Sphk1 regulates HMGB1 via HDAC4 and mediates epithelial pyroptosis in allergic rhinitis.

Background: Allergic rhinitis (AR) is a global health issue affecting millions of individuals worldwide. Pyroptosis has emerged as a major player in the development of AR, and targeting its inhibition with specific drugs holds promise for AR treatment. However, a comprehensive understanding of the precise mechanisms underlying pyroptosis in AR remains to be explored, warranting further investigation. Objective: This study aims to elucidate the roles of HMGB1, Sphk1, and HDAC4 in regulating human nasal epithelial cell (hNEC) pyroptosis and AR. Methods: An in vitro AR cell culture model and an in vivo AR mouse model were established. Western blot, ELISA, histological staining, and flow cytometry were utilized to confirm the gene and protein expression. The interactions among Sphk1, HDAC4, and HMGB1 were validated through ChIP, Co-IP, and Dual-luciferase assay. Results and conclusion: We identified that the expression levels of Sphk1, HMGB1, and inflammasome components, including IL-18, and IL-1ß were elevated in AR patients and mouse models. Knockdown of Sphk1 inhibited hNEC pyroptosis induced by dust mite allergen. Overexpression of HDAC4 suppressed HMGB1-mediated pyroptosis in hNECs. In addition, HDAC4 was found to mediate the transcriptional regulation of HMGB1 via MEF2C, a transcription factor. Additionally, Sphk1 was shown to interact with CaMKII-δ, promoting the phosphorylation of HDAC4 and inhibiting its cytoplasmic translocation. Knockdown of HDAC4 reversed the effect of Sphk1 knockdown on pyroptosis. These discoveries offer a glimpse into the molecular mechanisms underlying AR and suggest potential therapeutic targets for the treatment of this condition.

Elevated meteorin-like protein from high-intensity interval training improves heart function via AMPK/HDAC4 pathway.

High-intensity interval training (HIIT) has been found to be more effective in relieving heart failure (HF) symptoms, than moderate-intensity continuous aerobic training (MICT). Additionally, higher meteorin-like protein (Metrnl) levels are seen after HIIT versus MICT. We investigated whether Metrnl contributed to post-HF cardiac functional improvements, and the signaling pathways involved. 50 HF patients underwent MICT, and another 50, HIIT, which was followed by cardiac function and serum Metrnl measurements. Metrnl was also measured in both blood and skeletal muscle samples of mice with transverse aortic constriction-induced HF after undergoing HIIT. Afterward, shRNA-containing adenovectors were injected into mice, yielding five groups: control, HF, HF + HIIT + scrambled shRNA, HF + HIIT + shMetrnl, and HF + Metrnl (HF + exogenous Metrnl). Mass spectrometry identified specific signaling pathways associated with increased Metrnl, which was confirmed with biochemical analyses. Glucose metabolism and mitochondrial functioning were evaluated in cardiomyocytes from the five groups. Both HF patients and mice had higher circulating Metrnl levels post-HIIT. Metrnl activated AMPK in cardiomyocytes, subsequently increasing histone deacetylase 4 (HDAC4) phosphorylation, leading to its cytosolic sequestration and inactivation via binding with chaperone protein 14-3-3. HDAC4 inactivation removed its repression on glucose transporter type 4, which, along with increased mitochondrial complex I-V expression, yielded improved aerobic glucose respiration and alleviation of mitochondrial dysfunction. All these changes ultimately result in improved post-HF cardiac functioning. HIIT increased skeletal muscle Metrnl production, which then operated on HF hearts to alleviate their functional defects, via increasing aerobic glucose metabolism through AMPK-HDAC4 signaling.

SMP30 alleviates cerebral ischemia/reperfusion-induced neuronal injury by inhibiting HDAC4/PSD-95 to preserve mitochondrial function.

