VGLL4 promotes osteoblast differentiation by antagonizing TEADs-inhibited Runx2 transcription

Bu-Sui-Dan Enhances Osteoblast Differentiation by Upregulating VGLL4 to Counteract TEAD4-Mediated RUNX2 Transcription Suppression in Ovariectomized Rats

ETHNOPHARMACOLOGICAL RELEVANCE

Postmenopausal osteoporosis (PMOP) has been considered as a major causative factor for bone-joint pain and inducing pathologic fractures. Bu-Sui-Dan (BSD), a classic ancient herbal formula, has been shown to exhibit osteoprotective effects by promoting bone marrow development and bone growth. However, the exact mechanism of BSD are still unexplored.

AIM OF STUDY

The study aimed to investigate the protective effect of BSD against osteoporotic injury, and to explore whether BSD regulated BMSCs' osteogenic differentiation by targeting VGLL4, which in turn improved PMOP.

MATERIALS AND METHODS

The anti-osteoporotic effect of BSD was studied in ovariectomized (OVX) rats and bone marrow mesenchymal stem cells (BMSCs). Micro-CT imaging and HE staining were performed, and the levels of osteogenic protein RUNX2 and osteogenesis-related factor VGLL4 were determined. Co-immunoprecipitation (Co-IP) was further employed to delve into the effects of BSD on the interactions between TEAD4 and RUNX2. The key osteogenic factors 1ALP, COLl1A1, and Osterix expression were detected by RT-qPCR. Co-IP and proximity ligation assay (PLA) were employed to scrutinize the influence of BSD on TEAD4 and RUNX2 inter-binding. Moreover, VGLL4 knockdown in BMSCs was conducted to confirm the role of VGLL4 in the therapeutic mechanism of BSD.

RESULTS

BSD showed a dose-dependent protective effect against osteoporotic injury, as evidenced by improvement in bone volume, bone microarchitecture, and histomorphometry. Additionally, BSD treatment increased the levels of RUNX2 and its downstream target genes including ALP, COL1A1, and Osterix. Moreover, BSD upregulated VGLL4 expression and lessened TEAD4-RUNX2 interactions. In BMSCs experiment, BSD-containing serum could promote osteogenic differentiation of BMSCs, boosted the expression of osteogenesis-related factors and VGLL4 level. The knockdown of VGLL4 in BMSCs diminished the promotion effect of BSD in osteoblast differentiation, suggesting that VGLL4 play a vital role in the therapeutic effects exerted by BSD.

CONCLUSION

BSD ameliorated osteoporosis injury and promoted osteoblast differentiation through upregulation of VGLL4 levels, which in turn antagonized TEAD4-mediated RUNX2 transcriptional repression. Our study implied that BSD may be an osteoporosis therapeutic agent.

YAP/TAZ as mechanobiological signaling pathway in cardiovascular physiological regulation and pathogenesis

Cardiovascular diseases (CVDs) persistently rank as a leading cause of premature death and illness worldwide. The Hippo signaling pathway, known for its highly conserved nature and integral role in regulating organ size, tissue homeostasis, and stem cell function, has been identified as a critical factor in the pathogenesis of CVDs. Recent findings underscore the significance of the Yes-associated protein (YAP) and the Transcriptional Coactivator with PDZ-binding motif (TAZ), collectively referred to as YAP/TAZ. These proteins play pivotal roles as downstream components of the Hippo pathway, in the regulation of cardiovascular development and homeostasis. YAP/TAZ can regulate various cellular processes such as cell proliferation, migration, differentiation, and apoptosis through their interactions with transcription factors, particularly those within the transcriptional enhancer associate domain (TEAD) family. The aim of this review is to provide a comprehensive overview of the current understanding of YAP/TAZ signaling in cardiovascular physiology and pathogenesis. We analyze the regulatory mechanisms of YAP/TAZ activation, explore their downstream effectors, and examine their association across numerous cardiovascular disorders, including myocardial hypertrophy, myocardial infarction, pulmonary hypertension, myocardial ischemia-reperfusion injury, atherosclerosis, angiogenesis, restenosis, and cardiac fibrosis. Furthermore, we investigate the potential therapeutic implications of targeting the YAP/TAZ pathway for the treatment of CVDs. Through this comprehensive review, our aim is to elucidate the current understanding of YAP/TAZ signaling in cardiovascular biology and underscore its potential implications for the diagnosis and therapeutic intervention of CVDs.

Bmi-1 Epigenetically Orchestrates Osteogenic and Adipogenic Differentiation of Bone Marrow Mesenchymal Stem Cells to Delay Bone Aging

With the increase in the aging population, senile osteoporosis (SOP) has become a major global public health concern. Here, it is found that Prx1 and Bmi-1 co-localized in trabecular bone, bone marrow cavity, endosteum, and periosteum. Prx1-driven Bmi-1 knockout in bone-marrow mesenchymal stem cells (BMSCs) reduced bone mass and increased bone marrow adiposity by inhibiting osteoblastic bone formation, promoting osteoclastic bone resorption, downregulating the proliferation and osteogenic differentiation of BMSCs, and upregulating the adipogenic differentiation of BMSCs. However, Prx1-driven Bmi-1 overexpression showed a contrasting phenotype to Prx1-driven Bmi-1 knockout in BMSCs. Regarding mechanism, Bmi-1-RING1B bound to DNMT3A and promoted its ubiquitination and inhibited DNA methylation of Runx2 at the region from 45047012 to 45047313 bp, thus promoting the osteogenic differentiation of BMSCs. Moreover, Bmi-1-EZH2 repressed the transcription of Cebpa by promoting H3K27 trimethylation at the promoter region -1605 to -1596 bp, thus inhibiting the adipogenic differentiation of BMSCs. It is also found that Prx1-driven Bmi-1 overexpression rescued the SOP induced by Prx1-driven Bmi-1 knockout in BMSCs. Thus, Bmi-1 functioned as a hub protein in the epigenetic regulation of BMSCs differentiation to delay bone aging. The Prx1-driven Bmi-1 overexpression in BMSCs can be used as an approach for the translational therapy of SOP.

