Runt-Related Transcription Factor 2 Induction During Differentiation of Wharton's Jelly Mesenchymal Stem Cells to Osteoblasts Is Regulated by Jumonji AT-Rich Interactive Domain 1B Histone Demethylase

Molecular mechanism of miR-203a targeting Runx2 to regulate thiram induced-chondrocyte development

Thiram is a kind of organic compound, which is commonly used for sterilization, insecticidal and deodorization in daily life. Its toxicology has been broadly studied. Recently, more and more microRNAs have been shown to participate in the regulation of cartilage development. However, the potential mechanism by which microRNA regulates chondrocyte growth is still unclear. Our experiments have demonstrated that thiram can hamper chondrocytes development and cause a significant increase in miR-203a content in vitro and in vivo trials. miR-203a mimic significantly decrease in mRNA and protein expression of Wnt4, Runx2, COL2A1, β-catenin and ALP, and significantly enhance the mRNA and protein levels of GSK-3β. It has been observed that overexpression of miR-203a hindered chondrocytes development. In addition, Runx2 was confirmed to be a direct target of miR-203a by dual luciferase report gene assay. Transfection of si-Runx2 into chondrocytes reveals that significant downregulation of genes is associated with cartilage development. Overall, these results suggest that overexpression of miR-203a inhibits the expression of Runx2. These findings are conducive to elucidate the mechanism of chondrocytes dysplasia induced by thiram and provide new research ideas for the toxicology of thiram.

Peptide derived from stromal cell-derived factor 1δ enhances the in vitro expression of osteogenic proteins via bone marrow stromal cell differentiation and promotes bone formation in in vivo models

Mesenchymal stem cells (MSCs) rely on chemokines and chemokine receptors to execute their biological and physiological functions. Stromal cell-derived factor-1 (SDF-1) is upregulated in injury sites, where it acts as a chemotactic agent, attracting CXCR4-expressing MSCs, which play a pivotal role in the healing and regeneration of tissue throughout the body. Furthermore, SDF-1 expression has been observed in regions experiencing inflammation-induced bone destruction and fracture sites. In this study, we identified a novel peptide called bone-forming peptide-5 (BFP-5), derived from SDF-1δ, which can promote the osteogenesis of MSCs as well as bone formation and healing. Multipotent bone marrow stromal cells treated with BFP-5 showed enhanced alizarin red S staining and higher alkaline phosphatase (ALP) activity. Moreover, ALP and osterix proteins were more abundantly expressed when cells were treated with BFP-5 than SDF-1α. Histology and microcomputed tomography data at 12 weeks demonstrated that both rabbit and goat models transplanted with polycaprolactone (PCL) scaffolds coated with BFP-5 showed significantly greater bone formation than animals transplanted with PCL scaffolds alone. These findings suggest that BFP-5 could be useful in the development of related therapies for conditions associated with bones.

The Molecular Regulatory Mechanism in Multipotency and Differentiation of Wharton's Jelly Stem Cells

Wharton's jelly-derived mesenchymal stem cells (WJ-MSCs) are isolated from Wharton's jelly tissue of umbilical cords. They possess the ability to differentiate into lineage cells of three germ layers. WJ-MSCs have robust proliferative ability and strong immune modulation capacity. They can be easily collected and there are no ethical problems associated with their use. Therefore, WJ-MSCs have great tissue engineering value and clinical application prospects. The identity and functions of WJ-MSCs are regulated by multiple interrelated regulatory mechanisms, including transcriptional regulation and epigenetic modifications. In this article, we summarize the latest research progress on the genetic/epigenetic regulation mechanisms and essential signaling pathways that play crucial roles in pluripotency and differentiation of WJ-MSCs.

