PTHrP attenuates spontaneous contractions in detrusor smooth muscle of the rat bladder by activating spontaneous transient outward potassium currents

Parathyroid hormone-related protein (PTHrP) released from detrusor smooth muscle (DSM) cells upon bladder distension attenuates spontaneous phasic contractions (SPCs) in DSM and associated afferent firing to facilitate urine storage. Here, we investigate the mechanisms underlying PTHrP-induced inhibition of SPCs, focusing on large-conductance Ca2+-activated K+ channels (BK channels) that play a central role in stabilizing DSM excitability. Perforated patch-clamp techniques were applied to DSM cells of the rat bladder dispersed using collagenase. Isometric tension changes were recorded from DSM strips, while intracellular Ca2+ dynamics were visualized using Cal520 AM -loaded DSM bundles. DSM cells developed spontaneous transient outward potassium currents (STOCs) arising from the opening of BK channels. PTHrP (10 nM) increased the frequency of STOCs without affecting their amplitude at a holding potential of - 30 mV but not - 40 mV. PTHrP enlarged depolarization-induced, BK-mediated outward currents at membrane potentials positive to + 20 mV in a manner sensitive to iberiotoxin (100 nM), the BK channel blocker. The PTHrP-induced increases in BK currents were also prevented by inhibitors of sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) (CPA 10 µM), L-type voltage-dependent Ca2+ channel (LVDCC) (nifedipine 3 µM) or adenylyl cyclase (SQ22536 100 µM). PTHrP had no effect on depolarization-induced LVDCC currents. PTHrP suppressed and slowed SPCs in an iberiotoxin (100 nM)-sensitive manner. PTHrP also reduced the number of Ca2+ spikes during each burst of spontaneous Ca2+ transients. In conclusion, PTHrP accelerates STOCs discharge presumably by facilitating SR Ca2+ release which prematurely terminates Ca2+ transient bursts resulting in the attenuation of SPCs.

Parathyroid hormone related-protein (PTHrP) in tissues with poor prognosis in prostate cancer patients

BACKGROUND

Parathyroid hormone-related peptide (PTHrP) is known to have a pivotal role in the progression of various solid tumors, among which prostate cancer stands out. However, the extent of PTHrP expression and its clinical implications in prostate cancer patients remain shrouded in obscurity. The primary objective of this research endeavor was to shed light on the relevance of PTHrP in the context of prostate cancer patients and to uncover the potential underlying mechanisms.

METHODS

The expression of PTHrP, E-cadherin, and vimentin in tumor tissues of 88 prostate cancer patients was evaluated by immunohistochemical technique. Subsequently, the associations between PTHrP and clinicopathological parameters and prognosis of patients with prostate cancer were analyzed.

RESULTS

Immunohistochemical analysis showed that the expression rates of PTHrP, E-cadherin, and vimentin in prostate cancer tissues were 95.5%, 88.6%, and 84.1%, respectively. Patients with a high level of PTHrP had a decreased expression of E-cadherin (P = .013) and an increased expression of vimentin (P = .010) compared with patients with a low level of PTHrP. Besides, the high expression of PTHrP was significantly correlated with a higher level of initial prostate-specific antigen (P = .026), positive lymph node metastasis (P = .010), osseous metastasis (P = .004), and Gleason score (P = .026). Moreover, patients with a high level of PTHrP had shorter progression-free survival (P = .002) than patients with a low level of PTHrP.

CONCLUSION

The present study indicates that PTHrP is associated with risk factors of poor outcomes in prostate cancer, while epithelial-mesenchymal transition may be involved in this process.

PTHrP intracrine actions divergently influence breast cancer growth through p27 and LIFR

The role of parathyroid hormone (PTH)-related protein (PTHrP) in breast cancer remains controversial, with reports of PTHrP inhibiting or promoting primary tumor growth in preclinical studies. Here, we provide insight into these conflicting findings by assessing the role of specific biological domains of PTHrP in tumor progression through stable expression of PTHrP (-36-139aa) or truncated forms with deletion of the nuclear localization sequence (NLS) alone or in combination with the C-terminus. Although the full-length PTHrP molecule (-36-139aa) did not alter tumorigenesis, PTHrP lacking the NLS alone accelerated primary tumor growth by downregulating p27, while PTHrP lacking the NLS and C-terminus repressed tumor growth through p27 induction driven by the tumor suppressor leukemia inhibitory factor receptor (LIFR). Induction of p27 by PTHrP lacking the NLS and C-terminus persisted in bone disseminated cells, but did not prevent metastatic outgrowth, in contrast to the primary tumor site. These data suggest that the PTHrP NLS functions as a tumor suppressor, while the PTHrP C-terminus may act as an oncogenic switch to promote tumor progression through differential regulation of p27 signaling.

Local injection of abaloparatide promotes mandibular condyle lengthening in adolescent rats via enhancing chondrogenesis and ossification

BACKGROUND

Mandibular condylar hypoplasia negatively affects patient's facial appearance and dentofacial function.

OBJECTIVE

To investigate the effect of local injection of the drug abaloparatide (ABL), an analogue of parathyroid hormone related protein (PTHrP), on promoting lengthening of the mandibular condyle.

METHODS

Thirty adolescent male Sprague-Dawley rats were randomly divided into two groups, which received the injection of ABL or normal saline (the control) every 3 days in the temporomandibular joint (TMJ) cavity. Cone-beam computed tomography and immunohistochemistry assays were performed at 2, 4 and 6 weeks since the injection. Mandibular condylar chondrocytes (MCC) and pre-osteoblasts were treated with ABL or PBS, followed by the CCK-8 detection, IC50, real-time PCR assay, Western Blot and immunofluorescence staining.

RESULTS

In vivo, compared with the control, the ABL group significantly increased the mandibular condylar process length (by 1.34 ± 0.59 mm at 6 weeks), the thickness of the cartilage layer, and enhanced the matrix synthesis. The ABL group had significant up-regulation of SOX 9, COL II, PTHrP and PTH1R, down-regulation of COL X in the cartilage, up-regulation of RUNX 2, and unchanged osteoclastogenesis in the subchondral bone. In vitro, the intra-TMJ injection of ABL promoted the MCC proliferation, with up-regulated expression of chondrogenic genes, and enhanced osteogenic differentiation of the pre-osteoblasts.

CONCLUSIONS

Intra-TMJ injection of abaloparatide promotes mandibular condyle lengthening in the adolescent rats via enhancing chondrogenesis in the mandibular condylar cartilage and ossification in the subchondral bone.

Hedgehog activation promotes osteogenic fates of growth plate resting zone chondrocytes through transient clonal competency

The resting zone of the postnatal growth plate is organized by slow-cycling chondrocytes expressing parathyroid hormone-related protein (PTHrP), which include a subgroup of skeletal stem cells that contribute to the formation of columnar chondrocytes. The PTHrP-Indian hedgehog feedback regulation is essential for sustaining growth plate activities; however, molecular mechanisms regulating cell fates of PTHrP+ resting chondrocytes and their eventual transformation into osteoblasts remain largely undefined. Here, in a mouse model, we specifically activated Hedgehog signaling in PTHrP+ resting chondrocytes and traced the fate of their descendants using a tamoxifen-inducible Pthrp-creER line with patched-1-floxed and tdTomato reporter alleles. Hedgehog-activated PTHrP+ chondrocytes formed large, concentric, clonally expanded cell populations within the resting zone ("patched roses") and generated significantly wider columns of chondrocytes, resulting in hyperplasia of the growth plate. Interestingly, Hedgehog-activated PTHrP+ cell descendants migrated away from the growth plate and transformed into trabecular osteoblasts in the diaphyseal marrow space in the long term. Therefore, Hedgehog activation drives resting zone chondrocytes into transit-amplifying states as proliferating chondrocytes and eventually converts these cells into osteoblasts, unraveling a potentially novel Hedgehog-mediated mechanism that facilitates osteogenic cell fates of PTHrP+ skeletal stem cells.

