LGR6 promotes osteogenesis by activating the Wnt/β-catenin signaling pathway

Crosstalk between Wnt and bone morphogenetic protein signaling during osteogenic differentiation

Mesenchymal stem cells (MSCs) originate from many sources, including the bone marrow and adipose tissue, and differentiate into various cell types, such as osteoblasts and adipocytes. Recent studies on MSCs have revealed that many transcription factors and signaling pathways control osteogenic development. Osteogenesis is the process by which new bones are formed; it also aids in bone remodeling. Wnt/β-catenin and bone morphogenetic protein (BMP) signaling pathways are involved in many cellular processes and considered to be essential for life. Wnt/β-catenin and BMPs are important for bone formation in mammalian development and various regulatory activities in the body. Recent studies have indicated that these two signaling pathways contribute to osteogenic differentiation. Active Wnt signaling pathway promotes osteogenesis by activating the downstream targets of the BMP signaling pathway. Here, we briefly review the molecular processes underlying the crosstalk between these two pathways and explain their participation in osteogenic differentiation, emphasizing the canonical pathways. This review also discusses the crosstalk mechanisms of Wnt/BMP signaling with Notch- and extracellular-regulated kinases in osteogenic differentiation and bone development.

Maresin 1 repletion improves muscle regeneration after volumetric muscle loss

The acute traumatic or surgical loss of skeletal muscle, known as volumetric muscle loss (VML), is a devastating type of injury that results in exacerbated and persistent inflammation followed by fibrosis. The mechanisms that mediate the magnitude and duration of the inflammatory response and ensuing fibrosis after VML remain understudied, and as such, the development of regenerative therapies has been limited. To address this need, we profiled how lipid mediators, which are potent regulators of the immune response after injury, varied with VML injuries that heal or result in fibrosis. We observed that non-healing VML injuries displayed increased pro-inflammatory eicosanoids and a lack of pro-resolving lipid mediators. Treatment of VML with a pro-resolving lipid mediator synthesized from docosahexaenoic acid, called Maresin 1, ameliorated fibrosis through reduction of neutrophils and macrophages and enhanced recovery of muscle strength. These results expand our knowledge of the dysregulated immune response that develops after VML and identify a novel immuno-regenerative therapeutic modality in Maresin 1.

DNA methylation and expression of LGR6 gene in ankylosing spondylitis: A case-control study

OBJECTIVE

The objectives of the present research were to ascertain the relationship of Leucine-Rich Repeat-Containing G-Protein Coupled Receptors 6 (LGR6) methylation and transcript levels with ankylosing spondylitis (AS).

METHODS

Targeted bisulfite sequencing was applied to analyze LGR6 DNA methylation in 81 AS cases and 81 controls. Besides, the LGR6 transcription level of peripheral blood mononuclear cells (PBMCs) from 70 AS cases and 64 controls was measured utilizing quantitative real-time transcription-polymerase chain reaction (qRT-PCR).

RESULTS

The study detected the methylation levels of 43 sites in two CpG (cytosine-guanine dinucleotide) islands of LGR6 and found that LGR6 were significantly hypomethylated in AS patients (LGR6_1: P = 0.002; LGR6_2: P < 0.001). LGR6 transcript level was obviously reduced in AS (P = 0.001) and was positively related to DNA methylation level (CpG-1: P = 0.010; CpG-2: P = 0.007). Besides, the Receiver operating characteristic curve (ROC) exhibited good diagnostic performance of LGR6 methylation level (AUC = 0.676, 95% CI = 0.594-0.758, P < 0.001). Further subgroup analysis revealed that gender may affect the LGR6_1 methylation pattern.

CONCLUSION

The present study revealed that LGR6 DNA methylation dysregulation may be involved in the pathogenesis of AS from an epigenetic perspective for the first time, with the aim of providing new directions for biomarker identification and treatment development for AS patients.

Comparative transcriptomic analysis of mammary gland tissues reveals the critical role of GPR110 in palmitic acid-stimulated milk protein and fat synthesis

The G protein-coupled receptors (GPCR) sensing nutritional signals (amino acids, fatty acids, glucose, etc.) are not fully understood. In this research, we used transcriptome sequencing to analyse differentially expressed genes (DEG) in mouse mammary gland tissues at puberty, lactation and involution stages, in which eight GPCR were selected out and verified by qRT-PCR assay. It was further identified the role of GPR110-mediating nutrients including palmitic acid (PA) and methionine (Met) to improve milk synthesis using mouse mammary epithelial cell line HC11. PA but not Met affected GPR110 expression in a dose-dependent manner. GPR110 knockdown decreased milk protein and fat synthesis and cell proliferation and blocked the stimulation of PA on mechanistic target of rapamycin (mTOR) phosphorylation and sterol-regulatory element binding protein 1c (SREBP-1c) expression. In summary, these experimental results disclose DEG related to lactation and reveal that GPR110 mediates PA to activate the mTOR and SREBP-1c pathways to promote milk protein and fat synthesis.

