Spontaneously Hypertensive Rat Chromosome 2 with Mutant Connexin 50 Triggers Divergent Effects on Metabolic Syndrome Components.

Metabolic syndrome is a frequent condition with multifactorial aetiology. Previous studies indicated the presence of genetic determinants of metabolic syndrome components on rat chromosome 2 (RNO2) and syntenic regions of the human genome. Our aim was to further explore these findings using novel rat models. We derived the BN-Dca and BN-Lx.Dca congenic strains by introgression of a limited RNO2 region from a spontaneously hypertensive rat strain carrying a mutation in the Gja8 gene (SHR-Dca, dominant cataract) into the genomic background of Brown Norway strain and congenic strain BN-Lx, respectively. We compared morphometric, metabolic and cytokine profiles of adult male BN-Lx, BN-Dca and BN-Lx.Dca rats. We performed in silico comparison of the DNA sequences throughout RNO2 differential segments captured in the new congenic strains. Both BN-Dca and BN-Lx.Dca showed lower total triacylglycerols and cholesterol concentrations compared to BN-Lx. Fasting insulin in BN-Dca was higher than in BN-Lx.Dca and BN-Lx. Concentrations of several proinflammatory cytokines were elevated in the BN-Dca strain, including IL-1α, IL-1ß, IFN-γ and MCP-1. In silico analyses revealed over 740 DNA variants between BN-Lx and SHR genomes within the differential segment of the congenic strains. We derived new congenic models that prove that a limited genomic region of SHR-Dca RNO2 significantly affects lipid levels and insulin sensitivity in a divergent fashion.

Connexin 50 mutation lowers blood pressure in spontaneously hypertensive rat.

We assessed the effect of the previously uncovered gap junction protein alpha 8 (Gja8) mutation present in spontaneously hypertensive rat - dominant cataract (SHR-Dca) strain on blood pressure, metabolic profile, and heart and renal transcriptomes. Adult, standard chow-fed male rats of SHR and SHR-Dca strains were used. We found a significant, consistent 10-15 mmHg decrease in both systolic and diastolic blood pressures in SHR-Dca compared with SHR (P<0.01 and P<0.05, respectively; repeated measures analysis of variance (ANOVA)). With immunohistochemistry, we were able to localize Gja8 in heart, kidney, aorta, liver, and lungs, mostly in endothelium; with no differences in expression between strains. SHR-Dca rats showed decreased body weight, high-density lipoprotein cholesterol concentrations and basal insulin sensitivity in muscle. There were 21 transcripts common to the sets of 303 transcripts in kidney and 487 in heart showing >1.2-fold difference in expression between SHR and SHR-Dca. Tumor necrosis factor was the most significant upstream regulator and glial cell-derived neurotrophic factor family ligand-receptor interactions was the common enriched and downregulated canonical pathway both in heart and kidney of SHR-Dca. The connexin 50 mutation L7Q lowers blood pressure in the SHR-Dca strain, decreases high-density lipoprotein cholesterol, and leads to substantial transcriptome changes in heart and kidney.

CD36-deficient congenic strains show improved glucose tolerance and distinct shifts in metabolic and transcriptomic profiles.

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.

Impairment of Sox9 expression in limb buds of rats homozygous for hypodactyly mutation.

Rat hypodactyly (hd) is an autosomal recessive mutation manifesting in homozygotes as reduction or loss of digits II and III. We mapped the hd allele to a short segment of chromosome 10, containing 16 genes. None of these genes has been shown to influence limb development yet. In situ hybridization showed no changes in several important patterning genes (Shh, Fgf8, Bmp2, 4, 7). However, we found that expression of cartilage condensation marker Sox9, and Bmp receptor Bmpr1b (acting as an upstream activator of Sox9 expression) is absent from the subepithelial mesenchyme of the digit condensations II and III. The failure of the chondrogenic condensations to extend towards the subepithelial mesenchyme may reduce the size of digit primordia and underlie the subsequent loss of phalanges and reduction of metacarpals/metatarsals in hd rats.

Region of rat chromosome 8 determines complex nutrigenetic interactions under conditions of sucrose and cholesterol diets.

