HDAC6 inactivates Runx2 promoter to block osteogenesis of bone marrow stromal cells in age-related bone loss of mice

Acetylation of H3K18 activated by p300 promotes osteogenesis in human adipose-derived mesenchymal stem cells

Human adipose-derived mesenchymal stem cells (hAD-MSCs) have garnered significant interest as a viable alternative source of stem cells for applications in bone tissue engineering due to their high and ease availability. At present, the limited studies on potential epigenetic regulatory mechanism in hAD-MSCs greatly hinders its clinical application in bone repair. Histone acetylation has been identified as a critical regulator of the osteogenic differentiation of mesenchymal stem cells (MSCs), with increased levels of histone acetylation sites frequently correlating with enhanced osteogenic differentiation. However, their specific roles in MSCs osteogenesis remain unclear. In this study, we observed a significant up-regulation of H3K18 acetylation (H3K18ac) during the osteogenic induction of hAD-MSCs. This modification was notably enriched in the promoter regions of genes associated with osteogenesis, thereby facilitating osteogenic differentiation. Furthermore, the treatment of histone acetyltransferases p300 inhibitor A-485 in hAD-MSCs resulted in a reduction of H3K18 acetylation levels during the osteogenic differentiation, which corresponded with a diminished osteoblast phenotype and function. These results indicated that p300-mediated acetylation of H3K18 enhances the osteogenic differentiation of hAD-MSCs. It provides a novel insight into understanding the mechanism of osteogenic differentiation of hAD-MSCs and promoting its application in bone tissue engineering.

Posttranslational Modification in Bone Homeostasis and Osteoporosis

Bone is responsible for providing mechanical protection, attachment sites for muscles, hematopoiesis micssroenvironment, and maintaining balance between calcium and phosphorate. As a highly active and dynamically regulated organ, the balance between formation and resorption of bone is crucial in bone development, damaged bone repair, and mineral homeostasis, while dysregulation in bone remodeling impairs bone structure and strength, leading to deficiency in bone function and skeletal disorder, such as osteoporosis. Osteoporosis refers to compromised bone mass and higher susceptibility of fracture, resulting from several risk factors deteriorating the balanced system between osteoblast-mediated bone formation and osteoclast-mediated bone resorption. This balanced system is strictly regulated by translational modification, such as phosphorylation, methylation, acetylation, ubiquitination, sumoylation, glycosylation, ADP-ribosylation, S-palmitoylation, citrullination, and so on. This review specifically describes the updating researches concerning bone formation and bone resorption mediated by posttranslational modification. We highlight dysregulated posttranslational modification in osteoblast and osteoclast differentiation. We also emphasize involvement of posttranslational modification in osteoporosis development, so as to elucidate the underlying molecular basis of osteoporosis. Then, we point out translational potential of PTMs as therapeutic targets. This review will deepen our understanding between posttranslational modification and osteoporosis, and identify novel targets for clinical treatment and identify future directions.

Reinforced enzyme mineralized chitosan hydrogels with superior mechanical and osteogenic properties

As a natural cationic polymer material, the application of chitosan hydrogel for bone tissue engineering has been greatly limited due to its poor mechanical strength. Enzymatic mineralization has drawn increased attention to effectively improve the mechanical properties of hydrogels. In this study, carboxymethyl chitosan (CMCS) hydrogels cross-linked with different concentrations of genipin (2.5 %, 5 % and 10 %) were prepared and further mineralized through enzyme-induced biomimetic mineralization. The mechanical properties of the CMCS hydrogels were significantly increased as a result of mineralization, showing improvement of 1200-1500 % on storage moduli, and even exhibiting certain tensile behavior with the elongation rate of 30-35 %, likely due to the uniform formation and small size of mineralized products. Interestingly, the cationicity of chitosan also exerted an important modulation effect and the mineralization behavior and mechanical properties of mineralized hydrogels. In addition, the enzymatic mineralized hydrogels showed enhanced biocompatibility and osteogenic differentiation in-vitro, likely due to its superior mechanical properties and the introduction of calcium phosphate biominerals. In vivo experiments further suggest excellent bone-forming activity for the enzymatic mineralized hydrogels. Overall, tuning cationicity and enzymatic mineralization provide an effective approach for the preparation of chitosan hydrogels with superior mechanical and biological properties for bone tissue engineering application.

