Intermittent parathyroid hormone (1-34) application regulates cAMP-response element binding protein activity to promote the proliferation and osteogenic differentiation of bone mesenchymal stromal cells, via the cAMP/PKA signaling pathway

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.

Sex Hormone-Binding Globulin (SHBG) Maintains Proper Equine Adipose-Derived Stromal Cells (ASCs)' Metabolic Functions and Negatively Regulates their Basal Adipogenic Potential

BACKGROUND

Sex hormone binding globulin (SHBG) deteriorated expression has been recently strongly correlated to increased level of circulating pro-inflammatory cytokines and insulin resistance, which are typical manifestations of equine metabolic syndrome (EMS). Despite previous reports demonstrated the potential therapeutic application of SHBG for liver-related dysfunctions, whether SHBG might modulate equine adipose-derived stem/stromal cells (EqASCs) metabolic machinery remains unknown. Therefore, we evaluated for the first time the impact of SHBG protein on metabolic changes in ASCs isolated from healthy horses.

METHODS

Beforehand, SHBG protein expression has been experimentally lowered using a predesigned siRNA in EqASCs to verify its metabolic implications and potential therapeutic value. Then, apoptosis profile, oxidative stress, mitochondrial network dynamics and basal adipogenic potential have been evaluated using various molecular and analytical techniques.

RESULTS

The SHBG knockdown altered the proliferative and metabolic activity of EqASCs, while dampening basal apoptosis via Bax transcript suppression. Furthermore, the cells treated with siRNA were characterized by senescent phenotype, accumulation of reactive oxygen species (ROS), nitric oxide, as well as decreased mitochondrial potential that was shown by mitochondrial membrane depolarization and lower expression of key mitophagy factors: PINK, PARKIN and MFN. The addition of SHBG protein reversed the impaired and senescent phenotype of EMS-like cells that was proven by enhanced proliferative activity, reduced apoptosis resistance, lower ROS accumulation and greater mitochondrial dynamics, which is proposed to be related to a normalization of Bax expression. Crucially, SHBG silencing enhanced the expression of key pro-adipogenic effectors, while decreased the abundance of anti-adipogenic factors namely HIF1-α and FABP4. The addition of exogenous SHBG further depleted the expression of PPARγ and C/EBPα and restored the levels of FABP4 and HIF1-α evoking a strong inhibitory potential toward ASCs adipogenesis.

CONCLUSION

Herein, we provide for the first time the evidence that SHBG protein in importantly involved in various key metabolic pathways governing EqASCs functions, and more importantly we showed that SHBG negatively affect the basal adipogenic potential of tested ASCs through a FABP4-dependant pathway, and provide thus new insights for the development of potential anti-obesity therapeutic approach in both animals and humans.

Icariin Promotes Osteogenic Differentiation in a Cell Model with NF1 Gene Knockout by Activating the cAMP/PKA/CREB Pathway

Neurofibromatosis type 1 is a rare autosomal dominant genetic disorder, with up to 50% of patients clinically displaying skeletal defects. Currently, the pathogenesis of bone disorders in NF1 patients is unclear, and there are no effective preventive and treatment measures. In this study, we found that knockout of the NF1 gene reduced cAMP levels and osteogenic differentiation in an osteoblast model, and icariin activated the cAMP/PKA/CREB pathway to promote osteoblast differentiation of the NF1 gene knockout cell model by increasing intracellular cAMP levels. The PKA selective inhibitor H89 significantly impaired the stimulatory effect of icariin on osteogenesis in the NF1 cell model. In this study, an osteoblast model of NF1 was successfully constructed, and icariin was applied to the cell model for the first time. The results will help to elucidate the molecular mechanism of NF1 bone disease and provide new ideas for the clinical prevention and treatment of NF1 bone disease and drug development in the future.

In Vitro Effects of PTH (1-84) on Human Skeletal Muscle-Derived Satellite Cells

Parathyroid hormone (PTH) is a hormone secreted by the parathyroid glands. Despite its well-known characterized anabolic and catabolic actions on the skeleton, the in vitro effects of PTH on skeletal muscle cells are limited and generally performed on animal models. The aim of this study was to evaluate the effects of a short impulse of PTH (1-84) on the proliferation and the differentiation of skeletal muscle satellite cells isolated from human biopsies. The cells were exposed for 30 min to different concentrations of PTH (1-84), from 10−6 mol/L to 10−12 mol/L. ELISA was used to assay cAMP and the myosin heavy-chain (MHC) protein. The proliferation was assayed by BrdU and the differentiation by RealTime-qPCR. A statistical analysis was performed by ANOVA followed by Bonferroni’s test. No significant variations in cAMP and the proliferation were detected in the isolated cells treated with PTH. On the other hand, 10−7 mol/L PTH on differentiated myotubes has shown significant increases in cAMP (p ≤ 0.05), in the expression of myogenic differentiation genes (p ≤ 0.001), and in the MHC protein (p ≤ 0.01) vs. untreated controls. This work demonstrates for the first time the in vitro effects of PTH (1-84) on human skeletal muscle cells and it opens new fields of investigation in muscle pathophysiology.

