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Physiol. Genomics 27: 95-102, 2006. First published July 5, 2006; doi:10.1152/physiolgenomics.00039.2006
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Received 4 March 2006; accepted in final form 23 June 2006.
Physiological Genomics 27:95-102 (2006)
1094-8341/06 $8.00 © 2006 American Physiological Society

Novel double-congenic strain reveals effects of spontaneously hypertensive rat chromosome 2 on specific lipoprotein subfractions and adiposity

Ondrej Seda1,2,3, Lucie Sedová1, Frantisek Liska1, Drahomíra Krenová1, Vratislav Prejzek1, Ludmila Kazdová2, Johanne Tremblay3, Pavel Hamet3 and Vladimír Kren1

1 Institute of Biology and Medical Genetics of the First Faculty of Medicine of Charles University and the General Teaching Hospital, Prague, Czech Republic
2 Department of Metabolism and Diabetes, Institute for Clinical and Experimental Medicine, Prague, Czech Republic
3 Centre de Recherche, Centre Hospitalier de l'Universite de Montreal, Montreal, Canada


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
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.

BN-Lx; triacylglycerol; cholesterol; metabolic syndrome; insulin resistance; obesity; comparative genomics


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
THE IMPORTANCE OF ALTERED lipid allostasis is widely recognized as crucial risk factor of cardiovascular disease (CVD) as well as an important component of Type 2 diabetes and metabolic syndrome. In the latter two conditions, we are recently witnessing a conceptual shift toward a more "lipocentric perspective" of their pathogenesis (32). The combination of high triacylglycerol (TG), low-density lipoprotein cholesterol (LDL-C), and low high-density lipoprotein cholesterol (HDL-C) concentrations poses a major risk for CVD and forms an integral component of metabolic syndrome, together with insulin resistance, obesity, and hypertension. Although often clustering in a single subject, each member of the "lipid triad" has been shown to represent an independent risk factor of CVD with distinct underlying genomic determinants (6). It has been shown that certain lipoprotein particle types convey largely detrimental effects due to their biochemical characteristics and that specific pattern of lipoprotein profile may be correlated to amount of visceral fat (18), so they may serve as useful markers for clinical risk assessment (4, 9). Several lines of evidence from human and animal model studies point to a substantial genetic influence on the intermediate traits of dyslipidemia. Those include lipoprotein particle sizes (3), concentrations of specific lipoprotein fractions (41), and their changes in response to dietary, pharmacological, and other environmental stimuli (26). The potential success of the search for genomic determinants of complex metabolic traits depends on the degree and clarity of resolution achieved on both sides of the genotype-phenotype equation. Major issues thought to hamper such analyses are of several kinds, starting with the phenotype definition itself. Dichotomous division into affected and nonaffected status may well serve in a clinical setting as an initial step for risk assessment and selection of the treatment algorithm. However, from the genetic point of view, traits like hypertriacylglycerolemia (28), obesity (21), hypertension (11), or Type 2 diabetes (1) represent a heterogeneous mixture of oligogenic conditions with varying strength of environmental components. So, intermediate (or more "proximal") phenotypes are therefore often analyzed instead under an assumption of their reduced genetic complexity. Recently, encouraging results came from several human studies based on novel approaches designed to resolve the complicating issues (29). Apart from development of new statistical and bioinformatic techniques (Bayesian methods, admixture mapping, genetic genomics), there are now several available concepts of decreasing heterogeneity by identification of more homogeneous subsets of the complex traits, e.g., hypertension with and without obesity (7, 12, 13, 20, 43). In the experimental setting, genetically defined animal models (mostly rodent) kept within controlled environments and subjected to detailed phenotype sampling protocols may facilitate the resolution of genome-environment interactions in the pathogenesis of complex metabolic diseases. Then, given the availability of rat, mice, and human genome sequences, the comparative genomic approach allows validation of new allelic variants or potential clinical markers in human conditions.

