Parathyroid hormone and parathyroid hormone-related peptide, and their receptors

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.

Revisiting the evolution of Family B1 GPCRs and ligands: Insights from mollusca

Family B1 G protein-coupled receptors (GPCRs) are one of the most well studied neuropeptide receptor families since they play a central role in many biological processes including endocrine, gastrointestinal, cardiovascular and reproduction in animals. The genes for these receptors emerged from a common ancestral gene in bilaterian genomes and evolved via gene/genome duplications and deletions in vertebrate and invertebrate genomes. Their existence and function have mostly been characterized in vertebrates and few studies exist in invertebrate species. Recently, an increased interest in molluscs, means a series of genomes have become available, and since they are less modified than insect and nematode genomes, they are ideal to explore the origin and evolution of neuropeptide gene families. This review provides an overview of Family B1 GPCRs and their peptide ligands and incorporates new data obtained from Mollusca genomes and taking a comparative approach challenges existing models on their origin and evolution.

Cutaneous Calcified Mass of Foot in Pseudohypoparathyoidism: Case Report

Soft tissue calcifications frequently appear on imaging studies, representing a prevalent but non-specific discovery, varying from a local reaction without clear cause to suggesting an underlying systemic condition. Because calcifications like these can arise from various causes, an accurate differential diagnosis is crucial. Differential diagnosis entails a methodical assessment of the patient, encompassing clinical presentation, medical history, radiological and pathological findings, and other pertinent factors. Through scrutiny of the patient's medical and trauma history, we can refine potential causes of calcification to vascular, metabolic, autoimmune, neoplastic, or traumatic origins. Furthermore, routine laboratory assessments, including serum levels of calcium, phosphorus, ionized calcium, vitamin D metabolites, and parathyroid hormone (PTH), aid in identifying metabolic etiologies. We describe a rare occurrence of osteoma cutis in a 15-year-old female patient with a history of pseudohypoparathyroidism (PHP) and Albright's hereditary osteodystrophy (AHO). The patient presented with a painful mass on the lateral side of her left foot. The diagnosis was based on medical history, laboratory tests, and imaging, leading to an excisional biopsy and complete pain relief post-surgery. Understanding such rare occurrences and related conditions is crucial for accurate diagnosis and management.

A Case of Fibroblast Growth Factor Receptor Fusion-Positive Intrahepatic Cholangiocarcinoma With Humoral Hypercalcemia of Malignancy

Humoral hypercalcemia of malignancy (HHM) comprises the majority of cases with malignancy-related hypercalcemia and is mediated by elevated parathyroid hormone-related peptide (PTHrP). HHM is rare in cholangiocarcinoma and has been reported only in a few case reports and series. We report a case of a 63-year-old male with a history of locally advanced fibroblast growth factor receptor (FGFR) fusion-positive intrahepatic cholangiocarcinoma who presented with recurrent HHM. The first episode of his hypercalcemia occurred 15 months after the initial diagnosis of cholangiocarcinoma and coincided with disease progression. The hypercalcemia was treated with zoledronic acid, and an FGFR inhibitor was started for the treatment of his malignancy. The second hypercalcemia episode occurred nine months later, with evidence of further disease progression. HHM is associated with poor clinical outcomes; a high index of suspicion should be present to identify and treat this complication in cases of cholangiocarcinoma promptly. With an increased understanding of the molecular alterations underlying cholangiocarcinoma, it will also be necessary to further evaluate its co-occurrence with HHM as the specific molecular alterations in this setting could lay the groundwork for targeted therapies and improve risk stratification for these patients.

Squamous cell carcinoma of mandibular gingiva producing both parathyroid hormone-related protein and granulocyte colony-stimulating factor: a case report

We describe a case of mandibular gingival carcinoma with hypercalcaemia and leukocytosis caused by tumour-derived parathyroid hormone-related protein (PTHrP) and granulocyte colony-stimulating factor (G-CSF). A 54-year-old man presented to our Department of Oral and Maxillofacial Surgery with a chief complaint of a left-sided mandibular gingival ulcer. A 42 mm × 20 mm sized ulcer was found on the left lower molar gingiva. Squamous cell carcinoma was pathologically diagnosed. The patient underwent a hemimandibulectomy, left-sided radical neck dissection, plate reconstruction, pectoralis major musculocutaneous flap reconstruction, and tracheostomy under general anaesthesia. Pathologically, two metastatic lymph nodes were identified. Residual tumour was suspected at the resection margins. Eight weeks after surgery, the patient started postoperative concurrent chemoradiotherapy (CCRT). Two weeks after CCRT, the patient developed hypercalcaemia. Serum levels of PTHrP and G-CSF increased in parallel with the progression of hypercalcaemia and leukocytosis. Immunohistochemical analysis of the surgical specimen showed positivity for G-CSF. Based on these clinical and pathological findings, the patient was diagnosed with hypercalcaemia and leukocytosis associated with malignancy and was treated with denosumab. Irradiation was terminated at 50 Gy because CT showed rapid disease progression. Chemotherapy was initiated, however, four weeks after the start of chemotherapy, a CT scan showed increased metastases and pleural dissemination. Therefore, chemotherapy was discontinued. One week after the chemotherapy was discontinued, the patient died of respiratory failure.

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.

Parathyroid Hormone-Related Peptide-Producing Gallbladder Cancer Presenting With Humoral Hypercalcemia of Malignancy: A Case Report

Humoral hypercalcemia of malignancy (HHM) is often reported in cancers derived from the squamous epithelium; however, there are very few reports of HHM in patients with gallbladder cancer. We report a case of a parathyroid hormone-related protein (PTHrP)-producing gallbladder cancer presenting with HHM. A 43-year-old woman presented with appetite loss, nausea, and brown-colored urine. Blood tests revealed that she had hypercalcemia, high serum bilirubin, and high serum parathyroid hormone. Contrast-enhanced computed tomography revealed a gallbladder tumor, liver metastasis, and bile duct obstruction caused by the gallbladder tumor in the hilar region. No bone metastasis was observed. Endoscopic retrograde cholangiopancreatography revealed pancreaticobiliary maljunction. Metal biliary stents were placed, and a transpapillary biopsy of the gallbladder tumor revealed a pathological diagnosis of adenocarcinoma. The patient was diagnosed with HHM due to gallbladder cancer with liver metastasis. Although her hypercalcemia and jaundice improved, her appetite loss and nausea did not improve. Subsequently, the patient developed disseminated intravascular coagulation, and her general condition gradually deteriorated. Due to her poor general condition, chemotherapy could not be administered. The patient died six weeks after visiting our hospital. Although rare, some gallbladder cancers cause HHM due to PTHrP production.

