Calcilytic Ameliorates Abnormalities of Mutant Calcium-Sensing Receptor (CaSR) Knock-In Mice Mimicking Autosomal Dominant Hypocalcemia (ADH).

Abstract

Activating mutations of calcium-sensing receptor (CaSR) cause autosomal dominant hypocalcemia (ADH). ADH patients develop hypocalcemia, hyperphosphatemia, and hypercalciuria, similar to the clinical features of hypoparathyroidism. The current treatment of ADH is similar to the other forms of hypoparathyroidism, using active vitamin D3 or parathyroid hormone (PTH). However, these treatments aggravate hypercalciuria and renal calcification. Thus, new therapeutic strategies for ADH are needed. Calcilytics are allosteric antagonists of CaSR, and may be effective for the treatment of ADH caused by activating mutations of CaSR. In order to examine the effect of calcilytic JTT-305/MK-5442 on CaSR harboring activating mutations in the extracellular and transmembrane domains in vitro, we first transfected a mutated CaSR gene into HEK cells. JTT-305/MK-5442 suppressed the hypersensitivity to extracellular Ca(2+) of HEK cells transfected with the CaSR gene with activating mutations in the extracellular and transmembrane domains. We then selected two activating mutations locating in the extracellular (C129S) and transmembrane (A843E) domains, and generated two strains of CaSR knock-in mice to build an ADH mouse model. Both mutant mice mimicked almost all the clinical features of human ADH. JTT-305/MK-5442 treatment in vivo increased urinary cAMP excretion, improved serum and urinary calcium and phosphate levels by stimulating endogenous PTH secretion, and prevented renal calcification. In contrast, PTH(1-34) treatment normalized serum calcium and phosphate but could not reduce hypercalciuria or renal calcification. CaSR knock-in mice exhibited low bone turnover due to the deficiency of PTH, and JTT-305/MK-5442 as well as PTH(1-34) increased bone turnover and bone mineral density (BMD) in these mice. These results demonstrate that calcilytics can reverse almost all the phenotypes of ADH including hypercalciuria and renal calcification, and suggest that calcilytics can become a novel therapeutic agent for ADH.

• Authors: Bingzi Dong, Itsuro Endo, Yukiyo Ohnishi, Takeshi Kondo, Tomoka Hasegawa, Norio Amizuka, Hiroshi Kiyonari, Go Shioi, Masahiro Abe, Seiji Fukumoto, Toshio Matsumoto
• Journal: Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research (J Bone Miner Res) Vol. 30 Issue 11 Pg. 1980-93 (Nov 2015) ISSN: 1523-4681 [Electronic] United States
• PMID: 25967373 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: © 2015 American Society for Bone and Mineral Research.

Chemical References

• Benzoates
• FGF23 protein, human
• Fgf23 protein, mouse
• JTT 305
• Mutant Proteins
• Propanolamines
• Receptors, Calcium-Sensing
• Fibroblast Growth Factor-23
• Calcium

Topics

• Animals
• Base Sequence
• Benzoates (pharmacology, therapeutic use)
• Bone Remodeling (drug effects)
• Bone and Bones (drug effects, pathology)
• Calcium (metabolism)
• Disease Models, Animal
• Fibroblast Growth Factor-23
• Gene Knock-In Techniques
• HEK293 Cells
• Humans
• Hypercalciuria (drug therapy, genetics, pathology, physiopathology)
• Hypocalcemia (drug therapy, genetics, pathology, physiopathology)
• Hypoparathyroidism (congenital, drug therapy, genetics, pathology, physiopathology)
• Mice
• Molecular Sequence Data
• Mutant Proteins (metabolism)
• Mutation (genetics)
• Organ Size (drug effects)
• Phenotype
• Propanolamines (pharmacology, therapeutic use)
• Receptors, Calcium-Sensing (genetics)