Congenic strains for genetic analysis of hypertension and dyslipidemia in the spontaneously hypertensive rat

Functional genomics as an emerging strategy for the investigation of central mechanisms in experimental hypertension

Centrally mediated increases in sympathetic nerve activity and attenuated arterial baroreflexes contribute to the pathogenesis of hypertension. Despite the characterization of cellular and physiological mechanisms that regulate blood pressure and alterations that contribute to hypertension, the genetic and molecular basis of this pathophysiology remains poorly understood. Strategies to identify genes that contribute to central pathophysiologic mechanisms in hypertension include integrative biochemistry and physiology as well as functional genomics. This article summarizes recent progress in applying functional genomics to elucidate the genetic basis of altered central blood pressure regulatory mechanisms in hypertension. We describe approaches others and we have undertaken to investigate gene expression profiles in hypertensive models in order to identify genes that contribute to the pathogenesis of hypertension. Finally, we provide the readers a roadmap for negotiating the route from experimental findings of gene expression profiling to translating their therapeutic potential. The combination of gene expression profiling and the phenotypic characterization of in vitro and in vivo loss or gain of function experiments for candidate genes have the potential to identify genes involved in the pathogenesis of hypertension and may present novel targets for therapy.

Substitution mapping of a blood pressure quantitative trait locus to a 2.73 Mb region on rat chromosome 1

OBJECTIVE

To improve the localization of a blood pressure quantitative trait locus (BP QTL) on rat chromosome (RNO) 1.

METHODS

Congenic substrains were derived from the progenitor congenic strains S.LEW(D1Mco4X1) and S.LEW(D1Mco4X5) which previously localized a BP QTL (region 2) to a 17cM interval on RNO1. The newly developed congenic substrains, along with control Dahl salt-sensitive (S) rats were fed a 2% NaCl diet for 24 days before their BP was compared by both tail-cuff and radiotelemetry methods.

RESULTS

By comparing BP of these congenic substrains to that of S rats, we have refined the location of the BP QTL2 region to a 2.73 Mb genomic interval that contains 19 annotated genes in the latest rat genome assembly (version 2.1). Slc9a3, the gene encoding the Na(+)/H(+) exchanger 3, originally a candidate gene in the BP QTL2 region, is excluded based on its map location.

CONCLUSION

Substitution mapping was used to reduce a BP QTL on RNO1 from 17 centimorgans (cM) to approximately 1.4 cM (= 2.73 Mb). This region now contains 19 annotated rat candidate genes.

Y-chromosome transfer induces changes in blood pressure and blood lipids in SHR

Previous studies with chromosome-Y consomic strains of spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats suggest that a quantitative trait locus for blood pressure regulation exists on chromosome Y. To test this hypothesis in the SHR-Brown Norway (BN) model and to study the effects of chromosome Y on lipid and carbohydrate metabolism, we produced a new consomic strain of SHR carrying the Y chromosome transferred from the BN rat. We found that replacing the SHR Y chromosome with the BN Y chromosome resulted in significant decreases in systolic and diastolic blood pressures in the SHR.BN-Y consomic strain (P<0.05). To elicit possible dietary-induced variation in lipid and glucose metabolism between the SHR progenitor and chromosome-Y consomic strains, we fed rats a high-fructose diet for 15 days in addition to the normal diet. On the high-fructose diet, the SHR.BN-Y consomic rats exhibited significantly increased levels of serum triglycerides and decreased levels of serum HDL cholesterol versus the SHR progenitor rats. Glucose tolerance and insulin/glucose ratios, however, were similar in both strains on both normal and high-fructose diets. These findings provide direct evidence that a gene or genes on chromosome Y contribute to the pathogenesis of spontaneous hypertension in the SHR-BN model. These results also indicate that transfer of the Y chromosome from the BN rat onto the SHR background exacerbates dietary-induced dyslipidemia in SHR. Thus, genetic variation in genes on the Y chromosome may contribute to variation in blood pressure and lipid levels and may influence the risk for cardiovascular disease.