Adenosquamous carcinoma of the gallbladder simultaneously producing granulocyte-colony-stimulating factor and parathyroid hormone-related protein

We report a rare case of adenosquamous carcinoma of the gallbladder which simultaneously produces granulocyte-colony-stimulating factor (G-CSF) and parathyroid hormone-related protein (PTHrP), confirmed serologically and histologically. A 71-year-old man was examined for a gallbladder tumor with multiple lymph nodes and liver metastases. Histopathological evaluation by endoscopic ultrasound fine-needle aspiration revealed adenosquamous carcinoma of the gallbladder. Laboratory data showed markedly elevated white blood cell (WBC) count of 34,700 µL and corrected serum calcium level of 14.9 mg/dL. Serum G-CSF (191 pg/mL) and PTHrP (23.1 pmol/L) levels were high. Zoledronic acid and calcitonin were administered to treat hypercalcemia, which normalized serum calcium levels. Gemcitabine-cisplatin chemotherapy was started for cStage IVB gallbladder cancer. After chemotherapy initiation, WBCs showed a rapid downward trend; however, the patient suddenly developed acute respiratory distress syndrome; thus, chemotherapy was discontinued. Subsequently, WBC count increased again, and the patient's overall condition deteriorated. The patient died on day 27. Immunohistochemistry using autopsy specimens demonstrated patchy staining for G-CSF in the squamous cell carcinoma portion and diffuse and weak positive staining for PTHrP in the squamous cell carcinoma and poorly differentiated adenocarcinoma portions of the tumor, suggesting simultaneous G-CSF and PTHrP production by the tumor. This is the first report of a patient with gallbladder cancer with serological and histological evidence for G-CSF and PTHrP production.

Coexistence of a Calcium-Sensing Receptor Mutation and Primary Hyperparathyroidism

Primary hyperparathyroidism (PHPT) and familial hypocalciuric hypercalcemia (FHH) are the main differential diagnoses in a patient presenting with parathyroid hormone (PTH)-mediated hypercalcemia. PHPT is most often caused by a single-gland parathyroid adenoma and FHH is the result of an inactivating mutation of the calcium-sensing receptor (CaSR) gene. In this paper, we present a unique case of the co-existence of an inactivating CaSR gene mutation and PHPT due to a single-gland parathyroid adenoma. The patient is a 67-year-old female with a history of recurrent nephrolithiasis who presented with hypercalcemia, elevated PTH level, and hypocalciuria. As a result of the patient's hypocalciuria, familial hypocalciuric hypercalcemia was suspected, and genetic testing was pursued. CaSR gene analysis revealed a heterogeneous inactivating mutation of the CaSR gene. Additionally, nuclear imaging with technetium sestamibi revealed a large focus of activity on the right side of the neck suspicious of a parathyroid adenoma. This was resected and confirmed to be a hypercellular parathyroid adenoma. Two years after her surgery, the patient continues to have normal calcium levels with no further episodes of nephrolithiasis. She is currently undergoing treatment for osteoporosis and is being periodically monitored for recurrence of hypercalcemia due to the presence of the inactivating CaSR gene mutation. This case highlights an exceedingly rare case of a patient with both an inactivating CaSR gene mutation and PHPT due to a single parathyroid adenoma, and it underscores the importance of further research to determine any potential relationship between the two.

Improve the Crosslinking Reactivity of Nitrile: Design of Nitrile-Functionalized Pyrazine and its Hydrogen Bond-Assisted Nucleophilic Enhancement Study

In this study, molecular engineering and biomimetic principles are utilized to prepare highly effective nitrile-functionalized pyrazine crosslinking units by exploiting pyrazine's unique nucleophilic strengthening mechanism and proton bonding ability. The curing behaviors of pyrazine-2,3-dicarbonitrile and phthalonitrile are investigated through model curing systems and molecular simulation. The results indicate that pyrazine-2,3-dicarbonitrile exhibits higher reactivity than phthalonitrile, promoted by amine. The cured products of pyrazine-2,3-dicarbonitrile predominantly comprise thermally stable azaisoindoline and azaphthalocyanine. This novel type of highly effective crosslinking unit, and the comprehended mechanism of action of pyrazine at the molecular level, significantly expand the application of pyrazine in materials science.

Isochromosome 12p Formation Regulates Vitamin D Metabolism in Testicular Cancer

Isochromosome 12p (iChr12p) is typical in almost all invasive testicular cancers. Increased copy number of genes on 12p is associated with the development of a clinically manifest tumor; however, the causative genes have not yet been identified. Chromosome 12 harbors many genes involved in Vitamin D metabolism. RNAseq analysis of Vitamin D receptor (VDR) genes from the TCGA cohort revealed that clustering of VDR expression signatures could differentiate between pure seminomas and non-seminomatous germ cell tumors (NSGCT). Using TCGA mRNA expression of anabolic (CYP2R1, CYP27A1 and CYP27B1) and catabolic (CYP24A1) Vitamin D enzymes, positive (PTHLH, IFNG, and TNF) and negative (FGF23) feedback regulators could also clearly distinguish between pure seminomas and NSGCT. We hypothesize that the regulation of Vitamin D metabolism might be disturbed through iChr12p formation, influencing testicular carcinogenesis via increased FGF23 and PTHLH expression. While FGF23 represses CYP27B1 and activates catabolism of active hormone, increased PTHLH secretion can lead to hypercalcemia via inactivation of VDR. In conclusion, testicular cancer is associated with extensive modifications in intratesticular Vitamin D homeostasis. Further research is needed to clarify whether Vitamin D deficiency causes the formation of iChr12p and whether Vitamin D deficiency via iChr12p genomic aberration is involved in testicular carcinogenesis.

Parathyroid Hormone (PTH)-Related Peptides Family: An Intriguing Role in the Central Nervous System

Parathyroid Hormone (PTH) plays a crucial role in the maintenance of calcium homeostasis directly acting on bone and kidneys and indirectly on the intestine. However, a large family of PTH-related peptides exists that exerts other physiological effects on different tissues and organs, such as the Central Nervous System (CNS). In humans, PTH-related peptides are Parathyroid Hormone (PTH), PTH-like hormones (PTHrP and PTHLH), and tuberoinfundibular peptide of 39 (TIP39 or PTH2). With different affinities, these ligands can bind parathyroid receptor type 1 (PTH1R) and type 2 (PTH2R), which are part of the type II G-protein-coupled-receptors (GPCRs) family. The PTH/PTHrP/PTH1R system has been found to be expressed in many areas of the brain (hippocampus, amygdala, hypothalamus, caudate nucleus, corpus callosum, subthalamic nucleus, thalamus, substantia nigra, cerebellum), and literature data suggest the system exercises a protective action against neuroinflammation and neurodegeneration, with positive effects on memory and hyperalgesia. TIP39 is a small peptide belonging to the PTH-related family with a high affinity for PTH2R in the CNS. The TIP39/PTH2R system has been proposed to mediate many regulatory and functional roles in the brain and to modulate auditory, nociceptive, and sexual maturation functions. This review aims to summarize the knowledge of PTH-related peptides distribution and functions in the CNS and to highlight the gaps that still need to be filled.

The Serotonergic System and Bone Metabolism During Pregnancy and Lactation and the Implications of SSRI Use on the Maternal-Offspring Dyad

Lactation is a physiological adaptation of the class Mammalia and is a product of over 200 million years of evolution. During lactation, the mammary gland orchestrates bone metabolism via serotonin signaling in order to provide sufficient calcium for the offspring in milk. The role of serotonin in bone remodeling was first discovered over two decades ago, and the interplay between serotonin, lactation, and bone metabolism has been explored in the years following. It is estimated that postpartum depression affects 10-15% of the population, and selective serotonin reuptake inhibitors (SSRI) are often used as the first-line treatment. Studies conducted in humans, nonhuman primates, sheep, and rodents have provided evidence that there are consequences on both parent and offspring when serotonin signaling is disrupted during the peripartal period; however, the long-term consequences of disruption of serotonin signaling via SSRIs during the peripartal period on the maternal and offspring skeleton are not fully known. This review will focus on the relationship between the mammary gland, serotonin, and bone remodeling during the peripartal period and the skeletal consequences of the dysregulation of the serotonergic system in both human and animal studies.