Ischemic stroke is a major cause of global death and permanent disability. Major consequences of ischemic stroke include neuronal mitochondrial dysfunction. We investigated the effects of senescence marker protein 30 (SMP30) on mitochondria-mediated apoptosis and histone deacetylase 4 (HDAC4)/postsynaptic density-95 (PSD-95) signaling in stroke models in vivo and in vitro. Rats with middle cerebral artery occlusion/reperfusion (MCAO/R) were used to simulate cerebral ischemia/reperfusion (I/R) injury. SMP30 was downregulated in the brain tissues of rats after I/R induction. SMP30 overexpression decreased MCAO/R-induced infarct volumes and improved neurologic function and histopathological changes. Increasing SMP30 expression suppressed neuronal apoptosis and reduced mitochondrial dysfunction. SMP30 overexpression in SH-SY5Y and PC12 cells treated with oxygen-glucose deprivation/reoxygenation (OGD/R) decreased HDAC4 and PSD-95 expression; PSD-95 could bind to HDAC4. Furthermore, HDAC4 upregulation abolished the effects of SMP30 overexpression on OGD/R-induced apoptosis and mitochondrial dysfunction in SH-SY5Y cells. Together, these findings indicate that SMP30 alleviates cerebral I/R-induced neuronal injury by inhibiting HDAC4/PSD-95 to preserve mitochondrial function. These interactions might provide new treatment methods for patients with ischemic stroke.

Exploration of small molecule compounds targeting abdominal aortic aneurysm based on CMap database and molecular dynamics simulation.

OBJECTIVE: The mitigation of abdominal aortic aneurysm (AAA) growth through pharmaceutical intervention offers the potential to avert the perils associated with AAA rupture and the subsequent need for surgical intervention. Nevertheless, the existing effective drugs for AAA treatment are limited, necessitating a pressing exploration for novel therapeutic medications. METHODS: AAA-related transcriptome data were downloaded from GEO, and differentially expressed genes (DEGs) in AAA tissue were screened for GO and KEGG enrichment analyses. Small molecule compounds and their target proteins with negative connectivity to the AAA expression profile were predicted in the Connectivity Map (CMap) database. Molecular docking and molecular dynamics simulation were performed to predict the binding of the target protein to the small molecule compound, and the MM/GBSA method was used to calculate the binding free energy. Cluster analysis was performed using the cluster tool in the GROMACS package. An AAA cell-free model was built, and CETSA experiments were used to demonstrate the binding ability of small molecules to the target protein in cells. RESULTS: A total of 2244 DEGs in AAA were obtained through differential analysis, and the DEGs were mainly enriched in the tubulin binding biological function and cell cycle pathway. The CMap results showed that Apicidin had a potential therapeutic effect on AAA with a connectivity score of -97.74, and HDAC4 was the target protein of Apicidin. Based on literature, HDAC4-Apicidin was selected as the subsequent research object. The lowest affinity of Apicidin-HDAC4 molecular docking was -8.218 kcal/mol. Molecular dynamics simulation results indicated that Apicidin-HDAC4 could form a stable complex. MM/GBSA analysis showed a total binding free energy of -55.40 ± 0.79 kcal/mol, and cluster analysis showed that there were two main conformational clusters during the binding process, accounting for 22.4% and 57.8%, respectively. Apicidin could form hydrogen bonds with surrounding residues for stable binding. CETSA experiment proved the stable binding ability of Apicidin and HDAC4. CONCLUSION: Apicidin inhibited HDAC4 in AAA and exhibited favorable protein-ligand interactions and stability, making it a potential candidate drug for treating AAA.

LMK-235 suppresses osteoclastogenesis and promotes osteoblastogenesis by inhibiting HDAC4.