Exploring dual effects of dinutuximab beta on cell death and proliferation of insulinoma

Insulinoma INS-1 cells are pancreatic beta cell tumors. Dinutuximab beta (DB) is a monoclonal antibody used in the treatment of neuroblastoma. The aim of this study is to investigate the effects of DB on pancreatic beta cell tumors at the molecular level. DB (Qarziba®) was available from EUSA Pharma. Streptozotocin (STZ) was used induce to cell cytotoxicity. DB was applied to the cells before or after the STZ application. KCND3, KCNN4, KCNK1, and PTHrP gene expression levels were analyzed by q-RT-PCR, and protein levels were analyzed by Western blotting. Analysis of glucose-stimulated insulin secretion was performed. Ca+2 and CA19-9 levels were determined by the ELISA kit. PERK, CHOP, HSP90, p-c-Jun, p-Atf2, and p-Elk1 protein levels were analyzed by simple WES. Decreased KCND3, KCNK1, and PTHrP protein levels and increased KCND3, KCNN4, KCNK1, and PTHrP gene expression levels were observed with DB applied after STZ application. Cell dysfunction was detected with DB applied before and after STZ application. Ca19-9 and Ca+2 levels were increased with DB applied after STZ application. PERK, CHOP, and p-Elk1 levels decreased, while HSP90 levels increased with DB applied after STZ application. CHOP, p-Akt-2, and p-c-Jun levels increased in the DB group. As a result, INS-1 cells go to cell death via the ERK signaling pathway without ER stress and release insulin with the decrease of K+ channels and an increase in Ca+2 levels with DB applied after STZ application. Moreover, the cells proliferate via JNK signaling with DB application. DB holds promise for the treatment of insulinoma. The study should be supported by in vivo studies.

Comparative study in estrogen-depleted mice identifies skeletal and osteocyte transcriptomic responses to abaloparatide and teriparatide

Osteocytes express parathyroid hormone (PTH)/PTH-related protein (PTHrP) receptors and respond to the PTHrP analog abaloparatide (ABL) and to the PTH 1-34 fragment teriparatide (TPTD), which are used to treat osteoporosis. Several studies indicate overlapping but distinct skeletal responses to ABL or TPTD, but their effects on cortical bone may differ. Little is known about their differential effects on osteocytes. We compared cortical osteocyte and skeletal responses to ABL and TPTD in sham-operated and ovariectomized mice. Administered 7 weeks after ovariectomy for 4 weeks at a dose of 40 μg/kg/d, TPTD and ABL had similar effects on trabecular bone, but ABL showed stronger effects in cortical bone. In cortical osteocytes, both treatments decreased lacunar area, reflecting altered peri-lacunar remodeling favoring matrix accumulation. Osteocyte RNA-Seq revealed that several genes and pathways were altered by ovariectomy and affected similarly by TPTD and ABL. Notwithstanding, several signaling pathways were uniquely regulated by ABL. Thus, in mice, TPTD and ABL induced a positive osteocyte peri-lacunar remodeling balance, but ABL induced stronger cortical responses and affected the osteocyte transcriptome differently. We concluded that ABL affected the cortical osteocyte transcriptome in a manner subtly different from TPTD, resulting in more beneficial remodeling/modeling changes and homeostasis of the cortex.

Cranial Neural Crest Specific Deletion of Alpl (TNAP) via P0-Cre Causes Abnormal Chondrocyte Maturation and Deficient Cranial Base Growth

Bone growth plate abnormalities and skull shape defects are seen in hypophosphatasia, a heritable disorder in humans that occurs due to the deficiency of tissue nonspecific alkaline phosphatase (TNAP, Alpl) enzyme activity. The abnormal development of the cranial base growth plates (synchondroses) and abnormal skull shapes have also been demonstrated in global Alpl-/- mice. To distinguish local vs. systemic effects of TNAP on skull development, we utilized P0-Cre to knockout Alpl only in cranial neural crest-derived tissues using Alpl flox mice. Here, we show that Alpl deficiency using P0-Cre in cranial neural crest leads to skull shape defects and the deficient growth of the intersphenoid synchondrosis (ISS). ISS chondrocyte abnormalities included increased proliferation in resting and proliferative zones with decreased apoptosis in hypertrophic zones. ColX expression was increased, which is indicative of premature differentiation in the absence of Alpl. Sox9 expression was increased in both the resting and prehypertrophic zones of mutant mice. The expression of Parathyroid hormone related protein (PTHrP) and Indian hedgehog homolog (IHH) were also increased. Finally, cranial base organ culture revealed that inorganic phosphate (Pi) and pyrophosphate (PPi) have specific effects on cell signaling and phenotype changes in the ISS. Together, these results demonstrate that the TNAP expression downstream of Alpl in growth plate chondrocytes is essential for normal development, and that the mechanism likely involves Sox9, PTHrP, IHH and PPi.

Neonatal and Early Infancy Features of Patients With Inactivating PTH/PTHrP Signaling Disorders/Pseudohypoparathyroidism

BACKGROUND

Pseudohypoparathyroidism (PHP) and related disorders newly referred to as inactivating PTH/PTHrP signaling disorders (iPPSD) are rare endocrine diseases. Many clinical features including obesity, neurocognitive impairment, brachydactyly, short stature, parathyroid hormone (PTH) resistance, and resistance to other hormones such as thyroid-stimulating hormone (TSH) have been well described, yet they refer mainly to the full development of the disease during late childhood and adulthood.

OBJECTIVE

A significant delay in diagnosis has been reported; therefore, our objective is to increase awareness on neonatal and early infancy presentation of the diseases. To do so, we analyzed a large cohort of iPPSD/PHP patients.

METHODS

We included 136 patients diagnosed with iPPSD/PHP. We retrospectively collected data on birth and investigated the rate of neonatal complications occurring in each iPPSD/PHP category within the first month of life.

RESULTS

Overall 36% of patients presented at least one neonatal complication, far more than the general population; when considering only the patients with iPPSD2/PHP1A, it reached 47% of the patients. Neonatal hypoglycemia and transient respiratory distress appeared significantly frequent in this latter group, ie, 10.5% and 18.4%, respectively. The presence of neonatal features was associated with earlier resistance to TSH (P < 0.001) and with the development of neurocognitive impairment (P = 0.02) or constipation (P = 0.04) later in life.

CONCLUSION

Our findings suggest that iPPSD/PHP and especially iPPSD2/PHP1A newborns require specific care at birth because of an increased risk of neonatal complications. These complications may predict a more severe course of the disease; however, they are unspecific which likely explains the diagnostic delay.

Malignancy-related Hypercalcemia Caused by Metameric Cutaneous Metastasis of Parathyroid Hormone-related Protein-producing Bladder Carcinoma with Squamous Cell Differentiation: An Autopsy Case of Cobb Syndrome

A 74-year-old woman was admitted with hypercalcemia and prolonged disturbance of consciousness. The left buttock to the anterior aspect of the left thigh was swollen and erythematous, with a collection of 1.0-cm large, firm, elastic nodules distributed in a zosteriform pattern in the L1-L4 region. Based on autopsy findings, a very rare case of Cobb syndrome was diagnosed due to a spinal vascular malformation at the Th12-L4 level and L5 vertebral hemangioma. Cobb syndrome-associated cutaneous metastasis extending along the same metamere was complicated by immunohistochemically proven parathyroid hormone-related protein-producing advanced bladder carcinoma in this case.

Abaloparatide Maintains Normal Rat Blood Calcium Level in Part Via 1,25-Dihydroxyvitamin D/osteocalcin Signaling Pathway

The PTH-related peptide(1-34) analog, abaloparatide (ABL), is the second anabolic drug available for the treatment of osteoporosis. Previous research demonstrated that ABL had a potent anabolic effect but caused hypercalcemia at a significantly lower rate. However, the mechanism by which ABL maintains the stability of blood calcium levels remains poorly understood. Our in vivo data showed that ABL treatment (40 µg/kg/day for 7 days) significantly increased rat blood level of 1,25-dihydroxyvitamin D [1,25-(OH)2D] without raising the blood calcium value. ABL also significantly augmented the carboxylated osteocalcin (Gla-Ocn) in the blood and bone that is synthesized by osteoblasts, and increased noncarboxylated Ocn, which is released from the bone matrix to the circulation because of osteoclast activation. The in vitro data showed that ABL (10 nM for 24 hours) had little direct effects on 1,25-(OH)2D synthesis and Gla-Ocn formation in nonrenal cells (rat osteoblast-like cells). However, ABL significantly promoted both 1,25-(OH)2D and Gla-Ocn formation when 25-hydroxyvitamin D, the substrate of 1α-hydroxylase, was added to the cells. Thus, the increased 1,25-(OH)2D levels in rats treated by ABL result in high levels of Gla-Ocn and transient calcium increase in the circulation. Gla-Ocn then mediates calcium ions in the extracellular fluid at bone sites to bind to hydroxyapatite at bone surfaces. This regulation by Gla-Ocn at least, in part, maintains the stability of blood calcium levels during ABL treatment. We conclude that the signaling pathway of ABL/1,25-(OH)2D/Gla-Ocn contributes to calcium homeostasis and may help understand the mechanism of ABL for osteoporosis therapy.

