Shifting Paradigm from Gene Expressions to Pathways Reveals Physiological Mechanisms in Blood Pressure Control in Causation.

Genetics for blood pressure (BP) in human and animals has been partitioned into two separate specialties. However, this divide is mechanistically-misleading. BP physiology is mechanistically participated by products of quantitative trait loci (QTLs). The key to unlocking its mechanistic mystery lies in the past with mammalian ancestors before humans existed. By pivoting from effects to causes, physiological mechanisms determining BP by six QTLs have been implicated. Our work relies on congenic knock-in genetics in vivo using rat models, and has reproduced the physiological outcome based on a QTL being molecularly equal to one gene. A gene dose for a QTL is irrelevant to physiological BP controls in causation. Together, QTLs join one another as a group in modularized Mendelian fashion to achieve polygenicity. Mechanistically, QTLs in the same module appear to function in a common pathway. Each is involved in a different step in the pathway toward polygenic hypertension. This work has implicated previously-concealed components of these pathways. This emerging concept is a departure from the human-centric precept that the level of QTL expressions, not physiology, would ultimately determine BP. The modularity/pathway paradigm breaks a unique conceptual ground for unravelling the physiological mechanisms of polygenic and quantitative traits like BP.

Conserved mammalian modularity of quantitative trait loci revealed human functional orthologs in blood pressure control.

Genome-wide association studies (GWAS) have routinely detected human quantitative trait loci (QTLs) for complex traits. Viewing that most GWAS single nucleotide polymorphisms (SNPs) are found in non-coding regions unrelated to the physiology of a polygenic trait of interest, a vital question to answer is whether or not any of these SNPs can functionally alter the phenotype with which it is associated. The study of blood pressure (BP) is a case in point. Conserved mechanisms in controlling BP by modularity is now unifying differing mammalian orders in that understanding mechanisms in rodents is tantamount to revealing the same in humans, while overcoming experimental limitations imposed by human studies. As a proof of principle, we used BP QTLs from Dahl salt-sensitive rats (DSS) as substitutes to capture distinct human functional orthologs. 3 DSS BP QTLs are located into distinct genome regions and correspond to several human GWAS genes. Each of the QTLs independently exerted a major impact on BP in vivo. BP was functionally changed by normotensive alleles from each of these QTLs, and yet, the human GWAS SNPs do not exist in the rat. They cannot be responsible for physiological alterations in BP caused by these QTLs. These SNPs are genome emblems for QTLs nearby, rather than being QTLs per se, since they only emerged during primate evolution after BP-regulating mechanisms have been established. We then identified specific mutated coding domains that are conserved between rodents and humans and that may implicate different steps of a common pathway or separate pathways.

Functional Captures of Multiple Human Quantitative Trait Loci Regulating Blood Pressure with the Use of Orthologs in Genetically Defined Rat Models.

BACKGROUND: Most signals from human genome-wide association studies (GWAS) for blood pressure (BP) are single-nucleotide polymorphisms (SNPs). It was unknown if such SNPs can functionally affect BP. Because BP is similar between humans and rodents, unraveling basic mechanisms from rodents can reveal the same BP-modulating mechanisms in humans originating from their common ancestors while overcoming limitations in human epidemiology. METHODS: For the first time, we used quantitative trait loci (QTLs) from Dahl salt-sensitive (DSS) rats as functional surrogates to capture human BP QTLs. RESULTS: A total of 107 human GWAS genes may be classified into 2 common pathways of hypertension pathogeneses. Among them, 4 DSS BP QTLs correspond to 4 human GWAS genes. Each of them independently showed a major impact on BP in vivo and thus functional redundancy. BP was altered by each of these 4 QTLs, but human GWAS SNPs marking these QTLs do not exist in the rat. They cannot be responsible for physiological changes in BP caused by these QTLs and are genome signposts marking positions of the QTLs nearby, rather than being QTLs themselves. These SNPs appeared during primate evolution, independently of BP regulation. Because the functional dosage of QTLs, not their gene dose, determined hypertension pathogenesis, a role for the noncoding GWAS SNPs in BP via regulating gene expressions can be discounted. CONCLUSIONS: The human QTLs may function in a common pathway, with each involved in a different step in the pathway leading to BP control. These results may be conceptually paradigm shifting.

Biological convergence of three human and animal model quantitative trait loci for blood pressure.