Osteoblasts and osteoclasts play an important role in maintaining the structural integrity of bone tissue, in which osteoclasts degrade bone structure and osteoblasts restore bone tissue. The imbalance of osteoblast and osteoclast function can lead to many bone-related diseases, such as osteoporosis and inflammatory osteolysis. The drug that can both promote bone formation and inhibit bone loss will be able to treat those diseases. In this study, it was found that LMK-235, an selective HDAC4/5 inhibitor, inhibited the differentiation and maturation of osteoclasts by regulating NF-κB and p-Smad2/3 signaling pathways via inhibition of HDAC4. At the same time, we found that LMK-235 promoted osteoblast mineralization by upregulating Runx2 expression via inhibition of HDAC4. In vivo, LMK-235 was able to alleviate lipopolysaccharide (LPS)-induced calvarial osteolysis and promote the repair of bone defects. Taken together, LMK-235 suppresses osteoclast differentiation and promotes osteoblast formation by inhibiting HDAC4. This may provide a valuable treatment for bone diseases caused by abnormal osteoclast bone resorption and osteoblast bone regeneration.

Structure-Based Identification of Novel Histone Deacetylase 4 (HDAC4) Inhibitors.

Histone deacetylases (HDACs) are important cancer drug targets. Existing FDA-approved drugs target the catalytic pocket of HDACs, which is conserved across subfamilies (classes) of HDAC. However, engineering specificity is an important goal. Herein, we use molecular modeling approaches to identify and target potential novel pockets specific to Class IIA HDAC-HDAC4 at the interface between HDAC4 and the transcriptional corepressor component protein NCoR. These pockets were screened using an ensemble docking approach combined with consensus scoring to identify compounds with a different binding mechanism than the currently known HDAC modulators. Binding was compared in experimental assays between HDAC4 and HDAC3, which belong to a different family of HDACs. HDAC4 was significantly inhibited by compound 88402 but not HDAC3. Two other compounds (67436 and 134199) had IC50 values in the low micromolar range for both HDACs, which is comparable to the known inhibitor of HDAC4, SAHA (Vorinostat). However, both of these compounds were significantly weaker inhibitors of HDAC3 than SAHA and thus more selective, albeit to a limited extent. Five compounds exhibited activity on human breast carcinoma and/or urothelial carcinoma cell lines. The present result suggests potential mechanistic and chemical approaches for developing selective HDAC4 modulators.

Nanofiber-based delivery of evodiamine impedes malignant properties of intrahepatic cholangiocarcinoma cells by targeting HDAC4 and restoring TPM1 transcription.

The electrospun nanofiber system is correlated with high efficacy of drug delivery. This study aims to investigate the effect of nanofiber-based delivery of evodiamine, an indole alkaloid derived from Rutaceae plants Evodia rutaecarpa (Juss.) Benth, on intrahepatic cholangiocarcinoma (ICC), as well as to explore the molecular mechanisms. An electrospun nanofiber system carrying evodiamine was generated. Compared to evodiamine treatment alone, the nano-evodiamine exhibited more pronounced effects on suppressing proliferation, colony formation, invasiveness, migration, apoptosis resistance, cell cycle progression, and in vivo tumorigenesis of two ICC cell lines (HUCC-T1 and RBE). ICC cells exhibited increased expression of histone deacetylase 4 (HDAC4) while decreased tropomyosin 1 (TPM1). HDAC4 suppressed TPM1 expression by removing H3K9ac modifications from its promoter. Nano-evodiamine reduced HDAC4 protein levels in ICC cells, thus promoting transcription and expression of TPM1. Either overexpression of HDAC4 or downregulation of TPM1 negated the tumor-suppressive effects of nano-evodiamine. Collectively, this study demonstrates that the electrospun nanofiber system enhances the efficiency of evodiamine. Additionally, evodiamine suppresses the malignant properties of ICC cells. The findings may provide fresh insights into the application of electrospun nanofiber system for drug delivery and the effects of evodiamine on tumor suppression.

LINC00847 drives pancreatic cancer progression by targeting the miR-455-3p/HDAC4 axis.

