TG-interacting factor 1 (Tgif1)-deficiency attenuates bone remodeling and blunts the anabolic response to parathyroid hormone

Etiological Mechanisms and Genetic/Biological Modulation Related to PTH1R in Primary Failure of Tooth Eruption

Primary failure of eruption (PFE) is a rare disorder that is characterized by the inability of a molar tooth/teeth to erupt to the occlusal plane or to normally react to orthodontic force. This condition is related to hereditary factors and has been extensively researched over many years. However, the etiological mechanisms of pathogenesis are still not fully understood. Evidence from studies on PFE cases has shown that PFE patients may carry parathyroid hormone 1 receptor (PTH1R) gene mutations, and genetic detection can be used to diagnose PFE at an early stage. PTH1R variants can lead to altered protein structure, impaired protein function, and abnormal biological activities of the cells, which may ultimately impact the behavior of teeth, as observed in PFE. Dental follicle cells play a critical role in tooth eruption and root development and are regulated by parathyroid hormone-related peptide (PTHrP)-PTH1R signaling in their differentiation and other activities. PTHrP-PTH1R signaling also regulates the activity of osteoblasts, osteoclasts and odontoclasts during tooth development and eruption. When interference occurs in the PTHrP-PTH1R signaling pathway, the normal function of dental follicles and bone remodeling are impaired. This review provides an overview of PTH1R variants and their correlation with PFE, and highlights that a disruption of PTHrP-PTH1R signaling impairs the normal process of tooth development and eruption, thus providing insight into the underlying mechanisms related to PTH1R and its role in driving PFE.

Evaluating the association between lifestyle factors and heel bone mineral density in different inflammatory states

Rationale

It is unclear whether lifestyle factors affect bone mineral density (BMD) during different inflammatory states.

Objective

This study investigated the effects of coffee consumption, vitamin D (VD) intake, smoking, and alcohol consumption on heel BMD in adults with different inflammatory states.

Methods

The phenotypic data from 249,825 participants were analyzed using the UK Biobank cohort. The inflammatory status was evaluated using C-reactive protein (CRP) levels and the systemic immune-inflammation index. Linear regression analysis was used to examine the association between coffee consumption, VD, smoking, alcohol consumption, and heel BMD in adults with different inflammatory states. Linear regression models were used to analyze the interaction between inflammation and the four lifestyle factors with respect to their influence on heel BMD in adults.

Results

Our findings revealed that VD was positively associated with adult heel BMD (β = 2.41 × 10-2, SE = 5.14 × 10-3, P = 2.72 × 10-6), while alcohol consumption and smoking were negatively associated with adult heel BMD. Coffee was negatively associated with adult heel BMD in low inflammatory states (β = -1.27 × 10-2, SE = 4.79 × 10-3, P = 8.00 × 10-3), while there was no association between coffee and adult heel BMD in high inflammatory states. Overall, it was found that these four lifestyle factors interacted negatively with inflammatory states.

Conclusion

Our study suggests that VD is positively associated with adult heel BMD and that alcohol consumption and smoking are negatively associated with adult heel BMD. Coffee may reverse the adverse effects of inflammation on BMD when the patient is in a highly inflammatory state, thus acting as a protective agent against heel BMD in adults.

Tgif1-deficiency impairs cytoskeletal architecture in osteoblasts by activating PAK3 signaling

Osteoblast adherence to bone surfaces is important for remodeling bone tissue. This study demonstrates that deficiency of TG-interacting factor 1 (Tgif1) in osteoblasts results in altered cell morphology, reduced adherence to collagen type I-coated surfaces, and impaired migration capacity. Tgif1 is essential for osteoblasts to adapt a regular cell morphology and to efficiently adhere and migrate on collagen type I-rich matrices in vitro. Furthermore, Tgif1 acts as a transcriptional repressor of p21-activated kinase 3 (Pak3), an important regulator of focal adhesion formation and osteoblast spreading. Absence of Tgif1 leads to increased Pak3 expression, which impairs osteoblast spreading. Additionally, Tgif1 is implicated in osteoblast recruitment and activation of bone surfaces in the context of bone regeneration and in response to parathyroid hormone 1-34 (PTH 1-34) treatment in vivo in mice. These findings provide important novel insights in the regulation of the cytoskeletal architecture of osteoblasts.