Transgenerational bone toxicity in F3 medaka (Oryzias latipes) induced by ancestral benzo[a]pyrene exposure: Cellular and transcriptomic insights

Benzo[a]pyrene (BaP), a ubiquitous pollutant, raises environmental health concerns due to induction of bone toxicity in the unexposed offspring. Exposure of F0 ancestor medaka (Oryzias latipes) to 1 µg/L BaP for 21 days causes reduced vertebral bone thickness in the unexposed F3 male offspring. To reveal the inherited modifications, osteoblast (OB) abundance and molecular signaling pathways of transgenerational BaP-induced bone thinning were assessed. Histomorphometric analysis showed a reduction in OB abundance. Analyses of the miRNA and mRNA transcriptomes revealed the dysregulation of Wnt signaling (frzb/ola-miR-1-3p, sfrp5/ola-miR-96-5p/miR-455-5p) and bone morphogenetic protein (Bmp) signaling (bmp3/ola-miR-96-5p/miR-181b-5p/miR-199a-5p/miR-205-5p/miR-455-5p). Both pathways are major indicators of impaired bone formation, while the altered Rank signaling in osteoclasts (c-fos/miR-205-5p) suggests a potentially augmented bone resorption. Interestingly, a typical BaP-responsive pathway, the Nrf2-mediated oxidative stress response (gst/ola-miR-181b-5p/miR-199a-5p/miR-205), was also affected. Moreover, mRNA levels of epigenetic modification enzymes (e.g., hdac6, hdac7, kdm5b) were found dysregulated. The findings indicated that epigenetic factors (e.g., miRNAs, histone modifications) may directly regulate the expression of genes associated with transgenerational BaP bone toxicity and warrants further studies. The identified candidate genes and miRNAs may serve as potential biomarkers for BaP-induced bone disease and as indicators of historic exposures in wild fish for conservation purposes.

Temporal Modulation of DNA Methylation and Gene Expression in Monolayer and 3D Spheroids of Dental Pulp Stem Cells during Osteogenic Differentiation: A Comparative Study

BACKGROUND

Human mesenchymal stem cells are being used for various regenerative applications in past decades. This study chronicled a temporal profile of the transcriptional pattern and promoter methylation status of the osteogenic related gene in dental pulp stem cells (DPSCs) derived from 3-dimensional spheroid culture (3D) vis a vis 2-dimensional (2D) monolayer culture upon osteogenic induction.

METHODS

Biomimetic properties of osteogenesis were determined by alkaline phosphatase assay and alizarin red staining. Gene expression and promoter methylation status of osteogenic genes such as runt-related transcription factor-2, collagen1α1, osteocalcin (OCN), and DLX5 (distal-homeobox) were performed by qPCR assay and bisulfite sequencing, respectively. Furthermore, µ-Computed tomography (micro-CT) was performed to examine the new bone formation in critical-sized rat calvarial bone defect model.

RESULTS

Our results indicated a greater inclination of spheroid culture-derived DPSCs toward osteogenic lineage than the monolayer culture. The bisulfite sequencing of the promoter region of osteogenic genes revealed sustenance of low methylation levels in DPSCs during the progression of osteogenic differentiation. However, the significant difference in the methylation pattern between 2D and 3D derived DPSCs were identified only for OCN gene promoter. We observed differences in the mRNA expression pattern of epigenetic writers such as DNA methyltransferases (DNMTs) and methyl-cytosine dioxygenases (TET) between the two culture conditions. Further, the DPSC spheroids showed enhanced new bone formation ability in an animal model of bone defect compared to the cells cultivated in a 2D platform which further substantiated our in-vitro observations.

CONCLUSION

The distinct cellular microenvironment induced changes in DNA methylation pattern and expression of epigenetic regulators such as DNMTs and TETs genes may lead to increase expression of osteogenic markers in 3D spheroid culture of DPSCs which make DPSCs spheroids suitable for osteogenic regeneration compared to monolayers.

