Parathyroid Hormone-related Protein Research Articles

Abstract #1393925: An Interesting Case of Bisphosphonate Resistant Hypercalcemia in Acute Myelogenous Leukemia (AML)

Hypercalcemia of malignancy (HCM), a PTH-independent process, usually occurs in solid tumors, multiple myeloma, and occasionally lymphomas. It generally results from excess secretion of parathyroid hormone related protein (PTHrP) by the tumor, osteolytic metastases, or rarely, tumor production of 1,25-(OH)2 vitamin D. We present an unusual case of HCM in a patient with refractory acute myelogenous leukemia (AML) without a defined mechanism that was resistant to bisphosphonate therapy. A 49-year-old woman with refractory AML presented acutely with altered mental status, decreased appetite, nausea, and fatigue. She was found to have HCM with a low intact parathyroid hormone (PTH) level. Her PTHrP and 25-(OH) vitamin D levels were normal, and her 1,25-(OH)2 vitamin D level was suppressed. Other labs were unrevealing, and imaging showed no new osseous lesions. Her hypercalcemia was treated with normal saline, intravenous furosemide, calcitonin, and two doses of pamidronate. Her calcium level normalized but then rebounded and remained elevated despite pamidronate therapy. Denosumab was considered, but due to rapid clinical deterioration, the patient’s family pursued comfort care. AML is an extremely rare cause of HCM. This is the eighth reported case of AML-related HCM since 2000 and the first known case with bisphosphonate resistance. Our patient’s HCM was not explained by typical mechanisms. Based on similar cases, one plausible mechanism for our patient's hypercalcemia was upregulation of receptor activator of nuclear factor κB ligand (RANKL) on osteoblasts due to elevated proinflammatory cytokines. RANKL binds to receptor activator of nuclear factor κB (RANK) on osteoclasts to promote their maturation and thus bone resorption. Regarding treatment, several case reports have demonstrated that denosumab can successfully treat bisphosphonate resistant HCM and is a potential therapeutic option.

Abstract #1408170: Familial Hypocalciuric Hypercalcemia, Primary Hyperparathyroidism, or Both?

Primary hyperparathyroidism (PHPT) is the leading cause of hypercalcemia, and it is characterized by hypercalcemia and normal or inappropriately high levels of parathyroid hormone (PTH). Familial Hypocalciuric hypercalcemia (FHH) is a rare autosomal dominant benign disease caused by inactivating genetic mutations in the calcium sensing receptor. Genetic analyses are expensive and not widely available, making the differential diagnosis challenging. A 77-year-old male with a past medical history of hypertension and chronic kidney disease was referred to the endocrinology clinic for evaluation of hypercalcemia. Routine tests showed total corrected calcium level of 10.5 mg/dL, hypophosphatemia 2.6 mg/dL and low 24h urinary calcium of 79 mg/24h with calcium creatinine clearance ratio (CCCR) of 0.008. 25 hydroxyvitamin D, 1,25 Dihydroxyvitamin D and magnesium were normal. PTH level was 33 pg/dL (normal 15-65 pg/dL). Patient had no hypercalcemic symptoms, history of nephrolithiasis, or bone fractures. No family history of hypercalcemia. Cancer screening and PTH related peptide were normal. He was not taking hydrochlorothiazide or lithium. Renal ultrasound showed no nephrolithiasis and DXA revealed no osteoporosis. Thyroid ultrasound showed a right 1.2cm thyroid nodule without visualization of parathyroid glands. Fine-needle aspiration biopsy (FNA) of the nodule with PTH washout was benign with PTH<10. The patient was diagnosed with FHH and was monitored semiannually. Four years after the initial evaluation, total corrected calcium level was elevated at 14 mg/dL with PTH of 378 despite 25 hydroxyvitamin D level >40, repeated urinary calcium 90 mg/24h, and CCCR 0.01. His renal function was unchanged. Parathyroid scintigraphy revealed increased uptake in the right upper thyroid lobe, and thyroid ultrasound revealed increased right thyroid nodule volume. Repeat FNA was benign, this time with a PTH washout >200. The patient opted against surgical consultation for parathyroidectomy. He was treated with cinacalcet 30 mg twice daily. The co-existence of FHH and PHPT is rare. The few reported cases include patients who maintained hypercalcemia after surgical treatment of PHPT. The best cost-effective test available is a CCCR < 0.02. Our patient had CCCR measured at different times with values < 0.01 and a PTH level that over time increased by 900%. The overlap of biochemical values in patients with FHH and PHPT contributes to the challenges in the differential diagnosis and highlights the importance of close follow up with a high degree of clinical suspicion.

