酸乙酰化水平。敲减HDAC6可以显著下调FLOT2的蛋白质水平而不影响其mRNA水平；MG132可以阻止敲减HDAC6引起的FLOT2降解。敲减HDAC6，FLOT2的降解速率显著加快。转染FLOT2(K211R)突变体的鼻咽癌细胞增殖速度和侵袭能力显著强于转染FLOT2(WT)的细胞。结论: FLOT2 K211位点存在乙酰化修饰，HDAC6通过介导FLOT2 K211的去乙酰化修饰抑制FLOT2经蛋白酶体途径降解，维持其在鼻咽癌中的稳定和促瘤功能。.

BACKGROUND: Histone deacetylases (HDACs) are crucial regulators of gene expression, DNA synthesis, and cellular processes, making them essential targets in cancer research. HDAC6, specifically, influences protein stability and chromatin dynamics. Despite HDAC6\'s potential therapeutic value, its exact role in gene regulation and chromatin remodeling needs further clarification. This study examines how HDAC6 inactivation influences lysine acetyltransferase P300 stabilization and subsequent effects on chromatin structure and function in cancer cells.
RESULTS: We employed the HDAC6 inhibitor ITF3756, siRNA, or CRISPR/Cas9 gene editing to inactivate HDAC6 in different epigenomic backgrounds. Constantly, this inactivation led to significant changes in chromatin accessibility, particularly increased acetylation of histone H3 lysines 9, 14, and 27 (ATAC-seq and H3K27Ac ChIP-seq analysis). Transcriptomics, proteomics, and gene ontology analysis revealed gene changes in cell proliferation, adhesion, migration, and apoptosis. Significantly, HDAC6 inactivation altered P300 ubiquitination, stabilizing P300 and leading to downregulating genes critical for cancer cell survival.
CONCLUSIONS: Our study highlights the substantial impact of HDAC6 inactivation on the chromatin landscape of cancer cells and suggests a role for P300 in contributing to the anticancer effects. The stabilization of P300 with HDAC6 inhibition proposes a potential shift in therapeutic focus from HDAC6 itself to its interaction with P300. This finding opens new avenues for developing targeted cancer therapies, improving our understanding of epigenetic mechanisms in cancer cells.

OBJECTIVE: Multiple factors contribute to the development of perioperative neurocognitive disorders (PND). This study was designed to investigate whether Histone Deacetylase 6 (HDAC6) was involved in the formation of postoperative cognitive dysfunction in elderly mice by regulating the degree of acetylation of heat shock protein (HSP90) and related protein functions and quantities.
METHODS: C57BL/6 J male mice were randomly divided into six groups: control naive (group Control), anesthesia (group Anesthesia), splenectomy surgery (group Surgery), splenectomy surgery plus dissolvent (group Vehicles), splenectomy surgery plus the inhibitor ACY-1215 (group Ricolinostat), and splenectomy surgery plus the inhibitor RU-486(group Mifepristone). After the mice were trained for Morris Water Maze (MWM) test for five days, anesthesia and operational surgery were carried out the following day. Cognitive function was assessed on the 1st, 3rd and 7th days post-surgery. The hippocampi were harvested on days 1, 3, and 7 post-surgeries for Western blots and ELISA assays.
RESULTS: Mice with the splenectomy surgery displayed the activation of the hypothalamic-pituitary-adrenal axis (HPA-axis), marked an increase in adrenocorticotropic hormone (ACTH), glucocorticoid, mineralocorticoid at the molecular level and impaired spatial memory in the MWM test. The hippocampus of surgical groups showed a decrease in acetylated HSP90, a rise in glucocorticoid receptor (GR)-HSP90 association, and an increase in GR phosphorylation and translocation. HDAC6 was increased after the surgical treated. Using two specific inhibitors, HDAC6 inhibitor Ricolinostat (ACY-1215) and GR inhibitor Mifepristone (RU-486), can partially mitigate the effects caused by surgical operation.
CONCLUSIONS: Abdominal surgery may impair hippocampal spatial memory, possibly through the HDAC6-triggered increase in the function of HSP90, consequently strengthening the negative role of steroids in cognitive function. Targeting HDAC6- HSP90/GR signaling may provide a potential avenue for the treatment of the impairment of cognitive function after surgery.