M2 macrophages secrete glutamate-containing extracellular vesicles to alleviate osteoporosis by reshaping osteoclast precursor fate

Osteoclast precursors (OCPs) are thought to commit to osteoclast differentiation, which is accelerated by aging-related chronic inflammation, thereby leading to osteoporosis. However, whether the fate of OCPs can be reshaped to transition into other cell lineages is unknown. Here, we showed that M2 macrophage-derived extracellular vesicles (M2-EVs) could reprogram OCPs to downregulate osteoclast-specific gene expression and convert OCPs to M2 macrophage-like lineage cells, which reshaped the fate of OCPs by delivering the molecular metabolite glutamate. Upon delivery of glutamate, glutamine metabolism in OCPs was markedly enhanced, resulting in the increased production of α-ketoglutarate (αKG), which participates in Jmjd3-dependent epigenetic reprogramming, causing M2-like macrophage differentiation. Thus, we revealed a novel transformation of OCPs into M2-like macrophages via M2-EVs-initiated metabolic reprogramming and epigenetic modification. Our findings suggest that M2-EVs can reestablish the balance between osteoclasts and M2 macrophages, alleviate the symptoms of bone loss, and constitute a new approach for bone-targeted therapy to treat osteoporosis.

PTH and the Regulation of Mesenchymal Cells within the Bone Marrow Niche

Parathyroid hormone (PTH) plays a pivotal role in maintaining calcium homeostasis, largely by modulating bone remodeling processes. Its effects on bone are notably dependent on the duration and frequency of exposure. Specifically, PTH can initiate both bone formation and resorption, with the outcome being influenced by the manner of PTH administration: continuous or intermittent. In continuous administration, PTH tends to promote bone resorption, possibly by regulating certain genes within bone cells. Conversely, intermittent exposure generally favors bone formation, possibly through transient gene activation. PTH's role extends to various aspects of bone cell activity. It directly influences skeletal stem cells, osteoblastic lineage cells, osteocytes, and T cells, playing a critical role in bone generation. Simultaneously, it indirectly affects osteoclast precursor cells and osteoclasts, and has a direct impact on T cells, contributing to its role in bone resorption. Despite these insights, the intricate mechanisms through which PTH acts within the bone marrow niche are not entirely understood. This article reviews the dual roles of PTH-catabolic and anabolic-on bone cells, highlighting the cellular and molecular pathways involved in these processes. The complex interplay of these factors in bone remodeling underscores the need for further investigation to fully comprehend PTH's multifaceted influence on bone health.

MSU crystal deposition contributes to inflammation and immune responses in gout remission

As a prominent feature of gout, monosodium urate (MSU) crystal deposition induces gout flares, but its impact on immune inflammation in gout remission remains unclear. Using single-cell RNA sequencing (scRNA-seq), we characterize the transcription profiling of peripheral blood mononuclear cells (PBMCs) among intercritical remission gout, advanced remission gout, and normal controls. We find systemic inflammation in gout remission with MSU crystal deposition at the intercritical and advanced stages, evidenced by activated inflammatory pathways, strengthened inflammatory cell-cell interactions, and elevated arachidonic acid metabolic activity. We also find increased HLA-DQA1high classic monocytes and PTGS2high monocytes in advanced gout and overactivated CD8+ T cell subtypes in intercritical and advanced gout. Additionally, the osteoclast differentiation pathway is significantly enriched in monocytes, T cells, and B cells from advanced gout. Overall, we demonstrate systemic inflammation and distinctive immune responses in gout remission with MSU crystal deposition, allowing further exploration of the underlying mechanism and clinical significance in conversion from intercritical to advanced stage.

Eicosapentaenoic acid supplementation modulates the osteoblast/osteoclast balance in inflammatory environments and protects against estrogen deficiency-induced bone loss in mice

BACKGROUND

An imbalance of osteoblasts (OBs) and osteoclasts (OCs) in a chronic inflammatory microenvironment is an important pathological factor leading to osteoporosis. Eicosapentaenoic acid (EPA) has been shown to suppress inflammation in macrophages and adipocytes. However, the effect of EPA on OBs and OCs has yet to be fully elucidated.

AIMS

We explored the roles of EPA in the differentiation of OBs and OCs, as well as the coupling between OBs and OCs in an inflammatory microenvironment. The effects of EPA on estrogen deficiency-induced osteoporosis were also evaluated.

METHODS

Mouse bone marrow mesenchymal stem cells (mBMSCs) and mouse bone marrow-derived macrophages (mBMMs) were used for in vitro OBs and OCs differentiation. TNF-α was used to create an inflammatory microenvironment. We examined the effects of EPA on osteoblastogenesis in the absence or presence of TNF-α and collect OBs' culture medium as the conditioned medium (CM). Then we examined the effects of EPA and CM on RANKL-induced osteoclastogenesis. The in vivo effects of EPA were determined using an ovariectomized (OVX) mouse model treated with EPA or vehicle.