Umbilical cord mesenchymal stromal cells-from bench to bedside

In recent years, mesenchymal stromal cells (MSCs) have generated a lot of attention due to their paracrine and immuno-modulatory properties. mesenchymal stromal cells derived from the umbilical cord (UC) are becoming increasingly recognized as having increased therapeutic potential when compared to mesenchymal stromal cells from other sources. The purpose of this review is to provide an overview of the various compartments of umbilical cord tissue from which mesenchymal stromal cells can be isolated, the differences and similarities with respect to their regenerative and immuno-modulatory properties, as well as the single cell transcriptomic profiles of in vitro expanded and freshly isolated umbilical cord-mesenchymal stromal cells. In addition, we discuss the therapeutic potential and biodistribution of umbilical cord-mesenchymal stromal cells following systemic administration while providing an overview of pre-clinical and clinical trials involving umbilical cord-mesenchymal stromal cells and their associated secretome and extracellular vesicles (EVs). The clinical applications of umbilical cord-mesenchymal stromal cells are also discussed, especially in relation to obstacles and potential solutions for their effective translation from bench to bedside.

The expression and clinical significance of signal transducer and activator of transcription 3, tumor necrosis factor α induced protein 8-like 2, and runt-related transcription factor 1 in breast cancer patients

BACKGROUND

This study explored the expression and clinical significance of signal transducer and activator of transcription 3 (STAT3), tumor necrosis factor α induced protein 8-like 2 (TIPE2), and runt-related transcription factor 1 (RUNX1) in breast cancer tissue.

METHODS

From October 2014 to October 2017, 68 breast cancer patients (68 breast cancer tissue specimens) who underwent a radical mastectomy in our hospital were set as the observation group and the corresponding normal tissue 3 cm away from the cancer tissue was selected as the control group. The expression levels of STAT3, TIPE2, and RUNX1 in the two groups were compared via immunohistochemical staining. Multiple logistic regression was then used to analyze the related risk factors affecting the 2-year prognosis of breast cancer patients. The receiver operating characteristic (ROC) curve was then plotted and the area under the ROC curve was calculated. The predictive values of STAT3, TIPE2, and RUNX1, and the predictive value of the three transcription factors combined on the 2-year prognostic survival of breast cancer patients were determined.

RESULTS

(I) In the observation group, the positive expression of STAT3 and the negative expression of TIPE2 and RUNX1 were significantly higher than those in the control group (P<0.05). (II) Of the 68 patients, 51 survived within 2 years and 17 patients died. Positive STAT3 expression, negative TIPE2 expression, negative RUNX1 expression, poor histological differentiation, TNM stage III-IV, and distant metastasis were all identified as factors that can affect the 2-year prognosis of breast cancer patients (P<0.05). (III) The ROC curve analysis examining the 2-year prognostic survival of breast cancer patients showed that the area under the curve achieved the largest value when the predictive values of STAT3, TIPE2, RUNX1 were combined.

CONCLUSIONS

The levels of STAT3, TIPE2, and RUNX1 expression in breast cancer tissues were significantly different from that in adjacent normal tissues. This suggested that the combined detection of STAT3, TIPE2, and RUNX1 may improve the rate of early breast cancer diagnosis. Furthermore, STAT3, TIPE2, and RUNX1 may be useful in evaluating the prognosis of the patients with breast cancer.

Metabolism and chromatin: A dynamic duo that regulates development and ageing: Elucidating the metabolism-chromatin axis in bone-marrow mesenchymal stem cell fate decisions

Bone-marrow mesenchymal stem cell (BM-MSC) proliferation and lineage commitment are under the coordinated control of metabolism and epigenetics; the MSC niche contains low oxygen, which is an important determinant of the cellular metabolic state. In turn, metabolism drives stem cell fate decisions via alterations of the chromatin landscape. Due to the fundamental role of BM-MSCs in the development of adipose tissue, bones and cartilage, age-associated changes in metabolism and the epigenome perturb the balance between stem cell proliferation and differentiation leading to stem cell depletion, fat accumulation and bone-quality related diseases. Therefore, understanding the dynamics of the metabolism-chromatin interplay is crucial for maintaining the stem cell pool and delaying the development and progression of ageing. This review summarizes the current knowledge on the role of metabolism in stem cell identity and highlights the impact of the metabolic inputs on the epigenome, with regards to stemness and pluripotency.