One of the most extensive model sets for analysis of the genomic component of metabolic syndrome is the HXB/BXH recombinant inbred (RI) strain panel derived originally from the spontaneously hypertensive rat (SHR) and normotensive BN-Lx congenic strain (22). We tested the hypothesis that two defined regions of SHR chromosome 2 previously shown to influence blood pressure significantly (23) also harbor genes/genomic features affecting other facets of metabolic syndrome by means of derivation of a novel double-congenic strain from the two RI panel progenitors and phenotypic profiling, including detailed assessment of TG and cholesterol distribution into lipoprotein subfractions.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Rat strains.
The BN.PD-(D8Rat39-D8Rat35)/Cub [BN-Lx hereafter, Rat Genome Database (34) RGD ID: 728144] congenic strain was derived from the Brown Norway (BN/Cub) inbred strain. The introgression of the differential segment of chromosome 8 of the polydactylous rat (PD/Cub, RGD ID: 728161) origin was achieved by backcross breeding onto a BN/Cub genetic background (15, 16). The differential segment carries not only the Lx (Plzf or Zbtb16) mutant allele, apparently responsible for the polydactyly-luxate syndrome (30), but also other genes of PD/Cub origin, altogether resulting in decreased insulin sensitivity and dyslipidemia compared with the progenitor BN/Cub strain (27, 28).

The double-congenic BN.PD-(D8Rat39-D8Rat35).SHR(D2Mit4-D2Rat28).SHR(D2Rat103-D2Rat107) strain (BN-Lx.SHR2 hereafter) was derived by introgressing the rat chromosome 2 (RNO2) segment of SHR origin into the BN-Lx genetic background employing the marker-assisted approach. The identity of the rat chromosome 8 (RNO8) differential segment of PD/Cub origin in BN-Lx and the BN-Lx.SHR2 congenic strains was verified in this study by typing of 22 microsatellite markers polymorphic between the BN and PD/Cub (D8Mgh1, D8Mgh4, D8Mit2, D8Mit3, D8Mit4, D8Got72, D8Rat19, D8Rat20, D8Rat44, D8Rat46, D8Rat47, D8Rat49, D8Rat51, D8Rat53, D8Rat71, D8Rat75, D8Rat94, D8Rat112, D8Rat164, D8Rat213, D8Rat219, D8Rat226). The extent of the RNO2 differential segment was assessed by genotyping 40 markers polymorphic between the BN and SHR, evenly covering the RNO2 chromosome (Fig. 1). These were: D2Arb20, D2Arb42, D2Mco14, D2Mit4, D2Mit5, D2Mit6, D2Mit8, D2Mit12, D2Mit19, D2Mit21, D2Mgh8, D2Mgh9, D2Mgh10, D2Mgh12, D2Mgh16, D2Rat95, D2Rat19, D2Rat22, D2Rat24, D2Rat28, D2Rat33, D2Rat35, D2Rat37, D2Rat56, D2Rat60, D2Rat70, D2Rat79, D2Rat88, D2Rat94, D2Rat95 D2Rat107, D2Rat118, D2Rat133, D2Rat157, D2Rat189, D2Rat196, D2Rat199, D2Rat201, D2Rat285, D2Rat320.


Figure 1
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  		Fig. 1. The chromosome 2 differential segments in BN-Lx.SHR2 double-congenic strain and their relation to quantitative trait loci (QTLs) identified in rat studies. The markers genotyped in this study (left) define the chromosome 2 segments of Brown Norway (BN, open bars) and of spontaneously hypertensive rat (SHR, solid bars) origin. To the right of the chromosome, the extent of reported rat QTLs for phenotypes relevant to the current study are shown by vertical bars; if the peak of linkage was reported, it is indicated by a horizontal mark. The abbreviations of the QTLs followed by the relevant strain name in brackets are given according to the nomenclature of the Rat Genome Database (17). Kidm, kidney mass QTL; Gluco, glucose level QTL; Glu, glucose concentration QTL; Obs, mesenteric fat adipose index QTL; Scl, serum cholesterol level QTL; Slep, serum leptin concentration QTL; TC, total cholesterol QTL; Tgl, triglyceride level QTL; Niddm, noninsulin-dependent diabetes mellitus QTL; Iddm, insulin-dependent diabetes mellitus QTL; BB, BioBreeding rat; GK, Goto-Kakizaki rat; HTG, hereditary hypertriglyceridemic rat; LH, Lyon hypertensive rat; OLETF, Otsuka-Long-Evans-Tokushima fatty rat; PD, polydactylous rat; SDT, spontaneously diabetic Torii rat; SS, Dahl "salt-sensitive" rat.