RESULTS

High-dose EPA was shown to promote osteoblastogenesis in an inflammatory environment in vitro, as well as upregulate expression of OBs-specific proteins and genes. ARS and ALP staining also showed that high-dose EPA-treated groups restored mBMSCs' impaired osteogenic capacity caused by TNFa. Mechanistically, EPA suppressed the NF-κB pathway activated by TNF-α in mBMSCs and rescued TNF-α-mediated inhibition of osteoblastogenesis. EPA was also shown to inhibit expression of RANKL and decrease the RANKL/OPG ratio in OBs in an inflammatory environment. CM from TNF-α-stimulated OBs promoted osteoclastogenesis of mBMMs; EPA-treated CM prevented this. In the OVX mouse model, EPA supplementation prevented bone loss in an estrogen deficiency-induced inflammatory environment.

CONCLUSIONS

EPA was demonstrated for the first time to restore mBMSCs' impaired osteogenic capacity caused by TNFa-induced inflammation and rescue the OBs/OCs balance via regulation of RANKL and OPG expression in OBs. EPA showed a remarkable ability to prevent bone loss in OVX mice, suggesting a potential application of EPA in postmenopausal osteoporosis.

NPRC deletion attenuates cardiac fibrosis in diabetic mice by activating PKA/PKG and inhibiting TGF-β1/Smad pathways

Cardiac fibrosis plays a key role in the progression of diabetic cardiomyopathy (DCM). Previous studies demonstrated the cardioprotective effects of natriuretic peptides. However, the effects of natriuretic peptide receptor C (NPRC) on cardiac fibrosis in DCM remains unknown. Here, we observed that myocardial NPRC expression was increased in mice and patients with DCM. NPRC-/- diabetic mice showed alleviated cardiac fibrosis, as well as improved cardiac function and remodeling. NPRC knockdown in both cardiac fibroblasts and cardiomyocytes decreased collagen synthesis and proliferation of cardiac fibroblasts. RNA sequencing identified that NPRC deletion up-regulated the expression of TGF-β-induced factor homeobox 1 (TGIF1), which inhibited the phosphorylation of Smad2/3. Furthermore, TGIF1 up-regulation was mediated by the activation of cAMP/PKA and cGMP/PKG signaling induced by NPRC deletion. These findings suggest that NPRC deletion attenuated cardiac fibrosis and improved cardiac remodeling and function in diabetic mice, providing a promising approach to the treatment of diabetic cardiac fibrosis.

Multiple Genetic Loci Associated with Pug Dog Thoracolumbar Myelopathy

Pug dogs with thoracolumbar myelopathy (PDM) present with a specific clinical phenotype that includes progressive pelvic limb ataxia and paresis, commonly accompanied by incontinence. Vertebral column malformations and lesions, excessive scar tissue of the meninges, and central nervous system inflammation have been described. PDM has a late onset and affects more male than female dogs. The breed-specific presentation of the disorder suggests that genetic risk factors are involved in the disease development. To perform a genome-wide search for PDM-associated loci, we applied a Bayesian model adapted for mapping complex traits (BayesR) and a cross-population extended haplotype homozygosity test (XP-EHH) in 51 affected and 38 control pugs. Nineteen associated loci (harboring 67 genes in total, including 34 potential candidate genes) and three candidate regions under selection (with four genes within or next to the signal) were identified. The multiple candidate genes identified have implicated functions in bone homeostasis, fibrotic scar tissue, inflammatory responses, or the formation, regulation, and differentiation of cartilage, suggesting the potential relevance of these processes to the pathogenesis of PDM.

Novel genes linked to Class II Division 1 malocclusion with mandibular micrognathism

INTRODUCTION

Mandibular micrognathism (MM) is an underdeveloped mandible resulting from complex interactions between genetic and environmental factors. Prior research focused mainly on the genetic determinants of mandibular retrognathism, not necessarily reflecting micrognathism, thus supporting the need to study MM. This study aimed to explore the inheritance pattern and identify the candidate genes involved in the development and familial transmission of MM.

METHODS

Diagnosing probands with MM was based on clinical and lateral cephalometric data. The pedigrees were drawn for 11 identified families, 5 of whom accepted to undergo detailed data and biospecimen collection. These families included 15 MM and 13 non-MM subjects over 2-3 generations. The procedure involved the withdrawal of 5 mL of blood. Genomic DNA was isolated from blood cells to investigate protein-coding regions via whole exome sequencing. Standardized filtering steps were employed, and candidate genes were identified.

RESULTS

Most of the pedigrees suggested a Mendelian inheritance pattern and segregated in an autosomal-dominant manner. One of the families, which also underwent biospecimen, displayed an X-linked inheritance pattern of the trait. Genetic screening disclosed 8 potentially novel genes (GLUD2, ADGRG4, ARSH, TGIF1, FGFR3, ZNF181, INTS7, and WNT6). None of the recognized exonic regions were previously reported.