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.

GPR173 agonist phoenixin 20 promotes osteoblastic differentiation of MC3T3-E1 cells

Osteogenic differentiation is critical to bone homeostasis, and its imbalance plays a key role in the progression of osteoporosis. Osteoblast cells are responsible for synthesizing new bone tissue, and understanding how to control osteoblastic differentiation is vital to the treatment of osteoporosis. Herein, we show that GPR173 signaling is involved in the regulation of osteoblastic differentiation in MC3T3-E1 cells. Our data reveals that GPR173 is abundantly expressed in MC3T3-E1 cells, and its expression is inducible upon the introduction of osteogenic media. The activation of GPR173 by its selective agonist phoenixin 20 induces the expression of several osteoblast signature genes including collagen type 1 alpha 1 (Col-I), osteocalcin (OCN), alkaline phosphatase (ALP) as well as increased matrix mineralization and ALP activity, suggesting that the activation of GPR173 promotes osteoblastic differentiation. Moreover, we show that the effect of phoenixin 20 is mediated by its induction on the key regulator runt-Related Transcription Factor 2 (Runx2). Mechanistically, we display that the action of phoenixin 20 requires the activation of MAPK kinase p38, and deactivation of p38 by its inhibitor SB203580 weakens the phoenixin 20-mediated induction of RUNX-2, ALP, and matrix mineralization. Silencing of GPR173 attenuates phoenixin 20-mediated osteoblastic differentiation, indicating its dependence on the receptor. Collectively, our study reveals a new role of GPR173 and its agonist phoenixin 20 in osteoblastic differentiation.

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.

Osmolarity controls the differentiation of adipose-derived stem cells into nucleus pulposus cells via histone demethylase KDM4B

Adipose-derived stem cells (ADSCs) are an ideal source of cells for intervertebral disc (IVD) regeneration, but the effect of an increased osmotic microenvironment on ADSC differentiation remains unclear. Here, we aimed to elucidate whether hyperosmolarity facilitates ADSC nucleus pulposus (NP)-like differentiation and whether histone demethylase KDM4B is involved in this process. ADSCs were cultured under standard and increased osmolarity conditions for 1-3 weeks, followed by analysis for proliferation and viability. Differentiation was then quantified by gene and protein analysis. Finally, KDM4B knockdown ADSCs were generated using lentiviral vectors. The results showed that increasing the osmolarity of the differentiation medium to 400 mOsm significantly increased NP-like gene expression and the synthesis of extracellular matrix (ECM) components during ADSC differentiation; however, further increasing the osmolarity to 500 mOsm suppressed the NP-like differentiation of ADSCs. KDM4B, as well as the IVD formation regulators forkhead box (Fox)a1/2 and sonic hedgehog (Shh), were found to be significantly upregulated at 400 mOsm. KDM4B knockdown reduced Foxa1/2, Shh, and NP-associated markers' expression, as well as the synthesis of ECM components. The reduction in NP-like differentiation caused by KDM4B knockdown was partially rescued by Purmorphamine, a specific agonist of Shh. Moreover, we found that KDM4B can directly bind to the promoter region of Foxa1/2 and decrease the content of H3K9me3/2. In conclusion, our results indicate that a potential optimal osmolarity window might exist for successful ADSC differentiation. KDM4B plays an essential role in regulating the osmolarity-induced NP-like differentiation of ADSCs by interacting with Foxa1/2-Shh signaling.