Forskolin enhanced the osteogenic differentiation of human dental pulp stem cells in vitro and in vivo

Background/purpose

Human dental pulp stem cells (hDPSCs) are multipotent adult stem cells that can differentiate into various lineages such as odontoblasts, osteoblasts, and chondrocytes. Regulation of hDPSCs differentiation with small-molecule compounds can be a useful tool for tissue engineering and regenerative therapy. Forskolin is an agonist of adenylate cyclase that promotes cyclic adenosine monophosphate production. However, the role of Forskolin in regulating the osteogenic differentiation of hDPSCs is still unknown.

Materials and methods

A cell counting kit-8 (CCK-8) assay was performed to screen out the safety concentrations of Forskolin. Following, quantitative polymerase chain reaction (qPCR) and alizarin red staining were performed to detect bone-related gene expression and mineralized deposit formation. Furthermore, we prepared cell sheets which were followed by a 3D culture for cell pellet formation. Finally, the hDPSC cell pellets were transplanted into immunodeficient mice.

Results

CCK-8 assay showed 5 μM and 10 μM Forskolin had no significant inhibition on the proliferation of hDPSCs. The qPCR indicated Forskolin (5, 10 μM) enhanced osteogenic differentiation of hDPSCs by upregulating bone-related genes. Alizarin red staining and its quantification analysis demonstrated Forskolin in 5 μM and 10 μM similarly enhanced the mineralized deposit formation of hDPSCs in vitro. After six weeks of transplantation, immunohistochemical stains showed that osteopontin expression and bone formation were significantly boosted in the Forskolin-treated group than in the normal osteogenic inducing group.

Conclusion

Our results indicate Forskolin enhances osteogenic differentiation of hDPSCs in vitro and boosts bone formation in vivo.

Hormone and implant osseointegration: Elaboration of the relationship among function, preclinical, and clinical practice

As clusters of peptides or steroids capable of high-efficiency information transmission, hormones have been substantiated to coordinate metabolism, growth, development, and other physiological processes, especially in bone physiology and repair metabolism. In recent years, the application of hormones for implant osseointegration has become a research hotspot. Herein, we provide a comprehensive overview of the relevant reports on endogenous hormones and their corresponding supplementary preparations to explore the association between hormones and the prognosis of implants. We also discuss the effects and mechanisms of insulin, parathyroid hormone, melatonin, vitamin D, and growth hormone on osseointegration at the molecular and body levels to provide a foothold and guide future research on the systemic conditions that affect the implantation process and expand the relative contraindications of the implant, and the pre-and post-operative precautions. This review shows that systemic hormones can regulate the osseointegration of oral implants through endogenous or exogenous drug-delivery methods.

Maintenance of increased bone mass after PTH withdrawal by sequential medicarpin treatment via augmentation of cAMP-PKA pathway

Osteoporosis is a metabolic bone disorder associated with impaired bone microarchitecture leading to fragility fractures. Long-term usage of parathyroid hormone (PTH) enhances bone resorption and leads to osteosarcoma in rats which limits its exposure to maximum 2 years in human. Notably, the anabolic effects of PTH do not endure in the absence of sustained administration. Studies in our lab identified osteogenic and antiresorptive activity in medicarpin, a phytoestrogen belonging to the pterocarpan class. Considering dual-acting property of medicarpin and limitations of PTH therapy, we envisaged that medicarpin sequential treatment after PTH withdrawal could serve as promising therapeutic approach for osteoporosis treatment. As PTH exerts its bone anabolic effect by increasing osteoblast survival, our study aims to determine whether medicarpin amplifies this effect of PTH. Our results show that PTH withdrawal led to reduced bone mineral density and bone parameters, while sequential treatment of medicarpin after PTH withdrawal significantly enhanced these parameters. Remarkably, these effects were more pronounced than 8-week PTH treatment. Sequential therapy also significantly increased P1NP levels and decreased CTX levels and TRAP positive cells compared to PTH 8W group where CTX levels were quite high due to bone resorptive action of PTH. Protein expression studies revealed that medicarpin along with PTH betters the antiapoptotic potential compared to PTH alone, through augmentation of cyclic adenosine monophosphate-PKA-CREB pathway. These results proclaim that medicarpin sequential treatment prevented the reduction in bone accrual and strength accompanying PTH withdrawal and also aided in antiapoptotic role of PTH. The study points toward the potential use of medicarpin as a replacement therapeutic option postdiscontinuation of PTH.