Introduction: Pancreatic cancer (PC) is a common malignant tumor of the digestive system, posing a serious threat to the life of patients. This study aims to investigate the role of LINC00847 and the LINC00847/miR-455-3p/HDAC4 mechanism in PC progression. Material and methods: The RNA levels of LINC00847, miR-455-3p and HDAC4 were determined by RT-qPCR. HDAC4 protein level was assessed by western blotting. Colony formation and CCK-8 assays were employed to test the proliferation of PC cells. Transwell and scratch assays were conducted to evaluate the cell invasive and migratory abilities, respectively. The effect of LINC00847 silencing on PC cells in vivo was verified using a mouse xenograft model. The correlation among LINC00847, miR-455-3p and HDAC4 was ascertained by dual-luciferase reporter (DLR) assay and Pearson's correlation analysis. Results: The result showed that LINC00847 mainly localized in the cytoplasm was upregulated in PC cells and tissues. Downregulating LINC00847 hindered migration, proliferation, and invasion of PC cells in vitro. Moreover, it also suppressed tumor growth in an in vivo xenograft model. LINC00847 was found to directly target miR-455-3p. miR-455-3p overexpression inhibited cell proliferation and invasion. In addition, HDAC4 was confirmed to be a target gene of miR-455-3p, and HDAC4 overexpression overturned the impact of LINC00847 knockdown on PC cell progression. Conclusions: Our findings reveal that LINC00847 potentially plays a key role in the carcinogenesis of PC progression. This effect may be mediated via regulating the miR-455-3p/HDAC4 axis. This study provides insights into the intricate molecular mechanisms underlying PC and opens avenues for potential therapeutic interventions.

miR-1 as a Key Epigenetic Regulator in Early Differentiation of Cardiac Sinoatrial Region.

A large diversity of epigenetic factors, such as microRNAs and histones modifications, are known to be capable of regulating gene expression without altering DNA sequence itself. In particular, miR-1 is considered the first essential microRNA in cardiac development. In this study, miR-1 potential role in early cardiac chamber differentiation was analyzed through specific signaling pathways. For this, we performed in chick embryos functional experiments by means of miR-1 microinjections into the posterior cardiac precursors-of both primitive endocardial tubes-committed to sinoatrial region fates. Subsequently, embryos were subjected to whole mount in situ hybridization, immunohistochemistry and RT-qPCR analysis. As a relevant novelty, our results revealed that miR-1 increased Amhc1, Tbx5 and Gata4, while this microRNA diminished Mef2c and Cripto expressions during early differentiation of the cardiac sinoatrial region. Furthermore, we observed in this developmental context that miR-1 upregulated CrabpII and Rarß and downregulated CrabpI, which are three crucial factors in the retinoic acid signaling pathway. Interestingly, we also noticed that miR-1 directly interacted with Hdac4 and Calm1/Calmodulin, as well as with Erk2/Mapk1, which are three key factors actively involved in Mef2c regulation. Our study shows, for the first time, a key role of miR-1 as an epigenetic regulator in the early differentiation of the cardiac sinoatrial region through orchestrating opposite actions between retinoic acid and Mef2c, fundamental to properly assign cardiac cells to their respective heart chambers. A better understanding of those molecular mechanisms modulated by miR-1 will definitely help in fields applied to therapy and cardiac regeneration and repair.

Silica's silent threat: Contributing to skin fibrosis in systemic sclerosis by targeting the HDAC4/Smad2/3 pathway.

Nowadays, silica products are widely used in daily life, especially in skin applications, which inevitably increases the risk of silica exposure in general population. However, inadequate awareness of silica's potential hazards and lack of self-protection are of concern. Systemic sclerosis (SSc) is characterized by progressive tissue fibrosis under environmental and genetic interactions. Silica exposure is considered an important causative factor for SSc, but its pathogenesis remains unclear. Within this study, we showed that lower doses of silica significantly promoted the proliferation, migration, and activation of human skin fibroblasts (HSFs) within 24 h. Silica injected subcutaneously into mice induced and exacerbated skin fibrosis. Notably, silica increased histone deacetylase-4 (HDAC4) expression by inducing its DNA hypomethylation in normal HSFs. The elevated HDAC4 expression was also confirmed in SSc HSFs. Furthermore, HDAC4 was positively correlated with Smad2/3 phosphorylation and COL1, α-SMA, and CTGF expression. The HDAC4 inhibitor LMK235 mitigated silica-induced upregulation of these factors and alleviated skin fibrosis in SSc mice. Taken together, silica induces and exacerbates skin fibrosis in SSc patients by targeting the HDAC4/Smad2/3 pathway. Our findings provide new insights for evaluating the health hazards of silica exposure and identify HDAC4 as a potential interventional target for silica-induced SSc skin fibrosis.