CONCLUSIONS

Eight novel genes were identified in association with MM in the largest number of families reported to date. The genes were X-linked in 1 family, a finding previously not observed in mandibular genetics.

Antagonizing microRNA-19a/b augments PTH anabolic action and restores bone mass in osteoporosis in mice

Postmenopausal bone loss often leads to osteoporosis and fragility fractures. Bone mass can be increased by the first 34 amino acids of human parathyroid hormone (PTH), parathyroid hormone‐related protein (PTHrP), or by a monoclonal antibody against sclerostin (Scl‐Ab). Here, we show that PTH and Scl‐Ab reduce the expression of microRNA‐19a and microRNA‐19b (miR‐19a/b) in bone. In bones from patients with lower bone mass and from osteoporotic mice, miR‐19a/b expression is elevated, suggesting an inhibitory function in bone remodeling. Indeed, antagonizing miR‐19a/b in vivo increased bone mass without overt cytotoxic effects. We identified TG‐interacting factor 1 (Tgif1) as the target of miR‐19a/b in osteoblasts and essential for the increase in bone mass following miR‐19a/b inhibition. Furthermore, antagonizing miR‐19a/b augments the gain in bone mass by PTH and restores bone loss in mouse models of osteoporosis in a dual mode of action by supporting bone formation and decreasing receptor activator of NF‐κB ligand (RANKL)‐dependent bone resorption. Thus, this study identifies novel mechanisms regulating bone remodeling, which opens opportunities for new therapeutic concepts to treat bone fragility.

Crosstalk between axon guidance signaling and bone remodeling

The maintenance of skeletal integrity is tightly regulated by two cell types, bone forming osteoblasts and bone resorbing osteoclasts. Although the role of the nervous system in regulating osteoblasts and osteoclasts was identified over a decade ago, the molecular mechanism of skeletal-neural interactions in bone homeostasis has only been studied recently. In particular, the complex roles of axon guidance molecules, such as semaphorins and ephrins, in the bone have been studied extensively. In this review, we highlight the latest advances in determining the functions of semaphorins and ephrins in the establishment and maintenance of the skeletal system, with a focus on the functional interaction between the skeletal and nervous systems.

Procalcitonin is expressed in osteoblasts and limits bone resorption through inhibition of macrophage migration during intermittent PTH treatment

Intermittent injections of parathyroid hormone (iPTH) are applied clinically to stimulate bone formation by osteoblasts, although continuous elevation of parathyroid hormone (PTH) primarily results in increased bone resorption. Here, we identified Calca, encoding the sepsis biomarker procalcitonin (ProCT), as a novel target gene of PTH in murine osteoblasts that inhibits osteoclast formation. During iPTH treatment, mice lacking ProCT develop increased bone resorption with excessive osteoclast formation in both the long bones and axial skeleton. Mechanistically, ProCT inhibits the expression of key mediators involved in the recruitment of macrophages, representing osteoclast precursors. Accordingly, ProCT arrests macrophage migration and causes inhibition of early but not late osteoclastogenesis. In conclusion, our results reveal a potential role of osteoblast-derived ProCT in the bone microenvironment that is required to limit bone resorption during iPTH.

Metabolic and Transcriptional Changes across Osteogenic Differentiation of Mesenchymal Stromal Cells

Mesenchymal stromal cells (MSCs) are multipotent post-natal stem cells with applications in tissue engineering and regenerative medicine. MSCs can differentiate into osteoblasts, chondrocytes, or adipocytes, with functional differences in cells during osteogenesis accompanied by metabolic changes. The temporal dynamics of these metabolic shifts have not yet been fully characterized and are suspected to be important for therapeutic applications such as osteogenesis optimization. Here, our goal was to characterize the metabolic shifts that occur during osteogenesis. We profiled five key extracellular metabolites longitudinally (glucose, lactate, glutamine, glutamate, and ammonia) from MSCs from four donors to classify osteogenic differentiation into three metabolic stages, defined by changes in the uptake and secretion rates of the metabolites in cell culture media. We used a combination of untargeted metabolomic analysis, targeted analysis of ¹³C-glucose labelled intracellular data, and RNA-sequencing data to reconstruct a gene regulatory network and further characterize cellular metabolism. The metabolic stages identified in this proof-of-concept study provide a framework for more detailed investigations aimed at identifying biomarkers of osteogenic differentiation and small molecule interventions to optimize MSC differentiation for clinical applications.

