Histone demethylase JMJD3 is required for osteoblast differentiation in mice

KDM6B preferentially promotes bone formation over resorption to facilitate postnatal bone mass accrual through collagen triple helix repeat containing 1-mediated PKCδ/MAPKs signaling

Lysine demethylase 6B (KDM6B) plays a role in regulating osteoblast differentiation and fetal bone ossification. Nevertheless, its involvement in regulating postnatal bone homeostasis and bone mass accrual remains unclear. In this study, we generated mice lacking Kdm6b gene specifically in mesenchyme and osteoprogenitor cells using a conditional strategy. The adult mice of both mutant strains had decreased cancellous bone mass. The absence of Kdm6b in mesenchyme led to decreased numbers of osteoblasts and osteoclasts, increased marrow adipocytes, as well as repressed bone formation and resorption. Additionally, Kdm6b-deficient bone marrow stromal cells (BMSCs) displayed impaired osteogenic differentiation and exerted an inhibitory effect on osteoclastogenesis. RNA-seq combined with gene expression analysis uncovered downregulation of collagen triple helix repeat containing 1 (CTHRC1) and a lower RANKL/osteoprotegerin (OPG) ratio in BMSCs of the mutant mice. Further mechanistic explorations demonstrated that KDM6B epigenetically upregulated CTHRC1 expression by removing the repressive H3K27me3 mark from its promoter, thereby triggering PKCδ/MAPKs signaling to facilitate osteoblast differentiation. CTHRC1 was able to mitigate the dysregulated osteogenic and adipogenic differentiation induced by Kdm6b deficiency. This study provides evidence that KDM6B regulates postnatal bone homeostasis through balancing osteoblast and osteoclast differentiation. Given its predominant promotion of osteoblastic bone formation over osteoclastic bone resorption, KDM6B tends to promote postnatal bone mass accrual.

Impact of Environmental and Epigenetic Changes on Mesenchymal Stem Cells during Aging

Many crucial epigenetic changes occur during early skeletal development and throughout life due to aging, disease and are heavily influenced by an individual’s lifestyle. Epigenetics is the study of heritable changes in gene expression as the result of changes in the environment without any mutation in the underlying DNA sequence. The epigenetic profiles of cells are dynamic and mediated by different mechanisms, including histone modifications, non-coding RNA-associated gene silencing and DNA methylation. Given the underlining role of dysfunctional mesenchymal tissues in common age-related skeletal diseases such as osteoporosis and osteoarthritis, investigations into skeletal stem cells or mesenchymal stem cells (MSC) and their functional deregulation during aging has been of great interest and how this is mediated by an evolving epigenetic landscape. The present review describes the recent findings in epigenetic changes of MSCs that effect growth and cell fate determination in the context of aging, diet, exercise and bone-related diseases.

Epigenetic Crosstalk between Malignant Plasma Cells and the Tumour Microenvironment in Multiple Myeloma

In multiple myeloma, cells of the bone marrow microenvironment have a relevant responsibility in promoting the growth, survival, and drug resistance of multiple myeloma plasma cells. In addition to the well-recognized role of genetic lesions, microenvironmental cells also present deregulated epigenetic systems. However, the effect of epigenetic changes in reshaping the tumour microenvironment is still not well identified. An assortment of epigenetic regulators, comprising histone methyltransferases, histone acetyltransferases, and lysine demethylases, are altered in bone marrow microenvironmental cells in multiple myeloma subjects participating in disease progression and prognosis. Aberrant epigenetics affect numerous processes correlated with the tumour microenvironment, such as angiogenesis, bone homeostasis, and extracellular matrix remodelling. This review focuses on the interplay between epigenetic alterations of the tumour milieu and neoplastic cells, trying to decipher the crosstalk between these cells. We also evaluate the possibility of intervening specifically in modified signalling or counterbalancing epigenetic mechanisms.

Effects of GSK-J4 on JMJD3 Histone Demethylase in Mouse Prostate Cancer Xenografts

BACKGROUND/AIM

Histone methylation status is required to control gene expression. H3K27me3 is an epigenetic tri-methylation modification to histone H3 controlled by the demethylase JMJD3. JMJD3 is dysregulated in a wide range of cancers and has been shown to control the expression of a specific growth-modulatory gene signature, making it an interesting candidate to better understand prostate tumor progression in vivo. This study aimed to identify the impact of JMJD3 inhibition by its inhibitor, GSK4, on prostate tumor growth in vivo.