Novel scaffold platforms for simultaneous induction osteogenesis and angiogenesis in bone tissue engineering: a cutting-edge approach

Despite the recent advances in the development of bone graft substitutes, treatment of critical size bone defects continues to be a significant challenge, especially in the elderly population. A current approach to overcome this challenge involves the creation of bone-mimicking scaffolds that can simultaneously promote osteogenesis and angiogenesis. In this context, incorporating multiple bioactive agents like growth factors, genes, and small molecules into these scaffolds has emerged as a promising strategy. To incorporate such agents, researchers have developed scaffolds incorporating nanoparticles, including nanoparticulate carriers, inorganic nanoparticles, and exosomes. Current paper provides a summary of the latest advancements in using various bioactive agents, drugs, and cells to synergistically promote osteogenesis and angiogenesis in bone-mimetic scaffolds. It also discusses scaffold design properties aimed at maximizing the synergistic effects of osteogenesis and angiogenesis, various innovative fabrication strategies, and ongoing clinical studies.

Recent Advances in Stem Cell Differentiation Control Using Drug Delivery Systems Based on Porous Functional Materials

The unique characteristics of stem cells, which include self-renewal and differentiation into specific cell types, have paved the way for the development of various biomedical applications such as stem cell therapy, disease modelling, and drug screening. The establishment of effective stem cell differentiation techniques is essential for the effective application of stem cells for various purposes. Ongoing research has sought to induce stem cell differentiation using diverse differentiation factors, including chemicals, proteins, and integrin expression. These differentiation factors play a pivotal role in a variety of applications. However, it is equally essential to acknowledge the potential hazards of uncontrolled differentiation. For example, uncontrolled differentiation can give rise to undesirable consequences, including cancerous mutations and stem cell death. Therefore, the development of innovative methods to control stem cell differentiation is crucial. In this review, we discuss recent research cases that have effectively utilised porous functional material-based drug delivery systems to regulate stem cell differentiation. Due to their unique substrate properties, drug delivery systems based on porous functional materials effectively induce stem cell differentiation through the steady release of differentiation factors. These ground-breaking techniques hold considerable promise for guiding and controlling the fate of stem cells for a wide range of biomedical applications, including stem cell therapy, disease modelling, and drug screening.

Signalling pathways in the osteogenic differentiation of periodontal ligament stem cells

Periodontal ligament stem cells (PDLSCs) have multidirectional differentiation potential and self-renewal abilities and are important seed cells for the regenerative repair of periodontal tissues. In recent years, many studies have identified multiple signalling pathways involved in regulating the osteogenic differentiation of PDLSCs in an inflammatory environment. In this article, we review the osteogenic differentiation of PDLSCs in an inflammatory environment in terms of signalling pathways and provide new ideas for the regenerative treatment of periodontal tissues.

Overexpression of NT-3 in the hippocampus suppresses the early phase of the adult neurogenic process

The dentate gyrus (DG) of the hippocampus regulates stress-related emotional behaviors and ensures neurogenesis throughout life. Neurotrophin-3 (NT-3) is a neurotrophic factor that regulates neuronal differentiation, survival, and synaptic formation in both the peripheral and central nervous systems. NT-3 is expressed in the adult DG of the hippocampus; several chronic stress conditions enhance NT-3 expression in rodents. However, functional modulation of the adult DG by NT-3 signaling remains unclear. To directly investigate the impact of NT-3 on DG function, NT-3 was overexpressed in the hippocampal ventral DG by an adeno-associated virus carrying NT-3 (AAV-NT-3). Four weeks following the AAV-NT-3 injection, high NT-3 expression was observed in the ventral DG. We examined the influence of NT-3 overexpression on the neuronal responses and neurogenic processes in the ventral DG. NT-3 overexpression significantly increased the expression of the mature DG neuronal marker calbindin and immediate early genes, such as Fos and Fosb, thereby suggesting DG neuronal activation. During neurogenesis, the number of proliferating cells and immature neurons in the subgranular zone of the DG significantly decreased in the AAV-NT-3 group. Among the neurogenesis-related factors, Vegfd, Lgr6, Bmp7, and Drd1 expression significantly decreased. These results demonstrated that high NT-3 levels in the hippocampus regulate the activation of mature DG neurons and suppress the early phase of neurogenic processes, suggesting a possible role of NT-3 in the regulation of adult hippocampal function under stress conditions.