Single-cell RNA sequencing reveals the role of cell heterogeneity in the sex difference in primary hyperparathyroidism

OBJECTIVE

To explore the difference in parathyroid tissue-derived cells between male and female PHPT patients.

METHODS

Resected parathyroid tissues were collected from PHPT patients of both sexes. Single cells were isolated and sequenced for RNA expression profiles. The cell sequencing data were annotated by cell type, followed by population analysis, functional analysis, pathway analysis, cell communication analysis, differential gene expression analysis, and pseudotime trajectory analysis. The subcluster analyses were also performed in the parathyroid cells.

RESULTS

No substantial difference in the cell population, function, or communication is found between the two sexes. The interferon-a response, oxidative phosphorylation, and reactive oxygen species pathways are up-regulated in females than in male patients, mainly contributed by fibroblast cells, endothelial cells, parathyroid cells, and myeloid cells, which also have significantly more up-regulated pathways and cellular interactions than the other three cell types. The subcluster analysis of parathyroid cells identified five subpopulations: SPARCL1-OC and ISG15-OC are predominant in females, while more S100A13-PCC and PTHLH-OC are found in males. The cellular functions are also elevated in females compared with males. Cells from female patients show a higher expression level of parathyroid hormone (PTH) but a lower expression level of parathyroid hormone-like hormone (PTHLH). The cell pseudotime trajectory and pathway analyses show that the oxyphil cells may be more mature and functionally active than the chief cells in both sexes.

CONCLUSION

These findings suggest that the sex difference in PHPT may be caused by the differentially expressed genes and activated pathways in different cell types in the parathyroid tissue. The heterogeneity of parathyroid cell subpopulations, especially in oxyphil cells, may be associated with the sex differences in PHPT pathogenesis.

Interaction of Vitamin D with Peptide Hormones with Emphasis on Parathyroid Hormone, FGF23, and the Renin-Angiotensin-Aldosterone System

The seminal discoveries that parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23) are major endocrine regulators of vitamin D metabolism led to a significant improvement in our understanding of the pivotal roles of peptide hormones and small proteohormones in the crosstalk between different organs, regulating vitamin D metabolism. The interaction of vitamin D, FGF23 and PTH in the kidney is essential for maintaining mineral homeostasis. The proteohormone FGF23 is mainly secreted from osteoblasts and osteoclasts in the bone. FGF23 acts on proximal renal tubules to decrease production of the active form of vitamin D (1,25(OH)₂D) by downregulating transcription of 1α-hydroxylase (CYP27B1), and by activating transcription of the key enzyme responsible for vitamin D degradation, 24-hydroxylase (CYP24A1). Conversely, the peptide hormone PTH stimulates 1,25(OH)₂D renal production by upregulating the expression of 1α-hydroxylase and downregulating that of 24-hydroxylase. The circulating concentration of 1,25(OH)₂D is a positive regulator of FGF23 secretion in the bone, and a negative regulator of PTH secretion from the parathyroid gland, forming feedback loops between kidney and bone, and between kidney and parathyroid gland, respectively. In recent years, it has become clear that vitamin D signaling has important functions beyond mineral metabolism. Observation of seasonal variations in blood pressure and the subsequent identification of vitamin D receptor (VDR) and 1α-hydroxylase in non-renal tissues such as cardiomyocytes, endothelial and smooth muscle cells, suggested that vitamin D may play a role in maintaining cardiovascular health. Indeed, observational studies in humans have found an association between vitamin D deficiency and hypertension, left ventricular hypertrophy and heart failure, and experimental studies provided strong evidence for a role of vitamin D signaling in the regulation of cardiovascular function. One of the proposed mechanisms of action of vitamin D is that it functions as a negative regulator of the renin-angiotensin-aldosterone system (RAAS). This finding established a novel link between vitamin D and RAAS that was unexplored until then. During recent years, major progress has been made towards a more complete understanding of the mechanisms by which FGF23, PTH, and RAAS regulate vitamin D metabolism, especially at the genomic level. However, there are still major gaps in our knowledge that need to be filled by future research. The purpose of this review is to highlight our current understanding of the molecular mechanisms underlying the interaction between vitamin D, FGF23, PTH, and RAAS, and to discuss the role of these mechanisms in physiology and pathophysiology.

Parathyroid Hormone Secretion and Related Syndromes

In this article, we will get to know about the parathyroid hormone and the parathyroid gland. Its anatomy, physiology, and pathology will be delved into. There will be a brief discussion about its secretion and also about various clinical syndromes related to it. Parathormone, the parathyroid glands, regulate normal calcium and phosphorus levels in the body. An increase in the secretion of parathormone results in increased calcium uptake from the kidney, intestine, and bones, hence elevating the blood calcium level. A few mechanisms of action of this hormone are increased by the presence of vitamin D. The increase in the secretion of this hormone as compared to the normal levels is termed hyperparathyroidism. Incidence is maximum after 60 years of age. The ratio of females to males is 2:1. There are three types of hyperparathyroidism which will be described in this article. Clinical manifestations of hyperparathyroidism include skeletal disease, renal involvement, GI manifestations, psychiatric diseases, decreased neuro-muscular irritability, decreased deep tendon reflexes, muscular weakness, and atrophy. Assessment for hyperparathyroidism can be done by various diagnostic tests which are described further in this article. Medical/surgical management to cure this is also well-established nowadays. The decrease in the secretion of this hormone as compared to normal levels is termed hypoparathyroidism. Serum calcium levels are very low, serum phosphate levels are very high, and tetany can develop. The incidence is that females are more prone than males. Assessment for acute hypoparathyroidism will show positive Chvostek sign and trousseau sign, hyperactive deep tendon reflexes, and paresthesia. Assessment of chronic hypoparathyroidism will show lethargy, weakness, fatigue, cataracts, brittle nails, dry scaly skin, personality changes, and can even cause permanent brain damage. The normal secretion process of this hormone and diseases when its secretion becomes abnormal and why that happens are briefed in this article.

Cognitive deficits in primary hyperparathyroidism - what we know and what we do not know: A narrative review

Classic symptoms of primary hyperparathyroidism (PHPT) are seen in approximately 20% of patients. While features such as kidney stones and skeletal disease are often highlighted as directly related to the disease, others can be even more prevalent. For example, cognitive dysfunction and reduced quality of life are common complaints in many patients, even among those who are classified as being asymptomatic. The pathophysiology of PHPT involves the impact of excess parathyroid hormone (PTH) on calcium metabolism. Referencing putative neurocognitive issues, many animal studies have illustrated the potential roles of PTH and PTH receptors in the brain. Functional imaging and pre-and post-parathyroidectomy studies have suggested a link between the neuronal impact of elevated PTH levels on specific functional aspects of the central nervous system, such as cognition. Confounding a direct role for PTH are hypercalcemia and vitamin D deficiency, both of which could conceivably alter CNS function in PHPT. The lack of strong evidence that parathyroidectomy improves cognition in patients with PHPT raises the question as to whether parathyroid surgery should be recommended on this basis alone. This narrative review summarizes the available literature on neurocognitive function in PHPT.