Abstract #1399984: Hypercalcemia Secondary to Vitamin D Toxicity Treated with Glucocorticoids

Vitamin D toxicity is a rare cause of hypercalcemia and there is no consensus on active treatment. Though glucocorticoids can decrease intestinal calcium absorption, increase urinary calcium excretion, and reduce levels of biologically active vitamin D metabolites, its use in vitamin D toxicity is controversial. Here we present a case of hypercalcemia secondary to hypervitaminosis D treated with glucocorticoids. A 77-year-old female with a history of vitamin D deficiency and prior admission for hypercalcemia attributed to lithium use (discontinued in December 2021) presented to the emergency room for hypercalcemia on outpatient labs. Labs were notable for calcium 14.6 mg/dL, albumin 3.8 g/dL, ionized calcium above detectable limits (>7.3 mg/dL), PTH 22.9 pg/mL, 25-OH vitamin D 135 ng/mL, 1,25-OH vitamin D 67.2 pg/mL (reference range: 19.9-79.3 pg/mL), estimated GFR 23 mL/min/1.73 m2, and undetectable lithium level. Additional workup included normal SPEP/UPEP, parathyroid hormone-related peptide, retinol and retinyl palmitate vitamin A, and computed-tomography of the chest, abdomen, and pelvis without signs of malignancy. History obtained from family revealed the patient had been supplementing with at least 10,400 IU of cholecalciferol daily, along with at least 180 mg of calcium daily (unknown if elemental or calcium carbonate). She was hydrated with isotonic intravenous fluids, given calcitonin 4 units/kg for 3 days, and prednisone 20 mg daily for 2 days. Following day 3 of calcitonin, prednisone was replaced with hydrocortisone 40 mg twice daily. Calcium improved to 10.8 mg/dL and she was discharged on hydrocortisone at same dose and frequency. Upon two-week follow up, calcium had improved to 10.0 mg/dL thus hydrocortisone was tapered to 20 mg twice daily. Due to a misunderstanding, she discontinued hydrocortisone resulting in an increased calcium of 12.2 mg/dL several weeks later. Four weeks upon resumption of hydrocortisone, the calcium improved to 10.2 mg/dL and the hydrocortisone was tapered to 10 mg twice daily. Five weeks later (approximately 4 months since starting hydrocortisone), the calcium was 10.4 mg/dL, the PTH was 19 pg/mL, and 25-OH vitamin D was 37.1 ng/mL. There are no guidelines or consensus on the treatment for vitamin D-induced hypercalcemia. In this case, glucocorticoids were shown to be an effective treatment for hypercalcemia secondary to vitamin D toxicity; the worsening of hypercalcemia upon accidental discontinuation and resolution following resumption of hydrocortisone further supports this conclusion. Though the expected duration of treatment is unclear, our case suggests long-term glucocorticoids are likely necessary.

Abstract #1401609: A Case of Vitamin D Toxicity Associated with Weight Loss During a Low Carbohydrate Diet