Regenerative potential of Wharton's jelly-derived mesenchymal stem cells: A new horizon of stem cell therapy

Umbilical cord Wharton's jelly-derived mesenchymal stem cells (WJ-MSCs) have recently gained considerable attention in the field of regenerative medicine. Their high proliferation rate, differentiation ability into various cell lineages, easy collection procedure, immuno-privileged status, nontumorigenic properties along with minor ethical issues make them an ideal approach for tissue repair. Besides, the number of WJ-MSCs in the umbilical cord samples is high as compared to other sources. Because of these properties, WJ-MSCs have rapidly advanced into clinical trials for the treatment of a wide range of disorders. Therefore, this paper summarized the current preclinical and clinical studies performed to investigate the regenerative potential of WJ-MSCs in neural, myocardial, skin, liver, kidney, cartilage, bone, muscle, and other tissue injuries.

Wharton's jelly area and its association with placental morphometry and pathology

INTRODUCTION

Wharton's jelly (WJ) is the mucoid connective tissue that surrounds the vessels in the human umbilical cord and provides protection from compression and torsion in response to fetal movement. WJ is known to be altered in the presence of pregnancy complications such as gestational diabetes mellitus and preeclampsia. The present study examined associations between the cross-sectional area of WJ measured by ultrasound and postpartum placental pathology and morphometry.

METHODS

The area of WJ was measured by ultrasound in 156 eligible participants between 23 and 37 weeks' gestation. Morphometric assessment of fixed cord cross sections was conducted, together with assessment of the cord and placenta for specific pathologies using standard criteria.

RESULTS

From 156 participants, 123 ultrasound images met the data quality requirements and pathology reporting was completed for 99 placentas. 17 of the participants (14%) delivered a small for gestational age neonate and 32 of the 99 placentas examined (32%) had significant placental pathology findings. Area of WJ was associated with low birth weight (p = 0.002) and was associated with specific placental pathology (p = 0.01). WJ area was positively associated with placental dimensions such as width, length and surface area.

DISCUSSION

Decreased WJ area is associated with clinically-significant placental pathology and WJ area scales proportionally with placental size. These findings suggest that WJ area correlates with functional capacity of the placenta and thus merits further evaluation alongside currently-available tests of placental function in clinical practice.

Control of mesenchymal stem cell biology by histone modifications

Mesenchymal stem cells (MSCs) are considered the most promising seed cells for regenerative medicine because of their considerable therapeutic properties and accessibility. Fine-tuning of cell biological processes, including differentiation and senescence, is essential for achievement of the expected regenerative efficacy. Researchers have recently made great advances in understanding the spatiotemporal gene expression dynamics that occur during osteogenic, adipogenic and chondrogenic differentiation of MSCs and the intrinsic and environmental factors that affect these processes. In this context, histone modifications have been intensively studied in recent years and have already been indicated to play significant and universal roles in MSC fate determination and differentiation. In this review, we summarize recent discoveries regarding the effects of histone modifications on MSC biology. Moreover, we also provide our insights and perspectives for future applications.

Ezh2-dependent H3K27me3 modification dynamically regulates vitamin D3-dependent epigenetic control of CYP24A1 gene expression in osteoblastic cells

Epigenetic control is critical for the regulation of gene transcription in mammalian cells. Among the most important epigenetic mechanisms are those associated with posttranslational modifications of chromosomal histone proteins, which modulate chromatin structure and increased accessibility of promoter regulatory elements for competency to support transcription. A critical histone mark is trimethylation of histone H3 at lysine residue 27 (H3K27me3), which is mediated by Ezh2, the catalytic subunit of the polycomb group complex PRC2 to repress transcription. Treatment of cells with the active vitamin D metabolite 1,25(OH)₂ D₃ , results in transcriptional activation of the CYP24A1 gene, which encodes a 24-hydroxylase enzyme, that is, essential for physiological control of vitamin D3 levels. We report that the Ezh2-mediated deposition of H3K27me3 at the CYP24A1 gene promoter is a requisite regulatory component during transcriptional silencing of this gene in osteoblastic cells in the absence of 1,25(OH)₂ D₃ . 1,25(OH)₂ D₃ dependent transcriptional activation of the CYP24A1 gene is accompanied by a rapid release of Ezh2 from the promoter, together with the binding of the H3K27me3-specific demethylase Utx/Kdm6a and thereby subsequent erasing of the H3K27me3 mark. Importantly, we find that these changes in H3K27me3 enrichment at the CYP24A1 gene promoter are highly dynamic, as this modification is rapidly reacquired following the withdrawal of 1,25(OH)₂ D₃ .