 
Experimental protocol.
All experiments were performed in agreement with the Animal Protection Law of the Czech Republic (311/1997), which is in compliance with the European Community Council recommendations for the use of laboratory animals 86/609/ECC, and were approved by the ethical committee of the First Faculty of Medicine. Male BN-Lx (n = 6) and BN-Lx.SHR2 (n = 6) rats were fed standard laboratory chow (STD) ad libitum. At the age of 4 mo, the rats were fed a high-sucrose diet (HSD, 70% calories as sucrose) for 1 wk. Blood samples were drawn after overnight fasting, and the oral glucose tolerance test (OGTT) was performed before and after HSD administration. The rats were killed in a postprandial state, and the weights of heart, liver, kidneys, adrenals, epididymal, and retroperitoneal fat pads were determined.

DNA extraction, genotyping.
The rat genomic DNA was isolated from the tail incision samples by a modified phenol extraction method. Polymorphic microsatellite loci were amplified by PCR under conditions optimized for each marker. Sequences of the selected markers were retrieved from public databases (RGD, http://rgd.mcw.edu/; The Wellcome Trust Centre for Human Genetics, http://www.well.ox.ac.uk/; or Whitehead Institute/MIT Center for Genome Research, http://www-genome.wi.mit.edu/). The PCR products were separated on polyacrylamide (7–10%) or agarose (2–4%) gels, stained by ethidium bromide, and visualized using InstaDoc digital system (Bio-Rad Laboratories, Hercules, CA).

Metabolic measurements.
The OGTT was performed after overnight fasting. Blood for glycemia determination (Ascensia Elite Blood Glucose Meter, Bayer HealthCare, Mishawaka, IN; validated by Institute of Clinical Biochemistry and Laboratory Diagnostics of the First Faculty of Medicine) was drawn from the tail at intervals of 0, 30, 60, 120, and 180 min after intragastric glucose administration to conscious rats (3 g/kg total body wt, 30% aqueous solution). Plasma lipoproteins were analyzed by an on-line dual enzymatic method for simultaneous quantification of cholesterol and TG by HPLC at Skylight Biotech (Akita, Japan) according to the procedure described previously (37).

Statistical analysis.
When comparing total body weight and biochemical variables, we used two-way ANOVA with strain (BN-Lx, BN-Lx.SHR2) and diet (STD, HSD) followed by the post hoc Tukey's honest significance difference test for comparison of the specific pairs of variables (see Table 1). For comparisons of only two groups (organ weights), Student's t-test was used. Null hypothesis was rejected whenever P < 0.05. Correlational matrices were generated for the complete set of measured and derived variables using Pearson's correlation coefficient.


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  		Table 1. Two-way analysis of variance results for triacylglycerol and cholesterol concentration in major lipoprotein subfractions in BN-Lx vs. BN-Lx.SHR2 rats

 

   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 GRANTS
 REFERENCES
 
Genomic characteristics of the differential segments in the new BN-Lx.SHR2 double-congenic strain.
We found the differential segment of the chromosome 8 of PD/Cub origin in the BN-Lx.SHR2 to be identical with that of BN-Lx strain, as all the used marker's genotypes matched in the two strains. As for chromosome 2, our genotyping scan of 40 microsatellite markers revealed that the BN-Lx.SHR2 double congenic carries two distinct segments of SHR origin, spanning ~53 Mb (centromeric segment) and 92 Mb (telomeric segment), respectively (Fig. 1). Several total genome scans conducted throughout the BN-Lx.SHR2 derivation eventually excluded the presence of other non-BN alleles than those fixed on chromosomes 2 and 8, confirming the congenicity of the new strain. The two SHR-derived segments on chromosome 2 hence represent the only genomic differences between BN-Lx and BN-Lx.SHR2 congenic strains.