All-Trans Retinoic Acid-Responsive LGR6 Is Transiently Expressed during Myogenic Differentiation and Is Required for Myoblast Differentiation and Fusion

All-trans retinoic acid (ATRA) promotes myoblast differentiation into myotubes. Leucine-rich repeat-containing G-protein-coupled receptor 6 (LGR6) is a candidate ATRA-responsive gene; however, its role in skeletal muscles remains unclear. Here, we demonstrated that during the differentiation of murine C2C12 myoblasts into myotubes, Lgr6 mRNA expression transiently increased before the increase in the expression of the mRNAs encoding myogenic regulatory factors, such as myogenin, myomaker, and myomerger. The loss of LGR6 decreased the differentiation and fusion indices. The exogenous expression of LGR6 up to 3 and 24 h after the induction of differentiation increased and decreased the mRNA levels of myogenin, myomaker, and myomerger, respectively. Lgr6 mRNA was transiently expressed after myogenic differentiation in the presence of a retinoic acid receptor α (RARα) agonist and an RARγ agonist in addition to ATRA, but not in the absence of ATRA. Furthermore, a proteasome inhibitor or Znfr3 knockdown increased exogenous LGR6 expression. The loss of LGR6 attenuated the Wnt/β-catenin signaling activity induced by Wnt3a alone or in combination with Wnt3a and R-spondin 2. These results indicate that LGR6 promotes myogenic differentiation and that ATRA is required for the transient expression of LGR6 during differentiation. Furthermore, LGR6 expression appeared to be downregulated by the ubiquitin-proteasome system involving ZNRF3.

Maresin1: A multifunctional regulator in inflammatory bone diseases

Inflammation plays a crucial role in the physical response to danger signals, the elimination of toxic stimuli, and the restoration of homeostasis. However, dysregulated inflammatory responses lead to tissue damage, and chronic inflammation can disrupt osteogenic-osteoclastic homeostasis, ultimately leading to bone loss. Maresin1 (MaR1), a member of the specialized pro-resolving mediators (SPMs) family, has been found to possess significant anti-inflammatory, anti-allergic, pro-hemolytic, pro-healing, and pain-relieving properties. MaR1 is synthesized by macrophages (Mφs) and omega-3 fatty acids, and it may have the potential to promote bone homeostasis and treat inflammatory bone diseases. MaR1 has been found to stimulate osteoblast proliferation through leucine-rich repeat G protein-coupled receptor 6 (LGR6). It also activates Mφ phagocytosis and M2-type polarization, which helps to control the immune system. MaR1 can regulate T cells to exert anti-inflammatory effects and inhibit neutrophil infiltration and recruitment. In addition, MaR1 is involved in antioxidant signaling, including nuclear factor erythroid 2-related factor 2 (NRF2). It has also been found to promote the autophagic behavior of periodontal ligament stem cells, stimulate Mφs against pathogenic bacteria, and regulate tissue regeneration and repair. In summary, this review provides new information and a comprehensive overview of the critical roles of MaR1 in inflammatory bone diseases, indicating its potential as a therapeutic approach for managing skeletal metabolism and inflammatory bone diseases.

Wnt-associated adult stem cell marker Lgr6 is required for osteogenesis and fracture healing

Despite the remarkable regenerative capacity of skeletal tissues, nonunion of bone and failure of fractures to heal properly presents a significant clinical concern. Stem and progenitor cells are present in bone and become activated following injury; thus, elucidating mechanisms that promote adult stem cell-mediated healing is important. Wnt-associated adult stem marker Lgr6 is implicated in the regeneration of tissues with well-defined stem cell niches in stem cell-reliant organs. Here, we demonstrate that Lgr6 is dynamically expressed in osteoprogenitors in response to fracture injury. We used an Lgr6-null mouse model and found that Lgr6 expression is necessary for maintaining bone volume and efficient postnatal bone regeneration in adult mice. Skeletal progenitors isolated from Lgr6-null mice have reduced colony-forming potential and reduced osteogenic differentiation capacity due to attenuated cWnt signaling. Lgr6-null mice consist of a lower proportion of self-renewing stem cells. In response to fracture injury, Lgr6-null mice have a deficiency in the proliferation of periosteal progenitors and reduced ALP activity. Further, analysis of the bone regeneration phase and remodeling phase of fracture healing in Lgr6-null mice showed impaired endochondral ossification and decreased mineralization. We propose that in contrast to not being required for successful skeletal development, Lgr6-positive cells have a direct role in endochondral bone repair.