MATERIALS AND METHODS

Prostate cancer cell lines were implanted into Balb/c nude male mice. The effects of the selective JMJD3 inhibitor GSK-J4 on tumor growth were analyzed by bioluminescence assays and H3K27me3-regulated changes in gene expression were analyzed by ChIP-qPCR and RT-qPCR.

RESULTS

JMJD3 inhibition contributed to an increase in tumor growth in androgen-independent (AR-) xenografts and a decrease in androgen-dependent (AR+). GSK-J4 treatment modulated H3K27me3 enrichment on the gene panel in DU-145-luc xenografts while it had little effect on PC3-luc and no effect on LNCaP-luc. Effects of JMJD3 inhibition affected the panel gene expression.

CONCLUSION

JMJD3 has a differential effect in prostate tumor progression according to AR status. Our results suggest that JMJD3 is able to play a role independently of its demethylase function in androgen-independent prostate cancer. The effects of GSK-J4 on AR+ prostate xenografts led to a decrease in tumor growth.

Histone H3K27 demethylase, Utx, regulates osteoblast-to-osteocyte differentiation

Osteocytes are master regulators of skeletal homeostasis. However, little is known about the molecular mechanism of their differentiation. Epigenetic regulations, especially H3K27me3 modification, play critical roles in cell differentiation. Here, we found that H3K27me3 in the loci of osteocyte-expressing genes decreased during osteocyte differentiation and that H3K27me3 demethylase, Utx, was bound to the loci of those genes. To investigate the physiological functions of Utx in vivo, we generated late osteoblast-to-osteocyte specific Utx knockout mice using Dmp1-cre mice (UtxΔOcy/ΔOcy). Micro CT analyses showed that UtxΔOcy/ΔOcy displayed osteopenic phenotypes with lower bone volume and trabecular number, and greater trabecular separation. Bone histomorphometric analysis showed that bone mineralization and formation were significantly lower in UtxΔOcy/ΔOcy. Furthermore, Dmp1 expression and the number of osteocytes were significantly decreased in UtxΔOcy/ΔOcy. These results suggest that Utx in Dmp1-expressing osteoblast/osteocyte positively regulates osteoblast-to-osteocyte differentiation through H3K27me3 modifications in osteocyte genes. Our results provide new insight into the molecular mechanism of osteocyte differentiation.

Disruption of Jmjd3/p16Ink4a Signaling Pathway Causes Bizarre Parosteal Osteochondromatous Proliferation (BPOP)-like Lesion in Mice

Bizarre parosteal osteochondromatous proliferation (BPOP), or Nora's lesion, is a rare benign osteochondromatous lesion. At present, the molecular etiology of BPOP remains unclear. JMJD3(KDM6B) is an H3K27me3 demethylase and counteracts polycomb-mediated transcription repression. Previously, Jmjd3 was shown to be critical for bone development and osteoarthritis. Here, we report that conditional deletion of Jmjd3 in chondrogenic cells unexpectedly resulted in BPOP-like lesion in mice. Biochemical investigations revealed that Jmjd3 inhibited BPOP-like lesion through p16^Ink4a . Immunohistochemistry and RT-qPCR assays indicated JMJD3 and p16^INK4A level were significantly reduced in human BPOP lesion compared with normal subjects. This was further confirmed by Jmjd3/Ink4a double-gene knockout mice experiments. Therefore, our results indicated the pathway of Jmjd3/p16^Ink4a may be essential for the development of BPOP in human. © 2021 American Society for Bone and Mineral Research (ASBMR).

The Roles of Epigenetics Regulation in Bone Metabolism and Osteoporosis

Osteoporosis is a metabolic disease characterized by decreased bone mineral density and the destruction of bone microstructure, which can lead to increased bone fragility and risk of fracture. In recent years, with the deepening of the research on the pathological mechanism of osteoporosis, the research on epigenetics has made significant progress. Epigenetics refers to changes in gene expression levels that are not caused by changes in gene sequences, mainly including DNA methylation, histone modification, and non-coding RNAs (lncRNA, microRNA, and circRNA). Epigenetics play mainly a post-transcriptional regulatory role and have important functions in the biological signal regulatory network. Studies have shown that epigenetic mechanisms are closely related to osteogenic differentiation, osteogenesis, bone remodeling and other bone metabolism-related processes. Abnormal epigenetic regulation can lead to a series of bone metabolism-related diseases, such as osteoporosis. Considering the important role of epigenetic mechanisms in the regulation of bone metabolism, we mainly review the research progress on epigenetic mechanisms (DNA methylation, histone modification, and non-coding RNAs) in the osteogenic differentiation and the pathogenesis of osteoporosis to provide a new direction for the treatment of bone metabolism-related diseases.