CaSR modulates proliferation of the superficial zone cells in temporomandibular joint cartilage via the PTHrP nuclear localization sequence

The superficial zone cells in mandibular condylar cartilage are proliferative. The present purpose was to delineate the relation of calcium-sensing receptor (CaSR) and parathyroid hormone-related peptide nuclear localization sequence (PTHrP87-139 ), and their role in the proliferation behaviors of the superficial zone cells. A gain- and loss-of-function strategy were used in an in vitro fluid flow shear stress (FFSS) model and an in vivo bilateral elevation bite model which showed mandibular condylar cartilage thickening. CaSR and PTHrP87-139 were modulated through treating the isolated superficial zone cells with activator/SiRNA and via deleting CaSR or parathyroid hormone-related peptide (PTHrP) gene in mice with the promoter gene of proteoglycan 4 (Prg4-CreERT2 ) in the tamoxifen-inducible pattern with or without additional injection of Cinacalcet, the CaSR agonist, or PTHrP87-139 peptide. FFSS stimulated CaSR and PTHrP expression, and accelerated proliferation of the Prg4-expressing superficial zone cells, in which process CaSR acted as an up-streamer of PTHrP. Proteoglycan 4 specific knockout of CaSR or PTHrP reduced the cartilage thickness, suppressed the proliferation and early differentiation of the superficial zone cells, and inhibited cartilage thickening and matrix production promoted by bilateral elevation bite. Injections of CaSR agonist Cinacalcet could not improve the phenotype caused by PTHrP mutation. Injections of PTHrP87-139 peptide rescued the cartilage from knockout of CaSR gene. CaSR modulates proliferation of the superficial zone cells in mandibular condylar cartilage through activation of PTHrP nuclear localization sequence. Our data support the therapeutic target of CaSR in promoting PTHrP production in superficial zone cartilage.

Altered Signaling and Desensitization Responses in PTH1R Mutants Associated with Eiken Syndrome

The parathyroid hormone receptor type 1 (PTH1R) is a G protein-coupled receptor that plays key roles in regulating calcium homeostasis and skeletal development via binding the ligands, PTH and PTH-related protein (PTHrP), respectively. Eiken syndrome is a rare disease of delayed bone mineralization caused by homozygous PTH1R mutations. Of the three mutations identified so far, R485X, truncates the PTH1R C-terminal tail, while E35K and Y134S alter residues in the receptor's amino-terminal extracellular domain. Here, using a variety of cell-based assays, we show that R485X increases the receptor's basal rate of cAMP signaling and decreases its capacity to recruit β-arrestin2 upon ligand stimulation. The E35K and Y134S mutations each weaken the binding of PTHrP leading to impaired β-arrestin2 recruitment and desensitization of cAMP signaling response to PTHrP but not PTH. Our findings support a critical role for interaction with β-arrestin in the mechanism by which the PTH1R regulates bone formation.

Endogenous ligand recognition and structural transition of a human PTH receptor

Endogenous parathyroid hormone (PTH) and PTH-related peptide (PTHrP) bind to the parathyroid hormone receptor 1 (PTH1R) and activate the stimulatory G-protein (Gs) signaling pathway. Intriguingly, the two ligands have distinct signaling and physiological properties: PTH evokes prolonged Gs activation, whereas PTHrP evokes transient Gs activation with reduced bone-resorption effects. The distinct molecular actions are ascribed to the differences in ligand recognition and dissociation kinetics. Here, we report cryoelectron microscopic structures of six forms of the human PTH1R-Gs complex in the presence of PTH or PTHrP at resolutions of 2.8 -4.1 Å. A comparison of the PTH-bound and PTHrP-bound structures reveals distinct ligand-receptor interactions underlying the ligand affinity and selectivity. Furthermore, five distinct PTH-bound structures, combined with computational analyses, provide insights into the unique and complex process of ligand dissociation from the receptor and shed light on the distinct durations of signaling induced by PTH and PTHrP.

Parathyroid hormone-related protein (PTHrP) and malignancy

PTHrP (parathyroid hormone related protein) is an important mediator of malignancy-related tumor progression and hypercalcemia that shares considerable homology and functionality with parathyroid hormone. In this chapter, we review what has been elucidated to date regarding PTHrP's role in malignancies. Starting with a review of calcium metabolism and regulation, we then summarize the discovery and structure of PTHrP and development of sensitive immunoassays for specific measurement. Subsequently, we explore its role in tumor progression, with emphasis on the primary tumor as well as skeletal and non-osseus metastases. We then consider the clinical implications of PTHrP in cancer before concluding with a discussion of both established and potential treatments for malignancy associated hypercalcemia and bone metastases.

Cranial Base Synchondrosis Lacks PTHrP-Expressing Column-Forming Chondrocytes

The cranial base contains a special type of growth plate termed the synchondrosis, which functions as the growth center of the skull. The synchondrosis is composed of bidirectional opposite-facing layers of resting, proliferating, and hypertrophic chondrocytes, and lacks the secondary ossification center. In long bones, the resting zone of the epiphyseal growth plate houses a population of parathyroid hormone-related protein (PTHrP)-expressing chondrocytes that contribute to the formation of columnar chondrocytes. Whether PTHrP⁺ chondrocytes in the synchondrosis possess similar functions remains undefined. Using Pthrp-mCherry knock-in mice, we found that PTHrP⁺ chondrocytes predominantly occupied the lateral wedge-shaped area of the synchondrosis, unlike those in the femoral growth plate that reside in the resting zone within the epiphysis. In vivo cell-lineage analyses using a tamoxifen-inducible Pthrp-creER line revealed that PTHrP⁺ chondrocytes failed to establish columnar chondrocytes in the synchondrosis. Therefore, PTHrP⁺ chondrocytes in the synchondrosis do not possess column-forming capabilities, unlike those in the resting zone of the long bone growth plate. These findings support the importance of the secondary ossification center within the long bone epiphysis in establishing the stem cell niche for PTHrP⁺ chondrocytes, the absence of which may explain the lack of column-forming capabilities of PTHrP⁺ chondrocytes in the cranial base synchondrosis.

Involvement of Met receptor pathway in aggressive behavior of colorectal cancer cells induced by parathyroid hormone-related peptide

BACKGROUND

Parathyroid hormone-related peptide (PTHrP) plays a key role in the development and progression of many tumors. We found that in colorectal cancer (CRC) HCT116 cells, the binding of PTHrP to its receptor PTHR type 1 (PTHR1) activates events associated with an aggressive phenotype. In HCT116 cell xenografts, PTHrP modulates the expression of molecular markers linked to tumor progression. Empirical evidence suggests that the Met receptor is involved in the development and evolution of CRC. Based on these data, we hypothesized that the signaling pathway trigged by PTHrP could be involved in the transactivation of Met and consequently in the aggressive behavior of CRC cells.

AIM

To elucidate the relationship among PTHR1, PTHrP, and Met in CRC models.

METHODS

For in vitro assays, HCT116 and Caco-2 cells derived from human CRC were incubated in the absence or presence of PTHrP (1-34) (10^-8 M). Where indicated, cells were pre-incubated with specific kinase inhibitors or dimethylsulfoxide, the vehicle of the inhibitors. The protein levels were evaluated by Western blot technique. Real-time polymerase chain reaction (RT-qPCR) was carried out to determine the changes in gene expression. Wound healing assay and morphological monitoring were performed to evaluate cell migration and changes related to the epithelial-mesenchymal transition (EMT), respectively. The number of viable HCT116 cells was counted by trypan blue dye exclusion test to evaluate the effects of irinotecan (CPT-11), oxaliplatin (OXA), or doxorubicin (DOXO) with or without PTHrP. For in vivo tests, HCT116 cell xenografts on 6-wk-old male N:NIH (S)_nu mice received daily intratumoral injections of PTHrP (40 μg/kg) in 100 μL phosphate-buffered saline (PBS) or the vehicle (PBS) as a control during 20 d. Humanitarian slaughter was carried out and the tumors were removed, weighed, and fixed in a 4% formaldehyde solution for subsequent treatment by immunoassays. To evaluate the expression of molecular markers in human tumor samples, we studied 23 specimens obtained from CRC patients which were treated at the Hospital Interzonal de Graves y Agudos Dr. José Penna (Bahía Blanca, Buenos Aires, Argentina) and the Hospital Provincial de Neuquén (Neuquén, Neuquén, Argentina) from January 1990 to December 2007. Seven cases with normal colorectal tissues were assigned to the control group. Tumor tissue samples and clinical histories of patients were analyzed. Paraffin-embedded blocks from primary tumors were reviewed by hematoxylin-eosin staining technique; subsequently, representative histological samples were selected from each patient. From each paraffin block, tumor sections were stained for immunohistochemical detection. The statistical significance of differences was analyzed using proper statistical analysis. The results were considered statistically significant at P < 0.05.

