Dynamic and distinct histone modifications of osteogenic genes during osteogenic differentiation

Epigenetic changes in shear-stressed endothelial cells

Epigenetic changes, particularly histone compaction modifications, have emerged as critical regulators in the epigenetic pathway driving endothelial cell phenotype under constant exposure to laminar forces induced by blood flow. However, the underlying epigenetic mechanisms governing endothelial cell behavior in this context remain poorly understood. To address this knowledge gap, we conducted in vitro experiments using human umbilical vein endothelial cells subjected to various tensional forces simulating pathophysiological blood flow shear stress conditions, ranging from normotensive to hypertensive forces. Our study uncovers a noteworthy observation wherein endothelial cells exposed to high shear stress demonstrate a decrease in the epigenetic marks H3K4ac and H3K27ac, accompanied by significant alterations in the levels of HDAC (histone deacetylase) proteins. Moreover, we demonstrate a negative regulatory effect of increased shear stress on HOXA13 gene expression and a concomitant increase in the expression of the long noncoding RNA, HOTTIP, suggesting a direct association with the suppression of HOXA13. Collectively, these findings represent the first evidence of the role of histone-related epigenetic modifications in modulating chromatin compaction during mechanosignaling of endothelial cells in response to elevated shear stress forces. Additionally, our results highlight the importance of understanding the physiological role of HOXA13 in vascular biology and hypertensive patients, emphasizing the potential for developing small molecules to modulate its activity. These findings warrant further preclinical investigations and open new avenues for therapeutic interventions targeting epigenetic mechanisms in hypertensive conditions.

Tricarboxylic Acid Cycle Metabolite-Coordinated Biohydrogels Augment Cranial Bone Regeneration Through Neutrophil-Stimulated Mesenchymal Stem Cell Recruitment and Histone Acetylation-Mediated Osteogenesis

Cranial bone defects remain a major clinical challenge, increasing patients' life burdens. Tricarboxylic acid (TCA) cycle metabolites play crucial roles in facilitating bone tissue regeneration. However, the development of TCA cycle metabolite-modified biomimetic grafts for skull bone regeneration still needs to be improved. The mechanism underlying the release of TCA cycle metabolites from biomaterials in regulating immune responses and mesenchymal stem cell (MSC) fate (migration and differentiation) remains unknown. Herein, this work constructs biomimetic hydrogels composed of gelatin and chitosan networks covalently cross-linked by genipin (CGG hydrogels). A series of TCA cycle metabolite-coordinated CGG hydrogels with strong mechanical and antiswelling performances are subsequently developed. Remarkably, the citrate (Na3Cit, Cit)-coordinated CGG hydrogels (CGG-Cit hydrogels) with the highest mechanical modulus and strength significantly promote skull bone regeneration in rat and murine cranial defects. Mechanistically, using a transgenic mouse model, bulk RNA sequencing, and single-cell RNA sequencing, this work demonstrates that CGG-Cit hydrogels promote Gli1+ MSC migration via neutrophil-secreted oncostatin M. Results also indicate that citrate improves osteogenesis via enhanced histone H3K9 acetylation on osteogenic master genes. Taken together, the immune microenvironment- and MSC fate-regulated CGG-Cit hydrogels represent a highly efficient and facile approach toward skull bone tissue regeneration with great potential for bench-to-bedside translation.

Changes in bone mineral density in Down syndrome individuals: a systematic review and meta-analysis