Baicalin augments the differentiation of osteoblasts via enhancement of microRNA-217

Baicalin (BAI), a sort of flavonoid monomer, acquires from Scutellaria baicalensis Georgi, which was forcefully reported in diversified ailments due to the pleiotropic properties. But, the functions of BAI in osteoblast differentiation have not been addressed. The intentions of this study are to attest the influences of BAI in the differentiation of osteoblasts. MC3T3-E1 cells or rat primary osteoblasts were exposed to BAI, and then cell viability, ALP activity, mineralization process, and Runx2 and Ocn expression were appraised through implementing CCK-8, p-nitrophenyl phosphate (pNPP), Alizarin red staining, western blot, and RT-qPCR assays. The microRNA-217 (miR-217) expression was evaluated in MC3T3-E1 cells or rat primary osteoblasts after BAI disposition; meanwhile, the functions of miR-217 in BAI-administrated MC3T3-E1 cells were estimated after miR-217 inhibitor transfection. The impacts of BAI and miR-217 inhibition on Wnt/β-catenin and MEK/ERK pathways were probed to verify the involvements in BAI-regulated the differentiation of osteoblasts. BAI accelerated cell viability, osteoblast activity, and Runx2 and Ocn expression in MC3T3-E1 cells or rat primary osteoblasts, and the phenomena were mediated via activations of Wnt/β-catenin and MEK/ERK pathways. Elevation of miR-217 was observed in BAI-disposed MC3T3-E1 cells or rat primary osteoblasts, and miR-217 repression annulled the functions of BAI in MC3T3-E1 cell viability and differentiation. Additionally, the activations of Wnt/β-catenin and MEK/ERK pathways evoked by BAI were both restrained by repression of miR-217. These explorations uncovered that BAI augmented the differentiation of osteoblasts via activations of Wnt/β-catenin and MEK/ERK pathways by ascending miR-217 expression.

Osteogenic Induction of Wharton's Jelly-Derived Mesenchymal Stem Cell for Bone Regeneration: A Systematic Review

Wharton's jelly-derived mesenchymal stem cells (WJ-MSCs) are emerging as a promising source for bone regeneration in the treatment of bone defects. Previous studies have reported the ability of WJ-MSCs to be induced into the osteogenic lineage. The purpose of this review was to systematically assess the potential of WJ-MSC differentiation into the osteogenic lineage. A comprehensive search was conducted in Medline via Ebscohost and Scopus, where relevant studies published between 1961 and 2018 were selected. The main inclusion criteria were that articles must be primary studies published in English evaluating osteogenic induction of WJ-MSCs. The literature search identified 92 related articles, but only 18 articles met the inclusion criteria. These include two animal studies, three articles containing both in vitro and in vivo assessments, and 13 articles on in vitro studies, all of which are discussed in this review. There were two types of osteogenic induction used in these studies, either chemical or physical. The studies demonstrate that WJ-MSCs are able to differentiate into osteogenic lineage and promote osteogenesis. In light of these observations, it is suggested that WJ-MSCs can be a potential source of stem cells for osteogenic induction, as an alternative to bone marrow-derived mesenchymal stem cells.

