Parathyroid hormone-related protein and regulation of cell survival in the kidney

Association Between Parathyroid Hormone-Related Peptide Levels and Mortality in Patients With Malignancy

OBJECTIVE

Hypercalcemia of malignancy is a risk factor for mortality in patients with malignancies. Although the parathyroid hormone-related protein (PTHrP) secreted by tumor cells induces hypercalcemia, the association between serum PTHrP levels and mortality remains unclear. This study aimed to investigate the association between serum PTHrP levels and mortality in patients with malignancies.

METHODS

We included patients with hypercalcemia (>10 mg/dL) and elevated PTHrP levels (>1.1 pmol/L) and analyzed mortality (overall survival after cancer diagnosis, PTHrP measurement, and 5-year survival rate). Moreover, using Cox proportional hazard model analysis, we investigated the impact of PTHrP levels on survival prognosis, assessing whether this effect varied depending on calcium concentration.

RESULTS

We analyzed the data of 183 patients. The median PTHrP level, corrected calcium level, and age were 5.5 (3.0-10.6) pmol/L, 12.5 (11.5-13.4) mg/dl, and 70 (61-76) years, respectively. PTHrP was significantly and linearly associated with serum calcium levels (correlation coefficient, 0.06; 95% CI: 0.039-0.081, t: 5.69; P < .001). The group with the highest PTHrP levels had significantly worse survival rates than the group with the lowest PTHrP levels (hazard ratio: 1.68, 95% CI 1.03-2.77, P = .038).

CONCLUSION

This study showed an association between PTHrP and mortality in patients with malignancy after adjusting for serum calcium levels.

Hypercalcemia Secondary to Elevated PTHrP in an Infant Followed by Progression to Nephrotic Syndrome

In infants, hypercalcemia from elevated parathyroid hormone-related protein (PTHrP) is rare, often signaling neoplasm or renal or urinary anomalies. We report an infant who presented with failure to thrive and hypercalcemia at 10 months old, with initial evaluation showing elevated PTHrP of unclear etiology with imaging negative for neoplasm and no structural anomalies of the kidneys or ureters on ultrasound. Within 6 months of presentation, the patient developed nephrotic syndrome and by 2 years had progressed to end-stage kidney disease, necessitating kidney transplantation. Genetic testing was inconclusive but suggested congenital nephrotic syndrome. While reports of hypercalcemia secondary to elevated PTHrP exist in children with known structural renal anomalies, this is the first to demonstrate hypercalcemia and PTHrP elevation before detection of renal abnormalities. Experimental models have suggested a role for increased PTHrP expression in renal cells following acute kidney injury from nephrotic syndrome, and clinically detectable PTHrP levels may indicate progression of renal injury. We suggest monitoring of renal function for early detection of nephrotic syndrome in infants and children with elevated PTHrP who otherwise lack anatomical renal anomalies or detectable malignancies.

Parathyroid Hormone Related Protein (PTHrP)-Associated Molecular Signatures in Tissue Differentiation and Non-Tumoral Diseases

Parathyroid-hormone-related protein (PTHrP) is encoded by the PTHLH gene which, via alternative promoter usage and splicing mechanisms, can give rise to at least three isoforms of 139, 141, and 173 amino acids with distinct C-terminals. PTHrP is subjected to different post-translational processing that generates smaller bioactive forms, comprising amino terminus, mid-region (containing a nuclear/nucleolar targeting signal), and carboxy terminus peptides. Both the full-length protein and the discrete peptides are key controllers of viability, proliferation, differentiation, and apoptosis in diverse normal and pathological biological systems via the reprogramming of gene expression and remodulation of PKA or PKC-mediated signalization mechanisms. The aim of this review is to pick up selected studies on PTHrP-associated signatures as revealed by molecular profiling assays, focusing on the available data about exemplary differentiating, differentiated, or nontumoral cell and tissue models. In particular, the data presented relate to adipose, bone, dental, cartilaginous, and skin tissues, as well as intestinal, renal, hepatic, pulmonary, and pancreatic epithelia, with a focus on hepatic fibrosis-, pancreatitis-, and diabetes-related changes as diseased states. When reported, the biochemical and/or physiological aspects associated with the specific molecular modulation of gene expression and signal transduction pathways in the target model systems under examination are also briefly described.

Parathyroid Hormone-Related Peptide (PTHrP): Evaluation of Pediatric, Covariate-Stratified Reference Intervals

Parathyroid hormone-related peptide (PTHrP) is expressed at a wide range of sites in the body and performs different functions including vasodilation, relaxation of smooth muscle cells, and regulation of bone development. PTHrP also mediates hypercalcemia related to neoplastic diseases. However, reference ranges specific method and age were not evaluated. We establish PTHrP reference ranges in apparently healthy, normocalcemic, normophosphatemic pediatric individuals. In this observational prospective, study we measured PTHrP in serum from 178 samples (55.06% male 44.94% female) from apparently healthy pediatric subjects [median age 10 years (range 1–18)] subunit ELISA method The statistical analysis performed provided for the calculation of the 95% reference interval, right-sided, with a non-parametric percentile method (CLSI C28-A3). Upper reference limits (URL) for PTHrP was 2.89 ng/mL (2.60 to 3.18; 90% CI). No significant differences were found between the median PTHrP concentrations in males vs females and in the age range categories selected. Comprehensive normal values for PTHrP are indispensable to the assessment of calcium phosphorus dysfunction in children. Severe hypercalcemia is a rare, but clinically significant condition, in infancy and childhood. PTHrP values higher than the reference value may help to distinguish the hypercalcemic product of a malignancy, paraneoplastic syndromes mediated by PTHrP, from other causes.