PTHrP promotes subchondral bone formation in TMJ-OA

PTH-related peptide (PTHrP) improves the bone marrow micro-environment to activate the bone-remodelling, but the coordinated regulation of PTHrP and transforming growth factor-β (TGFβ) signalling in TMJ-OA remains incompletely understood. We used disordered occlusion to establish model animals that recapitulate the ordinary clinical aetiology of TMJ-OA. Immunohistochemical and histological analyses revealed condylar fibrocartilage degeneration in model animals following disordered occlusion. TMJ-OA model animals administered intermittent PTHrP (iPTH) exhibited significantly decreased condylar cartilage degeneration. Micro-CT, histomorphometry, and Western Blot analyses disclosed that iPTH promoted subchondral bone formation in the TMJ-OA model animals. In addition, iPTH increased the number of osterix (OSX)-positive cells and osteocalcin (OCN)-positive cells in the subchondral bone marrow cavity. However, the number of osteoclasts was also increased by iPTH, indicating that subchondral bone volume increase was mainly due to the iPTH-mediated increase in the bone-formation ability of condylar subchondral bone. In vitro, PTHrP treatment increased condylar subchondral bone marrow-derived mesenchymal stem cell (SMSC) osteoblastic differentiation potential and upregulated the gene and protein expression of key regulators of osteogenesis. Furthermore, we found that PTHrP-PTH1R signalling inhibits TGFβ signalling during osteoblastic differentiation. Collectively, these data suggested that iPTH improves OA lesions by enhancing osteoblastic differentiation in subchondral bone and suppressing aberrant active TGFβ signalling. These findings indicated that PTHrP, which targets the TGFβ signalling pathway, may be an effective biological reagent to prevent and treat TMJ-OA in the clinic.

Continuous and intermittent parathyroid hormone administration promotes osteogenic differentiation and activity of programmable cells of monocytic origin

Bone healing deficiencies are challenging for orthopedic practice. The use of stem cells with scaffolds to treat bone tissue losses currently is popular for promoting regeneration of tissue. Programmable cells of monocytic origin (PCMO) may differentiate into three germ layers and may be a promising alternative treatment due to their stem cell-like properties. Parathyroid hormone (PTH) participates in bone metabolism. Intermittent administration of PTH promotes osteogenic activity of mesenchymal stem cdells (MSC). We investigated the osteogenic effects of continuous and intermittent administration of PTH on PCMO. Mononuclear cells were harvested from the peripheral blood of healthy donors. Isolated cells were cultured for six days in a de-differentiation medium. Indirect immunocytochemistry using anti-CD14, anti-CD45 and anti-CD90 primary antibodies, as well as electron microscopy were used to detect PCMO. PCMO then were cultured in an osteogenic differentiation medium supplemented with continuous or intermittent 50 ng/ml PTH. The PTH-free control group (CG), intermittent PTH treated group (IPG) and continuous PTH treated group (CPG) were cultured and assessed for their differentiation into osteogenic lineage cells by indirect immunocytochemistry using anti-collagen I, anti-osteonectin and anti-osteocalcin primary antibodies. Osteoblast-like cells obtained by continuous or intermittent PTH administration exhibited increased levels of collagen I, osteonectin and osteocalcin immunoreactivity. We found that continuous and intermittent PTH administration to PCMO enhanced their differentiation to osteogenic lineage cells and increased osteoblastic activity.

CircRNA-miRNA networks in regulating bone disease

Circular RNA (circRNA) is a class of endogenous noncoding RNA (ncRNA), presenting as a special covalent closed loop without a 5' cap or 3' tail, maintaining resistance to RNA exonuclease and keeping high stability. Although lowly expressed in most situations, circRNA makes an active difference in regulating physiological or pathological processes by modulating gene expression by regulation of transcription, protein, and miRNA functions through various mechanisms in particular tissues. Recent studies have demonstrated the roles of the miRNA-circRNA network in the development of several bone diseases such as osteoporosis, a multiple-mechanism disease resulting from defective bone quality and low bone mass, osteoarthritis, whose main pathomechanism is inflammation and articular cartilage degradation, as well as osteosarcoma, known as one of the most common bone cancers. However, the specific mechanism of how circRNA along with miRNA influences those diseases is not well documented, showing potential for the development of new therapies for those bone diseases.

