PTH and PTHrP signaling in osteoblasts

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.

Hypercalcemia in Cancer: Causes, Effects, and Treatment Strategies

Calcium plays central roles in numerous biological processes, thereby, its levels in the blood are under strict control to maintain homeostatic balance and enable the proper functioning of living organisms. The regulatory mechanisms ensuring this balance can be affected by pathologies such as cancer, and as a result, hyper- or hypocalcemia can occur. These states, characterized by elevated or decreased calcium blood levels, respectively, have a significant effect on general homeostasis. This article focuses on a particular form of calcium metabolism disorder, which is hypercalcemia in neoplasms. It also constitutes a summary of the current knowledge regarding the diagnosis of hypercalcemia and its management. Hypercalcemia of malignancy is estimated to affect over 40% of cancer patients and can be associated with both solid and blood cancers. Elevated calcium levels can be an indicator of developing cancer. The main mechanism of hypercalcemia development in tumors appears to be excessive production of parathyroid hormone-related peptides. Among the known treatment methods, bisphosphonates, calcitonin, steroids, and denosumab should be mentioned, but ongoing research promotes progress in pharmacotherapy. Given the rising global cancer prevalence, the problem of hypercalcemia is of high importance and requires attention.

Only bioactive forms of PTH (n-oxPTH and Met18(ox)-PTH) inhibit synthesis of sclerostin - evidence from in vitro and human studies

Sclerostin (SOST) is produced by osteocytes and is known as a negative regulator of bone homeostasis. Parathyroid hormone (PTH) regulates calcium, phosphate as well as vitamin D metabolism, and is a strong inhibitor of SOST synthesis in vitro and in vivo. PTH has two methionine amino acids (positions 8 and 18) which can be oxidized. PTH oxidized at Met18 (Met18(ox)-PTH) continues to be bioactive, whereas PTH oxidized at Met8 (Met8(ox)-PTH) or PTH oxidized at Met8 and Met18 (Met8, Met18(di-ox)-PTH) has minor bioactivity. How non-oxidized PTH (n-oxPTH) and oxidized forms of PTH act on sclerostin synthesis is unknown. The effects of n-oxPTH and oxidized forms of PTH on SOST gene expression were evaluated in UMR106 osteoblast-like cells. Moreover, we analyzed the relationship of SOST with n-oxPTH and all forms of oxPTH in 516 stable kidney transplant recipients using an assay system that can distinguish in clinical samples between n-oxPTH and the sum of all oxidized PTH forms (Met8(ox)-PTH, Met18(ox)-PTH, and Met8, Met18(di-ox)-PTH). We found that both n-oxPTH and Met18(ox)-PTH at doses of 1, 3, 20, and 30 nmol/L significantly inhibit SOST gene expression in vitro, whereas Met8(ox)-PTH and Met8, Met18(di-ox)-PTH only have a weak inhibitory effect on SOST gene expression. In the clinical cohort, multivariate linear regression showed that only n-oxPTH, but not intact PTH (iPTH) nor oxPTH, is independently associated with circulating SOST after adjusting for known confounding factors. In conclusion, only bioactive PTH forms such as n-oxPTH and Met18(ox)-PTH, inhibit SOST synthesis.

IRE1α pathway: A potential bone metabolism mediator

Osteoblasts and osteoclasts collaborate in bone metabolism, facilitating bone development, maintaining normal bone density and strength, and aiding in the repair of pathological damage. Endoplasmic reticulum stress (ERS) can disrupt the intracellular equilibrium between osteoclast and osteoblast, resulting in dysfunctional bone metabolism. The inositol-requiring enzyme-1α (IRE1α) pathway-the most conservative unfolded protein response pathway activated by ERS-is crucial in regulating cell metabolism. This involvement encompasses functions such as inflammation, autophagy, and apoptosis. Many studies have highlighted the potential roles of the IRE1α pathway in osteoblasts, chondrocytes, and osteoclasts and its implication in certain bone-related diseases. These findings suggest that it may serve as a mediator for bone metabolism. However, relevant reviews on the role of the IRE1α pathway in bone metabolism remain unavailable. Therefore, this review aims to explore recent research that elucidated the intricate roles of the IRE1α pathway in bone metabolism, specifically in osteogenesis, chondrogenesis, osteoclastogenesis, and osteo-immunology. The findings may provide novel insights into regulating bone metabolism and treating bone-related diseases.

Effects of stepwise administration of osteoprotegerin and parathyroid hormone-related peptide DNA vectors on bone formation in ovariectomized rat model

Osteoporosis is a metabolic bone disease that impairs bone mineral density, microarchitecture, and strength. It requires continuous management, and further research into new treatment options is necessary. Osteoprotegerin (OPG) inhibits bone resorption and osteoclast activity. The objective of this study was to investigate the effects of stepwise administration of OPG-encoded minicircles (mcOPG) and a bone formation regulator, parathyroid hormone-related peptide (PTHrP)-encoded minicircles (mcPTHrP) in osteoporosis. The combined treatment with mcOPG and mcPTHrP significantly increased osteogenic marker expression in osteoblast differentiation compared with the single treatment groups. A model of postmenopausal osteoporosis was established in 12-week-old female rats through ovariectomy (OVX). After 8 weeks of OVX, mcOPG (80 µg/kg) was administered via intravenous injection. After 16 weeks of OVX, mcPTHrP (80 µg/kg) was injected once a week for 3 weeks. The bone microstructure in the femur was evaluated 24 weeks after OVX using micro-CT. In a proof-of-concept study, stepwise treatment with mcOPG and mcPTHrP on an OVX rat model significantly improved bone microstructure compared to treatment with mcOPG or mcPTHrP alone. These results suggest that stepwise treatment with mcOPG and mcPTHrP may be a potential treatment for osteoporosis.

Metabolic bone disorders and the promise of marine osteoactive compounds

Metabolic bone disorders and associated fragility fractures are major causes of disability and mortality worldwide and place an important financial burden on the global health systems. These disorders result from an unbalance between bone anabolic and resorptive processes and are characterized by different pathophysiological mechanisms. Drugs are available to treat bone metabolic pathologies, but they are either poorly effective or associated with undesired side effects that limit their use. The molecular mechanism underlying the most common metabolic bone disorders, and the availability, efficacy, and limitations of therapeutic options currently available are discussed here. A source for the unmet need of novel drugs to treat metabolic bone disorders is marine organisms, which produce natural osteoactive compounds of high pharmaceutical potential. In this review, we have inventoried the marine osteoactive compounds (MOCs) currently identified and spotted the groups of marine organisms with potential for MOC production. Finally, we briefly examine the availability of in vivo screening and validation tools for the study of MOCs.

Challenges in establishing animal models for studying osteoimmunology of hypoparathyroidism

Hypoparathyroidism is a relatively rare human and veterinary disease characterized by deficient or absent production of parathyroid hormone (PTH). PTH is known as a classical regulator of calcium and phosphorus homeostasis. Nevertheless, the hormone also appears to modulate immune functions. For example, increased CD4:CD8 T-cell ratios and elevated interleukin (IL)-6 and IL-17A levels were observed in patients with hyperparathyroidism, whereas gene expression of tumor necrosis factor-α (TNF-α) and granulocyte macrophage-colony stimulating factor (GM-CSF) was decreased in patients with chronic postsurgical hypoparathyroidism. Various immune cell populations are affected differently. So, there is a need for validated animal models for the further characterization of this disease for identifying targeted immune-modulatory therapies. In addition to genetically modified mouse models of hypoparathyroidism, there are surgical rodent models. Parathyroidectomy (PTX) can be well performed in rats-for pharmacological and associated osteoimmunological research and bone mechanical studies, a large animal model could be preferable, however. A major drawback for successfully performing total PTX in large animal species (pigs and sheep) is the presence of accessory glands, thus demanding to develop new approaches for real-time detection of all parathyroid tissues.