Cytokine-scavenging nanodecoys reconstruct osteoclast/osteoblast balance toward the treatment of postmenopausal osteoporosis

Imbalance between osteoblasts and osteoclasts accounts for the incidence and deterioration of postmenopausal osteoporosis. Abnormally elevated RANKL and TNF-α levels after menopause promote osteoclast formation and inhibit osteoblast differentiation, respectively. Here, nanodecoys capable of scavenging RANKL and TNF-α were developed from preosteoclast (RAW 264.7 cell) membrane–coated poly(lactic-co-glycolic acid) (PLGA) nanoparticles, which inhibited osteoporosis and maintained bone integrity. The nanodecoys effectively escaped from macrophage capture and enabled prolonged blood circulation after systemic administration. The abundant RANK and TNF-α receptor (TNF-αR) on the cell membranes effectively neutralized RANKL and TNF-α to prevent osteoclastogenesis and promote osteoblastogenesis, respectively, thus reversing the progression of osteoporosis in the ovariectomized (OVX) mouse model. These biomimetic nanodecoys provide an effective strategy for reconstructing the osteoclast/osteoblast balance and hold great potentials for the clinical management of postmenopausal osteoporosis.

Structural Insight into the Binding of TGIF1 to SIN3A PAH2 Domain through a C-Terminal Amphipathic Helix

TGIF1 is a transcriptional repressor playing crucial roles in human development and function and is associated with holoprosencephaly and various cancers. TGIF1-directed transcriptional repression of specific genes depends on the recruitment of corepressor SIN3A. However, to date, the exact region of TGIF1 binding to SIN3A was not clear, and the structural basis for the binding was unknown. Here, we demonstrate that TGIF1 utilizes a C-terminal domain (termed as SIN3A-interacting domain, SID) to bind with SIN3A PAH2. The TGIF1 SID adopts a disordered structure at the apo state but forms an amphipathic helix binding into the hydrophobic cleft of SIN3A PAH2 through the nonpolar side at the holo state. Residues F379, L382 and V383 of TGIF1 buried in the hydrophobic core of the complex are critical for the binding. Moreover, homodimerization of TGIF1 through the SID and key residues of F379, L382 and V383 was evidenced, which suggests a dual role of TGIF1 SID and a correlation between dimerization and SIN3A-PAH2 binding. This study provides a structural insight into the binding of TGIF1 with SIN3A, improves the knowledge of the structure–function relationship of TGIF1 and its homologs and will help in recognizing an undiscovered SIN3A-PAH2 binder and developing a peptide inhibitor for cancer treatment.

Anabolic actions of PTH in murine models: two decades of insights

Parathyroid hormone (PTH) is produced by the parathyroid glands in response to low serum calcium concentrations where it targets bones, kidneys, and indirectly, intestines. The N-terminus of PTH has been investigated for decades for its ability to stimulate bone formation when administered intermittently (iPTH) and is used clinically as an effective anabolic agent for the treatment of osteoporosis. Despite great interest in iPTH and its clinical use, the mechanisms of PTH action remain complicated and not fully defined. More than 70 gene targets in more than 90 murine models have been utilized to better understand PTH anabolic actions. Because murine studies utilized wild-type mice as positive controls, a variety of variables were analyzed to better understand the optimal conditions under which iPTH functions. The greatest responses to iPTH were in male mice, with treatment starting later than 12 weeks of age, a treatment duration lasting 5-6 weeks, and a PTH dose of 30-60 μg/kg/day. This comprehensive study also evaluated these genetic models relative to the bone formative actions with a primary focus on the trabecular compartment revealing trends in critical genes and gene families relevant for PTH anabolic actions. The summation of these data revealed the gene deletions with the greatest increase in trabecular bone volume in response to iPTH. These included PTH and 1-α-hydroxylase (Pth;1α(OH)ase, 62-fold), amphiregulin (Areg, 15.8-fold), and PTH related protein (Pthrp, 10.2-fold). The deletions with the greatest inhibition of the anabolic response include deletions of: proteoglycan 4 (Prg4, -9.7-fold), low-density lipoprotein receptor-related protein 6 (Lrp6, 1.3-fold), and low-density lipoprotein receptor-related protein 5 (Lrp5, -1.0-fold). Anabolic actions of iPTH were broadly affected via multiple and diverse genes. This data provides critical insight for future research and development, as well as application to human therapeutics. © 2021 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

TGFB-induced factor homeobox 1 (TGIF) expression in breast cancer

BACKGROUND

Breast cancer (BC) is the most frequent female cancer and preferentially metastasizes to bone. The transcription factor TGFB-induced factor homeobox 1 (TGIF) is involved in bone metabolism. However, it is not yet known whether TGIF is associated with BC bone metastasis or patient outcome and thus of potential interest.

METHODS

TGIF expression was analyzed by immunohistochemistry in 1197 formalin-fixed, paraffin-embedded tissue samples from BC patients treated in the GAIN (German Adjuvant Intergroup Node-Positive) study with two adjuvant dose-dense schedules of chemotherapy with or without bisphosphonate ibandronate. TGIF expression was categorized into negative/low and moderate/strong staining. Endpoints were disease-free survival (DFS), overall survival (OS) and time to primary bone metastasis as first site of relapse (TTPBM).