mPPTMP195 nanoparticles enhance fracture recovery through HDAC4 nuclear translocation inhibition.

Delayed repair of fractures seriously impacts patients' health and significantly increases financial burdens. Consequently, there is a growing clinical demand for effective fracture treatment. While current materials used for fracture repair have partially addressed bone integrity issues, they still possess limitations. These challenges include issues associated with autologous material donor sites, intricate preparation procedures for artificial biomaterials, suboptimal biocompatibility, and extended degradation cycles, all of which are detrimental to bone regeneration. Hence, there is an urgent need to design a novel material with a straightforward preparation method that can substantially enhance bone regeneration. In this context, we developed a novel nanoparticle, mPPTMP195, to enhance the bioavailability of TMP195 for fracture treatment. Our results demonstrate that mPPTMP195 effectively promotes the differentiation of bone marrow mesenchymal stem cells into osteoblasts while inhibiting the differentiation of bone marrow mononuclear macrophages into osteoclasts. Moreover, in a mouse femur fracture model, mPPTMP195 nanoparticles exhibited superior therapeutic effects compared to free TMP195. Ultimately, our study highlights that mPPTMP195 accelerates fracture repair by preventing HDAC4 translocation from the cytoplasm to the nucleus, thereby activating the NRF2/HO-1 signaling pathway. In conclusion, our study not only proposes a new strategy for fracture treatment but also provides an efficient nano-delivery system for the widespread application of TMP195 in various other diseases.

Class IIa HDAC4 and HDAC7 cooperatively regulate gene transcription in Th17 cell differentiation.

Class II histone deacetylases (HDACs) are important in regulation of gene transcription during T cell development. However, our understanding of their cell-specific functions is limited. In this study, we reveal that class IIa Hdac4 and Hdac7 (Hdac4/7) are selectively induced in transcription, guiding the lineage-specific differentiation of mouse T-helper 17 (Th17) cells from naive CD4+ T cells. Importantly, Hdac4/7 are functionally dispensable in other Th subtypes. Mechanistically, Hdac4 interacts with the transcription factor (TF) JunB, facilitating the transcriptional activation of Th17 signature genes such as Il17a/f. Conversely, Hdac7 collaborates with the TF Aiolos and Smrt/Ncor1-Hdac3 corepressors to repress transcription of Th17 negative regulators, including Il2, in Th17 cell differentiation. Inhibiting Hdac4/7 through pharmacological or genetic methods effectively mitigates Th17 cell-mediated intestinal inflammation in a colitis mouse model. Our study uncovers molecular mechanisms where HDAC4 and HDAC7 function distinctively yet cooperatively in regulating ordered gene transcription during Th17 cell differentiation. These findings suggest a potential therapeutic strategy of targeting HDAC4/7 for treating Th17-related inflammatory diseases, such as ulcerative colitis.

KN-93 promotes HDAC4 nucleus translocation to promote fatty acid oxidation in myocardial infarction.