Degradation-Resistant Hypoxia Inducible Factor-2α in Murine Osteocytes Promotes a High Bone Mass Phenotype

Molecular oxygen levels vary during development and disease. Adaptations to decreased oxygen bioavailability (hypoxia) are mediated by hypoxia-inducible factor (HIF) transcription factors. HIFs are composed of an oxygen-dependent α subunit (HIF-α), of which there are two transcriptionally active isoforms (HIF-1α and HIF-2α), and a constitutively expressed β subunit (HIFβ). Under normoxic conditions, HIF-α is hydroxylated via prolyl hydroxylase domain (PHD) proteins and targeted for degradation via Von Hippel-Lindau (VHL). Under hypoxic conditions, hydroxylation via PHD is inhibited, allowing for HIF-α stabilization and induction of target transcriptional changes. Our previous studies showed that Vhl deletion in osteocytes (Dmp1-cre; Vhl f/f ) resulted in HIF-α stabilization and generation of a high bone mass (HBM) phenotype. The skeletal impact of HIF-1α accumulation has been well characterized; however, the unique skeletal impacts of HIF-2α remain understudied. Because osteocytes orchestrate skeletal development and homeostasis, we investigated the role of osteocytic HIF-α isoforms in driving HBM phenotypes via osteocyte-specific loss-of-function and gain-of-function HIF-1α and HIF-2α mutations in C57BL/6 female mice. Deletion of Hif1a or Hif2a in osteocytes showed no effect on skeletal microarchitecture. Constitutively stable, degradation-resistant HIF-2α (HIF-2α cDR), but not HIF-1α cDR, generated dramatic increases in bone mass, enhanced osteoclast activity, and expansion of metaphyseal marrow stromal tissue at the expense of hematopoietic tissue. Our studies reveal a novel influence of osteocytic HIF-2α in driving HBM phenotypes that can potentially be harnessed pharmacologically to improve bone mass and reduce fracture risk. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

O-GlcNAc glycosylation orchestrates fate decision and niche function of bone marrow stromal progenitors

In mammals, interactions between the bone marrow (BM) stroma and hematopoietic progenitors contribute to bone-BM homeostasis. Perinatal bone growth and ossification provide a microenvironment for the transition to definitive hematopoiesis; however, mechanisms and interactions orchestrating the development of skeletal and hematopoietic systems remain largely unknown. Here, we establish intracellular O-linked β-N-acetylglucosamine (O-GlcNAc) modification as a posttranslational switch that dictates the differentiation fate and niche function of early BM stromal cells (BMSCs). By modifying and activating RUNX2, O-GlcNAcylation promotes osteogenic differentiation of BMSCs and stromal IL-7 expression to support lymphopoiesis. In contrast, C/EBPβ-dependent marrow adipogenesis and expression of myelopoietic stem cell factor (SCF) is inhibited by O-GlcNAcylation. Ablating O-GlcNAc transferase (OGT) in BMSCs leads to impaired bone formation, increased marrow adiposity, as well as defective B-cell lymphopoiesis and myeloid overproduction in mice. Thus, the balance of osteogenic and adipogenic differentiation of BMSCs is determined by reciprocal O-GlcNAc regulation of transcription factors, which simultaneously shapes the hematopoietic niche.

A Novel Heterozygous Missense Variant in Parathyroid Hormone 1 is Related to the Occurrence of Developmental Dysplasia of the Hip

Introduction: Developmental dysplasia of the hip (DDH) is one of the most common diseases in the pediatric orthopedics, with an incidence of 1-5%. Genetic factors are the bases of the pathogenesis of DDH, but the pathogenic variants and pathogenesis of DDH are still unknown. There are no key accurate diagnostic or prognostic molecular markers for DDH. The purpose of our study was to screen for genetic variant associated with DDH and explore its pathogenesis. Materials and Methods: The genetic variation of DDH was tested by variant NGS-based exome analyses, verified by the Sanger sequencing. Results: A four-generation family in which DDH was present in three generations was recruited. A novel heterozygous missense variant c.629C>T (p.(Ala210Val)) in exon 7/8 of the parathyroid hormone 1 receptor (PTH1R) gene was identified through screening of two affected and one unaffected family members. The candidate variant was validated in all available family members with all three affected members being positive for the PTH1R variant. Conclusion: Our results are highly supportive of PTH1R as a novel candidate gene for DDH and demonstrated that the combination of pedigree information and next-generation sequencing is an effective method for identifying pathogenic variants associated with DDH.

Abaloparatide outperforms teriparatide in protecting against alveolar bone loss in experimental periodontitis

BACKGROUND

The aim of this study was to compare the effects of two osteoanabolic drugs, abaloparatide (ABL) and teriparatide (TPTD), on protecting alveolar bone in experimental periodontitis.

METHODS

Twenty-four 9-week-old, male, Sprague-Dawley rats were placed with silk suture around the right maxillary second molar, and then were randomly divided into three groups, that is, the ABL, TPTD, and saline group, receiving intermittent subcutaneous injections of ABL (80 μg/kg), TPTD (80 μg/kg) or saline respectively every other day for 4 weeks. Samples on both sides were assessed through micro-computerized tomography, histological, and immunohistochemical analysis. Mouse pre-osteoblast MC3T3 cell was cultured with lipopolysaccharide (LPS) and treated with ABL or TPTD, before assays of cell proliferation, alkaline phosphatase (ALP) activity and real-time polymerase chain reaction.

RESULTS

On the ligature side, both ABL and TPTD significantly reduced alveolar bone loss, and ABL had significantly better effects with higher expression of runt-related transcription factor 2 (RUNX2) and Bglap (formerly called osteocalcin); meanwhile, the ligature induced osteoclastogenesis and down-regulation of osteoprotegerin (OPG) was affected by neither drug. On the non-ligature side, ABL also showed better osteoanabolic effects. In vitro studies revealed that, in the presence of LPS, ABL, and TPTD similarly promoted MC3T3 proliferation, whereas ABL induced higher ALP activity and osteoblastic gene expression compared to TPTD.

CONCLUSION

Both ABL and TPTD protect and regenerate alveolar bone in experimental periodontitis, and ABL behaves even better than TPTD at the same dose, attributed to its stronger osteoanabolic effects in this context.

Abaloparatide Has the Same Catabolic Effects on Bones of Mice When Infused as PTH (1-34)

Abaloparatide is a peptide analog of parathyroid hormone-related protein (PTHrP 1-34) and was approved in 2017 as the second osteoanabolic peptide for treating osteoporosis. We previously showed that intermittent abaloparatide is equally as effective as PTH (1-34). This study was designed to compare the catabolic effects of PTH (1-34) and abaloparatide on bone in young female wild-type mice. Two-month-old C57Bl/6J female mice were continuously infused with human PTH (1-34) or abaloparatide at 80 μg/kg BW/day or vehicle for 2 weeks. At euthanasia, DEXA-PIXImus was performed to assess bone mineral density (BMD) in the whole body, femurs, tibiae, and vertebrae. Bone turnover marker levels were measured in sera, femurs were harvested for micro-computer tomography (μCT) analyses and histomorphometry, and tibiae were separated into cortical and trabecular fractions for gene expression analyses. Our results demonstrated that the infusion of abaloparatide resulted in a similar decrease in BMD as infused PTH (1-34) at all sites. μCT and histomorphometry analyses showed similar decreases in cortical bone thickness and BMD associated with an increase in bone turnover from the increased bone formation rate found by in vivo double labeling and serum P1NP and increased bone resorption as shown by osteoclast numbers and serum cross-linked C-telopeptide. Trabecular bone did not show major changes with either treatment. Osteoblastic gene expression analyses of trabecular and cortical bone revealed that infusion of PTH (1-34) or abaloparatide led to similar and different actions in genes of osteoblast differentiation and activity. As with intermittent and in vitro treatment, both infused PTH (1-34) and abaloparatide similarly regulated downstream genes of the PTHR1/SIK/HDAC4 pathway such as Sost and Mmp13 but differed for those of the PTHR1/SIK/CRTC pathway. Taken together, at the same dose, infused abaloparatide causes the same high bone turnover as infused PTH (1-34) with a net resorption in female wild-type mice. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

A standardized extract of Coleus forskohlii root protects rats from ovariectomy-induced loss of bone mass and strength, and impaired bone material by osteogenic and anti-resorptive mechanisms

INTRODUCTION

In obese humans, Coleus forskohlii root extract (CF) protects against weight gain owing to the presence of forskolin, an adenylate cyclase (AC) activator. As AC increases intracellular cyclic adenosine monophosphate (cAMP) levels in osteoblasts that has an osteogenic effect, we thus tested the skeletal effects of a standardized CF (CFE) in rats.

METHODS

Concentrations of forskolin and isoforskolin were measured in CFE by HPLC. CFE and forskolin (the most abundant compound present in CFE) were studied for their osteogenic efficacy in vitro by alkaline phosphatase (ALP), cAMP and cyclic guanosine monophosphate (cGMP) assays. Femur osteotomy model was used to determine the osteogenic dose of CFE. In growing rats, CFE was tested for its osteogenic effect in intact bone. In adult ovariectomized (OVX) rats, we assessed the effect of CFE on bone mass, strength and material. The effect of forskolin was assessed in vivo by measuring the expression of osteogenic genes in the calvarium of rat pups.

