The Deletion of Hdac4 in Mouse Osteoblasts Influences Both Catabolic and Anabolic Effects in Bone

Epigenetic regulators controlling osteogenic lineage commitment and bone formation

Bone formation and homeostasis are controlled by environmental factors and endocrine regulatory cues that initiate intracellular signaling pathways capable of modulating gene expression in the nucleus. Bone-related gene expression is controlled by nucleosome-based chromatin architecture that limits the accessibility of lineage-specific gene regulatory DNA sequences and sequence-specific transcription factors. From a developmental perspective, bone-specific gene expression must be suppressed during the early stages of embryogenesis to prevent the premature mineralization of skeletal elements during fetal growth in utero. Hence, bone formation is initially inhibited by gene suppressive epigenetic regulators, while other epigenetic regulators actively support osteoblast differentiation. Prominent epigenetic regulators that stimulate or attenuate osteogenesis include lysine methyl transferases (e.g., EZH2, SMYD2, SUV420H2), lysine deacetylases (e.g., HDAC1, HDAC3, HDAC4, HDAC7, SIRT1, SIRT3), arginine methyl transferases (e.g., PRMT1, PRMT4/CARM1, PRMT5), dioxygenases (e.g., TET2), bromodomain proteins (e.g., BRD2, BRD4) and chromodomain proteins (e.g., CBX1, CBX2, CBX5). This narrative review provides a broad overview of the covalent modifications of DNA and histone proteins that involve hundreds of enzymes that add, read, or delete these epigenetic modifications that are relevant for self-renewal and differentiation of mesenchymal stem cells, skeletal stem cells and osteoblasts during osteogenesis.

Abaloparatide Has the Same Catabolic Effects on Bones of Mice When Infused as PTH (1-34)

Abaloparatide is a peptide analog of parathyroid hormone-related protein (PTHrP 1-34) and was approved in 2017 as the second osteoanabolic peptide for treating osteoporosis. We previously showed that intermittent abaloparatide is equally as effective as PTH (1-34). This study was designed to compare the catabolic effects of PTH (1-34) and abaloparatide on bone in young female wild-type mice. Two-month-old C57Bl/6J female mice were continuously infused with human PTH (1-34) or abaloparatide at 80 μg/kg BW/day or vehicle for 2 weeks. At euthanasia, DEXA-PIXImus was performed to assess bone mineral density (BMD) in the whole body, femurs, tibiae, and vertebrae. Bone turnover marker levels were measured in sera, femurs were harvested for micro-computer tomography (μCT) analyses and histomorphometry, and tibiae were separated into cortical and trabecular fractions for gene expression analyses. Our results demonstrated that the infusion of abaloparatide resulted in a similar decrease in BMD as infused PTH (1-34) at all sites. μCT and histomorphometry analyses showed similar decreases in cortical bone thickness and BMD associated with an increase in bone turnover from the increased bone formation rate found by in vivo double labeling and serum P1NP and increased bone resorption as shown by osteoclast numbers and serum cross-linked C-telopeptide. Trabecular bone did not show major changes with either treatment. Osteoblastic gene expression analyses of trabecular and cortical bone revealed that infusion of PTH (1-34) or abaloparatide led to similar and different actions in genes of osteoblast differentiation and activity. As with intermittent and in vitro treatment, both infused PTH (1-34) and abaloparatide similarly regulated downstream genes of the PTHR1/SIK/HDAC4 pathway such as Sost and Mmp13 but differed for those of the PTHR1/SIK/CRTC pathway. Taken together, at the same dose, infused abaloparatide causes the same high bone turnover as infused PTH (1-34) with a net resorption in female wild-type mice. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

FTY720 Attenuates LPS-Induced Inflammatory Bone Loss by Inhibiting Osteoclastogenesis via the NF-κB and HDAC4/ATF Pathways