Phactr1 negatively regulates bone mass by inhibiting osteogenesis and promoting adipogenesis of BMSCs via RhoA/ROCK2

The imbalance between osteogenic and adipogenic differentiation of Bone marrow-derived mesenchymal stem cells (BMSCs) is involved in the occurrence and development of osteoporosis (OP). Previous studies have indicated the potential of phosphatase and actin regulator 1 (Phactr1) in regulating osteogenic and adipogenic differentiation of BMSCs. The present study aims to investigate the function and mechanism of Phactr1 in regulating osteogenic and adipogenic differentiation of BMSCs. Herein, the expression of Phactr1 in bone and adipose tissue of OP rats was determined by immunohistochemical. BMSCs were subjected to osteogenic and adipogenic differentiation, and transfected with Phactr1 overexpression lentivirus, small interference RNA (siRNA) and KD025 (selective ROCK2 inhibitor). The relationship between Phactr1 and ROCK2 was detected by Co-IP experiment. The expression of Phactr1, Runx2, C/EBPα, RhoA and ROCK2 was detected by Western blot. Calcium nodule and lipid droplets were determined by alizarin red and Oil red O staining. Interestingly, Phactr1 increased in both bone and adipose tissue of OP rats. During osteogenic differentiation, Phactr1 decreased and active RhoA, ROCK2 increased, while overexpression Phactr1 inhibits the increase of Runx2. Phactr1 increased and active RhoA decreased, ROCK2 did not changed during adipogenic differentiation. While, Knockdown Phactr1 inhibits the increase of C/EBPα. Phactr1 and ROCK2 were combined in osteogenic differentiation, but not in adipogenic differentiation. By using KD025, the decrease of Phactr1 and increase of Runx2 were inhibited respectively in osteogenic differentiation. Meanwhile, when ROCK2 was inhibited, Phactr1, C/EBPα were significantly increased in adipogenic differentiation. These findings indicated that Phactr1 negatively regulates bone mass by inhibiting osteogenesis and promoting adipogenesis of BMSCs by activating RhoA/ROCK2.

Protective effects of berberine on senile osteoporosis in mice

INTRODUCTION

The incidence of osteoporosis is positively correlated with age. Berberine has been reported to treat osteoporosis due to its beneficial actions on bone formation. However, the direct effects of berberine on senile osteoporosis remain unclear. The present study investigated the protective effects of berberine on senile osteoporosis in mice and preliminarily evaluated its potential mechanism.

MATERIALS AND METHODS

20-month-old male C57BL/6 J mice were used as senile osteoporosis mouse model and treated with strontium ranelate (SR) or berberine or solvent control by daily gavage for 2 months. Thereafter, bone mass and microstructure parameters were assessed. Histological staining was performed to identify the osteogenic, adipogenic and osteoclastic activity of bone tissue. Moreover, role of cAMP/PKA/CREB signaling pathway in berberine affecting bone marrow mesenchymal stem cells (BMSCs) differentiation was clarified by enzyme-linked immunosorbent assay and western blot analysis.

RESULTS

The results showed that the SR-treated group displayed a high trabecular bone mass phenotype. For mice administrated with berberine, cancellous bone mass was upregulated in a dose-dependent manner, as indicated by gradually increased bone mass, trabecular bone volume fraction and trabecular number. Furthermore, berberine promotes osteogenic and inhibits adipogenic differentiation of BMSCs via cAMP/PKA/CREB signaling. Also, bone resorption effect becomes more obvious with increasing dose of berberine in vitro.

CONCLUSION

The present results suggest that berberine exerts potent bone protective effects by promoting bone formation, inhibiting marrow fat accumulation and bone resorption. This effect may be achieved through cAMP/PKA/CREB signaling pathway.