The expression of NOTUM in replantation of severed fingers may be an important treatment factor

BACKGROUND

After years of development, digital replantation has become a mature treatment. Although the NOTUM gene has been shown to be involved in the formation of vertebrate nerves, whether it contributes to the osteogenic mechanism of severed finger replantation remains unknown. In response to this, this study investigates the specific details of NOTUM involvement in replantation of severed fingers.

METHODS

The experimental subjects are patients with replantation of severed fingers from Shulan International Medical College of Shulan (Hangzhou) Hospital affiliated to Zhejiang Shuren University. In addition to using bone marrow mesenchymal stem cells (BMSCs) as an in vitro system, this experiment also involves quantitative polymerase chain reaction, microarray analysis, cell counting Kit-8, ethynyl deoxyuridine staining and Western blot analysis.

RESULTS

The expression level of NOTUM in the severed finger replantation group is lower than that in the normal group. NOTUM inhibits cell growth and cell transfer, osteogenic differentiation and β-catenin gene expression in BMSCs. Luciferase reporter assay illustrated that β-catenin wild type closely correlated with NOTUM. The inhibition of β-catenin increases the effects of NOTUM on cell growth, cell transfer and osteogenic differentiation of BMSCs.

CONCLUSIONS

Considering that NOTUM can inhibit cell growth, cell transfer, osteogenic differentiation of BMSCs, as well as the gene expression of β-catenin, it may be a biomarker of osteogenic differentiation and a potential therapeutic target for replantation of severed fingers.

The combination of BMP12 and KY02111 enhances tendon differentiation in bone marrow-derived equine mesenchymal stromal cells (BM-eMSCs)

The Wingless and Int-1 (WNT) and bone morphogenic protein/growth differentiation factor (BMP/GDF) signalling pathways contribute significantly to the development of the musculoskeletal system. The mechanism by which they contribute is as follows: BMP/GDF signalling usually promotes tendon differentiation, whereas WNT signalling inhibits it. We hypothesised that inhibiting WNT and subsequently stimulating BMP signalling may enhance the tenogenic differentiation of stem cells. The objective of this study was to determine whether a combination of WNT inhibitor (KY02111) and BMP12/GDF7 protein could enhance the differentiation of bone marrow-derived equine mesenchymal stromal cells (BM-eMSCs) into tenocytes. Cells were cultured in five treatments: control, BMP12, and three different combinations of BMP12 and KY02111. The results indicated that a 1-day treatment with KY02111 followed by a 13-day treatment with BMP12 resulted in the highest tenogenic differentiation score in this experiment. The effect of KY02111 is dependent on the incubation time, with 1 day being better than 3 or 5 days. This combination increased tenogenic gene marker expression, including SCX, TNMD, DCN, and TNC, as well as COL1 protein expression. In conclusion, we propose that a combination of BMP12 and KY02111 can enhance the in vitro tenogenic differentiation of BM-eMSCs more than BMP12 alone. The findings of this study might be useful for improving tendon differentiation protocols for stem cell transplantation and application to tendon regeneration.

Maresin 1 Alleviates Diabetic Kidney Disease via LGR6-Mediated cAMP-SOD2-ROS Pathway

Background. Chronic hyperglycemia-induced inflammation is recognized as the most important pathophysiological process in diabetic kidney disease (DKD). As maresin 1 (MaR1) is an extensive anti-inflammatory lipid mediator, the present study investigated the protective role of MaR1 in the pathogenesis of DKD and its clinical relevance. Methods. Serum MaR1 concentrations were analyzed in 104 subjects with normal glucose tolerant, type 2 diabetes (T2DM), or DKD. Streptozotocin (STZ) together with high fat diet was used to induce male C57BL/6 J mice into diabetic mice which were treated with MaR1. Human renal tubule epithelial cells (HK-2 cells) were treated by high glucose for glucotoxicity cell model and transfected with LGR6 siRNA for knockdown with MaR1 added，and detected oxidative stress and inflammatory related factors. Results. Serum MaR1 concentrations were significant decreased in T2DM with or without kidney disease compared with normal participant and were lowest in patients with DKD. Serum MaR1 concentrations were negatively correlated with hemoglobin A1c (HbA1c), duration of diabetes, urinary albumin to creatinine ratio (UACR), neutrophil, and neutrophil-lymphocyte ratio and were positively correlated with high-density lipoprotein-cholesterol (HDL-C) and estimated glomerular filtration rate (eGFR). In mouse model, MaR1 injection alleviated hyperglycemia, UACR and the pathological progression of DKD. Interestingly, the renal expression of LGR6 was down-regulated in DKD and high glucose treated HK-2 cells but up-regulated by MaR1 treatment. Mechanistically, MaR1 alleviated inflammation via LGR6-mediated cAMP-SOD2 antioxidant pathway in DKD mice and high glucose treated HK-2 cells. Conclusions. Our study demonstrates that decreased serum MaR1 levels were correlated with the development of DKD. MaR1 could alleviate DKD and glucotoxicity-induced inflammation via LGR6-mediated cAMP-SOD2 antioxidant pathway. Thus, our present findings identify MaR1 as a predictor and a potential therapeutic target for DKD.