Chromosome 2 segments of SHR origin decrease adiposity and induce glucose intolerance.
As shown in Table 2, there were no strain differences in total body weight or its change in response to HSD feeding. Compared with BN-Lx, the BN-Lx.SHR2 strain had higher kidney weight and significantly lower weights of both epididymal (visceral) and retroperitoneal fat pads. The weight of all other internal organs did not differ between the strains. Although displaying lower fasting plasma glucose concentrations under both dietary conditions (BN-Lx.SHR2: 79 ± 4 and 79 ± 2 vs. BN-Lx: 99 ± 5 and 108 ± 5 mg/dl for standard and sucrose diets, respectively; ANOVASTRAIN P < 0.0001), the double congenic showed reduced tolerance to glucose load under both standard and sucrose dietary conditions, as shown in Fig. 2.


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  		Table 2. Morphometric comparison of BN-Lx vs. BN-Lx.SHR2 rats

 

Figure 2
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  		Fig. 2. The glucose tolerance in BN-Lx vs. BN-Lx.SHR2 rats under conditions of standard (STD) and high-sucrose diets (HSD). The course of glycemic curves in BN-Lx (open symbols) vs. BN-Lx.SHR2 (closed symbols) under conditions of STD (A) and HSD (B). C: incremental areas under the glycemic curves (AUC) (180 min) for BN-Lx (open bars) vs. BN-Lx.SHR2 (closed bars) rats. Significance levels are given for strain comparison according to the post hoc Tukey's honest significance difference (HSD) test of the 2-way ANOVA with strain and diet as major factors. *P < 0.05; **P < 0.01; ***P < 0.001.

 
Chromosome 2 segments of SHR origin sensitize to sucrose-induced rise in TG concentrations.
When fed the standard diet, the double-congenic strain displayed higher TG concentrations only in the LDL subfractions (Fig. 3), resulting in fasting triacylglycerolemia comparable to that of BN-Lx (Table 2). However, in reaction to HSD feeding, concentration of total TG in BN-Lx.SHR2 has risen by 66% compared with a 30% rise in BN-Lx, driven mainly by an increase of very low-density lipoprotein (VLDL)-TG. Moreover, the HSD-induced decrease in LDL-TG was only 33% in BN-Lx.SHR2 compared with 48% in BN-Lx.


Figure 3
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  		Fig. 3. The triacylglycerol content in 20 lipoprotein subfractions in BN-Lx (open bars) vs. BN-Lx.SHR2 (closed bars) rats under conditions of STD (A) and HSD (B). Within the graph, the significance levels of strain comparison by post hoc Tukey's HSD test are shown as follows: *P < 0.05; **P < 0.01; ***P < 0.001. The allocation of individual lipoprotein subfractions to major lipoprotein classes is shown in order of particle's decreasing size from left to right. CM, chylomicron; VLDL, very low-density lipoprotein; LDL, low density lipoprotein; HDL, high-density lipoprotein.

 
Chromosome 2 segments of SHR origin induce unfavorable cholesterol distribution into specific lipoprotein subfractions.
Both under standard and sucrose diet conditions, the BN-Lx.SHR2 showed higher LDL-C and lower HDL-C concentrations (Table 3) although the total cholesterol was comparable between the two strains at STD and even lower in the HSD-fed double congenic. As in the case of TG, the direction of concentration changes within most individual lipoprotein subfractions was similar in both strains, differing though in their degree (Fig. 4). Under standard diet conditions the lipoprotein particle sizes did not differ between the two strains. HSD induced a complex shift toward smaller VLDL and larger LDL in BN-Lx.SHR2, combined with smaller HDL in the double-congenic strain (Table 4).


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  		Table 3. Major TG, cholesterol subfractions, and free glycerol comparison between STD- and HSD-fed BN-Lx vs. BN-Lx.SHR2 rats

 

Figure 4
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  		Fig. 4. The cholesterol content in 20 lipoprotein subfractions in BN-Lx (open bars) vs. BN-Lx.SHR2 (closed bars) rats under conditions of STD (A) and HSD (B). Within the graph, the significance levels of strain comparison by post hoc Tukey's HSD test are shown as follows: *P < 0.05; **P < 0.01; ***P < 0.001. The allocation of individual lipoprotein subfractions to major lipoprotein classes is shown in order of particle's decreasing size from left to right.