Hyperbaric oxygen promotes bone regeneration by activating the mechanosensitive Piezo1 pathway in osteogenic progenitors

Background

Hyperbaric oxygen (HBO) therapy is widely used to treat bone defects, but the correlation of high oxygen concentration and pressure to osteogenesis is unclear.

Methods

Bilateral monocortical tibial defect surgeries were performed on 12-week-old Prrx1-Cre; Rosa26-tdTomato and Prrx1-Cre; Piezo1fl/+ mice. Daily HBO treatment was applied on post-surgery day (PSD) 1-9; and daily mechanical loading on tibia was from PSD 5 to 8. The mice were euthanized on PSD 10, and bone defect repair in their tibias was evaluated using μCT, biomechanical testing, and immunofluorescence deep-tissue imaging. The degree of angiogenesis-osteogenesis coupling was determined through spatial correlation analysis. Bone marrow stromal cells from knockout mice were cultured in vitro, and their osteogenic capacities of the cells were assessed. The activation of genes in the Piezo1-YAP pathway was evaluated using RNA sequencing and quantitative real-time polymerase chain reaction.

Results

Lineage tracing showed HBO therapy considerably altered the number of Prrx1+ cells and their progeny in a healing bone defect. Using conditional knockdown mice, we found that HBO stimulation activates the Piezo1-YAP axis in Prrx1+ cells and promotes osteogenesis-angiogenesis coupling during bone repair. The beneficial effect of HBO was similar to that of anabolic mechanical stimulation, which also acts through the Piezo1-YAP axis. Subsequent transcriptome sequencing results revealed that similar mechanosensitive pathways are activated by HBO therapy in a bone defect.

Conclusion

HBO therapy promotes bone tissue regeneration through the mechanosensitive Piezo1-YAP pathway in a population of Prrx1+ osteogenic progenitors. Our results contribute to the understanding of the mechanism by which HBO therapy treats bone defects.

The Translational Potential of this Article

Hyperbaric oxygen therapy is widely used in clinical settings. Our results show that osteogenesis was induced by the activation of the Piezo1-YAP pathway in osteoprogenitors after HBO stimulation, and the underlying mechanism was elucidated. These results may help improve current HBO methods and lead to the formulation of alternative treatments that achieve the same functional outcomes.

Xenopus tropicalis osteoblast-specific open chromatin regions reveal promoters and enhancers involved in human skeletal phenotypes and shed light on early vertebrate evolution

While understanding the genetic underpinnings of osteogenesis has far-reaching implications for skeletal diseases and evolution, a comprehensive characterization of the osteoblastic regulatory landscape in non-mammalian vertebrates is still lacking. Here, we compared the ATAC-Seq profile of Xenopus tropicalis (Xt) osteoblasts to a variety of non mineralizing control tissues, and identified osteoblast-specific nucleosome free regions (NFRs) at 527 promoters and 6747 distal regions. Sequence analyses, Gene Ontology, RNA-Seq and ChIP-Seq against four key histone marks confirmed that the distal regions correspond to bona fide osteogenic transcriptional enhancers exhibiting a shared regulatory logic with mammals. We report 425 regulatory regions conserved with human and globally associated to skeletogenic genes. Of these, 35 regions have been shown to impact human skeletal phenotypes by GWAS, including one trps1 enhancer and the runx2 promoter, two genes which are respectively involved in trichorhinophalangeal syndrome type I and cleidocranial dysplasia. Intriguingly, 60 osteoblastic NFRs also align to the genome of the elephant shark, a species lacking osteoblasts and bone tissue. To tackle this paradox, we chose to focus on dlx5 because its conserved promoter, known to integrate regulatory inputs during mammalian osteogenesis, harbours an osteoblast-specific NFR in both frog and human. Hence, we show that dlx5 is expressed in Xt and elephant shark odontoblasts, supporting a common cellular and genetic origin of bone and dentine. Taken together, our work (i) unravels the Xt osteogenic regulatory landscape, (ii) illustrates how cross-species comparisons harvest data relevant to human biology and (iii) reveals that a set of genes including bnc2, dlx5, ebf3, mir199a, nfia, runx2 and zfhx4 drove the development of a primitive form of mineralized skeletal tissue deep in the vertebrate lineage.

KAT6A/YAP/TEAD4 pathway modulates osteoclastogenesis by regulating the RANKL/OPG ratio on the compression side during orthodontic tooth movement

BACKGROUND

Orthodontic tooth movement (OTM) is a dynamic equilibrium of bone remodeling, involving the osteogenesis of new bone and the osteoclastogenesis of old bone, which is mediated by mechanical force. Periodontal ligament stem cells (PDLCSs) in the periodontal ligament (PDL) space can transmit mechanical signals and regulate osteoclastogenesis during OTM. KAT6A is a histone acetyltransferase that plays a part in the differentiation of stem cells. However, whether KAT6A is involved in the regulation of osteoclastogenesis by PDLSCs remains unclear.

RESULTS

In this study, we used the force-induced OTM model and observed that KAT6A was increased on the compression side of PDL during OTM, and also increased in PDLSCs under compression force in vitro. Repression of KAT6A by WM1119, a KAT6A inhibitor, markedly decreased the distance of OTM. Knockdown of KAT6A in PDLSCs decreased the RANKL/OPG ratio and osteoclastogenesis of THP-1. Mechanistically, KAT6A promoted osteoclastogenesis by binding and acetylating YAP, simultaneously regulating the YAP/TEAD axis and increasing the RANKL/OPG ratio in PDLSCs. TED-347, a YAP-TEAD4 interaction inhibitor, partly attenuated the elevation of the RANKL/OPG ratio induced by mechanical force.