Citrate: a key signalling molecule and therapeutic target for bone remodeling disorder

Bone remodeling is a continuous cyclic process that maintains and regulates bone structure and strength. The disturbance of bone remodeling leads to a series of bone metabolic diseases. Recent studies have shown that citrate, an intermediate metabolite of the tricarboxylic acid (TCA) cycle, plays an important role in bone remodeling. But the exact mechanism is still unclear. In this study, we focused on the systemic regulatory mechanism of citrate on bone remodeling, and found that citrate is involved in bone remodeling in multiple ways. The participation of citrate in oxidative phosphorylation (OXPHOS) facilitates the generation of ATP, thereby providing substantial energy for bone formation and resorption. Osteoclast-mediated bone resorption releases citrate from bone mineral salts, which is subsequently released as an energy source to activate the osteogenic differentiation of stem cells. Finally, the differentiated osteoblasts secrete into the bone matrix and participate in bone mineral salts formation. As a substrate of histone acetylation, citrate regulates the expression of genes related to bone formation and bone reabsorption. Citrate is also a key intermediate in the metabolism and synthesis of glucose, fatty acids and amino acids, which are three major nutrients in the organism. Citrate can also be used as a biomarker to monitor bone mass transformation and plays an important role in the diagnosis and therapeutic evaluation of bone remodeling disorders. Citrate imbalance due to citrate transporter could result in the supression of osteoblast/OC function through histone acetylation, thereby contributing to disorders in bone remodeling. Therefore, designing drugs targeting citrate-related proteins to regulate bone citrate content provides a new direction for the drug treatment of diseases related to bone remodeling disorders.

NLRP3 Inflammasome-Mediated Osteoarthritis: The Role of Epigenetics

The prevalence of osteoarthritis (OA) notably surges with age and weight gain. The most common clinical therapeutic drugs are painkillers, yet they cannot impede the deteriorating course of OA. Thus, understanding OA's pathogenesis and devising effective therapies is crucial. It is generally recognized that inflammation, pyroptosis, and OA progression are tightly linked. The activation of NLRP3 inflammasome can lead to the discharge of the pro-inflammatory cytokines Interleukin-1β and IL-18, intensifying subsequent inflammatory reactions and promoting OA development. Conversely, the imbalance caused by deacetylase-regulated NLRP3 inflammasome underlies the chronic mild inflammation related to degenerative diseases. Therefore, this article expounds on the mechanism of OA pathogenesis and the role of histone deacetylases (HDACs) in NLRP3 inflammasome-triggered OA, and illustrates the application of HDAC inhibitors in OA, striving to provide more insights into novel OA treatment approaches.

Entinostat treatment causes hypophosphatemia and hypocalcemia by increasing Fgf23 in mice

Entinostat, a class I HDACs-selective inhibitor, is currently in clinical trials for treating cancers. In some of the trials, Entinostat treatment frequently causes hypophosphatemia and/or hypocalcemia. Moreover, the effect of Entinostat treatment on bone remains incompletely understood. In this study, we found that Entinostat treatment mildly increased the trabecular but not cortical bone volume, without compromising the bone strength, the numbers of Runx2-positive cells and TRAP-positive cells, and the serum levels of P1NP and TRAP-5b. Entinostat treatment significantly reduced the level of Runx2 mRNA but not Runx2 protein, and as a trend attenuated Ctsk expression. Furthermore, Entinostat treatment did not enhance MC3T3-E1 cell proliferation in vitro. These findings suggest that Entinostat increases trabecular bone volume not by regulating osteoblastogenesis or osteoclastogenesis, but possibly by attenuating the resorption capacity. Unexpectedly, Entinostat treatment increased the expression of Fgf23, whose protein is a hormone that regulates the serum level of phosphate (Pi). Meanwhile, Entinostat treatment increased the serum level of the active form (intact) Fgf23 and reduced that of Pi and calcium (Ca) as well. This study raised a concern about the anabolic effects of Entinostat in bone, and demonstrated that Entinostat treatment causes hypophosphatemia and hypocalcemia by upregulating Fgf23 mRNA and increasing intact Fgf23 protein in serum.