BACKGROUND: The global outbreak of COVID-19 caused by the SARS-CoV-2 has led to millions of deaths. This unanticipated emergency has prompted virologists across the globe to delve deeper into the intricate dynamicity of the host-virus interface with an aim to identify antiviral targets and elucidate host and viral determinants of severe disease.
OBJECTIVE: The present study was undertaken to analyse the role of histone deacetylase 6 (HDAC6) in regulating SARS-CoV-2 infection.
RESULTS: Gradual increase in HDAC6 expression was observed in different SARS-CoV-2-permissive cell lines following SARS-CoV-2 infection. The SARS-CoV-2 nucleocapsid protein (N protein) was identified as the primary viral factor responsible for upregulating HDAC6 expression. Downregulation of HDAC6 using shRNA or a specific inhibitor tubacin resulted in reduced viral replication suggesting proviral role of its deacetylase activity. Further investigations uncovered the interaction of HDAC6 with stress granule protein G3BP1 and N protein during infection. HDAC6-mediated deacetylation of SARS-CoV-2 N protein was found to be crucial for its association with G3BP1.
CONCLUSIONS: This study provides valuable insights into the molecular mechanisms underlying the disruption of cytoplasmic stress granules during SARS-CoV-2 infection and highlights the significance of HDAC6 in the process.

Lewy body disease (LBD), one of the most common neurodegenerative diseases (NDDs), is characterized by excessive accumulation of α-synuclein (α-syn) in neurons. In recent years, environmental factors such as exposure to herbicides and pesticides have been attributed to the development of this condition. While majority of the studies on neurotoxic effects of paraquat (PQ) have focused on α-syn-mediated neuronal damage in the early stages of α-syn accumulation in neurons, efforts to explore the key target for α-syn degradation are limited. Recent research has suggested that histone deacetylase 6 (HDAC6) might possibly regulate amyloid clearance, and that the metabolism of compounds in neurons is also directly affected by axonal transport in neurons. Dynein predominantly mediates reverse transportation of metabolites and uptake of signal molecules and other compounds at the end of axons, which is conducive to the reuse of cell components. However, the role of interaction of dynein with HDAC6 in metabolites transport is still unclear. Therefore, this study aimed to investigate the role of HDAC6 in α-syn accumulation/clearance in neurons and the associated possible influencing factors. The results revealed that HDAC6 could transport ubiquitinated α-syn, bind to dynein, form an aggresome, and relocate to the center of the microtubule tissue, ultimately reducing abnormal accumulation of α-syn. However, PQ treatment resulted in HDAC6 upregulation, causing abnormal aggregation of α-syn. Taken together, these findings indicated that PQ exposure caused abnormal accumulation of α-syn and decreased effective degradation of α-syn by HDAC6-mediated aggresome-autophagy-lysosome pathway.

The primary cilium behaves as a platform for sensing and integrating extracellular cues to control a plethora of cellular activities. However, the functional interaction of this sensory organelle with epithelial-mesenchymal transition (EMT) during pulmonary fibrosis remains unclear. Here, we reveal a critical role for cylindromatosis (CYLD) in reciprocally linking the EMT program and ciliary homeostasis during pulmonary fibrosis. A close correlation between the EMT program and primary cilia is observed in bleomycin-induced pulmonary fibrosis as well as TGF-β-induced EMT model. Mechanistic study reveals that downregulation of CYLD underlies the crosstalk between EMT and ciliary homeostasis by inactivating histone deacetylase 6 (HDAC6) during pulmonary fibrosis. Moreover, manipulation of primary cilia is an effective means to modulate the EMT program. Collectively, these results identify a pivotal role for the CYLD/HDAC6 signaling in regulating the reciprocal interplay between the EMT program and ciliary homeostasis during pulmonary fibrosis.

Cardiotoxicity associated with chemotherapy has gradually become the major cause of death in cancer patients. The development of bifunctional drugs with both cardioprotective and antitumor effects has become the future direction. HDAC6 plays important roles in the progression, treatment, and prognosis of cancer and cardiovascular diseases, but bifunctional inhibitors have not been reported. Herein, structure-activity relationship studies driven by pharmacophore-based remodification and fragment-based design were performed to yield highly potent HDAC6 inhibitor I-c4 containing imidazo[1,2-a]pyridine. Importantly, I-c4 effectively suppressed the growth of MGC-803 xenografts in vitro and in vivo by inhibiting the deacetylation pathway without causing myocardial damage after long-term administration. Meanwhile, I-c4 could mitigate severe myocardial damage against H2O2 or myocardial ischemia/reperfusion in vitro and in vivo. Further studies revealed that the cardioprotective effect of I-c4 was associated with reduction of inflammatory cytokines. Taken together, I-c4 may represent a novel lead compound for further development of an anticarcinogen with a cardioprotective effect.