Mouse LGR6 regulates osteogenesis in vitro and in vivo through differential ligand use

Leucine-rich repeat containing G-protein-coupled receptor 6 (LGR6) is a marker of osteoprogenitor cells and is dynamically expressed during in vitro osteodifferentation of mouse and human mesenchymal stem cells (MSCs). While the Lgr6 genomic locus has been associated with osteoporosis in human cohorts, the precise molecular function of LGR6 in osteogenesis and maintenance of bone mass are not yet known. In this study, we performed in vitro Lgr6 knockdown and overexpression experiments in murine osteoblastic cells and find decreased Lgr6 levels results in reduced osteoblast proliferation, differentiation, and mineralization. Consistent with these data, overexpression of Lgr6 in these cells leads to significantly increased proliferation and osteodifferentiation. To determine whether these findings are recapitulated in vivo, we performed microCT and ex vivo osteodifferentiation analyses using our newly generated CRISPR-Cas9 mediated Lgr6 mouse knockout allele (Lgr6-KO). We find that ex vivo osteodifferentiation of Lgr6-KO primary MSCs is significantly reduced, and 8 week-old Lgr6-KO mice have less trabecular bone mass as compared to Lgr6 wildtype controls, indicating that Lgr6 is necessary for normal osteogenesis and bone mass. Towards mechanism, we analyzed in vitro signaling in the context of two LGR6 ligands, RSPO2 and MaR1. We find that RSPO2 stimulates LGR6-mediated WNT/β-catenin signaling whereas MaR1 stimulates LGR6-mediated cAMP activity, suggesting two ligand-dependent functions for LGR6 receptor signaling during osteogenesis. Collectively, this study reveals that Lgr6 is necessary for wildtype levels of proliferation and differentiation of osteoblasts, and achieving normal bone mass.

LINC01119 negatively regulates osteogenic differentiation of mesenchymal stem cells via the Wnt pathway by targeting FZD4

Background

Mesenchymal stem cells (MSCs) can differentiate into diverse cell types under specific conditions. Dysfunction in the osteogenic differentiation of MSCs can result in bone metabolism-related diseases, including osteoporosis. Accumulating evidence has revealed that long non-coding RNA (lncRNAs) play critical regulatory roles during MSC differentiation.

Methods

In the present study, we identified an evolutionarily conserved lncRNA expressed during the osteogenic differentiation of MSCs, which we termed LINC01119. We first identified LINC01119 as a negative regulator of the osteogenic differentiation of MSCs.

Results

LINC01119 knockdown markedly induced calcium deposition in bone marrow MSCs and promoted the osteogenic differentiation of MSCs. More importantly, we demonstrated the underlying molecular basis through which LINC01119 regulates osteogenesis via the Wnt pathway by targeting FZD4. Furthermore, we observed that transcription factor EBF3 could directly bind the promoter site of LINC01119.

Conclusions

We first explored the molecular regulatory mechanism of LINC01119 during the osteogenic differentiation of MSCs and revealed that LINC01119 negatively regulates osteogenesis through the Wnt pathway by targeting FZD4.

Wnt Pathway Extracellular Components and Their Essential Roles in Bone Homeostasis

The Wnt pathway is involved in several processes essential for bone development and homeostasis. For proper functioning, the Wnt pathway is tightly regulated by numerous extracellular elements that act by both activating and inhibiting the pathway at different moments. This review aims to describe, summarize and update the findings regarding the extracellular modulators of the Wnt pathway, including co-receptors, ligands and inhibitors, in relation to bone homeostasis, with an emphasis on the animal models generated, the diseases associated with each gene and the bone processes in which each member is involved. The precise knowledge of all these elements will help us to identify possible targets that can be used as a therapeutic target for the treatment of bone diseases such as osteoporosis.