Roles of HIF and 2-Oxoglutarate-Dependent Dioxygenases in Controlling Gene Expression in Hypoxia

Simple Summary

Hypoxia—reduction in oxygen availability—plays key roles in both physiological and pathological processes. Given the importance of oxygen for cell and organism viability, mechanisms to sense and respond to hypoxia are in place. A variety of enzymes utilise molecular oxygen, but of particular importance to oxygen sensing are the 2-oxoglutarate (2-OG) dependent dioxygenases (2-OGDs). Of these, Prolyl-hydroxylases have long been recognised to control the levels and function of Hypoxia Inducible Factor (HIF), a master transcriptional regulator in hypoxia, via their hydroxylase activity. However, recent studies are revealing that such dioxygenases are involved in almost all aspects of gene regulation, including chromatin organisation, transcription and translation.

Abstract

Hypoxia—reduction in oxygen availability—plays key roles in both physiological and pathological processes. Given the importance of oxygen for cell and organism viability, mechanisms to sense and respond to hypoxia are in place. A variety of enzymes utilise molecular oxygen, but of particular importance to oxygen sensing are the 2-oxoglutarate (2-OG) dependent dioxygenases (2-OGDs). Of these, Prolyl-hydroxylases have long been recognised to control the levels and function of Hypoxia Inducible Factor (HIF), a master transcriptional regulator in hypoxia, via their hydroxylase activity. However, recent studies are revealing that dioxygenases are involved in almost all aspects of gene regulation, including chromatin organisation, transcription and translation. We highlight the relevance of HIF and 2-OGDs in the control of gene expression in response to hypoxia and their relevance to human biology and health.

The Functions of the Demethylase JMJD3 in Cancer

Cancer is a major cause of death worldwide. Epigenetic changes in response to external (diet, sports activities, etc.) and internal events are increasingly implicated in tumor initiation and progression. In this review, we focused on post-translational changes in histones and, more particularly, the tri methylation of lysine from histone 3 (H3K27me3) mark, a repressive epigenetic mark often under- or overexpressed in a wide range of cancers. Two actors regulate H3K27 methylation: Jumonji Domain-Containing Protein 3 demethylase (JMJD3) and Enhancer of zeste homolog 2 (EZH2) methyltransferase. A number of studies have highlighted the deregulation of these actors, which is why this scientific review will focus on the role of JMJD3 and, consequently, H3K27me3 in cancer development. Data on JMJD3’s involvement in cancer are classified by cancer type: nervous system, prostate, blood, colorectal, breast, lung, liver, ovarian, and gastric cancers.

Pharmacological targeting of KDM6A and KDM6B, as a novel therapeutic strategy for treating craniosynostosis in Saethre-Chotzen syndrome

BACKGROUND

During development, excessive osteogenic differentiation of mesenchymal progenitor cells (MPC) within the cranial sutures can lead to premature suture fusion or craniosynostosis, leading to craniofacial and cognitive issues. Saethre-Chotzen syndrome (SCS) is a common form of craniosynostosis, caused by TWIST-1 gene mutations. Currently, the only treatment option for craniosynostosis involves multiple invasive cranial surgeries, which can lead to serious complications.

METHODS

The present study utilized Twist-1 haploinsufficient (Twist-1^del/+) mice as SCS mouse model to investigate the inhibition of Kdm6a and Kdm6b activity using the pharmacological inhibitor, GSK-J4, on calvarial cell osteogenic potential.