RESULTS

By Western blot analysis and using total Met antibody, we found that PTHrP regulated Met expression in HCT116 cells but not in Caco-2 cells. In HCT116 cells, Met protein levels increased at 30 min (P < 0.01) and at 20 h (P < 0.01) whereas the levels diminished at 3 min (P < 0.05), 10 min (P < 0.01), and 1 h to 5 h (P < 0.01) of PTHrP treatment. Using an active Met antibody, we found that where the protein levels of total Met decreased (3 min, 10 min, and 60 min of PTHrP exposure), the status of phosphorylated/activated Met increased (P < 0.01) at the same time, suggesting that Met undergoes proteasomal degradation after its phosphorylation/activation by PTHrP. The increment of its protein level after these decreases (at 30 min and 20 h) suggests a modulation of Met expression by PTHrP in order to improve Met levels and this idea is supported by our observation that the cytokine increased Met mRNA levels at least at 15 min in HCT116 cells as revealed by RT-qPCR analysis (P < 0.05). We then proceeded to evaluate the signaling pathways that mediate the phosphorylation/ activation of Met induced by PTHrP in HCT116 cells. By Western blot technique, we observed that PP1, a specific inhibitor of the activation of the proto-oncogene protein tyrosine kinase Src, blocked the effect of PTHrP on Met phosphorylation (P < 0.05). Furthermore, the selective inhibition of the ERK 1/2 mitogen-activated protein kinase (ERK 1/2 MAPK) using PD98059 and the p38 MAPK using SB203580 diminished the effect of PTHrP on Met phosphorylation/activation (P < 0.05). Using SU11274, the specific inhibitor of Met activation, and trypan blue dye exclusion test, Western blot, wound healing assay, and morphological analysis with a microscope, we observed the reversal of cell events induced by PTHrP such as cell proliferation (P < 0.05), migration (P < 0.05), and the EMT program (P < 0.01) in HCT116 cells. Also, PTHrP favored the chemoresistance to CPT-11 (P < 0.001), OXA (P < 0.01), and DOXO (P < 0.01) through the Met pathway. Taken together, these findings suggest that Met activated by PTHrP participates in events associated with the aggressive phenotype of CRC cells. By immunohistochemical analysis, we found that PTHrP in HCT116 cell xenografts enhanced the protein expression of Met (0.190 ± 0.014) compared to tumors from control mice (0.110 ± 0.012; P < 0.05) and of its own receptor (2.27 ± 0.20) compared to tumors from control mice (1.98 ± 0.14; P < 0.01). Finally, assuming that the changes in the expression of PTHrP and its receptor are directly correlated, we investigated the expression of both Met and PTHR1 in biopsies of CRC patients by immunohistochemical analysis. Comparing histologically differentiated tumors with respect to those less differentiated, we found that the labeling intensity for Met and PTHR1 increased and diminished in a gradual manner, respectively (P < 0.05).

CONCLUSION

PTHrP acts through the Met pathway in CRC cells and regulates Met expression in a CRC animal model. More basic and clinical studies are needed to further evaluate the PTHrP/Met relationship.

Actions of Parathyroid Hormone Ligand Analogues in Humanized PTH1R Knockin Mice

Rodent models are commonly used to evaluate parathyroid hormone (PTH) and PTH-related protein (PTHrP) ligands and analogues for their pharmacologic activities and potential therapeutic utility toward diseases of bone and mineral ion metabolism. Divergence, however, in the amino acid sequences of rodent and human PTH receptors (rat and mouse PTH1Rs are 91% identical to the human PTH1R) can lead to differences in receptor-binding and signaling potencies for such ligands when assessed on rodent vs human PTH1Rs, as shown by cell-based assays in vitro. This introduces an element of uncertainty in the accuracy of rodent models for performing such preclinical evaluations. To overcome this potential uncertainty, we used a homologous recombination-based knockin (KI) approach to generate a mouse (in-host strain C57Bl/6N) in which complementary DNA encoding the human PTH1R replaces a segment (exon 4) of the murine PTH1R gene so that the human and not the mouse PTH1R protein is expressed. Expression is directed by the endogenous mouse promoter and hence occurs in all biologically relevant cells and tissues and at appropriate levels. The resulting homozygous hPTH1R-KI (humanized) mice were healthy over at least 10 generations and showed functional responses to injected PTH analog peptides that are consistent with a fully functional human PTH1R in target bone and kidney cells. The initial evaluation of these mice and their potential utility for predicting behavior of PTH analogues in humans is reported here.

Mammary homeostasis in the mother-offspring dyad

Homeostasis during lactation is a special case in which the unit for regulation is a dyad comprising the mother and her currently nursing offspring (the mother-offspring dyad). This arrangement is not a trivial. A litter of mice can have a mass greater than the mother and nutrient demands that far exceed her. Homeostasis for milk secretion, appetite, and calcium metabolism must come under integrated control, responding seamlessly to the needs of the mother and the offspring. Serotonin (5-HT) is a primary local regulator of mammary homeostasis. 5-HT synthesis in the mammary epithelium is high during lactation and increases during milk stasis. Two important functions are attributed to the 5-HT system. Firstly, when alveolar spaces are filled with milk 5-HT inhibits milk secretion and opens tight junctions. This feedback induces early phases of involution. Secondly, 5-HT induces synthesis and secretion of parathyroid hormone-related peptide (PTHrP).

Exogenous growth hormone functionally alleviates glucocorticoid-induced longitudinal bone growth retardation in male rats by activating the Ihh/PTHrP signaling pathway

Glucocorticoid (GC)-induced longitudinal bone growth retardation is a common and severe adverse effect in pediatric patients receiving GC immunosuppressive therapy. Molecular mechanisms underlying GC-induced growth inhibition are unclear. GC withdrawal following short-term high-dose use is common, including in the immediate post-transplant period. However, whether skeleton growth recovery is sufficient or whether growth-promoting therapy is required following GC withdrawal is unknown. The aim of this study was to investigate the effect of exogenous growth hormone (GH) on growth plate impairment in GC-induced longitudinal bone growth retardation. Here, apoptotic chondrocytes in the hypertrophic layer of growth plates increased whereas Indian Hedgehog (Ihh) and Parathyroid Hormone Related Peptide (PTHrP) protein levels in the growth plate decreased following GC exposure. The hypertrophic zone of the growth plate expanded following GC withdrawal. Subcutaneously injected GH penetrated the growth plate and modified its organization in rats following GC withdrawal. Ihh and PTHrP expression in GC-induced apoptotic chondrocytes decreased in vitro. GH promoted chondrocyte proliferation by activating Ihh/PTHrP signaling. Downregulating Ihh using specific siRNAs increased chondrocyte apoptosis and inhibited PTHrP, Sox9, and type II collagen (Col2a1) protein expression. GH inhibited apoptosis of Ihh-deficient growth plate chondrocytes by upregulating PTHrP, Sox9, and Col2a1 expression. Thus, reversal of the effect of GC on growth plate impairment following its withdrawal is insufficient, and exogenous GH provides growth plate chondral protection and improved longitudinal growth following GC withdrawal by acting on the Ihh/PTHrP pathway.

Parathyroid hormone-related protein prevents high-fat-diet-induced obesity, hepatic steatosis and insulin resistance in mice

Obesity, closely related to systematic metabolic disorders, has become a major public health problem in recent decades. Here, we aimed to study the function of Parathyroid hormone-related protein (PTHrP) on high fat diet (HFD) induced murine obesity. Male C57BL/6J mice were transduced with adeno-associated virus vector encoding PTHrP (AAV-PTHrP) or adeno-associated virus control vector (AAV-Vehicle), following with HFD for 8 weeks. In addition, mice without transduction were fed on normal diet or HFD, respectively. Histological, metabolic and biochemical changes were detected. At the endpoint of experiment, body weight of mice treated with AAV-PTHrP did not increase as much as mice with AAV-Vehicle, but similar as mice with normal diet. Food efficiency ratio and weight of interscapular brown adipose tissue and epididymal white adipose tissue in mice overexpressed PTHrP were also lower than mice transducted with AAV-Vehicle. Besides, administration of AAV-PTHrP inhibited HFD-induced adipocyte hypertrophy. Protein level of PKA signaling pathway and thermogenic gene in adipose tissue exhibited a significant raise in HFD + AAV-PTHrP group, whereas transcription of inflammatory gene were decreased. Additionally, PTHrP overexpression ameliorated HFD-induced dyslipidemia, hepatic steatosis and insulin sensitivity. In HFD-induced murine obesity model, PTHrP is crucial to maintain metabolic homeostasis. PTHrP drives white adipose tissue browning and inhibits whitening of brown adipose tissue. Most importantly, PTHrP prevented HFD-induced obesity, hepatic steatosis and insulin resistance.