Unlocking the potential of histone modification in regulating bone metabolism

Bone metabolism plays a crucial role in maintaining normal bone tissue homeostasis and function. Imbalances between bone formation and resorption can lead to osteoporosis, osteoarthritis, and other bone diseases. The dynamic and complex process of bone remodeling is driven by various factors, including epigenetics. Histone modification, one of the most important and well-studied components of epigenetic regulation, has emerged as a promising area of research in bone metabolism. Different histone proteins and modification sites exert diverse effects on osteogenesis and osteoclastogenesis. In this review, we summarize recent progress in understanding histone modifications in bone metabolism, including specific modification sites and potential regulatory enzymes. Comprehensive knowledge of histone modifications in bone metabolism could reveal new therapeutic targets and treatment strategies for bone diseases.

RUNX2 regulation in osteoblast differentiation: A possible therapeutic function of the lncRNA and miRNA-mediated network

Osteogenic differentiation is a crucial process in the formation of the skeleton and the remodeling of bones. It relies on a complex system of signaling pathways and transcription factors, including Runt-related transcription factor 2 (RUNX2). Non-coding RNAs (ncRNAs) control the bone-specific transcription factor RUNX2 through post-transcriptional mechanisms to regulate osteogenic differentiation. The most research has focused on microRNAs (miRNAs) and long ncRNAs (lncRNAs) in studying how they regulate RUNX2 for osteogenesis in both normal and pathological situations. This article provides a concise overview of the recent advancements in understanding the critical roles of lncRNA/miRNA/axes in controlling the expression of RUNX2 during bone formation. The possible application of miRNAs and lncRNAs as therapeutic agents for the treatment of disorders involving the bones and bones itself is also covered.

CGRP promotes osteogenic differentiation by regulating macrophage M2 polarization through HDAC6/AKAP12 signaling pathway

Aim: To determine the mechanism of Calcitonin gene-related peptide (CGRP) in bone healing.Materials & methods: Alkaline phosphatase (ALP) activity and inflammatory-factor levels were detected using ELISA. Osteogenic differentiation was assessed using Alizarin red staining technique. The interaction between histone deacetylase 6 (HDAC6) and A-kinase anchoring protein 12 (AKAP12) was investigated through Co- immunoprecipitation.Results: CGRP treatment promoted rat bone marrow-derived macrophages (BMDMs) M2 polarization. CGRP facilitated osteogenic differentiation by enhancing M2 polarization of BMDMs. Mechanistically, CGRP promoted AKAP12 acetylation to activate the extracellular regulated protein kinases pathway by HDAC6 inhibition.Conclusion: CGRP promoted M2 polarization of rat BMDMs and facilitated osteogenic differentiation through the HDAC6/AKAP12/extracellular regulated protein kinases signaling pathway, thereby promoting bone healing.

Regulatory cellular and molecular networks in the bone microenvironment during aging

Age-induced abnormalities in bone metabolism disrupt the equilibrium between bone resorption and formation. This largely stems from disturbances in bone homeostasis, in which signaling pathways exert a significant regulatory influence. Aging compromises the functionality of the bone marrow mesenchymal stem cells (BMSCs), ultimately resulting in tissue dysfunction and pathological aging. Age-related bone degradation primarily manifests as reduced bone formation and the increased accumulation of bone marrow fat. Cellular senescence diminishes bone cell vitality, thereby disrupting the balance of bone remodeling. Intensive osteoclast differentiation leads to the generation of more osteoclasts and increased bone resorption. This review provides insight into the impact of aging on bone, encompassing bone cell states during the aging process and bone signaling pathway transformations. It primarily delves into aging-related signaling pathways, such as the bone morphogenetic protein/Smad, Wnt/β-catenin, osteoprotegerin/receptor activator of NF-κB ligand/receptor activator of NF-κB, connexin43/miR21, and nuclear factor erythroid 2-related factor 2/antioxidant response element pathways, seeking to enhance our comprehension of crucial bone cells and their secretory phenotypes during aging. Furthermore, the precise molecular regulatory mechanisms underlying the interactions between bone signaling pathways and aging are investigated.