CONCLUSION

Our study showed that the PDLSCs modulated osteoclastogenesis and increased the RANKL/OPG ratio under mechanical force through the KAT6A/YAP/TEAD4 pathway. KAT6A might be a novel target to accelerate OTM.

Cell signaling and transcriptional regulation of osteoblast lineage commitment, differentiation, bone formation, and homeostasis

The initiation of osteogenesis primarily occurs as mesenchymal stem cells undergo differentiation into osteoblasts. This differentiation process plays a crucial role in bone formation and homeostasis and is regulated by two intricate processes: cell signal transduction and transcriptional gene expression. Various essential cell signaling pathways, including Wnt, BMP, TGF-β, Hedgehog, PTH, FGF, Ephrin, Notch, Hippo, and Piezo1/2, play a critical role in facilitating osteoblast differentiation, bone formation, and bone homeostasis. Key transcriptional factors in this differentiation process include Runx2, Cbfβ, Runx1, Osterix, ATF4, SATB2, and TAZ/YAP. Furthermore, a diverse array of epigenetic factors also plays critical roles in osteoblast differentiation, bone formation, and homeostasis at the transcriptional level. This review provides an overview of the latest developments and current comprehension concerning the pathways of cell signaling, regulation of hormones, and transcriptional regulation of genes involved in the commitment and differentiation of osteoblast lineage, as well as in bone formation and maintenance of homeostasis. The paper also reviews epigenetic regulation of osteoblast differentiation via mechanisms, such as histone and DNA modifications. Additionally, we summarize the latest developments in osteoblast biology spurred by recent advancements in various modern technologies and bioinformatics. By synthesizing these insights into a comprehensive understanding of osteoblast differentiation, this review provides further clarification of the mechanisms underlying osteoblast lineage commitment, differentiation, and bone formation, and highlights potential new therapeutic applications for the treatment of bone diseases.

Biomimetic Bone-Like Composite Hydrogel Scaffolds Composed of Collagen Fibrils and Natural Hydroxyapatite for Promoting Bone Repair

Bone is a complex organic-inorganic composite tissue composed of ∼30% organics and ∼70% hydroxyapatite (HAp). Inspired by this, we used 30% collagen and 70% HAp extracted from natural bone using the calcination method to generate a biomimetic bone composite hydrogel scaffold (BBCHS). In one respect, BBCHS, with a fixed proportion of inorganic and organic components similar to natural bone, exhibits good physical properties. In another respect, the highly biologically active and biocompatible HAp from natural bone effectively promotes osteogenic differentiation, and type I collagen facilitates cell adhesion and spreading. Additionally, the well-structured porosity of the BBCHS provides sufficient growth space for bone marrow mesenchymal stem cells (BMSCs) while promoting substance exchange. Compared to the control group, the new bone surface of the defective location in the B-HA70+Col group is increased by 3.4-fold after 8 weeks of in vivo experiments. This strategy enables the BBCHS to closely imitate the chemical makeup and physical structure of natural bone. With its robust biocompatibility and osteogenic activity, the BBCHS can be easily adapted for a wide range of bone repair applications and offers promising potential for future research and development.

Maternal vgll4a regulates zebrafish epiboly through Yap1 activity

Gastrulation in zebrafish embryos commences with the morphogenetic rearrangement of blastodermal cells, which undergo a coordinated spreading from the animal pole to wrap around the egg at the vegetal pole. This rearrangement, known as epiboly, relies on the orchestrated activity of maternal transcripts present in the egg, compensating for the gradual activation of the zygotic genome. Epiboly involves the mechano-transducer activity of yap1 but what are the regulators of yap1 activity and whether these are maternally or zygotically derived remain elusive. Our study reveals the crucial role of maternal vgll4a, a proposed Yap1 competitor, during zebrafish epiboly. In embryos lacking maternal/zygotic vgll4a (MZvgll4a), the progression of epiboly and blastopore closure is delayed. This delay is associated with the ruffled appearance of the sliding epithelial cells, decreased expression of yap1-downstream targets and transient impairment of the actomyosin ring at the syncytial layer. Our study also shows that, rather than competing with yap1, vgll4a modulates the levels of the E-cadherin/β-catenin adhesion complex at the blastomeres' plasma membrane and hence their actin cortex distribution. Taking these results together, we propose that maternal vgll4a acts at epiboly initiation upstream of yap1 and the E-cadherin/β-catenin adhesion complex, contributing to a proper balance between tissue tension/cohesion and contractility, thereby promoting a timely epiboly progression.

Transcriptomic landscape of human induced pluripotent stem cell-derived osteogenic differentiation identifies a regulatory role of KLF16

Osteogenic differentiation is essential for bone development and metabolism, but the underlying gene regulatory networks have not been well investigated. We differentiated mesenchymal stem cells, derived from 20 human induced pluripotent stem cell lines, into preosteoblasts and osteoblasts, and performed systematic RNA-seq analyses of 60 samples for differential gene expression. We noted a highly significant correlation in expression patterns and genomic proximity among transcription factor (TF) and long noncoding RNA (lncRNA) genes. We identified TF-TF regulatory networks, regulatory roles of lncRNAs on their neighboring coding genes for TFs and splicing factors, and differential splicing of TF, lncRNA, and splicing factor genes. TF-TF regulatory and gene co-expression network analyses suggested an inhibitory role of TF KLF16 in osteogenic differentiation. We demonstrate that in vitro overexpression of human KLF16 inhibits osteogenic differentiation and mineralization, and in vivo Klf16+/- mice exhibit increased bone mineral density, trabecular number, and cortical bone area. Thus, our model system highlights the regulatory complexity of osteogenic differentiation and identifies novel osteogenic genes.