Heparin promotes rapid fibrillation of the basic Parathyroid Hormone at physiological pH

In acidic secretory granules of mammalian cells, peptide hormones including the parathyroid hormone (PTH) are presumably stored in the form of functional amyloid fibrils. Mature PTH, however, is considerably positively charged in acidic environments, a condition known to impede unassisted self-aggregation into fibrils. Here, we studied the role of the polyanion heparin on promoting fibril formation of PTH. Employing ITC, CD spectroscopy, NMR, SAXS and fluorescence-based assays we could demonstrate that heparin binds PTH with submicromolar affinity and facilitates its conversion into fibrillar seeds, enabling rapid formation of amyloid fibrils under acidic conditions. In absence of heparin, PTH remained in a soluble monomeric state. We suspect that heparin-like surfaces are required in vivo to convert PTH efficiently into fibrillar deposits.

Structural pharmacology of PTH and PTHrP

Parathyroid hormone (PTH) and PTH-related peptide (PTHrP) regulate extracellular phosphate and calcium homeostasis as well as bone remodeling. PTH is a classic endocrine peptide hormone whose synthesis and negative feedback by multiple factors control release from the parathyroid glands. PTHrP is ubiquitously expressed (pre- and postnatally) and acts in an autocrine/paracrine manner. This review considers the structural pharmacology and actions of PTH and PTHrP, biological consequences of inherited mutations, engineered analogs that illuminate similarities and differences in physiologic actions, and targeted therapeutic opportunities.

Proteolytic Cleavage of the Extracellular Domain Affects Signaling of Parathyroid Hormone 1 Receptor

Parathyroid hormone 1 receptor (PTH1R) is a member of the class B family of G protein-coupled receptors, which are characterized by a large extracellular domain required for ligand binding. We have previously shown that the extracellular domain of PTH1R is subject to metalloproteinase cleavage in vivo that is regulated by ligand-induced receptor trafficking and leads to impaired stability of PTH1R. In this work, we localize the cleavage site in the first loop of the extracellular domain using amino-terminal protein sequencing of purified receptor and by mutagenesis studies. We further show, that a receptor mutant not susceptible to proteolytic cleavage exhibits reduced signaling to G_s and increased activation of G_q compared to wild-type PTH1R. These findings indicate that the extracellular domain modulates PTH1R signaling specificity, and that its cleavage affects receptor signaling.

Involvement of the Parathyroid Hormone-Related Protein on Changes in the CYP3A Expression in Cancer Cachexia

Parathyroid hormone-related protein (PTHrP), which is secreted from a tumor, contributes to the progression of cachexia, a condition that is observed in half of all cancer patients. Although drug clearance was reported to decrease in patients with cancer cachexia, the details have not been clarified. The present study reports on an investigation of whether PTHrP is involved in the alternation of drug metabolism in cases of cancer cachexia. Cancer cachexia model rats with elevated serum PTHrP levels showed a significant decrease in hepatic and intestinal CYP3A2 protein expression. When midazolam, a CYP3A substrate drug, was administered intravenously or orally to the cancer cachexia rats, its area under the curve (AUC) was increased by about 2 and 5 times, as compared to the control group. Accordingly, the bioavailability of midazolam was increased by about 3 times, thus enhancing its pharmacological effect. In vitro experiments using HepG2 cells and Caco-2 cells showed that the addition of serum from cancer cachexia rats or active PTHrP (1-34) to each cell resulted in a significant decrease in the expression of CYP3A4 mRNA. Treatment with a cell-permeable cAMP analog also resulted in a decreased CYP3A4 expression. Pretreatment with protein kinase A (PKA), protein kinase C (PKC), and nuclear factor-kappa B (NF-κB) inhibitors recovered the decrease in CYP3A4 expression that was induced by PTHrP (1-34). These results suggest that PTHrP suppresses CYP3A expression via the cAMP/PKA/PKC/NF-κB pathway. Therefore, it is likely that PTHrP would be involved in the changes in drug metabolism observed in cancer cachexia.

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.

PTH resistance

Parathyroid hormone (PTH), which is primarily regulated by extracellular calcium changes, controls calcium and phosphate homeostasis. Different diseases are derived from PTH deficiency (hypoparathyroidism), excess (hyperparathyroidism) and resistance (pseudohypoparathyroidism, PHP). Pseudohypoparathyroidism was historically classified into subtypes according to the presence or not of inherited PTH resistance associated or not with features of Albright's hereditary osteodystrophy and deep and progressive ectopic ossifications. The growing knowledge on the PTH/PTHrP signaling pathway showed that molecular defects affecting different members of this pathway determined distinct, yet clinically related disorders, leading to the proposal of a new nomenclature and classification encompassing all disorders, collectively termed inactivating PTH/PTHrP signaling disorders (iPPSD).

Parathyroid Hormone Secretion and Receptor Expression Determine the Age-Related Degree of Osteogenic Differentiation in Dental Pulp Stem Cells

Objective: To demonstrate the levels of parathyroid hormone secretion and genetic expressions of parathyroid hormone (PTH) and PTH1 receptor (PTH1R) genes in the dental pulp stem cells (DPSCs) from different age groups before and after induction of osteogenic differentiation. In addition, we also wanted to check their correlation with the degree of osteogenic differentiation. Methods: Human primary DPSCs from three age groups (milk tooth (SHEDs), 7–12 years old; young DPSCs (yDPSCs), 20–40 years old; old DPSCs (oDPSCs), 60+ years old) were characterized for mesenchymal stem cell (MSC) markers. DPSCs were subjected to osteogenic differentiation and functional staining. Gene expression levels were analyzed by qRT-PCR. Surface receptor analysis was done by flow cytometry. Comparative protein levels were evaluated by ELISA. Results: All SHEDs, yDPSCs, and oDPSCs were found to be expressing mesenchymal stem cell markers. SHEDs showed more mineralization than yDPSCs and oDPSCs after osteogenic induction. SHEDs exhibited higher expression of PTH and PTH1R before and after osteogenic induction, and after osteogenic induction, SHEDs showed more expression for RUNX2, ALPL, and OCN. Higher levels of PTH were observed in SHEDs and yDPSCs, and the number of PTH1R positive cells was relatively lower in yDPSCs and oDPSCs than in SHEDs. After osteogenic induction, SHEDs were superior in the secretion of OPG, and the secretions of ALPL and PTH and the number of PTH1R positive cells were relatively low in the oDPSCs. Conclusions: The therapeutic quality of dental pulp stem cells is largely based on their ability to retain their stemness characteristics. This study emphasizes the criterion of aging, which affects the secretion of PTH by these cells, which in turn attenuates their osteogenic potential.

Roles of Parathyroid Hormone-Related Protein (PTHrP) and Its Receptor (PTHR1) in Normal and Tumor Tissues: Focus on Their Roles in Osteosarcoma

Osteosarcoma (OS) is the most common primary bone tumor and originates from bone forming mesenchymal cells and primarily affects children and adolescents. The 5-year survival rate for OS is 60 to 65%, with little improvement in prognosis during the last four decades. Studies have demonstrated the evolving roles of parathyroid hormone-related protein (PTHrP) and its receptor (PTHR1) in bone formation, bone remodeling, regulation of calcium transport from blood to milk, regulation of maternal calcium transport to the fetus and reabsorption of calcium in kidneys. These two molecules also play critical roles in the development, progression and metastasis of several tumors such as breast cancer, lung carcinoma, chondrosarcoma, squamous cell carcinoma, melanoma and OS. The protein expression of both PTHrP and PTHR1 have been demonstrated in OS, and their functions and proposed signaling pathways have been investigated yet their roles in OS have not been fully elucidated. This review aims to discuss the latest research with PTHrP and PTHR1 in OS tumorigenesis and possible mechanistic pathways.

This review is dedicated to Professor Michael Day who died in May 2020 and was a very generous collaborator.

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.

The Dramatic Role of IFN Family in Aberrant Inflammatory Osteolysis

Skeletal system has been considered a highly dynamic system, in which bone-forming osteoblasts and bone-resorbing osteoclasts go through a continuous remodeling cycle to maintain homeostasis of bone matrix. It has been well acknowledged that interferons (IFNs), acting as a subgroup of cytokines, not only have crucial effects on regulating immunology but also could modulate the dynamic balance of bone matrix. In the light of different isoforms, IFNs have been divided into three major categories in terms of amino acid sequences, recognition of specific receptors and biological activities. Currently, type I IFNs consist of a multi-gene family with several subtypes, of which IFN-α exerts pro-osteoblastogenic effects to activate osteoblast differentiation and inhibits osteoclast fusion to maintain bone matrix integrity. Meanwhile, IFN-β suppresses osteoblast-mediated bone remodeling as well as exhibits inhibitory effects on osteoclast differentiation to attenuate bone resorption. Type II IFN constitutes the only type, IFN-γ, which exerts regulatory effects on osteoclastic bone resorption and osteoblastic bone formation by biphasic ways. Interestingly, type III IFNs are regarded as new members of IFN family composed of four members, including IFN-λ1 (IL-29), IFN-λ2 (IL-28A), IFN-λ3 (IL-28B) and IFN-λ4, which have been certified to participate in bone destruction. However, the direct regulatory mechanisms underlying how type III IFNs modulate the metabolic balance of bone matrix, remains poorly elucidated. In this review, we have summarized functions of IFN family during physiological and pathological conditions and described the mechanisms by which IFNs maintain bone matrix homeostasis via affecting the osteoclast-osteoblast crosstalk. In addition, the potential therapeutic effects of IFNs on inflammatory bone destruction diseases such as rheumatoid arthritis (RA), osteoarthritis (OA) and infectious bone diseases are also well displayed, which are based on the predominant role of IFNs in modulating the dynamic equilibrium of bone matrix.

Immune-related gene signature predicts overall survival of gastric cancer patients with varying microsatellite instability status

Purpose: Gastric cancer (GC) is one of the most common and fatal malignancies globally. While microsatellite instability (MSI) index has earlier been correlated with survival outcome in gastric cancer patients, the present study aims to construct a risk-stratification model based on immune-related genes in GC patients with varying MSI status.

Results: The univariate and multivariate Cox regression analyses identified SEMA7A, NUDT6, SCGB3A1, NPR3, PTH1R, and SHC4 as signature genes, which were used to build the prognostic model for GC patients with microsatellite instability-low (MSI-L) and microsatellite stable (MSS). Whereas, for GC patients with microsatellite instability-high (MSI-H), prognostic model was established with three genes (SEMA6A, LTBP1, and BACH2), based on the univariate and multivariate Cox regression, and Kaplan-Meier survival analyses.

Conclusion: The prognostic immune-related gene signature identified in this study may offer new targets for personalized treatment and immunotherapy for GC patients with MSI-H or MSI-L/MSS status.

Methods: The Cancer Genome Atlas (TCGA) and ImmPort databases were used to extract expression data and to explore prognostic genes from the immune-related genes (IRGs), respectively. Univariate and multivariate Cox regression analysis were applied to identify IRGs correlated with patient prognosis. The regulatory network between prognostic IRGs and TFs were performed using R software.

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.

Osteocyte-Related Cytokines Regulate Osteoclast Formation and Bone Resorption

The process of bone remodeling is the result of the regulated balance between bone cell populations, namely bone-forming osteoblasts, bone-resorbing osteoclasts, and the osteocyte, the mechanosensory cell type. Osteoclasts derived from the hematopoietic stem cell lineage are the principal cells involved in bone resorption. In osteolytic diseases such as rheumatoid arthritis, periodontitis, and osteoporosis, the balance is lost and changes in favor of bone resorption. Therefore, it is vital to elucidate the mechanisms of osteoclast formation and bone resorption. It has been reported that osteocytes express Receptor activator of nuclear factor κΒ ligand (RANKL), an essential factor for osteoclast formation. RANKL secreted by osteocytes is the most important factor for physiologically supported osteoclast formation in the developing skeleton and in pathological bone resorption such as experimental periodontal bone loss. TNF-α directly enhances RANKL expression in osteocytes and promotes osteoclast formation. Moreover, TNF-α enhances sclerostin expression in osteocytes, which also increases osteoclast formation. These findings suggest that osteocyte-related cytokines act directly to enhance osteoclast formation and bone resorption. In this review, we outline the most recent knowledge concerning bone resorption-related cytokines and discuss the osteocyte as the master regulator of bone resorption and effector in osteoclast formation.

Parathyroid hormone receptor 1 (PTHR1) is a prognostic indicator in canine osteosarcoma

Osteosarcoma (OS) is the most common malignant primary bone tumour in humans and dogs. Several studies have established the vital role of parathyroid hormone-related protein (PTHrP) and its receptor (PTHR1) in bone formation and remodeling. In addition, these molecules play a role in the progression and metastasis of many human tumour types. This study investigated the expression of PTHR1 and PTHrP in canine OS tissues and assessed their prognostic value. Formalin-fixed, paraffin-embedded tissue samples from 50 dogs diagnosed with primary OS were immunolabeled with antibodies specific for PTHR1 and PTHrP. The immunostaining intensity of tumours from patients with OS was correlated with survival time. Both PTHR1 and PTHrP were detected in all OS samples (n = 50). Dogs with OS tumours showing high immunostaining intensity for PTHR1 (n = 36) had significantly shorter survival times (p = 0.028, Log Rank; p = 0.04, Cox regression) when compared with OS that had low immunostaining intensity for PTHR1 (n = 14).PTHrP immunostaining intensity did not correlate with survival time (p > 0.05). The results of this study indicate that increased expression of PTHR1 antigen in canine OS is associated with poor prognosis. This suggests that PTHR1 may be useful as a prognostic indicator in canine OS.

The Effects of Tocotrienol on Bone Peptides in a Rat Model of Osteoporosis Induced by Metabolic Syndrome: The Possible Communication between Bone Cells

A positive association between metabolic syndrome (MetS) and osteoporosis has been demonstrated in previous animal studies. The mechanisms of MetS in orchestrating the bone remodelling process have traditionally focused on the interactions between mature osteoblasts and osteoclasts, while the role of osteocytes is unexplored. Our earlier studies demonstrated the bone-promoting effects of tocotrienol using a rat model of osteoporosis induced by MetS. This study aimed to investigate the expression of osteocyte-derived peptides in the bone of rats with MetS-induced osteoporosis treated with tocotrienol. Age-matched male Wistar rats (12-week-old; n = 42) were divided into seven experimental groups. Two groups served as the baseline and normal group, respectively. The other five groups were fed with a high-carbohydrate high-fat (HCHF) diet to induce MetS. The five groups of HCHF animals were treated with tocopherol-stripped corn oil (vehicle), annatto tocotrienol (60 and 100 mg/kg), and palm tocotrienol (60 and 100 mg/kg) starting from week 8. At the end of the study, the rats were sacrificed and their right tibias were harvested. Protein was extracted from the metaphyseal region of the proximal right tibia and levels of bone peptides, including osteoprotegerin (OPG), soluble receptor activator of nuclear factor-kappa B ligand (sRANKL), sclerostin (SOST), Dickkopf-related protein 1 (DKK-1), fibroblast growth factor-23 (FGF-23), and parathyroid hormone (PTH), were measured. The vehicle-treated animals displayed higher levels of sRANKL, SOST, DKK-1, FGF-23, and PTH as compared to the normal animals. Oral supplementation of annatto and palm tocotrienol (60 and 100 mg/kg) reduced the levels of sRANKL and FGF-23 in the HCHF animals. Only 100 mg/kg annatto and palm tocotrienol lowered SOST and DKK-1 levels in the HCHF animals. In conclusion, tocotrienol exerts potential skeletal-promoting benefit by modulating the levels of osteocytes-derived bone-related peptides.