Role of epigenetic regulatory mechanisms in age-related bone homeostasis imbalance

Alterations to the human organism that are brought about by aging are comprehensive and detrimental. Of these, an imbalance in bone homeostasis is a major outward manifestation of aging. In older adults, the decreased osteogenic activity of bone marrow mesenchymal stem cells and the inhibition of bone marrow mesenchymal stem cell differentiation lead to decreased bone mass, increased risk of fracture, and impaired bone injury healing. In the past decades, numerous studies have reported the epigenetic alterations that occur during aging, such as decreased core histones, altered DNA methylation patterns, and abnormalities in noncoding RNAs, which ultimately lead to genomic abnormalities and affect the expression of downstream signaling osteoporosis treatment and promoter of fracture healing in older adults. The current review summarizes the impact of epigenetic regulation mechanisms on age-related bone homeostasis imbalance.

Different Sources of Bone Marrow Mesenchymal Stem Cells: A Comparison of Subchondral, Mandibular, and Tibia Bone-derived Mesenchymal Stem Cells

BACKGROUND

Stem cell properties vary considerably based on the source and tissue site of mesenchymal stem cells (MSCs). The mandibular condyle is a unique kind of craniofacial bone with a special structure and a relatively high remodeling rate. MSCs here may also be unique to address specific physical needs.

OBJECTIVE

The aim of this study was to compare the proliferation and multidirectional differentiation potential among MSCs derived from the tibia (TMSCs), mandibular ramus marrow (MMSCs), and condylar subchondral bone (SMSCs) of rats in vitro.

METHODS

Cell proliferation and migration were assessed by CCK-8, laser confocal, and cell scratch assays. Histochemical staining and real-time PCR were used to evaluate the multidirectional differentiation potential and DNA methylation and histone deacetylation levels.

RESULTS

The proliferation rate and self-renewal capacity of SMSCs were significantly higher than those of MMSCs and TMSCs. Moreover, SMSCs possessed significantly higher mineralization and osteogenic differentiation potential. Dnmt2, Dnmt3b, Hdac6, Hdac7, Hdac9, and Hdac10 may be instrumental in the osteogenesis of SMSCs. In addition, SMSCs are distinct from MMSCs and TMSCs with lower adipogenic differentiation and chondrogenic differentiation potential. The multidirectional differentiation capacities of TMSCs were exactly the opposite of those of SMSCs, and the results of MMSCs were intermediate.

CONCLUSION

This research offers a new paradigm in which SMSCs could be a useful source of stem cells for further application in stem cell-based medical therapies due to their strong cell renewal and osteogenic capacity.

Bioinspired synthetic peptide-based biomaterials regenerate bone through biomimicking of extracellular matrix

There have been remarkable advancements in regenerative medicine for bone regeneration, tackling the worldwide health concern of tissue loss. Tissue engineering uses the body's natural capabilities and applies biomaterials and bioactive molecules to replace damaged or lost tissues and restore their functionality. While synthetic ceramics have overcome some challenges associated with allografts and xenografts, they still need essential growth factors and biomolecules. Combining ceramics and bioactive molecules, such as peptides derived from biological motifs of vital proteins, is the most effective approach to achieve optimal bone regeneration. These bioactive peptides induce various cellular processes and modify scaffold properties by mimicking the function of natural osteogenic, angiogenic and antibacterial biomolecules. The present review aims to consolidate the latest and most pertinent information on the advancements in bioactive peptides, including angiogenic, osteogenic, antimicrobial, and self-assembling peptide nanofibers for bone tissue regeneration, elucidating their biological effects and potential clinical implications.

Identification of neutrophil extracellular traps and crosstalk genes linking inflammatory bowel disease and osteoporosis by integrated bioinformatics analysis and machine learning

Musculoskeletal deficits are among the most common extra-intestinal manifestations and complications of inflammatory bowel disease (IBD). This study aimed to identify crosstalk genes between IBD and osteoporosis (OP) and potential relationships between crosstalk and neutrophil extracellular traps (NETs)-related genes. Three common hub genes from different compared groups are actually the same, namely HDAC6, IL-8, and PPIF. ROC showed that the combined diagnostic value of HDAC6, IL-8, and PPIF was higher than each of the three key hub genes. Immune infiltration results showed that HDAC6 and IL-8 key genes negatively correlated with CD65 bright natural killer cells. USF1 was the common upstream TFs between HDAC6 and PPIF, and MYC was the common upstream TFs between IL-8 and PPIF in RegNetwork. Taken together, this study shows a linked mechanism between IBD and OP via NETs and crosstalk genes. These findings may show light on better diagnosis and treatment of IBD complicated with OP.