Treadmill exercise influences the microRNA profiles in the bone tissues of mice

As an important regulator involved in cell activity, microRNAs (miRNAs) are important in the process of exercise influencing bone metabolism. The present study aimed to detect and select differentially expressed miRNAs in the bone tissues of mice trained on a treadmill, predict the target genes of these differentially expressed miRNAs and lay a foundation for exploring the effect of treadmill training on bone metabolism through miRNAs. In this experiment, after the mice were trained on a treadmill for 8 weeks, the mechanical properties of mouse femur bone were assessed, and the alkaline phosphatase (ALP) activity and osteocalcin (OCN) protein levels of the bone were assayed. miRNA microarray and reverse transcription-quantitative (RT-q)PCR were performed to select and validate differentially expressed miRNAs in the bone, and the target genes of these miRNAs were predicted with bioinformatics methods. In addition, the differentially expressed miRNAs in the bone tissues were compared with those in mechanically strained osteocytes in vitro. Treadmill training improved the mechanical properties of the femur bones of mice, and elevated the ALP activity and OCN protein level in the bone. In addition, 122 differentially expressed miRNAs were detected in the bone, of which nine were validated via RT-qPCR. Among the target genes of these differentially expressed miRNAs, certain candidates were involved in bone metabolism. A total of eight miRNAs were differentially expressed in both bone tissue and osteocytes, exhibiting the same expression trends, and various target genes of these eight miRNAs were also involved in bone metabolism. Treadmill training resulted in altered miRNA expression profiles in the bones of mice (mainly in osteocytes) and the differentially expressed miRNAs may serve important roles in regulating bone metabolism and osteogenic differentiation.

Parathyroid hormone and its related peptides in bone metabolism

Parathyroid hormone (PTH) is an 84-amino-acid peptide hormone that is secreted by the parathyroid gland. It has different administration modes in bone tissue through which it promotes bone formation (intermittent administration) and bone resorption (continuous administration) and has great potential for application in sbone defect repair. PTH regulates bone metabolism by binding to PTH1R. PTH plays an osteogenic role by acting directly on mesenchymal stem cells, cells with an osteoblastic lineage, osteocytes, and T cells. It also participates as an osteoclast by indirectly acting on osteoclast precursor cells and osteoclasts and directly acting on T cells. In these cells, PTH activates the Wnt signaling, cAMP/PKA, cAMP/PKC, and RANKL/RANK/OPG pathways and other signaling pathways. Although PTH(1-34), also known as teriparatide, has been used clinically, it still has some disadvantages. Developing improved PTH-related peptides is a potential solution to teriparatide's shortcomings. The action mechanism of these PTH-related peptides is not exactly the same as that of PTH. Thus, the mechanisms of PTH and PTH-related peptides in bone metabolism were reviewed in this paper.

SETD4 in the Proliferation, Migration, Angiogenesis, Myogenic Differentiation and Genomic Methylation of Bone Marrow Mesenchymal Stem Cells

Epigenetic modification is a crucial mechanism affecting the biological function of stem cells. SETD4 is a histone methyltransferase, and its biological role in bone marrow mesenchymal stem cells (BMSCs) is currently unknown. In this study, we employed CRISPR/Cas9 technology edited mouse model and found that SETD4 knockout significantly promoted the proliferation of BMSCs, impaired BMSCs migration and differentiation potentials of lineages of cardiacmyocyte and smooth muscle cell, and even the angiogenesis via paracrine of VEGF. Through Reduced Representation Bisulfite Sequencing (RRBS) method, we verified that the overall genomic methylation of BMSCs in the SETD4 knockout group only was decreased by 0.47 % compared with wild type. However, the changed genomic methylation covers a total of 96,331 differential methylated CpG sites and 8,692 differential methylation regions (DMRs), with part of them settled in promoter regions. Bioinformatic analysis revealed that differential CpG islands and DMRs in promoter impacted 270 GO functions and 34 KEGG signaling pathways, with some closely related to stem cell biology. Mechanismly, SETD4 knockout inhibited sets of monomethylases and dimethylases for histone lysine, along with significant changes in some factors including Nkx2.5, Gata4, Gli2, Grem2, E2f7, Map7, Nr2f2 and Shox2 that associated with stem cell biology. These results are the first to reveal that even though SETD4 changes the genome's overall methylation to a limited extent in BMSCs, it still affects the numerous cellular functions and signaling pathways, implying SETD4-altered genomic methylation serves a crucial molecular role in BMSCs' biological functions.

Effects of intermittent treatment with parathyroid hormone (PTH) on osteoblastic differentiation and mineralization of mouse induced pluripotent stem cells in a 3D culture model

BACKGROUND/OBJECTIVES

PTH plays an important role in bone remodeling, and different actions have been reported depending on its administration method. iPSCs are promising as a cell source for regeneration of periodontal tissue due to their ability of proliferation and pluripotency. However, the effects of PTH on iPSCs remain mostly unknown. The purpose of this study was to investigate in vitro effects of parathyroid hormone (PTH) on osteoblastic differentiation of induced pluripotent stem cells (iPSCs) in a 3D culture model.

