The Dual AngII/AVP Receptor Gene N119S/C163R Variant Exhibits Sodium-Induced Dysfunction and Cosegregates With Salt-Sensitive Hypertension in the Dahl Salt-Sensitive Hypertensive Rat Model

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A Functional 12T-insertion polymorphism in the <i>ATP1A1</i> promoter confers decreased susceptibility to hypertension in a male Sardinian population

Identification of susceptibility genes for essential hypertension in humans has been a challenge due to its multifactorial pathogenesis complicated by gene-gene and gene-environment interactions, developmental programing and sex specific differences. These concurrent features make identification of causal hypertension susceptibility genes with a single approach difficult, thus requiring multiple lines of evidence involving genetic, biochemical and biological experimentation to establish causal functional mutations. Here we report experimental evidence encompassing genetic, biochemical and in vivo modeling that altogether support ATP1A1 as a hypertension susceptibility gene in males in Sardinia, Italy. ATP1A1 encodes the α1Na,K-ATPase isoform, the sole sodium pump in vascular endothelial and renal tubular epithelial cells. DNA-sequencing detected a 12-nucleotide long thymidine (12T) insertion(ins)/deletion(del) polymorphism within a poly-T sequence (38T vs 26T) in the ATP1A1 5’-regulatory region associated with hypertension in a male Sardinian population. The 12T-insertion allele confers decreased susceptibility to hypertension (P = 0.035; OR = 0.50 [0.28–0.93]) accounting for 12.1 mmHg decrease in systolic BP (P = 0.02) and 6.6 mmHg in diastolic BP (P = 0.046). The ATP1A1 promoter containing the 12T-insertion exhibited decreased transcriptional activity in in vitro reporter-assay systems, indicating decreased α1Na,K-ATPase expression with the 12T-insertion, compared with the 12T-deletion ATP1A1 promoter. To test the effects of decreased α1Na,K-ATPase expression on blood pressure, we measured blood pressure by radiotelemetry in three month-old, highly inbred heterozygous knockout ATP1A1+/− male mice with resultant 58% reduction in ATP1A1 protein levels. Male ATP1A1+/− mice showed significantly lower blood pressure (P &#60; 0.03) than age-matched male wild-type littermate controls. Concordantly, lower ATP1A1 expression is expected to lower Na-reabsorption in the kidney thereby decreasing sodium-associated risk for hypertension and sodium-induced endothelial stiffness and dysfunction. Altogether, data support ATP1A1 as a hypertension susceptibility gene in a male Sardinian population, and mandate further investigation of its involvement in hypertension in the general population

Sex-specific effects of NLRP6/AVR and ADM <i>loci</i> on susceptibility to essential hypertension in a Sardinian population

Coronary artery disease, heart failure, fatal arrhythmias, stroke, and renal disease are the most common causes of mortality for humans, and essential hypertension remains a major risk factor. Elucidation of susceptibility loci for essential hypertension has been difficult because of its complex, multifactorial nature involving genetic, environmental, and sex- and age-dependent nature. We investigated whether the 11p15.5 region syntenic to rat chromosome 1 region containing multiple blood pressure quantitative trait loci (QTL) detected in Dahl rat intercrosses harbors polymorphisms that contribute to susceptibility/resistance to essential hypertension in a Sardinian population. Initial testing performed using microsatellite markers spanning 18 Mb of 11p15.5 detected a strong association between D11S1318 (at 2.1 Mb, P = 0.004) and D11S1346 (at 10.6 Mb, P = 0.00000004), suggesting that loci in close proximity to these markers may contribute to susceptibility in our Sardinian cohort. NLR family, pyrin domain containing 6/angiotensin-vasopressin receptor (NLRP6/AVR), and adrenomedullin (ADM) are in close proximity to D11S1318 and D11S1346, respectively; thus we tested single nucleotide polymorphisms (SNPs) within NLRP6/AVR and ADM for their association with hypertension in our Sardinian cohort. Upon sex stratification, we detected one NLRP6/AVR SNP associated with decreased susceptibility to hypertension in males (rs7948797G, P = 0.029; OR = 0.73 [0.57-0.94]). For ADM, sex-specific analysis showed a significant association between rs4444073C, with increased susceptibility to essential hypertension only in the male population (P = 0.006; OR = 1.44 [1.13-1.84]). Our results revealed an association between NLRP6/AVR and ADM loci with male essential hypertension, suggesting the existence of sex-specific NLRP6/AVR and ADM variants affecting male susceptibility to essential hypertension