Hypoxia dissociates HDAC6/FOXO1 complex and aggregates them into nucleus to regulate autophagy and osteogenic differentiation

OBJECTIVE

This research aimed to elucidate the molecular mechanisms underlying the periodontitis-associated bone loss, with particular emphasis on the contributory role of hypoxic microenvironment in this process.

BACKGROUND

Periodontitis generally causes alveolar bone loss and is often associated with a hypoxic microenvironment, which affects bone homeostasis. However, the regulating mechanism between hypoxia and jaw metabolism remains unclear. Hypoxia triggers autophagy, which is closely related to osteogenic differentiation, but how hypoxia-induced autophagy regulates bone metabolism is unknown. HDAC6 and FOXO1 are closely related to bone metabolism and autophagy, respectively, but whether they are related to hypoxia-induced bone loss and their internal mechanisms is still unclear.

METHODS

Established rat nasal obstruction model and hypoxia cell model. Immunohistochemistry was performed to detect the expression and localization of HDAC6 and FOXO1 proteins, analysis of autophagic flux and transmission electron microscopy was used to examine the autophagy level and observe the autophagosomes, co-immunoprecipitation and chromatin immunoprecipitation were preformed to investigate the interaction of HDAC6 and FOXO1.

RESULTS

Hypoxia causes increased autophagy and reduced osteogenic differentiation in rat mandibles and BMSCs, and blocking autophagy can attenuate hypoxia-induced osteogenic differentiation decrease. Moreover, hypoxia dissociated the FOXO1-HDAC6 complex and accumulated them in the nucleus. Knocking down of FOXO1 or HDAC6 alleviated hypoxia-induced autophagy elevation or osteogenic differentiation reduction by binding to related genes, respectively.

CONCLUSION

Hypoxia causes mandibular bone loss and autophagy elevation. Mechanically, hypoxia dissociates the FOXO1-HDAC6 complex and aggregates them in the nucleus, whereas HDAC6 decreases osteogenic differentiation and FOXO1 enhances autophagy to inhibit osteogenic differentiation.

Attributes of Nanomaterials and Nanotopographies for Improved Bone Tissue Engineering and Regeneration

Bone tissue engineering (BTE) is a multidisciplinary area that can solve the limitation of conventional grafting methods by developing viable and biocompatible bone replacements. The three essential components of BTE, i.e., Scaffold material and Cells and Growth factors altogether, facilitate support and guide for bone formation, differentiation of the bone tissues, and enhancement in the cellular activities and bone regeneration. However, there is a scarcity of the appropriate materials that can match the mechanical property as well as functional similarity to native tissue, considering the bone as hard tissue. In such scenarios, nanotechnology can be leveraged upon to achieve the desired aspects of BTE, and that is the key point of this review article. This review article examines the significant areas of nanotechnology research that have an impact on regeneration of bone: (a) scaffold with nanomaterials helps to enhance physicochemical interactions, biocompatibility, mechanical stability, and attachment; (b) nanoparticle-based approaches for delivering bioactive chemicals, growth factors, and genetic material. The article begins with the introduction of components and healing mechanisms of bone and the factors associated with them. The focus of this article is on the various nanotopographies that are now being used in scaffold formation, by describing how they are made, and how these nanotopographies affect the immune system and potential underlying mechanisms. The advantages of 4D bioprinting in BTE by using nanoink have also been mentioned. Additionally, we have investigated the importance of an in silico approach for finding the interaction between drugs and their related receptors, which can help to formulate suitable systems for delivery. This review emphasizes the role of nanoscale approach and how it helps to increase the efficacy of parameters of scaffold as well as drug delivery system for tissue engineering and bone regeneration.