Vitamin D is a commonly prescribed, fat-soluble vitamin important for calcium homeostasis and bone health. Vitamin D Toxicity (VDT) is rare and typically caused by aggressive supplementation or manufacturing errors. In epidemiologic studies, vitamin D levels correlate inversely with adiposity, and dietary weight loss is associated with increases in 25-hydroxyvitamin D [25(OH)D] level. Vitamin D is stored in adipose tissue and it is postulated that weight loss is a risk factor for the development of VDT. Here we present a case of VDT associated with weight loss during a low carbohydrate diet. A 74-year-old man with CKD stage 3a and benign prostatic hyperplasia presented to the ED with intractable emesis preceded by subacute nausea, anorexia, and constipation. He reported following a very low carbohydrate diet with intentional weight loss from 83.9kg (BMI 25.86) to 71.9kg (BMI 21.7) over five months. He reported taking Vitamin D3 250μg (10,000 IU) daily which was self-prescribed prior to admission for at least 12 months. On admission, he was mildly bradycardic and hypertensive. Laboratory evaluation in the ED revealed serum creatinine (sCr) 5.2 mg/dL (0.66-1.28, baseline 1.24 mg/dL 3 months prior), calcium 12.9 mg/dL (8.4-10.2), albumin 3.8 g/dL (3.2-4.8), and 25(OH)D >150 ng/dL (30-100). Intact PTH was suppressed at 13.2 pg/mL (14-72) and 1,25-dihydroxyvitamin D was 71 pg/mL (18-72). PTH-related protein, and serum and urine electrophoresis were within reference ranges. The patient was treated for hypercalcemia with intravenous fluids, prednisone 20mg daily, and on hospital day eight, intravenous pamidronate 30mg. Upon discharge on hospital day nine, calcium was 10.5 mg/dL. He was instructed to stop all vitamin D containing supplements. One month after discharge, sCr was 1.9 mg/dL and calcium was 8.7 mg/dL. Vitamin D is theorized to be stored in adipose tissue in clinically relevant quantities and released during weight loss. Due to the rare presentation of VDT in the setting of dietary weight loss, there are a limited number of cases described. Few clinical trials measuring serum 25(OH)D concentrations in people with obesity following weight loss have been performed. One study confirmed that patients with obesity have lower vitamin D levels that normalize after significant weight loss, supporting the hypothesis that vitamin D is stored in the adipose tissue and released following weight loss. Here we present a case of acute VDT causing symptomatic hypercalcemia after intentional dietary weight loss in the setting of chronic supratherapeutic vitamin D supplementation. As illustrated in this case, rapid weight loss in the setting of supratherapeutic doses of Vitamin D can result in VDT. Additional studies are needed to clarify the mechanisms that regulate the kinetics of vitamin D in the adipose tissue of persons with obesity.

Establishment and characterization of long-term human primary parathyroid tumor subclones derived from Indian PHPT.

The continuous cell line of epithelial human parathyroid cells has been proven difficult. Previously, PTH-C1 cell line was only established rat parathyroid tissue cell line known to express the parathyroid hormone-related peptide (Pthrp) gene. The paucity of continuous cell line of human parathyroid cells secreting parathyroid hormone (PTH) has imposed hurdle in in vitro assessment of the mechanisms involved in the control of parathyroid cell function and proliferation. The primary cell cultures of human parathyroid cells were derived from parathyroid adenoma tissue biopsy (n = 5). The cells were subsequently subcultured to maintained primary subclones. Karyotyping analysis was performed to analyze the genotypic identity of derived subclones. The expression of calcium-sensing receptor (CaSR) and intact parathyroid hormone (iPTH) were analyzed using immunocytochemistry and immunofluorescence. In the present study, we have used a defined condition medium to generate the continuous culture of human parathyroid cells derived from patients with parathyroid adenoma due to primary hyperparathyroidism. The subcultured primary subclones were maintained epithelial and polygonal morphology, doubling time of approximately 25h, displaying a diploid chromosome number, and secretion of PTH. This cell line produces PTH and expresses the calcium-sensing receptor (CaSR) known to be involved in parathyroid function. Altogether these findings indicate the uniqueness of the human parathyroid cell line as an in vitro model for cellular and molecular studies on parathyroid physiopathology.

Parathyroid hormone receptors in GtoPdb v.2023.1

The parathyroid hormone receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Parathyroid Hormone Receptors [50]) are class B G protein-coupled receptors. The parathyroid hormone (PTH)/parathyroid hormone-related peptide (PTHrP) receptor (PTH1 receptor) is activated by precursor-derived peptides: PTH (84 amino acids), and PTHrP (141 amino-acids) and related peptides (PTH-(1-34), PTHrP-(1-36)). The parathyroid hormone 2 receptor (PTH2 receptor) is activated by the precursor-derived peptide TIP39 (39 amino acids). [125I]PTH may be used to label both PTH1 and PTH2 receptors. The structure of a long-active PTH analogue (LA-PTH, an hybrid of PTH-(1-13) and PTHrP-(14-36)) bound to the PTH1 receptor-Gs complex has been resolved by cryo-electron microscopy [148]. Another structure of a PTH-(1-34) analog bound to a thermostabilized inactive PTH1 receptor has been obtained with X-ray crytallography [35].