Data evaluating changes in bone mineral density (BMD) in Down syndrome (DS) individuals remains controversial. Therefore, we conducted a systematic review and meta-analysis to better understand associations between BMD and DS. A systematic literature search of PubMed, EMBASE, Web of Science, and the Cochrane Library up until 1st January 2021 was conducted. We used the keywords "bone mineral density" and "Down Syndrome." Fifteen studies were included. Overall, our results showed a significant decrease in BMD of total body (TB BMD) [MD =  - 0.18; 95% CI (- 0.23 and - 0.12), P < 0.00001, I2 = 89%], total hip (TH BMD) [MD =  - 0.12; 95% CI (- 0.15 and - 0.10), P < 0.00001, I2 = 0%], lumbar spine (LS BMD) [MD =  - 0.12; 95% CI (- 0.14 and - 0.09), P < 0.00001, I2 = 18%], and femoral neck (FN BMD) [MD =  - 0.08; 95% CI (- 0.10 and - 0.06), P < 0.00001, I2 = 0%] in DS individuals when compared with controls. Moreover, the volumetric BMD of lumbar spine (LS vBMD) [MD =  - 0.01; 95% CI (- 0.02 and - 0.01), P = 0.0004, I2 = 19%] also showed a decreasing tendency while the volumetric BMD of the femoral neck (FN vBMD) [MD = 0.01; 95% CI (0.00 and 0.02), P = 0.02, I2 = 0%] was elevated in DS individuals versus controls. These findings demonstrated that individuals with DS had a decreased total and regional (TH, LS, and FN) BMD when compared with the general population. Additionally, when BMD was adjusted for skeletal volume, LS vBMD was also lower, while FN vBMD was elevated in DS individuals versus controls.

Recent advances in the epigenetics of bone metabolism

Osteoporosis is a common form of metabolic bone disease that is costly to treat and is primarily diagnosed on the basis of bone mineral density. As the influences of genetic lesions and environmental factors are increasingly studied in the pathological development of osteoporosis, regulated epigenetics are emerging as the important pathogenesis mechanisms in osteoporosis. Recently, osteoporosis genome-wide association studies and multi-omics technologies have revealed that susceptibility loci and the misregulation of epigenetic modifiers are key factors in osteoporosis. Over the past decade, extensive studies have demonstrated epigenetic mechanisms, such as DNA methylation, histone/chromatin modifications, and non-coding RNAs, as potential contributing factors in osteoporosis that affect disease initiation and progression. Herein, we review recent advances in epigenetics in osteoporosis, with a focus on exploring the underlying mechanisms and potential diagnostic/prognostic biomarker applications for osteoporosis.

Exendin-4 may improve type 2 diabetes by modulating the epigenetic modifications of pancreatic histone H3 in STZ-induced diabetic C57BL/6 J mice

Type 2 diabetes (T2D) is a complicated systemic disease that might be improved by exendin-4, although the epigenetic role remains unclear. In the current study, C57BL/6 J mice were used to generate a T2D model, followed by treatment with exendin-4 (10 μg/kg). Histone H3K9 and H3K23 acetylation, H3K4 mono-methylation, and H3K9 di-methylation were explored by western blot analysis of pancreatic histone extracts. Real-time polymerase chain reaction (PCR) was used to examine the expression levels of pancreatic beta cell development-related genes, and chromatin immunoprecipitation (ChIP) was applied to analyze H3 and H3K9 acetylation, H3K4 mono-methylation, and H3K9 di-methylation in the promoter region of the pancreatic and duodenal homeobox 1 (Pdx1) gene. The results showed that total H3K9 di-methylation and H3K9 and H3K23 acetylation increased in pancreatic tissues of diabetic mice, whereas H3K4 mono-methylation was reduced. All of these changes could be abrogated by treatment with exendin-4. Our data indicated that T2D progression might be improved by exendin-4 treatment through the reversal of global pancreatic histone H3K9 and H3K23 acetylation, H3K4 mono-methylation, and H3K9 di-methylation. A better understanding of these epigenetic alterations may, therefore, lead to novel therapeutic strategies for T2D.

SENP3-Mediated PPARγ2 DeSUMOylation in BM-MSCs Potentiates Glucocorticoid-Induced Osteoporosis by Promoting Adipogenesis and Weakening Osteogenesis

Glucocorticoid-induced osteoporosis (GIOP) is the most common secondary osteoporosis and reduced bone formation was the main pathological change in GIOP. Our previous studies have shown that there was an imbalance between adipogenic and osteogenic differentiation in GIOP BM-MSCs and peroxisome proliferator-activated receptor γ2 (PPARγ2) played a vital role in this disorders. Here, we reported that there was an increase in ROS level and SENP3 expression in Dex-induced osteoporotic BM-MSCs, and enhanced adipogenesis and weakened osteogenesis in osteoporotic BM-MSCs might be caused by upregulated SENP3. Then we found that SENP3 de-SUMOylated PPARγ2 on K107 site to potentiate adipogenesis and weaken osteogenesis. These results may provide new strategy and target in the clinical diagnosis and treatment of GIOP.