We have previously established a congenic strain SHR-Lx that carries a differential segment of rat chromosome 8 introgressed from a model of metabolic syndrome--the polydactylous rat strain--on the genomic background of spontaneously hypertensive rat (SHR). We compared the glucose tolerance and lipid profile of adult SHR and SHR-Lx males under conditions of standard diet and diets enriched in sucrose and cholesterol, respectively. While there was no evident difference between the SHR and SHR-Lx on standard diet, the one-week sucrose administration revealed the congenic strain sensitivity to carbohydrate-induced dyslipidemia conferred by the differential segment with only mild derangement of glucose tolerance. On the other hand, the high-cholesterol diet administration for three-weeks resulted in a contrasting pattern as the congenic strain displayed significantly lower concentrations of free fatty acids and improved glucose tolerance compared to SHR. After one-month washout period, the SHR-Lx showed higher insulin, triglyceride and cholesterol concentrations together with diminished insulin sensitivity of visceral adipose tissue. In summary, we have identified a genomic region syntenic to human chromosome 11q23, which determines complex nutrigenetic interactions under conditions of sucrose- and cholesterol-enriched diets.

A 14-gene region of rat chromosome 8 in SHR-derived polydactylous congenic substrain affects muscle-specific insulin resistance, dyslipidaemia and visceral adiposity.

The SHR and the PD/Cub are two established rodent models of human metabolic syndrome. Introgression of a ca 30 cM region of rat chromosome 8 from PD/Cub onto the genetic background of SHR was previously shown to influence several of the metabolic syndrome-related traits along with causing the PLS in the SHR-Lx congenic strain. In the process of identification of the causative alleles, we have produced several congenic sublines. The differential segment of SHR-Lx PD5 congenic substrain [SHR.PD(D8Rat42-D8Arb23)/Cub] spans approximately 1.4 Mb encompassing only 14 genes. When comparing the metabolic, morphometric and gene expression profiles of the SHR-Lx PD5 vs. SHR, the polydactyly and several distinct metabolic features observed in the original SHR-Lx congenic were still manifested, suggesting that the responsible genes were "trapped" within the relatively short differential segment of PD/Cub origin in SHR-Lx PD5. Particularly, the SHR-Lx PD5 displayed substantial reduction of insulin sensitivity confined to skeletal muscle. Among the candidate genes, the promyelocytic leukaemia zinc-finger Plzf (Zbtb16) transcription repressor is most likely responsible for the Lx mutation resulting in PLS and could also be involved in the alteration of metabolic pathways. The sequence analysis of the Plzf gene revealed a SNP leading to a threonine to serine substitution in SHR at aminoacid position 208 (T208S). In summary, we have isolated a 1.4 Mb genomic region syntenic to human chromosome 11q23, which, apart from causing polydactyly-luxate syndrome (PLS), affects total body weight, adiposity, lipid profile, insulin sensitivity of skeletal muscle and related gene expression as shown in the SHR-Lx PD5 congenic substrain.

Molecular analysis of the sex hormone-binding globulin gene in the rat hypodactylous mutation (Hd).

Sex hormone-binding globulin or ABP/SHBG is an extracellular androgen and oestrogen carrier. In the rat, ABP/SHBG is secreted by Sertoli cells of the testis and is thought to regulate androgen bioavailability in the male reproductive tract. During ontogenesis, ABP/SHBG is expressed in many mesoderm-derived tissues, including interdigital mesenchyme of the developing autopodium. Shbg is thus a candidate for Hd, comprising autopodium (hand and foot) reduction and male sterility resulting from spermatogenesis impairment. Moreover, linkage mapping of Hd revealed that an intragenic marker for Shbg, D10Wox12, was non-recombinant with Hd. Sequencing of the entire coding sequence of Shbg failed to identify any variation in hypodactylous animals, distinct from two control strains. However, RT-PCR analysis revealed a significantly higher level of the Shbg transcript in hypodactylous rats compared to SHR controls. Whether Shbg expression is upregulated due to a cis-acting mutation in regulatory elements of the Shbg gene or it is a secondary result of spermatogenesis failure remains to be determined.

Genetic analysis of "metabolic syndrome" in the spontaneously hypertensive rat.

In the current review, we summarize results of genetic analyses of "metabolic syndrome" in the spontaneously hypertensive rat (SHR). These results include (1) linkage analyses in the HXB/BXH recombinant inbred (RI) strains derived from SHR and Brown Norway (BN-Lx) strains which revealed quantitative trait loci (QTL) for hemodynamic and metabolic traits on several chromosomes, (2) genetic isolation of these putative QTL within differential chromosome segments of SHR.BN congenic strains, (3) detailed mapping of these QTL within limited chromosome segments of SHR.BN congenic sublines, (4) sequencing of selected positional candidate genes which revealed important mutations in the Cd36 and Srebp1 SHR genes, (5) functional tests of these candidate genes in SHR transgenic lines, and (6) integrated gene expression profiling and linkage mapping in RI strains which will be used to identify co-regulated genes and to determine co-segregation of transcriptional profiles with physiological and pathophysiological phenotypes.