Mobilization of monocytic myeloid-derived suppressor cells is regulated by PTH1R activation in bone marrow stromal cells

Myeloid-derived suppressor cells (MDSCs) are bone marrow (BM)-derived immunosuppressive cells in the tumor microenvironment, but the mechanism of MDSC mobilization from the BM remains unclear. We investigated how BM stromal cell activation by PTH1R contributes to MDSC mobilization. PTH1R activation by parathyroid hormone (PTH) or PTH-related peptide (PTHrP), a tumor-derived counterpart, mobilized monocytic (M-) MDSCs from murine BM without increasing immunosuppressive activity. In vitro cell-binding assays demonstrated that α4β1 integrin and vascular cell adhesion molecule (VCAM)-1, expressed on M-MDSCs and osteoblasts, respectively, are key to M-MDSC binding to osteoblasts. Upon PTH1R activation, osteoblasts express VEGF-A and IL6, leading to Src family kinase phosphorylation in M-MDSCs. Src inhibitors suppressed PTHrP-induced MDSC mobilization, and Src activation in M-MDSCs upregulated two proteases, ADAM-17 and MMP7, leading to VCAM1 shedding and subsequent disruption of M-MDSC tethering to osteoblasts. Collectively, our data provide the molecular mechanism of M-MDSC mobilization in the bones of tumor hosts.

PTHrP Modulates the Proliferation and Osteogenic Differentiation of Craniofacial Fibrous Dysplasia-Derived BMSCs.

Fibrous dysplasia (FD) is a skeletal stem cell disease caused by mutations in the guanine nucleotide-binding protein, alpha-stimulating activity polypeptide (GNAS) gene, which results in the abnormal accumulation of cyclic adenosine monophosphate (cAMP) and hyperactivation of downstream signaling pathways. Parathyroid hormone-related protein (PTHrP) is secreted by the osteoblast lineage and is involved in various physiological and pathological activities of bone. However, the association between the abnormal expression of PTHrP and FD, as well as its underlying mechanism, remains unclear. In this study, we discovered that FD patient-derived bone marrow stromal cells (FD BMSCs) expressed significantly higher levels of PTHrP during osteogenic differentiation and exhibited greater proliferation capacity but impaired osteogenic ability compared to normal control patient-derived BMSCs (NC BMSCs). Continuous exogenous PTHrP exposure on the NC BMSCs promoted the FD phenotype in both in vitro and in vivo experiments. Through the PTHrP/cAMP/PKA axis, PTHrP could partially influence the proliferation and osteogenesis capacity of FD BMSCs via the overactivation of the Wnt/β-Catenin signaling pathway. Furthermore, PTHrP not only directly modulated cAMP/PKA/CREB transduction but was also demonstrated as a transcriptional target of CREB. This study provides novel insight into the possible pathogenesis involved in the FD phenotype and enhances the understanding of its molecular signaling pathways, offering theoretical evidence for the feasibility of potential therapeutic targets for FD.

Nephrolithiasis and Multicystic Kidneys in a Young Patient: A Quiz

Nephrolithiasis and Multicystic Kidneys in a Young Patient: A Quiz

Abstract NG12: Altered calcium signaling in cancer: PTHrP-KRAS collateral amplification governs pancreatic cancer metastasis, cachexia, and immunosuppression