Myocardial infarction (MI) is a potentially fatal disease that causes a significant number of deaths worldwide. The strategy of increasing fatty acid oxidation in myocytes is considered a therapeutic avenue to accelerate metabolism to meet energy demands. We conducted the study aiming to investigate the effect of KN-93, which induces histone deacetylase (HDAC)4 shuttling to the nucleus, on fatty acid oxidation and the expression of related genes. A mouse model of myocardial infarction was induced by isoprenaline administration. Heart damage was assessed by the detection of cardiac injury markers. The level of fatty acid oxidation level was evaluated by testing the expression of related genes. Both immunofluorescence and immunoblotting in the cytosol or nucleus were utilized to observe the distribution of HDAC4. The interaction between HDAC4 and specificity protein (SP)1 was confirmed by co-immunoprecipitation. The acetylation level of SP1 was tested after KN-93 treatment and HDAC4 inhibitor. Oxygen consumption rate and immunoblotting experiments were used to determine whether the effect of KN-93 on increasing fatty acid oxidation is through HDAC4 and SP1. Administration of KN-93 significantly reduced cardiac injury in myocardial infarction and promoted fatty acid oxidation both in vitro and in vivo. KN-93 was shown to mediate nuclear translocation of HDAC4. HDAC4 was found to interact with SP1 and reduce SP1 acetylation. HDAC4 or SP1 inhibitors attenuated the effect of KN-93 on fatty acid oxidation. In conclusion, KN-93 promotes HDAC4 translocation to the nucleus, thereby potentially enhancing fatty acid oxidation by SP1.

Human Umbilical Cord-Derived Mesenchymal Stem Cells-Exosomes-Delivered miR-375 Targets HDAC4 to Promote Autophagy and Suppress T Cell Apoptosis in Sepsis-Associated Acute Kidney Injury.

This study sought to elucidate the mechanism of human umbilical cord-derived mesenchymal stem cells (HUCMSCs)-exosomes (Exos) in sepsis-associated acute kidney injury (SAKI). Exos were isolated from HUCMSCs and co-cultured with CD4+ T cells exposed to lipopolysaccharide to detect the effects of HUCMSCs-Exos on CD4+ T cell apoptosis and autophagy. miR-375 expression in CD4+ T cells and HUCMSCs-Exos was examined. The relationship between miR-375 and HDAC4 was analyzed. A mouse model of SAKI was established and injected with HUCMSCs-Exos to verify the function of HUCMSCs-Exos in vivo. HUCMSCs-Exos inhibited lipopolysaccharide-induced apoptosis of CD4+ T cells and promoted autophagy. miR-375 expression was noted to be elevated in the HUCMSCs-Exos. Importantly, HUCMSCs-Exos could deliver miR-375 into CD4+ T cells where miR-375 targeted HDAC4 and negatively regulated its expression. By this mechanism, HUCMSCs-Exos decreased CD4+ T cell apoptosis and augmented autophagy. This finding was further confirmed in an in vivo SAKI model. Collectively, HUCMSCs-Exos can protect against SAKI via delivering miR-375 that promotes autophagy and arrests T cell apoptosis through HDAC4 downregulation. These findings suggest a promising therapeutic potential for HUCMSCs-Exos in the context of SAKI.

HBB contributes to individualized aconitine-induced cardiotoxicity in mice via interfering with ABHD5/AMPK/HDAC4 axis.

The root of Aconitum carmichaelii Debx. (Fuzi) is an herbal medicine used in China that exerts significant efficacy in rescuing patients from severe diseases. A key toxic compound in Fuzi, aconitine (AC), could trigger unpredictable cardiotoxicities with high-individualization, thus hinders safe application of Fuzi. In this study we investigated the individual differences of AC-induced cardiotoxicities, the biomarkers and underlying mechanisms. Diversity Outbred (DO) mice were used as a genetically heterogeneous model for mimicking individualization clinically. The mice were orally administered AC (0.3, 0.6, 0.9 mg· kg-1 ·d-1) for 7 d. We found that AC-triggered cardiotoxicities in DO mice shared similar characteristics to those observed in clinic patients. Most importantly, significant individual differences were found in DO mice (variation coefficients: 34.08%-53.17%). RNA-sequencing in AC-tolerant and AC-sensitive mice revealed that hemoglobin subunit beta (HBB), a toxic-responsive protein in blood with 89% homology to human, was specifically enriched in AC-sensitive mice. Moreover, we found that HBB overexpression could significantly exacerbate AC-induced cardiotoxicity while HBB knockdown markedly attenuated cell death of cardiomyocytes. We revealed that AC could trigger hemolysis, and specifically bind to HBB in cell-free hemoglobin (cf-Hb), which could excessively promote NO scavenge and decrease cardioprotective S-nitrosylation. Meanwhile, AC bound to HBB enhanced the binding of HBB to ABHD5 and AMPK, which correspondingly decreased HDAC-NT generation and led to cardiomyocytes death. This study not only demonstrates HBB achievement a novel target of AC in blood, but provides the first clue for HBB as a novel biomarker in determining the individual differences of Fuzi-triggered cardiotoxicity.