RESULTS

Forskolin content in CFE was 20.969%. CFE increased osteoblast differentiation and intracellular cAMP and cGMP levels in rat calvarial osteoblasts. At 25 mg/kg (half of human equivalent dose), CFE significantly enhanced calcein deposition at the osteotomy site. In growing rats, CFE promoted modeling-directed bone formation. In OVX rats, CFE maintained bone mass and microarchitecture to the level of sham-operated rats. Moreover, surface-referent bone formation in CFE treated rats was significantly increased over the OVX group and was comparable with the sham group. CFE also increased the pro-collagen type-I N-terminal propeptide: cross-linked C-telopeptide of type-I collagen (PINP : CTX-1) ratio over the OVX rats, and maintained it to the sham level. CFE treatment decreased the OVX-induced increases in the carbonate-to-phosphate, and carbonate-to-amide-I ratios. CFE also prevented the OVX-mediated decrease in mineral crystallinity. Nanoindentation parameters, including modulus and hardness, were decreased by OVX but CFE maintained these to the sham levels. Forskolin stimulated ALP, cAMP and cGMP in vitro and upregulated osteogenic genes in vivo.

CONCLUSION

CFE, likely due to the presence of forskolin displayed a bone-conserving effect via osteogenic and anti-resorptive mechanisms resulting in the maintenance of bone mass, microarchitecture, material, and strength.

The associations of gut microbiota, endocrine system and bone metabolism

Gut microbiota is of great importance in human health, and its roles in the maintenance of skeletal homeostasis have long been recognized as the "gut-bone axis." Recent evidence has indicated intercorrelations between gut microbiota, endocrine system and bone metabolism. This review article discussed the complex interactions between gut microbiota and bone metabolism-related hormones, including sex steroids, insulin-like growth factors, 5-hydroxytryptamine, parathyroid hormone, glucagon-like peptides, peptide YY, etc. Although the underlying mechanisms still need further investigation, the regulatory effect of gut microbiota on bone health via interplaying with endocrine system may provide a new paradigm for the better management of musculoskeletal disorders.

Transplantation of Parathyroid Hormone-Treated Achilles Tendon Promotes Meniscal Regeneration in a Rat Meniscal Defect Model

BACKGROUND

Autologous tendon grafts are used for meniscal reconstruction of surgically removed knee joint meniscus. However, as meniscal reconstruction cannot prevent the progression of cartilage degeneration, additional procedures that confer meniscus-like histological properties to the transplanted tendon are required for improved outcomes.

HYPOTHESES

Parathyroid hormone (PTH)(1-34) induces cartilage formation in the rat tendon, and transplantation of PTH-treated tendon promotes meniscal regeneration.

STUDY DESIGN

Controlled laboratory study.

METHODS

Rat Achilles tendon-derived cells were cultured with or without PTH for 28 days and stained with Alcian blue to determine chondrogenic differentiation. After 14 and 28 days of incubation, gene expression was assessed using quantitative real-time polymerase chain reaction. In an in vivo study, rat Achilles tendon was injected with PTH and then transplanted onto a medial meniscal defect. Macroscopic and histological assessments of the regenerated meniscus and of cartilage degeneration in the tibial plateau were performed at 4 and 8 weeks after surgery.

RESULTS

In vitro, PTH-treated cells showed better staining with Alcian blue than the control (normal medium) group. PTH1R, Col2a1, Sox9, and RUNX2 were significantly upregulated in PTH-treated cells (P < .05). Macroscopically, the in vivo results revealed more prominent meniscal coverage and lesser progression of articular cartilage degeneration in the PTH group than in the phosphate-buffered saline-injected group. Histologically, toluidine blue staining revealed metachromasia in the PTH-injected tissue at 4 and 8 weeks. The PTH-treated regenerated meniscus showed positive immunostaining for type II collagen in the area exhibiting metachromasia. Moreover, PTH-treated tendon had an enhanced histological score compared with the untreated group at 4 and 8 weeks (P < .05).

CONCLUSION

PTH(1-34) induced cartilage formation in the rat tendon. Transplantation of PTH(1-34)-treated Achilles tendon in a rat meniscal defect model induced meniscal regeneration and preserved knee articular cartilage. Macroscopically, PTH groups showed a greater coverage of the regenerated meniscus. Histologically, the regenerated meniscus had higher cartilaginous matrix content in rats transplanted with PTH-treated tendons. PTH(1-34) stimulated tendon-derived cells to promote chondrogenic differentiation.

CLINICAL RELEVANCE

Meniscal transplantation using PTH-injected autologous tendon grafts might promote meniscal regeneration and prevent progression of cartilage degeneration by stimulating chondrogenic differentiation of tendon-derived cells.

Modulation of PTH1R signaling by an extracellular binding antibody

Parathyroid hormone receptor 1 (PTH1R) is a class B G-protein coupled receptor with key roles in bone development. The receptor signals through both the G_s and G_q G-proteins as well as through β-arrestin in a G-protein independent manner. Current treatments for bone disorders, such as osteoporosis, target the PTH1R but are suboptimal in their efficacy. Monoclonal antibodies represent a major growth area in therapeutics as a result of their superior specificity and long serum half-life. Here, we discovered antibodies against the extracellular domain (ECD) of PTH1R from a phage display library. One of these antibodies, ECD-ScFvhFc, binds PTH1R with high affinity and although it has little or no effect on G-protein dependent receptor signaling, it does reduce PTH1R mediated β-arrestin signaling. Hydrogen-deuterium exchange mass spectrometry (HDX-MS) demonstrated that the ECD-ScFvhFc binding site overlapped partially with that of the cognate ligand, PTH. The results of this study demonstrate the suitability of PTH1R as a target for therapeutic antibody development.

Parathyroid Hormone-Related Peptide and Its Analog, Abaloparatide, Attenuate Lethal Myocardial Ischemia-Reperfusion Injury

Parathyroid hormone-related peptide (PTHrP) is well-known to play a role in bone formation, and abaloparatide, an analog of PTHrP(1-34), is approved for the treatment of osteoporosis in post-menopausal women. PTHrP has also been reported to have cardiovascular effects, with recent data demonstrating that exogenously administered PTHrP can limit the death of isolated cardiomyocytes subjected to oxidative stress via upregulation of classic ‘survival kinase’ signaling. Our aim in the current study was to extend this concept and, employing both in vitro and in vivo models, establish whether PTHrP(1-36) and abaloparatide are cardioprotective in the setting of lethal myocardial ischemia-reperfusion injury. We report that preischemic administration of PTHrP(1-36) and abaloparatide attenuated cell death in HL-1 cardiomyocytes subjected to simulated ischemia-reperfusion, an effect that was accompanied by the augmented expression of phospho-ERK and improved preservation of phospho-Akt, and blocked by co-administration of the MEK-ERK inhibitor PD98059. Moreover, using the translationally relevant swine model of acute coronary artery occlusion-reperfusion, we make the novel observation that myocardial infarct size was significantly reduced in pigs pretreated with PTHrP(1-36) when compared with placebo-controls (13.1 ± 3.3% versus 42.0 ± 6.6% of the area of at-risk myocardium, respectively; p < 0.01). Taken together, these data provide the first evidence in support of the concept that pretreatment with PTHrP(1-36) and abaloparatide renders cardiomyocytes resistant to lethal myocardial ischemia-reperfusion injury.

Parathyroid hormone (PTH) regulation of metabolic homeostasis: An old dog teaches us new tricks

BACKGROUND

Late in the nineteenth century, it was theorized that a circulating product produced by the parathyroid glands could negatively impact skeletal homeostasis. A century later, intermittent administration of that protein, namely parathyroid hormone (PTH), was approved by the FDA and EMA as the first anabolic agent to treat osteoporosis. Yet, several unanswered but important questions remain about the skeletal actions of PTH.

SCOPE OF REVIEW

Current research efforts have focused on improving the efficacy of PTH treatment by designing structural analogs and identifying other targets (e.g., the PTH or the calcium sensing receptor). A unique but only recently described aspect of PTH action is its regulation of cellular bioenergetics and metabolism, namely in bone and adipose tissue but also in other tissues. The current review aims to provide a brief background on PTH's previously described actions on bone and highlights how PTH regulates osteoblast bioenergetics, contributing to greater bone formation. It will also shed light on how PTH could alter metabolic homeostasis through its actions in other cells and tissues, thereby impacting the skeleton in a cell non-autonomous manner.