MATERIALS AND METHODS

Following embryoid body (EB) induction from mouse iPSCs (miPSCs), dissociated cells (miPS-EB-derived cells) were seeded onto atelocollagen sponge (ACS) in osteoblast differentiation medium (OBM). Cell-ACS constructs were divided into three groups: continuous treatment with human recombinant PTH (1-34) (PTH-C), intermittent PTH treatment (PTH-I) or OBM control. To confirm the expression of PTH receptor-1(PTH1R), the expression of Pth1r and cAMP production over time were assessed. Real-time PCR was used to assess the expression of genes encoding osterix (Sp7), runt-related transcription factor 2 (Runx2), collagen type 1 (Col1a1), and osteocalcin (Bglap) at different time points. Mineralization was assessed by von Kossa staining. Histochemical staining was used to analyze alkaline phosphatase (ALP) activity, and immunolocalization of SP7 and BGLAP was analyzed by confocal laser scanning microscopy (CLSM).

RESULTS

On days 7 and 14, expression of the Pth1r in miPS-EB-derived cells was increased in all groups. Production of cAMP, the second messenger of the PTH1R, tended to increase in the PTH-I group compared with PTH-C group on day 14. Expression of Col1a1 in the PTH-I group on day 14 was significantly higher than other groups. There was a time-dependent increase in the expression of Sp7 in all groups. On day 14, the expression level of Sp7 in the PTH-I group was significantly higher than other groups. In von Kossa staining, the PTH-I group showed higher level of staining compared with other groups on day 14, whereas the level was slightly attenuated in the PTH-C group. In histochemical staining, ALP-positive cells were significantly increased in the PTH-I group compared with other groups on day 14. In CLSM analysis, the numbers of SP7- and BGLAP-positive cells showed a gradual increase over time, and on day 14, a significantly greater SP7 expression was observed in the PTH-I group than other groups.

CONCLUSION

These results suggested that the intermittent PTH treatment promotes osteoblastic differentiation and mineralization of miPSCs in the ACS scaffold.

Intermittent administration of parathyroid hormone improves bone quality and quantity around implants in rat tibiae

OBJECTIVES

Intermittent injection of parathyroid hormone (PTH) is used to treat osteoporosis. The concept of bone quality was updated 20 years ago; however, these updates have not been adopted in implant dentistry. This study aimed to investigate the effects of intermittent administration of PTH on bone quality around implants in rat tibiae.

METHODS

Grade IV-titanium-threaded implants that were 3.5 mm long and 2.0 mm wide were placed in a randomly selected side of the proximal tibiae of 12-week-old female Wistar rats. Three weeks after implant placement, the rats were randomly divided into PTH-administration and saline-injection groups (PTH and VC, respectively; n = 7 per group). Micro-computed tomographical, histomorphometric, and immunohistochemical analyses were performed to evaluate bone quality and quantity surrounding the implants.

RESULTS

PTH significantly increased bone volume and bone mineral density in bones not associated with the implants as compared to these values in the VC group. PTH significantly increased bone area and the amount of collagen within the total inside areas of all implant threads compared to that observed in VC. Moreover, PTH significantly increased the number of osteoblasts, osteocytes, and osteoclasts in the total inside and/or outside areas of all implant threads and altered the ratio of type I and III collagen to total collagen fibers.

CONCLUSIONS

Within the limitations of this study, intermittent administration of PTH improved both bone quantity and bone quality based on the types and numbers of bone cells and the types of collagen fibers surrounding implants placed into rat tibiae.

Regulation of body length and bone mass by Gpr126/Adgrg6

Adhesion G protein-coupled receptor G6 (Adgrg6; also named GPR126) single-nucleotide polymorphisms are associated with human height in multiple populations. However, whether and how GPR126 regulates body height is unknown. In this study, we found that mouse body length was specifically decreased in Osx-Cre;Gpr126^fl/fl mice. Deletion of Gpr126 in osteoblasts resulted in a remarkable delay in osteoblast differentiation and mineralization during embryonic bone formation. Postnatal bone formation, bone mass, and bone strength were also significantly affected in Gpr126 osteoblast deletion mice because of defects in osteoblast proliferation, differentiation, and ossification. Furthermore, type IV collagen functioned as an activating ligand of Gpr126 to regulate osteoblast differentiation and function by stimulating cAMP signaling. Moreover,the cAMP activator PTH(1-34), could partially restore the inhibition of osteoblast differentiation and the body length phenotype induced by Gpr126 deletion.Together, our results demonstrated that COLIV-Gpr126 regulated body length and bone mass through cAMP-CREB signaling pathway.

