Action Of Parathyroid Hormone Research Articles

New PTH Signals Mediating Bone Anabolism

Because of its clinical relevance, extensive work has been performed to uncover the signaling pathways modulated by parathyroid hormone (PTH). This review focuses on the recent identification of novel effectors of the anabolic effect of PTH in bone. PTH-induced activation of PKA leads to inactivation of SIK2 and nuclear translocation of HDAC4/5. This inhibits MEF2C-dependent Sost expression. However, the phenotypic characterization of the HDAC4/5 double knockout mice shows normal anabolic response to intermittent PTH, supporting the notion that HDAC/Sost-independent mechanisms must exist. Lrp6 and a member of the Usp gene family have been identified as novel targets of the transcriptional coregulator Nascent polypeptide-associated complex And Coregulator alpha (αNAC) downstream from PTH activation. We propose that the αNAC cascade is involved in the transmission of the anabolic PTH signal. Further deciphering the signaling pathways transducing the anabolic effects of PTH will allow to develop novel therapeutically relevant molecules.

The Parathyroid Gland and Heart Disease.

The parathyroid glands are critical to maintaining calcium homeostasis through actions of parathyroid hormone (PTH). Recent clinical and molecular research has shown that direct and indirect actions of PTH also affect the heart and vasculature through downstream actions of G protein-coupled receptors in the myocardium and endothelial cells. Patients with disorders of the parathyroid gland have higher incidences of hypertension, arrhythmias, left ventricular hypertrophy, heart failure, and calcific disease which translate into increased cardiac morbidity and mortality. Importantly, clinical research also suggests that early treatment of parathyroid disorders through medical or surgical management may reverse cardiovascular remodeling and mitigate cardiac risk factors.

Heterotrimeric G proteins in the control of parathyroid hormone actions.

Parathyroid hormone (PTH) is a key regulator of skeletal physiology and calcium and phosphate homeostasis. It acts on bone and kidney to stimulate bone turnover, increase the circulating levels of 1,25 dihydroxyvitamin D and calcium and inhibit the reabsorption of phosphate from the glomerular filtrate. Dysregulated PTH actions contribute to or are the cause of several endocrine disorders. This calciotropic hormone exerts its actions via binding to the PTH/PTH-related peptide receptor (PTH1R), which couples to multiple heterotrimeric G proteins, including Gs and Gq/11 Genetic mutations affecting the activity or expression of the alpha-subunit of Gs, encoded by the GNAS complex locus, are responsible for several human diseases for which the clinical findings result, at least partly, from aberrant PTH signaling. Here, we review the bone and renal actions of PTH with respect to the different signaling pathways downstream of these G proteins, as well as the disorders caused by GNAS mutations.

Role of Parathormone in Parthenogenesis of Rickets

Parathormone (PTH) is composed of four glands embedded in the thyroid gland, but its function is mainly to keep calcium in the blood within normal range. It has got sensitive receptors that trigger the PTH to act in correcting serum calcium. As calcium is important for the normal functioning of many organs including vital organs like heart and brain, the PTH has to be prompt in maintaining calcium in the blood within normal. The function of PTH is to increase absorption of calcium in the gut and to reduce its excretion in the kidneys. When vitamin is low it leads to drop of calcium in the blood leading to calcium being mobilized from the high calcium reserves in the bone by the action of PTH. The loss of calcium in the bones leads to decalcification of the bones which makes the clinical features of rickets in the bones. In case of rickets bones become soft leading to bow legs in walking infants. All these features are the result of action of Parathormone as with the rise of PTH it is noticed the gradual increase of calcium together with high alkaline phosphatase as an indication of activity of rickets in infants and osteomalacia in the mothers. This review is to express the mechanism of causation of rickets and osteomalacia by the activity of the hyperparathyroidism which is secondary to hypocalcemia due to vitamin D deficiency in the breast feeding infant and their mothers where the latter is considered in the phase of biochemical osteomalacia.