MAJOR CONCLUSIONS

PTH administration enhances bone formation by targeting the osteoblast through transcriptional changes in several pathways; the most prominent is via adenyl cyclase and PKA. PTH and its related protein, PTHrP, also induce glycolysis and fatty acid oxidation in bone cells and drive lipolysis and thermogenic programming in adipocytes; the latter may indirectly but positively influence skeletal metabolism. While much work remains, alterations in cellular metabolism may also provide a novel mechanism related to PTH's temporal actions. Thus, the bioenergetic impact of PTH can be considered another of the myriad anabolic effects of PTH on the skeleton. Just as importantly from a translational perspective, the non-skeletal metabolic effects may lead to a better understanding of whole-body homeostasis along with new and improved therapies to treat musculoskeletal conditions.

Exogenous Parathyroid Hormone Alleviates Intervertebral Disc Degeneration through the Sonic Hedgehog Signalling Pathway Mediated by CREB

As an important hormone that regulates the balance of calcium and phosphorus, parathyroid hormone (PTH) has also been found to have an important function in intervertebral disc degeneration (IVDD). Our aim was to investigate the mechanism by which PTH alleviates IVDD. In this study, the PTH 1 receptor was found to be highly expressed in severely degenerated human nucleus pulposus (NP) cells. We found in the mouse model of IVDD that supplementation with exogenous PTH alleviated the narrowing of the intervertebral space and the degradation of the extracellular matrix (ECM) caused by tail suspension (TS). In addition, inflammation, oxidative stress, and apoptosis levels were significantly increased in the intervertebral disc tissues of TS-induced mice, and the activity of NP cells was decreased. TS also led to the downregulation of Sonic hedgehog (SHH) signalling pathway-related signal molecules in NP cells such as SHH, Smoothened, and GLI1. However, supplementation with exogenous PTH can reverse these changes. In vitro, PTH also promotes the activity of NP cells and the secretion of ECM. However, the antagonist of the SHH signalling pathway can inhibit the therapeutic effect of PTH on NP cells. In addition, a cAMP-response element-binding protein, as an important transcription factor, was found to mediate the promotion of PTH on the SHH signalling pathway. Our results revealed that PTH can alleviate IVDD by inhibiting inflammation, oxidative stress, and apoptosis and improving the activity of NP cells via activating the SHH signalling pathway.

PTHG2 Reduces Bone Loss in Ovariectomized Mice by Directing Bone Marrow Mesenchymal Stem Cell Fate

Teriparatide, also known as 1-34 parathyroid hormone (PTH (1-34)), is commonly used for the treatment of osteoporosis in postmenopausal women. But its therapeutic application is restricted by poor metabolic stability, low bioavailability, and rapid clearance. Herein, PTHG2, a glycosylated teriparatide derivative, is designed and synthesized to improve PTH stability and exert more potent antiosteoporosis effect. Surface plasmon resonance (SPR) analysis shows that PTHG2 combines to PTH 1 receptor. Additional acetylglucosamine covalent bonding in the first serine at the N terminal of PTH (1-34) improves stability and increases protein hydrolysis resistance. Intermittent administration of PTHG2 preserves bone quality in ovariectomy- (OVX-) induced osteoporosis mice model, along with increased osteoblastic differentiation and bone formation, and reduced marrow adipogenesis. In vitro, PTHG2 inhibits adipogenic differentiation and promotes osteoblastic differentiation of bone marrow mesenchymal stem cells (BMSCs). For molecular mechanism, PTHG2 directs BMSCs fate through stimulating the cAMP-PKA signaling pathway. Blocking PKA abrogates the pro-osteogenic effect of PTHG2. In conclusion, our study reveals that PTHG2 can accelerate osteogenic differentiation of BMSCs and inhibit adipogenic differentiation of BMSCs and show a better protective effect than PTH (1-34) in the treatment of osteoporosis.

Osteoporosis therapies and their mechanisms of action (Review)

Osteoporosis is a common disease that affects millions of patients worldwide and is most common in menopausal women. The main characteristics of osteoporosis are low bone density and increased risk of fractures due to deterioration of the bone architecture. Osteoporosis is a chronic disease that is difficult to treat; thus, investigations into novel effective therapeutic methods are required. A number of studies have focused on determining the most effective treatment options for this disease. There are several treatment options for osteoporosis that differ depending on the characteristics of the disease, and these include both well-established and newly developed drugs. The present review focuses on the various drugs available for osteoporosis, the associated mechanisms of action and the methods of administration.

Molecular insights for an anti-osteoporotic properties of Litsea glutinosa on Saos-2 cells: An in-vitro approach

Osteoporosis is a skeletal disease that is identified by the deterioration of micro-architecture of bone tissue, leading to enhanced bone brittleness and a consequential increase in fracture threat. There are many treatments available for osteoporosis such as bisphosphonate therapy, hormonal replacement therapy, herbal therapy etc. For decades, there are several herbs that are attributed to have anti-osteoporotic effects however the candidate genes involved in it remained unknown. In line with this, the present study is focused to elucidate the anti-osteoporotic property of Litsea glutinosa (LG). To understand the proliferative effect and identify involved players, gene expression was studied on the Saos-2 osteocytes in-vitro. The expression profile of candidate genes involved in different signaling pathways such as Egr-2, RUNX2, MAPK3, NFATc1, CREB, ERβ, along with proliferation and apoptotic markers in osteoporosis were selected for the study. The gene expression profile demonstrated a significant up-regulation of Egr-2, RUNX2, MAPK3, CREB, EBβ in the range of 1.5–2.2 folds, whereas NFATc1 was found to be down-regulated up to 0.4 times compared to control when treated with 250 μg/mL of LG. Besides this, anti-apoptosis effect of LG was also supported by flow cytometry results which also proved that LG induces proliferation and inhibits apoptosis, suggesting the proliferative role of LG. In conclusion, the present study gathers the potency of LG extract for its proliferative and anti-apoptotic effect on Saos-2 osteocytes and opens a new avenue for detailing the mechanistic actions of it on mitigating the pathophysiology of osteoporosis.

Progress of Signaling Pathways, Stress Pathways and Epigenetics in the Pathogenesis of Skeletal Fluorosis

Fluorine is widely dispersed in nature and has multiple physiological functions. Although it is usually regarded as an essential trace element for humans, this view is not held universally. Moreover, chronic fluorosis, mainly characterized by skeletal fluorosis, can be induced by long-term excessive fluoride consumption. High concentrations of fluoride in the environment and drinking water are major causes, and patients with skeletal fluorosis mainly present with symptoms of osteosclerosis, osteochondrosis, osteoporosis, and degenerative changes in joint cartilage. Etiologies for skeletal fluorosis have been established, but the specific pathogenesis is inconclusive. Currently, active osteogenesis and accelerated bone turnover are considered critical processes in the progression of skeletal fluorosis. In recent years, researchers have conducted extensive studies in fields of signaling pathways (Wnt/β-catenin, Notch, PI3K/Akt/mTOR, Hedgehog, parathyroid hormone, and insulin signaling pathways), stress pathways (oxidative stress and endoplasmic reticulum stress pathways), epigenetics (DNA methylation and non-coding RNAs), and their inter-regulation involved in the pathogenesis of skeletal fluorosis. In this review, we summarised and analyzed relevant findings to provide a basis for comprehensive understandings of the pathogenesis of skeletal fluorosis and hopefully propose more effective prevention and therapeutic strategies.