New Insights into YAP/TAZ-TEAD-Mediated Gene Regulation and Biological Processes in Cancer

The Hippo pathway is conserved across species. Key mammalian Hippo pathway kinases, including MST1/2 and LATS1/2, inhibit cellular growth by inactivating the TEAD coactivators, YAP, and TAZ. Extensive research has illuminated the roles of Hippo signaling in cancer, development, and regeneration. Notably, dysregulation of Hippo pathway components not only contributes to tumor growth and metastasis, but also renders tumors resistant to therapies. This review delves into recent research on YAP/TAZ-TEAD-mediated gene regulation and biological processes in cancer. We focus on several key areas: newly identified molecular patterns of YAP/TAZ activation, emerging mechanisms that contribute to metastasis and cancer therapy resistance, unexpected roles in tumor suppression, and advances in therapeutic strategies targeting this pathway. Moreover, we provide an updated view of YAP/TAZ's biological functions, discuss ongoing controversies, and offer perspectives on specific debated topics in this rapidly evolving field.

Biallelic truncating variants in VGLL2 cause syngnathia in humans

BACKGROUND

Syngnathia is an ultrarare craniofacial malformation characterised by an inability to open the mouth due to congenital fusion of the upper and lower jaws. The genetic causes of isolated bony syngnathia are unknown.

METHODS

We used whole exome and Sanger sequencing and microsatellite analysis in six patients (from four families) presenting with syngnathia. We used CRISPR/Cas9 genome editing to generate vgll2a and vgll4l germline mutant zebrafish, and performed craniofacial cartilage analysis in homozygous mutants.

RESULTS

We identified homozygous truncating variants in vestigial-like family member 2 (VGLL2) in all six patients. Two alleles were identified: one in families of Turkish origin and the other in families of Moroccan origin, suggesting a founder effect for each. A shared haplotype was confirmed for the Turkish patients. The VGLL family of genes encode cofactors of TEAD transcriptional regulators. Vgll2 is regionally expressed in the pharyngeal arches of model vertebrate embryos, and morpholino-based knockdown of vgll2a in zebrafish has been reported to cause defects in development of pharyngeal arch cartilages. However, we did not observe craniofacial anomalies in vgll2a or vgll4l homozygous mutant zebrafish nor in fish with double knockout of vgll2a and vgll4l. In Vgll2 -/- mice, which are known to present a skeletal muscle phenotype, we did not identify defects of the craniofacial skeleton.

CONCLUSION

Our results suggest that although loss of VGLL2 leads to a striking jaw phenotype in humans, other vertebrates may have the capacity to compensate for its absence during craniofacial development.

Generation of Vgll4-DreER transgenic mouse for visualizing and manipulating VGLL4-expressing cells in vivo

Vestigial like family member 4 (VGLL4), a member of the Hippo pathway, is a transcriptional cofactor involved in many biological processes, such as tumor progression, postnatal heart growth, and muscle regeneration. However, the VGLL4 expression pattern in vivo remains unclear. To detect and trace Vgll4-expressing cells and their progeny, we generated and characterized a new tamoxifen-inducible Dre knock-in mouse line, Vgll4-DreER. This mouse line expressed DreER (Dre recombinase fused to the estrogen receptor) under the control of the endogenous Vgll4 promoter. After crossing the Vgll4-DreER mouse line with the Dre-responsive reporter H11-rRFP, Dre-mediated recombination in the tissue was monitored on the basis of red fluorescent protein (RFP) signals, which indicated the distribution of VGLL4-positive cells in vivo. Our data revealed that VGLL4 is widely expressed in various cell types at embryonic and neonatal stages. After comparison with our previously reported Vgll4-GFP mouse, we found that the RFP signal profile was wider than the green fluorescent protein (GFP) pattern, indicating that Vgll4-DreER is more sensitive for labeling VGLL4-expressing cells. We next used a dual-recombination system to simultaneously label VGLL4- and keratin 5 (KRT5)-positive cell populations, and no crosstalk was observed in the Krt5-CreER;Vgll4-DreER;R26-rGlR mice. Taken together, the Vgll4-DreER mouse line is a valuable new tool for examining the precise VGLL4 expression profile and conditional manipulating of VGLL4-expressing cells and their progeny.

VGLL4 promotes vascular endothelium specification via TEAD1 in the vascular organoids and human pluripotent stem cells-derived endothelium model

BACKGROUND

We have shown that Hippo-YAP signaling pathway plays an important role in endothelial cell differentiation. Vestigial-like family member 4 (VGLL4) has been identified as a YAP inhibitor. However, the exact function of VGLL4 in vascular endothelial cell development remains unclear. In this study, we investigated the role of VGLL4, in human endothelial lineage specification both in 3D vascular organoid and 2D endothelial cell differentiation.

METHODS AND RESULTS

In this study, we found that VGLL4 was increased during 3D vascular organoids generation and directed differentiation of human embryonic stem cells H1 towards the endothelial lineage. Using inducible ectopic expression of VGLL4 based on the piggyBac system, we proved that overexpression of VGLL4 in H1 promoted vascular organoids generation and endothelial cells differentiation. In contrast, VGLL4 knockdown (heterozygous knockout) of H1 exhibited inhibitory effects. Using bioinformatics analysis and protein immunoprecipitation, we further found that VGLL4 binds to TEAD1 and facilitates the expression of endothelial master transcription factors, including FLI1, to promote endothelial lineage specification. Moreover, TEAD1 overexpression rescued VGLL4 knockdown-mediated negative effects.

CONCLUSIONS

In summary, VGLL4 promotes EC lineage specification both in 3D vascular organoid and 2D EC differentiation from pluripotent stem cell, VGLL4 interacts with TEAD1 and facilitates EC key transcription factor, including FLI1, to enhance EC lineage specification.