Pthlha and mechanical force control early patterning of growth zones in the zebrafish craniofacial skeleton

Secreted signals in patterning systems often induce repressive signals that shape their distributions in space and time. In developing growth plates (GPs) of endochondral long bones, Parathyroid hormone-like hormone (Pthlh) inhibits Indian hedgehog (Ihh) to form a negative-feedback loop that controls GP progression and bone size. Whether similar systems operate in other bones and how they arise during embryogenesis remain unclear. We show that Pthlha expression in the zebrafish craniofacial skeleton precedes chondrocyte differentiation and restricts where cells undergo hypertrophy, thereby initiating a future GP. Loss of Pthlha leads to an expansion of cells expressing a novel early marker of the hypertrophic zone (HZ), entpd5a, and later HZ markers, such as ihha, whereas local Pthlha misexpression induces ectopic entpd5a expression. Formation of this early pre-HZ correlates with onset of muscle contraction and requires mechanical force; paralysis leads to loss of entpd5a and ihha expression in the pre-HZ, mislocalized pthlha expression and no subsequent ossification. These results suggest that local Pthlh sources combined with force determine HZ locations, establishing the negative-feedback loop that later maintains GPs.

MiR-556-5p modulates migration, invasion, and epithelial-mesenchymal transition in breast cancer cells via targeting PTHrP

Breast cancer bone metastases may block normal bone remodeling and promote bone degradation, during which several signaling pathways and small non-coding miRNAs might all play a role. miRNAs and target mRNAs that might be associated with breast cancer bone metastasis were analyzed and selected using bioinformatics analyses based on online data. The 3' untranslated region of key factors associated with breast cancer metastasis were examined for candidate miRNA binding site using Targetscan. The predicted binding was validated. The specific effects of single miRNA and dynamic effects of the miRNA-mRNA axis on breast cancer cell metastasis were investigated. miR-556-5p was downregulated in breast cancer samples according to online datasets and experimental analyses. In breast cancer cells, miR-556-5p overexpression inhibited, whereas miR-556-5p inhibition promoted cancer cell invasion and migration. Among key factors associated with breast cancer bone metastasis, parathyroid hormone related protein (PTHrP) 3'UTR possessed miR-556-5p binding site. Through direct binding, miR-556-5p negatively regulated PTHrP expression. In breast cancer cell lines, miR-556-5p inhibition promoted, whereas PTHrP silencing suppressed cancer cell migration, invasion, and epithelial-mesenchymal transition; the effects of miR-556-5p inhibition were partially reversed by PTHrP silencing. In summary, miR-556-5p targets PTHrP to modulate the cell migration and invasion of breast cancer.

Parathyroid hormone-related protein in breast cancer bone metastasis

Parathyroid hormone-related protein (PTHrP) was discovered as the tumor product causing the humoral hypercalcemia of malignancy. Its structural similarity to the hormone, PTH, with 8 of the first 13 amino acids identical, was sufficient to explain the sharing by PTHrP and PTH of a common receptor, PTH1R, although the remainder of the sequences are unique. PTHrP has important roles in development of several organs, including breast and bone, and functions as a paracrine factor postnatally in these and other tissues. In addition to its hormonal role in cancer, PTHrP is produced by two thirds of primary breast cancers and 90% of bone metastases from breast cancer, leading to the concept that its production in bone by breast cancer cells promotes bone resorption, thus favoring tumor establishment and expansion, and an exit from tumor dormancy in bone through downregulation of leukemia inducing factor receptor (LIFR). Cancer production of PTHrP is increased by bone-derived growth factors, with particular attention paid to TGFβ, as well as by promoter-driven transcriptional effects, such as the hedgehog signaling factor, GLI2, and microenvironment effects including changes in underlying stiffness of substrates for cells. Although interest has been focused on PTHrP-induced bone resorption in bone metastasis, a mechanistically separate, protective effect against tumor progression has been proposed. Although there is conflicting mouse data, there are clinical studies suggesting that increased production of PTHrP by breast cancers confers upon them a less invasive phenotype, an effect distinct from the bone resorption-stimulating action that favors bone metastasis.

Calcium transport in male reproduction is possibly influenced by vitamin D and CaSR

Vitamin D is important for gonadal function in rodents, and improvement of vitamin D status in men with low sperm counts increases live birth rate. Vitamin D is a regulator of transcellular calcium transport in the intestine and kidney and may influence the dramatic changes in the luminal calcium concentration in epididymis. Here, we show spatial expression in the male reproductive tract of vitamin D receptor (VDR)-regulated factors involved in calcium transport: transient receptor potential vanilloid 5/6 , sodium/calcium exchanger 1, plasma membrane calcium ATPase 1, calbindin D9k, calcium-sensing receptor (CaSR), and parathyroid hormone-related peptide (PTHrP) in mouse and human testis and epididymis. Testicular Casr expression was lower in Vdr ablated mice compared with controls. Moreover, expression levels of Casr and Pthrp were strongly correlated in both testis and epididymis and Pthrp was suppressed by 1,25(OH)2D3 in a spermatogonial cell line. The expression of CaSR in epididymis may be of greater importance than in the gonad in mice as germ cell-specific Casr deficient mice had no major reproductive phenotype, and coincubation with a CaSR-agonist had no effect on human sperm-oocyte binding. In humans, seminal calcium concentration between 5 and 10 mM was associated with a higher fraction of motile and morphologically normal sperm cells, and the seminal calcium concentration was not associated with serum calcium levels. In conclusion, VDR regulates CaSR and PTHrP, and both factors may be involved in the regulation of calcium transport in the male reproductive tract with possible implications for sperm function and storage.

Rare Causes of Hypercalcemia: 2021 Update

CONTEXT

Primary hyperparathyroidism and malignancy are the etiologies in 90% of cases of hypercalcemia. When these entities are not the etiology of hypercalcemia, uncommon conditions need to be considered. In 2005, Jacobs and Bilezikian published a clinical review of rare causes of hypercalcemia, focusing on mechanisms and pathophysiology. This review is an updated synopsis of rare causes of hypercalcemia, extending the observations of the original article.

EVIDENCE ACQUISITION

Articles reporting rare associations between hypercalcemia and unusual conditions were identified through a comprehensive extensive PubMed-based search using the search terms "hypercalcemia" and "etiology," as well as examining the references in the identified case reports. We categorized the reports by adults vs pediatric and further categorized the adult reports based on etiology. Some included reports lacked definitive assessment of etiology and are reported as unknown mechanism with discussion of likely etiology.

EVIDENCE SYNTHESIS

There is a growing understanding of the breadth of unusual causes of hypercalcemia. When the cause of hypercalcemia is elusive, a focus on mechanism and review of prior reported cases is key to successful determination of the etiology.

CONCLUSIONS

The ever-expanding reports of patients with rare and even unknown mechanisms of hypercalcemia illustrate the need for continued investigation into the complexities of human calcium metabolism.

Chondrocytes in the resting zone of the growth plate are maintained in a Wnt-inhibitory environment

Chondrocytes in the resting zone of the postnatal growth plate are characterized by slow cell cycle progression, and encompass a population of parathyroid hormone-related protein (PTHrP)-expressing skeletal stem cells that contribute to the formation of columnar chondrocytes. However, how these chondrocytes are maintained in the resting zone remains undefined. We undertook a genetic pulse-chase approach to isolate slow cycling, label-retaining chondrocytes (LRCs) using a chondrocyte-specific doxycycline-controllable Tet-Off system regulating expression of histone 2B-linked GFP. Comparative RNA-seq analysis identified significant enrichment of inhibitors and activators for Wnt signaling in LRCs and non-LRCs, respectively. Activation of Wnt/β-catenin signaling in PTHrP+ resting chondrocytes using Pthlh-creER and Apc-floxed allele impaired their ability to form columnar chondrocytes. Therefore, slow-cycling chondrocytes are maintained in a Wnt-inhibitory environment within the resting zone, unraveling a novel mechanism regulating maintenance and differentiation of PTHrP+ skeletal stem cells of the postnatal growth plate.