OBJECTIVES: Blood pressure (BP) is comparable among different mammalian orders, despite their evolution divergence. Because of it, fundamental mechanisms should connect humans and rodents by their shared BP physiology. We hypothesized that similar quantitative trait loci (QTLs) function in both humans and rodents in controlling BP. METHODS: We utilized inbred hypertensive Dahl salt-sensitive rats (DSS) as a functional proxy to evaluate the relevance of human genome-wide association studies (GWAS) genes in BP regulation. RESULTS: First, three DSS BP QTLs functionally captured three specific human GWAS genes. Each QTL has a major biological impact, not a miniscule effect, on BP, in causation by function. Second, noncoding single-nucleotide polymorphisms (SNPs) found in GWAS are by products of primate evolution, instead of mechanistic drivers in regulating BP, because their absence did not impact on BP of mammals. Third, a missense mutation, rather than a noncoding GWAS SNP marking it nearby, is the priority functional basis for a given QTL. Depleting such a noncoding GWAS SNP had no impact, whereas eliminating the muscarinic cholinergic receptor 3 (M3R) signaling decreased BP. Finally, epistatic modularity biologically organizes multiple QTLs with redundant functions, and is the genetic mechanism that modulates the BP homeostasis when QTLs function collectively. CONCLUSIONS: Two pathogenic pathways of hypertension biologically unify mechanisms of BP regulations for humans and their functional surrogates. The mechanism-based biology for the M3R-mediated pathway in raising BP has established M3R as a novel pathogenesis-driven target for antihypertension therapies.

Functional Dosage of Muscarinic Cholinergic Receptor 3 Signalling, Not the Gene Dose, Determines Its Hypertension Pathogenesis.

BACKGROUND: Multiple quantitative trait loci for blood pressure (BP) have been localized throughout human and rodent genomes. Few of them have been functionally identified especially in humans, and little is known about their pathogenic directionality when identified. We focused on Chrm3 encoding the muscarinic cholinergic receptor 3 (M3R) as the causal gene for C17QTL1 in the Dahl salt-sensitive rat model. METHODS AND RESULTS: Congenic knock-ins, gene-specific knockout, and ex vivo and in vivo function studies were applied in the Dahl salt-sensitive rat model of polygenic hypertension. A Chrm3 missense T1667C mutation in the last intracellular domain functionally correlated with a rise in BP increased the M3R signalling and resensitization, and adrenal epinephrogenesis. Gene targeting that abolished the M3R function without affecting any of noncoding Chrm3 variants caused a decrease in BP, indicating that the M3R-mediated signalling promotes hypertension. In contrast, removing 8 amino acids from the M3R first extracellular loop had no effect on BP. CONCLUSIONS: The M3R-specialized signalling constitutes a new pathway of hypertension pathogenesis within the context of a polygenic and quantitative trait. Increased epinephrine in the circulation and secreted from the adrenal glands are suggestive of a molecular mechanism partially mediating M3R to promote hypertension. The structure-function relationships for various M3R domains in their effects on BP pave the way for identifying missense mutations that impact functions on BP as potential diagnostic targets.

Novel Pathogenesis of Hypertension and Diastolic Dysfunction Caused by M3R (Muscarinic Cholinergic 3 Receptor) Signaling.

Multiple quantitative trait loci for blood pressure (BP) are localized in humans and rodent models. Model studies have not only produced human quantitative trait loci homologues but also provided unforeseen mechanistic insights into the function modality of quantitative trait loci actions. Presently, congenic knockins, gene-specific knockout, and in vitro and in vivo function studies were used in a rat model of polygenic hypertension, DSS (Dahl salt sensitive) rats. One gene previously unknown in regulating BP was detected with 1 structural mutation(s) for each of 2 quantitative trait loci classified into 2 separate epistatic modules 1 and 3. C17QTL1 in epistatic module 2 was identified to be the gene Chrm3 encoding the M3R (muscarinic cholinergic 3 receptor), since a single function-enhancing M3RT556M conversion correlated with elevated BP. To definitively prove that the enhanced M3R function is responsible for BP changes by the DSS alleles of C17QTL1, we generated a Chrm3 gene-specific rat knockout. We observed a reduction in BP without tachycardia in both sexes, regardless of the amount of dietary salt, and an improvement in diastolic and kidney dysfunctions. All occurred in spite of a significant reduction in M3R-dependent vasodilation. The previously seen sexual dimorphism for C17QTL1 on BP disappeared in the absence of M3R. A Chrm3-coding variation increased M3R signaling, correlating with higher BP. Removing the M3R signaling led to a decrease in BP and improvements in cardiac and renal malfunctions. A novel pathogenic pathway accounted for a portion of polygenic hypertension and has implications in applying new diagnostic and therapeutic uses against hypertension and diastolic dysfunction.