Abstract Purpose: Metastasis is the leading cause of cancer-related death in pancreatic ductal adenocarcinoma (PDAC), yet very little is understood regarding the underlying biology. As a result, targeted therapies to inhibit metastasis are lacking. Whole-genome sequencing has established that the squamous/quasi-mesenchymal/basal-like PDAC subtype, which is characterized by its high metastatic proclivity, is annotated by KRAS gene amplification. Here, we report that the squamous lineage gene parathyroid hormone-related protein (PTHrP encoded by the PTHLH gene) is located directly adjacent to KRAS and is co-amplified as part of the KRAS amplicon in metastatic PDAC patients. We hypothesize that this collateral amplification of PTHrP, and downstream activation of calcium signaling, exerts its own oncogenic and pro-metastatic phenotypes beyond KRAS and set out to determine if this will confer a novel therapeutic vulnerability. Finally, we postulate that PTHrP-mediated Calcium signaling may be responsible for driving other non-cell autonomous PDAC-associated phenotypes, including cancer cachexia and the organization of an immunosuppressive microenvironment. Methods: We generated a novel genetically engineered mouse model whereby we deleted the cytokine PTHrP in the autochthonous KPCY model of pancreatic cancer (mutant Kras and mutant p53 activated in the pancreatic epithelium). To functionally demonstrate the pro-metastatic and cachexia-inducing roles of PTHrP, we further employed genetic deletion and pharmacological inhibition in orthotopic injection and mouse hospital pre-clinical trials. Results: In silico analysis established that PTHLH (the gene encoding the PTHrP protein) is co-amplified along with KRAS in TCGA and correlates with significantly decreased overall survival. We generated KPCY-PthlhCKO mice and showed that they have significantly reduced primary and metastatic tumor burden and dramatically increased overall survival relative to KPCY controls. In parallel experiments, we treated mice with an anti-PTHrP neutralizing monoclonal antibody, which similarly reduced primary and metastatic tumor growth. Mechanistic studies revealed that intracellular calcium was responsible for turning on an epithelial-to-mesenchymal (EMT) program that could be impeded by inhibiting PTHrP, thus blocking tumor cells from entering the metastatic cascade. Additionally, both genetic deletion and pharmacological inhibition of PTHrP in vivo led to a profound reduction in cachexia-related adipose tissue wasting and muscle atrophy. Re-introduction of PTHrP into a PDAC cell line with low cachexia-inducing potential (and low baseline PTHrP) dramatically increased the degree of cachexia and metastasis observed upon orthotopic implantation. Thus, PTHrP is both necessary and sufficient to induce cachexia and metastasis. Additionally, mice implanted with PTHrP overexpressing tumor cells had a dramatic reduction in overall survival. Finally, we demonstrated that PTHrP is responsible for organizing a pro-tumor immunosuppressive microenvironment by recruiting Myeloid Derived Suppressive Cells (MDSCs). Blocking PTHrP signaling reduces the degree of local immune suppression allowing for the enhanced recruitment of CD8+ T cells. Thus, PTHrP is a pleiotropic molecule that governs many pancreatic cancer-associated disease phenotypes. Conclusions: This work has demonstrated the importance of the previously unappreciated roles of PTHrP signaling in driving diverse pancreatic cancer phenotypes from metastasis to cachexia to immunosuppression, and future studies will look to translate anti-PTHrP therapy into clinical trials. Citation Format: Jason Robert Pitarresi. Altered calcium signaling in cancer: PTHrP-KRAS collateral amplification governs pancreatic cancer metastasis, cachexia, and immunosuppression. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr NG12.

An uncanny case of paraneoplastic calcitriol mediated hypercalcaemia.

A 77-year-old female patient with a history of treated breast cancer and a recently diagnosed laryngeal cancer presented with severe hypercalcaemia associated with suppressed parathyroid hormone (PTH) levels. Her initial investigations included 25-hydroxy vitamin D levels, short synacthen test, bone scan, myeloma screen and thyroid function tests which were within normality. A computerised tomography (CT) scan showed some right lung apical fibrotic changes. Her PTH-related peptide (PTHrP) was normal and sarcoidosis was also excluded. Her previous and current malignancies were thought to be unlikely behind her hypercalcaemia. Her 1,25-dihydroxy vitamin D (calcitriol) levels were found to be elevated. Her hypercalcaemia was initially managed with intravenous fluids and intermittent bisphosphonates infusions which would transiently reduce her calcium levels. Steroid treatment was initiated which improved her hypercalcaemia; however, the calcium levels rebounded on tapering the steroids down, a pre-requisite prior to a positron emission computerised tomography (PET-CT) scan to determine the source of the excess calcitriol production. This was cancelled following an emergency admission with marked hypercalcaemia and acute renal and liver injury. A contemporary CT scan showed a right apical lung mass with hepatic lesions suggestive of a disseminated lung primary. The histology obtained from a liver biopsy was compatible with metastatic small-cell lung carcinoma. Unfortunately, her clinical condition deteriorated further and she did not survive. To the best of our knowledge, this is the first report in the literature describing calcitriol-mediated hypercalcaemia due to a small-cell lung cancer. Paraneoplastic hypercalcaemia may manifest even without overt detection of the primary cancer. The workup for paraneoplastic hypercalcaemia should be meticulous. Both bisphosphonates and steroids are useful in the initial management of calcitriol-mediated hypercalcaemia, but the definitive management is the treatment of the cause.

Correlation between serum parathyroid hormone-associated protein concentration and acute ischemic stroke

