Interaction Between Chromosome 2 and 3 Regulates Pulse Pressure in the Stroke-Prone Spontaneously Hypertensive Rat

Abstract

H uman essential hypertension is a complex, multifactorial, quantitative trait under polygenic control, with inherited factors contributing ≤30% of the variation in blood pressure (BP). 1 The search for the specific genetic variations contributing to this heritability remains challenging. Recent genome-wide association studies collectively explain only a very small proportion of the total variation in systolic BP (SBP) or diastolic BP (DBP; ≈2.2%), 2,3 which suggests the existence of many more undiscovered BP-related variants.Genetic detection of complex polygenic diseases is complicated by potential gene-gene, gene-environment interactions, and nonsequence epigenetic modifications. In particular, there is growing evidence for epistasis among BP quantitative trait loci (QTL) in inbred rat models of hypertension. 4-11We have previously identified BP QTL on rat chromosomes (RNO) 2 and RNO3 in a linkage analysis of an F2 cross between stroke-prone spontaneously hypertensive (SHRSP) and Wistar Kyoto (WKY) rats. 12 We subsequently confirmed the RNO2 loci with the production of congenic strains and identified candidate genes for baseline BP and response to salt loading. [13][14][15] The aims of this study were to confirm the RNO3 QTL and to investigate interaction between the loci on RNO2 and RNO3 through the generation and phenotypic assessment of single and bicongenic strains. Methods Animal StrainsInbred colonies of SHRSP and WKY have been developed and maintained at the University of Glasgow since 1991, as described previously.12 All animals were housed under controlled environmental conditions, fed standard rat chow (rat and mouse no No. 1 maintenance diet, Special Diet Services) and water provided ad libitum. At 18 weeks of age, rats were given a salt challenge (1% NaCl in drinking water) for 3 weeks. All animal procedures performed were approved Abstract-In an F2 cross between stroke-prone spontaneously hypertensive (SHRSP) and Wistar Kyoto (WKY) rats, we previously identified blood pressure quantitative trait loci (QTL) on rat chromosome (RNO) 2 and a pulse pressure QTL on RNO3. The aims of this study were to confirm the QTL on RNO3 and to investigate interaction between RNO2 and RNO3 loci through the generation and phenotypic assessment of single RNO3 congenic (SP.WKY Gla 3a) and bicongenic (SP.WKY Gla 2a/3a) strains. Hemodynamic profiling, vascular function, and renal histology were examined in these newly generated strains along with the previously reported RNO2 congenic strain (SP.WKY Gla 2a). Our results demonstrate significant equivalent reduction in systolic, diastolic, and pulse pressure phenotypes in SP.WKY Gla 3a and SP.WKY Gla 2a rats, whereas greater reductions were observed with the SP.WKY Gla 2a/3a bicongenic strain achieving blood pressure levels similar to normotensive WKY rats. Epistasis was observed between pulse pressure QTL on RNO2 and 3 at baseline and during 1% salt challenge. Vascular function and renal pathology studies indicate that QTL on RNO3 are responsible for salt-induced kidney p...

Dissecting the genetic components of a quantitative trait locus for blood pressure and renal pathology on rat chromosome 3

“…Inbred colonies of SHRSP and WKY rats have been developed and maintained at the University of Glasgow since 1991, as described previously [18,19]. All animals were housed under controlled environmental conditions, fed standard rat chow (rat and mouse no.…”

“…1 maintenance diet, Special Diet Services) and water provided ad libitum . The RNO3-congenic strain, SP.WKY Gla 3a (D3Mgh16-D3Wox28), is a previously published strain [18]. Genotyping was carried out as previously described using genomic DNA isolated from a 4-mm ear notch at weaning [19].…”

“…Grey and white bars indicate regions of WKY and SHRSP homozygosity, respectively, whereas hatched bars indicate areas containing a recombination. The location of previously identified systolic blood pressure (SBP), diastolic blood pressure (DBP) and pulse pressure (PP) loci [18] is indicated to the right of the figure. Mean change in baseline and salt-loaded SBP in comparison to the SHRSP parental strain is illustrated below each of the respective congenic sub-strains.…”

“…For renal histology, adjacent transverse sections of kidney (3 μm thick) were stained with haematoxylin and eosin (H&E), elastin muscle fibrin stain (EMSB) or periodic acid Schiff (PAS), and scored for renal changes according to a previously described scoring system [18,20]. All images shown were viewed on an Olympus BX51 microscope with an attached Olympus DP72 digital camera and DP2-BSW software.…”

“…We have previously utilized congenic (SP.WKY Gla 3a) and bicongenic (SP.WKY Gla 2a/3a) strains generated on the stroke-prone spontaneously hypertensive (SHRSP) genetic background to confirm the importance of RNO3 genetic loci on BP elevation, pulse pressure (PP) variability and renal pathology during baseline and salt-challenge periods [18]. In this previous study, the introgressed congenic interval within the SP.WKY Gla 3a strain was large, spanning 155.4 Mbp and encompassing approximately 85% of the length of RNO3.…”