We used next-generation sequencing to identify IGH genetic variation in two closely related hypertensive rat lines that differ in susceptibility to end-organ disease (SHR-A3 and SHR-B2). The two SHR lines differ extensively at the IGH locus from the rat reference genome sequence (RRGS) and from each other, creating 306 sequence unique IGH genes. Compared to IGH genes mapped in the RRGS, 98 are null gene alleles (31 are null in both SHR lines, 45 are null in SHR-A3 only, and 23 are null in SHR-B2 only). Of the 306 divergent gene sequences, 126 result in amino acid substitution and, among these, SHR-A3 and SHR-B2 differ from one another at the amino acid level in 96 segments. Twelve pseudogenes in the RRGS had changes displacing the stop codon and creating probable functional genes in either or both SHR-A3 and SHR-B2. A further 5 alleles that encoded functional RRGS genes or open reading frames were converted to pseudogenes in either or both SHR-A3 and SHR-B2. These studies reveal that the pre-immune immunoglobulin repertoire is highly divergent among SHR lines differing in end organ injury susceptibility and this may modify immune mechanisms in hypertensive renal injury.

High blood pressure exerts its deleterious effects on health largely through acceleration of end organ diseases. Among these, progressive loss of renal function is particularly important, not only for the direct consequences of kidney damage, but also because loss of renal function is associated with amplification of other adverse cardiovascular outcomes. Genetic susceptibility to hypertension and associated end organ disease is non-Mendelian in both humans and in a rodent model, the spontaneously hypertensive rat (SHR). Here we report that hypertensive end organ disease in the inbred SHR-A3 line is attributable to genetic variation in the immunoglobulin heavy chain on chromosome 6. This variation coexists with variation in a 10 Mbase block on chromosome 17 that contains genetic variation in two genes involved in immunoglobulin Fc receptor signaling. Substitution of these genomic regions into the SHR-A3 genome from the closely-related, but injury resistant, SHR-B2 line normalizes both biomarker and histological measures of renal injury. Our findings indicate that genetic variation leads to a contribution by immune mechanisms hypertensive end organ injury and that, in this rat model, disease is influenced by differences in germ-line antibody repertoire.

BackgroundWe have investigated serum levels of immunoreactive marinobufagenin (MBG) in 16‐ to 20‐week‐old spontaneously hypertensive rats (SHRs)‐A3 and in the normotensive Wistar‐Kyoto (WKY) rat strain in the absence of salt loading, and we have investigated the genetic control of serum MBG.Methods and ResultsWe genotyped the F2 progeny of an SHR‐A3×WKY intercross using a genome‐wide panel of 253 single‐nucleotide polymorphism markers that were dimorphic between SHR‐A3 and WKY and measured serum MBG by ELISA. Serum MBG levels were lower in SHR‐A3 than WKY rats (0.39±0.07 and 1.27±0.40 nmol/L, respectively), suggesting that MBG may not play a role in the markedly divergent blood pressure measured by telemetry in rats of these 2 strains (SHR‐A3 and WKY, 198.3±4.43 and 116.8±1.51 mm Hg, respectively). The strain difference in serum MBG was investigated to determine whether genomic regions influencing MBG might be identified by genetic mapping. Quantitative trait locus mapping indicated a single locus influencing serum MBG in the region of chromosome 6q12. Homozygosity of WKY alleles at this locus was associated with increased serum MBG levels. We surveyed whole genome sequences from our SHR‐A3 and WKY lines, seeking coding sequence variation between SHR‐A3 and WKY within the mapped locus that might explain the inherited strain difference in serum MBG.ConclusionsWe identified amino acid substitution in the sterol transport protein Abcg5, present in SHR‐A3, but absent in WKY, that is a potential mechanism influencing MBG levels.