Increased LGR6 Expression Sustains Long-Term Wnt Activation and Acquisition of Senescence in Epithelial Progenitors in Chronic Lung Diseases

Chronic lung diseases (CLDs) represent a set of disorders characterized by the progressive loss of proper lung function. Among severe CLDs, the incidence of chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF) has grown over the last decades, mainly in the elderly population. Several studies have highlighted an increased expression of senescence-related markers in the resident progenitor cells in COPD and IPF, possibly undermining epithelial integrity and contributing to the progression and the aggravation of both diseases. Recently, the chronic activation of the canonical Wnt/β-catenin pathway was shown to induce cellular senescence. Here, we investigated the localization and the expression of leucin-rich repeat-containing G-protein-coupled receptor 6 (LGR6), a protein that activates and potentiates the canonical Wnt signalling. Through immunohistochemical analyses, we identified a lesion-associated rise in LGR6 levels in abnormal lung epithelial progenitors in COPD and IPF when compared to histologically normal tissues. Moreover, in areas of aberrant regeneration, chronic damage and fibrosis, LGR6-expressing epithelial progenitors displayed a major increase in the expression of senescence-associated markers. Our study suggests the involvement of LGR6 in the chronic activation of the Wnt/β-catenin pathway, mediating the impairment and exhaustion of epithelial progenitors in COPD and IPF.

Integrative Analysis of LGR5/6 Gene Variants, Gut Microbiota Composition and Osteoporosis Risk in Elderly Population

Objective: This study aimed to explore the relationships between the common variants of R-spondin/Wnt signaling genes, gut microbiota composition, and osteoporosis (OP) risk in elderly Chinese Han population.

Design: Dual-energy X-ray absorptiometry was used to obtain the OP-associated measurements at multiple skeleton sites among all 1,168 participants. Genotyping data was obtained by using the next-generation sequencing in the discovery stage (n = 400, 228 OP patients) and SNPscan technology in the replication stage (n = 768, 356 OP patients). Bioinformatic analysis was performed to provide more evidence for the genotype-OP associations. The 16S ribosomal RNA gene high-throughput sequencing technology was adopted to explore OP-associated gut microbiota variations.

Results: The genetic variants of rs10920362 in the LGR6 gene (P-FDR = 1.19 × 10^–6) and rs11178860 in the LGR5 gene (P-FDR = 1.51 × 10^–4) were found to associate with OP risk significantly. Several microbial taxa were associated with the BMDs and T-scores at multiple skeleton sites. The associations between rs10920362 and BMD-associated microbiota maintained significance after adjusting confounders. The rs10920362 CT/TT genotype associated with a decreased relative abundance of Actinobacteria (β = −1.32, P < 0.001), Bifidobacteriaceae (β = −1.70, P < 0.001), and Bifidobacterium (β = −1.70, P < 0.001) compared to the CC genotype.

Conclusion: Our findings suggested that the variants loci of LGR6 may be associate with OP pathogenesis via gut microbiota modifications. The relationship between host genetics and gut microbiome provides new perspectives about OP prevention and treatment.

Critical roles of microRNA-196 in normal physiology and non-malignant diseases: Diagnostic and therapeutic implications

MicroRNAs (miRNAs) have emerged as a critical component of regulatory networks that modulate and fine-tune gene expression in a post-transcriptional manner. The microRNA-196 family is encoded by three loci in the human genome, namely hsa-mir-196a-1, hsa-mir-196a-2, and hsa-mir-196b. Increasing evidence supports the roles of different components of this miRNA family in regulating key cellular processes during differentiation and development, ranging from inflammation and differentiation of stem cells to limb development and remodeling and structure of adipose tissue. This review first discusses about the genomic context and regulation of this miRNA family and then take a bird's eye view on the updated list of its target genes and their biological processes to obtain insights about various functions played by members of the microRNA-196 family. We then describe evidence supporting the involvement of the human microRNA-196 family in regulating critical cellular processes both in physiological and non-malignant inflammatory conditions, highlighting recent seminal findings that carry implications for developing novel therapeutic or diagnostic strategies.