Epigenetic regulation of bone remodeling by natural compounds

Osteoporosis and osteopenia impact more than 54 million Americans, resulting in significant morbidity and mortality. Alterations in bone remodeling are the hallmarks for osteoporosis, and thus the development of novel treatments that will prevent or treat bone diseases would be clinically significant, and improve the quality of life for these patients. Bone remodeling involves the removal of old bone by osteoclasts and the formation of new bone by osteoblasts. This process is tightly coupled, and is essential for the maintenance of bone strength and integrity. Since the osteoclast is the only cell capable of bone resorption, the development of drugs to treat bone disorders has primarily focused on reducing osteoclast differentiation, maturation, and bone resorption mechanisms, and there are few treatments that actually increase bone formation. Evidence from observational, experimental, and clinical studies demonstrate a positive link between naturally occurring compounds and improved indices of bone health. While many natural extracts and compounds are reported to have beneficial effects on bone, only resveratrol, sulforaphane, specific phenolic acids and anthocyanins, have been shown to both increase bone formation and reduce resorption through their effects on the bone epigenome. Each of these compounds alters specific aspects of the bone epigenome to improve osteoblast differentiation, reduce osteoblast apoptosis, improve bone mineralization, and reduce osteoclast differentiation and function. This review focuses on these specific natural compounds and their epigenetic regulation of bone remodeling.

Parathyroid hormone-related protein induces fibronectin up-regulation in rat mesangial cells through reactive oxygen species/Src/EGFR signaling

Parathyroid hormone-related protein (PTHrP) is known to be up-regulated in both glomeruli and tubules in patients with diabetic kidney disease (DKD), but its role remains unclear. Previous studies show that PTHrP-induced hypertrophic response in mesangial cells (MCs) and epithelial-mesenchymal transition (EMT) in tubuloepithelial cells can be mediated by TGF-β1. In the present study, although long-term PHTrP (1-34) treatment increased the mRNA and protein level of TGF-β1 in primary rat MCs, fibronectin up-regulation occurred earlier, suggesting that fibronectin induction is independent of TGF-β1/Smad signaling. We thus evaluated the involvement of epidermal growth factor receptor (EGFR) signaling and found that nicotinamide adenine dinucleotide phosphate oxidase-derived reactive oxygen species mediates PTHrP (1-34)-induced Src kinase activation. Src phosphorylates EGFR at tyrosine 845 and then transactive EGFR. Subsequent PI3K activation mediates Akt and ERK1/2 activation. Akt and ERK1/2 discretely lead to excessive protein synthesis of fibronectin. Our study thus demonstrates the new role of PTHrP in fibronectin up-regulation for the first time in glomerular MCs. These data also provided new insights to guide development of therapy for glomerular sclerosis.

The Molecular Mechanism of Vitamin E as a Bone-Protecting Agent: A Review on Current Evidence

Bone remodelling is a tightly-coordinated and lifelong process of replacing old damaged bone with newly-synthesized healthy bone. In the bone remodelling cycle, bone resorption is coupled with bone formation to maintain the bone volume and microarchitecture. This process is a result of communication between bone cells (osteoclasts, osteoblasts, and osteocytes) with paracrine and endocrine regulators, such as cytokines, reactive oxygen species, growth factors, and hormones. The essential signalling pathways responsible for osteoclastic bone resorption and osteoblastic bone formation include the receptor activator of nuclear factor kappa-B (RANK)/receptor activator of nuclear factor kappa-B ligand (RANKL)/osteoprotegerin (OPG), Wnt/β-catenin, and oxidative stress signalling. The imbalance between bone formation and degradation, in favour of resorption, leads to the occurrence of osteoporosis. Intriguingly, vitamin E has been extensively reported for its anti-osteoporotic properties using various male and female animal models. Thus, understanding the underlying cellular and molecular mechanisms contributing to the skeletal action of vitamin E is vital to promote its use as a potential bone-protecting agent. This review aims to summarize the current evidence elucidating the molecular actions of vitamin E in regulating the bone remodelling cycle.

Novel therapies in osteoporosis: PTH-related peptide analogs and inhibitors of sclerostin

Bone-forming approaches to treat patients with severe osteoporosis are effective, but treatment options are limited, and there is an unmet clinical need for additional drugs. This review discusses two novel and advanced anabolic therapeutic concepts that have successfully completed phase 3 trials. Romosozumab is a monoclonal antibody that targets the Wnt inhibitor sclerostin. Two phase 3 trials (FRAME and ARCH) of romosozumab for the treatment of postmenopausal osteoporosis have been completed. Both trials successfully reached their primary endpoint by reducing vertebral fractures by 75% compared to placebo (FRAME trial) and 48% compared to alendronate (ARCH trial), respectively. Abaloparatide is a PTH-related protein (PTHrP) analog that has displayed bone anabolic activity. In the phase 3 ACTIVE trial, abaloparatide was compared to placebo and teriparatide for 18 months in postmenopausal women who had already experienced an osteoporotic fracture. Abaloparatide successfully reduced the rate of new vertebral fractures by 86% compared to placebo. Furthermore, abaloparatide achieved greater BMD increases at all measured sites compared to both placebo and teriparatide. Based on these results, abaloparatide was FDA approved in April 2017. This review discusses available data of both agents with regard to efficacy and safety as well as their possible future application.

Loss of the PTH/PTHrP receptor along the osteoblast lineage limits the anabolic response to exercise

Exercise and physical activity are critical to maintain bone mass and strength throughout life. Both exercise and physical activity subject bone to a unique combination of stimuli in the forms of dynamic loading and a systemic increase in parathyroid hormone (PTH). Although dynamic loading is considered to be the primary osteogenic stimuli, the influence of increasing PTH levels remains unclear. We hypothesize that activation of the PTH/PTH-related peptide type 1 receptor (PPR) along the osteoblast lineage facilitates bone formation and improved mechanical properties in response to exercise. To test this hypothesis, conditional PPR-knockout mice (PPRcKO) were generated in which PPR expression was deleted along the osteoblast lineage under the osterix promoter. At 8-weeks of age, both PPRfl/fl and PPRcKO mice were subjected to treadmill running or sedentary conditions for 5-weeks. Under sedentary conditions, PPRcKO mice displayed significantly less bone mass as well as smaller structural-level strength (yield-load and ultimate load), while tissue level properties were largely unaffected. However, PPRcKO mice exposed to exercise displayed significantly less structural-level and tissue-level mechanical properties when compared to exercised PPRfl/fl mice. Overall, these data demonstrate that PPR expression along the osteoblast lineage is essential for exercise to improve the mechanical properties of cortical bone. Furthermore, the influence of PPR activation on material properties is unique to exercise and not during normal growth and development.