Calcification of Soft Tissues in a Family, Case Report and Review of Pseudohypoparathyroidism

Pseudohypoparathyroidism and pseudo-pseudohypoparathyroidism are rare genetic disorders of calcium metabolism and resistance to the action of Parathormone. Although the genetic details of these conditions are not fully diagnosed, role of gene coding for stimulatory G protein locus was studied and imprinting in its inheritance was proved. We report three cases of a family member with calcification in soft tissues that show Pseudohypoparathyroidism in father and his sister and pseudo-pseudohypoparathyroidism in his son.

Preprogrammed Long-Term Systemic Pulsatile Delivery of Parathyroid Hormone to Strengthen Bone.

Parathyroid hormone (PTH) is the only US Food and Drug Administration (FDA)-approved anabolic agent for the treatment of osteoporosis. The anabolic action of PTH depends on the mode of PTH administration. Pulsatile administration promotes bone formation, however continuous PTH exposure results in bone resorption. In addition, the therapeutic effect of PTH is optimal when the dose and duration fit the therapeutic window. Current PTH treatment requires daily injection, which is neither a convenient nor a favorable choice of patients. Here, an implantable and biodegradable device capable of long-term pulsatile delivery of PTH is developed as a patient-friendly alternative. The advanced materials and fabrication techniques developed in this work enable us to preprogram a pulsatile delivery device to systemically deliver 21 daily pulses of PTH that build bone in vivo. In addition, the device is biodegradable and absorbable in vivo so that no retraction procedure is needed. Therefore, this implantable and biodegradable pulsatile device holds promise to promote bone growth and treat various conditions of bone loss without the burden of daily injections or secondary surgeries.

Sunlight exposure vs. vitamin D supplementation on bone homeostasis of vitamin D deficient rats

Summary Background & aim of the work Vitamin D deficiency is highly prevalent in our locality and worldwide. Two major sources of Vit D replenishment are available; sun exposure and dietary supplementation. This study compared sun exposure with vitamin D3 supplementation on restoring bone homeostasis in a vitamin D deficient (VDD) versus vitamin D sufficient (VDS) rat models. Methods Vitamin D deficient-normocalcemic diet was used for 6 weeks to produce a group of VDD rats (n = 21), then were subdividedinto three equal subgroups: direct sunlight exposure subgroup (Sd subgroup), vitamin D3 treated subgroup (Tt subgroup), and a Control subgroup (Ct group). Normal rats (group II) (n = 14) were fed on normal vitamin D-diet for equal period and then subdivided into two equal subgroups: direct sunlight exposure subgroup (Ss subgroup), and a control (C) subgroup. For all of the subgroups, Exposures and supplementations were continued for 10 days, then the plasma 25 hydroxy vitamin D3, parathyroid hormone, calcium, phosphorus levels and alkaline phosphatase activity were estimated and femur bones were used to prepare histopathological sections. Results The sun-exposed vitamin D deficient group showed a significant reduction of parathyroid hormone more than that in vitamin D supplemented group vs. VDD controls (67.69 ± 13.18 and 78.93 ± 8.31 vs. 86.05 ± 9.67 pg/ml, respectively), while sun-exposed vitamin D sufficient group showed an insignificant change (15.56 ± 2.73 vs. 16.84 ± 3.16 pg/ml). Furthermore, the improvement of osteoid area and the reduction of trabecular separation in the bone sections among vitamin D deficient rats, after sunlight exposure, were better. Conclusions Sunlight-exposure have a more positive effect on bone structure and homeostasis than vitamin D supplementation and control. This effect was more with vitamin D deficient than vitamin D sufficient rats.

Parathyroid function: Action of parathyroid hormone in osteocytes.

Parathyroid function: Action of parathyroid hormone in osteocytes.

CD8+ T cells mediate the regenerative PTH effect in hPDL cells via Wnt10b signaling.