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).

Role of SPARC in the epithelial-mesenchymal transition induced by PTHrP in human colon cancer cells

Parathyroid hormone-related peptide (PTHrP) exerts its effects on cells derived from colorectal cancer (CRC) and tumor microenvironment and is involved in processes requiring the epithelial-mesenchymal transition (EMT). Here, we report that PTHrP modulates factors expression and morphological changes associated with EMT in HCT116 cells from CRC. PTHrP increased the protein expression of SPARC, a factor involved in EMT, in HCT116 cells but not in Caco-2 cells also from CRC but with less aggressiveness. PTHrP also increased SPARC expression and its subsequent release from endothelial HMEC-1 cells. The conditioned media of PTHrP-treated HMEC-1 cells induced early changes related to EMT in HCT116 cells. Moreover, SPARC treatment on HCT116 cells potentiated PTHrP modulation in E-cadherin expression and cell migration. In vivo PTHrP also increased SPARC expression and decreased E-cadherin expression. These results suggest a novel PTHrP action on CRC progression involving the microenvironment in the modulation of events associated with EMT.

The Effect of Orally Supplemented Melatonin on Larval Performance and Skeletal Deformities in Farmed Gilthead Seabream (Sparus aurata)

The gilthead seabream larval rearing in continuous light is common in most Mediterranean hatcheries to stimulate larval length growth and increase food consumption. Several studies have shown that continuous light affects larval development and increases the prevalence of skeletal deformities. Melatonin is a crucial pineal neurohormone that displays daily secretion patterns, stimulates cell proliferation and embryonic development in Atlantic salmon and zebrafish, and improves osseointegration in mice and humans. However, no studies have examined the effects of orally supplemented melatonin on skeletal deformities in Sparus aurata larvae. We administered exogenous melatonin to gilthead seabream larvae via enriched rotifers and nauplii of Artemia. Exogenous melatonin induced bone deformities and stimulated parathyroid hormone-related protein-coding gene (PTHrP) mRNA expression. In addition to the melatonin-induced PTHrP high expression level, the recorded non coordinated function of skeletal muscle and bone during growth can be the fountainhead of bone deformities. Both myosin light chain 2 (mlc2) and bone gamma-carboxyglutamate protein-coding gene (bglap) expression levels were significantly affected by melatonin administration in an inverse dose–response manner during the exogenous melatonin administration. This is the first study to report the effect of inducing melatonin bone deformities on Sparus aurata larvae reared under ordinary hatchery conditions.

Serotonin stimulated parathyroid hormone related protein induction in the mammary epithelia by transglutaminase-dependent serotonylation

Mammary-derived serotonin has been implicated in breast-to-bone communication during lactation by increasing parathyroid hormone related-protein (PTHrP) in the mammary gland. It is well established that PTHrP acts on the bone to liberate calcium for milk synthesis during lactation; however, the mechanism of serotonin’s regulation of PTHrP has not been fully elucidated. Recently, serotonylation has been shown to be involved in a variety of physiological processes mediated by serotonin. Therefore, we investigated whether serotonylation is involved in serotonin’s regulation of PTHrP in the mammary gland using lactogenically differentiated mouse mammary epithelial cells. We investigated the effect of increased intracellular serotonin using the antidepressant fluoxetine or 5-hydroxytryptophan (serotonin precursor), with or without transglutaminase inhibition and the corresponding action on PTHrP induction and activity. Treatment with fluoxetine or 5-hydroxytryptophan significantly increased intracellular serotonin concentrations and subsequently increased PTHrP gene expression, which was reduced with transglutaminase inhibition. Furthermore, we determined that transglutaminase activity is increased with lactogenic differentiation and 5-hydroxytryptophan or fluoxetine treatment. We investigated whether RhoA, Rac1, and Rab4 were potential serotonylation target proteins. We speculate that RhoA is potentially a serotonylation target protein. Our data suggest that serotonin regulates PTHrP induction in part through the process of serotonylation under lactogenic conditions in mouse mammary epithelial cells.

Concomitant Primary Hyperparathyroidism in Patients with Multiple Myeloma: A Possible Link?

Hypercalcemia is a significant feature of patients with active multiple myeloma (MM) with extensive bone disease. Among the causes of non-neoplastic hypercalcemia, primary hyperparathyroidism (PHPT) is one of the most common, leading to osteoporosis and bone fractures. Interestingly, some preclinical data indicate that high secretion of parathyroid hormone (PTH) may have a negative impact on bone disease and MM progression. However, concomitant diagnosis of MM and PHPT has rarely been described. Here, we present 4 cases of patients with active MM and hypercalcemia with high or inappropriately normal PTH levels. Interestingly, CD138+ cells from these 4 MM patients lack PTH receptor 1 and PTH-related peptide expressions, indicating that PTH could have a paracrine rather than a direct pro-tumoral effect. Moreover, these cases suggest that the concomitant diagnosis of MM and PHTP may not be so rare and should be considered for the clinical management of MM patients with hypercalcemia.

High endogenous expression of parathyroid hormone-related protein (PTHrP) supports osteogenic differentiation in human dental follicle cells

Dental follicle cells (DFCs) are progenitor cells for mineralizing cells such as alveolar osteoblasts, but little is known about the mechanisms of the differentiation. Interestingly, different cell lines sometimes have different potentials to differentiate into mineralizing cells. In this study, we compared two different DFC lines, with one cell line (DFC_B) showing a high alkaline phosphatase (ALP) activity in long-term cultures with standard medium and a reliable mineralizing potential. However, the other cell line DFC_A shows low ALP activity in standard medium and almost no mineralization. Known osteogenic markers such as RUNX2 were similarly expressed in both cell lines. However, the proosteogenic signaling pathway of the bone morphogenetic protein (BMP) is induced in DFC_B, and the parathyroid hormone-related protein (PTHrP), which is involved in tooth root development, was also expressed more strongly. Previous studies have shown that the secreted PTHrP negatively regulate the transition from pre-osteoblastic progenitors to osteoblasts, but we showed that an inhibition of PTHrP gene expression reduced the ALP activity and the BMP-signaling pathway. In addition, endogenously expressed PTHrP is located in the cell nucleus. In contrast, supplementation of PTHrP or an inhibitor for the PTHrP receptor did not affect the ALP activity of DFC_B. In conclusion, our data suggest that a high endogenous expression of PTHrP in DFCs supports the induction of osteogenic differentiation via an intracrine mode.

Switching Homes: How Cancer Moves to Bone

Bone metastases (BM) are a very common complication of the most prevalent human cancers. BM are extremely painful and may be life-threatening when associated with hypercalcaemia. BM can lead to kidney failure and cardiac arrhythmias and arrest, but why and how do cancer cells decide to "switch homes" and move to bone? In this review, we will present what answers science has provided so far, with focus on the molecular mechanisms and cellular aspects of well-established findings, such as the concept of "vicious cycle" and "osteolytic" vs. "osteosclerotic" bone metastases; as well as on novel concepts, such as cellular dormancy and extracellular vesicles. At the molecular level, we will focus on hypoxia-associated factors and angiogenesis, the Wnt pathway, parathyroid hormone-related peptide (PTHrP) and chemokines. At the supramolecular/cellular level, we will discuss tumour dormancy, id est the mechanisms through which a small contingent of tumour cells coming from the primary site may be kept dormant in the endosteal niche for many years. Finally, we will present a potential role for the multimolecular mediators known as extracellular vesicles in determining bone-tropism and establishing a premetastatic niche by influencing the bone microenvironment.

The Actions of IGF-1 in the Growth Plate and Its Role in Postnatal Bone Elongation

PURPOSE OF REVIEW

Bone elongation is a complex process driven by multiple intrinsic (hormones, growth factors) and extrinsic (nutrition, environment) variables. Bones grow in length by endochondral ossification in cartilaginous growth plates at ends of developing long bones. This review provides an updated overview of the important factors that influence this process.

RECENT FINDINGS

Insulin-like growth factor-1 (IGF-1) is the major hormone required for growth and a drug for treating pediatric skeletal disorders. Temperature is an underrecognized environmental variable that also impacts linear growth. This paper reviews the current state of knowledge regarding the interaction of IGF-1 and environmental factors on bone elongation. Understanding how internal and external variables regulate bone lengthening is essential for developing and improving treatments for an array of bone elongation disorders. Future studies may benefit from understanding how these unique relationships could offer realistic new approaches for increasing bone length in different growth-limiting conditions.