RESULTS

We found associations of higher TGIF protein expression with smaller tumor size (p = 0.015), well differentiated phenotype (p < 0.001) and estrogen receptor (ER)-positive BC (p < 0.001). Patients with higher TGIF expression levels showed a significantly longer disease-free (DFS: HR 0.75 [95%CI 0.59-0.95], log-rank p = 0.019) and overall survival (OS: HR 0.69 [95%CI 0.50-0.94], log-rank p = 0.019), but no association with TTPBM (HR 0.77 [95%CI 0.51-1.16]; p = 0.213). Univariate analysis in molecular subgroups emphasized that elevated TGIF expression was prognostic for both DFS and OS in ER-positive BC patients (DFS: HR 0.68 [95%CI 0.51-0.91]; log-rank p = 0.009, interaction p = 0.130; OS: HR 0.60 [95%CI 0.41-0.88], log-rank p = 0.008, interaction p = 0.107) and in the HER2-negative subgroup (DFS:HR 0.67 [95%CI 0.50-0.88], log-rank p = 0.004, interaction p = 0.034; OS: HR 0.57 [95%CI 0.40-0.81], log-rank p = 0.002, interaction p = 0.015).

CONCLUSIONS

Our results suggest that moderate to high TGIF expression is a common feature of breast cancer cells and that this is not associated with bone metastases as first site of relapse. However, a reduced expression is linked to tumor progression, especially in HER2-negative breast cancer.

TRIAL REGISTRATION

This clinical trial has been registered with ClinicalTrials.gov ; registration number: NCT00196872 .

Regulation and Role of Transcription Factors in Osteogenesis

Bone is a dynamic tissue constantly responding to environmental changes such as nutritional and mechanical stress. Bone homeostasis in adult life is maintained through bone remodeling, a controlled and balanced process between bone-resorbing osteoclasts and bone-forming osteoblasts. Osteoblasts secrete matrix, with some being buried within the newly formed bone, and differentiate to osteocytes. During embryogenesis, bones are formed through intramembraneous or endochondral ossification. The former involves a direct differentiation of mesenchymal progenitor to osteoblasts, and the latter is through a cartilage template that is subsequently converted to bone. Advances in lineage tracing, cell sorting, and single-cell transcriptome studies have enabled new discoveries of gene regulation, and new populations of skeletal stem cells in multiple niches, including the cartilage growth plate, chondro-osseous junction, bone, and bone marrow, in embryonic development and postnatal life. Osteoblast differentiation is regulated by a master transcription factor RUNX2 and other factors such as OSX/SP7 and ATF4. Developmental and environmental cues affect the transcriptional activities of osteoblasts from lineage commitment to differentiation at multiple levels, fine-tuned with the involvement of co-factors, microRNAs, epigenetics, systemic factors, circadian rhythm, and the microenvironments. In this review, we will discuss these topics in relation to transcriptional controls in osteogenesis.

Fluoropolymer-Mediated Intracellular Delivery of miR-23b for the Osteocyte Differentiation in Osteoblasts

Emerging evidence suggests that microRNAs (miRNAs) play key roles in the regulation of multiple biological processes, including the differentiation of osteoblasts. Although miRNA-based gene therapy holds immense potential in the treatment of a variety of diseases, the intracellular delivery of miRNA remains challenging owing to the lack of efficient and safe gene carriers. In this study, a fluoropolymer (FP) is constructed through the modification of polyamidoamine (PAMAM) using heptafluorobutyric anhydride and then is used as a carrier for miR-23b transfection to induce osteocyte differentiation of osteoblasts. The derivative FP is found to facilitate miR-23b transfection due to its favorable endosomal escape from the "proton sponge" effect. Compared to PAMAM/miR-23b, the FP/miR-23b nanocomplex efficiently promotes the differentiation of osteoblasts and formation of calcified nodules, attributable to enhanced expression of various osteogenesis genes (runt-related transfection factor 2 [RUNX2], alkaline phosphatase [ALP], osteopontin [OPN], and osteocalcin [OCN]). Thus, FP-mediated miR-23b transfection may be used as an effective strategy to facilitate osteogenic differentiation.

Hepatocyte growth factor overexpression promotes osteoclastogenesis and exacerbates bone loss in CIA mice

Background

Hepatocyte growth factor (HGF) is a multifunctional growth factor that promotes various biological processes. However, the effect of HGF on bone metabolism in rheumatoid arthritis (RA) remains unknown. Here, we investigated the role of HGF in regulating osteoclastogenesis and bone resorption in RA.