It was the aim of the present investigation to examine whether the stimulating effect of parathyroid hormone (PTH) on human periodontal ligament (hPDL) cell proliferation and differentiation would be enhanced by hPDL/T-cell interaction involving Wnt10b signaling as a mediating pathway. hPDL cells were cultured from healthy premolar tissues of three adolescent orthodontic patients and exposed to PTH(1-34) in monocultures or co-cultures with CD8+ T cells. At harvest, proliferation, alkaline phosphatase-specific activity (ALP), and osteocalcin production were determined by immunofluorescence cytochemistry, real-time PCR, biochemical assay, and ELISA. Wnt10b signaling was analyzed by the use of a specific WNT10b neutralizing antibody. PTH(1-34) stimulation of T cells significantly increased Wnt10b expression and production. Wnt10b exposure of hPDL cells enhanced proliferation and differentiation. PDL cells co-cultured with T cells showed a Wnt10b-dependent regulation of proliferation and differentiation parameters. The addition of a Wnt10b-neutralizing Ab to the co-culture medium resulted in a significant inhibition of the PTH(1-34) effect on proliferation, ALP-specific activity, and osteocalcin protein expression. Our findings provide novel insight into the mechanism of action of PTH on hPDL cells and establish the interplay of T cells and hPDL cells via the Wnt10b pathway as a modulating factor for the anabolic properties of the hormone in periodontal regeneration.

Anabolic action of parathyroid hormone (PTH) does not compromise bone matrix mineral composition or maturation

Intermittent administration of parathyroid hormone (PTH) is used to stimulate bone formation in patients with osteoporosis. A reduction in the degree of matrix mineralisation has been reported during treatment, which may reflect either production of undermineralised matrix or a greater proportion of new matrix within the bone samples assessed. To explore these alternatives, high resolution synchrotron-based Fourier Transform Infrared Microspectroscopy (sFTIRM) coupled with calcein labelling was used in a region of non-remodelling cortical bone to determine bone composition during anabolic PTH treatment compared with region-matched samples from controls.8week old male C57BL/6 mice were treated with vehicle or 50μg/kg PTH, 5 times/week for 4weeks (n=7–9/group). Histomorphometry confirmed greater trabecular and periosteal bone formation and 3-point bending tests confirmed greater femoral strength in PTH-treated mice. Dual calcein labels were used to match bone regions by time-since-mineralisation (bone age) and composition was measured by sFTIRM in six 15μm2 regions at increasing depth perpendicular to the most immature bone on the medial periosteal edge; this allowed in situ measurement of progressive changes in bone matrix during its maturation.The sFTIRM method was validated in vehicle-treated bones where the expected progressive increases in mineral:matrix ratio and collagen crosslink type ratio were detected with increasing bone maturity. We also observed a gradual increase in carbonate content that strongly correlated with an increase in longitudinal stretch of the collagen triple helix (amide I:amide II ratio). PTH treatment did not alter the progressive changes in any of these parameters from the periosteal edge through to the more mature bone.These data provide new information about how the bone matrix matures in situ and confirm that bone deposited during PTH treatment undergoes normal collagen maturation and normal mineral accrual.

Calcium-Sensing Receptor Promotes Breast Cancer by Stimulating Intracrine Actions of Parathyroid Hormone-Related Protein.