Retinoblastoma-associated protein 140 as a candidate for a novel etiological gene to hypertension.

Gene discovery in animal models may lead to the revelation of therapeutic targets for essential hypertension as well as mechanistic insights into blood pressure (BP) regulation. Our aim was to identify a disease-causing gene for a component of polygenic hypertension contrasting inbred hypertensive Dahl salt-sensitive (DSS) and normotensive Lewis rats. The chromosome segment harboring a quantitative trait locus (QTL), C16QTL, was first isolated from the rat genome via congenic strains. A candidate gene responsible for C16QTL causing a BP difference between DSS and Lewis rats was then identified using molecular analyses combining our independently-conducted total genome and gene-specific sequencings. The retinoblastoma-associated protein 140 (Rap140)/family with sequence similarity 208 member A (Fam208a) is the only candidate gene supported to be C16QTL among three genes in genome block 1 present in the C16QTL-residing interval. A mode of its actions could be to influence the expressions of genes that are downstream in a pathway potentially leading to BP regulation such as that encoding the solute carrier family 7 (cationic amino acid transporter, y+ system) member 12 (Slc7a12), which is specifically expressed in kidneys. Thus, Rap140/Fam208a probably encoding a transcription factor is the strongest candidate for a novel BP QTL that acts via a putative Rap140/Fam208a-Slc7a12-BP pathway. These data implicate a premier physiological role for Rap140/Fam208 beyond development and a first biological function for the Slc7a12 protein in any organism.

Alterations in Fibronectin Type III Domain Containing 1 Protein Gene Are Associated with Hypertension.

Multiple quantitative trait loci (QTLs) for blood pressure (BP) have been detected in rat models of human polygenic hypertension. Great challenges confronting us include molecular identifications of individual QTLs. We first defined the chromosome region harboring C1QTL1 to a segment of 1.9 megabases that carries 9 genes. Among them, we identified the gene encoding the fibronectin type III domain containing 1 protein (Fndc1)/activator of G protein signaling 8 (Ags8) to be the strongest candidate for C1QTL1, since numerous non-synonymous mutations are found. Moreover, the 5' Fndc1/Ags8 putative promoter contains numerous mutations that can account for its differential expression in kidneys and the heart, prominent organs in modulating BP, although the Fndc1/Ags8 protein was not detectable in these organs under our experimental conditions. This work has provided the premier evidence that Fndc1/Ags8 is a novel and strongest candidate gene for C1QTL1 without completely excluding other 8 genes in the C1QTL1-residing interval. If proven true by future in vivo function studies such as single-gene Fndc1/Ags8 congenics, transgenesis or targeted-gene modifications, it might represent a part of the BP genetic architecture that operates in the upstream position distant from the end-phase physiology of BP control, since it activates a Gbetagamma component in a signaling pathway. Its functional role could validate the concept that a QTL in itself can influence BP 'indirectly' by regulating other genes downstream in a pathway. The elucidation of the mechanisms initiated by Fndc/Ags8 variations will reveal novel insights into the BP modulation via a regulatory hierarchy.

Two candidate genes for two quantitative trait loci epistatically attenuate hypertension in a novel pathway.