Parathyroid Hormone-Related Protein Inhibition Blocks Triple-Negative Breast Cancer Expansion in Bone Through Epithelial to Mesenchymal Transition Reversal

Parathyroid hormone-related protein (PTHrP) plays a major role in skeletal metastasis but its action mechanism has not been fully defined. We previously demonstrated the crucial importance of PTHrP in promoting mammary tumor initiation, growth, and metastasis in a mouse model with a mammary epithelium-targeted Pthlh gene ablation. We demonstrate here a novel mechanism for bone invasion involving PTHrP induction of epithelial to mesenchymal transition (EMT) and cancer stem cells (CSCs) regulation. Clustered regularly interspaced short palindromic repeats (CRISPR)-mediated Pthlh gene ablation was used to study EMT markers, phenotype, and invasiveness in two triple-negative breast cancer (TNBC) cell types (established MDA-MB-231 and patient-derived PT-TNBC cells). In vitro, Pthlh ablation in TNBC cells reduced EMT markers, mammosphere-forming ability, and CD44high/CD24low cells ratio. In vivo, cells were injected intratibially into athymic nude mice, and therapeutic treatment with our anti-PTHrP blocking antibody was started 2 weeks after skeletal tumors were established. In vivo, compared to control, lytic bone lesion from Pthlh -ablated cells decreased significantly over 2 weeks by 27% for MDA-MB-231 and by 75% for PT-TNBC-injected mice (p < 0.001). Micro-CT (μCT) analyses also showed that antibody therapy reduced bone lytic volume loss by 52% and 48% for non-ablated MDA-MB-231 and PT-TNBC, respectively (p < 0.05). Antibody therapy reduced skeletal tumor burden by 45% and 87% for non-ablated MDA-MB-231 and PT-TNBC, respectively (p < 0.002) and caused a significant decrease of CSC/EMT markers ALDH1, vimentin, and Slug, and an increase in E-cadherin in bone lesions. We conclude that PTHrP is a targetable EMT molecular driver and suggest that its pharmacological blockade can provide a potential therapeutic approach against established TNBC-derived skeletal lesions. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Effect of free running wheel exercise on renal expression of parathyroid hormone receptor type 1 in spontaneously hypertensive rats

An active lifestyle is generally recommended for hypertensive patients to prevent subsequent end-organ damage. However, experimental data on long-term effects of exercise on hypertension are insufficient and underlying mechanisms are not well understood. This study was aimed to investigate the effect of exercise on renal expression of parathyroid hormone-related protein (PTHrP) and parathyroid hormone receptor type 1 (PTHR1) in spontaneously hypertensive rats (SHR). Twenty-four rats started free running wheel exercise at the age of 1.5 months (pre-hypertensive state) and proceeded for 1.5, 3.0, 6.0, and 10.0 months. Thirty rats kept under standard housing conditions were used as sedentary controls. Kidney function was assessed by measuring plasma creatinine levels and urine albumin-to-creatinine ratios. Renal expression of PTHrP and PTHR1 was analyzed by qRT-PCR and western blot. Renal expression of PTHR1 was markedly increased between the 6th and 10th months in sedentary rats and this increase was significantly lower in SHRs with high physical activity on mRNA (-30%) and protein level (-27%). At the same time, urine albumin-to-creatinine ratio increased (from 65 to 231 mg/g) but somehow lower in exercise performing SHRs (48-196 mg/g). Our data suggest that enhanced exercise, stimulated by allocation of a free running wheel, is associated with lower PTHR1 expression in SHRs and this may contribute to preserved kidney function.

PTHrP-related Hypercalcaemia in Infancy and Congenital Anomalies of the Kidney and Urinary Tract (CAKUT)

Background

Severe hypercalcaemia is a rare but clinically significant condition in infancy and childhood. Parathyroid hormone-related peptide (PTHrP)-mediated hypercalcaemia resulting from a malignancy is rare and only a handful of case reports have outlined its incidence alongside a benign condition.

Objectives

To describe the diagnostic workup and management of an infant with hypercalcaemia, renal dysplasia, and elevated PTHrP levels.

Design

Case report.

Setting

The Victoria Hospital campus of the London Health Sciences Centre in London, Ontario, Canada.

Patients

A child with congenital anomalies of the kidneys and urinary tract (CAKUT), stage 2 chronic kidney disease (CKD), and renal dysplasia who presented with severe hypercalcaemia.

Measurements

Weight, renal ultrasound, creatinine, cystatin C, eGFR, calcium, urea, bicarbonate, serum sodium, fractional sodium excretion, urine calcium to creatinine ratio, PTH, TSH, Free T4, AM cortisol, HMA, VMA, 25-vitamin D, 1,25 dihydroxy-vitamin D, calcitriol, vitamin A, ACE levels, skull and chest x-rays, alkaline phosphatase, CBC, tumour lysis profile, catecholamine breakdown, whole-body MRI, PTHrP.

Methods

Full diagnostic workup and patient management. Patient treated with intravenous hydration, furosemide, calcitonin and CalciLo.

Results

PTHrP was elevated and no evidence of a malignancy was found. Treatment consisting of a low-calcium CalciLo diet (in place of breast milk) adequately controlled the patient’s hypercalcaemia. Hypercalcaemia associated with CAKUT in infancy is not all that uncommon and was reported in 15/99 infants in another study, most of whom had a suppressed PTH similar to that of our patient. PTHrP was not measured in these cases and may have also been elevated.

Limitations

The study is limited in that it is a description of a single patient case. Future measurement of PTHrP in similar patients is necessary to confirm our results.

Conclusions

The possibility of elevated PTHrP levels must be considered in patients with known renal dysplasia who are differentially diagnosed with hypercalcaemia.