 

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  		Table 4. Lipoprotein particle size comparison between STD- and HSD-fed BN-Lx vs. BN-Lx.SHR2 rats

 
Chromosome 2 segments of SHR origin modify the reaction patterns to HSD administration.
We generated the correlational matrices similar to "physiological profiles" (33) to systematically compare the reaction patterns of the two strains to HSD stimulus. Although these findings should not be overestimated, we found that especially for HDL and LDL fractions there are markedly distinct reaction profiles attributable to the genomic regions of RNO2 constituting the differential segments in BN-Lx.SHR2 (Fig. 5). Although there was no observable correlation of cholesterol concentrations in small LDL particles between standard and HSD conditions in BN-Lx, the BN-Lx.SHR2 showed consistently strong positive correlations across several fractions constituting this class (r > 0.8, P < 0.001).


Figure 5
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  		Fig. 5. Correlations of concentrations and particle sizes of LDL and HDL cholesterol (-C) in BN-Lx ({circ}) vs. BN-Lx.SHR2 (•). On x- and y-axes, variables for STD and HSD conditions are shown, respectively. The Pearson correlation coefficient (r) with corresponding P value is indicated for BN-Lx.SHR2 (bold) and BN-Lx.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
GRANTS
 REFERENCES
 
We employed a detailed lipoprotein profiling protocol in a functional genomic setting, utilizing novel double-congenic strain BN-Lx.SHR2. This strain was derived by targeted combination of genomic information of the two progenitors of the HXB/BXH RI set, one of the prime available rodent sets used for genetic analysis of metabolic syndrome (5, 13, 22, 25). The SHR chromosome region overlapping with the two segments present in the BN-Lx.SHR2 strain was shown to strongly influence systolic and diastolic blood pressures, an observation validated by their reduction in the SHR.BN2 congenic strain (23). Linkage studies in crosses derived from the SHR including the HXB/BXH RI panel also identified several candidate loci for features of dyslipidemia (24); however, so far none has been localized on RNO2. In this study, the detrimental lipid profile, together with tendency to deterioration of glucose tolerance, has resulted from introgression of two blood pressure-related chromosome 2 segments of SHR into the genomic background of BN-Lx, a congenic strain with already aberrant carbohydrate and lipid metabolism (27). Somewhat surprisingly, the metabolic effects were accompanied by an overall decrease in adiposity. These findings seem to be consistent with the emerging concepts of metabolic syndrome, atherosclerosis, and other complex metabolic diseases as series of clinically and genetically distinct conditions (29). In humans, similar dissociation of metabolic syndrome features has been shown for hypertension-associated vs. hypertension-dissociated obesity (19, 20) or subsets of metabolic syndrome (31). Creation and utilization of models replicating particular setups of CVD risk factors and their specific environmental sensitivity as found in human subjects will probably become essential in dissecting the genomic and pathophysiological drivers of particular conditions, as well as identifying specific biomarkers (e.g., sequence variants, biochemical traits). Here, detailed assessment of lipoprotein subfractions has led to allocation of specific genomic regions to shifts in TG and cholesterol distribution within 20 distinct lipoprotein subfractions. Moreover, the introgressed segments in the new double-congenic strain were shown to be involved in regulation of nutrient-driven changes of the distribution profile, so acute exposure to a diet rich in sucrose revealed the sensitization effect of the differential RNO2 segments in the BN-Lx.SHR2 strain, resulting in greater differences in sucrose-induced concentrations of TG and cholesterol in most lipoprotein subclasses (Figs. 3 and 4) compared with the BN-Lx. There is no clear-cut dependence on a genome x diet interaction for the small LDL, and the overall mean of LDL particle size is even higher in BN-Lx.SHR2. However, if the traditional definition of small dense LDL is applied (classes 10–13 in Fig. 4), the overall concentration of cholesterol in these particles is higher in BN-Lx.SHR2. Also, the correlational profiles (Fig. 5) suggest exclusively in BN-Lx.SHR2 the tendency toward a positive correlation of cholesterol concentrations in LDL between standard and sucrose diets with the opposite for LDL particle size. The interaction with sucrose also enhanced the difference in the proportion of cholesterol abundance in large vs. small HDL particles toward smaller, less favorable values in the double-congenic strain, opposite to "atheroprotective" elevated HDL2/HDL3 ratio. On the other hand, there was virtually no effect of diet on overall glucose tolerance in either of the strains, corresponding to previous observations of a major impact of 1-wk sucrose/fructose intervention on triacylglycerolemia without substantial reduction in insulin sensitivity of peripheral tissues (38).