Parathyroid hormone-related protein (PTHrP) contributes to the development and metastatic progression of breast cancer by promoting hypercalcemia, tumor growth, and osteolytic bone metastases, but it is not known how PTHrP is upregulated in breast tumors. Here we report a central role in this process for the calcium-sensing receptor, CaSR, which enables cellular responses to changes in extracellular calcium, through studies of CaSR-PTHrP interactions in the MMTV-PymT transgenic mouse model of breast cancer and in human breast cancer cells. CaSR activation stimulated PTHrP production by breast cancer cells in vitro and in vivo Tissue-specific disruption of the casr gene in mammary epithelial cells in MMTV-PymT mice reduced tumor PTHrP expression and inhibited tumor cell proliferation and tumor outgrowth. CaSR signaling promoted the proliferation of human breast cancer cell lines and tumor cells cultured from MMTV-PyMT mice. Further, CaSR activation inhibited cell death triggered by high extracellular concentrations of calcium. The actions of the CaSR appeared to be mediated by nuclear actions of PTHrP that decreased p27(kip1) levels and prevented nuclear accumulation of the proapoptotic factor apoptosis inducing factor. Taken together, our findings suggest that CaSR-PTHrP interactions might be a promising target for the development of therapeutic agents to limit tumor cell growth in bone metastases and in other microenvironments in which elevated calcium and/or PTHrP levels contribute to breast cancer progression. Cancer Res; 76(18); 5348-60. ©2016 AACR.

Convergent Signaling Pathways Regulate Parathyroid Hormone and Fibroblast Growth Factor-23 Action on NPT2A-mediated Phosphate Transport

Parathyroid hormone (PTH) and FGF23 are the primary hormones regulating acute phosphate homeostasis. Human renal proximal tubule cells (RPTECs) were used to characterize the mechanism and signaling pathways of PTH and FGF23 on phosphate transport and the role of the PDZ protein NHERF1 in mediating PTH and FGF23 effects. RPTECs express the NPT2A phosphate transporter, αKlotho, FGFR1, FGFR3, FGFR4, and the PTH receptor. FGFR1 isoforms are formed from alternate splicing of exon 3 and of exon 8 or 9 in Ir-like loop 3. Exon 3 was absent, but mRNA containing both exons 8 and 9 is present in cytoplasm. Using an FGFR1c-specific antibody together with mass spectrometry analysis, we show that RPTECs express FGFR-β1C. The data are consistent with regulated FGFR1 splicing involving a novel cytoplasmic mechanism. PTH and FGF23 inhibited phosphate transport in a concentration-dependent manner. At maximally effective concentrations, PTH and FGF23 equivalently decreased phosphate uptake and were not additive, suggesting a shared mechanism of action. Protein kinase A or C blockade prevented PTH but not FGF23 actions. Conversely, inhibiting SGK1, blocking FGFR dimerization, or knocking down Klotho expression disrupted FGF23 actions but did not interfere with PTH effects. C-terminal FGF23(180-251) competitively and selectively blocked FGF23 action without disrupting PTH effects. However, both PTH and FGF23-sensitive phosphate transport were abolished by NHERF1 shRNA knockdown. Extended treatment with PTH or FGF23 down-regulated NPT2A without affecting NHERF1. We conclude that FGFR1c and PTHR signaling pathways converge on NHERF1 to inhibit PTH- and FGF23-sensitive phosphate transport and down-regulate NPT2A.

Claude D Arnaud, Jr, MD (1929–2016): ASBMR Loses a Founding Father

Claude D Arnaud, Jr, MD (1929–2016): ASBMR Loses a Founding Father

BMP signaling is required for adult skeletal homeostasis and mediates bone anabolic action of parathyroid hormone

Bmp2 and Bmp4 genes were ablated in adult mice (KO) using a conditional gene knockout technology. Bones were evaluated by microcomputed tomography (μCT), bone strength tester, histomorphometry and serum biochemical markers of bone turnover. Drill-hole was made at femur metaphysis and bone regeneration in the hole site was measured by calcein binding and μCT. Mice were either sham operated (ovary intact) or ovariectomized (OVX), and treated with human parathyroid hormone (PTH), 17β-estradiol (E2) or vehicle. KO mice displayed trabecular bone loss, diminished osteoid formation and reduced biomechanical strength compared with control (expressing Bmp2 and Bmp4). Both osteoblast and osteoclast functions were impaired in KO mice. Bone histomorphomtery and serum parameters established a low turnover bone loss in KO mice. Bone regeneration at the drill-hole site in KO mice was lower than control. However, deletion of Bmp2 gene alone had no effect on skeleton, an outcome similar to that reported previously for deletion of Bmp4 gene. Both PTH and E2 resulted in skeletal preservation in control-OVX, whereas in KO-OVX, E2 but not PTH was effective which suggested that the skeletal action of PTH required Bmp ligands but E2 did not. To determine cellular effects of Bmp2 and Bmp4, we used bone marrow stromal cells in which PTH but not E2 stimulated both Bmp2 and Bmp4 synthesis leading to increased Smad1/5 phosphorylation. Taken together, we conclude that Bmp2 and Bmp4 are essential for maintaining adult skeletal homeostasis and mediating the anabolic action of PTH.