Isotretinoin and fenofibrate induce adiposity with distinct effect on metabolic profile in a rat model of the insulin resistance syndrome.

OBJECTIVE: To investigate the effect of transcription-modulating drugs, fenofibrate and isotretinoin, on metabolic profile, insulin sensitivity of adipose and muscle tissues and gene expression in a genetic model of insulin resistance syndrome, polydactylous rat strain (PD/Cub). DESIGN: Administration of fenofibrate (100 mg/kg/day), isotretinoin (30 mg/kg/day) or vehicle to adult male PD/Cub rats fed standard laboratory chow for 15 days. MEASUREMENTS: Parameters of lipid and carbohydrate metabolism-oral glucose tolerance test, serum concentrations of insulin, triglycerides (TG), free fatty acids (FFA), glycerol, total cholesterol (CH); morphometric variables, in vitro insulin sensitivity of adipose and muscle tissues, catecholamine-stimulated lipolysis and the expression of ApoC-III and Hnf-4 genes in liver. RESULTS: Both experimental groups displayed an increase in adiposity with contrasting effects on TG (lowered by fenofibrate and increased by isotretinoin) and gene expression (no change in fibrate-treated rats and increased expression of ApoC-III and Hnf-4 in isotretinoin-treated group). Fenofibrate-treated rats also showed decreased concentrations of FFA and CH with concomitant decrease of catecholamine-induced lipolysis in adipocytes, but also hyperinsulinemia and the highest insulin/glucose ratio. Isotretinoin increased glycerol concentrations and decreased the insulin sensitivity of peripheral tissues. CONCLUSION: The PD/Cub rat showed a distinct pharmacogenetic reaction to fenofibrate and isotretinoin administration. Several lines of evidence now implicate specific variant(s) of ApoC-III and/or ApoA-V alleles as responsible for the dyslipidemia observed in this genetic model. The PD/Cub strain may also serve as a pharmacogenetic model for dissection of the retinoid-induced hypertriglyceridemia.

PXO set of recombinant inbred strains of the rat: a new strain distribution pattern containing 448 markers.

A new PXO set of RIS represents a fixed F2 population derived from polydactylous (P) congenic strain SHR.Lx and oligodactylous (O) RI strain BXH2. The PXO strains were derived as a complementary set to current RIS (HXB, BXH) of the laboratory rat. All PXO strains are homozygous in the Lx allele and express different morphological phenotypes of the polydactyly-luxate syndrome (PLS) due to variable combinations of Lx modifying genes of either SHR or BN origin. The SDP is being built up by genotyping polymorphic microsatellite markers and several gene polymorphisms. The markers were ordered according to data from public mapping resources such as the Rat Genome Database (rgd.mcw.edu) and current SDP of the other RI strain sets (HXB, BXH). The resulting map corresponding to the common SDP of HXB, BXH RIS sets consists of 448 markers, from which 261 were proven to be polymorphic in the PXO set. The SDP of PXO strains with polymorphic markers arranged in approximately 5 cM intervals is ready for the association analysis and interval mapping in interconnection with the SDP of HXB/BXH strains.

Genetic isolation of quantitative trait loci for blood pressure development and renal mass on chromosome 5 in the spontaneously hypertensive rat.

Total genome scans of genetically segregating populations derived from spontaneously hypertensive rats (SHR) and other rat models of essential hypertension suggested a presence of quantitative trait loci (QTL) regulating blood pressure on multiple chromosomes, including chromosome 5. The objective of the current study was to test directly a hypothesis that chromosome 5 of the SHR carries a blood pressure regulatory QTL. A new congenic strain was derived by replacing a segment of chromosome 5 in the SHR/Ola between the D5Wox20 and D5Rat63 markers with the corresponding chromosome segment from the normotensive Brown Norway (BN/Crl) rat. Arterial pressures were directly monitored in conscious, unrestrained rats by radiotelemetry. The transfer of a segment of chromosome 5 from the BN strain onto the SHR genetic background was associated with a significant decrease of systolic blood pressure, that was accompanied by amelioration of renal hypertrophy. The heart rates were not significantly different in the SHR compared to SHR chromosome 5 congenic strain. The findings of the current study demonstrate that gene(s) with major effects on blood pressure and renal mass exist in the differential segment of chromosome 5 trapped within the new SHR.BN congenic strain.

