Genetic determinants of water balance in the elderly

描述（由申请人提供）：全身性水平衡紊乱（即低钠血症和高钠血症）在老年人、慢性病患者和住院患者中极为常见。低钠血症，特别是严重的低钠血症，即使没有明显的合并症，也会显著增加死亡率。阳离子通道TRPV4被认为是长期寻找的全体性低渗的中心传感器：它被相对水分过剩（即低钠血症/低渗）激活；它在大脑的渗透调节核中表达；删除该基因的小鼠表现出异常的水代谢。我们已经确定了人类TRPV4基因的两个非同义单核苷酸多态性（即，导致氨基酸变化）。当在培养细胞中表达时，由这些次要等位基因中的任何一个编码的TRPV4蛋白对低毒性的反应都不如野生型通道。此外，我们以初步的方式显示，一个次要的等位基因在异常水代谢的人类受试者中显着过度代表。在209名健康老年受试者中，该TRPV4等位基因在血清钠浓度< 135 mEq/l的受试者中的患病率约为正常血钠受试者的5倍。

DESCRIPTION (provided by applicant): Disorders of systemic water balance (i.e., hypo- and hypernatremia) are extremely common among the elderly, chronically ill, and hospitalized patients. Hyponatremia, particularly if severe, is associated with markedly increased mortality, even in the absence of evident comorbidity. The cation channel TRPV4 is believed to be the long-sought central sensor of systemic hypotonicity: it is activated by relative water excess (i.e., hyponatremia/hypotonicity); it is expressed in the osmoregulatory nuclei of the brain; and mice deleted for the gene exhibit abnormal water metabolism. We have identified two non-synonymous single nucleotide polymorphisms in the human TRPV4 gene (i.e., resulting in an amino acid change). When expressed in cultured cells, TRPV4 protein encoded by either of these minor alleles is less responsive to hypotonicity than is the wild-type channel. Furthermore, we show in preliminary fashion that one minor allele is significantly over-represented among human subjects with aberrant water metabolism. In 209 healthy elderly subjects, this TRPV4 allele was approximately five-fold more prevalent among subjects with a serum sodium concentration of < 135 mEq/liter than in normonatremic subjects. We propose to investigate this functionally significant TRPV4 minor allele on two levels. In Aim I, we will phase, in preliminary fashion, the haplotype(s) that includes this minor allele of interest, to exclude the possibility that a tightly linked polymorphism contributes to the hyponatremic phenotype. Any newly identified polymorphisms in the haplotype will be tested for functional significance using in vitro assays addressing transcription, mRNA stability and splicing, and protein function. In Aim II, we will test for an association between the TRPV4 minor allele and the presence of clinical hyponatremia in a second, much larger, data set. Banked serum and DNA from 6000 healthy elderly subjects in the Osteoporotic Fractures in Men (MrOS) study will be analyzed for serum sodium concentration (as an index of water balance) and TRPV4 genotype, respectively. With this combined approach, we will address the physiological significance of the TRPV4 alleles at the cellular level, and at the human population level. The over-all objective is to prospectively identify patients at increased risk for potentially life-threatening retention of free water, for example when treated with hypotonic fluids in the post-operative setting, or when treated with a thiazide-type diuretic. Many chronic disease states and several widely prescribed medications can cause dangerous abnormalities in water balance in an unpredictable fashion; perturbed water balance can generally only be detected through measurement of the serum sodium concentration . This proposal aims to increase our understanding of disorders of water balance among the elderly, and to genetically identify patients who may be at increased risk for potentially life-threatening retention of water.