Phenotypic and genetic analyses of subcongenic BB.SHR rat lines shorten the region on chromosome 4 bearing gene(s) for underlying facets of metabolic syndrome

Abstract

Congenic BB.SHR ( D4Got41-Npy-Tacr1; BB.4S) rats develop an incomplete metabolic syndrome with obesity, hyperleptinemia, and dyslipidemia compared with their progenitor strain, the diabetes-prone BB/OK rat. To narrow down the underlying gene(s), two subcongenic BB.SHR rat lines, briefly termed BB.4Sa and BB.4Sb, were generated. Male BB.4S ( n = 20), BB.4Sa ( n = 24), and BB.4Sb ( n = 26) were longitudinally characterized for facets of the metabolic syndrome and analyzed for expression of genes located in the region of interest in liver and blood. Body weight gain was comparable, serum triglycerides and leptin were significantly increased, and total cholesterol and HDL-cholesterol ratio were decreased in BB.4S compared with both subcongenics. Serum insulin was significantly higher in BB.4S and BB.4Sa than in BB.4Sb. The adiposity index showed a graduated decrease from BB.6S to BB.4Sb. Obvious differences in relative expression were found in 6 of 10 genes in liver and in 2 of 9 genes in blood. Only one gene, the eukaryotic translation initiation factor 2α kinase 3 ( Eif2ak3 also called Perk or Pek), was significantly less expressed in liver and in blood of both subcongenic BB.4Sa and BB.4Sb compared with their “parental” BB.4S rats. Based on the phenotype and genotype in BB.4S and its subcongenic derivatives, the most important region on chromosome 4 can be said to lie between D4Got72 and Tacr1. Eif2ak3 is mapped in this region. Considering the function of Eif2ak3, it may be a candidate gene for the development of glucose intolerance found in both subcongenics but not in BB.4S. Allelic variants between BB/OK and SHR could influence Eif2ak3 function, possibly leading not only to glucose intolerance but also to the disturbances in hepatic and renal function found in human Wolcott-Rallison syndrome.