Dysregulation of histone modifications in bone marrow mesenchymal stem cells during skeletal ageing: roles and therapeutic prospects

Age-associated bone diseases such as osteoporosis (OP) are common in the elderly due to skeletal ageing. The process of skeletal ageing can be accelerated by reduced proliferation and osteogenesis of bone marrow mesenchymal stem cells (BM-MSCs). Senescence of BM-MSCs is a main driver of age-associated bone diseases, and the fate of BM-MSCs is tightly regulated by histone modifications, such as methylation and acetylation. Dysregulation of histone modifications in BM-MSCs may activate the genes related to the pathogenesis of skeletal ageing and age-associated bone diseases. Here we summarize the histone methylation and acetylation marks and their regulatory enzymes that affect BM-MSC self-renewal, differentiation and senescence. This review not only describes the critical roles of histone marks in modulating BM-MSC functions, but also underlines the potential of epigenetic enzymes as targets for treating age-associated bone diseases. In the future, more effective therapeutic approaches based on these epigenetic targets will be developed and will benefit elderly individuals with bone diseases, such as OP.

CCL12 induces trabecular bone loss by stimulating RANKL production in BMSCs during acute lung injury

In the last three years, the capacity of health care systems and the public health policies of governments worldwide were challenged by the spread of SARS-CoV-2. Mortality due to SARS-CoV-2 mainly resulted from the development of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). Moreover, millions of people who survived ALI/ARDS in SARS-CoV-2 infection suffer from multiple lung inflammation-induced complications that lead to disability and even death. The lung-bone axis refers to the relationship between lung inflammatory diseases (COPD, asthma, and cystic fibrosis) and bone diseases, including osteopenia/osteoporosis. Compared to chronic lung diseases, the influence of ALI on the skeleton has not been investigated until now. Therefore, we investigated the effect of ALI on bone phenotypes in mice to elucidate the underlying mechanisms. In vivo bone resorption enhancement and trabecular bone loss were observed in LPS-induced ALI mice. Moreover, chemokine (C-C motif) ligand 12 (CCL12) accumulated in the serum and bone marrow. In vivo global ablation of CCL12 or conditional ablation of CCR2 in bone marrow stromal cells (BMSCs) inhibited bone resorption and abrogated trabecular bone loss in ALI mice. Furthermore, we provided evidence that CCL12 promoted bone resorption by stimulating RANKL production in BMSCs, and the CCR2/Jak2/STAT4 axis played an essential role in this process. Our study provides information regarding the pathogenesis of ALI and lays the groundwork for future research to identify new targets to treat lung inflammation-induced bone loss.

Chidamide suppresses adipogenic differentiation of bone marrow derived mesenchymal stem cells via increasing REEP2 expression

Increased propensity of bone marrow-derived mesenchymal stem cells (BM-MSCs) toward adipogenic differentiation at the expense of osteogenesis has been implicated in obesity, diabetes, and age-related osteoporosis as well as various hematopoietic disorders. Defining small molecules with role in rectifying the adipo-osteogenic differentiation imbalance is of great significance. Here, we unexpectedly found that Chidamide, a selective histone deacetylases inhibitor, exhibited remarkably suppressive effect on the in vitro induced adipogenic differentiation of BM-MSCs. Multifaceted alterations in the spectrum of gene expression were observed in Chidamide-managed BM-MSCs during adipogenic induction. Finally, we focused on REEP2, which presented decreased expression in BM-MSCs-mediated adipogenesis and was restored by Chidamide treatment. REEP2 was subsequently demonstrated as a negative regulator of adipogenic differentiation of BM-MSCs and mediated the suppressive effect of Chidamide on adipocyte development. Our findings provide the theoretical and experimental foundation for the clinical application of Chidamide for disorders associated with excessive marrow adipocytes.

Epigenetic regulation in metabolic diseases: mechanisms and advances in clinical study

Epigenetics regulates gene expression and has been confirmed to play a critical role in a variety of metabolic diseases, such as diabetes, obesity, non-alcoholic fatty liver disease (NAFLD), osteoporosis, gout, hyperthyroidism, hypothyroidism and others. The term 'epigenetics' was firstly proposed in 1942 and with the development of technologies, the exploration of epigenetics has made great progresses. There are four main epigenetic mechanisms, including DNA methylation, histone modification, chromatin remodelling, and noncoding RNA (ncRNA), which exert different effects on metabolic diseases. Genetic and non-genetic factors, including ageing, diet, and exercise, interact with epigenetics and jointly affect the formation of a phenotype. Understanding epigenetics could be applied to diagnosing and treating metabolic diseases in the clinic, including epigenetic biomarkers, epigenetic drugs, and epigenetic editing. In this review, we introduce the brief history of epigenetics as well as the milestone events since the proposal of the term 'epigenetics'. Moreover, we summarise the research methods of epigenetics and introduce four main general mechanisms of epigenetic modulation. Furthermore, we summarise epigenetic mechanisms in metabolic diseases and introduce the interaction between epigenetics and genetic or non-genetic factors. Finally, we introduce the clinical trials and applications of epigenetics in metabolic diseases.