Dose-dependent effects of pharmaceutical treatments on bone matrix properties in ovariectomized rats

As both anabolic and anti-catabolic osteoporosis drugs affect bone formation and resorption processes, they may contribute to bone's overall mechanical behavior by altering the quality of the bone matrix. We used an ovariectomized rat model and a novel fracture mechanics approach to investigate whether treatment with an anabolic (parathyroid hormone) or anti-catabolic (alendronate) osteoporosis drugs will alter the organic and mineral matrix components and consequently cortical bone fracture toughness. Ovariectomized (at 5 months age) rats were treated with either parathyroid hormone or alendronate at low and high doses for 6 months (age 6–12 months). Specifically, treatment groups included untreated ovariectomized controls (n = 9), high-dose alendronate (n = 10), low-dose alendronate (n = 9), high-dose parathyroid hormone (n = 10), and low-dose parathyroid hormone (n = 9). After euthanasia, cortical microbeams from the lateral quadrant were extracted, notched, and tested in 3-point bending to measure fracture toughness. Portions of the bone were used to measure changes in the 1) organic matrix through quantification of advanced glycation end-products (AGEs) and non-collagenous proteins, and 2) mineral matrix through assessment of mineral crystallinity. Compared to the ovariectomized group, rats treated with high doses of parathyroid hormone and alendronate had significantly increased cortical bone fracture toughness, which corresponded primarily to increased non-collagenous proteins while there was no change in AGEs. Additionally, low-dose PTH treatment increased matrix crystallinity and decreased AGE levels. In summary, ovariectomized rats treated with pharmaceutical drugs had increased non-collagenous matrix proteins and improved fracture toughness compared to controls. Further investigation is required for different doses and longer treatment periods.

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Alendronate increases non-collagenous proteins and improves fracture toughness.

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Parathyroid hormone also increases collagen maturity and mineral crystallinity.

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Both treatments minimize accumulation of advanced glycation end-products.

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).

Therapeutic potential of phosphodiesterase inhibitors in the treatment of osteoporosis: Scopes for therapeutic repurposing and discovery of new oral osteoanabolic drugs

Cyclic nucleotide phosphodiesterases (PDEs) are ubiquitously expressed enzymes that hydrolyze phosphodiester bond in the second messenger molecules including cAMP and cGMP. A wide range of drugs blocks one or more PDEs thereby preventing the inactivation of cAMP/cGMP. PDEs are differentially expressed in bone cells including osteoblasts, osteoclasts and chondrocytes. Intracellular increases in cAMP/cGMP levels in osteoblasts result in osteogenic response. Acting via the type 1 PTH receptor, teriparatide and abaloparatide increase intracellular cAMP and induce osteoanabolic effect, and many PDE inhibitors mimic this effect in preclinical studies. Since all osteoanabolic drugs are injectable and that oral drugs are considered to improve the treatment adherence and persistence, osteogenic PDE inhibitors could be a promising alternative to the currently available osteogenic therapies and directly assessed clinically in drug repurposing mode. Similar to teriparatide/abaloparatide, PDE inhibitors while stimulating osteoblast function also promote osteoclast function through stimulation of receptor activator of nuclear factor kappa-B ligand production from osteoblasts. In this review, we critically discussed the effects of PDE inhibitors in bone cells from cellular signalling to a variety of preclinical models that evaluated the bone formation mechanisms. We identified pentoxifylline (a non-selective PDE inhibitor) and rolipram (a PDE4 selective inhibitor) being the most studied inhibitors with osteogenic effect in preclinical models of bone loss at ≤ human equivalent doses, which suggest their potential for post-menopausal osteoporosis treatment through therapeutic repurposing. Subsequently, we treated pentoxifylline and rolipram as prototypical osteogenic PDEs to predict new chemotypes via the computer-aided design strategies for new drugs, based on the structural biology of PDEs.

Effects of acidosis on the structure, composition, and function of adult murine femurs

Physiologic pH is maintained in a narrow range through multiple systemic buffering systems. Metabolic Acidosis (MA) is an acid-base disorder clinically characterized by a decrease in systemic pH and bicarbonate (HCO₃^-) levels. Acidosis affects millions annually, resulting in decreased bone mineral density and bone volume and an increased rate of fracture. We developed an adult murine model of diet-induced metabolic acidosis via graded NH₄Cl administration that successfully decreased systemic pH over a 14 day period to elucidate the effects of acidosis on the skeletal system. Blood gas analyses measured an increase in blood calcium and sodium levels indicating a skeletal response to 14 days of acidosis. MA also significantly decreased femur ultimate strength, likely due to modifications in bone morphology as determined from decreased microcomputed tomography values of centroid distance and area moment of inertia. These structural changes may be caused by aberrant remodeling based on histological data evidencing altered OCL activity in acidosis. Additionally, we found that acidosis significantly decreased bone CO₃ content in a site-specific manner similar to the bone phenotype observed in human MA. We determined that MA decreased bone strength thus increasing fracture risk, which is likely caused by alterations in bone shape and compounded by changes in bone composition. Additionally, we suggest the temporal regulation of cell-mediated remodeling in MA is more complex than current literature suggests. We conclude that our model reliably induces MA and has deleterious effects on skeletal form and function, presenting similarly to the MA bone phenotype in humans.

PTH1-34 inhibited TNF-α expression and antagonized TNF-α-induced MMP13 expression in MIO mice

This study aims to investigate the effects and mechanisms of parathyroid hormone [1-34] (PTH1-34) on TNF-α-stimulated mice chondrocytes, as well as cartilage from a meniscus injury induced osteoarthritis (MIO) mice model. The C57BL/6J mice received medial meniscectomy, and then administrated with PTH1-34. The results showed that PTH1-34 administration decreased secondary allodynia and the pain-related transcripts. The IHC, ELISA, Micro-CT imaging and histopathology analysis revealed the significantly improved subchondral plate thickness and bone porosity, the reduced pro-inflammatory cytokines in serum and joint fluid. In vitro, mice chondrocyte was treated with TNF-α or co-cultured with synovial cells. The results showed that TNF-α markedly upregulated the MMP13 expression, and the ERK1/2, NF-κB or PI3K signaling pathway inhibitors could reverse the induction effect of TNF-α on expression of MMP13 in chondrocytes. PTH1-34 alone has no effect on the expression of MMP13 and NF-κB signaling pathways, but the PTH1-34 could reverse the induction effect of TNF-α on MMP13 expression and NF-κB signaling pathway activation in chondrocytes. In addition, PTH1-34 administration inhibited the expression of TNF-α and MMP13, and chondrocyte viability, while the PKA repressor reversed the effect of PTH1-34 in chondrocytes co-cultured with synovial cells. In conclusion, PTH1-34 has an obvious analgesic and anti-inflammatory effect, inhibits the matrix synthesis and alleviates the progression of osteoarthritis. In vitro, PTH1-34 inhibited TNF-α expression and antagonized TNF-α-induced MMP13 expression via the PKA pathway and the NF-κB signaling pathways, respectively.

Inactivation of parathyroid hormone: perspectives of drug discovery to combating hyperparathyroidism

Hormonal coordination is tightly regulated within the human body and thus regulates human physiology. The parathyroid hormone (PTH), a member of the endocrine system, regulates the calcium and phosphate level within the human body. Under non-physiological conditions, PTH levels get upregulated (hyperparathyroidism) or downregulated (hypoparathyroidism) due to external or internal factors. In the case of hyperparathyroidism, elevated PTH stimulates cellular receptors present in the bones, kidneys, and intestines to increase the blood calcium level, leading to calcium deposition. This eventually causes various symptoms including kidney stones. Currently, there is no known medication that directly targets PTH in order to suppress its function. Therefore, it is of great interest to find novel small molecules or any other means that can modulate PTH function. The molecular signaling of PTH starts by binding of its N-terminus to the G-protein coupled PTH1/2 receptor. Therefore, any intervention that affects the N-terminus of PTH could be a lead candidate for treating hyperparathyroidism. As a proof-of-concept, there are various possibilities to inhibit molecular PTH function by (i) a small molecule, (ii) N-terminal PTH phosphorylation, (iii) fibril formation and (iv) residue-specific mutations. These modifications put PTH into an inactive state, which will be discussed in detail in this review article. We anticipate that exploring small molecules or other means that affect the N-terminus of PTH could be lead candidates in combating hyperparathyroidism.

A single day of TGF-β1 exposure activates chondrogenic and hypertrophic differentiation pathways in bone marrow-derived stromal cells

Virtually all bone marrow-derived stromal cell (BMSC) chondrogenic induction cultures include greater than 2 weeks exposure to transforming growth factor-β (TGF-β), but fail to generate cartilage-like tissue suitable for joint repair. Herein we used a micro-pellet model (5 × 103 BMSC each) to determine the duration of TGF-β1 exposure required to initiate differentiation machinery, and to characterize the role of intrinsic programming. We found that a single day of TGF-β1 exposure was sufficient to trigger BMSC chondrogenic differentiation and tissue formation, similar to 21 days of TGF-β1 exposure. Despite cessation of TGF-β1 exposure following 24 hours, intrinsic programming mediated further chondrogenic and hypertrophic BMSC differentiation. These important behaviors are obfuscated by diffusion gradients and heterogeneity in commonly used macro-pellet models (2 × 105 BMSC each). Use of more homogenous micro-pellet models will enable identification of the critical differentiation cues required, likely in the first 24-hours, to generate high quality cartilage-like tissue from BMSC.