Differential linkage of triglyceride and glucose levels on rat chromosome 4 in two segregating rat populations.

The PD/Cub is a recently established model of the IRS. The BN.SHR4 congenic strain was derived by introgression of the chromosome 4 segment of SHR origin (including the defective Cd36/Fat allele) onto the BN/Cub genetic background. We investigated the linkage of metabolic and morphometric phenotypes (total body weight, OGTT, fasting serum levels of TG, FFA) on chromosome 4 in two separate F2 rat populations: the PD/Cub x BN/Cub and PD/Cub x BN.SHR4 (total N = 243). In the PD/Cub x BN.SHR4 F2s, we found significant linkage for fasting TG levels (LOD = 3.26) and suggestive linkage for fasting glycaemia (LOD = 2.80) in the interval Il-6 - D4Bro1, i.e. the part of chromosome 4 of SHR origin in the BN.SHR4 congenic. However, no linkage for fasting TG concentrations, fasting glycaemia or any other followed parameter was found in the second, PD/Cub x BN/Cub F2. The differential linkage of TG and glucose levels to the centromeric part of rat chromosome 4q in the studied F2s points to the importance of this region for the lipid and carbohydrate metabolism at the specific age (10 months) and diet (standard chow) combination. The Cd36/Fat and Il-6 genes are the preliminary positional candidates for the observed effect.

Metabolic characterization of insulin resistance syndrome feature loci in three brown Norway-derived congenic strains.

Studies on genetic determination of the insulin resistance syndrome in rat models revealed several susceptibility loci for features of this complex phenotype, i.e. dyslipidemia, insulin resistance and obesity. We analysed the influence of introgression of the RNO4, RNO20 segments of SHR origin and RNO8 segment of PD/Cub origin (all previously shown to be involved in (dys)regulation of carbohydrate and lipid metabolism) onto the genetic background of a common progenitor, the Brown Norway (BN/Cub) rat. The differential segments were genetically characterized in the BN.PD-D8Rat39/D8Rat35 (BN-Lx, RNO8 congenic), BN.SHR-Il6/Cd36 (BN.SHR4, RNO4 congenic) and BN.PD-D8Rat39/D8Rat3, SHR-D4Mgh2/Cd36,SHR-D20Wox3/D20Mgh5 (BN-Lx 1K, RNO4, 8, 20 triple congenic) strains and their metabolic profiling was performed. After one week of high-sucrose diet, all congenic strains showed substantially higher levels of serum triglycerides and free fatty acids as well as impaired glucose tolerance in comparison with the BN/Cub progenitor strain. The BN-Lx 1K triple congenic strain displayed the most profound dyslipidemia, glucose intolerance and highest increase of triglyceridemia in response to high-sucrose diet overall, though accompanied with the significantly lowest adiposity index. These results further support the role of genes present within the studied chromosomal regions in observed metabolic disturbances. Furthermore, these findings point to the studied loci within the gene-gene and gene-environment interactions involved in pathogenesis of the insulin resistance syndrome. The set of defined congenic strains provides a possibility of assessing individual features of such a complex phenotype.

Rosiglitazone improves insulin resistance, lipid profile and promotes adiposity in a genetic model of metabolic syndrome X.

RSG is a member of the TZD group of drugs widely used in treatment of type 2 diabetes. The underlying mechanism of TZD action in insulin-sensitive tissues is not fully understood. In this study we show that 14-day RSG administration in a new rodent model of metabolic syndrome X, polydactylous rat strain (PD/Cub), substantially improves its lipid profile (serum TGs 4.20 +/- 0.23 vs 2.34 +/- 0.14 mmol/l, P < 0.0001; FFA 0.46 +/- 0.05 vs 0.33 +/- 0.02 mmol/l, P = 0.017), diminishes the liver TG depots (15.76 +/- 0.60 vs 8.44 +/- 0.55 micromol/g, P < 0.0001), serum insulin concentrations (1.10 +/- 0.08 vs 0.63 +/- 0.02 nmol/l, P < 0.0001) and promotes visceral adiposity (adiposity index 1.28 +/- 0.03 vs 1.85 +/- 0.07, P < 0.0001). No changes were observed in serum or liver concentrations of cholesterol. Concomitantly, both basal and insulin-stimulated glycogen synthesis in red-fibre type muscle (m. soleus) was enhanced, as well as glucose uptake into adipose tissue. However, glucose oxidation in soleus (basal and insulin-stimulated) remained unchanged. In consent with previously published data we suggest the current pharmacogenetic study as a further proof of substantial influence of genetic background on the physiological outcome of TZD therapy.