Tea domain transcription factor TEAD4 mitigates TGF-β signaling and hepatocellular carcinoma progression independently of YAP

Tea domain transcription factor 4 (TEAD4) plays a pivotal role in tissue development and homeostasis by interacting with Yes-associated protein (YAP) in response to Hippo signaling inactivation. TEAD4 and YAP can also cooperate with transforming growth factor-β (TGF-β)-activated Smad proteins to regulate gene transcription. Yet, it remains unclear whether TEAD4 plays a YAP-independent role in TGF-β signaling. Here, we unveil a novel tumor suppressive function of TEAD4 in liver cancer via mitigating TGF-β signaling. Ectopic TEAD4 inhibited TGF-β-induced signal transduction, Smad transcriptional activity, and target gene transcription, consequently suppressing hepatocellular carcinoma cell proliferation and migration in vitro and xenograft tumor growth in mice. Consistently, depletion of endogenous TEAD4 by siRNAs enhanced TGF-β signaling in cancer cells. Mechanistically, TEAD4 associates with receptor-regulated Smads (Smad2/3) and Smad4 in the nucleus, thereby impairing the binding of Smad2/3 to the histone acetyltransferase p300. Intriguingly, these negative effects of TEAD4 on TGF-β/Smad signaling are independent of YAP, as impairing the TEAD4-YAP interaction through point mutagenesis or depletion of YAP and/or its paralog TAZ has little effect. Together, these results unravel a novel function of TEAD4 in fine tuning TGF-β signaling and liver cancer progression in a YAP-independent manner.

Janus porous polylactic acid membranes with versatile metal-phenolic interface for biomimetic periodontal bone regeneration

Conventional treatment to periodontal and many other bone defects requires the use of barrier membranes to guided tissue regeneration (GTR) and guided bone regeneration (GBR). However, current barrier membranes normally lack of the ability to actively regulate the bone repairing process. Herein, we proposed a biomimetic bone tissue engineering strategy enabled by a new type of Janus porous polylactic acid membrane (PLAM), which was fabricated by combining unidirectional evaporation-induced pore formation with subsequent self-assembly of a bioactive metal-phenolic network (MPN) nanointerface. The prepared PLAM-MPN simultaneously possesses barrier function on the dense side and bone-forming function on the porous side. In vitro, the presence of MPN nanointerface potently alleviated the proinflammatory polarization of mice bone marrow-derived macrophages (BMDMs), induced angiogenesis of human umbilical vein endothelial cells (HUVECs), and enhanced the attachment, migration and osteogenic differentiation of human periodontal ligament stem cells (hPDLSCs). The implantation of PLAM-MPN into rat periodontal bone defects remarkably enhanced bone regeneration. This bioactive MPN nanointerface within a Janus porous membrane possesses versatile capacities to regulate cell physiology favoring bone regeneration, demonstrating great potential as GTR and GBR membranes for clinical applications.

Accelerated aging in articular cartilage by ZMPSTE24 deficiency leads to osteoarthritis with impaired metabolic signaling and epigenetic regulation

Osteoarthritis (OA) is an age-related degenerative disease without disease-modifying therapy. The lack of aging-induced osteoarthritis models makes the discovery of therapeutic drugs more challenging. The deficiency of ZMPSTE24 could induce Hutchinson-Gilford progeria syndrome (HGPS), a genetic disorder of rapid aging. However, the relationship between HGPS and OA remains unclear. Our results found that the expression of Zmpste24 was decreased in the articular cartilage during the aging process. Zmpste24 knockout mice, Prx1-Cre; Zmpste24^fl/fl mice and Col2-CreERT2; Zmpste24^fl/fl mice displayed OA phenotype. Loss of Zmpste24 in articular cartilage could exacerbate the occurrence and development of osteoarthritis. Transcriptome sequencing revealed that deletion of Zmpste24 or accumulation of progerin affects chondrocyte metabolism, inhibits cell proliferation and promotes cell senescence. Using this animal model, we elucidate the upregulation of H3K27me3 during chondrocyte senescence and discover the molecular mechanism by which lamin A mutant stabilizes EZH2 expression. The construction of aging-induced osteoarthritis models and the elucidation of the signaling pathways and molecular mechanisms of articular chondrocyte senescence would benefit the discovery and development of new drugs for OA.

METTL5 regulates cranial suture fusion via Wnt signaling

METTL5 is a methyltransferase that mediates eukaryotic 18S ribosomal RNA m6A modification, and its mutations lead to intellectual disability, microcephaly, and facial dysmorphism in patients. However, the role of METTL5 in craniofacial development remains poorly understood. This study demonstrates that Mettl5 knockout mice exhibit poor ossification, widened cranial sutures, and a cleidocranial dysplasia-like phenotype. Deletion of Mettl5 leads to increased proliferation and decreased osteogenic differentiation of suture mesenchymal stem cells. Mechanistically, we find that Wnt signaling is significantly downregulated after Mettl5 knockout. Overall, we reveal an essential role of METTL5 in craniofacial development and osteogenic differentiation of suture mesenchymal stem cells, making METTL5 a potential diagnostic and therapeutic target for craniofacial developmental diseases.

Hippo Pathway in Schwann Cells and Regeneration of Peripheral Nervous System

Hippo pathway is an evolutionarily conserved signaling pathway comprising a series of MST/LATS kinase complexes. Its key transcriptional coactivators YAP and TAZ regulate transcription factors such as TEAD family to direct gene expression. The regulation of Hippo pathway, especially the nuclear level change of YAP and TAZ, significantly influences the cell fate switching from proliferation to differentiation, regeneration, and postinjury repair. This review outlines the main findings of Hippo pathway in peripheral nerve development, regeneration, and tumorigenesis, especially the studies in Schwann cells. We also summarize other roles of Hippo pathway in damage repair of the peripheral nerve system and discuss the potential future research which probably contributes to novel therapeutic strategies.