HDAC5 enhances IRF3 activation and is targeted for degradation by protein C6 from orthopoxviruses including Monkeypox virus and Variola virus.

Histone deacetylases (HDACs) regulate gene expression and innate immunity. Previously, we showed that HDAC5 is degraded during Vaccinia virus (VACV) infection and is a restriction factor for VACV and herpes simplex virus type 1. Here, we report that HDAC5 promotes interferon regulatory factor 3 (IRF3) activation downstream of Toll-IL-1 receptor (TIR) domain-containing adaptor molecule-1 or Sendai virus-mediated stimulation without requiring HDAC activity. Loss of HDAC5-mediated IRF3 activation is restored by re-introduction of HDAC5 but not HDAC1 or HDAC4. The antiviral activity of HDAC5 is antagonized by VACV protein C6 and orthologs from the orthopoxviruses cowpox, rabbitpox, camelpox, monkeypox, and variola. Infection by many of these viruses induces proteasomal degradation of HDAC5, and expression of C6 alone can induce HDAC5 degradation. Mechanistically, C6 binds to the dimerization domain of HDAC5 and prevents homodimerization and heterodimerization with HDAC4. Overall, this study describes HDAC5 as a positive regulator of IRF3 activation and provides mechanistic insight into how the poxviral protein C6 binds to HDAC5 to antagonize its function.

Growth disorders caused by variants in epigenetic regulators: progress and prospects.

Epigenetic modifications play an important role in regulation of transcription and gene expression. The molecular machinery governing epigenetic modifications, also known as epigenetic regulators, include non-coding RNA, chromatin remodelers, and enzymes or proteins responsible for binding, reading, writing and erasing DNA and histone modifications. Recent advancement in human genetics and high throughput sequencing technology have allowed the identification of causative variants, many of which are epigenetic regulators, for a wide variety of childhood growth disorders that include skeletal dysplasias, idiopathic short stature, and generalized overgrowth syndromes. In this review, we highlight the connection between epigenetic modifications, genetic variants in epigenetic regulators and childhood growth disorders being established over the past decade, discuss their insights into skeletal biology, and the potential of epidrugs as a new type of therapeutic intervention.

The catalytic domain of free or ligand bound histone deacetylase 4 occurs in solution predominantly in closed conformation.

Human histone deacetylase 4 (HDAC4) is a key epigenetic regulator involved in a number of important cellular processes. This makes HDAC4 a promising target for the treatment of several cancers and neurodegenerative diseases, in particular Huntington's disease. HDAC4 is highly regulated by phosphorylation and oxidation, which determine its nuclear or cytosolic localization, and exerts its function through multiple interactions with other proteins, forming multiprotein complexes of varying composition. The catalytic domain of HDAC4 is known to interact with the SMRT/NCOR corepressor complex when the structural zinc-binding domain (sZBD) is intact and forms a closed conformation. Crystal structures of the HDAC4 catalytic domain have been reported showing an open conformation of HDAC4 when bound to certain ligands. Here, we investigated the relevance of this HDAC4 conformation under physiological conditions in solution. We show that proper zinc chelation in the sZBD is essential for enzyme function. Loss of the structural zinc ion not only leads to a massive decrease in enzyme activity, but it also has serious consequences for the overall structural integrity and stability of the protein. However, the Zn2+ free HDAC4 structure in solution is incompatible with the open conformation. In solution, the open conformation of HDAC4 was also not observed in the presence of a variety of structurally divergent ligands. This suggests that the open conformation of HDAC4 cannot be induced in solution, and therefore cannot be exploited for the development of HDAC4-specific inhibitors.