RESULTS

This study showed that the histone methyltransferase EZH2, an osteogenesis inhibitor, is downregulated in calvarial cells derived from Twist-1^del/+ mice, whereas the counter histone demethylases, Kdm6a and Kdm6b, known promoters of osteogenesis, were upregulated. In vitro studies confirmed that siRNA-mediated inhibition of Kdm6a and Kdm6b expression suppressed osteogenic differentiation of Twist-1^del/+ calvarial cells. Moreover, pharmacological targeting of Kdm6a and Kdm6b activity, with the inhibitor, GSK-J4, caused a dose-dependent suppression of osteogenic differentiation by Twist-1^del/+ calvarial cells in vitro and reduced mineralized bone formation in Twist-1^del/+ calvarial explant cultures. Chromatin immunoprecipitation and Western blot analyses found that GSK-J4 treatment elevated the levels of the Kdm6a and Kdm6b epigenetic target, the repressive mark of tri-methylated lysine 27 on histone 3, on osteogenic genes leading to repression of Runx2 and Alkaline Phosphatase expression. Pre-clinical in vivo studies showed that local administration of GSK-J4 to the calvaria of Twist-1^del/+ mice prevented premature suture fusion and kept the sutures open up to postnatal day 20.

CONCLUSION

The inhibition of Kdm6a and Kdm6b activity by GSK-J4 could be used as a potential non-invasive therapeutic strategy for preventing craniosynostosis in children with SCS. Pharmacological targeting of Kdm6a/b activity can alleviate craniosynostosis in Saethre-Chotzen syndrome. Aberrant osteogenesis by Twist-1 mutant cranial suture mesenchymal progenitor cells occurs via deregulation of epigenetic modifiers Ezh2 and Kdm6a/Kdm6b. Suppression of Kdm6a- and Kdm6b-mediated osteogenesis with GSK-J4 inhibitor can prevent prefusion of cranial sutures.

Epigenetic silencing of the osteoblast-lineage gene program during hippocampal maturation

Accumulating evidence indicates that epigenetic control of gene expression plays a significant role during cell lineage commitment and subsequent cell fate maintenance. Here, we assess epigenetic mechanisms operating in the rat brain that mediate silencing of genes that are expressed during early and late stages of osteogenesis. We report that repression of the osteoblast master regulator Sp7 in embryonic (E18) hippocampus is mainly mediated through the Polycomb complex PRC2 and its enzymatic product H3K27me3. During early postnatal (P10), juvenile (P30), and adult (P90) hippocampal stages, the repressive H3K27me3 mark is progressively replaced by nucleosome enrichment and increased CpG DNA methylation at the Sp7 gene promoter. In contrast, silencing of the late bone phenotypic Bglap gene in the hippocampus is PRC2-independent and accompanied by strong CpG methylation from E18 through postnatal and adult stages. Forced ectopic expression of the primary master regulator of osteogenesis Runx2 in embryonic hippocampal neurons activates the expression of its downstream target Sp7 gene. Moreover, transcriptomic analyses show that several genes associated with the mesenchymal-osteogenic lineages are transcriptionally activated in these hippocampal cells that express Runx2 and Sp7. This effect is accompanied by a loss in neuronal properties, including a significant reduction in secondary processes at the dendritic arbor and reduced expression of critical postsynaptic genes like PSD95. Together, our results reveal a developmental progression in epigenetic control mechanisms that repress the expression of the osteogenic program in hippocampal neurons at embryonic, postnatal, and adult stages.

Epidrugs: novel epigenetic regulators that open a new window for targeting osteoblast differentiation

Efficient osteogenic differentiation of mesenchymal stem cells (MSCs) is a critical step in the treatment of bone defects and skeletal disorders, which present challenges for cell-based therapy and regenerative medicine. Thus, it is necessary to understand the regulatory agents involved in osteogenesis. Epigenetic mechanisms are considered to be the primary mediators that regulate gene expression during MSC differentiation. In recent years, epigenetic enzyme inhibitors have been used as epidrugs in cancer therapy. A number of studies mentioned the role of epigenetic inhibitors in the regulation of gene expression patterns related to osteogenic differentiation. This review attempts to provide an overview of the key regulatory agents of osteogenesis: transcription factors, signaling pathways, and, especially, epigenetic mechanisms. In addition, we propose to introduce epigenetic enzyme inhibitors (epidrugs) and their applications as future therapeutic approaches for bone defect regeneration.