Osteoclast (OC) abnormalities lead to many osteolytic diseases, such as osteoporosis, inflammatory bone erosion, and tumor-induced osteolysis. Exploring effective strategies to remediate OCs dysregulation is essential. FTY720, also known as fingolimod, has been approved for the treatment of multiple sclerosis and has anti-inflammatory and immunosuppressive effects. Here, we found that FTY720 inhibited osteoclastogenesis and OC function by inhibiting nuclear factor kappa-B (NF-κB) signaling. Interestingly, we also found that FTY720 inhibited osteoclastogenesis by upregulating histone deacetylase 4 (HDAC4) expression levels and downregulating activating transcription factor 4 (ATF4) expression levels. In vivo, FTY720 treatment prevented lipopolysaccharide- (LPS-) induced calvarial osteolysis and significantly reduced the number of tartrate-resistant acid phosphatase- (TRAP-) positive OCs. Taken together, these results demonstrate that FTY720 can inhibit osteoclastogenesis and ameliorate inflammation-induced bone loss. Which may provide evidence of a new therapeutic target for skeletal diseases caused by OC abnormalities.

Hdac4 Regulates the Proliferation of Neural Crest-Derived Osteoblasts During Murine Craniofacial Development

Craniofacial development involves the regulation of a compendium of transcription factors, signaling molecules, and epigenetic regulators. Histone deacetylases (HDACs) are involved in the regulation of cell proliferation, differentiation, and homeostasis across a wide range of tissues, including the brain and the cardiovascular, muscular, and skeletal systems. However, the functional role of Hdac4 during craniofacial development remains unclear. In this study, we investigated the effects of knocking out Hdac4 on craniofacial skeletal development by conditionally disrupting the Hdac4 gene in cranial neural crest cells (CNCCs) using Cre-mediated recombination. Mice deficient for Hdac4 in CNCC-derived osteoblasts demonstrated a dramatic decrease in frontal bone formation. In vitro, pre-osteoblasts (MC3T3-E1 cells) lacking Hdac4 exhibited reduced proliferative activity in association with the dysregulation of cell cycle-related genes. These findings suggested that Hdac4 acts, at least in part, as a regulator of craniofacial skeletal development by positively regulating the proliferation of CNCC-derived osteoblasts.

Comprehensive analysis of Transcription Factors identified novel prognostic biomarker in human bladder cancer

Background: Transcriptional factors (TFs) are responsible for regulating the transcription of pro-oncogenes and tumor suppressor genes in the process of tumor development. However, the role of these transcription factors in Bladder cancer (BCa) remains unclear. And the main purpose of this research is to explore the possibility of these TFs serving as biomarkers for BCa.

Methods: We analyzed the differential expression of TFs in BCa from The Cancer Genome Atlas (TCGA) online database, identified 408 up-regulated TFs and 751down-regulated TFs. We obtained some hub genes via WGCNA model and detected the RNAs level in BCa cells and tissues. Then, the relationship between the expression and clinicopathological parameters was further investigated. Kaplan-Meier curves and the log-rank test were carried out to analyze the relationship between NFATC1, AKNA and five-TFs combination and overall survival (OS). And RT-PCR assay was conducted to further consolidate and verify these results.

Results: There were significant differences in the expression of five TFs (CBX7, AKNA, HDAC4, EBF2 and NFATC1) between bladder cancer and normal bladder tissue. In BCa tissue and cell lines, the five TFs were frequently down-regulated, and closely related to poor prognosis. Moreover, the RT-PCR results of five TFs in bladder cancer and normal bladder tissue were consistent with the database results, and reduced TFs could significantly induce or restrain the transcription of many critical factors. The expression level of AKNA and NFATC1 could serve as independent biomarker to predict the overall survival (P<0.05). And the above five TFs combined detection of bladder cancer has higher sensitivity and specificity. Furthermore, differential neutrophils expression between high-risk and low-risk were found, which consolidated the role and function of the five TFs combination model in the progression of BCa.

Conclusions: Our analysis effectively provides a newly TFs-associated prognostic model for bladder cancer. The combination of five identified-TFs is an independent prognostic biomarker, which could serve as a more effective therapeutic target for BCa patients.