ZIP4 upregulation aggravates nucleus pulposus cell degradation by promoting inflammation and oxidative stress by mediating the HDAC4-FoxO3a axis.

BACKGROUND: Extracellular matrix metabolism dysregulation in nucleus pulposus (NP) cells represents a crucial pathophysiological feature of intervertebral disc degeneration (IDD). Our study elucidates the role and mechanism of Testis expressed 11 (TEX11, also called ZIP4) extracellular matrix degradation in the NP. MATERIALS AND METHODS: Interleukin-1ß (IL-1ß) and H2O2 were used to treat NP cells to establish an IDD cell model. Normal NP tissues and NP tissues from IDD patients were harvested. ZIP4 mRNA and protein profiles in NP cells and tissues were examined. Enzyme-linked immunosorbent assay (ELISA) confirmed the profiles of TNF-α, IL-6, MDA, and SOD in NP cells. The alterations of reactive oxygen species (ROS), lactate dehydrogenase (LDH), COX2, iNOS, MMP-3, MMP-13, collagen II, aggrecan, FoxO3a, histone deacetylase 4 (HDAC4), Sirt1 and NF-κB levels in NP cells were determined using different assays. RESULTS: The ZIP4 profile increased in the NP tissues of IDD patients and IL-1ß- or H2O2-treated NP cells. ZIP4 upregulation bolstered inflammation and oxidative stress in NP cells undergoing IL-1ß treatment and exacerbated their extracellular matrix degradation, whereas ZIP4 knockdown produced the opposite outcome. Mechanistically, ZIP4 upregulated HDAC4 and enhanced NF-κB phosphorylation while repressing Sirt1 and FoxO3a phosphorylation levels. HDAC4 knockdown or Sirt1 promotion attenuated the effects mediated by ZIP4 overexpression in NP cells. CONCLUSIONS: ZIP4 upregulation aggravates the extracellular matrix (ECM) degradation of NP cells by mediating inflammation and oxidative stress through the HDAC4-FoxO3a axis.

Transcription Factor SATB2 Regulates Skeletal Muscle Cell Proliferation and Migration via HDAC4 in Pigs.

Skeletal muscle development remarkably affects meat production and growth rate, regulated by complex regulatory mechanisms in pigs. Specific AT sequence-binding protein 2 (SATB2) is a classic transcription factor and chromatin organizer, which holds a profound effect in the regulation of chromatin remodeling. However, the regulation role of SATB2 concerning skeletal muscle cell fate through chromatin remodeling in pigs remains largely unknown. Here, we observed that SATB2 was expressed higher in the lean-type compared to the obese-type pigs, which also enriched the pathways of skeletal muscle development, chromatin organization, and histone modification. Functionally, knockdown SATB2 led to decreases in the proliferation and migration markers at the mRNA and protein expression levels, respectively, while overexpression SATB2 had the opposite effects. Further, we found histone deacetylase 4 (HDAC4) was a key downstream target gene of SATB2 related to chromatin remodeling. The binding relationship between SATB2 and HDAC4 was confirmed by a dual-luciferase reporter system and ChIP-qPCR analysis. Besides, we revealed that HDAC4 promoted the skeletal muscle cell proliferation and migration at the mRNA and protein expression levels, respectively. In conclusion, our study indicates that transcription factor SATB2 binding to HDAC4 positively contributes to skeletal muscle cell proliferation and migration, which might mediate the chromatin remodeling to influence myogenesis in pigs. This study develops a novel insight into understanding the molecular regulatory mechanism of myogenesis, and provides a promising gene for genetic breeding in pigs.