Osteoblastic differentiation of bone marrow mesenchymal stem cells in uremic rats

Severe secondary hyperparathyroidism (SHPT) represents a high turnover bone disease, osteitis fibrosa, but the pathogenesis of osteitis fibrosa remains to be fully elucidated. We examined the characteristics of the differentiation of bone marrow mesenchymal stem cells (BMSCs) into osteoblasts in uremic rats. We bred 5/6 nephrectomized (Nx) rats with a high phosphorus (P) diet to induce SHPT (Nx + HP), or Nx (Nx + ND) and normal rats (Nc + ND) fed a standard diet (ND). After 8 weeks, BMSCs were isolated from the femur and serum were analyzed. BMSCs underwent flow cytometric examination for the expression patterns of cell surface markers (CD90⁺, CD29⁺, CD45^-, and CD31^-). Serum creatinine (Cre) levels were significantly elevated in the Nx + NP rats compared with the Nc + NP rats. Cre levels in the Nx + HP rats were levels to those in the Nx + ND rats. Serum P and PTH levels were significantly elevated in the Nx + HP rats compared with the Nx + ND rats. Bone morphometrical analysis showed increases in both osteoid volume and eroded surfaces in the Nx + HP but not in the Nx + ND rats. The populations of harvested BMSCs were similar between all three groups. Alp, Runx2, Pth1r and Cyclin D1 mRNA expression in the BMSCs from the Nx + ND rats were significantly suppressed compared with those isolated from the Nc + ND groups. Alizarin red staining tended to be similar to the expression of these mRNA. These results suggest that the BMSCs differentiation into osteoblasts was disturbed in the uremic rats.

Glycoprotein Nonmetastatic Melanoma Protein B (GPNMB) Ameliorates the Inflammatory Response in Periodontal Disease

Glycoprotein nonmetastatic melanoma protein B (GPNMB) is a type I transmembrane protein that can modulate osteoblasts and bone mineralization. Periodontal disease (PD) is characterized by gum inflammation, alveolar bone resorption, and tooth loss. In this study, we found that GPNMB is highly expressed in inflamed periodontal tissue through microarray and immunohistochemistry (IHC) assays. The role of GPNMB in the pathogenesis of PD was evaluated with primary human periodontal ligament cells (hPDLCs) treated with lipopolysaccharide (LPS) and a GPNMB-expressing lentivirus (lenti-GP). In the hPDLCs treated with LPS and lenti-GP, the expression of tumor necrosis factor (TNF)-α and interleukin (IL)-6 was suppressed and that of IL-10 was upregulated. GPNMB significantly decreased apoptosis in the hPDLCs treated with LPS. GPNMB could upregulate the expression of Jumonji domain-containing protein 3 (Jmjd3), a histone 3 lysine 27 (H3K27) demethylase that is linked to the modulation of the inflammatory response and apoptosis. Taken together, our data find that GPNMB is highly expressed in gum tissue with PD and may be an anti-inflammatory player in the pathogenesis of PD.

Epigenetic-Based Mechanisms of Osteoblast Suppression in Multiple Myeloma Bone Disease

Multiple myeloma (MM) bone disease is characterized by the development of osteolytic lesions, which cause severe complications affecting the morbidity, mortality, and treatment of myeloma patients. Myeloma tumors seeded within the bone microenvironment promote hyperactivation of osteoclasts and suppression of osteoblast differentiation. Because of this prolonged suppression of bone marrow stromal cells’ (BMSCs) differentiation into functioning osteoblasts, bone lesions in patients persist even in the absence of active disease. Current antiresorptive therapy provides insufficient bone anabolic effects to reliably repair MM lesions. It has become widely accepted that myeloma‐exposed BMSCs have an altered phenotype with pro‐inflammatory, immune‐modulatory, anti‐osteogenic, and pro‐adipogenic properties. In this review, we focus on the role of epigenetic‐based modalities in the establishment and maintenance of myeloma‐induced suppression of osteogenic commitment of BMSCs. We will focus on recent studies demonstrating the involvement of chromatin‐modifying enzymes in transcriptional repression of osteogenic genes in MM‐BMSCs. We will further address the epigenetic plasticity in the differentiation commitment of osteoprogenitor cells and assess the involvement of chromatin modifiers in MSC‐lineage switching from osteogenic to adipogenic in the context of the inflammatory myeloma microenvironment. Lastly, we will discuss the potential of employing small molecule epigenetic inhibitors currently used in the MM research as therapeutics and bone anabolic agents in the prevention or repair of osteolytic lesions in MM. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Specific functions of TET1 and TET2 in regulating mesenchymal cell lineage determination

Background

The 5 hydroxymethylation (5hmC) mark and TET DNA dioxygenases play a pivotal role in embryonic stem cell differentiation and animal development. However, very little is known about TET enzymes in lineage determination of human bone marrow-derived mesenchymal stem/stromal cells (BMSC). We examined the function of all three TET DNA dioxygenases, responsible for DNA hydroxymethylation, in human BMSC cell osteogenic and adipogenic differentiation.