OBJECTIVES: Multiple quantitative trait loci (QTLs) for blood pressure (BP) have been detected in rat models of human polygenic hypertension. They influence BP physiologically via epistatic modules. Little is known about the causal genes and virtually nothing is known on modularized mechanisms governing their regulatory connections. METHODS AND RESULTS: Two genes responsible for two individual BP QTLs on rat Chromosome 18 have been identified that belong to the same epistatic module. Treacher Collins-Franceschetti syndrome 1 (Tcof1) gene is the only function candidate for C18QTL3. Haloacid dehalogenase like hydrolase domain containing 2 (Hdhd2), although a gene of previously unknown function, is C18QTL4, and encodes a newly identified phosphatase. The current work has provided the premier evidence that Hdhd2/C18QTL4 and Tcof1/C18QTL3 may be involved in polygenic hypertension. Hdhd2/C18QTL4 can regulate the function of Tcof1/C18QTL3 via de-phosphorylation, and, for the first time, furbishes a molecular mechanism in support of a genetically epistatic hierarchy between two BP QTLs, and thus authenticates the epistasis-common pathway paradigm. CONCLUSION: The pathway initiated by Hdhd2/C18QTL4 upstream of Tcof1/C18QTL3 reveals novel mechanistic insights into BP modulations. Their discovery might yield innovative therapeutic targets and diagnostic tools predicated on a novel BP cause and mechanism that is determined by a regulatory hierarchy. Optimizing the de-phosphorylation capability and its downstream target could be antihypertensive. The conceptual paradigm of an order and regulatory hierarchy may help unravel genetic and molecular relationships among certain human BP QTLs.

Hypertension Suppression, Not a Cumulative Thrust of Quantitative Trait Loci, Predisposes Blood Pressure Homeostasis to Normotension.

BACKGROUND: Genetics of high blood pressure (BP) has revealed causes of hypertension. The cause of normotension, however, is poorly understood. Inbred Lewis rats sustain normotension despite a genetic push in altering BP. It was unknown whether this rigid resistance to BP changes is because of an insufficient hypertensive impact from limited alleles of quantitative trait loci (QTLs) or because of an existence of a master control superseding the combined strength of hypertensive QTL alleles. METHODS AND RESULTS: Currently, BP-elevating QTL alleles from hypertensive Dahl salt-sensitive rats (DSS) replaced those of Lewis on chromosomes 7, 8, 10, and 17 on the Lewis background. These hypertensive QTL alleles were then merged to systematically achieve multiple combinations. Results showed that there was no quantitative correlation between BP variations and the number of hypertensive QTL alleles, and that BP was only slightly elevated from a combined force of normotensive alleles from 7 QTLs. Thus, a genetic factor aside from the known QTLs seemed to be at play in preserving normotension and act as a hypertension suppressor. A follow-up study using consecutive backcrosses from Dahl salt-sensitive rats and Lewis identified a chromosome segment where a hypertension suppressor might reside. CONCLUSIONS: Our results provide the first evidence that normotension is not enacted via a numeric advantage of BP-lowering QTL alleles, and instead can be achieved by a particular genetic component actively suppressing hypertensive QTL alleles. The identification of this hypertension suppressor could result in formulating unique diagnostic and therapeutic targets, and above all, preventive measures against essential hypertension.

Modularization and epistatic hierarchy determine homeostatic actions of multiple blood pressure quantitative trait loci.

Hypertension, the most frequently diagnosed clinical condition world-wide, predisposes individuals to morbidity and mortality, yet its underlying pathological etiologies are poorly understood. So far, a large number of quantitative trait loci (QTLs) have been identified in both humans and animal models, but how they function together in determining overall blood pressure (BP) in physiological settings is unknown. Here, we systematically and comprehensively performed pair-wise comparisons of individual QTLs to create a global picture of their functionality in an inbred rat model. Rather than each of numerous QTLs contributing to infinitesimal BP increments, a modularized pattern arises: two epistatic 'blocks' constitute basic functional 'units' for nearly all QTLs, designated as epistatic module 1 (EM1) and EM2. This modularization dictates the magnitude and scope of BP effects. Any EM1 member can contribute to BP additively to that of EM2, but not to those of the same module. Members of each EM display epistatic hierarchy, which seems to reflect a related functional pathway. Rat homologues of 11 human BP QTLs belong to either EM1 or EM2. Unique insights emerge into the novel genetic mechanism and hierarchy determining BP in the Dahl salt-sensitive SS/Jr (DSS) rat model that implicate a portion of human QTLs. Elucidating the pathways underlying EM1 and EM2 may reveal the genetic regulation of BP.

Combining distinctive and novel loci doubles BP reduction, reverses diastolic dysfunction and mitigates LV hypertrophy.