The Chromatin Regulator Ankrd11 Controls Palate and Cranial Bone Development

Epigenetic and chromatin regulation of craniofacial development remains poorly understood. Ankyrin Repeat Domain 11 (ANKRD11) is a chromatin regulator that has previously been shown to control neural stem cell fates via modulation of histone acetylation. ANKRD11 gene variants, or microdeletions of the 16q24.3 chromosomal region encompassing the ANKRD11 gene, cause KBG syndrome, a rare autosomal dominant congenital disorder with variable neurodevelopmental and craniofacial involvement. Craniofacial abnormalities include a distinct facial gestalt, delayed bone age, tooth abnormalities, delayed fontanelle closure, and frequently cleft or submucosal palate. Despite this, the dramatic phenotype and precise role of ANKRD11 in embryonic craniofacial development remain unexplored. Quantitative analysis of 3D images of KBG syndromic subjects shows an overall reduction in the size of the middle and lower face. Here, we report that mice with heterozygous deletion of Ankrd11 in neural crest cells (Ankrd11nchet) display a mild midfacial hypoplasia including reduced midfacial width and a persistent open fontanelle, both of which mirror KBG syndrome patient facial phenotypes. Mice with a homozygous Ankrd11 deletion in neural crest cells (Ankrd11ncko) die at birth. They show increased severity of several clinical manifestations described for KBG syndrome, such as cleft palate, retrognathia, midfacial hypoplasia, and reduced calvarial growth. At E14.5, Ankrd11 expression in the craniofacial complex is closely associated with developing bony structures, while expression at birth is markedly decreased. Conditional deletion of Ankrd11 leads to a reduction in ossification of midfacial bones, with several ossification centers failing to expand and/or fuse. Intramembranous bones show features of delayed maturation, with bone remodeling severely curtailed at birth. Palatal shelves remain hypoplastic at all developmental stages, with a local reduction in proliferation at E13.5. Our study identifies Ankrd11 as a critical regulator of intramembranous ossification and palate development and suggests that Ankrd11nchet and Ankrd11ncko mice may serve as pre-clinical models for KBG syndrome in humans.

Epigenetic Control of Osteogenic Lineage Commitment

Within the eukaryotic nucleus the genomic DNA is organized into chromatin by stably interacting with the histone proteins as well as with several other nuclear components including non-histone proteins and non-coding RNAs. Together these interactions distribute the genetic material into chromatin subdomains which can exhibit higher and lower compaction levels. This organization contributes to differentially control the access to genomic sequences encoding key regulatory genetic information. In this context, epigenetic mechanisms play a critical role in the regulation of gene expression as they modify the degree of chromatin compaction to facilitate both activation and repression of transcription. Among the most studied epigenetic mechanisms we find the methylation of DNA, ATP-dependent chromatin remodeling, and enzyme-mediated deposition and elimination of post-translational modifications at histone and non-histone proteins. In this mini review, we discuss evidence that supports the role of these epigenetic mechanisms during transcriptional control of osteoblast-related genes. Special attention is dedicated to mechanisms of epigenetic control operating at the Runx2 and Sp7 genes coding for the two principal master regulators of the osteogenic lineage during mesenchymal stem cell commitment.

Epigenetic Regulators of Mesenchymal Stem/Stromal Cell Lineage Determination

PURPOSE OF REVIEW

Although many signalling pathways have been discovered to be essential in mesenchymal stem/stromal (MSC) differentiation, it has become increasingly clear in recent years that epigenetic regulation of gene transcription is a vital component of lineage determination, encompassing diet, lifestyle and parental influences on bone, fat and cartilage development.

RECENT FINDINGS

This review discusses how specific enzymes that modify histone methylation and acetylation or DNA methylation orchestrate the differentiation programs in lineage determination of MSC and the epigenetic changes that facilitate development of bone related diseases such as osteoporosis. The review also describes how environmental factors such as mechanical loading influence the epigenetic signatures of MSC, and how the use of chemical agents or small peptides can regulate epigenetic drift in MSC populations during ageing and disease. Epigenetic regulation of MSC lineage commitment is controlled through changes in enzyme activity, which modifies DNA and histone residues leading to alterations in chromatin structure. The co-ordinated epigenetic regulation of transcriptional activation and repression act to mediate skeletal tissue homeostasis, where deregulation of this process can lead to bone loss during ageing or osteoporosis.