A severe inactivating PTH/PTHrP signaling disorder type 2 in a patient carrying a novel large deletion of the GNAS gene: a case report and review of the literature

PURPOSE

Pseudohypoparathyroidism (PHP), characterized by multihormone resistance and Albright's hereditary osteodystrophy (AHO), is caused by GNAS mutations. Whole or partial gene deletions are rare. All disorders due to inactivating mutations of the GNAS gene are now classified as "inactivating PTH/PTHrP signaling disorder type 2" (iPPSD2). This study reports a family harboring a large GNAS gene deletion in order to improve the knowledge of genotype-phenotype correlation of this disease.

METHODS

An 18-year-old man with severe diffuse soft ossifications and multihormone resistance underwent to clinical, biochemical, radiological, and genetic studies. A review of the literature of other cases of iPPSD2 due to GNAS large deletions was performed focusing on clinical and biochemical features.

RESULTS

The proband presented signs of hypocalcemia and marked AHO features. Laboratory tests revealed hypocalcemia, high levels of serum phosphate, PTH, TSH, and calcitonin despite therapy with calcium carbonate, calcitriol, and levothyroxine. Diffuse soft tissue ossifications and brain calcifications were shown by radiological exams. Family history was remarkable for hypocalcemia, neurocognitive impairment, and cerebral calcifications in his brother and AHO features in the maternal grandfather. The proband's mother showed short stature, whereas physical examination of the father was unremarkable. Genetic analysis of the GNAS gene revealed an unreported large deletion encompassing exons 1-7 in the proband, brother, and mother. By reviewing the literature, only six other cases were described.

CONCLUSIONS

We report a kindred harboring a large GNAS deletion. A genotype-phenotype correlation was observed in term of severity of tissue ossifications in the siblings but not in the mother.

Monocyte Chemoattractant Protein-1 (MCP-1/CCL2) Drives Activation of Bone Remodelling and Skeletal Metastasis

PURPOSE OF REVIEW

The purpose of this review is to explore the role of monocyte chemoattractant protein-1 (MCP-1 or CCL2) in the processes that underpin bone remodelling, particularly the action of osteoblasts and osteoclasts, and its role in the development and metastasis of cancers that target the bone.

RECENT FINDINGS

MCP-1 is a key mediator of osteoclastogenesis, being the highest induced gene during intermittent treatment with parathyroid hormone (iPTH), but also regulates catabolic effects of continuous PTH on bone including monocyte and macrophage recruitment, osteoclast formation and bone resorption. In concert with PTH-related protein (PTHrP), MCP-1 mediates the interaction between tumour-derived factors and host-derived chemokines to promote skeletal metastasis. In breast and prostate cancers, an osteolytic cascade is driven by tumour cell-derived PTHrP that upregulates MCP-1 in osteoblastic cells. This relationship between PTHrP and osteoblastic expression of MCP-1 may drive the colonisation of disseminated breast cancer cells in the bone. There is mounting evidence to suggest a pivotal role of MCP-1 in many diseases and an important role in the establishment of comorbidities. Coupled with its role in bone remodelling and the regulation of bone turnover, there is the potential for pathological relationships between bone disorders and bone-related cancers driven by MCP-1. MCP-1's role in bone remodelling and bone-related cancers highlights its potential as a novel anti-resorptive and anti-metastatic target.

Idiopathic gigantomastia: newer mechanistic insights implicating the paracrine milieu

PURPOSE

Gigantomastia refers to pathological breast enlargement usually occurring in the peripubertal or peripartum period. Idiopathic gigantomastia, however, is a rare entity with hypotheses citing local expression of hormones and growth factors in causing this disease, none of which have been systemically analysed. The purpose of this study was to delve deeper into the mechanistic pathways causing this condition.

METHODS

Herein, we describe three patients of idiopathic gigantomastia, all of whom had had normal puberty and uneventful pregnancies. Further, one of the patients had postmenopausal gigantomastia which is extremely rare, with only four cases described in the literature. Serum markers of autoimmunity, incriminated hormones and growth factors analysed, were normal in all the cases. Breast tissue specimens were subjected to histopathological examination and immunohistochemistry for ER, PR and Her-2-Neu. Quantitative immunofluorescence for aromatase, IGF2, EGFR, TGF-β, PDGFR-α, β, IGF1 and PTHrP was also performed.

RESULTS

Of these, the tissue expression of aromatase, IGF2, EGFR, TGF-β, PDGFR-α and β were found to be upregulated, whereas IGF1 and PTHrP were comparable to normal breast.

CONCLUSION

This observation that paracrine overexpression of these factors is responsible for the pathogenesis of apparently idiopathic gigantomastia may have therapeutic ramifications in the future for patients with this debilitating condition.

Experimental Induction of Physeal Injuries by Fracture, Drill, and Ablation Techniques: Analyses of Immunohistochemical Findings

BACKGROUND

Although physeal fractures and physeal bars can result in significant clinical consequences to growth and development of the injured physis, little orthopaedic research has focused upon this topic. Our objective was to extend a previously developed rat model to examine the immunohistochemical features following surgical application of techniques disrupting the physis.

METHODS

Physes were surgically disrupted using fracture (control), epiphyseal scrape (ES), or epiphyseal drill (ED). After 1, 3, 6, 10, or 21 days, animals were euthanized, sites processed for histology and immunohistochemical localization of vascular endothelial growth factor (VEGF), Factor VIII, Sox-9, PTHrP (parathyroid hormone-related protein) and PTHrP-R (parathyroid hormone-related protein receptor) in resting, proliferative, and hypertrophic physeal zones. Incidence of physeal bars, vertical septa and islands within the metaphysis was quantified. Semiquantitative analysis of immunohistochemistry was performed.

RESULTS

Physeal bars, vertical septa, and displaced cartilage islands were present each of the surgical treatments. Fisher's exact test showed a statistically significant increase in the presence of physeal bars (P=0.002) and vertical septa (P=0.012) in the ED group at 10 and 21 days. Analysis of VEGF showed significant differences among the surgical treatments involving the resting zone, and the proliferative zone for days 1, 6, and 21 (P≤0.02) with greater mean scores present in the fracture (control) group, followed by the ED group; the lowest scores were present in the ES group. PTHrP-R immunolocalization showed significant differences among treatments in the hypertrophic zone at days 6 and 21 (P=0.022 and 0.044, respectively).

CONCLUSIONS

On the basis of the type of surgical treatment, results show significant differences in the presence of VEGF (reflecting the vascular bed) in the resting and proliferating zones at days 1, 6, and 21. VEGF localization was less abundant in the ED group (which had more physeal bars), suggesting that lack of vascular ingrowth plays a role in physeal bar formation.

CLINICAL RELEVANCE

Basic science data presented here provide insight into the importance of the various regions of the physis and its repair and continued growth after physeal fracture. We suggest that a better understanding of the cellular basis of physeal arrest following physeal fracture may have future relevance for the development of treatments to prevent or correct arrest.

miR-195 contributes to human osteoarthritis via targeting PTHrP

The dysregulated expression of the osteoarthritis (OA)-related genes in cartilage, such as matrix metalloproteinase 13 (MMP-13) and type X collagen (Col X), facilitates the onset and progression of OA. Reduced parathyroid hormone-related protein (PTHrP) may also accelerate this progression. Furthermore, miRNAs, endogenous regulators of mRNAs, are thought to play key roles in the pathogenesis of OA. In this study, we found that miR-195 levels were significantly upregulated in OA tissue, while PTHrP mRNA/protein expression was substantially downregulated, and there was a negative correlation between miR-195 and PTHrP. Upregulated miR-195 strongly inhibited Aggrecan, type II collagen (Col II) mRNA/protein expression, while it enhanced the expression of MMP-13 and Col X at mRNA/protein level; conversely, downregulated miR-195 significantly increased Col II mRNA/protein expression, while it decreased the expression of MMP-13 and Col X mRNA/protein. Moreover, our study demonstrated that PTHrP is a novel target of miR-195 using dual luciferase reporter assay. Finally, miR-195-mediated changes of Col II and OA-related genes were substantially attenuated by siRNA_PTHrP treatment. These results suggested that miR-195 is involved in the pathogenesis of OA via PTHrP.