LGR5 enhances the osteoblastic differentiation of MC3T3-E1 cells through the Wnt/β-catenin pathway

Leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5) is a Wnt-associated gene that contributes to cell proliferation and self-renewal in various organs. LGR5 is expressed in Ewing sarcoma, and LGR5-overexpressing mesenchymal stem cells promote fracture healing. However, the effects of LGR5 on osteoblastic differentiation remain unclear. The aim of the present study was to explore the function of LGR5 in osteoblastic differentiation. LGR5 was overexpressed or knocked down in the MC3T3-E1 pre-osteoblastic cell line via lentiviral transfection and its function in osteoblastic differentiation was investigated. The mRNA expression levels of the osteoblast differentiation markers alkaline phosphatase (ALP), osteocalcin and collagen type I a1 were determined, and ALP and Alizarin red staining were performed. In addition, the effects of LGR5 modulation on β-catenin and the expression of target genes in the Wnt pathway were investigated. The results revealed that the overexpression of LGR5 promoted osteoblastic differentiation. This was associated with enhancement of the stability of β-catenin and its levels in the cell nucleus, which enabled it to activate Wnt signaling. By contrast, the inhibition of LGR5 decreased the osteogenic capacity of MC3T3-E1 cells. These results indicate that LGR5 is a positive regulator of osteoblastic differentiation, whose effects are mediated through the Wnt/β-catenin signaling pathway. This suggests suggesting that the regulation of LGR5/Wnt/β-catenin signaling has potential as a therapy for osteoporosis.

GPR35 regulates osteogenesis via the Wnt/GSK3β/β-catenin signaling pathway

It is well known that osteoporosis is a significant chronic disease with the increase of the aging population. Here, we report that expression of G protein-coupled receptor 35 (GPR35) in bone marrow mesenchymal stem cells (BMSCs) is suppressed in diagnosed osteoporosis patients and osteoporotic mice. The expression of GPR35 on BMSCs is enhanced during osteogenic differentiation. GPR35 knockout suppresses the proliferation and osteogenesis of BMSCs and deteriorates bone mass in both sham-treated and ovariectomized mice. Moreover, GPR35 deficiency reduces β-catenin activity in BMSCs. In contrast, the overexpression of GPR35 contributes to these processes in BMSCs. Finally, using zaprinast, a synthetic GPR35 agonist, we show that zaprinast rescues OVX-induced bone loss and promotes bone generation in mice. Thus, GPR35 may as a new target and its agonist zaprinast may serve as a novel treatment for osteoporosis.

Biomimetic, Stiff, and Adhesive Periosteum with Osteogenic-Angiogenic Coupling Effect for Bone Regeneration

Current periosteal grafts have limitations related to low mechanical strength, tissue adhesiveness, and poor osteogenesis and angiogenesis potential. Here, a periosteum mimicking bone aid (PMBA) with similar structure and function to natural periosteum is developed by electrospinning photocrosslinkable methacrylated gelatin (GelMA), l-arginine-based unsaturated poly(ester amide) (Arg-UPEA), and methacrylated hydroxyapatite nanoparticles (nHAMA). Such combination of materials enhances the material mechanical strength, favors the tissue adhesion, and guarantees the sustained activation of nitric oxide-cyclic guanosine monophosphate (NO-cGMP) signaling pathway, with well-coordinated osteogenic-angiogenic coupling effect for accelerated bone regeneration. This work presents a proof-of-concept demonstration of thoroughly considering the progression of implant biomaterials: that is, the initial material components (i.e., GelMA, Arg-UPEA, and nHAMA) equip the scaffold with suitable structure and function, while its degradation products (i.e., Ca²⁺ and l-arginine) are involved in long-term mediation of physiological activities. It is envisioned that the strategy will inspire the design of high-performance bioscaffolds toward bone and periosteum tissue engineering.

Fibronectin 1 activates WNT/β-catenin signaling to induce osteogenic differentiation via integrin β1 interaction

Osteoporosis (OP) is a systemic skeletal disease leading to fragility fractures and is a major health issue globally. WNT/β-catenin signaling regulates bone-remodeling processes and plays vital roles in OP development. However, the underlying regulatory mechanisms behind WNT/β-catenin signaling in OP requires clarification, as further studies are required to identify novel alternate therapeutic agents to improve OP. Here we report that fibronectin 1 (FN-1) promoted differentiation and mineralization of osteoblasts by activating WNT/β-catenin pathway, in cultured pre-osteoblasts. With isobaric tags for relative and absolute quantitation labeling proteomics analysis, we investigated protein changes in bone samples from OP patients and normal controls. FN-1 accumulated in osteoblasts in bone samples from OP patients and age-related OP mice compared to control group. In addition, we observed that integrin β1 (ITGB1) acts as an indispensable signaling molecule for the interplay between FN-1 and β-catenin, and that FN-1 expression increased, but ITGB1 expression decreased in osteoblasts during OP progression. Therefore, our study reveals a novel explanation for WNT/β-catenin pathway inactivation in OP pathology. Supplying of FN-1 and ITGB1 may provide a potential therapeutic strategy in improving bone formation during OP.