Vulpinic Acid Controls Stem Cell Fate toward Osteogenesis and Adipogenesis

Vulpinic acid, a naturally occurring methyl ester of pulvinic acid, has been reported to exert anti-fungal, anti-cancer, and anti-oxidative effects. However, its metabolic action has not been implicated yet. Here, we show that vulpinic acid derived from a mushroom, Pulveroboletus ravenelii controls the cell fate of mesenchymal stem cells and preadipocytes by inducing the acetylation of histone H3 and α-tubulin, respectively. The treatment of 10T1/2 mesenchymal stem cells with vulpinic acid increased the expression of Wnt6, Wnt10a, and Wnt10b, which led to osteogenesis inhibiting the adipogenic lineage commitment, through the upregulation of H3 acetylation. By contrast, treatment with vulpinic acid promoted the terminal differentiation of 3T3-L1 preadipocytes into mature adipocytes. In this process, the increase in acetylated tubulin was accompanied, while acetylated H3 was not altered. As excessive generation of adipocytes occurs, the accumulation of lipid drops was not concentrated, but dispersed into a number of adipocytes. Consistently, the expressions of lipolytic genes were upregulated and inflammatory factors were downregulated in adipocytes exposed to vulpinic acid during adipogenesis. These findings reveal the multiple actions of vulpinic acid in two stages of differentiation, promoting the osteogenesis of mesenchymal stem cells and decreasing hypertrophic adipocytes, which can provide experimental evidence for the novel metabolic advantages of vulpinic acid.

Regulation of Breast Cancer-Induced Osteoclastogenesis by MacroH2A1.2 Involving EZH2-Mediated H3K27me3

Breast cancer cells relocate to bone and activate osteoclast-induced bone resorption. Soluble factors secreted by breast cancer cells trigger a cascade of events that stimulate osteoclast differentiation in the bone microenvironment. MacroH2A is a unique histone variant with a C-terminal non-histone domain and plays a crucial role in modulating chromatin organization and gene transcription. Here, we show that macroH2A1.2, one of the macroH2A isoforms, has an intrinsic ability to inhibit breast cancer-derived osteoclastogenesis. This repressive effect requires macroH2A1.2-dependent attenuation of expression and secretion of lysyl oxidase (LOX) in breast cancer cells. Furthermore, our mechanistic studies reveal that macroH2A1.2 physically and functionally interacts with the histone methyltransferase EZH2 and elevates H3K27me3 levels to keep LOX gene in a repressed state. Collectively, this study unravels a role for macroH2A1.2 in regulating osteoclastogenic potential of breast cancer cells, suggesting possibilities for developing therapeutic tools to treat osteolytic bone destruction.

Ubiquitylomes Analysis of the Whole blood in Postmenopausal Osteoporosis Patients and healthy Postmenopausal Women

Objectives

To determine the mechanisms of ubiquitination in postmenopausal osteoporosis and investigate the ubiquitinated spectrum of novel targets between healthy postmenopausal women and postmenopausal osteoporosis patients, we performed ubiquitylome analysis of the whole blood of postmenopausal women and postmenopausal osteoporosis patients.

Methods

To obtain a more comprehensive understanding of the postmenopausal osteoporosis mechanism, we performed a quantitative assessment of the ubiquitylome in whole blood from seven healthy postmenopausal women and seven postmenopausal osteoporosis patients using high‐performance liquid chromatography fractionation, affinity enrichment, and liquid chromatography coupled to tandem mass spectrometry (LC‐MS/MS). To examine the ubiquitylome data, we performed enrichment analysis using an ubiquitylated amino acid motif, Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway.

