MOLECULAR GENETICS OF LOW RENIN HYPERTENSION

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DESCRIPTION (Adapted from applicant's abstract): The investigators' laboratory continues to study the biochemistry, regulation and genetics of the kidney (K or type 2) isozyme of 11 Beta-hydroxysteroid dehydrogenase (11-HSD) and its gene (HSD11K). This enzyme plays a crucial role in maintaining the specificity of the mineralocorticoid receptor. Mutations in the gene cause a Mendelian form of hypertension, the syndrome of apparent mineralocorticoid excess. In biochemical studies, they will express the wild type 11-HSD K isozyme in E. coli and compare its kinetic properties with those of the native enzyme in placenta and the recombinant enzyme expressed in cultured mammalian cells. They will then modify the enzyme to increase its solubility and activity, and use affinity chromatography to purify the enzyme to homogeneity in an active form. The investigators will characterize the relationship between the membrane spanning domains and enzymatic activity, and will characterize the nucleotide binding site of the enzyme. They will recreate mutations causing the syndrome of apparent mineralocorticoid excess in order to detect low levels of residual activity. The investigators will identify and characterize transcriptional regulatory elements in HSD11K. The investigators will use transient transfection of reporter constructs, electrophoretic mobility shift assays and DNAse I footprinting assays to study enhancer and silencer elements, and will identify possible locus control regions by looking for tissue-specific DNAse I hypersensitivity in chromatin. The investigators will confirm functioning of putative locus control regions by producing appropriate strains of transgenic mice. In genetic studies, they will identify additional mutations causing the syndrome of apparent mineralocorticoid excess and determine their functional effects in mammalian and/or bacterial expression systems. The investigators will determine the role of 11-HSD K in the development of essential hypertension, using both linkage and association studies.