Application of microRNA in Human Osteoporosis and Fragility Fracture: A Systemic Review of Literatures

MicroRNAs (miRNAs) could serve as ideal entry points to the deregulated pathways in osteoporosis due to their relatively simple upstream and downstream relationships with other molecules in the signaling cascades. Our study aimed to give a comprehensive review of the already identified miRNAs in osteoporosis from human blood samples and provide useful information for their clinical application. A systematic literature search for relevant studies was conducted in the Pubmed database from inception to December 2020. We set two essential inclusion criteria: human blood sampling and design of controlled studies. We sorted the results of analysis on human blood samples according to the study settings and compiled the most promising miRNAs with analyzed diagnostic values. Furthermore, in vitro and in vivo evidence for the mechanisms of the identified miRNAs was also illustrated. Based on both diagnostic value and evidence of mechanism from in vitro and in vivo experiments, miR-23b-3p, miR-140-3p, miR-300, miR-155-5p, miR-208a-3p, and miR-637 were preferred candidates in diagnostic panels and as therapeutic agents. Further studies are needed to build sound foundations for the clinical usage of miRNAs in osteoporosis.

Role of histone deacetylases in bone development and skeletal disorders

Bone cells must constantly respond to hormonal and mechanical cues to change gene expression programs. Of the myriad of epigenomic mechanisms used by cells to dynamically alter cell type-specific gene expression, histone acetylation and deacetylation has received intense focus over the past two decades. Histone deacetylases (HDACs) represent a large family of proteins with a conserved deacetylase domain first described to deacetylate lysine residues on histone tails. It is now appreciated that multiple classes of HDACs exist, some of which are clearly misnamed in that acetylated lysine residues on histone tails is not the major function of their deacetylase domain. Here, we will review the roles of proteins bearing deacetylase domains in bone cells, focusing on current genetic evidence for each individual HDAC gene. While class I HDACs are nuclear proteins whose primary role is to deacetylate histones, class IIa and class III HDACs serve other important cellular functions. Detailed knowledge of the roles of individual HDACs in bone development and remodeling will set the stage for future efforts to specifically target individual HDAC family members in the treatment of skeletal diseases such as osteoporosis.

Osteoblastic monocyte chemoattractant protein-1 (MCP-1) mediation of parathyroid hormone's anabolic actions in bone implicates TGF-β signaling

Parathyroid hormone (PTH) is necessary for the regulation of calcium homeostasis and PTH (1-34) was the first approved osteoanabolic therapy for osteoporosis. It is well established that intermittent PTH increases bone formation and that bone remodeling and several cytokines and chemokines play an essential role in this process. Earlier, we had established that the chemokine, monocyte chemoattractant protein-1 (MCP-1/CCL2), was the most highly stimulated gene in rat bone after intermittent PTH injections. Nevertheless, MCP-1 function in bone appears to be complicated. To identify the primary cells expressing MCP-1 in response to PTH, we performed in situ hybridization of rat bone sections after hPTH (1-34) injections and showed that bone-lining osteoblasts are the primary cells that express MCP-1 after PTH treatment. We previously demonstrated MCP-1's importance by showing that PTH's anabolic effects are abolished in MCP-1 null mice, further implicating a role for the chemokine in this process. To establish whether rhMCP-1 peptide treatment could rescue the anabolic effect of PTH in MCP-1 null mice, we treated 4-month-old wild-type (WT) mice with hPTH (1-34) and MCP-1^-/- mice with rhMCP-1 and/or hPTH (1-34) for 6 weeks. Micro-computed tomography (μCT) analysis of trabecular and cortical bone showed that MCP-1 injections for 6 weeks rescued the PTH anabolic effect in MCP-1^-/- mice. In fact, the combination of rhMCP-1 and hPTH (1-34) has a synergistic anabolic effect compared with monotherapies. Mechanistically, PTH-enhanced transforming growth factor-β (TGF-β) signaling is abolished in the absence of MCP-1, while MCP-1 peptide treatment restores TGF-β signaling in the bone marrow. Here, we have shown that PTH regulates the transcription of the chemokine MCP-1 in osteoblasts and determined how MCP-1 affects bone cell function in PTH's anabolic actions. Taken together, our current work indicates that intermittent PTH stimulates osteoblastic secretion of MCP-1, which leads to increased TGF-β signaling, implicating it in PTH's anabolic actions.

Genome-wide association study implicates novel loci and reveals candidate effector genes for longitudinal pediatric bone accrual

BACKGROUND

Bone accrual impacts lifelong skeletal health, but genetic discovery has been primarily limited to cross-sectional study designs and hampered by uncertainty about target effector genes. Here, we capture this dynamic phenotype by modeling longitudinal bone accrual across 11,000 bone scans in a cohort of healthy children and adolescents, followed by genome-wide association studies (GWAS) and variant-to-gene mapping with functional follow-up.