Results

We used siRNA knockdown and retroviral mediated enforced expression of TET molecules and discovered TET1 to be a repressor of both osteogenesis and adipogenesis. TET1 was found to recruit the co-repressor proteins, SIN3A and the histone lysine methyltransferase, EZH2 to osteogenic genes. Conversely, TET2 was found to be a promoter of both osteogenesis and adipogenesis. The data showed that TET2 was directly responsible for 5hmC levels on osteogenic and adipogenic lineage-associated genes, whereas TET1 also played a role in this process. Interestingly, TET3 showed no functional effect in BMSC osteo-/adipogenic differentiation. Finally, in a mouse model of ovariectomy-induced osteoporosis, the numbers of clonogenic BMSC were dramatically diminished corresponding to lower trabecular bone volume and reduced levels of TET1, TET2 and 5hmC.

Conclusion

The present study has discovered an epigenetic mechanism mediated through changes in DNA hydroxymethylation status regulating the activation of key genes involved in the lineage determination of skeletal stem cells, which may have implications in BMSC function during normal bone regulation. Targeting TET molecules or their downstream targets may offer new therapeutic strategies to help prevent bone loss and repair following trauma or disease.

Electronic supplementary material

The online version of this article (10.1186/s13072-018-0247-4) contains supplementary material, which is available to authorized users.

A tale of two cities: The genetic mechanisms governing calvarial bone development

The skull bones must grow in a coordinated, three-dimensional manner to coalesce and form the head and face. Mammalian skull bones have a dual embryonic origin from cranial neural crest cells (CNCC) and paraxial mesoderm (PM) and ossify through intramembranous ossification. The calvarial bones, the bones of the cranium which cover the brain, are derived from the supraorbital arch (SOA) region mesenchyme. The SOA is the site of frontal and parietal bone morphogenesis and primary center of ossification. The objective of this review is to frame our current in vivo understanding of the morphogenesis of the calvarial bones and the gene networks regulating calvarial bone initiation in the SOA mesenchyme.

Mll-COMPASS complexes mediate H3K4me3 enrichment and transcription of the osteoblast master gene Runx2/p57 in osteoblasts

Expression of Runx2/p57 is a hallmark of the osteoblast-lineage identity. Although several regulators that control the expression of Runx2/p57 during osteoblast-lineage commitment have been identified, the epigenetic mechanisms that sustain this expression in differentiated osteoblasts remain to be completely determined. Here, we assess epigenetic mechanisms associated with Runx2/p57 gene transcription in differentiating MC3T3 mouse osteoblasts. Our results show that an enrichment of activating histone marks at the Runx2/p57 P1 promoter is accompanied by the simultaneous interaction of Wdr5 and Utx proteins, both are components of COMPASS complexes. Knockdown of Wdr5 and Utx expression confirms the activating role of both proteins at the Runx2-P1 promoter. Other chromatin modifiers that were previously described to regulate Runx2/p57 transcription in mesenchymal precursor cells (Ezh2, Prmt5, and Jarid1b proteins) were not found to contribute to Runx2/p57 transcription in full-committed osteoblasts. We also determined the presence of additional components of COMPASS complexes at the Runx2/p57 promoter, evidencing that the Mll2/COMPASS- and Mll3/COMPASS-like complexes bind to the P1 promoter in osteoblastic cells expressing Runx2/p57 to modulate the H3K4me1 to H3K4me3 transition.

Flavonoid compound icariin enhances BMP-2 induced differentiation and signalling by targeting to connective tissue growth factor (CTGF) in SAMP6 osteoblasts

BACKGROUND

Icariin, a major active flavonoid glucoside, is widely used for the treatment of bone injury and rebuilding in the clinic because of its roles in suppressing osteoblastogenesis and promoting osteogenesis. The senescence-accelerated mouse SAMP6 was accepted as a useful murine model to reveal the mechanism of senile osteoporosis and the therapeutic mechanism of drug activity. However, little is known about the characteristics of SAMP6 osteoblasts and the associated regulatory roles of icariin.