Activin type IIA decoy receptor and intermittent parathyroid hormone in combination overturns the bone loss in disuse-osteopenic mice

Damage of the lower motor neuron cell bodies or their axons results in reduced or abolished voluntary movement accompanied by a substantial loss of bone and muscle mass. Intermittent parathyroid hormone 1-34 (PTH) (teriparatide) is one of the most potent bone-anabolic treatment regimens. ActRIIA-mFc is an activin type IIA decoy receptor that increases bone mass mediated by inhibition of the activin receptor signaling pathway. We investigated whether PTH or ActRIIA-mFc alone or in combination could prevent loss of bone and muscle mass induced by injecting botulinum toxin A (BTX) into the right hind limb in mice. Seventy-two 16-week-old female C57BL/6 mice were allocated to the following groups: Baseline, Control, BTX, BTX + ActRIIA-mFc (10 mg/kg), BTX + PTH (100 μg/kg), and BTX + ActRIIA-mFc + PTH. The mice were sacrificed after three weeks of disuse and treatment. In contrast to monotherapy with PTH, ActRIIA-mFc alone or in combination with PTH was able partly or completely to prevent disuse-induced loss of whole femoral bone mass, trabecular thickness, and bone strength. Moreover, an additive effect of ActRIIA-mFc and PTH on areal bone mineral density and trabecular bone volume was found. In summary, ActRIIA-mFc and PTH in combination were more effective in preventing disuse-induced bone loss and deterioration of trabecular micro-architecture than either treatment alone.

Emerging insights into the comparative effectiveness of anabolic therapies for osteoporosis

Over the past three decades, the mainstay of treatment for osteoporosis has been antiresorptive agents (such as bisphosphonates), which have been effective with continued administration in lowering fracture risk. However, the clinical landscape has changed as adherence to these medications has declined due to perceived adverse effects. As a result, decreases in hip fracture rates that followed the introduction of bisphosphonates have now levelled off, which is coincident with a decline in the use of the antiresorptive agents. In the past two decades, two types of anabolic agents (including three new drugs), which represent a novel approach to improving bone quality by increasing bone formation, have been approved. These therapies are expected to lead to a new clinical paradigm in which anabolic agents will be used either alone or in combination with antiresorptive agents to build new bone and reduce fracture risk. This Review examines the mechanisms of action for these anabolic agents by detailing their receptor-activating properties for key cell types in the bone and marrow niches. Using these advances in bone biology as context, the comparative effectiveness of these anabolic agents is discussed in relation to other therapeutic options for osteoporosis to better guide their clinical application in the future.

Molecular Signaling Pathways and Essential Metabolic Elements in Bone Remodeling: An Implication of Therapeutic Targets for Bone Diseases

Bone is one of the dynamic tissues in the human body that undergoes continuous remodelling through subsequent actions of bone cells, osteoclasts, and osteoblasts. Several signal transduction pathways are involved in the transition of mesenchymal stem cells into osteoblasts. These primarily include Runx2, ATF4, Wnt signaling and sympathetic signalling. The differentiation of osteoclasts is controlled by M-CSF, RANKL, and costimulatory signalling. It is well known that bone remodelling is regulated through receptor activator of nuclear factor-kappa B ligand followed by binding to RANK, which eventually induces the differentiation of osteoclasts. The resorbing osteoclasts secrete TRAP, cathepsin K, MMP-9 and gelatinase to digest the proteinaceous matrix of type I collagen and form a saucer-shaped lacuna along with resorption tunnels in the trabecular bone. Osteoblasts secrete a soluble decoy receptor, osteoprotegerin that prevents the binding of RANK/RANKL and thus moderating osteoclastogenesis. Moreover, bone homeostasis is also regulated by several growth factors like, cytokines, calciotropic hormones, parathyroid hormone and sex steroids. The current review presents a correlation of the probable molecular targets underlying the regulation of bone mass and the role of essential metabolic elements in bone remodelling. Targeting these signaling pathways may help to design newer therapies for treating bone diseases.

ZnO-mesoporous glass scaffolds loaded with osteostatin and mesenchymal cells improve bone healing in a rabbit bone defect

The use of 3D scaffolds based on mesoporous bioactive glasses (MBG) enhanced with therapeutic ions, biomolecules and cells is emerging as a strategy to improve bone healing. In this paper, the osteogenic capability of ZnO-enriched MBG scaffolds loaded or not with osteostatin (OST) and human mesenchymal stem cells (MSC) was evaluated after implantation in New Zealand rabbits. Cylindrical meso-macroporous scaffolds with composition (mol %) 82.2SiO₂-10.3CaO-3.3P₂O₅-4.2ZnO (4ZN) were obtained by rapid prototyping and then, coated with gelatin for easy handling and potentiating the release of inorganic ions and OST. Bone defects (7.5 mm diameter, 12 mm depth) were drilled in the distal femoral epiphysis and filled with 4ZN, 4ZN + MSC, 4ZN + OST or 4ZN + MSC + OST materials to evaluate and compare their osteogenic features. Rabbits were sacrificed at 3 months extracting the distal third of bone specimens for necropsy, histological, and microtomography (µCT) evaluations. Systems investigated exhibited bone regeneration capability. Thus, trabecular bone volume density (BV/TV) values obtained from µCT showed that the good bone healing capability of 4ZN was significantly improved by the scaffolds coated with OST and MSC. Our findings in vivo suggest the interest of these MBG complete systems to improve bone repair in the clinical practice.

Growth hormone effects on healing efficacy, bone resorption and renal morphology of rats: histological and histometric study in rat calvaria

Previous reports demonstrated the utility of systemic application of growth hormone (GH) in the treatment of bone defects. Very few studies correlated bone repair efficacy with hepatic and renal side effects promoted by locally-delivered GH. The objectives of this study were to assess the bone repair properties along with hepatic and renal adverse effects promoted by local application of GH in a rat model. Thirty-two rats were randomly divided (4 groups; n = 8/group), as follows: (i) AB (autogenous bone + local application of saline solution [SS]), (ii) AB+ (autogenous bone + SS local application + SS irrigation), (iii) AB/GH+ (autogenous bone + SS local application + GH irrigation) and (iv) AB/GHL+ (autogenous bone + GH local application + GH irrigation). Critical-sized defects (diameter = 5.0 mm) were surgically created by a single operator in the calvaria of rats. Defects were filled with ground autogenous bone. Defects pertaining to AB+ and AB/GH+ received a mixture of autogenous bone and a SS-saturated (0.02 mL) collagen sponge covered with bovine cortical membrane. Defects in group AB/GHL+, were filled with the same biomaterials saturated with GH (0.02 mL). SS (0.1 mL) or GH (0.1 mL, equivalent to 0.4 IU) were applied locally on alternate days (8 weeks) in animals in groups AB, AB+ and AB/GH+ or AB/GHL+, respectively. Bone repair properties was determined in hematoxylin/eosin-stained slices using traditional histologic and histomorphometric techniques along with optical microscopy and digital image analysis. Statistical differences among groups was determined using Kruskal-Wallis and Tukey post hoc tests (α = 0.05). Histology results indicated that AB and AB+ displayed greater presence of autogenous bone as compared to AB/GH+ and AB/GHL+. Histomorphometric results indicated significantly higher osteoid matrix formation in AB and AB+ when compared to AB/GHL+ (p = 0.009). Kidneys and livers were found to have their glomeruli preserved in AB and AB+. Strong glomeruli necrosis and large areas of protein deposition were found in AB/GH+. Abnormal small-sized glomeruli were found in AB/GHL+. The utilization of autogenous bone graft associated with local application and irrigation with GH was shown to not improve the bone repair in calvarial critical-sized defects in a rat model.

Brown tumor complicating end-stage kidney disease

Longstanding, severe hyperparathyroidism (HPT) can lead to the formation of "brown tumors". A brown tumor is a radiolucent bone lesion that is locally destructive; it is not a neoplasm, but rather a stromal mass consisting of fibrous tissue, poorly mineralized woven bone, and supporting vasculature. These tumors are a rare complication of advanced primary or secondary HPT. We present a young female with chronic kidney disease (CKD) on hemodialysis with uncontrolled secondary HPT (SHPT). The patient presented with progressive lower extremity weakness and back pain. CT imaging showed multiple lytic bone lesions involving several ribs and the spine. Subsequent MRI imaging of the thoracic and lumbar spine confirmed expansile bone lesions consistent with brown tumors. One mass protruded into the spinal canal causing severe stenosis at T3 with underlying cord edema. The other lesion at T12 caused only moderate spinal canal stenosis. Our patient underwent urgent neurosurgical resection of the tumor at T3 followed by subtotal parathyroidectomy (PTX).