Objective To investigate the correlation between serum Parathyroid hormone-related protein (PTHrP) and acute ischemic stroke (AIS). Methods from October 2020 to March 2021, 134 patients with AIS and 34 healthy individuals were enrolled. Serum PTHrP concentration was measured by enzyme-linked immunosorbent assay (ELISA) and subgroup analysis was performed according to Trial of Org 10 172 in acute stroke treatment (TOAST) classification. The severity of AIS was assessed by the National Institutes of Health stroke scale (NIHSS) score and the volume of cerebral infarction was assessed based on head magnetic resonance imaging. The correlation of serum PTHrP concentration with various indicators was analyzed. The 90-day functional prognosis of patients was assessed by the modified Rankin scale. Patients were divided into favorable outcomes group and unfavorable outcomes group and the difference in serum PTHrP concentration between the two groups was compared. Whether serum PTHrP was associated with AIS prognosis was analyzed by Logistic regression.Results The serum PTHrP concentration in AIS group was higher than that in the control group (P=0.000), and the serum PTHrP concentrations of the three common etiological subtypes, LAA, CE and SAO, were higher than those in the control group (all P&lt;0.01). The AUC for distinguishing AIS patients and healthy control by serum PTHrP concentration was 0.751(P&lt;0.0001). The serum PTHrP concentration in the AIS group was associated with the cumulative smoking volume (r=0.201, P=0.021) and APTT (r=-0.188, p=0.034). Serum PTHrP was not associated with TOAST classification (P=0.091), NIHSS score and cerebral infarction volume (all P&gt;0.05), and there was no significant difference in serum PTHrP concentration between the favorable outcomes group and unfavorable outcomes group (P&gt; 0.05). Univariate logistic regression showed that serum PTHrP concentration was not a prognostic factor of AIS [OR=1.000 95% CI (0.999, 1.002) P=0.678]. Conclusion Serum PTHrP concentration was significantly increased in AIS patients. Serum PTHrP might be ancillary for early identification of AIS. Serum PTHrP concentration correlated with cumulative smoking volume and APTT in AIS patients, and could possibly be used to assess the true smoking volume of patients and analyze coagulation function. However, serum PTHrP concentration was not associated with TOAST classification, NIHSS score, cerebral infarction volume and 90-day prognosis, which meant it cannot be used to evaluated the etiology, severity and prognosis of AIS patients.

Parathyroid hormone 1 receptor signaling mediates breast cancer metastasis to bone in mice.

Bone metastases are a common complication of breast cancer. We have demonstrated that intermittent administration of parathyroid hormone (PTH[1-34]) reduces the incidence of bone metastases in murine models of breast cancer by acting on osteoblasts to alter the bone microenvironment. Here, we examined the role of signaling mediated by PTH 1 receptor (PTH1R) in both osteoblasts and breast cancer cells in influencing bone metastases. In mice with impaired PTH1R signaling in osteoblasts, intermittent PTH did not reduce bone metastasis. Intermittent PTH also did not reduce bone metastasis when expression of PTH1R was knocked down in 4T1 murine breast cancer cells by shRNA. In 4T1 breast cancer cells, PTH decreased expression of PTH-related protein (PTHrP), implicated in the vicious cycle of bone metastases. Knockdown of PTHrP in 4T1 cells significantly reduced migration toward MC3T3-E1 osteoblasts, and migration was further inhibited by treatment with intermittent PTH. Conversely, overexpression of PTHrP in 4T1 cells increased migration toward MC3T3-E1 osteoblasts, and this was not inhibited by PTH. In conclusion, PTH1R expression is crucial in both osteoblasts and breast cancer cells for PTH to reduce bone metastases, and in breast cancer cells, this may be mediated in part by suppression of PTHrP.

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

To explore the difference in parathyroid tissue-derived cells between male and female PHPT patients. Resected parathyroid tissues were collected from PHPT patients of both sexes. Single cells were isolated and sequenced for RNA expression profiles. The cell sequencing data were annotated by cell type, followed by population analysis, functional analysis, pathway analysis, cell communication analysis, differential gene expression analysis, and pseudotime trajectory analysis. The subcluster analyses were also performed in the parathyroid cells. No substantial difference in the cell population, function, or communication is found between the two sexes. The interferon-a response, oxidative phosphorylation, and reactive oxygen species pathways are up-regulated in females than in male patients, mainly contributed by fibroblast cells, endothelial cells, parathyroid cells, and myeloid cells, which also have significantly more up-regulated pathways and cellular interactions than the other three cell types. The subcluster analysis of parathyroid cells identified five subpopulations: SPARCL1-OC and ISG15-OC are predominant in females, while more S100A13-PCC and PTHLH-OC are found in males. The cellular functions are also elevated in females compared with males. Cells from female patients show a higher expression level of parathyroid hormone (PTH) but a lower expression level of parathyroid hormone-like hormone (PTHLH). The cell pseudotime trajectory and pathway analyses show that the oxyphil cells may be more mature and functionally active than the chief cells in both sexes. These findings suggest that the sex difference in PHPT may be caused by the differentially expressed genes and activated pathways in different cell types in the parathyroid tissue. The heterogeneity of parathyroid cell subpopulations, especially in oxyphil cells, may be associated with the sex differences in PHPT pathogenesis.