Epigenetic Control of Mesenchymal Stem Cell Fate Decision via Histone Methyltransferase Ash1l

Previous research indicates that knocking out absent, small, or homeotic-like (Ash1l) in mice, a histone 3 lysine 4 (H3K4) trimethyltransferase, can result in arthritis with more severe cartilage and bone destruction. Research has documented the essential role of Ash1l in stem cell fate decision such as hematopoietic stem cells and the progenitors of keratinocytes. Following up on those insights, our research seeks to document the function of Ash1l in skeletal formation, specifically whether it controls the fate decision of mesenchymal progenitor cells. Our findings indicate that in osteoporotic bones, Ash1l was significantly decreased, indicating a positive correlation between bone mass and the expression of Ash1l. Silencing of Ash1l that had been markedly upregulated in differentiated C3H10T1/2 (C3) cells hampered osteogenesis and chondrogenesis but promoted adipogenesis. Consistently, overexpression of an Ash1l SET domain-containing fragment 3 rather than Ash1lΔN promoted osteogenic and chondrogenic differentiation of C3 cells and simultaneously inhibited adipogenic differentiation. This indicates that the role of Ash1l in regulating the differentiation of C3 cells is linked to its histone methyltransferase activity. Subcutaneous ex vivo transplantation experiments confirmed the role of Ash1l in the promotion of osteogenesis. Further experiments proved that Ash1l can epigenetically affect the expression of essential osteogenic and chondrogenic transcription factors. It exerts this impact via modifications in the enrichment of H3K4me3 on their promoter regions. Considering the promotional action of Ash1l on bone, it could potentially prompt new therapeutic strategy to promote osteogenesis. Stem Cells 2019;37:115-127.

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.

TGFβ3 recruits endogenous mesenchymal stem cells to initiate bone regeneration

Background

The recruitment of a sufficient number of endogenous mesenchymal stem cells (MSCs) is the first stage of in-situ tissue regeneration. Transforming growth factor beta-3 (TGFβ3) could recruit stem or progenitor cells and endothelial cells to participate in tissue regeneration. However, the mechanism of TGFβ3 recruiting MSCs toward bone regeneration has remained obscure.

Methods

We estimated the promigratory property of TGFβ3 on human bone marrow MSCs (hBMSCs) cocultured with the vascular cells (human umbilical artery smooth muscle cells or human umbilical vein endothelial cells) or not by Transwell assay. After the addition of the inhibitor (SB431542) or Smad3 siRNA, the levels of MCP1 and SDF1 in coculture medium were tested by ELISA kit, and then the migratory signaling pathway of hBMSCs induced by TGFβ3 was investigated by western blot analysis. In vivo, a 2-mm FVB/N mouse femur defect model was used to evaluate chemokine secretion, endogenous cell homing, and bone regeneration induced by scaffolds loading 1 μg TGFβ3 through qPCR, immunofluorescent staining, immunohistochemical analysis, and Micro-CT, compared to the vehicle group.

Results

TGFβ3 (25 ng/ml) directly showed a nearly 40% increase in migrated hBMSCs via the TGFβ signaling pathway, compared to the vehicle treatment. Then, in the coculture system of hBMSCs and vascular cells, TGFβ3 further upregulated nearly 3-fold MCP1 secretion from vascular cells in a Smad3-dependent manner, to indirectly enhance nearly more than 50% of migrated hBMSCs. In vivo, TGFβ3 delivery improved MCP1 expression by nearly 7.9-fold, recruited approximately 2.0-fold CD31⁺ vascular cells and 2.0-fold Sca-1⁺ PDGFR-α⁺ MSCs, and achieved 2.5-fold bone volume fraction (BV/TV) and 2.0-fold bone mineral density, relative to TGFβ3-free delivery.

Conclusions

TGFβ3, as a MSC homing molecule, recruited MSCs to initiate bone formation in the direct-dependent and indirect-dependent mechanisms. This may shed light on the improvement of MSC homing in bone regeneration.