Results

Altogether, 133 ubiquitinated sites and 102 proteins were quantified. A difference of more than 1.2 times is considered significant upregulation and less than 0.83 significant downregulation; 32 ubiquitinated sites on 25 proteins were upregulated and 101 ubiquitinated sites on 77 proteins were downregulated. These quantified proteins, both with differently ubiquitinated sites, participated in various cellular processes, such as cellular processes, biological regulation processes, response to stimulus processes, single‐organism and metabolic processes. Ubiquitin conjugating enzyme activity and ubiquitin‐like protein conjugating enzyme activity were the most highly enriched in molecular function of upregulated sites with corresponding proteins, but they were not enriched in downregulated in sites with corresponding proteins. The KEGG pathways analysis of quantified proteins with differentiated ubiquitinated sites found 13 kinds of molecular interactions and functional pathways, such as glyoxylate and decarboxylate metabolism, dopaminergic synapse, ubiquitin‐mediated proteolysis, salivary secretion, coagulation and complement cascades, Parkinson's disease, and hippo signaling pathway. In addition, hsa04120 ubiquitin‐mediated proteolysis was the most highly enriched in proteins with upregulated sites, hsa04610 complement and coagulation cascades was the most highly enriched in proteins with downregulated ubiquitinated sites, and hsa04114 Oocyte meiosis was the most highly enriched among all differential proteins.

Conclusion

Our study expands the understanding of the spectrum of novel targets that are differentially ubiquitinated in whole blood from healthy postmenopausal women and postmenopausal osteoporosis patients. The findings will contribute toward our understanding of the underlying proteostasis pathways in postmenopausal osteoporosis and the potential identification of diagnostic biomarkers in whole blood.

Single-cell high-content imaging parameters predict functional phenotype of cultured human bone marrow stromal stem cells

Cultured human bone marrow stromal (mesenchymal) stem cells (hBM-MSCs) are heterogenous cell populations exhibiting variable biological properties. Quantitative high-content imaging technology allows identification of morphological markers at a single cell resolution that are determinant for cellular functions. We determined the morphological characteristics of cultured primary hBM-MSCs and examined their predictive value for hBM-MSC functionality. BM-MSCs were isolated from 56 donors and characterized for their proliferative and differentiation potential. We correlated these data with cellular and nuclear morphological features determined by Operetta; a high-content imaging system. Cell area, cell geometry, and nucleus geometry of cultured hBM-MSCs exhibited significant correlation with expression of hBM-MSC membrane markers: ALP, CD146, and CD271. Proliferation capacity correlated negatively with cell and nucleus area and positively with cytoskeleton texture features. In addition, in vitro differentiation to osteoblasts as well as in vivo heterotopic bone formation was associated with decreased ratio of nucleus width to length. Multivariable analysis applying a stability selection procedure identified nuclear geometry and texture as predictors for hBM-MSCs differentiation potential to osteoblasts or adipocytes. Our data demonstrate that by employing a limited number of cell morphological characteristics, it is possible to predict the functional phenotype of cultured hBM-MSCs and thus can be used as a screening test for "quality" of hBM-MSCs prior their use in clinical protocols.

The emerging role of microRNAs in bone remodeling and its therapeutic implications for osteoporosis

Osteoporosis, a common and multifactorial disease, is influenced by genetic factors and environments. However, the pathogenesis of osteoporosis has not been fully elucidated yet. Recently, emerging evidence suggests that epigenetic modifications may be the underlying mechanisms that link genetic and environmental factors with increased risks of osteoporosis and bone fracture. MicroRNA (miRNA), a major category of small noncoding RNA with 20–22 bases in length, is recognized as one important epigenetic modification. It can mediate post-transcriptional regulation of target genes with cell differentiation and apoptosis. In this review, we aimed to profile the role of miRNA in bone remodeling and its therapeutic implications for osteoporosis. A deeper insight into the role of miRNA in bone remodeling and osteoporosis can provide unique opportunities to develop a novel diagnostic and therapeutic approach of osteoporosis.

Systemic tracking of diagnostic function modules for post-menopausal osteoporosis in a differential co-expression network view

Post-menopausal osteoporosis is one of the most common bone diseases in women. The aim of the present study was to predict the diagnostic function modules from a differential co-expression gene network in order to enhance the current understanding of the biological processes and to promote the early prevention and intervention of post-menopausal osteoporosis. The diagnostic function modules were extracted from a differential co-expression network by the established protein-protein interaction (PPI) network analysis. First, significant genes were identified from the differential co-expression network, which were regarded as seed genes. Starting from the seed genes, the sub-networks in this disease, referred to as diagnostic function modules, were exhaustively searched and prioritized through a snowball sampling strategy to identify genes to accurately predict clinical outcomes. In addition, crucial function inference was performed for each diagnostic function module. Based on the microarray and PPI data, the differential co-expression network was constructed, which contained 1,607 genes and 4,197 interactions. A total of 110 seed genes were identified, and nine diagnostic modules that accurately distinguished post-menopausal osteoporosis from healthy controls were screened out from these seed genes. The diagnostic modules may be associated with five functional pathways with emphasis on metabolism. A total of nine diagnostic functional modules screened in the present study may be considered as potential targets for predicting the clinical outcomes of post-menopausal osteoporosis, and may contribute to the early diagnosis and therapy of osteoporosis.