Methods

The expression of HGF in RA patients and collagen-induced arthritis (CIA) mice was examined. The role of HGF on osteoclastogenesis was analysed by osteoclastogenesis and bone resorption assays. The effect of HGF inhibition was evaluated in a CIA mice model. The mechanism of HGF in regulating osteoclastogenesis and bone resorption was explored by a series of in vitro studies.

Results

HGF was overexpressed in CIA and RA. HGF stimulated osteoclastogenesis in vitro. SU11274, a selective small molecule blocker of c-Met, impeded the effect of HGF on osteoclastogenesis and bone resorption. HGF regulated osteoclastogenesis by JNK and AKT-GSK-3β-NFATc1 signallings. SU11274 protected CIA mice from pathological bone loss.

Conclusions

These data strongly suggest that the highly expressed HGF in the joint tissues contributes to bone loss in RA. Inhibition of HGF/c-Met could effectively alleviate pathological bone loss and inflammatory symptoms in CIA mice. HGF/c-Met may be used as a new target for the treatment of bone loss in RA.

Breast cancer bone metastases are attenuated in a Tgif1-deficient bone microenvironment

Background

Osteoclast activation is a hallmark of breast cancer-induced bone disease while little is known about the role of osteoblasts in this process. Recently, we identified the homeodomain protein TG-interacting factor-1 (Tgif1) as a crucial regulator of osteoblast function. In this study, we demonstrate that lack of Tgif1 also restricts the progression of breast cancer bone metastases.

Methods

Transwell migration assays were used to investigate the osteoblast-breast cancer cell interaction in vitro. Molecular analyses included RNA sequencing, immunoblotting, and qRT-PCR. To determine the role of Tgif1 in metastatic bone disease, 4T1 breast cancer cells were injected intracardially into mice with a germ line deletion of Tgif1 (Tgif1^−/−) or control littermates (Tgif1^+/+). Progression of bone metastases and alterations in the bone microenvironment were assessed using bioluminescence imaging, immunofluorescence staining, confocal microscopy, and histomorphometry.

Results

Medium conditioned by osteoblasts stimulated breast cancer cell migration, indicating a potential role of osteoblasts during bone metastasis progression. Tgif1 expression was strongly increased in osteoblasts upon stimulation by breast cancer cells, demonstrating the implication of Tgif1 in the osteoblast-breast cancer cell interaction. Indeed, conditioned medium from osteoblasts of Tgif1^−/− mice failed to induce breast cancer cell migration compared to control, suggesting that Tgif1 in osteoblasts augments cancer cell motility. Semaphorin 3E (Sema3E), which is abundantly secreted by Tgif1^−/− osteoblasts, dose-dependently reduced breast cancer cell migration while silencing of Sema3E expression in Tgif1^−/− osteoblasts partially restored the impaired migration. In vivo, we observed a decreased number of breast cancer bone metastases in Tgif1^−/− mice compared to control littermates. Consistently, the presence of single breast cancer cells or micro-metastases in the tibiae was reduced in Tgif1^−/− mice. Breast cancer cells localized in close proximity to Endomucin-positive vascular cells as well as to osteoblasts. Although Tgif1 deficiency did not affect the bone marrow vasculature, the number and activity of osteoblasts were reduced compared to control. This suggests that the protective effect on bone metastases might be mediated by osteoblasts rather than by the bone marrow vasculature.

Conclusion

We propose that the lack of Tgif1 in osteoblasts increases Sema3E expression and attenuates breast cancer cell migration as well as metastases formation.

PTH Derivative promotes wound healing via synergistic multicellular stimulating and exosomal activities

BACKGROUND

Diabetic wounds are a disturbing and rapidly growing clinical problem. A novel peptide, parathyroid hormone related peptide (PTHrP-2), is assumed as multifunctional factor in angiogenesis, fibrogenesis and re-epithelization. This study aims to test PTHrP-2 efficiency and mechanism in wound healing.

METHODS

Through repair phenomenon in vivo some problems were detected, and further research on their mechanisms was made. In vivo therapeutic effects of PTHrP-2 were determined by HE, Masson, microfil and immunohistochemical staining. In vitro direct effects of PTHrP-2 were determined by proliferation, migration, Vascular Endothelial Grown Factor and collagen I secretion of cells and Akt/ Erk1/2 pathway change. In vitro indirect effects of PTHrP-2 was study via exosomes. Exosomes from PTHrP-2 untreated and treated HUVECs and HFF-1 cells were insolated and identified. Exosomes were co-cultured with original cells, HUVECs or HFF-1 cells, and epithelial cells. Proliferation and migration and pathway change were observed. PTHrP-2-HUVEC-Exos were added into in vivo wound to testify its hub role in PTHrP-2 indirect effects in wound healing.