Hypercalcemia of malignancy with simultaneous production of parathyroid hormone-related peptide and 1,25-Dihydroxyvitamin D by non-Hodgkin lymphoma: Case report &amp; brief review

We report the case of a 63-year-old man with severe hypercalcemia, acute kidney injury, and concomitant diagnosis of germinal center diffuse large B-cell lymphoma (nHL). Hypercalcemia is a common finding in patients with cancer. Multiple mechanisms can lead to hypercalcemia of malignancy, and different malignancies are often associated with a specific mechanism of hypercalcemia. Parathyroid hormone-related protein (PTHrP) and excessive production of 1,25-dihydroxyvitamin D can independently (and rarely, concomitantly) lead to development of hypercalcemia in patients with a variety of malignancies. Literature review of hypercalcemia related with PTHrP and 1,25-dihydroxyvitamin D co-secretion shows that most reported cases are associated with solid tumors and responded to tumor directed therapy. Our case of nHL was associated with increased PTHrP and 1,25-dihydroxyvitamin D making this an unusual presentation.

Streptonigrin Mitigates Lung Cancer-induced Cachexia by Suppressing TCF4/TWIST1-induced PTHLH Expression.

Cachexia - a wasting disorder of adipose and skeletal muscle tissue - is the most common driver of poor prognosis in patients with advanced lung cancer. Parathyroid hormone-like hormone (PTHLH) is potentially a critical factor in cancer-associated cachexia. We previously showed that streptonigrin - an aminoquinone with antitumor effects - inhibited the interaction between TCF4 and TWIST1. This study aimed to determine the anti-cachectic performance of streptonigrin in lung cancer. We assessed the effect of streptonigrin on the interaction of TCF4 and TWIST1 using co-immunoprecipitation and a mammalian-two hybrid luciferase assay, which was confirmed by an in vitro GST pull-down assay using recombinant bHLH domain-containing TCF4 and TWIST1. We assessed the anti-cachectic effect of streptonigrin in vivo using an LLC1 cell-induced tumour-bearing mouse model. Changes in the degree of skeletal muscle and adipose tissue wasting were determined by measuring the weights of gastrocnemius and epidydimal white adipose tissue. Streptonigrin was found to inhibit the interaction of TCF4 with TWIST1 in a dose-dependent manner. The in vitro GST pull-down assay revealed that streptonigrin directly inhibited the interaction between TCF4 and TWIST1. The expression of PTHLH mRNA, which is transcriptionally regulated by the TCF4/TWIST1 complex in response to TGF-β1 signalling, was decreased in streptonigrin-treated lung cancer cells. Streptonigrin significantly decreased the expression of proteolysis-related genes in skeletal muscle and browning-related genes in white adipose tissues of LLC1-induced tumour-bearing mice. Streptonigrin exerts potent therapeutic effects on lung cancer-induced cachexia by suppressing TCF4/TWIST1-mediated PTHLH expression.

1α,25-Dihydroxyvitamin D3 Regulates microRNA Packaging in Extracellular Matrix Vesicles and Their Release in the Matrix.

Growth plate chondrocytes are regulated by numerous factors and hormones as they mature during endochondral bone formation, including transforming growth factor beta-1 (TGFb1), bone morphogenetic protein 2 (BMP2), insulin-like growth factor-1 (IFG1), parathyroid hormone and parathyroid hormone related peptide (PTH, PTHrP), and Indian hedgehog (IHH). Chondrocytes in the growth plate's growth zone (GC) produce and export matrix vesicles (MVs) under the regulation of 1α,25-dihydroxyvitamin D3 [1α,25(OH)2D3]. 1α,25(OH)2D3 regulates MV enzyme composition genomically and 1α,25(OH)2D3 secreted by the cells acts on the MV membrane nongenomically, destabilizing it and releasing MV enzymes. This study examined the regulatory role 1α,25(OH)2D3 has over production and packaging of microRNA (miRNA) into MVs by GC cells and the release of miRNA by direct action on MVs. Costochondral cartilage GC cells were treated with 1α,25(OH)2D3 and the miRNA in the cells and MVs sequenced. We also treated MVs with 1α,25(OH)2D3 and determined if the miRNA was released. To assess whether MVs can act directly with chondrocytes and if this is regulated by 1α,25(OH)2D3, we stained MVs with a membrane dye and treated GC cells with them. 1α,25(OH)2D3 regulated production and packaging of a unique population of miRNA into MVs compared to the vehicle control population. 1α,25(OH)2D3 treatment of MVs did not release miRNA. Stained MVs were endocytosed by GC cells and this was increased with 1α,25(OH)2D3 treatment. This study adds new regulatory roles for 1α,25(OH)2D3 with respect to packaging and transport of MV miRNAs.