Y-chromosome transfer induces changes in blood pressure and blood lipids in SHR.

Previous studies with chromosome-Y consomic strains of spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats suggest that a quantitative trait locus for blood pressure regulation exists on chromosome Y. To test this hypothesis in the SHR-Brown Norway (BN) model and to study the effects of chromosome Y on lipid and carbohydrate metabolism, we produced a new consomic strain of SHR carrying the Y chromosome transferred from the BN rat. We found that replacing the SHR Y chromosome with the BN Y chromosome resulted in significant decreases in systolic and diastolic blood pressures in the SHR.BN-Y consomic strain (P<0.05). To elicit possible dietary-induced variation in lipid and glucose metabolism between the SHR progenitor and chromosome-Y consomic strains, we fed rats a high-fructose diet for 15 days in addition to the normal diet. On the high-fructose diet, the SHR.BN-Y consomic rats exhibited significantly increased levels of serum triglycerides and decreased levels of serum HDL cholesterol versus the SHR progenitor rats. Glucose tolerance and insulin/glucose ratios, however, were similar in both strains on both normal and high-fructose diets. These findings provide direct evidence that a gene or genes on chromosome Y contribute to the pathogenesis of spontaneous hypertension in the SHR-BN model. These results also indicate that transfer of the Y chromosome from the BN rat onto the SHR background exacerbates dietary-induced dyslipidemia in SHR. Thus, genetic variation in genes on the Y chromosome may contribute to variation in blood pressure and lipid levels and may influence the risk for cardiovascular disease.

Rat inbred PD/cub strain as a model of dyslipidemia and insulin resistance.

Genome scan and metabolic profile of the PD/Cub rat inbred strain in comparison with SHR and BN strains is presented. The PD/Cub strain has been bred by brother sister mating for more than 60 generations since 1969. Its highly inbred status has been confirmed by PCR genotyping with more than 170 microsatellite markers. No case of residual heterozygosity has been recorded. Accordingly, the values obtained by the analysis of metabolic phenotypes are homogeneous with low variance. The PD/Cub strain has significantly higher triglyceride levels and epididymal fat weight as compared to both SHR and BN strains. The PD strain also displays the lowest incorporation of 14C-U glucose into the epididymal adipose tissue. The data on glucose metabolism clearly indicate that the PD/Cub strain is insulin resistant. Genetic homogeneity and reproducibility of experimental results qualify the PD/Cub rats as an animal model for analysis of the syndrome X.

Mapping of quantitative trait loci (QTL) of differential stress gene expression in rat recombinant inbred strains.

OBJECTIVE: Stress has been shown to be a major environmental contributor to cardiovascular diseases through its effects on blood pressure variability and cardiac function. The cellular stress response is characterized by the expression of specific heat stress genes (hsps), under the transcriptional control of heat shock transcription factors (HSTFs). The levels of hsp mRNA depend on the severity of the stress, with hstf1 acting as a stress sensor. The aim of this work was to evaluate the genetic contribution of the variability in hsp expression, and to identify its putative quantitative trait loci (QTL). METHODS: Twenty recombinant inbred rat strains (RIS) were studied. The animals underwent a standardized, identical 1 h immobilization stress in restraint cages, followed by 1 h of rest before sacrifice. Total RNA was extracted from the heart kidneys and adrenals, and the mRNA levels of hsp27, hsp70, hsp84, hsp86 and hsp105 were measured. The strain distribution pattern (SDP) of hsp expression was correlated with that of 475 polymorphic markers distributed throughout the RIS genome. A polymorphism of rat hstf1 in RIS was used for its mapping in RIS. RESULTS: Despite an identical stress being applied to all strains, hsp expression showed up to a 1 2-fold gradient with little intra-strain variability, indicative of a strong genetic contribution to the trait Heritability ranged from 50 to 77% for most hsp genes in the three target organs. The continuous SDP of stress gene expression indicated the polygenic nature of the trait A common locus on chromosome 7 (at D7Cebrp187s3 marker) was consistently associated with all hsp expression in most of the organs [with a likelihood of odds (LOD) score of 3.0 for hsp27 expression]. We have mapped rat hstf1 on chromosome 7 at the same locus. Finally, the D4Mit19 marker was significantly associated with hsp84 expression in the heart (LOD score of 3.1). CONCLUSION: Two loci were linked with the differential expression of HSPs in response to immobilization stress in target organs of RIS. The chromosome 7 locus unveiled for all HSPs could explain up to 42% of the observed inter-strain variability of hsp levels in response to stress. We propose hstf1 as a positional candidate at this locus.