Energy metabolism: A newly emerging target of BMP signaling in bone homeostasis

Energy metabolism is the process of generating energy (i.e. ATP) from nutrients. This process is indispensable for cell homeostasis maintenance and responses to varying conditions. Cells require energy for growth and maintenance and have evolved to have multiple pathways to produce energy. Both genetic and functional studies have demonstrated that energy metabolism, such as glucose, fatty acid, and amino acid metabolism, plays important roles in the formation and function of bone cells including osteoblasts, osteocytes, and osteoclasts. Dysregulation of energy metabolism in bone cells consequently disturbs the balance between bone formation and bone resorption. Metabolic diseases have also been reported to affect bone homeostasis. Bone morphogenic protein (BMP) signaling plays critical roles in regulating the formation and function of bone cells, thus affecting bone development and homeostasis. Mutations of BMP signaling-related genes in mice have been reported to show abnormalities in energy metabolism in many tissues, including bone. In addition, BMP signaling correlates with critical signaling pathways such as mTOR, HIF, Wnt, and self-degradative process autophagy to coordinate energy metabolism and bone homeostasis. These findings will provide a newly emerging target of BMP signaling and potential therapeutic strategies and the improved management of bone diseases. This review summarizes the recent advances in our understanding of (1) energy metabolism in regulating the formation and function of bone cells, (2) function of BMP signaling in whole body energy metabolism, and (3) mechanistic interaction of BMP signaling with other signaling pathways and biological processes critical for energy metabolism and bone homeostasis.

Parathyroid hormone

Parathyroid hormone is an essential regulator of extracellular calcium and phosphate. PTH enhances calcium reabsorption while inhibiting phosphate reabsorption in the kidneys, increases the synthesis of 1,25-dihydroxyvitamin D, which then increases gastrointestinal absorption of calcium, and increases bone resorption to increase calcium and phosphate. Parathyroid disease can be an isolated endocrine disorder or part of a complex syndrome. Genetic mutations can account for diseases of parathyroid gland formulation, dysregulation of parathyroid hormone synthesis or secretion, and destruction of the parathyroid glands. Over the years, a number of different options are available for the treatment of different types of parathyroid disease. Therapeutic options include surgical removal of hypersecreting parathyroid tissue, administration of parathyroid hormone, vitamin D, activated vitamin D, calcium, phosphate binders, calcium-sensing receptor, and vitamin D receptor activators to name a few. The accurate assessment of parathyroid hormone also provides essential biochemical information to properly diagnose parathyroid disease. Currently available immunoassays may overestimate or underestimate bioactive parathyroid hormone because of interferences from truncated parathyroid hormone fragments, phosphorylation of parathyroid hormone, and oxidation of amino acids of parathyroid hormone.

MALDI-TOF-MS-based high throughput genotyping of mutations associated with body measurement traits in cattle

Exploration of genes in relation to body measurement traits through large-scaled mutation identification is highly conductive for the genomics-assisted breeding of superior productivity cattle. In this investigation, 31 objective mutations were genotyped synchronously in 384 yellow cattle of 8 breeds through the application of optimized MALDI-TOF-MS and multiplex PCR techniques. High genotyping rate was obtained as well as greatly decreased cost which was below one thirtieth of the routine analysis. Results from genotyping revealed 23 mutations as valid mutations in the studied cattle population with gene heterozygosity and effective allele number varying from 0.0052 to 0.4998 and 1.0052 to 1.9991, respectively. Among the 23 effective mutations, 12 was classified as moderate polymorphism (0.25 < PIC < 0.5) while the other 11 belonged to low polymorphism (PIC < 0.25), 7 mutations did not obey the HW equilibrium (p < 0.05) and linkage mainly appeared between mutations of UCP2 and PTHR1 genes. Furthermore, 8 body measurement traits in the 384 cattle were recorded to validate their association with tag mutations, and significant correlations were found in 12 mutations of 9 genes including PTHR1, CDK6, IHH, HHIP, GHRL, COL1A1, INS, GDF5 and UCP2, of which, PTHR1 was proved to be the most potential contributor to bone modeling in cattle. Results highlight the potential application value of 12 novel mutations in enhancing cattle production traits as well as the high genotyping rate achieved by MALDI-TOF-MS coupled with multiplex PCR technique.

Expression of PTHrP and RANKL in acquired middle ear cholesteatoma epithelium

Background: Regarded as the most important clinical characteristic of middle ear cholesteatoma, the exact mechanism of bone resorption in cholesteatoma still remains unknown.Objectives: To investigate protein expression of PTHrP and RANKL in acquired middle ear cholesteatoma epithelium and analyze their functional roles in the etiopathogenesis of bone resorption in middle ear cholesteatoma.Material and methods: A total of 22 patients who underwent surgical treatment for middle ear cholesteatoma were recruited in the study. Protein expression of PTHrP and RANKL in middle ear cholesteatoma and normal postauricular skin was investigated by immunohistochemical staining. Correlations between bone resorption degree and expression of PTHrP and RANKL were also analyzed.Results: Protein expression of PTHrP and RANKL in cholesteatoma epithelium significantly increased when compared with normal postauricular skin epithelium. In cholesteatoma epithelium, a significantly positive association was observed between PTHrP and RANKL expression. Meanwhile, obviously positive correlations between protein expression of PTHrP and RANKL and bone resorption degree were discovered.Conclusions and significance: The increased protein expression of PTHrP and RANKL in cholesteatoma epithelium, and their associations with the degree of bone resorption, revealing that PTHrP might promote bone resorption process in middle ear cholesteatoma through RANKL signaling pathway.

Effect of parathyroid hormone-related protein on odontogenic differentiation in human dental pulp cells

BACKGROUND

Parathyroid hormone-related protein (PTHrP) plays an important role in many physiological processes, including bone regeneration. The function of PTHrP is similar to PTH. It promotes osteogenic differentiation in MC3T3-E1 cells. The aim of this study was to investigate whether PTHrP might have odontogenic differentiation ability in human dental pulp cells (hDPCs).

METHODS

The viability of hDPCs after stimulation with PTHrP was measured. Real-time polymerase chain reaction and Western blot analysis were performed to evaluate the expression levels of odontogenic markers and activation of protein kinase B (PKB/AKT), extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK). To evaluate mineralized nodule formation, alkaline phosphatase (ALP) staining and alizarin red S staining were performed.

RESULTS

PTHrP promoted odontogenic differentiation as evidenced by the formation of mineralized nodules, the induction of ALP activity, and the upregulation of odontogenic markers (dentin sialophosphoprotein and dentin matrix protein-1). The phosphorylation of AKT, ERK, JNK, and p38 was increased by PTHrP. However, an AKT inhibitor (LY294002), an ERK inhibitor (U0126), a JNK inhibitor (SP600125), and a p38 inhibitor (SB203580) inhibited the increase of mineralization induced by PTHrP.

CONCLUSION

The present study revealed that PTHrP could promote odontogenic differentiation and mineralization through activating the AKT, ERK, JNK, and p38 signaling pathways. These results provide novel insights into the odontogenic action of PTHrP.