METHODS

We isolated and cultured osteoblasts from SAMP6 or SAMR1 mice and compared their proliferation, migration, and differentiation by performing the CCK-8 assay, cell counting assay, EdU staining, cell cycle analysis, ALP staining and activity measurement, Alizarin red staining, and RT-qPCR analysis to measure the levels of osteoblast markers, including RUNX2, Colla1 and Oc. To assess the effects of icariin on BMP-2-induced osteoblast differentiation, after BMP-2 treatment, osteoblast markers were analyzed by RT-qPCR and semi-quantitative Western blotting. The effects of icariin on connective tissue growth factor (CTGF) were measured by RT-qPCR. shRNA targeting CTGF mRNA was employed to knockdown its expression level in osteoblasts.

RESULTS

The SAMP6 osteoblasts presented decreased the development and differentiation activity compared with SAMR1 osteoblasts, indicating that they are the potential mechanisms underlying age-associated disease. Moreover, SAMP6 osteoblasts presented upregulated CTGF compared with SAMR1 osteoblasts. Icariin enhanced BMP-2-induced osteoblast differentiation by downregulating CTGF expression, which tightly regulates osteoblast differentiation. By downregulating CTGF, icariin treatment upregulated phosphate-Smad1/5/8, indicating its activating effects on the BMP signaling pathway.

CONCLUSION

These results suggest that decreased osteoblast development and function potentially contributes to age-associated disease. Icariin exerts enhancing effects on BMP-2-mediated osteoblast development via downregulating CTGF.

Tet-Mediated DNA Demethylation Is Required for SWI/SNF-Dependent Chromatin Remodeling and Histone-Modifying Activities That Trigger Expression of the Sp7 Osteoblast Master Gene during Mesenchymal Lineage Commitment

Here we assess histone modification, chromatin remodeling, and DNA methylation processes that coordinately control the expression of the bone master transcription factor Sp7 (osterix) during mesenchymal lineage commitment in mammalian cells. We find that Sp7 gene silencing is mediated by DNA methyltransferase1/3 (DNMT1/3)-, histone deacetylase 1/2/4 (HDAC1/2/4)-, Setdb1/Suv39h1-, and Ezh1/2-containing complexes. In contrast, Sp7 gene activation involves changes in histone modifications, accompanied by decreased nucleosome enrichment and DNA demethylation mediated by SWI/SNF- and Tet1/Tet2-containing complexes, respectively. Inhibition of DNA methylation triggers changes in the histone modification profile and chromatin-remodeling events leading to Sp7 gene expression. Tet1/Tet2 silencing prevents Sp7 expression during osteoblast differentiation as it impairs DNA demethylation and alters the recruitment of histone methylase (COMPASS)-, histone demethylase (Jmjd2a/Jmjd3)-, and SWI/SNF-containing complexes to the Sp7 promoter. The dissection of these interconnected epigenetic mechanisms that govern Sp7 gene activation reveals a hierarchical process where regulatory components mediating DNA demethylation play a leading role.

Macrophage Kdm6b controls the pro-fibrotic transcriptome signature of foam cells

AIM

In order to identify regulators of foam cells, we studied the H3K27 demethylase Kdm6b (also known as Jmjd3), a known regulator of macrophages, in controlling the transcriptional profile of foam cells.

MATERIALS & METHODS

Foam cells from Kdm6b-deleted or Kdm6b wild-type mice were isolated and used for RNA-sequencing analysis.

RESULTS

Pathway analysis revealed that pro-fibrotic pathways were strongly suppressed in Kdm6b-deleted foam cells. Analysis of published datasets showed that foam cell formation induces these pro-fibrotic characteristics. Overlay of both datasets indicated that fibrotic genes which are induced upon foam cell formation, are reduced in the absence of Kdm6b. These data suggest that foam cell formation induces a pro-fibrotic gene signature in a Kdm6b-dependent manner.

CONCLUSION

We identified Kdm6b as a novel regulator of the pro-fibrotic signature of peritoneal foam cells.