Contribution of autosomal loci and the Y chromosome to the stress response in rats.

Stress is a critical contributor to cardiovascular diseases through its impact on blood pressure variability and cardiac function. Familial clustering of reactivity to stress has been demonstrated in human subjects, and some rodent models of hypertension are hyperresponsive to stress. Therefore, the present study was designed to uncover the genetic determinants of the stress response. We performed a total genome linkage search to identify the loci of the body temperature response to immobilization stress in a set of recombinant inbred strains (RIS) originating from reciprocal crosses of spontaneously hypertensive rats (SHR) with a normotensive Brown Norway Lx strain. Two quantitative trait loci (QTLs) were revealed on chromosomes (Chrs) 10 and 12 (logarithm of odds scores, 2.2 and 1. 3, respectively). The effects of these QTLs were enhanced by a high sodium diet (logarithm of odds scores, 4.0 and 3.3 for Chrs 10 and 12, respectively), which is suggestive of a salt-sensitive component for the phenotype. Congenics for Chr 10 confirmed both the QTL and the salt effect in RIS. Negatively associated loci were also identified on Chrs 8 and 11. Interaction between the loci of Chrs 10 and 12 was demonstrated, with the rat strains bearing SHR alleles at both loci having the highest thermal response to stress. Furthermore, the Y Chr of SHR origin enhanced the response to immobilization stress, as demonstrated in 2 independent models, RIS and Y Chr consomics. However, its full effect requires autosomes of the SHR strain. These findings provide the first evidence for the genetic determination of reactivity to stress with interactions between autosomal loci and between the Y and autosomal Chrs that contribute to the explanation of the 46% of variance in the stress response.

Genetic analysis of cardiovascular risk factor clustering in spontaneous hypertension.

The SHR is the most widely studied animal model of hypertension. In this strain, as in many humans with essential hypertension, increased blood pressure has been reported to cluster with other risk factors for cardiovascular disease, including insulin resistance and dyslipidemia. However, the genetic mechanisms that mediate this clustering of risk factors for cardiovascular disease or the hypertension "metabolic syndrome" remain poorly understood. In the current studies, we have demonstrated (1) that a gene or genes responsible for a whole spectrum of cardiovascular risk factors mapped to a limited segment of the centromeric region of rat chromosome 4, (2) that a spontaneous deletion in the gene for Cd36 that encodes a fatty acid transporter and is located directly at the peak of QTL linkages on chromosome 4 has been indirectly linked to the transmission of insulin resistance, defective fatty acid metabolism, and increased blood pressure, and (3) based on complementation analysis in two transgenic lines expressing wild-type Cd36 on the genetic background of the SHR strain harboring the deletion variant of Cd36, we have established that defective Cd36 can be a determinant of disordered fatty acid metabolism, glucose intolerance, and insulin resistance in spontaneous hypertension.

Genetics of Cd36 and the clustering of multiple cardiovascular risk factors in spontaneous hypertension.

Disorders of carbohydrate and lipid metabolism have been reported to cluster in patients with essential hypertension and in spontaneously hypertensive rats (SHRs). A deletion in the Cd36 gene on chromosome 4 has recently been implicated in defective carbohydrate and lipid metabolism in isolated adipocytes from SHRs. However, the role of Cd36 and chromosome 4 in the control of blood pressure and systemic cardiovascular risk factors in SHRs is unknown. In the SHR. BN-Il6/Npy congenic strain, we have found that transfer of a segment of chromosome 4 (including Cd36) from the Brown Norway (BN) rat onto the SHR background induces reductions in blood pressure and ameliorates dietary-induced glucose intolerance, hyperinsulinemia, and hypertriglyceridemia. These results demonstrate that a single chromosome region can influence a broad spectrum of cardiovascular risk factors involved in the hypertension metabolic syndrome. However, analysis of Cd36 genotypes in the SHR and stroke-prone SHR strains indicates that the deletion variant of Cd36 was not critical to the initial selection for hypertension in the SHR model. Thus, the ability of chromosome 4 to influence multiple cardiovascular risk factors, including hypertension, may depend on linkage of Cd36 to other genes trapped within the differential segment of the SHR. BN-Il6/Npy strain.