Guideline for design of substrate stiffness for mesenchymal stem cell culture based on heterogeneity of YAP and RUNX2 responses

Mesenchymal stem cells (MSCs) have the potential for self-renewal and multipotency to differentiate into various lineages. Thus, they are of great interest in regenerative medicine as a cell source for tissue engineering. Substrate stiffness is one of the most extensively studied exogenous physical factors; however, consistent results have not always been reported for controlling MSCs. Conventionally used stiff culture substrates, such as tissue-culture polystyrene and glass, enhance nuclear localization of a mechanotransducer YAP and a pre-osteogenic transcription factor RUNX2, and bias MSCs towards the osteogenic lineage, even without osteogenic-inducing soluble factors. The mechanosensitive nature and intrinsic heterogeneity present challenges for obtaining reproducible results. This review summarizes the heterogeneity in human MSC response, specifically, nuclear/cytoplasmic localization changes in the mechanotransducer yes-associated protein (YAP) and the osteogenic transcription factor RUNX2, in response to substrate stiffness. In addition, a perspective on the intracellular factors attributed to response heterogeneity is discussed. The optimal range of stiffness parameters, Young's modulus, for MSC expansion culture to suppress osteogenic differentiation bias through the suppression of YAP and RUNX2 nuclear localization, and cell cycle progression is likely to be surprisingly narrow for a cell population from an identical donor and vary among cell populations from different donors. We believe that characterization of the heterogeneity of MSCs and understanding their biological meaning is an exciting research direction to establish guidelines for the design of culture substrates for the sophisticated control of MSC properties.

VGLL4-TEAD1 promotes vascular smooth muscle cell differentiation from human pluripotent stem cells via TET2

The Hippo signaling pathway plays a critical role in cardiovascular development and stem cell differentiation. Using microarray profiling, we found that the Hippo pathway components vestigial-like family member 4 (VGLL4) and TEA domain transcription factor 1 (TEAD1) were upregulated during vascular smooth muscle cell (VSMC) differentiation from H1 ESCs (H1 embryonic stem cells). To further explore the role and molecular mechanisms of VGLL4 in regulating VSMC differentiation, we generated a VGLL4-knockdown H1 ESC line (heterozygous knockout) using the CRISPR/Cas9 system and found that VGLL4 knockdown inhibited VSMC specification. In contrast, overexpression of VGLL4 using the PiggyBac transposon system facilitated VSMC differentiation. We confirmed that this effect was mediated via TEAD1 and VGLL4 interaction. In addition, bioinformatics analysis revealed that Ten-eleven-translocation 2 (TET2), a DNA dioxygenase, is a target of TEAD1, and a luciferase assay further verified that TET2 is the target of the VGLL4-TEAD1 complex. Indeed, TET2 overexpression promoted VSMC marker gene expression and countered the VGLL4 knockdown-mediated inhibitory effects on VSMC differentiation. In summary, we revealed a novel role of VGLL4 in promoting VSMC differentiation from hESCs and identified TET2 as a new target of the VGLL4-TEAD1 complex, which may demethylate VSMC marker genes and facilitate VSMC differentiation. This study provides new insights into the VGLL4-TEAD1-TET2 axis in VSMC differentiation and vascular development.

Inhibition of miR338 rescues cleidocranial dysplasia in Runx2 mutant mice partially via the Hif1a-Vegfa axis

Haploinsufficiency of Runt-related transcription factor-2 (RUNX2) is responsible for cleidocranial dysplasia (CCD), a rare hereditary disease with a range of defects, including delayed closure of the cranial sutures and short stature. Symptom-based treatments, such as a combined surgical-orthodontic approach, are commonly used to treat CCD patients. However, there have been few reports of treatments based on Runx2-specific regulation targeting dwarfism symptoms. Previously, we found that the miR338 cluster, a potential diagnostic and therapeutic target for postmenopausal osteoporosis, could directly target Runx2 during osteoblast differentiation in vitro. Here, we generated miR338^-/-;Runx2^+/- mice to investigate whether inhibition of miR338 could rescue CCD defects caused by Runx2 mutation in vivo. We found that the dwarfism phenotype caused by Runx2 haploinsufficiency was recovered in miR338^-/-;Runx2^+/- mice, with complete bone density restoration and quicker closure of fontanels. Single-cell RNA-seq analysis revealed that knockout of miR338 specifically rescued the osteoblast lineage priming ability of bone marrow stromal cells in Runx2^+/- femurs, which was further confirmed by Osterix-specific conditional knockout of miR338 in Runx2^+/- mice (OsxCre; miR338 ^fl/fl;Runx2^+/-). Mechanistically, ablation of the miR338 cluster in Runx2^+/- femurs directly rescued the Hif1a-Vegfa pathway in Runx2^+/- osteoblasts, as proven by gene expression profiles and ChIP and Re-ChIP assays. Collectively, our data revealed the genetic interaction between Runx2 and the miR338 cluster during osteoblast differentiation and implied that the miR338 cluster could be a potential therapeutic target for CCD.

Amyloid-mediated remineralization for tooth hypoplasia of cleidocranial dysplasia

Introduction

Cleidocranial dysplasia (CCD) is an autosomal-dominant, heritable skeletal and dental disease, involving hypoplastic clavicles, defective ossification of the anterior fontanelle, dentin and enamel hypoplasia, and supernumerary teeth, which can seriously affect the oral and mental health of patients. Amyloid-like protein aggregation, which is established by lysozyme conjugated with polyethylene glycol (Lyso-PEG), forms a mineralized nanofilm layer on a healthy enamel surface. However, whether it can form a remineralization layer in dental tissues from CCD remains unclear.

Methods

This study evaluated deciduous teeth from healthy individuals and a patient with CCD. Because pulp and dentin are functionally closely related, stem cells from human exfoliated deciduous teeth (SHED) from CCD patients and healthy individuals were collected to compare their biological properties.

Results

The results found that deciduous teeth from patients with CCD exhibited dentin hypoplasia. In addition, the proliferative ability and osteogenic potential of SHED from patients with CCD were lower than those of control individuals. Finally, Lyso-PEG was applied to dentin from the CCD and control groups, showing a similar remineralization-induced effect on the dentin surfaces of the two groups.

Conclusion

These results extend our understanding of the dentin and SHED of patients with CCD, exhibiting good caries-preventive capacity and good biocompatibility of Lyso-PEG, thus providing a novel dental therapy for CCD and patients with tooth hypoplasia.

