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Background: Glucocorticoids are potent therapeutic agents frequently used for treatment of number of conditions, including hematologic, inflammatory and allergic diseases. Both their therapeutic and adverse effects display significant interindividual variation, partially attributable to genetic factors. We have previously isolated a seven-gene region of rat chromosome 8 sensitizing to dexamethasone (DEX)-induced dyslipidemia and insulin resistance of skeletal muscle. Using two newly derived congenic strains we aimed to investigate the effect of one of the prime candidates for this pharmacogenetic interaction, the Zbtb16 gene. Methods. Adult male rats of SHR-Lx.PD5PD-Zbtb16 (n = 9) and SHR-Lx.PD5SHR-Zbtb16 (n = 8) were fed standard diet (STD) and subsequently treated with DEX in drinking water (2.6 μg/ml) for three days. The morphometric and metabolic profiles of both strains including oral glucose tolerance test, triacylglycerols, free fatty acids, insulin and C-reactive protein levels were assessed before and after the DEX treatment. Insulin sensitivity of skeletal muscle and visceral adipose tissue was determined by incorporation of radioactively labelled glucose. Results. The differential segment of SHR-Lx.PD5SHR-Zbtb16 rat strain spans 563kb and contains six genes: Htr3a, Htr3b, Usp28, Zw10, Tmprss5, and part of Drd2. The SHR-Lx.PD5PD-Zbtb16 minimal congenic strain contains only Zbtb16 gene on SHR genomic background and its differential segment spans 254kb. Total body weight was significantly increased in SHR-Lx.PD5PD-Zbtb16 strain compared to SHR-Lx.PD5SHR-Zbtb16, however, no differences in the weights of adipose tissue depots were observed. While STD-fed rats of both strains did not show major differences in their metabolic profiles, after DEX treatment the SHR-Lx.PD5PD-Zbtb16 congenic strain showed increased levels of triacylglycerols, glucose and blunted inhibition of lipolysis by insulin. Both basal and insulin-stimulated incorporation of radioactively labeled glucose into skeletal muscle glycogen were significantly reduced in SHR-Lx.PD5PD-Zbtb16 strain but the insulin sensitivity of adipose tissue was comparable between the two strains. Conclusion. The metabolic disturbances including impaired glucose tolerance, dyslipidemia and insulin resistance of skeletal muscle observed after DEX treatment in the congenic SHR-Lx.PD5PD-Zbtb16 reveal the Zbtb16 locus as a possible sensitizing factor for side-effects of glucocorticoid therapy.

BACKGROUND The spontaneously hypertensive rat (SHR) is the most widely used model of essential hypertension and is susceptible to left ventricular hypertrophy (LVH) and myocardial fibrosis. Recently, a quantitative trait locus (QTL) that influences heart interstitial fibrosis was mapped to chromosome 8. Our aim was to dissect the genetic basis of this QTL(s) predisposing SHR to hypertension, LVH, and interstitial fibrosis. METHODS Hemodynamic and histomorphometric analyses were performed in genetically defined SHR.PD-chr.8 minimal congenic strain (PD5 subline) rats. RESULTS The differential segment, genetically isolated within the PD5 subline, spans 788kb and contains 7 genes, including the promyelocytic leukemia zinc finger (Plzf) gene that has been implicated in hypertrophy and cardiac fibrosis. Mutant Plzf allele contains a 2,964-bp deletion in intron 2. The PD5 congenic strain, when compared with the SHR, showed significantly reduced systolic blood pressure by approximately 15mm Hg (P = 0.002), amelioration of LVH (0.23±0.02 vs. 0.39±0.02g/100g body weight; P < 0.00001), and reduced interstitial fibrosis (17,478±1,035 vs. 41,530±3,499 μm(2); P < 0.0001). The extent of amelioration of LVH and interstitial fibrosis was disproportionate to blood pressure decrease in congenic rats, suggesting an important role for genetic factors. Cardiac expression of Plzf was significantly reduced in prehypertensive (8 and 21 days) congenic animals compared with controls. CONCLUSIONS These results provide compelling evidence of a significant role for genetic factors in regulating blood pressure, LVH, and cardiac fibrosis and identify mutant Plzf as a prominent candidate gene.

Deficiency of fatty acid translocase Cd36 has been shown to have a major role in the pathogenesis of metabolic syndrome in the spontaneously hypertensive rat (SHR). We have tested the hypothesis that the effects of Cd36 mutation on the features of metabolic syndrome are contextually dependent on genomic background. We have derived two new congenic strains by introgression of limited chromosome 4 regions of SHR origin, both including the defective Cd36 gene, into the genetic background of a highly inbred model of insulin resistance and dyslipidemia, polydactylous (PD) rat strain. We subjected standard diet-fed adult males of PD and the congenic PD.SHR4 strains to metabolic, morphometric and transcriptomic profiling. We observed significantly improved glucose tolerance and lower fasting insulin levels in PD.SHR4 congenics than in PD. One of the PD.SHR4 strains showed lower triglyceride concentrations across major lipoprotein fractions combined with higher levels of low-density lipoprotein cholesterol compared with the PD progenitor. The hepatic transcriptome assessment revealed a network of genes differentially expressed between PD and PD.SHR4 with significant enrichment by members of the circadian rhythmicity pathway (Arntl (Bmal1), Clock, Nfil3, Per2 and Per3). In summary, the introduction of the chromosome 4 region of SHR origin including defective Cd36 into the PD genetic background resulted in disconnected shifts of metabolic profile along with distinct changes in hepatic transcriptome. The synthesis of the current results with those obtained in other Cd36-deficient strains indicates that the eventual metabolic effect of a deleterious mutation such as that of SHR-derived Cd36 is not absolute, but rather a function of complex interactions between environmental and genomic background, upon which it operates.