Fibroblast growth factor receptor 3 deficiency does not impair the osteoanabolic action of parathyroid hormone on mice

Fibroblast growth factor receptor 3 deficiency does not impair the osteoanabolic action of parathyroid hormone on mice

Fgf23 and parathyroid hormone signaling interact in kidney and bone

Fibroblast growth factor-23 (FGF23) is a bone-derived hormone, suppressing renal phosphate reabsorption and vitamin D hormone synthesis in proximal tubules, and stimulating calcium reabsorption in distal tubules of the kidney. Here, we analyzed the long term sequelae of deficient Fgf23 signaling on bone and mineral metabolism in 9-month-old mice lacking both Fgf23 or Klotho and a functioning vitamin D receptor (VDR). To prevent hypocalcemia in VDR deficient mice, all mice were kept on a rescue diet enriched with calcium, phosphate, and lactose. VDR mutants were normocalcemic and normophosphatemic, and had normal tibial bone mineral density. Relative to VDR mutants, Fgf23/VDR and Klotho/VDR compound mutants were characterized by hypocalcemia, hyperphosphatemia, and very high serum parathyroid hormone (PTH). Despite ∼10-fold higher serum PTH levels in compound mutants, urinary excretion of phosphate and calcium as well as osteoclast numbers in bone remained unchanged relative to VDR mutants. The increase in plasma cAMP after hPTH(1–34) injection was similar in all genotypes. However, a 5-day infusion of hPTH(1–34) via osmotic minipumps resulted in reduced phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) in bone and kidney of Fgf23/VDR and Klotho/VDR compound mutants, relative to VDR and WT controls. Similarly, the PTH-mediated ERK1/2 phosphorylation was reduced in primary osteoblasts isolated from Fgf23 and Klotho deficient mice, but was restored by concomitant treatment with recombinant FGF23. Collectively, our data indicate that the phosphaturic, calcium-conserving, and bone resorption-stimulating actions of PTH are blunted by Fgf23 or Klotho deficiency. Hence, FGF23 may be an important modulator of PTH signaling in bone and kidney.

Prolonged Pharmacokinetic and Pharmacodynamic Actions of a Pegylated Parathyroid Hormone (1-34) Peptide Fragment.

Polyethylene glycol (PEG) addition can prolong the pharmacokinetic and pharmacodynamic actions of a bioactive peptide in vivo, in part by impeding rates of glomerular filtration. For parathyroid hormone (PTH) peptides, pegylation could help in exploring the actions of the hormone in the kidney; e.g., in dissecting the relative roles that filtered versus blood-borne PTH play in regulating phosphate transport. It could also lead to potential alternate forms of treatment for hypoparathyroidism. We thus synthesized the fluorescent pegylated PTH derivative [Lys13 (tetramethylrhodamine {TMR}), Cys35 (PEG-20,000 Da)]PTH(1-35) (PEG-PTHTMR ) and its non-pegylated counterpart [Lys13 (TMR), Cys35 ]PTH(1-35) (PTHTMR ) and assessed their properties in cells and in mice. In PTHR1-expressing HEK-293 cells, PEG-PTHTMR and PTHTMR exhibited similar potencies for inducing cAMP signaling, whereas when injected into mice, the pegylated analog persisted much longer in the circulation (>24 hours versus ∼ 1 hour) and induced markedly more prolonged calcemic and phosphaturic responses than did the non-pegylated control. Fluorescence microscopy analysis of kidney sections obtained from the injected mice revealed much less PEG-PTHTMR than PTHTMR on the luminal brush-border surfaces of renal proximal tubule cells (PTCs), on which PTH regulates phosphate transporter function, whereas immunostained phosphorylated PKA substrate, a marker of cAMP signaling, was increased to similar extents for the two ligands and for each, was localized to the basolateral portion of the PTCs. Pegylation of a bioactive PTH peptide thus led to prolonged pharmacokinetic/pharmacodynamic properties in vivo, as well as to new in vivo data that support a prominent role for PTH action at basolateral surfaces of renal proximal tubule cells. © 2016 American Society for Bone and Mineral Research.