RESULTS

In vivo, PTHrP-2 exerted multifunctional pro-angiogenesis, pro-firbogenesis and re-epithelization effects. In vitro, PTHrP-2 promoted proliferation and migration of endothelial and fibroblast cells, but had no effect on epithelial cells. Therefore, we tested PTHrP-2 indirect effects via exosomes. PTHrP-2 intensified intercellular communication between endothelial cells and fibroblasts and initiated endothelial-epithelial intercellular communication. PTHrP-2-HUVEC-Exos played a hub role in PTHrP-2 indirect effects in wound healing.

CONCLUSION

These findings of this study indicated that PTHrP-2, a multifunctional factor, could promote wound healing via synergistic multicellular stimulating and exosomal activities.

Vindoline Inhibits RANKL-Induced Osteoclastogenesis and Prevents Ovariectomy-Induced Bone Loss in Mice

Osteolytic bone diseases, for example postmenopausal osteoporosis, arise from the imbalances between osteoclasts and osteoblasts in the bone remodeling process, whereby osteoclastic bone resorption greatly exceeds osteoblastic bone formation resulting in severe bone loss and deterioration in bone structure and microarchitecture. Therefore, the identification of agents that can inhibit osteoclast formation and/or function for the treatment of osteolytic bone disease has been the focus of bone and orthopedic research. Vindoline (Vin), an indole alkaloid extracted from the medicinal plant Catharanthus roseus, has been shown to possess extensive biological and pharmacological benefits, but its effects on bone metabolism remains to be documented. Our study demonstrated for the first time, that Vin could inhibit osteoclast differentiation from bone marrow macrophages (BMMs) precursor cells as well as mature osteoclastic bone resorption. We further determined that the underlying molecular mechanism of action of Vin is in part due to its inhibitory effect against the activation of MAPK including p38, JNK, and ERK and intracellular reactive oxygen species (ROS) production. This effect ultimately suppressed the induction of c-Fos and NFATc1, which consequently downregulated the expression of the genes required for osteoclast formation and bone resorption. Consistent with our in vitro findings, in vivo administration of Vin protected mice against ovariectomy (OVX)-induced bone loss and trabecular bone deterioration. These results provided promising evidence for the potential therapeutic application of Vin as a novel treatment option against osteolytic diseases.

Backbone and side chain resonance assignments of the C-terminal domain of human TGIF1

TGIF1 is an essential regulator of cell differentiation in various biological processes, and is associated with holoprosencephaly and many cancers. The C-terminal domain of TGIF1 that was originally defined as repressive domain 2 can interact with a variety of proteins, such as transcription factor Smad2 and co-repressor Sin3A, to mediate the regulative roles of TGIF1 in diverse cell signaling pathways. However, the recognition mechanism of TGIF1 C-terminal domain for different interacting proteins remains unknown. Here, we report the nearly complete ¹H, ¹³C, and ¹⁵N backbone and side chain resonance assignments of TGIF1 C-terminal domain (residues 256-375), laying a foundation for further research on the structure-function relationship of TGIF1.

Brief exposure to full length parathyroid hormone-related protein (PTHrP) causes persistent generation of cyclic AMP through an endocytosis-dependent mechanism

Parathyroid hormone (PTH)-related protein (PTHrP) (gene name Pthlh) was discovered as the factor responsible for the humoral hypercalcemia of malignancy. It shares such sequence similarity with PTH in the amino-terminal region that the two are equally able to act through a single G protein-coupled receptor, PTH1R. A number of biological activities are ascribed to domains of PTHrP beyond the amino-terminal domain. PTH functions as a circulating hormone, but PTHrP is generated locally in many tissues including bone, where it acts as a paracrine factor on osteoblasts and osteocytes. The present study compares how PTH and PTHrP influence cyclic AMP (cAMP) formation through adenylyl cyclase, the first event in cell activation through PTH1R. Brief exposure to full length PTHrP(1-141) in several osteoblastic cell culture systems was followed by sustained adenylyl cyclase activity for more than an hour after ligand washout. This effect was dose-dependent and was not found with shorter PTHrP or PTH peptides even though they were fully able to activate adenylyl cyclase with acute treatment. The persistent activation response to PTHrP(1-141) was seen also with later events in the cAMP/PKA pathway, including persistent activation of CRE-luciferase and sustained regulation of several CREB-responsive mRNAs, up to 24 h after the initial exposure. Pharmacologic blockade of endocytosis prevented the persistent activation of cAMP and gene responses. We conclude that full length PTHrP, the likely local physiological effector in bone, differs in intracellular action to PTH by undergoing endosomal translocation to induce a prolonged adenylyl cyclase activation in its target cells.