RESULTS

We identify 40 loci, 35 not previously reported, with various degrees of supportive evidence, half residing in topological associated domains harboring known bone genes. Of several loci potentially associated with later-life fracture risk, a candidate SNP lookup provides the most compelling evidence for rs11195210 (SMC3). Variant-to-gene mapping combining ATAC-seq to assay open chromatin with high-resolution promoter-focused Capture C identifies contacts between GWAS loci and nearby gene promoters. siRNA knockdown of gene expression supports the putative effector gene at three specific loci in two osteoblast cell models. Finally, using CRISPR-Cas9 genome editing, we confirm that the immediate genomic region harboring the putative causal SNP influences PRPF38A expression, a location which is predicted to coincide with a set of binding sites for relevant transcription factors.

CONCLUSIONS

Using a new longitudinal approach, we expand the number of genetic loci putatively associated with pediatric bone gain. Functional follow-up in appropriate cell models finds novel candidate genes impacting bone accrual. Our data also raise the possibility that the cell fate decision between osteogenic and adipogenic lineages is important in normal bone accrual.

Histone deacetylase 4 deletion results in abnormal chondrocyte hypertrophy and premature ossification from collagen type 2α1‑expressing cells

Histone deacetylase 4 (HDAC4) plays a vital role in chondrocyte hypertrophy and bone formation. To investigate the function of HDAC4 in postnatal skeletal development, the present study developed lineage‑specific HDAC4‑knockout mice [collagen type 2α1 (Col2α1)‑Cre, HDAC4d/d mice] by crossing transgenic mice expressing Cre recombinase. Thus, a specific ablation of HDAC4 was performed in Col2α1‑expressing mice cells. The knee joints of HDAC4fl/fl and Col2α1‑Cre, HDAC4d/d mice were analyzed at postnatal day (P)2‑P21 using an in vivo bromodeoxyuridine (BrdU) assay, and Safranin O, Von Kossa and whole‑body staining were used to evaluate the developmental growth plate, hypertrophic differentiation, mineralization and skeletal mineralization patterns. The trabecular bone was analyzed using microcomputed tomography. The expressions of BrdU, proliferating cell nuclear antigen (PCNA), matrix metalloproteinase (MMP)‑13, runt‑related transcription factor (Runx)‑2, osteoprotegerin (OPG), CD34, type X collagen (ColX), osteocalcin and Wnt5a were determined using immunohistochemistry, in situ hybridization (ISH) and reverse transcription‑quantitative (RT‑q)PCR. The results demonstrated that HDAC4‑null mice (HDAC4d/d mice) were severely runted; these mice had a shortened hypertrophic zone (histopathological evaluation), accelerated vascular invasion and articular mineralization (Von Kossa staining), elevated expressions of MMP‑13, Runx2, OPG and CD34 (RT‑qPCR and immunohistochemistry), downregulated expression of the proliferative marker BrdU and PCNA (immunohistochemistry), increased expression of ColX and decreased expression of Wnt5a (ISH). In conclusion, chondrocyte‑derived HDAC4 was responsible for regulating chondrocyte proliferation and differentiation as well as endochondral bone formation.

Abaloparatide at the Same Dose Has the Same Effects on Bone as PTH (1-34) in Mice