Roles of Local Soluble Factors in Maintaining the Growth Plate: An Update

The growth plate is a cartilaginous tissue found at the ends of growing long bones, which contributes to the lengthening of bones during development. This unique structure contains at least three distinctive layers, including resting, proliferative, and hypertrophic chondrocyte zones, maintained by a complex regulatory network. Due to its soft tissue nature, the growth plate is the most susceptible tissue of the growing skeleton to injury in childhood. Although most growth plate damage in fractures can heal, some damage can result in growth arrest or disorder, impairing leg length and resulting in deformity. In this review, we re-visit previously established knowledge about the regulatory network that maintains the growth plate and integrate current research displaying the most recent progress. Next, we highlight local secretary factors, such as Wnt, Indian hedgehog (Ihh), and parathyroid hormone-related peptide (PTHrP), and dissect their roles and interactions in maintaining cell function and phenotype in different zones. Lastly, we discuss future research topics that can further our understanding of this unique tissue. Given the unmet need to engineer the growth plate, we also discuss the potential of creating particular patterns of soluble factors and generating them in vitro.

MiR-190a regulates milk protein biosynthesis through the mTOR and JAK2–STAT5 signaling pathways by targeting PTHLH in buffalo mammary epithelial cells

Milk protein is a key quality indicator of milk, so elucidating its synthesis mechanism has been the focus of research in recent years. Studies have shown that both miRNAs and mRNA genes play important roles in the regulation of milk protein synthesis. In this study, a total of 7 and 4073 differentially expressed miRNA and mRNA genes were identified between early and peak lactation, respectively. Overexpression and knockdown experiments of parathyroid hormone like hormone gene (PTHLH) gene showed that it can promote milk protein synthesis in buffalo mammary epithelial cells (BuMECs) through mammalian target of rapamycin (mTOR) and janus kinase 2/signal transducer and activator of transcription 5 (JAK2–STAT5) signaling pathways, and the experiments treated with miR-190a mimic or inhibitor showed that miR-190a inhibited the expression of PTHLH gene. In addition, miR-190a inhibited milk protein synthesis by targeting PTHLH through mTOR and JAK2–STAT5 signaling pathways in BuMECs. Collectively, these findings reveal a novel miR-190a–PTHLH pathway that has a significant role in regulating milk protein synthesis.

Skeletal diseases caused by mutations in PTH1R show aberrant differentiation of skeletal progenitors due to dysregulation of DEPTOR.

Alterations in the balance between skeletogenesis and adipogenesis is a pathogenic feature in multiple skeletal disorders. Clinically, enhanced bone marrow adiposity in bones impairs mobility and increases fracture risk, reducing the quality of life of patients. The molecular mechanism that underlies the balance between skeletogenesis and adipogenesis is not completely understood but alterations in skeletal progenitor cells' differentiation pathway plays a key role. We recently demonstrated that parathyroid hormone (PTH)/PTH-related peptide (PTHrP) control the levels of DEPTOR, an inhibitor of the mechanistic target of rapamycin (mTOR), and that DEPTOR levels are altered in different skeletal diseases. Here, we show that mutations in the PTH receptor-1 (PTH1R) alter the differentiation of skeletal progenitors in two different skeletal genetic disorders and lead to accumulation of fat or cartilage in bones. Mechanistically, DEPTOR controls the subcellular localization of TAZ (transcriptional co-activator with a PDZ-binding domain), a transcriptional regulator that governs skeletal stem cells differentiation into either bone and fat. We show that DEPTOR regulation of TAZ localization is achieved through the control of Dishevelled2 (DVL2) phosphorylation. Depending on nutrient availability, DEPTOR directly interacts with PTH1R to regulate PTH/PTHrP signaling or it forms a complex with TAZ, to prevent its translocation to the nucleus and therefore inhibit its transcriptional activity. Our data point DEPTOR as a key molecule in skeletal progenitor differentiation; its dysregulation under pathologic conditions results in aberrant bone/fat balance.