Vestigial-Like 3 Plays an Important Role in Osteoblast Differentiation by Regulating the Expression of Osteogenic Transcription Factors and BMP Signaling

Our previous gene profiling analysis showed that the transcription cofactor vestigial-like 3 (VGLL3) gene expression was upregulated by mechanical tension in the mouse cranial suture, coinciding with accelerated osteoblast differentiation. Therefore, we hypothesized that VGLL3 plays a significant role in osteogenic differentiation. To clarify the function of VGLL3 in osteoblasts, we examined its expression characteristics in mouse bone tissue and the osteoblastic cell line MC3T3-E1. We further examined the effects of Vgll3 knockdown on osteoblast differentiation and bone morphogenetic protein (BMP) signaling. In the mouse cranial suture, where membranous ossification occurs, VGLL3 was immunohistochemically detected mostly in the nucleus of osteoblasts, preosteoblasts, and fibroblastic cells. VGLL3 expression in MC3T3-E1 cells was transient and peaked at a relatively early stage of differentiation. RNA sequencing revealed that downregulated genes in Vgll3-knockdown cells were enriched in gene ontology terms associated with osteoblast differentiation. Interestingly, most of the upregulated genes were related to cell division. Targeted Vgll3 knockdown markedly suppressed the expression of major osteogenic transcription factors (Runx2, Sp7/osterix, and Dlx5) and osteoblast differentiation. It also attenuated BMP signaling; moreover, exogenous BMP2 partially restore osteogenic transcription factors' expression in Vgll3-knockdown cells. Furthermore, overexpression of Vgll3 increased the expression of osteogenic transcription factors. These results suggest that VGLL3 plays a critical role in promoting osteoblast differentiation and that part of the process is mediated by BMP signaling. Further elucidation of VGLL3 function will increase our understanding of osteogenesis and skeletal disease etiology.

TET enzymes regulate skeletal development through increasing chromatin accessibility of RUNX2 target genes

The Ten-eleven translocation (TET) family of dioxygenases mediate cytosine demethylation by catalyzing the oxidation of 5-methylcytosine (5mC). TET-mediated DNA demethylation controls the proper differentiation of embryonic stem cells and TET members display functional redundancy during early gastrulation. However, it is unclear if TET proteins have functional significance in mammalian skeletal development. Here, we report that Tet genes deficiency in mesoderm mesenchymal stem cells results in severe defects of bone development. The existence of any single Tet gene allele can support early bone formation, suggesting a functional redundancy of TET proteins. Integrative analyses of RNA-seq, Whole Genome Bisulfite Sequencing (WGBS), 5hmC-Seal and Assay for Transposase-Accessible Chromatin (ATAC-seq) demonstrate that TET-mediated demethylation increases the chromatin accessibility of target genes by RUNX2 and facilities RUNX2-regulated transcription. In addition, TET proteins interact with RUNX2 through their catalytic domain to regulate cytosine methylation around RUNX2 binding region. The catalytic domain is indispensable for TET enzymes to regulate RUNX2 transcription activity on its target genes and to regulate bone development. These results demonstrate that TET enzymes function to regulate RUNX2 activity and maintain skeletal homeostasis.

Here the authors investigate the role of the TET family of DNA demethylases in mammalian skeletal development. They find that loss of TETs leads to hypermethylation that results in decreased chromatin accessibility of RUNX2 target genes, repressing osteoblast differentiation and leading to skeletal defects in mouse such as short limbs.

Selective YAP activation in Procr cells is essential for ovarian stem/progenitor expansion and epithelium repair

Ovarian surface epithelium (OSE) undergoes recurring ovulatory rupture and OSE stem cells rapidly generate new cells for the repair. How the stem cell activation is triggered by the rupture and promptly turns on proliferation is unclear. Our previous study has identified that Protein C Receptor (Procr) marks OSE progenitors. In this study, we observed decreased adherent junction and selective activation of YAP signaling in Procr progenitors at OSE rupture site. OSE repair is impeded upon deletion of Yap1 in these progenitors. Interestingly, Procr+ progenitors show lower expression of Vgll4, an antagonist of YAP signaling. Overexpression of Vgll4 in Procr+ cells hampers OSE repair and progenitor proliferation, indicating that selective low Vgll4 expression in Procr+ progenitors is critical for OSE repair. In addition, YAP activation promotes transcription of the OSE stemness gene Procr. The combination of increased cell division and Procr expression leads to expansion of Procr+ progenitors surrounding the rupture site. These results illustrate a YAP-dependent mechanism by which the stem/progenitor cells recognize the murine ovulatory rupture, and rapidly multiply their numbers, highlighting a YAP-induced stem cell expansion strategy.

Melatonin enhances osteoblastogenesis of senescent bone marrow stromal cells through NSD2-mediated chromatin remodelling

BACKGROUND

Aging-associated osteoporosis is frequently seen in the elderly in clinic, but efficient managements are limited because of unclear nosogenesis. The current study aims to investigate the role of melatonin on senescent bone marrow stromal cells (BMSCs) and the underlying regulating mechanism.

METHODS

Melatonin levels were tested by ELISA. Gene expression profiles were performed by RNA-sequencing, enrichment of H3K36me2 on gene promoters was analyzed by Chromatin Immunoprecipitation Sequencing (ChIP-seq), and chromatin accessibility was determined by Assay for Transposase-Accessible Chromatin with high-throughput sequencing (ATAC-seq). Osteogenesis of BMSCs in vitro was measured by Alizarin Red and Alkaline Phosphatase staining, and in vivo effects of melatonin was assessed by histological staining and micro computed tomography (micro-CT) scan. Correlation of NSD2 expression and severity of senile osteoporosis patients were analyzed by Pearson correlation.