Abaloparatide, a novel analog of parathyroid hormone-related protein (PTHrP 1-34), became in 2017 the second osteoanabolic therapy for the treatment of osteoporosis. This study aims to compare the effects of PTH (1-34), PTHrP (1-36), and abaloparatide on bone remodeling in male mice. Intermittent daily subcutaneous injections of 80 μg/kg/d were administered to 4-month-old C57Bl/6J male mice for 6 weeks. During treatment, mice were followed by DXA-Piximus to assess changes in bone mineral density (BMD) in the whole body, femur, and tibia. At either 4 or 18 hours after the final injection, femurs were harvested for μCT analyses and histomorphometry, sera were assayed for bone turnover marker levels, and tibias were separated into cortical, trabecular, and bone marrow fractions for gene expression analyses. Our results showed that, compared with PTH (1-34), abaloparatide resulted in a similar increase in BMD at all sites, whereas no changes were found with PTHrP (1-36). With both PTH (1-34) and abaloparatide, μCT and histomorphometry analyses revealed similar increases in bone volume associated with an increased trabecular thickness, in bone formation rate as shown by P1NP serum level and in vivo double labeling, and in bone resorption as shown by CTX levels and osteoclast number. Gene expression analyses of trabecular and cortical bone showed that PTH (1-34) and abaloparatide led to different actions in osteoblast differentiation and activity, with increased Runx2, Col1A1, Alpl, Bsp, Ocn, Sost, Rankl/Opg, and c-fos at different time points. Abaloparatide seems to generate a faster response on osteoblastic gene expression than PTH (1-34). Taken together, abaloparatide at the same dose is as effective as PTH (1-34) as an osteoanabolic, with an increase in bone formation but also an increase in bone resorption in male mice. © 2019 American Society for Bone and Mineral Research.

Histone Acetylation as a Regenerative Target in the Dentine-Pulp Complex

If dental caries (or tooth decay) progresses without intervention, the infection will advance through the dentine leading to severe pulpal inflammation (irreversible pulpitis) and pulp death. The current management of irreversible pulpits is generally root-canal-treatment (RCT), a destructive, expensive, and often unnecessary procedure, as removal of the injurious stimulus alone creates an environment in which pulp regeneration may be possible. Current dental-restorative-materials stimulate repair non-specifically and have practical limitations; as a result, opportunities exist for the development of novel therapeutic strategies to regenerate the damaged dentine-pulp complex. Recently, epigenetic modification of DNA-associated histone ‘tails’ has been demonstrated to regulate the self-renewal and differentiation potential of dental-stem-cell (DSC) populations central to regenerative endodontic treatments. As a result, the activities of histone deacetylases (HDAC) are being recognised as important regulators of mineralisation in both tooth development and dental-pulp-repair processes, with HDAC-inhibition (HDACi) promoting pulp cell mineralisation in vitro and in vivo. Low concentration HDACi-application can promote de-differentiation of DSC populations and conversely, increase differentiation and accelerate mineralisation in DSC populations. Therapeutically, various HDACi solutions can release bioactive dentine-matrix-components (DMCs) from the tooth’s extracellular matrix; solubilised DMCs are rich in growth factors and can stimulate regenerative processes such as angiogenesis, neurogenesis, and mineralisation. The aim of this mini-review is to discuss the role of histone-acetylation in the regulation of DSC populations, while highlighting the importance of HDAC in tooth development and dental pulp regenerative-mineralisation processes, before considering the potential therapeutic application of HDACi in targeted biomaterials to the damaged pulp to stimulate regeneration.

Hepatic Osteodystrophy-Molecular Mechanisms Proposed to Favor Its Development

Almost all patients with chronic liver diseases (CLD) show altered bone metabolism. Depending on the etiology, this manifests in a severe osteoporosis in up to 75% of the affected patients. Due to high prevalence, the generic term hepatic osteodystrophy (HOD) evolved, describing altered bone metabolism, decreased bone mineral density, and deterioration of bone structure in patients with CLD. Once developed, HOD is difficult to treat and increases the risk of fragility fractures. Existing fractures affect the quality of life and, more importantly, long-term prognosis of these patients, which presents with increased mortality. Thus, special care is required to support the healing process. However, for early diagnosis (reduce fracture risk) and development of adequate treatment strategies (support healing of existing fractures), it is essential to understand the underlying mechanisms that link disturbed liver function with this bone phenotype. In the present review, we summarize proposed molecular mechanisms favoring the development of HOD and compromising the healing of associated fractures, including alterations in vitamin D metabolism and action, disbalances in transforming growth factor beta (TGF-β) and bone morphogenetic protein (BMP) signaling with histone deacetylases (HDACs) as secondary regulators, as well as alterations in the receptor activator of nuclear factor kappa B ligand (RANKL)–osteoprotegerin (OPG) system mediated by sclerostin. Based on these mechanisms, we give an overview on the limitations of early diagnosis of HOD with established serum markers.