Serotonin regulates maternal calcium homeostasis during the perinatal period of sheep

The goal of this experiment was to demonstrate the ability of an infusion of serotonin (5-HT; 5-hydroxytryptamine) precursors to increase 5-HT production during the transition from pregnancy to lactation and its effects on gene expression related to calcium (Ca) transporters in the mammary gland and bone resorption markers in the femur. Thirty pregnant Bamei mutton sheep were randomly assigned to 3 experimental groups. All groups received a daily intravenous infusion of saline (control group; n = 10), saline containing 0.178 mg of L-tryptophan/kg body weight (BW) (TRP group, n = 10) or 0.178 mg of 5-hydroxytryptophan/kg BW (5-HTP group, n = 10), beginning on day 7 of prepartum and continuing until delivery. Serum (pre- and postpartum), milk (postpartum), and femur and mammary gland tissue (day 9) were collected. Sheep infused with 5-HTP had a larger total serum Ca concentration on days 3, 6, 15, and 30 of lactation and total milk Ca concentration on days 3, 6, 12, and 15 of lactation compared with that of the control group. Sheep infused with 5-HTP and TRP increased blood and milk concentrations of 5-HT on days 3, 6, 9, and 30 of lactation and parathyroid hormone-related protein (PTHrP) on day 3 of prepartum and on days 3, 6, and 15 of lactation (P < 0.05). In addition, compared to that of the control group, the TRP or 5-HTP infusion upregulated PTHrP, a sodium/calcium exchanger, plasma membrane Ca2+ ATPase 2, secretory pathway Ca2+ ATPase 1, and calcium sensing receptor mRNA expression in mammary gland and receptor-activated nuclear factor kappa-B ligand mRNA expression in the femur, but had no effect on receptor-activated nuclear factor kappa-B and osteoprotegerin mRNA expression in the femur (P < 0.05). This suggests that 5-HT and PTHrP may be involved in regulating maternal Ca homeostasis during the transition from pregnancy to lactation in the sheep.

A DRAMATIC RESPONSE TO DENOSUMAB: PROTRACTED HYPOCALCEMIA RELATED TO HUMAN T-CELL LYMPHOTROPIC VIRUS TYPE 1-ASSOCIATED ADULT T-CELL LEUKEMIA/LYMPHOMA

Objective

Adult T-cell leukemia/lymphoma (ATL) is known for its aggressive behavior, frequently presenting with hypercalcemia. ATL tumor cells uniquely secrete parathyroid hormone-related protein, viral peptides, and inflammatory cytokines, inducing a state of high bone turnover and activation of the receptor activator of nuclear factor kappa-B signaling pathway resulting in hypercalcemia.

Methods

A 54-year-old woman diagnosed with ATL presented with severe hypercalcemia refractory to bisphosphonate therapy. Treatment with denosumab was followed by protracted hypocalcemia and hypophosphatemia lasting approximately 5 months.

Results

Hypercalcemia due to acute ATL was responsive in this case to denosumab therapy.

Conclusion

Clinicians should be aware of the possibility of protracted hypocalcemia in patients with ATL exposed to denosumab therapy.

The Effects of Continual Intermittent Parathyroid Hormone Treatment on Human Periodontal Ligament Fibroblasts in an In Vitro Wound Repopulation Model

INTRODUCTION

Periodontal ligament fibroblasts (PDLFs) play a vital role in periodontal regeneration. Parathyroid hormone (PTH) is important in catabolic regulation on osteoclasts; it also has anabolic effects on hard tissue formation. Using an in vitro wound repopulation model, this study investigated the effect of continual intermittent administration of PTH on PDLFs wound repopulation. Methods and Materials: PDLFs were grown in 12-well plates and divided into 0 (control), 5, 10, 20, 40, and 80 nM of PTH treatments. A 3-mm wound was created on confluent and synchronized cells. Six PTH treatments were initiated using serum-free medium with supplements. Cell repopulation was measured at four time points: 5, 10, 15, and 20 days.

RESULTS

A 5% increase wound repopulation showed an enhancement on day 10 for all treatment groups as compared to control groups. On days 15 and 20, treatment groups showed a decrease in proliferation and migration compared to controls with significant decreases at concentrations of 40 and 80 nM.

CONCLUSION

Continual intermittent treatment with PTH has the potential to enhance proliferation and migration of PDLFs for wound repopulation at early time points. A dose-dependent correlation was seen with a positive trend on day 10 while a significant decrease on day 20.

Both JNK1 and JNK2 Are Indispensable for Sensitized Extracellular Matrix Mineralization in IKKβ-Deficient Osteoblasts

Extracellular matrix mineralization is critical for osteogenesis, and its dysregulation could result in osteoporosis and vascular calcification. IKK/NF-κB activation inhibits differentiation of osteoblasts, and reduces extracellular matrix mineralization, however the underlying mechanisms are poorly understood. In this study, we used CRISPR/Cas9 system to permanently inactivate IKKβ in preosteoblast cells and confirmed that such cells displayed dramatic increase in extracellular matrix mineralization associated with JNK phosphorylation. Such observation was also found in our study using IKKβ-deficient primary murine osteoblasts. Interestingly, we found that in Ikbkb^-/-Mapk8^-/- or Ikbkb^-/-Mapk9^-/- double knockout cells, the enhanced mineralization caused by IKKβ deficiency was completely abolished, and deletion of either Mapk8 or Mapk9 was sufficient to dampen c-Jun phosphorylation. In further experiments, we discovered that absence of JNK1 or JNK2 on IKKβ-deficient background resulted in highly conserved transcriptomic alteration in response to osteogenic induction. Therefore, identification of the indispensable roles of JNK1 and JNK2 in activating c-Jun and promoting osteoblast differentiation on IKKβ-deficient background provided novel insights into restoring homeostasis in extracellular matrix mineralization.

The Efficacy of PTH and Abaloparatide to Counteract Immobilization-Induced Osteopenia Is in General Similar

Immobilization results in a substantial bone loss and increased fracture risk. Powerful bone anabolic therapies are necessary to counteract the bone loss and reduce fracture risk during periods with immobilization. Intermittent parathyroid hormone 1-34 (PTH) (teriparatide) and PTH related peptide analog abaloparatide (ABL) are potent bone anabolic therapies acting through the same receptor, but induce different durations of signaling response. We investigated the efficacy of PTH or ABL in preventing immobilization-induced bone loss in rats in a direct mole-to-mole comparison. Immobilization was achieved by injecting botulinum toxin type A (BTX) into the right hindlimb musculature. Sixty 14-week-old female Wistar rats were allocated to the following groups: Baseline, Control, BTX, BTX + PTH (80 μg/kg/day), and BTX + ABL (77 μg/kg/day). Immobilization resulted in a substantial and significant reduction in bone mineral density (aBMD), metaphyseal and epiphyseal trabecular bone volume fraction (BV/TV) and trabecular thickness (Tb.Th), metaphyseal trabecular number (Tb.N), and femoral neck bone strength. Both PTH and ABL prevented the immobilization-induced decrease in aBMD, metaphyseal and epiphyseal Tb.Th, and metaphyseal Tb.N. In addition, PTH rescued the reduction in metaphyseal BV/TV and femoral neck strength, while ABL did not. However, the effect of PTH and ABL did not differ significantly for serum calcium, aBMD, metaphyseal, and epiphyseal BV/TV, Tb.Th, or Tb.N. In conclusion, in a mole-to-mole comparison the efficacy of PTH and ABL is similar in counteracting immobilization-induced reduction in bone mineral density, deterioration in trabecular microarchitecture, and decrease in bone strength.

Cyclic adenosine monophosphate-dependent activation of transient receptor potential vanilloid 4 (TRPV4) channels in osteoblast-like MG-63 cells

Parathyroid hormone (PTH) directly interacts with bone remodeling osteoblasts and osteocytes expressing the G-protein coupled receptor PTH receptor 1 (PTH1R), and its osteoanabolic effects mostly involve the cAMP/PKA signaling cascade. Considering that PTH-dependent calcium entry in rat enterocytes is reproduced by the adenylate cyclase agonist forskolin or by cAMP analogues, possible involvement of calcium as a second messenger in PTH-dependent cAMP signaling was investigated in MG-63 cells. First, Ca²⁺ influx was confirmed in Fluo3-loaded MG-63 cells treated with a cell-permeable cAMP analog. Second, PTH (1-34) and forskolin promoted calcium influxes that were completely abrogated by the PKA inhibitor H-89. Ca²⁺ entry was not reproduced when PTH (1-34) was combined with the PKC-activating competitor PTH (3-34). Vanilloid transient potential (TRPV) channel inhibitor Ruthenium Red, but not a voltage-dependent calcium channel (VDCC) inhibitor nifedipine, efficiently stunted Ca²⁺ entry, and comparable abrogation was reproduced in cells treated with TRPV4-selective inhibitor RN-1734 or transfected with TRPV4-specific siRNA. Interestingly, PTH-driven Ca²⁺ through TRPV4 significantly inhibited MG63 cell migration through a mechanism requiring extracellular Ca²⁺. In contrast, the inhibitory effects of forskolin on migration were refractory to TRPV4 silencing or to RN-1734. Altogether, our results indicate that single treatment with PTH (1-34) promotes extracellular calcium entry through TRPV4 channels in MG-63 cells through a cAMP/PKA-dependent mechanism, and that this influx affects cell migration.