SummaryLarge numbers of inbred laboratory rat strains have been developed for a range of complex disease phenotypes. To gain insights into the evolutionary pressures underlying selection for these phenotypes, we sequenced the genomes of 27 rat strains, including 11 models of hypertension, diabetes, and insulin resistance, along with their respective control strains. Altogether, we identified more than 13 million single-nucleotide variants, indels, and structural variants across these rat strains. Analysis of strain-specific selective sweeps and gene clusters implicated genes and pathways involved in cation transport, angiotensin production, and regulators of oxidative stress in the development of cardiovascular disease phenotypes in rats. Many of the rat loci that we identified overlap with previously mapped loci for related traits in humans, indicating the presence of shared pathways underlying these phenotypes in rats and humans. These data represent a step change in resources available for evolutionary analysis of complex traits in disease models.PaperClip

Abstract-Using congenic strains of the Dahl salt-sensitive (S) rat introgressed with genomic segments from the normotensive Lewis rat, a blood pressure quantitative trait locus was previously mapped within 104 kb on chromosome 10. The goal of the current study was to conduct extensive phenotypic studies and to further fine-map this locus. At 14 weeks of age, the blood pressure of the congenic rats fed a low-salt diet was significantly higher by 47 mm Hg (PϽ0.001) compared with that of the S rat. A time-course study showed that the blood pressure effect was significant from very young ages of 50 to 52 days (13 mm Hg; PϽ0.01). The congenic strain implanted with electrocardiography transmitters demonstrated shorter-QT intervals and increased heart rate compared with S rats (PϽ0.01). The average survival of the congenic strain was shorter (134 days) compared with the S rat (175 days; PϽ0.0007). The critical region was narrowed to Ͻ42.5 kb containing 171 variants and a single gene, rififylin. Both the mRNA and protein levels of rififylin were significantly higher in the hearts of the congenic strain. Overexpression of rififylin is known to delay endocytic recycling. Endocytic recycling of fluorescently labeled holotransferrin from cardiomyocytes of the congenic strain was slower than that of S rats (PϽ0.01). Frequency of cardiomyocyte beats in the congenic strain (62Ϯ9 bpm) was significantly higher than that of the S rat (24Ϯ6 bpm; PϽ0.001). Taken together, our study provides evidence to suggest that early perturbations in endocytic recycling caused by the overexpression of Rffl is a novel physiological mechanism potentially underlying the development of hypertension.

Elevated maternal testosterone levels are shown to cause fetal growth restriction, eventually culminating in sex-specific adult-onset hypertension that is more pronounced in males than females. In this study, we tested whether utero- and feto-placental disturbances underlie fetal growth restriction and if these changes vary in male and female placentas. Pregnant Sprague-Dawley rats were injected with vehicle (n=16) or testosterone propionate (0.5 mg/Kg/day from gestation day 15–19; n=16). On gestation day 20, we quantified uterine artery blood flow using microultrasound, visualized placental arterial network using x-ray microcomputed tomography, determined fetoplacental hypoxia using pimonidazole and hypoxia-inducible factor-1α, and used Affymetrix array to determine changes in placental expression of genes involved in vascular development. Plasma testosterone levels increased 2-fold in testosterone-injected rats. Placental and fetal weights were lower in rats with elevated testosterone. Uterine artery blood flow was lower and resistance index was higher in testosterone group. Radial and spiral artery diameter and length, number of fetoplacental arterial branches, and umbilical artery diameter were reduced in the testosterone group. In addition, markers of hypoxia in the placentas and fetuses were elevated in the testosterone group. The magnitude of changes in placental vasculature and hypoxia were greater in males than females and were associated with sex-specific alteration of unique sets of genes involved in angiogenesis and blood vessel morphogenesis. The results demonstrate that elevated testosterone during gestation induces a decrease in uterine arterial blood flow and fetal sex-related uteroplacental vascular changes, which may set the stage for subsequent sex differences in adult-onset diseases.

A disintegrin-like metalloproteinase with thrombospondin motifs-16 (Adamts16) is an important candidate gene for hypertension. The goal of the present study was to further assess the candidacy of Adamts16 by targeted disruption of this gene in a rat genetic model of hypertension. A rat model was generated by manipulating the genome of the Dahl Salt-sensitive (S) rat using zinc-finger nucleases, wherein the mutant rat had a 17 bp deletion in the first exon of Adamts16, introducing a stop codon in the transcript. Systolic blood pressure (BP) of the homozygous Adamts16 mutant rats was lower by 36 mmHg compared with the BP of the S rats. The Adamts16 mutant rats exhibited significantly lower aortic pulse wave velocity and vascular media thickness compared with S rats. Scanning electron and fluorescence microscopic studies indicated that the mechanosensory cilia of vascular endothelial cells from the Adamts16 mutant rats were longer than that of the S rats. Furthermore, Adamts16 mutant rats showed splitting and thickening of glomerular capillaries and had a longer survival rate, compared with the S rats. Taken together, these physiological observations functionally link Adamts16 to BP regulation and suggest the vasculature as the potential site of action of Adamts16 to lower BP.espite strong evidence that susceptibility or resistance to the development of hypertension is heritable, the identification of genetic variants that cause blood pressure (BP) to rise into a hypertensive state has remained difficult (1, 2). Classic genetic mapping and association studies in both humans and in rats point to several genetic elements as potential candidates causing hypertension (3, 4). Most of the prioritized candidate genes for hypertension await functional assessments.Linkage analysis in the Quebec Family Study identified a quantitative trait locus (QTL) for systolic BP on human chromosome 5p15 (5). The corresponding comparative segment of human chromosome 5p15 on rat chromosome 1 is also linked to a BP QTL in rats (6). Improved resolutions of this locus in rats were obtained through iterative substitution mapping using strains differentially susceptible to the development of hypertension (6-10). A disintegrin-like metalloproteinase with thrombospondin motifs-16 (Adamts16), which was the only known gene with exonic variants within the highly resolved congenic interval, was prioritized as a candidate BP quantitative trait gene (QTG) (8). More importantly, following the congenic mapping study in rats, human allelic variants of Adamts16 were confirmed as being associated with BP in two independent cohorts, one of which was the Quebec Family Study (8). Taken together, all these studies point to Adamts16 as a prominent candidate locus linked to BP control across two species. However, due to the limitations of recombination frequencies, both the linkage and substitution mapping studies in rats cannot validate Adamts16 as the BP QTG because of the presence of other candidate variants within the linked or introgressed flanking genomic ...

Chromatin remodeling complex SWI/SNF plays important roles in many cellular processes including transcription, proliferation, differentiation and DNA repair. In this report, we investigated the role of SWI/SNF catalytic subunits Brg1 and Brm in the cellular response to cisplatin in lung cancer and head/neck cancer cells. Stable knockdown of Brg1 and Brm enhanced cellular sensitivity to cisplatin. Repair kinetics of cisplatin DNA adducts revealed that downregulation of Brg1 and Brm impeded the repair of both intrastrand adducts and interstrand crosslinks (ICLs). Cisplatin ICL-induced DNA double strand break repair was also decreased in Brg1 and Brm depleted cells. Altered checkpoint activation with enhanced apoptosis as well as impaired chromatin relaxation was observed in Brg1 and Brm deficient cells. Downregulation of Brg1 and Brm did not affect the recruitment of DNA damage recognition factor XPC to cisplatin DNA lesions, but affected ERCC1 recruitment, which is involved in the later stages of DNA repair. Based on these results, we propose that SWI/SNF chromatin remodeling complex modulates cisplatin cytotoxicity by facilitating efficient repair of the cisplatin DNA lesions.