Summary Rat hypodactyly was originally described by Moutier et al. (1973) as an autosomal recessive trait. The determining gene Hd has been recently mapped to rat chromosome 10 and is closely linked to the D10Rat31/32, D10Rat30 , and Myh3 loci ( Křenova et al. 1998). In homozygous state (Hd/Hd) , there is a variable reduction in the number of fingers and metacarpals — metatarsals of front and hind feet in males and females. Moreover, there is a male sterility in homozygotes whereas male heterozygotes are fertile. The light and electron microscopic examination confirmed disorder of spermatogenesis, loosening and vacuolization of seminiferous epithelium accompanied with a significantly decreased number of germ cells in testes of homozygotes. In an intercross population (Wistar Hd×BN-Lx)F2, an independent segregation of the major genes Lx , coding for the PLS (polydactyly-luxate syndrome), and Hd — hypodactyly was found together with irregular interactions of Hd and Lx genes in double homozygotes ( Hd/Hd, Lx/Lx ). The variable phenotype manifestation of foot malformation in double homozygous animals indicated modifying influences of genes of the genetic background. In order to study more precisely the role of the determining major gene Hd as well as the role of the putative modifying genes in the development of the foot malformation and male sterility, we started the production of two congenic strains by introgressing the Hd mutant gene onto the genetic backgrounds of the BN and SHR inbred strains.

Summary The SHR- Lx congenic strain carrying a differential segment of chromosome 8 of BN and PD origin was recently shown to exhibit a significant decrease in blood pressure as compared to the SHR strain. There were two positional candidate genes for blood pressure control mapped to the differential segment: the rat kidney epithelial potassium channel gene ( Kcnj1 ) and brain dopamine receptor 2 gene ( Drd2 ). Bot these genes were separated into SHR.BN-RNO8 congenic substrains. In this communication, we are presenting the assignment of two further putative candidate genes, which might be involved in blood pressure control to the BN/PD differential segment of the SHR- Lx congenic strain. These are: the gene coding for smooth muscle cell specific protein 22 ( Sm22 ) defined by the D8Mcw1 marker and neuronal nicotinic acetylcholine receptor gene cluster, defined by the D8Bord1 marker. Moreover, the glutamate receptor gene Grik4 which also maps to the differential segment of the SHR- Lx should be taken into account. The genetic separation of all these putative candidate genes of blood pressure control is being performed by recombinations and subsequent selection using (SHR×SHR- Lx ) intercross population.

Summary A new set of recombinant inbred [RI]strains has been developed complementary to the original RI strains BXH/HXB using the BXH2 RI strain and the SHR- Lx congenic strain as progenitors, both homozygous in Lx locus. The reason behind the production of this lies in a special SHR/BN gene combination in the BXH2 strain which is increasing the expressivity of the Lx gene and sensitizes this strain to teratogenic effects. On the contrary, the SHR genetic background minimizes the Lx gene expression as well as the teratogenic action of retinoic acid. There are 10 PXO strains in 17 th up to 21 st generation of inbreeding. The variability of leg malformation on PXO strains is similar to that in BXH/HXB polydactylous RI strains. The genotyping of PXO RI set has been started showing relatively high degree of homozygosity [over 90%] in individual RI strains. After inbreeding is accomplished the PXO will have become a useful complement to the original RI strain system. In preliminary teratologic testing, variable sensitivity to retinoic acid has been shown in 3 PXO strains.

We have developed a new, double-congenic rat strain BN- Lx.SHR2, which carries two distinct segments of chromosome 2 introgressed from the spontaneously hypertensive rat strain (SHR) into the genetic background of congenic strain BN- Lx, which was previously shown to express variety of metabolic syndrome features. In 16-wk-old male rats of BN- Lx and BN- Lx.SHR2 strains, we compared their glucose tolerance and triacylglycerol and cholesterol concentrations in 20 lipoprotein subfractions and the lipoprotein particle sizes under conditions of feeding standard and high-sucrose diets. Introgression of two distinct SHR-derived chromosome 2 segments resulted in decreased adiposity together with aggravation of glucose intolerance in the double-congenic strain. The BN- Lx.SHR2 rats were more sensitive to sucrose-induced rise in triacylglycerolemia. Although the total cholesterol concentrations of the two strains were comparable after the standard diet and even lower in BN- Lx.SHR2 after sucrose feeding, detailed analysis revealed that under both dietary conditions, the double-congenic strain had significantly higher cholesterol concentrations in low-density lipoprotein fractions and lower high-density lipoprotein fractions. We established a new inbred model showing dyslipidemia and mild glucose intolerance without obesity, attributable to specific genomic regions. For the first time, the chromosome 2 segments of SHR origin are shown to influence other than blood pressure-related features of metabolic syndrome or to be involved in relevant nutrigenomic interactions.