Effects of chromosome 17 on features of the metabolic syndrome in the Lyon hypertensive rat

The metabolic syndrome (involving obesity, hypertension, dyslipidemia, insulin resistance, and a proinflammatory/prethrombotic state) is a major risk factor for cardiovascular disease. Its incidence continues to rise, in part because of the epidemic increase in obesity. The Lyon hypertensive (LH) rat is a model for hypertension and several other features of the metabolic syndrome, having high body weight, plasma cholesterol, and triglycerides, increased insulin-to-glucose ratio, and salt-sensitive hypertension. Previous genetic studies in LH/Mav rats and a normotensive control (LN/Mav) identified quantitative trait loci (QTLs) on rat chromosome (RNO)17 for multiple features of the metabolic syndrome. To further evaluate the role of RNO17 in the LH rat, we generated a consomic strain (LH-17(BN)) by substituting LH RNO17 with that of the sequenced Brown Norway (BN/NHsdMcwi) rat. Male LH and BN rats and LH-17(BN) rats were characterized for blood pressure and metabolic and morphological parameters. Similar to the protective effect of LN alleles, the LH-17(BN) rat also showed decreased body weight, triglycerides, and blood pressure; however, there was no significant difference in cholesterol or insulin-to-glucose ratio. Therefore, the substitution of the LH chromosome 17 is sufficient to recapitulate some, but not all, of the traits previously mapped to this chromosome. This could be due to the lack of a susceptible LH genome background or due to the introgression of chromosome 17 from another strain. Regardless, this study provides a single-chromosome genetic model for further dissection of blood pressure and morphological and metabolic traits on this chromosome.

[Importance of chromosome 17 in genetically hypertensive rats of the Lyon strain (LH): study of a consomic strain]

Genetically hypertensive rats of the Lyon strain (LH) associate high blood pressure (BP), exaggerated salt-sensitivity, and a metabolic syndrome made of overweight together with increased plasma lipids and insulin/glucose ratio. A genetic mapping study in a large population of F2 rats derived from a cross between hypertensive (LH) and normotensive rats (LN) showed the existence, on chromosome 17, of two clusters of Quantitative Traits Loci (QTLs). The first one was associated to morphological parameters whereas the second influenced blood pressure and plasma lipids level. In order to determine the functional importance of this QTLs, we generated a consomic strain LH-17BN in which the LH chromosome 17 has been fully substituted by a normotensive Brown Norway (BN) one. These LH-17BN, as well as LH and BN male rats of the parental strain were phenotyped. This included radio telemetric measurement of BP during normal and elevated salt intake (1% and then 2% in the drinking water) as well as the determination of morphological, metabolic (triglycerides, cholesterol) and renal (creatinine clearance, proteinuria) parameters. LH-17BN, compared to LH rats, exhibited significant decreases in body weight and blood pressure. Renal functions are improved (decreased of proteinuria). Finally, plasma triglycerides were reduced and reach the level observed in BN rats. In conclusion, the present work demonstrates that, in our model, chromosome 17 contains genes which influence morphology, blood pressure, renal function, and lipid metabolism. Interestingly, chromosome 17 almost completely explains the spontaneous hypertriglyceridemia observed in Lyon Hypertensive rats.