Multiple susceptibility loci for radiation-induced mammary tumorigenesis in F2[Dahl S x R]-intercross rats.

Although two major breast cancer susceptibility genes, BRCA1 and BRCA2, have been identified accounting for 20% of breast cancer genetic risk, identification of other susceptibility genes accounting for 80% risk remains a challenge due to the complex, multi-factorial nature of breast cancer. Complexity derives from multiple genetic determinants, permutations of gene-environment interactions, along with presumptive low-penetrance of breast cancer predisposing genes, and genetic heterogeneity of human populations. As with other complex diseases, dissection of genetic determinants in animal models provides key insight since genetic heterogeneity and environmental factors can be experimentally controlled, thus facilitating the detection of quantitative trait loci (QTL). We therefore, performed the first genome-wide scan for loci contributing to radiation-induced mammary tumorigenesis in female F2-(Dahl S x R)-intercross rats. Tumorigenesis was measured as tumor burden index (TBI) after induction of rat mammary tumors at forty days of age via ¹²⁷Cs-radiation. We observed a spectrum of tumor latency, size-progression, and pathology from poorly differentiated ductal adenocarcinoma to fibroadenoma, indicating major effects of gene-environment interactions. We identified two mammary tumorigenesis susceptibility quantitative trait loci (Mts-QTLs) with significant linkage: Mts-1 on chromosome-9 (LOD-2.98) and Mts-2 on chromosome-1 (LOD-2.61), as well as two Mts-QTLs with suggestive linkage: Mts-3 on chromosome-5 (LOD-1.93) and Mts-4 on chromosome-18 (LOD-1.54). Interestingly, Chr9-Mts-1, Chr5-Mts-3 and Chr18-Mts-4 QTLs are unique to irradiation-induced mammary tumorigenesis, while Chr1-Mts-2 QTL overlaps with a mammary cancer susceptibility QTL (Mcs 3) reported for 7,12-dimethylbenz-[α]antracene (DMBA)-induced mammary tumorigenesis in F2[COP x Wistar-Furth]-intercross rats. Altogether, our results suggest at least three distinct susceptibility QTLs for irradiation-induced mammary tumorigenesis not detected in genetic studies of chemically-induced and hormone-induced mammary tumorigenesis. While more study is needed to identify the specific Mts-gene variants, elucidation of specific variant(s) could establish causal gene pathways involved in mammary tumorigenesis in humans, and hence novel pathways for therapy

Dahl (S × R) rat congenic strain analysis confirms and defines a chromosome 17 spatial navigation quantitative trait locus to <10 Mbp.

A quantitative trait locus (QTL) linked with ability to find a platform in the Morris Water Maze (MWM) was located on chromosome 17 (Nav-5 QTL) using intercross between Dahl S and Dahl R rats. We developed two congenic strains, S.R17A and S.R17B introgressing Dahl R-chromosome 17 segments into Dahl S chromosome 17 region spanning putative Nav-5 QTL. Performance analysis of S.R17A, S.R17B and Dahl S rats in the Morris water maze (MWM) task showed a significantly decreased spatial navigation performance in S.R17B congenic rats when compared with Dahl S controls (P = 0.02). The S.R17A congenic segment did not affect MWM performance delimiting Nav-5 to the chromosome 17 65.02-74.66 Mbp region. Additional fine mapping is necessary to identify the specific gene variant accounting for Nav-5 effect on spatial learning and memory in Dahl rats