OBJECTIVES: Diastolic dysfunction often represents the onset of diastolic heart failure (DHF). We previously showed in principle that diastolic function in Dahl salt-sensitive rats (DSS) can be genetically determined by quantitative trait loci (QTLs) that also modulate blood pressure (BP). METHODS: We analyzed cardiac phenotypes of four 'single' congenic strains by echocardiography, in which a specific DSS chromosome segment was replaced by its normotensive Lewis homologue. RESULTS: Two of the strains permanently lowered BP, and but attenuated diastolic dysfunction only in rats at 10 weeks of age, not at 15 weeks fed on a 2% NaCl diet starting from 8 weeks of age. We then combined multiple QTLs by integrating several 'single' congenic strains. As a result, BP was greatly reduced. Cardiac dysfunction and LV hypertrophy were continuously improved from 10 to 15 weeks, although the degree and timing of the improvement varied among different congenic combinations. CONCLUSION: Distinct QTLs exist that simultaneously modulate BP and diastolic function. These QTLs, in combination, synergistically lowered BP and permanently alleviated or reversed diastolic dysfunction. The genes that are contained in the congenic strains affecting diastolic function are not known for their specific influence on BP. Novel long-term strategies of prognosis, diagnosis and therapy for hypertensive DHF appear from this work.

Novel genes as primary triggers for polygenic hypertension.

OBJECTIVES: The discovery of causative genes leading to hypertension in animal models can reveal new mechanistic insights into blood pressure (BP) regulations. Previously, we isolated segments that harbor BP quantitative trait loci (QTLs) on rat chromosome 10 as defined by congenic strains made from crosses of inbred hypertensive Dahl salt-sensitive (DSS) and normotensive Lewis rats. The aim of the current study was to identify hypertension-causing genes for each QTL. METHODS: Molecular analysis was performed. RESULTS: A systematic and comprehensive molecular analysis divulged particular genes that carry nonconserved mutations. Specifically, the proline rich 11 gene is likely responsible for C10QTL5. C10QTL1 is one of five genes, namely Benzodiazepine receptor associated protein 1, Loc689764, myotubularin related protein 4, protein phosphatase 1E, PP2C domain containing and ring finger protein 43. Loc100363423 with no known function is a candidate for C10QTL3. The ATP-binding cassette, subfamily A (ABC1), member 8a gene is probably responsible for C10QTL2. CONCLUSIONS: Primary genes initiating polygenic hypertension are those not known to be involved in BP modulation. Novel pathways towards BP homeostasis appear to underlie the functionality of C10QTL5, C10QTL1 and C10QTL3 and C10QTL2. Moreover, these genes may become innovative targets for the diagnosis and therapeutics of essential hypertension.

α-Kinase 2 is a novel candidate gene for inherited hypertension in Dahl rats.

OBJECTIVES: The interval harboring a quantitative trait locus for blood pressure (BP), C18QTL3, contains ß-2 adrenergic receptor (Adrb2) and neural precursor cell expressed, developmentally downregulated 4-like (Nedd4l) genes. None of the other genes in the C18QTL3-residing interval is known to affect BP. The identification of C18QTL3 might uncover a brand new gene that could prosper into a novel diagnostic and/or therapeutic target for essential hypertension, if neither Adrb2 nor Nedd4l could be upheld as candidate genes. METHODS: Congenic fine resolution was combined with gene analyses. RESULTS: The gene encoding α-kinase 2 (Alpk2) contains a three base-pair deletion and multiple nonconserved mutations in its coding region in Dahl salt-sensitive (DSS) rats. In contrast, the gastrin-releasing peptide gene (Grp) possesses two nonconserved mutations, designated as single nucleotide polymorphisms 1 and 2 (i.e. SNP1 and SNP2), but could not be supported as a candidate gene because the C18S.L14 congenic strain displayed a homozygous DSS genotype at both SNP1 and SNP2. Furthermore, Adrb2 and Nedd4l could not account for the BP-diminishing effect of Lewis alleles in C18S.L14, as their DSS alleles bear functionally identical domains as those of Lewis, and no evidence of differential expression and splicing was evident. No significant nucleotide variations were found in 13 other genes closely linked to Alpk2. CONCLUSION: Alpk2 emerged as a strong candidate gene for C18QTL3. The present study is the first to implicate Alpk2 in the genetics of polygenic hypertension and paves the way for novel gene discovery.

Normotension in Lewis and Dahl salt-resistant rats is governed by different genes.