Maresin-1 and Resolvin E1 Promote Regenerative Properties of Periodontal Ligament Stem Cells Under Inflammatory Conditions

Maresin-1 (MaR1) and Resolvin E1 (RvE1) are specialized pro-resolving lipid mediators (SPMs) that regulate inflammatory processes. We have previously demonstrated the hard and soft tissue regenerative capacity of RvE1 in an in vivo model of the periodontal disease characterized by inflammatory tissue destruction. Regeneration of periodontal tissues requires a well-orchestrated process mediated by periodontal ligament stem cells. However, limited data are available on how SPMs can regulate the regenerative properties of human periodontal ligament stem cells (hPDLSCs) under inflammatory conditions. Thus, we measured the impact of MaR1 and RvE1 in an in vitro model of hPDLSC under stimulation with IL-1β and TNF-α by evaluating pluripotency, migration, viability/cell death, periodontal ligament markers (α-smooth muscle actin, tenomodulin, and periostin), cementogenic-osteogenic differentiation, and phosphoproteomic perturbations. The data showed that the pro-inflammatory milieu suppresses pluripotency, viability, and migration of hPDLSCs; MaR1 and RvE1 both restored regenerative capacity by increasing hPDLSC viability, accelerating wound healing/migration, and up-regulating periodontal ligament markers and cementogenic-osteogenic differentiation. Protein phosphorylation perturbations were associated with the SPM-induced regenerative capacity of hPDLSCs. Together, these results demonstrate that MaR1 and RvE1 restore or improve the regenerative properties of highly specialized stem cells when inflammation is present and offer opportunities for direct pharmacologic treatment of lost tissue integrity.

LGRs in Skeletal Tissues: An Emerging Role for Wnt-Associated Adult Stem Cell Markers in Bone

Leucine‐rich repeat‐containing G protein‐coupled receptors (LGRs) are adult stem cell markers that have been described across various stem cell niches, and expression of LGRs and their corresponding ligands (R‐spondins) has now been reported in multiple bone‐specific cell types. The skeleton harbors elusive somatic stem cell populations that are exceedingly compartment‐specific and under tight regulation from various signaling pathways. Skeletal progenitors give rise to multiple tissues during development and during regenerative processes of bone, requiring postnatal endochondral and intramembranous ossification. The relevance of LGRs and the LGR/R‐spondin ligand interaction in bone and tooth biology is becoming increasingly appreciated. LGRs may define specific stem cell and progenitor populations and their behavior during both development and regeneration, and their role as Wnt‐associated receptors with specific ligands poses these proteins as unique therapeutic targets via potential R‐spondin agonism. This review seeks to outline the current literature on LGRs in the context of bone and its associated tissues, and points to key future directions for studying the functional role of LGRs and ligands in skeletal biology. © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Differentially expressed circular RNAs in maternal and neonatal umbilical cord plasma from SGA compared with AGA

Small for gestational age (SGA) has a high risk of mortality and morbidity and is common in obstetrics. To date, no effective prediction and treatment tools are available. Acting as microRNA (miRNA) sponges and disease biomarkers are clear functions of circular RNAs (circRNAs). However, it is still unknown what role circRNAs act in SGA. To explore the role of circRNAs in SGA, circRNA expression patterns of the umbilical cord and maternal plasma in SGA was assessed. We first evaluated circRNAs in umbilical cord blood of the SGA and appropriate for gestational age (AGA) groups by microarray sequencing. In total, 170 340 circRNAs were sequenced, and 144 circRNAs were significantly upregulated while 977 were markedly downregulated. Has_circRNA15994-13, has_circ_0001359, and has_circ_0001360 were abundant and differentially expressed between the SGA and AGA groups, and confirmed in the umbilical cord and maternal blood specimens by reverse transcription polymerase chain reaction. By combining miRNA microarray data of the SGA placenta tissue in NCBI, it was found that two miRNAs were both hsa_circRNA15994-13 targets and differentially expressed, including hsa-miR-3619-5p and hsa-miR-4741. Further KEEG analysis revealed that the most significant pathway enriched by hsa-miR-3619-5p was Wnt signaling that is closely related to SGA; meanwhile, previous reports demonstrated that hsa-miR-3619-5p directly binds to β-catenin to accommodate the Wnt/β-catenin pathway, whereby the suggestive hsa_circRNA15994-13 → hsa-miR-3619-5p → β-catenin signaling pathway may play an important part in SGA.