The rat STSL locus: characterization, chromosomal assignment, and genetic variations in sitosterolemic hypertensive rats

Abstract

BackgroundElevated plant sterol accumulation has been reported in the spontaneously hypertensive rat (SHR), the stroke-prone spontaneously hypertensive rat (SHRSP) and the Wistar-Kyoto (WKY) rat. Additionally, a blood pressure quantitative trait locus (QTL) has been mapped to rat chromosome 6 in a New Zealand genetically hypertensive rat strain (GH rat). ABCG5 and ABCG8 (encoding sterolin-1 and sterolin-2 respectively) have been shown to be responsible for causing sitosterolemia in humans. These genes are organized in a head-to-head configuration at the STSL locus on human chromosome 2p21.MethodsTo investigate whether mutations in Abcg5 or Abcg8 exist in SHR, SHRSP, WKY and GH rats, we initiated a systematic search for the genetic variation in coding and non-coding region of Abcg5 and Abcg8 genes in these strains. We isolated the rat cDNAs for these genes and characterized the genomic structure and tissue expression patterns, using standard molecular biology techniques and FISH for chromosomal assignments.ResultsBoth rat Abcg5 and Abcg8 genes map to chromosome band 6q12. These genes span ~40 kb and contain 13 exons and 12 introns each, in a pattern identical to that of the STSL loci in mouse and man. Both Abcg5 and Abcg8 were expressed only in liver and intestine. Analyses of DNA from SHR, SHRSP, GH, WKY, Wistar, Wistar King A (WKA) and Brown Norway (BN) rat strains revealed a homozygous G to T substitution at nucleotide 1754, resulting in the coding change Gly583Cys in sterolin-1 only in rats that are both sitosterolemic and hypertensive (SHR, SHRSP and WKY).ConclusionsThe rat STSL locus maps to chromosome 6q12. A non-synonymous mutation in Abcg5, Gly583Cys, results in sitosterolemia in rat strains that are also hypertensive (WKY, SHR and SHRSP). Those rat strains that are hypertensive, but not sitosterolemic (e.g. GH rat) do not have mutations in Abcg5 or Abcg8. This mutation allows for expression and apparent apical targeting of Abcg5 protein in the intestine. These rat strains may therefore allow us to study the pathophysiological mechanisms involved in the human disease of sitosterolemia.

Sterolins ABCG5 and ABCG8: regulators of whole body dietary sterols

“…Thirdly, despite the close proximity and homology between ABCG5 and ABCG8, considerably more polymorphisms are present in ABCG8 compared to ABCG5. This seems to be a phenomenon confined to man, as analyses of the rodent STSL loci indicate an almost equal level of variability [40,63]. It is not clear if this is an indication that ABCG5 and ABCG8 may also have a function, independent of their role as heterodimers.…”

Missense Mutation inAbcg5in SHRSP Rats Does Not Accelerate Intestinal Absorption of Plant Sterols: Comparison with Wistar Rats

“…We concluded that one of the causes of deposition of plant sterols in SHRSP rats is acceleration of plant sterol absorption in the intestine. Since Scoggan et al 7) and Yu et al 8) found that WKY, SHR, and SHRSP rats have the same mutation in Abcg5, we concluded that accelerated absorption of plant sterols is caused by a malfunction of ABCG5, but no quantitative estimation of reduced excretion of plant sterols by intestinal ABCG5 and ABCG8 to the intestinal lumen in SHRSP rats has been done. In the present study, we compared the lymphatic absorption of various plant sterols between SHRSP and Wistar rats.…”

Missense Mutation ofAbcg5in Stroke-Prone Spontaneously Hypertensive Rats Does Not Influence Lymphatic Sitosterol Absorption Regardless of the Dose: Comparison with Wistar Rats

“…4) We have previously found that Wistar Kyoto (WKY) rats, spontaneously hypertensive rats (SHRs) and stroke-prone spontaneously hypertensive rats (SHRSPs) deposited plant sterols in the body. 5) Since Scoggan et al and Yu et al have shown all of these strains to have the same mutation of Abcg5, 6,7) it has been thought that the intestinal absorption of plant sterols by these strains would be accelerated by a malfunction of ABCG5 and hence that they would accumulate plant sterols in the body. However, inconsistent results have been obtained in plant sterol absorption studies of rat strains having the mutation of Abcg5.…”