Heterozygous Mutation (Q459R) in the Calcium-Sensing Receptor Gene Causes Familial Hypocalciuric Hypercalcemia 1 (FHH1)

Detailed functional characterization of four nanobodies as positive allosteric modulators of the human Calcium-Sensing receptor

The calcium-sensing receptor (CaSR) plays a key role in calcium homeostasis, and small-molecule and peptide positive allosteric modulators (PAMs) of CaSR, so-called calcimimetics, are used in the treatment of hyperparathyroidism and hypocalcemic disorders. In this study, four monovalent nanobodies - representing four distinct nanobody families with CaSR PAM activity - were subjected to elaborate pharmacological profiling at the receptor. While Nb5 displayed negligible PAM activity at CaSR in all assays, Nb4, Nb10 and Nb45 all potently potentiated Ca2+-evoked signalling through a myc epitope-tagged CaSR expressed in HEK293 or HEK293T cells in Gαq and Gαi1 protein activation assays and in a Ca2+/Fluo-4 assay. Nb4 and Nb10 also displayed comparable PAM properties at a stable CaSR-HEK293 cell line in a Ca2+/Fura-2 imaging assay, but surprisingly Nb45 was completely inactive at this cell line in both the Ca2+/Fura-2 and Ca2+/Fluo-4 assays. Investigations into this binary difference in Nb45 activity revealed that the nanobody only possesses modulatory activity at CaSRs tagged N-terminally with various epitopes (myc, HA, Flag-SNAP), whereas it is inactive at the untagged wild-type receptor. In conclusion, overall each of the nanobodies exhibit similar CaSR PAM properties in a range of assays, and thus none of them display pathway bias as modulators. However, of the four nanobodies Nb4 and Nb10 would be applicable as pharmacological tools for the wild-type CaSR, and the complete inactivity of Nb45 at the untagged CaSR serves as an reminder that epitope-tagging of a receptor, even if deemed functionally silent, can have profound implications for ligand discovery efforts.

Calcium and vitamin D homoeostasis in male fertility

Calcium and vitamin D have well-established roles in maintaining calcium balance and bone health. Decades of research in human subjects and animals have revealed that calcium and vitamin D also have effects on many other organs including male reproductive organs. The presence of calcium-sensing receptor, vitamin D receptor, vitamin D activating and inactivating enzymes and calcium channels in the testes, male reproductive tract and human spermatozoa suggests that vitamin D and calcium may modify male reproductive function. Functional animal models have shown that vitamin D deficiency in male rodents leads to a decrease in successful mating and fewer pregnancies, often caused by impaired sperm motility and poor sperm morphology. Human studies have to a lesser extent validated these findings; however, newer studies suggest a positive effect of vitamin D supplementation on semen quality in cases with vitamin D deficiency, which highlights the need for initiatives to prevent vitamin D deficiency. Calcium channels in male reproductive organs and spermatozoa contribute to the regulation of sperm motility and capacitation, both essential for successful fertilisation, which supports a need to avoid calcium deficiency. Studies have demonstrated that vitamin D, as a regulator of calcium homoeostasis, influences calcium influx in the testis and spermatozoa. Emerging evidence suggests a potential link between vitamin D deficiency and male infertility, although further investigation is needed to establish a definitive causal relationship. Understanding the interplay between vitamin D, calcium and male reproductive health may open new avenues for improving fertility outcomes in men.

The Calcium-Sensing Receptor Is Essential for Calcium and Bicarbonate Sensitivity in Human Spermatozoa

CONTEXT

The calcium-sensing receptor (CaSR) is essential to maintain a stable calcium concentration in serum. Spermatozoa are exposed to immense changes in concentrations of CaSR ligands such as calcium, magnesium, and spermine during epididymal maturation, in the ejaculate, and in the female reproductive environment. However, the role of CaSR in human spermatozoa is unknown.

OBJECTIVE

This work aimed to investigate the role of CaSR in human spermatozoa.

METHODS

We identified CaSR in human spermatozoa and characterized the response to CaSR agonists on intracellular calcium, acrosome reaction, and 3',5'-cyclic adenosine 5'-monophosphate (cAMP) in spermatozoa from men with either loss-of-function or gain-of-function mutations in CASR and healthy donors.