Epigenetics and Bone Remodeling

PURPOSE OF REVIEW

Bone remodeling is a diverse field of study with many direct clinical applications; past studies have implicated epigenetic alterations as key factors of both normal bone tissue development and function and diseases of pathologic bone remodeling. The purpose of this article is to review the most important recent advances that link epigenetic changes to the bone remodeling field.

RECENT FINDINGS

Epigenetics describes three major phenomena: DNA modification via methylation, histone side chain modifications, and short non-coding RNA sequences which work in concert to regulate gene transcription in a heritable fashion. Recent findings include the role of DNA methylation changes of Wnt, RANK/RANKL, and other key signaling pathways, epigenetic regulation of osteoblast and osteoclast differentiation, and others. Although much work has been done, much is still unknown. Future epigenome-wide studies should focus on extending the tissue coverage, integrating multiple epigenetic analyses with transcriptome data, and working to uncover epigenetic changes linked with early events in aberrant bone remodeling.

PHF20 positively regulates osteoblast differentiation via increasing the expression and activation of Runx2 with enrichment of H3K4me3

Plant homeodomain finger protein 20 (PHF20), a methyl lysine effector protein, is a component MOF-NSL lysine acetyltranferase complex. Global deletion of PHF20 has shown spinal bone defects and reduced skeletal formation. However, the molecular basis of PHF20 involved in skeletal development has not been elucidated yet. The objective of this study was to determine the role of PHF20 in osteoblast differentiation and mineralization. Expression of PHF20 was gradually increased during osteoblast differentiation. Overexpression of PHF20 enhanced ALP activity and mineralized nodule formation as well as the expression of osteogenic markers including Runx2. In contrast, inhibition of PHF20 expression reduced osteoblast differentiation and mineralization. Mechanistically, PHF20 increased the promoter activity of osteogenic genes including Og2, Alp, and Bsp through direct association with Runx2. Moreover, PHF20 increased the enrichment of H3K4me3 on the promoter of Runx2 followed by increased Runx2 promoter activity. Interestingly, Bix-01294, a histone methylation inhibitor, decreased mineralized nodule formation through decreasing the levels of H3K4me3 and Runx2. Overexpression of PHF20 restored the Bix-01294 effects. Taken together, these results indicate that methyl lysine-binding protein PHF20 might be a novel regulator of osteoblast differentiation.

Histone demethylase UTX counteracts glucocorticoid deregulation of osteogenesis by modulating histone-dependent and -independent pathways

Excess glucocorticoid administration impairs osteogenic activities, which raises the risk of osteoporotic disorders. Epigenetic methylation of DNA and histone regulates the lineage commitment of progenitor cells. This study was undertaken to delineate the actions of histone lysine demethylase 6a (UTX) with regard to the glucocorticoid impediment of osteogenic differentiation. Osteogenic progenitor cells responded to supraphysiological glucocorticoid by elevating CpG dinucleotide methylation proximal to transcription start sites within Runx2 and osterix promoters and Wnt inhibitor Dickkopf-1 (Dkk1) expression concomitant with low UTX expression. 5'-Aza-deoxycystidine demethylation of Runx2 and osterix promoters abolished the glucocorticoid inhibition of mineralized matrix accumulation. Gain of UTX function attenuated the glucocorticoid-induced loss of osteogenic differentiation, whereas UTX silencing escalated adipogenic gene expression and adipocyte formation. UTX sustained osteogenic gene transcription through maintaining its occupancy to Runx2 and osterix promoters. It also mitigated the trimethylation of histone 3 at lysine 27 (H3K27me3), which reduced H3K27me3 enrichment to Dkk1 promoter and thereby lowered Dkk1 transcription. Modulation of β-catenin and Dkk1 actions restored UTX signaling in glucocorticoid-stressed cells. In vivo, UTX inhibition by exogenous methylprednisolone and GSK-J4 administration, an effect that disturbed H3K27me3, β-catenin, Dkk1, Runx2, and osterix levels, exacerbated trabecular microarchitecture loss and marrow adiposity. Taken together, glucocorticoid reduction of UTX function hindered osteogenic differentiation. Epigenetic hypomethylation of osteogenic transcription factor promoters and H3K27 contributed to the UXT alleviation of Dkk1 transcription and osteogenesis in glucocorticoid-stressed osteogenic progenitor cells. Control of UTX action has an epigenetic perspective of curtailing glucocorticoid impairment of osteogenic differentiation and bone mass.