STC1 and PTHrP Modify Carbohydrate and Lipid Metabolism in Liver of a Teleost Fish

Stanniocalcin 1 (STC1) and parathyroid hormone-related protein (PTHrP) are calciotropic hormones in vertebrates. Here, a recently hypothesized metabolic role for these hormones is tested on European sea bass treated with: (i) teleost PTHrP(1-34), (ii) PTHrP(1-34) and anti-STC1 serum (pro-PTHrP groups), (iii) a PTHrP antagonist PTHrP(7-34) or (iv) PTHrP(7-34) and STC1 (pro-STC1 groups). Livers were analysed using untargeted metabolic profiling based on proton nuclear magnetic resonance (¹H-NMR) spectroscopy. Concentrations of branched-chain amino acid (BCAA), alanine, glutamine and glutamate increased in pro-STC1 groups suggesting their mobilization from the muscle to the liver for degradation and gluconeogenesis from alanine and glutamine. In addition, only STC1 treatment decreased the concentrations of succinate, fumarate and acetate, indicating slowing of the citric acid cycle. In the pro-PTHrP groups the concentrations of glucose, erythritol and lactate decreased, indicative of gluconeogenesis from lactate. Taurine, trimethylamine, trimethylamine N-oxide and carnitine changed in opposite directions in the pro-STC1 versus the pro-PTHrP groups, suggesting opposite effects, with STC1 stimulating lipogenesis and PTHrP activating lipolysis/β-oxidation of fatty acids. These findings suggest a role for STC1 and PTHrP related to strategic energy mechanisms that involve the production of glucose and safeguard of liver glycogen reserves for stressful situations.

Oleanolic Acid and Ursolic Acid Improve Bone Properties and Calcium Balance and Modulate Vitamin D Metabolism in Aged Female Rats

Oleanolic acid (OA) and ursolic acid (UA) are the major chemical constituents in Fructus Ligustri Lucidi (FLL), a kidney-tonifying Chinese herb that is previously shown to improve bone properties and enhance calcium balance in aged female rats. The present study was designed to study if OA and UA act as the active ingredients in FLL to exert the positive effects on bone and mineral metabolism in aged rats. Aged (13-month-old) Sprague-Dawley female rats were randomly assigned to four groups with oral administration of drug or vehicle treatment for 12 weeks: medium calcium diet (MCD, 0.6% calcium), high calcium diet (HCD, 1.2% calcium), MCD + FLL (700 mg/kg/day), MCD + OA (23.6 mg/kg/day) + UA (8.6 mg/kg/day). A group of mature (3-month-old) female rats fed with MCD was included as positive control. The results demonstrated that FLL and OA+UA increased bone mineral density and improved microarchitectural properties of aged female rats. The osteoprotective effects of FLL and OA+UA might be, at least in part, associated with their actions on enhancing calcium balance and suppressing age-induced secondary hyperparathyroidism in aged female rats. FLL and OA+UA also significantly induced renal CYP27B1 protein expression and OA+UA treatment decreased CYP24A1 mRNA and protein expressions in aged female rats. In addition, FLL and OA+UA significantly increased the promoter activity, mRNA and protein expressions of renal CYP27B1 in vitro in human proximal tubule HKC-8 cells. The present findings suggest that OA+UA can be regarded as the active ingredients of FLL and might be a potential drug candidate for prevention and treatment of osteoporosis.

Parathyroid hormone resistance syndromes - Inactivating PTH/PTHrP signaling disorders (iPPSDs)

Metabolic disorders caused by impairments of the Gsα/cAMP/PKA pathway affecting the signaling of PTH/PTHrP lead to features caused by non-responsiveness of target organs, in turn leading to manifestations similar to the deficiency of the hormone itself. Pseudohypoparathyroidism (PHP) and related disorders derive from a defect of the α subunit of the stimulatory G protein (Gsα) or of downstream effectors of the same pathway, such as the PKA regulatory subunit 1A and the phosphodiesterase type 4D. The increasing knowledge on these diseases made the actual classification of PHP outdated as it does not include related conditions such as acrodysostosis (ACRDYS) or progressive osseous heteroplasia (POH), so that a new nomenclature and classification has been recently proposed grouping these disorders under the term "inactivating PTH/PTHrP signaling disorder" (iPPSD). This review will focus on the pathophysiology, clinical and molecular aspects of these rare, heterogeneous but closely related diseases.

Probing Polymer Chain Conformation and Fibril Formation of Peptide Conjugates

Covalent conjugates between a synthetic polymer and a peptide hormone were used to probe the molecular extension of these macromolecules and how the polymer modifies the fibril formation of the hormone. NMR spectroscopy of ¹⁵ N labeled parathyroid hormone (PTH) was employed to visualize the conformation of the conjugated synthetic polymer, triggered by small temperature changes via its lower critical solution temperature. A shroud-like polymer conformation dominated the molecular architecture of the conjugated chimeras. PTH readily forms amyloid fibrils, which is probably the physiological storage form of the hormone. The polyacrylate based polymers stimulated the nucleation processes of the peptide.

Regulation of Bone Remodeling by Parathyroid Hormone

Parathyroid hormone (PTH) exerts profound effects on skeletal homeostasis through multiple cellular and molecular mechanisms. Continuous hyperparathyroidism causes net loss of bone mass, despite accelerating bone formation by osteoblasts. Intermittent treatment with PTH analogs represents the only Food and Drug Administration (FDA)-approved bone anabolic osteoporosis treatment strategy. Functional PTH receptors are present on cells of the osteoblast lineage, ranging from early skeletal stem cells to matrix-embedded osteocytes. In addition, bone remodeling by osteoclasts liberates latent growth factors present within bone matrix. Here, we will provide an overview of the multiple cellular and molecular mechanisms through which PTH influences bone homeostasis. Notably, net skeletal effects of continuous versus intermittent can differ significantly. Where possible, we will highlight mechanisms through which continuous hyperparathyroidism leads to bone loss, and through which intermittent hyperparathyroidism boosts bone mass. Given the therapeutic usage of intermittent PTH (iPTH) treatment for osteoporosis, particular attention will be paid toward mechanisms underlying the bone anabolic effects of once daily PTH administration.

Constitutive stimulatory G protein activity in limb mesenchyme impairs bone growth

GNAS mutations leading to constitutively active stimulatory G protein alpha-subunit (Gsα) cause different tumors, fibrous dysplasia of bone, and McCune-Albright syndrome, which are typically not associated with short stature. Enhanced signaling of the parathyroid hormone/parathyroid hormone-related peptide receptor, which couples to multiple G proteins including Gsα, leads to short bones with delayed endochondral ossification. It has remained unknown whether constitutive Gsα activity also impairs bone growth. Here we generated mice expressing a constitutively active Gsα mutant (Gsα-R201H) conditionally upon Cre recombinase (cGsα^R201H mice). Gsα-R201H was expressed in cultured bone marrow stromal cells from cGsα^R201H mice upon adenoviral-Cre transduction. When crossed with mice in which Cre is expressed in a tamoxifen-regulatable fashion (CAGGCre-ER™), tamoxifen injection resulted in mosaic expression of the transgene in double mutant offspring. We then crossed the cGsα^R201H mice with Prx1-Cre mice, in which Cre is expressed in early limb-bud mesenchyme. The double mutant offspring displayed short limbs at birth, with narrow hypertrophic chondrocyte zones in growth plates and delayed formation of secondary ossification center. Consistent with enhanced Gsα signaling, bone marrow stromal cells from these mice demonstrated increased levels of c-fos mRNA. Our findings indicate that constitutive Gsα activity during limb development disrupts endochondral ossification and bone growth. Given that Gsα haploinsufficiency also leads to short bones, as in patients with Albright's hereditary osteodystrophy, these results suggest that a tight control of Gsα activity is essential for normal growth plate physiology.