RESULTS

CaSR is expressed in human spermatozoa and is essential for sensing extracellular free ionized calcium (Ca2+) and Mg2+. Activators of CaSR augmented the effect of sperm-activating signals such as the response to HCO3- and the acrosome reaction, whereas spermatozoa from men with a loss-of-function mutation in CASR had a diminished response to HCO3-, lower progesterone-mediated calcium influx, and were less likely to undergo the acrosome reaction in response to progesterone or Ca2+. CaSR activation increased cAMP through soluble adenylyl cyclase (sAC) activity and increased calcium influx through CatSper. Moreover, external Ca2+ or Mg2+ was indispensable for HCO3- activation of sAC. Two male patients with a CASR loss-of-function mutation in exon 3 presented with normal sperm counts and motility, whereas a patient with a loss-of-function mutation in exon 7 had low sperm count, motility, and morphology.

CONCLUSION

CaSR is important for the sensing of Ca2+, Mg2+, and HCO3- in spermatozoa, and loss-of-function may impair male sperm function.

Radiofrequency Ablation of Parathyroid Glands to Treat a Patient With Hypercalcemia Caused by a Novel Inactivating Mutation in CaSR

OBJECTIVE

We identified a novel inactivating mutation in the calcium-sensing receptor (CaSR) gene in a patient with refractory hypocalciuric hypercalcemia and analyzed its function. The effectiveness of radiofrequency ablation of the parathyroid glands to treat hypercalcemia caused by this mutation was explored.

METHODS

Clinical data of patients before and after radiofrequency ablation were retrospectively analyzed. The CaSR mutation (D99N) found in the patient was studied in cell lines. HEK-293 cells were transfected with plasmids containing wild-type (WT) or mutant CaSR genes (D99N and W718X). Expression levels of the respective CaSR proteins were measured, and their functions were assessed by examining the effect of NPS R-568 (a CaSR agonist) on intracellular Ca²⁺ oscillations and that of exogenous parathyroid hormone (PTH) on intracellular cyclic adenosine monophosphate (cAMP) levels.

RESULTS

The effectiveness of pharmacological treatment was poor, whereas radiofrequency ablation of the parathyroid glands resulted in controlled blood calcium and PTH levels in the patient. In cell lines, upon NPS R-568 administration, the amplitude of intracellular Ca²⁺ oscillations in the D99N group was lower than that in the WT group and higher than that in the W718X group. Upon administration of PTH, intracellular cAMP levels in the D99N group were higher than those in the WT group and lower than those in the W718X group.

CONCLUSION

The homozygous mutation D99N reduced CaSR activity and caused more severe hypocalciuric hypercalcemia. For patients with this type of hypercalcemia and poor response to pharmacological treatments, radiofrequency ablation of the parathyroid glands may be a suitable treatment option.

CellCountCV-A Web-Application for Accurate Cell Counting and Automated Batch Processing of Microscopic Images Using Fully Convolutional Neural Networks

In vitro cellular models are promising tools for studying normal and pathological conditions. One of their important applications is the development of genetically engineered biosensor systems to investigate, in real time, the processes occurring in living cells. At present, there are fluorescence, protein-based, sensory systems for detecting various substances in living cells (for example, hydrogen peroxide, ATP, Ca²⁺ etc.,) or for detecting processes such as endoplasmic reticulum stress. Such systems help to study the mechanisms underlying the pathogenic processes and diseases and to screen for potential therapeutic compounds. It is also necessary to develop new tools for the processing and analysis of obtained microimages. Here, we present our web-application CellCountCV for automation of microscopic cell images analysis, which is based on fully convolutional deep neural networks. This approach can efficiently deal with non-convex overlapping objects, that are virtually inseparable with conventional image processing methods. The cell counts predicted with CellCountCV were very close to expert estimates (the average error rate was < 4%). CellCountCV was used to analyze large series of microscopic images obtained in experimental studies and it was able to demonstrate endoplasmic reticulum stress development and to catch the dose-dependent effect of tunicamycin.