RESULTS

Melatonin levels were decreased during aging in human bone marrow, accompanied by downregulation of the histone methyltransferase nuclear receptor binding SET domain protein 2 (NSD2) expression in the senescent BMSCs. Melatonin stimulated the expression of NSD2 through MT1/2-mediated signaling pathways, resulting in the rebalancing of H3K36me2 and H3K27me3 modifications to increase chromatin accessibility of the osteogenic genes, runt-related transcription factor 2 (RUNX2) and bone gamma-carboxyglutamate protein (BGLAP). Melatonin promoted osteogenesis of BMSCs in vitro, and alleviates osteoporosis progression in the aging mice. In clinic, severity of senile osteoporosis (SOP) was negatively correlated with melatonin level in bone marrow, as well as NSD2 expression in BMSCs. Similarly, melatonin remarkably enhanced osteogenic differentiation of BMSCs derived from SOP patients in vitro.

CONCLUSIONS

Collectively, our study dissects previously unreported mechanistic insights into the epigenetic regulating machinery of melatonin in meliorating osteogenic differentiation of senescent BMSC, and provides evidence for application of melatonin in preventing aging-associated bone loss.

Context-dependent transcriptional regulations of YAP/TAZ in stem cell and differentiation

Hippo pathway is initially identified as a master regulator for cell proliferation and organ size control, and the subsequent researches show this pathway is also involved in development, tissue regeneration and homeostasis, inflammation, immunity and cancer. YAP/TAZ, the downstream effectors of Hippo pathway, usually act as coactivators and are dependent on other transcription factors to mediate their transcriptional outputs. In this review, we will first provide an overview on the core components and regulations of Hippo pathway in mammals, and then systematically summarize the identified transcriptional factors or partners that are responsible for the transcriptional output of YAP/TAZ in stem cell and differentiation. More than that, we will discuss the potential applications and future directions based on these findings.

Protective effects of naringin on glucocorticoid-induced osteoporosis through regulating the PI3K/Akt/mTOR signaling pathway

OBJECTIVE

To investigate the protective effects of Naringin on glucocorticoid-induced osteoporosis (GIOP) through the PI3K/AKT/mTOR signaling pathway in vivo and in vitro.

METHODS

Osteoblasts were cultured from the differentiated bone marrow mesenchymal stem cells (BM-MSCs) and were grouped as follows: the PBS group (the control group), the model group (Dexamethasone intervention), the LY294002 group (PI3K/AKT/mTOR pathway inhibitor intervention), the Naringin group (Naringin intervention), and the LY294002+ Naringin intervention group. Cell proliferation and differentiation were detected through cell counting kit-8 (CCK8) assay and alkaline phosphatase (ALP) staining, respectively. The formation of autophagosome was observed by Monodansylcadaverine (MDC) staining. Expressions of signaling pathway and autophagy related factors such as Beclin-1 and p62 were detected by qRT-PCR and western blot. Then, the rats were grouped as the PBS group (normal rats injected with PBS), the model group (GIOP rats injected with dexamethasone), the LY294002 group (GIOP rats injected with PI3K/AKT/mTOR pathway inhibitor LY294002), the Naringin group (GIOP rats injected with Naringin) and the LY294002+ Naringin group (GIOP rats injected with PI3K/AKT/mTOR pathway inhibitor LY294002 and Naringin). Bone mineral density and bone histomorphometry parameters of rats in each group were compared. In addition, the expressions of pathway and autophagy related factors in cartilage tissue of rats in each groups were also detected.

RESULTS

The proliferation and differentiation abilities of osteoblasts were increased with an increasing concentration of Naringin in a dose-dependent manner. Compared with the model group, the expression of PI3K/AKT/mTOR pathway related phosphorylated proteins, the proliferation and differentiation abilities of osteoblasts, the expression of autophagosome and autophagy related factors were all increased in the Naringin group, but contrary results were found in the LY294002 group (all P<0.05). In vivo, GIOP rats had improved bone mineral density and bone morphology parameters , and elevated expressions of autophagy related factors in cartilage tissue compared to the model group through Naringin intervention, while LY294002 intervention showed the opposite effects (all P<0.05). What is more, LY294002 partially reversed the effects of Naringin on osteogenic differentiation and bone morphological parameters in GIOP.

CONCLUSION

Naringin exerts protective effects in GIOP by the PI3K/AKT/mTOR pathway, which may be related to autophagy induction and enhanced proliferation of osteoblasts.

TEAD family transcription factors in development and disease

The balance between stem cell potency and lineage specification entails the integration of both extrinsic and intrinsic cues, which ultimately influence gene expression through the activity of transcription factors. One example of this is provided by the Hippo signalling pathway, which plays a central role in regulating organ size during development. Hippo pathway activity is mediated by the transcriptional co-factors Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ), which interact with TEA domain (TEAD) proteins to regulate gene expression. Although the roles of YAP and TAZ have been intensively studied, the roles played by TEAD proteins are less well understood. Recent studies have begun to address this, revealing that TEADs regulate the balance between progenitor self-renewal and differentiation throughout various stages of development. Furthermore, it is becoming apparent that TEAD proteins interact with other co-factors that influence stem cell biology. This Primer provides an overview of the role of TEAD proteins during development, focusing on their role in Hippo signalling as well as within other developmental, homeostatic and disease contexts.

Molecular mechanisms of intermuscular bone development in fish: a review

Intermuscular bones (IBs) are slender linear bones embedded in muscle, which ossify from tendons through a process of intramembranous ossification, and only exist in basal teleosts. IBs are essential for fish swimming, but they present a choking risk during human consumption, especially in children, which can lead to commercial risks that have a negative impact on the aquaculture of these fish. In this review, we discuss the morphogenesis and functions of IBs, including their underlying molecular mechanisms, as well as the advantages and disadvantages of different methods for IB studies and techniques for breeding and generating IB-free fish lines. This review reveals that the many key genes involved in tendon development, osteoblast differentiation, and bone formation, e.g., scxa, msxC, sost, twist, bmps, and osterix, also play roles in IB development. Thus, this paper provides useful information for the breeding of new fish strains without IBs via genome editing and artificial selection.