The centromeric differential segment in BN-Lx.SHR2 corresponds to several parts of murine chromosomes 15 yet is clearly distinct from those bearing quantitative trait loci (QTLs) for lipid-related traits (40, 41). Neither of the syntenic portions of human chromosomes 5 and 8 was reported to bear any linkage or association signals relevant to traits analyzed in the current study. Outside the numerous accounts of blood pressure linkage and association in various rodent models, there is corroborating evidence in support of importance of both segments "captured" in BN-Lx.SHR2 for kidney weight (Fig. 1), in Lyon hypertensive rats (2), and hereditary hypertriglyceridemic (HTG) rats (36).

As shown in Fig. 1, triacylglycerolemia was linked to the regions overlapping with the telomeric differential segment of BN-Lx.SHR2 in HTG (34, 14), a strain originally derived from Wistar rats (39), like the SHR (17). This may suggest the existence of an ancestral variant common to the two strains, although confirmation will be necessary due to the rather large extent of the overlap. A mouse QTL dubbed Cq3 that controls plasma cholesterol and phospholipid levels was identified in C57BL/6J (B6) x KK-A(y) F2 mice in a region of murine chromosome 3 corresponding to the telomeric RNO2 differential segment of BN-Lx.SHR2. Syntenic to the same region, the AMP deaminase 1 gene has been recently shown to be associated with a highly heritable trait of insulin clearance in Mexican Americans (10). Thus there is only limited comparative genomic evidence for the metabolic importance of this genomic region. Nevertheless, it is possible to speculate that it may be rather a reflection of the small number of human and mouse studies performed so far with rigorous assessment of detailed lipoprotein profile and relatively strong involvement of the region in gene-nutrient interactions.

Adding the SHR strain to the group of inbred models sharing the genomic feature (present within the chromosome 2 segments in question) with the strong influence on metabolic parameters thus enhances the chance of identification of corresponding variants responsible for human dyslipidemia and glucose intolerance. Because of the relatively large span of the differential segments, it is premature to pinpoint individual candidate genes for the observed differences between BN-Lx and BN-Lx.SHR2. Although it may be tempting to mention several genes present in the introgressed segments of RNO2 like fatty acid binding protein 2, a gene associated with metabolic syndrome features (42), there would be a great risk of being lured by genes with known function, possibly missing the causative alleles that may not have been previously linked to adiposity, glucose intolerance, or dyslipidemia. This is even more pertinent in light of recent findings of the Japanese FANTOM consortium, further stressing the importance of nonprotein coding genes (8). Rather, a hypothesis-free extension of this experiment, like a microarray study, should give clearer answer, possibly in combination with narrowing the extent of the differential segment in the process of derivation of congenic substrains. Moreover, the observed difference between the two strains can be attributed not only directly to the introgressed SHR alleles, but also to the re-established gene-gene interactive networks between the introgressed segments and the genomic background.

In summary, we present a newly derived double-congenic rat strain that exhibits a distinct combination of dyslipidemia and mild glucose intolerance in a nonobese setting. To our knowledge, this is the first proof of involvement of chromosome 2 alleles of spontaneously hypertensive rat in other than hemodynamic traits. The new BN-Lx.SHR2 strain may serve as a useful genetic model for detailed dissection of genomic architecture of its particular presentation of metabolic syndrome features and related nutrigenomic aspects.


   GRANTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
REFERENCES
 
This work was supported by Czech Science Foundation Grant GACR 301/04/0248, Internal Grant Agency of the Ministry of Health of Czech Republic Grant NR/7888, Canadian Institutes of Health Research Grant GEI-53958 "CardioGEN", and the Research Project MSM 0021620807.


   ACKNOWLEDGMENTS
 
Special acknowledgment is expressed to Michaela Janku for excellent technical assistance.


   FOOTNOTES
 
Address for reprint requests and other correspondence: V. Kren, Inst. of Biology and Medical Genetics, First Faculty of Medicine, Charles Univ., Prague, Albertov 4, 12800 Prague 2, Czech Republic (e-mail: vkren{at}lf1.cuni.cz)

Article published online before print. See web site for date of publication (http://physiolgenomics.physiology.org).


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 

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