KEY MESSAGES

UTX attenuates glucocorticoid deregulation of osteogenesis and adipogenesis. UTX reduces Runx2 promoter methylation and H3K27me3 enrichment in the Dkk1 promoter. β-catenin and Dkk1 modulate the glucocorticoid inhibition of UTX signaling. UTX inhibition exacerbates bone mass, trabecular microstructure and fatty marrow. UTX signaling is indispensable in fending off glucocorticoid-impaired osteogenesis.

Polycomb PRC2 complex mediates epigenetic silencing of a critical osteogenic master regulator in the hippocampus

During hippocampal neuron differentiation, the expression of critical inducers of non-neuronal cell lineages must be efficiently silenced. Runx2 transcription factor is the master regulator of mesenchymal cells responsible for intramembranous osteoblast differentiation and formation of the craniofacial bone tissue that surrounds and protects the central nervous system (CNS) in mammalian embryos. The molecular mechanisms that mediate silencing of the Runx2 gene and its downstream target osteogenic-related genes in neuronal cells have not been explored. Here, we assess the epigenetic mechanisms that mediate silencing of osteoblast-specific genes in CNS neurons. In particular, we address the contribution of histone epigenetic marks and histone modifiers on the silencing of the Runx2/p57 bone-related isoform in rat hippocampal tissues at embryonic to adult stages. Our results indicate enrichment of repressive chromatin histone marks and of the Polycomb PRC2 complex at the Runx2/p57 promoter region. Knockdown of PRC2 H3K27-methyltransferases Ezh2 and Ezh1, or forced expression of the Trithorax/COMPASS subunit Wdr5 activates Runx2/p57 mRNA expression in both immature and mature hippocampal cells. Together these results indicate that complementary epigenetic mechanisms progressively and efficiently silence critical osteoblastic genes during hippocampal neuron differentiation.

IL-6 Contributes to the Defective Osteogenesis of Bone Marrow Stromal Cells from the Vertebral Body of the Glucocorticoid-Induced Osteoporotic Mouse

Osteoporosis is one of the most prevalent skeletal system diseases. It is characterized by a decrease in bone mass and microarchitectural changes in bone tissue that lead to an attenuation of bone resistance and susceptibility to fracture. Vertebral fracture is by far the most prevalent osteoporotic fracture. In the musculoskeletal system, osteoblasts, originated from bone marrow stromal cells (BMSC), are responsible for osteoid synthesis and mineralization. In osteoporosis, BMSC osteogenic differentiation is defective. However, to date, what leads to the defective BMSC osteogenesis in osteoporosis remains an open question. In the current study, we made attempts to answer this question. A mouse model of glucocorticoid-induced osteoporosis (GIO) was established and BMSC were isolated from vertebral body. The impairment of osteogenesis was observed in BMSC of osteoporotic vertebral body. The expression profiles of thirty-six factors, which play important roles in bone metabolisms, were compared through antibody array between normal and osteoporotic BMSC. Significantly higher secretion level of IL-6 was observed in osteoporotic BMSCs compared with normal control. We provided evidences that IL-6 over-secretion impaired osteogenesis of osteoporotic BMSC. Further, it was observed that β-catenin activity was inhibited in response to IL-6 over-secretion. More importantly, in vivo administration of IL-6 neutralizing antibody was found to be helpful to rescue the osteoporotic phenotype of mouse vertebral body. Our study provides a deeper insight into the pathophysiology of osteoporosis and identifies IL-6 as a promising target for osteoporosis therapy.