Prospective Review of Mesenchymal Stem Cells Differentiation into Osteoblasts

Stem cell research has been a popular topic in the past few decades. This review aims to discuss factors that help regulate, induce, and enhance mesenchymal stem cell (MSC) differentiation into osteoblasts for bone regeneration. The factors analyzed include bone morphogenic protein (BMP), transforming growth factor β (TGF-β), stromal cell-derived factor 1 (SDF-1), insulin-like growth factor type 1 (IGF-1), histone demethylase JMJD3, cyclin dependent kinase 1 (CDK1), fucoidan, Runx2 transcription factor, and TAZ transcriptional coactivator. Methods promoting bone healing are also evaluated in this review that have shown promise in previous studies. Methods tested using animal models include low intensity pulsed ultrasound (LIPUS) with MSC, micro motion, AMD3100 injections, BMP delivery, MSC transplantation, tissue engineering utilizing scaffolds, anti-IL-20 monoclonal antibody, low dose photodynamic therapy, and bone marrow stromal cell transplants. Human clinical trial methods analyzed include osteoblast injections, bone marrow grafts, bone marrow and platelet rich plasma transplantation, tissue engineering using scaffolds, and recombinant human BMP-2. These methods have been shown to promote and accelerate new bone formation. These various methods for enhanced bone regeneration have the potential to be used, following further research, in clinical practice.

The Roles of Histone Demethylase Jmjd3 in Osteoblast Differentiation and Apoptosis

Posttranslational modifications including histone methylation regulate gene transcription through directly affecting the structure of chromatin. Trimethylation of histone 3 lysine 27 (H3K27me3) is observed at the promoters of a wide variety of important genes, especially for mammalian development, and contributes to gene silencing. Demethylase Jumonji domain-containing 3 (Jmjd3) catalyzes the transition of H3K27me3 to H3K27me1, therefore from a repressive to an active status of gene expression. Jmjd3 plays important roles in cell differentiation, inflammation, and tumorigenesis by targeting distinct transcription factors. In this review, we summarize the pivotal roles of Jmjd3 in maintaining skeletal homeostasis through regulating osteoblast differentiation, maturation, and apoptosis.

Epigenetic regulation of bone cells

Bone is a major organ in the skeletal system that supports and protects muscles and other organs, facilitates movement and hematopoiesis, and forms a reservoir of minerals including calcium. The cells in the bone, such as osteoblasts, osteoclasts, and osteocytes, orchestrate sequential and balanced regulatory mechanisms to maintain bone and are capable of differentiating in bones. Bone development and remodeling require a precise regulation of gene expressions in bone cells, a process governed by epigenetic mechanisms such as histone modification, DNA methylation, and chromatin structure. Importantly, lineage-specific transcription factors can determine the epigenetic regulation of bone cells. Emerging data suggest that perturbation of epigenetic programs can affect the function and activity of bone cells and contributes to pathogenesis of bone diseases, including osteoporosis. Thus, understanding epigenetic regulations in bone cells would be important for early diagnosis and future therapeutic approaches.

The Maternal Effect Genes UTX and JMJD3 Play Contrasting Roles in Mus musculus Preimplantation Embryo Development

During the process of embryonic development in mammals, epigenetic modifications must be erased and reconstructed. In particular, the trimethylation of histone 3 lysine 27 (H3K27me3) is associated with gene-specific transcriptional repression and contributes to the maintenance of the pluripotent embryos. In this study, we determined that the global levels of the H3K27me3 marker were elevated in MII oocyte chromatin and decrease to minimal levels at the 8-cell and morula stages. When the blastocyst hatched, H3K27me3 was re-established in the inner cell mass. We also determined that H3K27me3-specific demethylases, UTX and JMJD3, were observed at high transcript and protein levels in mouse preimplantation embryos. In the activated oocytes, when the H3K27me3 disappeared at the 8-cell stage, the UTX (but not JMJD3) protein levels were undetectable. Using RNA interference, we suppressed UTX and JMJD3 gene expression in the embryos and determined that the functions of UTX and JMJD3 were complementary. When JMJD3 levels were decreased by RNA interference, the embryo development rate and quality were improved, but the knockdown of UTX produced the opposite results. Understanding the epigenetic mechanisms controlling preimplantation development is critical to comprehending the basis of embryonic development and to devise methods and approaches to treat infertility.

Osteoporosis: The Result of an 'Aged' Bone Microenvironment

Osteoporosis is an age-related progressive bone disease. Recent advances in epigenetics, cell biology, osteoimmunology, and genetic epidemiology have unraveled new mechanisms and players underlying the pathology of osteoporosis, supporting a model of age-related dysregulation and crosstalk in the bone microenvironment.