Various studies, including our own, demonstrate a role for the extracellular calcium-sensing receptor (CaR)in the regulation of renal calcium handling. Population studies have suggested a role for genetic variants inCaR in contributing to the human variation in renal calcium excretion. Here we will further explore the role ofCaR in the kidney, with a focus on proximal tubule function. We will use two complementary mouse modelsas well as human studies to further these goals.
In Aim 1, we will focus on the role of CaR in the proximaltubule. We will use our existing CaR deficient model to examine the role of CaR in specific aspects ofproximal nephron physiology; elements of this study will be extended to mice generated in Aim 2 withproximal nephron-specific ablation of CaR. Prior data suggest that extracellular calcium modulates 1a-hydroxylation of vitamin D by the proximal tubule, hence we will assess the regulation of 1a-hydroxylaseexpression and function in CaR-deficient mice. As luminal calcium in the proximal nephron affects thereabsorption of several solutes, we will examine the role of CaR in regulating proximal tubular fluid andsolute transport using tubule perfusion, confocal immunofluorescence, and eventually transport assays inprimary cell culture.
In Aim 2, we will develop a mouse harboring a 'floxed' CaR allele. We will use proximaltubule Cre transgenic mice to allow us to target CaR inactivation to this renal segment. These mice will beused in Aim 1 studies also. Whole animal studies in this new model will help clarify the in vivo contributionsof proximal tubule CaR to kidney function.
In Aim 3, we will study common variation in human CaR withProjects 4 and Core A. We will perform functional studies to assess the biological effects of known and thenewly identified non-synonymouscSNPs (including effects on signaling, cell-surface expression, anddimerization). We will genotype DMA and assay CaR transcript expression using a series of humanlymphoblastoid cell lines in order to determine the correlation between genetic haplotype and CaRexpression level. This last 'Subaim' will serve as a pilot for possible further exploration ofhaplotype/expression correlation studies of other genes in Core A.
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