Icariin Promotes the Osteogenic Action of BMP2 by Activating the cAMP Signaling Pathway

Icariin (ICA) is the main active flavonoid glucoside from herbs of the genus Epimedium; in traditional Chinese medicine, these herbs have long been prescribed for the treatment of bone fractures and osteoporosis. Several studies have shown that treatment with ICA can increase osteogenic differentiation and reduce bone loss in vivo and in vitro. However, the definite signaling pathway of this osteogenic effect remains unclear. In this study, we selected bone morphogenetic protein 2 (BMP2)-induced osteoblastic differentiation of multipotent mesenchymal progenitor C2C12 cells as a model of osteoblast differentiation. We investigated the effects of ICA on C2C12 cells osteogenic differentiation and the underlying molecular mechanisms. We found that ICA could enhance BMP2-mediated osteoblastic differentiation of C2C12 cells in a dose-dependent manner. Treatment with ICA activated the cAMP/PKA/CREB signaling axis in a time-dependent manner. Blocking cAMP signaling using the PKA selective inhibitor H89 significantly inhibited the stimulatory effect of ICA on osteogenesis. Therefore, the osteoinductive potential and the low cost of ICA indicate that it is a promising alternative treatment or promoter for enhancing the therapeutic effects of BMP2.

A Study of the Effects of Doxorubicin-Containing Liposomes on Osteogenesis of 3D Stem Cell Spheroids Derived from Gingiva

The objective of the present investigation is to determine the effects of neutral, anionic, and cationic liposomes loaded with doxorubicin with thin-lipid-film-hydration method on the cellular viability and osteogenesis of stem cell spheroids. Spheroid formation and morphology of the three-dimensional spheroid were noted with an inverted microscope. Quantitative cellular viability was assessed using a commercially available kit. Osteogenic potential was evaluated by applying alkaline phosphatase activity and anthraquinone dye of Alizarin Red S. Western blot analysis was performed using collagen I expression. Spheroids were formed in each silicon elastomer-based concave microwell on Day 1. Noticeable changes of the spheroid were seen with a higher concentration of doxorubicin, especially in the cationic liposome group at Days 5 and 7. We found that the application of doxorubicin for 5 days significantly reduced the cellular viability. A higher concentration of doxorubicin produced a significant decrease in alkaline phosphatase activity. Alizarin Red S staining showed that extracellular calcium deposits were evenly noted in each group. An increase of calcium deposits was noted on Day 14 when compared to Day 7. The morphology of the groups with higher concentrations of doxorubicin showed to be more dispersed. We noticed that doxorubicin-loaded cationic liposomes resulted in the highest uptake of the examined cell spheroids and that doxorubicin-loaded liposomes affected the osteogenic differentiation. The implication of this study is that the type of liposome should be selected based on the purpose of the application.

Pulsed electromagnetic fields promote bone formation by activating the sAC-cAMP-PKA-CREB signaling pathway

The application of pulsed electromagnetic fields (PEMFs) in the prevention and treatment of osteoporosis has long been an area of interest. However, the clinical application of PEMFs remains limited because of the poor understanding of the PEMF action mechanism. Here, we report that PEMFs promote bone formation by activating soluble adenylyl cyclase (sAC), cyclic adenosine monophosphate (cAMP), protein kinase A (PKA), and cAMP response element-binding protein (CREB) signaling pathways. First, it was found that 50 Hz 0.6 millitesla (mT) PEMFs promoted osteogenic differentiation of rat calvarial osteoblasts (ROBs), and that PEMFs activated cAMP-PKA-CREB signaling by increasing intracellular cAMP levels, facilitating phosphorylation of PKA and CREB, and inducing nuclear translocation of phosphorylated (p)-CREB. Blocking the signaling by adenylate cyclase (AC) and PKA inhibitors both abolished the osteogenic effect of PEMFs. Second, expression of sAC isoform was found to be increased significantly by PEMF treatment. Blocking sAC using sAC-specific inhibitor KH7 dramatically inhibited the osteogenic differentiation of ROBs. Finally, the peak bone mass of growing rats was significantly increased after 2 months of PEMF treatment with 90 min/day. The serum cAMP content, p-PKA, and p-CREB as well as the sAC protein expression levels were all increased significantly in femurs of treated rats. The current study indicated that PEMFs promote bone formation in vitro and in vivo by activating sAC-cAMP-PKA-CREB signaling pathway of osteoblasts directly or indirectly.

Aquaporins 1, 3 and 8 expression and cytokines in irritable bowel syndrome rats' colon via cAMP-PKA pathway

BACKGROUND

Irritable bowel syndrome (IBS) is one of the most common gastrointestinal (GI) disorders. The cAMP-PKA pathway plays a key role in mediating cell responses to various stimuli both of which might play an important role in IBS.

OBJECTIVE

Our research aimed to detect the mechanism of IBS rat models via the cAMP-PKA pathway so as to further detect the mechanisms of IBS.

METHODS

IBS rats were built by stress and conditioned stimulus. The study was divided into 3 groups (a control group, a model group, and a forskolin group). The expressions of AQP1, AQP3, AQP8, and CREB (Serl33) in the colons of rats were detected by immunohistochemistry. The expressions of AQP1, AQP3, AQP8, IL-1β, TGF β, and TNF α in the colon were detected by the PCR technique.

RESULTS

The IBS rats were built successfully. The expressions of AQP1, AQP3, AQP8, and CREB (Serl33) were down-regulated in the colons of IBS rats and were up-regulated with the intervention of the activator of AMP (P<0.05). The expressions of IL-1β, TGF β and TNF α were up-regulated in the colons of IBS rats and were down-regulated with the intervention of the activator of AMP (P<0.05).

CONCLUSIONS

The release of inflammatory cytokines, the activation of the immune system and liquid water metabolic abnormalities are the mechanisms of IBS via the cAMP-PKA pathway.

The flavonol glycoside icariin promotes bone formation in growing rats by activating the cAMP signaling pathway in primary cilia of osteoblasts

Icariin, a prenylated flavonol glycoside isolated from the herb Epimedium, has been considered as a potential alternative therapy for osteoporosis. Previous research has shown that, unlike other flavonoids, icariin is unlikely to act via the estrogen receptor, but its exact mechanism of action is unknown. In this study, using rat calvarial osteoblast culture and rat bone growth models, we demonstrated that icariin promotes bone formation by activating the cAMP/protein kinase A (PKA)/cAMP response element-binding protein (CREB) pathway requiring functional primary cilia of osteoblasts. We found that icariin increases the peak bone mass attained by young rats and promotes the maturation and mineralization of rat calvarial osteoblasts. Icariin activated cAMP/PKA/CREB signaling of the osteoblasts by increasing intracellular cAMP levels and facilitating phosphorylation of both PKA and CREB. Blocking cAMP/PKA/CREB signaling with inhibitors of the cAMP-synthesizing adenylyl cyclase (AC) and PKA inhibitors significantly inhibited the osteogenic effect of icariin in the osteoblasts. Icariin-activated cAMP/PKA/CREB signaling was localized to primary cilia, as indicated by localization of soluble AC and phosphorylated PKA. Furthermore, blocking ciliogenesis via siRNA knockdown of a cilium assembly protein, IFT88, inhibited icariin-induced PKA and CREB phosphorylation and also abolished icariin's osteogenic effect. Finally, several of these outcomes were validated in icariin-treated rats. Together, these results provide new insights into icariin function and its mechanisms of action and strengthen existing ties between cAMP-mediated signaling and osteogenesis.

ClC-3 chloride channel mediates the role of parathyroid hormone [1-34] on osteogenic differentiation of osteoblasts

INTRODUCTION

Different concentrations of parathyroid hormone [1-34] (PTH [1-34]) can have totally opposite effects on osteoblasts. Intermittent stimulation with PTH can significantly increase bone mineral density in vitro, mainly through the protein kinase A (PKA) signaling pathway, which phosphorylates runt-related transcription factor 2 (Runx2). The ClC-3 chloride channel, an important anion channel, can also promote osteogenesis via the Runx2 pathway based on recent studies. The purpose of our study, therefore, is to research whether the ClC-3 chloride channel has an effect on PTH osteodifferentiation in MC3T3-E1 cells.

METHODS AND RESULTS

A cell counting kit (CCK-8) and real-time PCR were used to investigate the impact of different PTH stimulation modes on MC3T3-E1 cell proliferation and osteogenesis-related gene expression, respectively. We found that the minimum inhibitory concentration of PTH was 10-9 M, and the expression of alkaline phosphatase (Alpl) and Runx2 were at the highest levels when treated with 10-9 M PTH. Next, we used real-time PCR and immunofluorescence technique to detect changes in ClC-3 in MC3T3-E1 cells under PTH treatment. The results showed higher expression of the ClC-3 chloride channel at 10-9 M intermittent PTH administration than in the other groups. Finally, we used the ClC-3 siRNA technique to examine the role of the ClC-3 chloride channel in the effect of PTH on the osteogenesis of osteoblasts, and we found an obvious decrease in the expression of bone sialoprotein (Ibsp), osteocalcin (Bglap), osterix (Sp7), Alpl and Runx2, the formation of mineralization nodules as well.

CONCLUSIONS

From the above data, we conclude that the expression of ClC-3 chloride channels in osteoblasts helps them respond to PTH stimulation, which mediates osteogenic differentiation.