miR-34a-5p facilitates osteogenic differentiation of bone marrow mesenchymal stem cells and modulates bone metabolism by targeting HDAC1 and promoting ER-α transcription

OBJECTIVE

Metabolism is essential for bone development. The expressions of catabolic markers in chondrocytes show association with miR-34a-5p. This study discussed the mechanism by which miR-34a-5p regulates osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) as well as bone metabolism.

METHODS

Expressions of BMSC surface markers were determined via flow cytometry. Osteogenic differentiation of BMSCs was subsequently induced. miR-34a-5p mimic, oe-HDAC1, or ER-α activator Ferutinin was introduced in BMSCs. Alkaline phosphatase activity and calcification were detected. Expressions of miR-34a-5p, HDAC1, ER-α, and osteogenic markers were determined via RT-qPCR and Western blot. The binding relationship between miR-34a-5p and HDAC1 was verified by a dual-luciferase assay. Mice at the age of 6 months and 18 months were assigned to the young group and age group for in vivo experiments, and aged mice were treated with agomiR miR-34a-5p. Expressions of serum miR-34a-5p, HDAC1, ER-α, and bone metabolism markers in mice were determined.

RESULTS

Osteogenic medium-induced BMSCs manifested increased expressions of miR-34a-5p and ER-α and decreased HDAC1 expression. miR-34a-5p overexpression promoted osteogenic differentiation of BMSCs. miR-34a-5p targeted HDAC1. HDAC1 overexpression partially counteracted the promotional action of miR-34a-5p overexpression on osteogenic differentiation of BMSCs. miR-34a-5p overexpression activated ER-α. ER-α activator Ferutinin partially nullified the regulatory function of miR-34a-5p/HDAC1 on osteogenic differentiation of BMSCs. In vivo experiments showed that miR-34a-5p overexpression enhanced the potential of bone metabolism in aged mice.

CONCLUSION

miR-34a-5p overexpression promoted osteogenic differentiation of BMSCs and enhanced bone metabolism by promoting ER-α activation via targeting HDAC1.

Circ_CUX1/miR-130b-5p/p300 axis for parathyroid hormone-stimulation of Runx2 activity in rat osteoblasts: A combined bioinformatic and experimental approach

Parathyroid hormone (PTH) regulates the expression of bone remodeling genes by enhancing the activity of Runx2 in osteoblasts. p300, a histone acetyltransferase, acetylated Runx2 to activate the expression of its target genes. PTH stimulated the expression of p300 in rat osteoblastic cells. Increasing studies suggested the potential of non-coding RNAs (ncRNAs), such as microRNAs (miRNAs) and circular RNAs (circRNAs), in regulating gene expression under both physiological and pathological conditions. In this study, we hypothesized that PTH regulates Runx2 activity via ncRNAs-mediated p300 expression in rat osteoblastic cells. Bioinformatics and experimental approaches identified PTH-upregulation of miR-130b-5p and circ_CUX1 that putatively target p300 and miR-130b-5p, respectively. An antisense-mediated knockdown of circ_CUX1 was performed to determine the sponging activity of circ_CUX1. Knockdown of circ_CUX1 promoted miR-130b-5p activity and reduced p300 expression, resulting in decreased Runx2 acetylation in rat osteoblastic cells. Further, bioinformatics analysis identified the possible signaling pathways that regulate Runx2 activity and osteoblast differentiation via circ_CUX1/miR-130b-5p/p300 axis. The predicted circ_CUX1/miR-130b-5p/p300 axis might pave the way for better diagnostic and therapeutic approaches for bone-related diseases.