Lack of endogenous parathyroid hormone delays fracture healing by inhibiting vascular endothelial growth factor‑mediated angiogenesis

Intermittent low-dose injections of parathyroid hormone (PTH) have been reported to exert bone anabolic effects and to promote fracture healing. As an important proangiogenic cytokine, vascular endothelial growth factor (VEGF) is secreted by bone marrow mesenchymal stem cells (BMSCs) and osteoblasts, and serves a crucial regulatory role in the process of vascular development and regeneration. To investigate whether lack of endogenous PTH causes reduced angiogenic capacity and thereby delays the process of fracture healing by downregulating the VEGF signaling pathway, a PTH knockout (PTHKO) mouse fracture model was generated. Fracture healing was observed using X-ray and micro-computerized tomography. Bone anabolic and angiogenic markers were analyzed by immunohistochemistry and western blot analysis. The expression levels of VEGF and associated signaling pathways in murine BMSC-derived osteoblasts were measured by quantitative polymerase chain reaction and western blot analysis. The expression levels of protein kinase A (PKA), phosphorylated-serine/threonine protein kinase (pAKT), hypoxia-inducible factor-1α (HIF1α) and VEGF were significantly decreased in BMSC-derived osteoblasts from PTHKO mice. In addition, positive platelet endothelial cell adhesion molecule staining was reduced in PTHKO mice, as determined by immunohistochemistry. The expression levels of HIF1α, VEGF, runt-related transcription factor 2, osteocalcin and alkaline phosphatase were also decreased in PTHKO mice, and fracture healing was delayed. In conclusion, lack of endogenous PTH may reduce VEGF expression in BMSC-derived osteoblasts by downregulating the activity of the PKA/pAKT/HIF1α/VEGF pathway, thus affecting endochondral bone formation by causing a reduction in angiogenesis and osteogenesis, ultimately leading to delayed fracture healing.

Multiple hormone resistance and alterations of G-protein-coupled receptors signaling

Metabolic disorders deriving from the non-responsiveness of target organs to hormones, which manifest clinically similar to the deficiency of a given hormone itself, derive from molecular alterations affecting specific hormone receptors. Pseudohypoparathyroidism (PHP) and related disorders exemplify an unusual form of hormone resistance as the underlying molecular defect is a partial deficiency of the α subunit of the stimulatory G protein (Gsα), a key regulator of cAMP signaling pathway, or, as more recently described, of downstream effector proteins of the same pathway, such as PKA regulatory subunit 1A (R1A) and phosphodyestarase type 4D (PDE4D). In this group of diseases, resistance to hormones such as PTH, TSH, gonadotropins and GHRH may be variably present, so that the clinical and molecular overlap among these different but related disorders represents a challenge for endocrinologists as to differential diagnosis and genetic counseling. This review will describe the presenting features of multiple resistance in PHP and related disorders, focusing on both our current understanding and future challenges.

Expression of parathyroid hormone related protein (PTHRP) in ameloblastomas

BACKGROUND

Presence of parathyroid hormone related protein (PTHrP) might suggest that ameloblastomas recapitulate features of the enamel epithelium and induce bone resorption, which would facilitate their growth and local invasion. The aim of this study was to determine the expression of PTHrP in ameloblastomas.

MATERIAL AND METHODS

An observational research study was designed including 39 cases of histologically diagnosed ameloblastomas (39 out of 42 patients gave consent for the use of their medical records and all data required for this study). Gender, age, tumor location, histological type and subtype of the tumor were recorded and PTHrP expression was determined by indirect immunohistochemistry using monoclonal anti-human PTHrP (1D1 / Santa Cruz Biotechnology). Protein expression and intensity were evaluated under light microscope and finally data recorded and statistically analyzed. This research was approved by the Caracas West General Hospital review board.

RESULTS

39 cases of ameloblastomas were evenly distributed between genders (49% male and 51% female) with a mean age of 33 ± 3.53 years, mainly affecting the posterior mandible. 20 cases (51.28%) showed positive cytoplasmic immunoreactivity to PTHrP. 8 out of 15 cases of solid/multicystic ameloblastomas and 12 out of 23 cases of unicystic ameloblastomas were PTHrP positive. Intense expression of PTHrP was observed in 4 unicystic ameloblastomas (all luminal subtype) and in 5 cases of conventional ameloblastomas.

CONCLUSIONS

In the present study PTHrP expression in solid multicystic and unicystic ameloblastoma suggests its possible function in the biological behavior of the tumor. More studies are needed in order to determine the possible role of this protein related to bone invasion processes. Key words:Parathyroid hormone related protein, PTHrP, ameloblastoma, bone.

Parathyroid Hormone Signaling in Osteocytes

Osteocytes are the most abundant cell type in bone and play a central role in orchestrating skeletal remodeling, in part by producing paracrine‐acting factors that in turn influence osteoblast and osteoclast activity. Recent evidence has indicated that osteocytes are crucial cellular targets of parathyroid hormone (PTH). Here, we will review the cellular and molecular mechanisms through which PTH influences osteocyte function. Two well‐studied PTH target genes in osteocytes are SOST and receptor activator of NF‐κB ligand (RANKL). The molecular mechanisms through which PTH regulates expression of these two crucial target genes will be discussed. Beyond SOST and RANKL, PTH/PTH‐related peptide (PTHrP) signaling in osteocytes may directly influence the way osteocytes remodel their perilacunar environment to influence bone homeostasis in a cell‐autonomous manner. Here, I will highlight novel, additional mechanisms used by PTH and PTHrP to modulate bone homeostasis through effects in osteocytes. © 2017 The Authors. JBMR Plus is published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.

Dual roles of parathyroid hormone related protein in TGF-β1 signaling and fibronectin up-regulation in mesangial cells

Little is known about the cross-talk between parathyroid hormone (PTH) related protein (PTHrP) and TGF-β1 in mesangial cells (MCs). Our results showed that PTHrP treatment (≤3 h) induced internalization of PTH1R (PTH/PTHrP receptor)–TβRII (TGF-β type 2 receptor) complex and suppressed TGF-β1-mediated Smad2/3 activation and fibronectin (FN) up-regulation. However, prolonged PTHrP treatment (12–48 h) failed to induce PTH1R–TβRII association and internalization. Total protein levels of PTH1R and TβRII were unaffected by PTHrP treatment. These results suggest that internalization of PTH1R and TβRII after short PTHrP treatment might not lead to their proteolytic destruction, allowing the receptors to be recycled back to the plasma membrane during prolonged PTHrP exposure. Receptor re-expression at the cell surface allows PTHrP to switch from its initial inhibitory effect to promote induction of FN. Our study thus demonstrates the dual roles of PTHrP on TGF-β1 signaling and FN up-regulation for the first time in glomerular MCs. These data also provided new insights to guide development of therapy for diabetic kidney disease (DKD).