OBJECTIVES: Inbred rodent models simulating essential hypertension and normotension are useful tools in discovering genes controlling blood pressure (BP) homeostasis. An analysis of a F2 population made from crosses of hypertensive Dahl salt-sensitive (DSS) and normotensive Lewis rats did not detect a BP quantitative trait locus (QTL) on chromosome 7 (Chr 7). However, false negativity could not be excluded. If a BP QTL could be proven to exist, what gene(s) may be responsible for this QTL. METHODS: We first constructed reciprocal congenic strains for a Chr 7 segment and determined functional domains of prominent candidate genes. RESULTS: A congenic strain made in the DSS rat background exhibited a BP effect, indicating that a BP QTL, C7QTL, inhabits Chr 7. Contrarily, a congenic strain constructed in the Lewis rat background did not change BP, demonstrating a dependence of C7QTL on the DSS rats environment. Among the candidate genes, tachykinin 2 (Tac2), neurexophilin 4 (Nxph4) and retinol dehydrogenase 2 (Rdh2) bear nonsynonymous changes comparing DSS and Lewis rats, but are the same comparing DSS and Dahl salt-resistant (DSR) rats. In contrast, the Lewis alleles of 11-beta-hydroxylase (Cyp11b1), aldosterone synthase (Cyp11b2) and Cytochrome P-450 11B3 (Cyp11b3) are identical to those of DSS rats, but different from those of DSR rats. CONCLUSION: Thus, the failure to detect a linkage between a Chr 7 segment and BP in F2(DSS × Lewis) can be attributed to false negativity. Tac2, Nxph4 and Rdh2 are priority candidate genes for C7QTL. Lewis and DSR rats are both normotensive, but their underlying genetic determinants are different.

Cardiac pathways distinguish two epistatic modules enacting BP quantitative trait loci and candidate gene analysis.

Animal models emulating essential hypertension are an informative means by which to elucidate the physiological mechanisms and gene-gene interactions underlying blood pressure (BP) regulation. We have localized earlier quantitative trait loci (QTLs) for BP on Chromosome (Chr) 2 of Dahl salt-sensitive (DSS) rats, but their chromosome delineations were too large for gene identification. To advance toward positional cloning of these QTLs, we constructed congenic strains that systematically dissect a Chr 2 segment with no overlaps. BP and cardiac functions were measured by telemetry and echocardiography. Six QTLs were delimited, each independently influencing BP. The intervals lodging two of them harbor 10-15 genes and undefined loci. These six QTLs can be grouped into two epistatic modules distinguishable by cardiac pathways/cascades. None of the genes known to exert physiological effects on BP in the segments harboring the six QTLs are leading candidates, as their protein products are the same in DSS rats and similar to those in their Milan normotensive counterparts. Specifically, the lack of an amino-acid alteration, coupled with a lack of difference in the alpha1-Na-K-ATPase activity, excluded ATPase, Na+/K+-transporting, alpha-1 polypeptide as a candidate gene for C2QTL6. The identification of the six QTLs will likely develop into a novel diagnostic and/or therapeutic target for essential hypertension and hypertension-associated diseases.

Sexual dimorphism on hypertension of quantitative trait loci entrapped in Dahl congenic rats.

Although it is well-known that quantitative trait loci (QTLs) influence blood pressure (BP) in male Dahl salt-sensitive rats (DSS), few studies have been carried out to ascertain the BP effect of these QTLs in females. In the current work, we analyzed BP of seven selected congenic strains constructed in the DSS background. One QTL, C8QTL2, exhibited similar effects on systolic (SAP), diastolic (DAP), and mean arterial (MAP) pressures in females as previously shown in males. In contrast, six QTLs that previously demonstrated influences on SAP, DAP, and MAP in males did not have effects in females. These male-specific QTLs are likely regulated differently in males than in females and emphasize the necessity of identifying female-specific QTLs for diagnosing and treating hypertension in women. Current findings may have implications in genetic research of essential hypertension, and association and linkage analyses should be performed in separate genders. Men and women may possess distinctive as well as shared genetic determinants for SAP, DAP, and MAP. The data on a single gene or marker might be pooled from both genders only when evidence favors the sex-independence in a study.

Distinct genomic replacements from Lewis correct diastolic dysfunction, attenuate hypertension, and reduce left ventricular hypertrophy in Dahl salt-sensitive rats.