Epigenetics: Novel crucial approach for osteogenesis of mesenchymal stem cells

Bone has a robust regenerative potential, but its capacity to repair critical-sized bone defects is limited. In recent years, stem cells have attracted significant interest for their potential in tissue engineering. Applying mesenchymal stem cells (MSCs) for enhancing bone regeneration is a promising therapeutic strategy. However, maintaining optimal cell efficacy or viability of MSCs is limited by several factors. Epigenetic modification can cause changes in gene expression levels without changing its sequence, mainly including nucleic acids methylation, histone modification, and non-coding RNAs. This modification is believed to be one of the determinants of MSCs fate and differentiation. Understanding the epigenetic modification of MSCs can improve the activity and function of stem cells. This review summarizes recent advances in the epigenetic mechanisms of MSCs differentiation into osteoblast lineages. We expound that epigenetic modification of MSCs can be harnessed to treat bone defects and promote bone regeneration, providing potential therapeutic targets for bone-related diseases.

Epigenetic control of mesenchymal stem cells orchestrates bone regeneration

Recent studies have revealed the vital role of MSCs in bone regeneration. In both self-healing bone regeneration processes and biomaterial-induced healing of bone defects beyond the critical size, MSCs show several functions, including osteogenic differentiation and thus providing seed cells. However, adverse factors such as drug intake and body senescence can significantly affect the functions of MSCs in bone regeneration. Currently, several modalities have been developed to regulate MSCs' phenotype and promote the bone regeneration process. Epigenetic regulation has received much attention because of its heritable nature. Indeed, epigenetic regulation of MSCs is involved in the pathogenesis of a variety of disorders of bone metabolism. Moreover, studies using epigenetic regulation to treat diseases are also being reported. At the same time, the effects of epigenetic regulation on MSCs are yet to be fully understood. This review focuses on recent advances in the effects of epigenetic regulation on osteogenic differentiation, proliferation, and cellular senescence in MSCs. We intend to illustrate how epigenetic regulation of MSCs orchestrates the process of bone regeneration.

Osteogenic Commitment of Human Periodontal Ligament Cells Is Predetermined by Methylation, Chromatin Accessibility and Expression of Key Transcription Factors

Periodontal ligament stem cells (PDLCs) can be used as a valuable source in cell therapies to regenerate bone tissue. However, the potential therapeutic outcomes are unpredictable due to PDLCs’ heterogeneity regarding the capacity for osteoblast differentiation and mineral nodules production. Here, we identify epigenetic (DNA (hydroxy)methylation), chromatin (ATAC-seq) and transcriptional (RNA-seq) differences between PDLCs presenting with low (l) and high (h) osteogenic potential. The primary cell populations were investigated at basal state (cultured in DMEM) and after 10 days of osteogenic stimulation (OM). At a basal state, the expression of transcription factors (TFs) and the presence of gene regulatory regions related to osteogenesis were detected in h-PDLCs in contrast to neuronal differentiation prevalent in l-PDLCs. These differences were also observed under stimulated conditions, with genes and biological processes associated with osteoblast phenotype activated more in h-PDLCs. Importantly, even after the induction, l-PDLCs showed hypermethylation and low expression of genes related to bone development. Furthermore, the analysis of TFs motifs combined with TFs expression suggested the relevance of SP1, SP7 and DLX4 regulation in h-PDLCs, while motifs for SIX and OLIG2 TFs were uniquely enriched in l-PDLCs. Additional analysis including a second l-PDLC population indicated that the high expression of OCT4, SIX3 and PPARG TFs could be predictive of low osteogenic commitment. In summary, several biological processes related to osteoblast commitment were activated in h-PDLCs from the onset, while l-PDLCs showed delay in the activation of the osteoblastic program, restricted by the persistent methylation of gene related to bone development. These processes are pre-determined by distinguishable epigenetic and transcriptional patterns, the recognition of which could help in selection of PDLCs with pre-osteoblastic phenotype.

Role of histone modification in the occurrence and development of osteoporosis

Osteoporosis is a systemic degenerative bone disease characterized by low bone mass and damage to bone microarchitecture, which increases bone fragility and susceptibility to fracture. The risk of osteoporosis increases with age; with the aging of the global population, osteoporosis is becoming more prevalent, adding to the societal healthcare burden. Histone modifications such as methylation, acetylation, ubiquitination, and ADP-ribosylation are closely related to the occurrence and development of osteoporosis. This article reviews recent studies on the role of histone modifications in osteoporosis. The existing evidence indicates that therapeutic targeting of these modifications to promote osteogenic differentiation and bone formation may be an effective treatment for this disease.