IL-1β enhances inflammatory TH2 differentiation

IL-1β enhances inflammatory TH2 differentiation

PTH signaling mediates perilacunar remodeling during exercise

Mechanical loading and release of endogenous parathyroid hormone (PTH) during exercise facilitate the adaptation of bone. However, it remains unclear how exercise and PTH influence the composition of bone and how exercise and PTH-mediated compositional changes influence the mechanical properties of bone. Thus, the primary purpose of this study was to establish compositional changes within osteocytes' perilacunar region of cortical bone following exercise, and evaluate the influence of endogenous PTH signaling on this perilacunar adaptation. Raman spectroscopy, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) were used to evaluate tissue composition surrounding individual lacuna within the tibia of 19week old male mice exposed to treadmill running for 3weeks. As a result of exercise, tissue within the perilacunar region (within 0–5μm of the lacuna wall) had a lower mineral-to-matrix ratio (MMR) compared to sedentary controls. In addition, exercise also increased the carbonate-to-phosphate ratio (CPR) across both perilacunar and non-perilacunar regions (5–10μm and 10–15μm from the lacuna walls). Tibial post-yield work had a significant negative correlation with perilacunar MMR. Inhibition of PTH activity with PTH(7-34) demonstrated that perilacunar remodeling during exercise was dependent on the cellular response to endogenous PTH. The osteocytes' response to endogenous PTH during exercise was characterized by a significant reduction in SOST expression and significant increase in FGF-23 expression. The potential reduction in phosphate levels due to FGF-23 expression may explain the increase in carbonate substitution. Overall, this is the first study to demonstrate that adaptation in tissue composition is localized around individual osteocytes, may contribute to the changes in whole bone mechanics during exercise, and that PTH signaling during exercise contributes to these adaptations.

The Role of IL-17 and TH17 Cells in the Bone Catabolic Activity of PTH.

Osteoimmunology is field of research dedicated to the study of the interactions between the immune system and bone. Among the cells of the immune system that regulate the skeleton in health and disease are T lymphocytes, T cells secrete inflammatory/osteoclastogenic cytokines such as RANKL, TNF, and IL-17, as well as factors that stimulate bone formation, including Wnt ligands. In addition, T cells regulate the differentiation and life span of stromal cells via CD40L and other costimulatory molecules expressed on their surface. Consensus exists that parathyroid hormone (PTH) induces bone loss by increasing the production of RANKL by osteocytes and osteoblast. However, new evidence suggests that PTH expands Th17 cells and increases IL-17 levels in mice and humans. Studies in the mouse of further shown that Th17 cell produced IL-17 acts as an “upstream cytokine” that increases the sensitivity of osteoblasts and osteocytes to PTH. As a result, PTH stimulates osteocytic and osteoblastic release of RANKL. Therefore, PTH cause bone loss only in the presence of IL-17 signaling. This article reviews the evidence that the effects of PTH are mediated not only by osteoblasts and osteocytes, but also T cells and IL-17.