Proteolytic Regulation of Parathyroid Hormone-Related Protein: Functional Implications for Skeletal Malignancy

Parathyroid hormone-related protein (PTHrP), with isoforms ranging from 139 to 173 amino acids, has long been implicated in the development and regulation of multiple tissues, including that of the skeleton, via paracrine and autocrine signaling. PTHrP is also known as a potent mediator of cancer-induced bone disease, contributing to a vicious cycle between tumor cells and the bone microenvironment that drives the formation and progression of metastatic lesions. The abundance of roles ascribed to PTHrP have largely been attributed to the N-terminal 1-36 amino acid region, however, activities for mid-region and C-terminal products as well as additional shorter N-terminal species have also been described. Studies of the protein sequence have indicated that PTHrP is susceptible to post-translational proteolytic cleavage by multiple classes of proteases with emerging evidence pointing to novel functional roles for these PTHrP products in regulating cell behavior in homeostatic and pathological contexts. As a consequence, PTHrP products are also being explored as potential biomarkers of disease. Taken together, our enhanced understanding of the post-translational regulation of PTHrP bioactivity could assist in developing new therapeutic approaches that can effectively treat skeletal malignancies.

Prostate Cancer and Bone Metastases: The Underlying Mechanisms

Patients with advanced prostate cancer often develop bone metastases, leading to bone pain, skeletal fracture, and increased mortality. Bone provides a hospitable microenvironment to tumor cells. The disease manifestation is driven by the interaction between invading tumor cells, bone-forming osteoblasts, and bone-resorbing osteoclasts. The increased level of osteoclast-activating factor (parathyroid hormone-related peptide, PTHrP) is believed to induce bone resorption by upregulating receptor activator of nuclear factor-kappa B ligand (RANKL) and the release of various growth factors into the bone microenvironment to enhance cancer cell growth. However, the underlying molecular mechanisms remain poorly understood. This review outlines the possible molecular mechanisms involved in governing bone metastases driven by prostate cancer, which further provide the basis in searching for new molecular targets for the development of potential therapy.

PTHrP treatment of colon cancer cells promotes tumor associated-angiogenesis by the effect of VEGF

We showed that Parathyroid Hormone-related Peptide (PTHrP) induces proliferation, migration, survival and chemoresistance via MAPKs and PI3K/AKT pathways in colorectal cancer (CRC) cells. The objective of this study was to investigate if PTHrP is also involved in tumor angiogenesis. PTHrP increased VEGF expression and the number of structures with characteristics of neoformed vessels in xenografts tumor. Also, PTHrP increased mRNA levels of VEGF, HIF-1α and MMP-9 via ERK1/2 and PI3K/Akt pathways in Caco-2 and HCT116 cells. Tumor conditioned media (TCMs) from both cell lines treated with PTHrP increases the number of cells, the migration and the tube formation in the endothelial HMEC-1 cells, whereas the neutralizing antibody against VEGF diminished this response. In contrast, PTHrP by direct treatment only increased ERK1/2 phosphorylation and the HMEC-1 cells number. These results provide the first evidence related to the mode of action of PTHrP that leads to its proangiogenic effects in the CRC.

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.

Involvement of Aryl Hydrocarbon Receptor in L-Kynurenine-Mediated Parathyroid Hormone-Related Peptide Expression

Parathyroid hormone-related peptide (PTHrP), produced by specific cancers such as lung cancer, profoundly influences the formation of bone metastatic lesions via the "vicious cycle" of tumor growth and bone resorption. The changes in gene expression regulated by the abnormal microenvironment components play key roles in maintaining the biological characteristics of cells, such as the organotropism of cancer metastasis. A recent study has shown that L-kynurenine (L-Kyn), one of microenvironment components, induced a substantial increase in the metastasis of lung cancer cells. What remains unclear, however, is the linkage between L-Kyn and bone metastatic lesions. In the present paper, we found that a significant upregulation of PTHrP expression was detected when 95D cells, a lung cancer cell line, were incubated with 50 μM of L-Kyn. Meanwhile, L-Kyn (50/100 μM) strongly strengthened aryl hydrocarbon receptor (Ahr) expression. Additionally, L-Kyn (50 μM) increased the expression of the nuclear translocation of Ahr and cytochrome P450 1A1. Most importantly, the L-Kyn-induced upregulation of migration was significantly reduced when cells were co-incubated with siRNA_Ahr. Notably, the L-Kyn-mediated increase in PTHrP was also substantially attenuated upon siRNA_Ahr treatment in 95D cells. These results suggest that Ahr is involved in the L-Kyn-induced enhancement of PTHrP expression.

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.

Upregulated osterix promotes invasion and bone metastasis and predicts for a poor prognosis in breast cancer

Approximately 70% of patients with advanced breast cancer develop bone metastases, accompanied by complications, such as bone pain, fracture, and hypercalcemia. However, our understanding of the molecular mechanisms that govern this process remains fragmentary. Osterix (Osx) is a zinc finger-containing transcription factor essential for osteoblast differentiation and bone formation. Here, we identified the functional roles of Osx in facilitating breast cancer invasion and bone metastasis. Osx upregulation was associated with lymph node metastasis and was negatively prognostic for overall survival. Knockdown of Osx inhibited invasion of breast cancer and osteolytic metastasis by downregulating MMP9, MMP13, VEGF, IL-8, and PTHrP, which are involved in invasion, angiogenesis, and osteolysis; overexpression of Osx had the opposite effect. Moreover, MMP9 was a direct target of Osx and mediated the Osx-driven invasion of breast cancer cells. Together, our data showed that Osx facilitates bone metastasis of breast cancer by upregulating the expression of a cohort of genes that contribute to steps in the metastatic cascade. These findings suggest that Osx is an attractive target for the control of bone metastasis of breast cancers.

Induced lesion and inhibited Ihh-PTHrP signalling pathway activity in the articular cartilage of rats caused by T-2 toxin

This study aims to investigate the role of Ihh-PTHrP signalling pathway in the articular cartilage injury of rats caused by T-2 toxin. Sixty male Wistar rats were randomly divided into four groups: group A, normal diet; group B, normal diet plus the dissolvent (0.9% sodium chloride sterile aqueous solution containing ethanol); group C, normal diet plus low T-2 toxin (0.1 mg/kg BW/day) and group D, normal diet plus high T-2 toxin (0.2 mg/kg BW/day) by intragastric administration daily for 4 weeks. Histological changes in articular cartilage were assessed by HE staining and scanning electron microscopy. The expression of Ihh and PTHrP in cartilage was assessed by immunohistochemistry. There is a significant difference in average weight gain between group A and group D P < 0.01, groups A and D P < 0.001, respectively. The result of scanning electron microscopy and HE staining showed that the damage of articular cartilage was much severe with the increase of T-2 toxin. Immunohistochemical analysis indicated that the expression of Ihh in group A and group B was higher than that of group C and group D (P < 0.05, <0.01, respectively). However, the expression of PTHrP was lower in group A and group B than that of group C and group D (P < 0.001, <0.001, respectively). These results indicated that T-2 toxin can cause the damage to articular cartilage and weight loss in rats. The effect of T-2 toxin on articular cartilage of rat may be related to the Ihh-PTHrP pathway.

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.

Inactivating PTH/PTHrP Signaling Disorders

Pseudohypoparathyroidism (PHP), pseudo-PHP, acrodysostosis, and progressive osseous heteroplasia are heterogeneous disorders characterized by physical findings, differently associated in each subtype, including short bones, short stature, a stocky build, ectopic ossifications (features associated with Albright's hereditary osteodystrophy), as well as laboratory abnormalities consistent with hormone resistance, such as hypocalcemia, hyperphosphatemia, and elevated parathyroid hormone (PTH) and thyroid-stimulating hormone levels. All these disorders are caused by impairments in the cAMP-mediated signal transduction pathway and, in particular, in the PTH/PTHrP signaling pathway: the main subtypes of PHP and related disorders are caused by de novo or autosomal dominantly inherited inactivating genetic mutations, and/or epigenetic, sporadic, or genetic-based alterations within or upstream of GNAS, PRKAR1A, PDE4D, and PDE3A. Here we will review the impressive progress that has been made over the past 30 years on the pathophysiology of these diseases and will describe the recently proposed novel nomenclature and classification. The new term "inactivating PTH/PTHrP signaling disorder," iPPSD: (1) defines the common mechanism responsible for all diseases, (2) does not require a confirmed genetic defect, (3) avoids ambiguous terms like "pseudo," and (4) eliminates the clinical or molecular overlap between diseases.