BACKGROUND: Hypertension and diastolic heart failure are two common cardiovascular diseases that inflict heavy morbidity and mortality, yet relatively little is understood about their pathophysiology. The identification of quantitative trait loci for blood pressure is important in unveiling the causes of polygenic hypertension. Although Dahl salt-sensitive strain is also an excellent model for the study of diastolic heart failure, virtually nothing is known about the quantitative trait loci determining diastolic heart failure. Diastolic dysfunction often represents the onset of diastolic heart failure. METHODS: We first characterized the cardiac phenotype of Dahl salt-sensitive strain and normotensive Lewis control rats by echocardiography to ascertain diastolic function. We then analyzed corresponding features of four newly developed and two existing congenic strains, each of which carries a specific chromosome substitution of Dahl salt-sensitive strain by its Lewis homologue and each lowering blood pressure. RESULTS: Dahl salt-sensitive strain displayed diastolic dysfunction that was rectified in two of six congenic strains, designated as positive congenic strains, which represent the first rodent models exhibiting functional normalization of diastolic dysfunction caused by naturally occurring genetic variants. The two positive congenic strains also showed a reduction in left ventricular mass. In contrast, four of six congenic strains did not change diastolic function despite their blood pressure-lowering effects. CONCLUSION: Genes present in the replaced chromosome segments of the two positive congenic strains are not commonly known to affect blood pressure, diastolic function or left ventricular mass. Consequently, novel prognostic, diagnostic and therapeutic strategies for hypertensive diastolic heart failure likely emerge from this work.

Submegabase resolution of epistatically interacting quantitative trait loci for blood pressure applicable for essential hypertension.

OBJECTIVE: Although genetic mapping of quantitative trait loci for blood pressure to large chromosome segments is readily achievable, their final identification confronts formidable hurdles. Restriction of the genes lodging in one quantitative trait locus interval to experimental limitation can facilitate their positional cloning. We previously delineated several quantitative trait loci for blood pressure on chromosome 10 of Dahl salt-sensitive rats, but their chromosome delimitations were either large or not definitive. METHODS: In this study, we systematically and comprehensively constructed congenic strains with submegabase (Mb) genome resolution and analyzed their blood pressure by telemetry. RESULTS: Three quantitative trait loci have been conclusively delimited by three congenic strains, each independently lowering the blood pressure. Their intervals are demarcated by genomic regions between 350 and 910 kilobases (kb) in size. Two of the three quantitative trait loci share an epistatic relationship and are separated from one another by less than 170 kb. Two additional quantitative trait loci for blood pressure were also tentatively delineated and their intervals range from 520 kb to 1.75 Mb. Possible genes dwelling in each quantitative trait locus-interval number between 11 and 17. None of these genes is known to exert a functional impact on blood pressure. Work is underway to find candidate genes with mutations that could be responsible for the blood pressure effect. CONCLUSION: Novel diagnostic, prognostic, preventive and/or therapeutic targets for essential hypertension and hypertension-associated diseases are likely to emerge from the identification of these quantitative trait loci. Potential applications of these quantitative trait loci to humans are suggested from the positive results from several association studies, demonstrating the existence of quantitative trait loci in the broad homologous regions.

Distinct quantitative trait loci for kidney, cardiac, and aortic mass dissociated from and associated with blood pressure in Dahl congenic rats.

Blood pressure (BP) is largely determined by quantitative trait loci (QTLs) in Dahl salt-sensitive (DSS) rats. Little is known about QTLs controlling kidney (K), cardiac (C), and aortic (A) mass (i.e. Km, Cm, and Am, respectively) of DSS rats independent of BP. Their identification can facilitate our understanding of end organ damage. In this work, 36 congenic strains were employed to define QTLs for Km, Cm, and Am either independent of or associated with BP. Five new QTLs, i.e., KmQTLs, that influence Km independent of Cm, Am, and BP were defined. Four new CakmQTLs were defined for Cm, Am, and Km independent of BP. Among them, the CakmC10QTL1 interval contained 13 genes and undefined loci, and none was known to influence the phenotypes in question, paving the way for a novel gene discovery. Among 17 individual QTLs for BP, 14 also affected Cm, Km, and Am, i.e., they are BpcakmQTLs. In contrast, one BpQTL had no effect on Cm, Am, and Kam. Therefore, BP and Cm, Am, and Km have distinct and shared genetic determinants. The discovery of individual Km and Cakm QTLs will likely facilitate the identification of mechanisms underlying renal, cardiac, and/or aortic hypertrophy independent of hypertension.