Molecular pathophysiology of the calcium-sensing receptor

Thesis

The calcium-sensing receptor (CaSR) is a parathyroid and kidney expressed G-protein-coupled receptor that regulates extracellular calcium (Ca²⁺_o) homeostasis. The CaSR mainly couples to G-protein subunit-α₁₁ (Gα₁₁), and germline Gα11 mutations have recently been identified in patients with hypercalcaemia and hypocalcaemia. The CaSR is also expressed in non-Ca²⁺_o-regulating tissues such as the vasculature and pancreatic islets, where it is implicated in vascular calcification and insulin secretion, respectively. The aims of the studies described in this thesis were to: 1) Functionally characterise Gα₁₁ mutations and evaluate the effect of CaSR-targeted drugs in cells expressing mutant Gα₁₁ proteins; 2) Investigate for associations between common CaSR single nucleotide polymorphisms (SNPs) and vascular calcification; 3) Determine whether the CaSR may influence systemic glucose homeostasis; and 4) Evaluate the effect of a CaSR-targeted allosteric modulator on glucose homeostasis. These studies demonstrated germline Gα11 mutations to influence the responsiveness of CaSR-expressing cells to Ca²⁺o in vitro, and these abnormalities were rectified by CaSR-targeted drugs. Moreover, patient-based studies revealed CaSR SNPs not to be major determinants for vascular calcification. However, a common CaSR SNP was significantly associated with serum glucose concentrations. Furthermore, metabolic studies of mice with a gain-of-function CaSR mutation, known as Nuf, revealed impaired glucose tolerance in association with reduced plasma insulin concentrations and diminished pancreatic islet mass. An examination of isolated Nuf islets demonstrated alterations in insulin and glucagon secretion. Administration of a negative allosteric CaSR modulator to Nuf mice significantly improved the impaired glucose tolerance in vivo. In summary, the in vitro, animal model and patient-based studies encompassed in this thesis have revealed the effectiveness of CaSR-targeted drugs in modulating alterations in downstream signalling proteins, demonstrated a role for the CaSR in pancreatic islet function and glucose homeostasis, and indicate a potential application of CaSR-targeted drugs in modulating glucose metabolism.

Authors: Babinsky, V

• DOI: 10.5287/ora-vm54kywoj
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford