Maternal diet during gestation and lactation modifies the severity of salt-induced hypertension and renal injury in Dahl salt-sensitive rats

T-cells regulate albuminuria but not hypertension, renal histology, or the medullary transcriptome in the Dahl SSCD247+/+ rat

In the current study, we took advantage of the loss of protection from hypertension in SSCD247-/- rats to characterize the pathological effects of renal T-cells in isolation from the confounding effects of elevated renal perfusion pressure. Male SSCD247-/- and SSCD247+/+ littermates were fed 4.0% NaCl (high salt) diet to induce hypertension. Blood pressure was assessed continuously throughout the time course with radiotelemetry. Urine albumin and protein excretion were assessed on the final day of high salt. Renal injury and medullary transcriptome were assessed after completion of the high salt protocol. In contrast to previous studies, mean arterial pressure was not significantly different between SSCD247-/- and SSCD247+/+ rats. Despite this lack of pressure difference, urinary albumin was significantly lower in SSCD247-/- rats than their wild-type littermates. In the outer medulla, substantially more transcriptomic changes were found to correlate with endpoint blood pressure than with the absence of presence of renal T-cells. We also demonstrated that renal histological damage was driven by elevated renal perfusion pressure rather than the presence of renal T-cells. In conclusion, using the loss of protection from hypertension in SSCD247-/- rats, we demonstrated that renal perfusion pressure has more profound pathological effects on the kidney than renal T-cells. However, renal T-cells, independently of blood pressure, modulate the progression of albuminuria.NEW & NOTEWORTHY In vivo studies in a T-cell-deficient rat model of salt-sensitive hypertension (SSCD247-/- rats) were used to evaluate the role of T-cells on the development of hypertension and renal damage. Detailed physiological and transcriptomic analysis demonstrated no difference in blood pressure between rats with (SSCD247+/+) or without (SSCD247-/-) T-cells. Despite this, albuminuria was significantly lower in SSCD247-/- rats than SSCD247+/+ rats.

Dietary Protein, Chronic Salt-Sensitive Hypertension, and Kidney Damage

It has been estimated that over a fifth of deaths worldwide can be attributed to dietary risk factors. A particularly serious condition is salt-sensitive (SS) hypertension and renal damage, participants of which demonstrate increased morbidity and mortality. Notably, a large amount of evidence from humans and animals has demonstrated that other components of the diet can also modulate hypertension and associated end-organ damage. Evidence presented in this review provides support for the view that immunity and inflammation serve to amplify the development of SS hypertension and leads to malignant disease accompanied by tissue damage. Interestingly, SS hypertension is modulated by changes in dietary protein intake, which also influences immune mechanisms. Together, the evidence presented in this review from animal and human studies indicates that changes in dietary protein source have profound effects on the gut microbiota, microbiota-derived metabolites, gene expression, immune cell activation, the production of cytokines and other factors, and the development of SS hypertension and kidney damage.

Brown-Norway chromosome 1 mitigates the upregulation of proinflammatory pathways in mTAL cells and subsequent age-related CKD in Dahl SS/JrHsdMcwi rats

Chronic kidney disease (CKD) has a strong genetic component; however, the underlying pathways are not well understood. Dahl salt-sensitive (SS)/Jr rats spontaneously develop CKD with age and are used to investigate the genetic determinants of CKD. However, there are currently several genetically diverse Dahl SS rats maintained at various institutions and the extent to which some exhibit age-related CKD is unclear. We assessed glomerulosclerosis (GS) and tubulointerstitial fibrosis (TIF) in 3- and 6-mo-old male and female SS/JrHsdMcwi, BN/NHsd/Mcwi [Brown-Norway (BN)], and consomic SS-Chr 1BN/Mcwi (SS.BN1) rats, in which chromosome 1 from the BN rat was introgressed into the genome of the SS/JrHsdMcwi rat. Rats were fed a 0.4% NaCl diet. GS (31 ± 3% vs. 7 ± 1%) and TIF (2.3 ± 0.2 vs. 0.5 ± 0.1) were significantly greater in 6-mo-old compared with 3-mo-old SS/JrHsdMcwi rats, and CKD was exacerbated in males. GS was minimal in 6- and 3-mo-old BN (3.9 ± 0.6% vs. 1.2 ± 0.4%) and SS.BN1 (2.4 ± 0.5% vs. 1.0 ± 0.3%) rats, and neither exhibited TIF. In SS/JrHsdMcwi and SS.BN1 rats, mean arterial blood pressure was significantly greater in 6-mo-old compared with 3-mo-old SS/JrHsdMcwi (162 ± 4 vs. 131 ± 2 mmHg) but not SS.BN1 (115 ± 2 vs. 116 ± 1 mmHg) rats. In 6-mo-old SS/JrHsdMcwi rats, blood pressure was significantly greater in females. RNA-sequencing analysis revealed that inflammatory pathways were upregulated in isolated medullary thick ascending tubules in 7-wk-old SS/JrHsdMcwi rats, before the development of tubule pathology, compared with SS.BN1 rats. In summary, SS/JrHsdMcwi rats exhibit robust age-related progression of medullary thick ascending limb abnormalities, CKD, and hypertension, and gene(s) on chromosome 1 have a major pathogenic role in such changes.NEW & NOTEWORTHY This study shows that the robust age-related progression of kidney disease in Dahl SS/JrHsdMcw rats maintained on a normal-salt diet is abolished in consomic SS.BN1 rats. Evidence that medullary thick ascending limb segments of SS/JrHsdMcw rats are structurally abnormal and enriched in proinflammatory pathways before the development of protein casts provides new insights into the pathogenesis of kidney disease in this model.

Microbiota-associated mechanisms underlying sexual dimorphism in hypertension

Consistent research over the last 20 years has shown that there are clear sex differences in the pathogenesis of hypertension, the leading risk factor for the development of cardiovascular diseases. More recently, there is evidence in both humans and experimental animal models that causally implicates the gut microbiota in hypertension. It therefore follows that sex differences in the gut microbiota may mediate the extent of disease between sexes. This new field is rapidly changing and advancing, and the purpose of this review is to cover the most up-to-date evidence regarding the sexual dimorphism of the gut microbiota and its potential influence on the differential manifestation of hypertension in males versus females. Emphasis will be placed on the mechanisms thought to contribute to these sex differences in both the gut microbiota and hypertension, including sex steroid hormones, gut-derived metabolites, the immune system, and pregnancy.

Impact of bedding on Dahl salt-sensitive hypertension and renal damage

Salt-sensitive hypertension, increases in blood pressure in response to increased salt intake, is associated with an increased risk of morbidity, mortality, and end-organ damage compared with salt-resistant hypertension. The Dahl salt-sensitive (SS) rat mimics the phenotypic characteristics observed in human hypertension when rats are challenged with a high-salt diet. Our previous work demonstrated that environmental factors, such as dietary protein, alter the severity of salt sensitivity in Dahl SS rats and should be an important consideration in experimental design. The present study investigated how the bedding on which animals were maintained (wood vs. corncob) could impact the SS phenotype in the Dahl SS rat. Animals that were maintained on corncob bedding exhibited a significant attenuation in blood pressure and renal end-organ damage in response to a high-salt diet compared with animals maintained on wood bedding. This attenuation was associated with an improvement in renal function and reduction in immune cell infiltration into the kidneys of Dahl SS rats maintained on corncob bedding. These results indicate that the type of bedding impacts the SS phenotype in the Dahl SS rat and that the bedding used in experiments can be a confounding factor to consider during data interpretation and experimental design.NEW & NOTEWORTHY Results from our present study demonstrate the profound effect of animal bedding on the severity of salt-sensitive hypertension, renal damage, and inflammation in Dahl salt-sensitive rats. This study highlights the important consideration that should be given to environmental factors, namely, the type of bedding in animal facilities, in experimental design and data interpretation.

Gut-Immune-Kidney Axis: Influence of Dietary Protein in Salt-Sensitive Hypertension

Humans with salt-sensitive hypertension demonstrate increased morbidity, increased mortality, and renal end-organ damage when compared with normotensive subjects or those with salt-resistant hypertension. Substantial evidence from humans and animals has also demonstrated the role of dietary components other than salt to modulate hypertension. Evidence presented in this review provides support for the view that immunity and inflammation serve to amplify the development of salt-sensitive hypertension and leads to malignant disease accompanied by end-organ damage. Interestingly, salt-sensitive disease is modulated by changes in dietary protein intake, which also influences immune mechanisms. Together, the evidence presented in this review from animal and human studies indicates that changes in dietary protein source have profound effects on the gut microbiota, microbiota-derived metabolites, DNA methylation, gene expression, immune cell activation, the production of cytokines and other factors, and the development of salt-sensitive hypertension and related disease phenotypes.

T Cell Immunometabolism and Redox Signaling in Hypertension

PURPOSE OF REVIEW

In this article, we summarize the current literature supporting metabolic and redox signaling pathways as important mechanisms underlying T cell activation in the context of hypertension.

RECENT FINDINGS

T cell immunometabolism undergoes dramatic remodeling in order to meet the demands of T cell activation, differentiation, and proliferation. Recent evidence demonstrates that the T cell oxidation-reduction (redox) system also undergoes significant changes upon activation, which can itself modulate metabolic processes and T cell function. Dysregulation of these signaling pathways can lead to aberrant T cell activation and inappropriate ROS production, both of which are linked to pathological conditions like hypertension. While the contribution of T cells to the progression of hypertension has been thoroughly investigated, how T cell metabolism and redox signaling changes, both separately and together, is an area of study that remains largely untouched. This review presents evidence from our own laboratory as well as others to highlight the importance of these two mechanisms in the study of hypertension.

Dietary influences on the Dahl SS rat gut microbiota and its effects on salt-sensitive hypertension and renal damage

AIM

Our previous studies have demonstrated the importance of dietary factors in the determination of hypertension in Dahl salt-sensitive (SS) rats. Since the gut microbiota has been implicated in chronic diseases like hypertension, we hypothesized that dietary alterations shift the microbiota to mediate the development of salt-sensitive hypertension and renal disease.

METHODS

This study utilized SS rats from the Medical College of Wisconsin (SS/MCW) maintained on a purified, casein-based diet (0.4% NaCl AIN-76A, Dyets) and from Charles River Laboratories (SS/CRL) fed a whole grain diet (0.75% NaCl 5L79, LabDiet). Faecal 16S rDNA sequencing was used to phenotype the gut microbiota. Directly examining the contribution of the gut microbiota, SS/CRL rats were administered faecal microbiota transfer (FMT) experiments with either SS/MCW stool or vehicle (Vehl) in conjunction with the HS AIN-76A diet.

RESULTS

SS/MCW rats exhibit renal damage and inflammation when fed high salt (HS, 4.0% NaCl AIN-76A), which is significantly attenuated in SS/CRL. Gut microbiota phenotyping revealed distinct profiles that correlate with disease severity. SS/MCW FMT worsened the SS/CRL response to HS, evidenced by increased albuminuria (67.4 ± 6.9 vs 113.7 ± 25.0 mg/day, Vehl vs FMT, P = .007), systolic arterial pressure (158.6 ± 5.8 vs 177.8 ± 8.9 mmHg, Vehl vs FMT, P = .09) and renal T-cell infiltration (1.9-fold). Amplicon sequence variant (ASV)-based analysis of faecal 16S rDNA sequencing data revealed taxa that significantly shifted with FMT: Erysipelotrichaceae_2, Parabacteroides gordonii, Streptococcus alactolyticus, Bacteroidales_1, Desulfovibrionaceae_2, Ruminococcus albus.

CONCLUSIONS

These data demonstrate that dietary modulation of the gut microbiota directly contributes to the development of Dahl SS hypertension and renal injury.

Dietary Sodium Restriction Results in Tissue-Specific Changes in DNA Methylation in Humans

[Figure: see text].

Dietary protein source contributes to the risk of developing maternal syndrome in the Dahl salt-sensitive rat

Preeclampsia (PE) is a disorder of pregnancy, which is categorized by hypertension and proteinuria or signs of end-organ damage. Though PE is the leading cause of maternal and fetal morbidity and mortality, the mechanisms leading to PE remain unclear. The present study examined the contribution of dietary protein source (casein versus wheat gluten) to the risk of developing maternal syndrome utilizing two colonies of Dahl salt-sensitive (SS/JrHsdMcwi) rats. While the only difference between the colonies is the diet, the colonies exhibit profound differences in the pregnancy phenotypes. The SS rats maintained on the wheat gluten (SSWG) chow are protected from developing maternal syndrome; however, approximately half of the SS rats fed a casein-based diet (SSC) exhibit maternal syndrome. Those SSC rats that develop pregnancy-specific increases in blood pressure and proteinuria have no observable differences in renal or placental immune profiles compared to the protected SS rats. A gene profile array of placental tissue revealed a downregulation in Nos3 and Cyp26a1 in the SSC rats that develop maternal syndrome accompanied with increases in uterine artery resistance index suggesting the source of this phenotype could be linked to inadequate remodeling within the placenta. Investigations into the effects of multiple pregnancies on maternal health replicated similar findings. The SSC colony displayed an exacerbation in proteinuria, renal hypertrophy and renal immune cell infiltration associated with an increased mortality rate while the SSWG colony were protected highlighting how dietary protein source could have beneficial effects in PE.

Abnormal neonatal sodium handling in skin precedes hypertension in the SAME rat

We discovered high Na⁺ and water content in the skin of newborn Sprague–Dawley rats, which reduced ~ 2.5-fold by 7 days of age, indicating rapid changes in extracellular volume (ECV). Equivalent changes in ECV post birth were also observed in C57Bl/6 J mice, with a fourfold reduction over 7 days, to approximately adult levels. This established the generality of increased ECV at birth. We investigated early sodium and water handling in neonates from a second rat strain, Fischer, and an Hsd11b2-knockout rat modelling the syndrome of apparent mineralocorticoid excess (SAME). Despite Hsd11b2^−/− animals exhibiting lower skin Na⁺ and water levels than controls at birth, they retained ~ 30% higher Na⁺ content in their pelts at the expense of K⁺ thereafter. Hsd11b2^−/− neonates exhibited incipient hypokalaemia from 15 days of age and became increasingly polydipsic and polyuric from weaning. As with adults, they excreted a high proportion of ingested Na⁺ through the kidney, (56.15 ± 8.21% versus control 34.15 ± 8.23%; n = 4; P < 0.0001), suggesting that changes in nephron electrolyte transporters identified in adults, by RNA-seq analysis, occur by 4 weeks of age. Our data reveal that Na⁺ imbalance in the Hsd11b2^−/− neonate leads to excess Na⁺ storage in skin and incipient hypokalaemia, which, together with increased, glucocorticoid-induced Na⁺ uptake in the kidney, then contribute to progressive, volume contracted, salt-sensitive hypertension. Skin Na⁺ plays an important role in the development of SAME but, equally, may play a key physiological role at birth, supporting post-natal growth, as an innate barrier to infection or as a rudimentary kidney.

Renal metabolism and hypertension

Hypertension is a leading risk factor for disease burden worldwide. The kidneys, which have a high specific metabolic rate, play an essential role in the long-term regulation of arterial blood pressure. In this review, we discuss the emerging role of renal metabolism in the development of hypertension. Renal energy and substrate metabolism is characterized by several important and, in some cases, unique features. Recent advances suggest that alterations of renal metabolism may result from genetic abnormalities or serve initially as a physiological response to environmental stressors to support tubular transport, which may ultimately affect regulatory pathways and lead to unfavorable cellular and pathophysiological consequences that contribute to the development of hypertension.

Sexual Dimorphic Role of CD14 (Cluster of Differentiation 14) in Salt-Sensitive Hypertension and Renal Injury

Genomic sequence and gene expression association studies in animals and humans have identified genes that may be integral in the pathogenesis of various diseases. CD14 (cluster of differentiation 14)-a cell surface protein involved in innate immune system activation-is one such gene associated with cardiovascular and hypertensive disease. We previously showed that this gene is upregulated in renal macrophages of Dahl salt-sensitive animals fed a high-salt diet; here we test the hypothesis that CD14 contributes to the elevated pressure and renal injury observed in salt-sensitive hypertension. Using CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/clustered regularly interspaced short palindromic repeat-associated 9), we created a targeted mutation in the CD14 gene on the Dahl SS (SS/JrHSDMcwi) background and validated the absence of CD14 peptides via mass spectrometry. Radiotelemetry was used to monitor blood pressure in wild-type and CD14^-/- animals challenged with high salt and identified infiltrating renal immune cells via flow cytometry. Germline knockout of CD14 exacerbated salt-sensitive hypertension and renal injury in female animals but not males. CD14^-/- females demonstrated increased infiltrating macrophages but no difference in infiltrating lymphocytes. Transplant of CD14^+/+ or CD14^-/- bone marrow was used to isolate the effects of CD14 knockout to hematopoietic cells and confirmed that the differential phenotype observed was due to knockout of CD14 in hematopoietic cells. Ovariectomy was used to remove the influence of female sex hormones, which completely abrogated the effect of CD14 knockout. These studies provide a novel treatment target and evidence of a new dichotomy in immune activation between sexes within the context of hypertensive disease where CD14 regulates immune cell activation and renal injury.

Prenatal High-Salt Diet-Induced Metabolic Disorders via Decreasing Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1α in Adult Male Rat Offspring

SCOPE

Although prenatal high-salt (HS) intake leads to physiological complications in the offspring, little is known regarding its effects on the offspring's glucose metabolism. Therefore, the objectives of this study are to determine the consequences of prenatal HS diet on the offspring's metabolism and to test a potential therapy.

METHODS AND RESULTS

Pregnant rats are fed either a normal-salt (1% NaCl) or high-salt (8% NaCl) diet during the whole pregnancy. Experiments are conducted in five-month-old male offspring. It is found that the prenatal HS diet reduced the glucose tolerance and insulin sensitivity of the offspring. Additionally, there is down-regulation of peroxisome proliferator-activated receptor gamma coactivator 1 alpha (Ppargc1a/PPARGC1A) at the transcript and protein level, which leads to decreased mitochondrial biogenesis and oxidative respiration in skeletal muscle. Moreover, the down-regulation of Ppargc1a is accompanied by decreases in the expression of glucose transporter type 4 (Glut4). With endurance exercise training, these changes are mitigated, which ultimately resulted in improved insulin resistance.

CONCLUSION

These findings suggest that prenatal HS intake induces metabolic disorders via the decreased expression of Ppargc1a in the skeletal muscle of adult offspring, providing novel information concerning the mechanisms and early prevention of metabolic diseases of fetal origins.

Influences of environmental factors during preeclampsia

Preeclampsia is a pregnancy-specific disorder that impacts 5-8% of pregnancies and has long-term cardiovascular and metabolic implications for both mother and fetus. The mechanisms are unclear; however, it is believed that preeclampsia is characterized by abnormal vascularization during placentation resulting in the manifestation of clinical signs such as hypertension, proteinuria, and endothelial dysfunction. Although there is no current cure to alleviate the clinical signs, an emerging area of interest in the field is the influence of environmental factors including diet on the risk of preeclampsia. Because preeclampsia has serious cardiovascular implications to both the mother and fetus and most antihypertensive medications are contraindicated in pregnancy, it is important to investigate other potential therapeutic options such as dietary manipulation. The emerging field of nutrigenomics links diet with the gene expression of known pathways such as oxidative stress and inflammation via microbiome-mediated metabolites and could serve as one potential avenue of therapeutic targets for preeclampsia. Although the exact role of nutrition in the pathogenesis of preeclampsia is unknown, this review will focus on known pathways involved in the development of preeclampsia and how dietary intake modulates the microbiome, oxidative stress, and inflammation with an emphasis on nutrigenomics as a potential avenue of further investigation to better understand this pathology.

Chromosomal Substitution Strategies to Localize Genomic Regions Related to Complex Traits

Chromosomal substitution strategies provide a powerful tool to anonymously reveal the relationship between DNA sequence variants and a normal or disease phenotype of interest. Even in this age of CRISPR-Cas9 genome engineering, the knockdown or overexpression of a gene provides relevant information to our understanding of complex disease only when a close association of an allelic variant with the phenotype has first been established. Limitations of genetic linkage approaches led to the development of more efficient breeding strategies to substitute chromosomal segments from one animal strain into the genetic background of a different strain, enabling a direct comparison of the phenotypes of the strains with variant(s) that differ only at a defined locus. This substitution can be a whole chromosome (consomic), a part of a chromosome (congenic), or as small as only a single or several alleles (subcongenics). In contrast to complete knockout of a specific candidate gene of interest, which simply studies the effects of complete elimination of the gene, the substitution of naturally occurring variants can provide special insights into the functional actions of wild-type alleles. Strategies for production of these inbred strains are reviewed, and a number of examples are used to illustrate the utility of these model systems. Consomic/congenic strains provide a number of experimental advantages in the study of functions of genes and their variants, which are emphasized in this article, such as replication of experimental studies; determination of temporal relationships throughout a life; rigorously controlled experiments in which relations between genotype and phenotype can be tested with the confounding effects of heterogeneous genetic backgrounds, both targeted and multilayered; and "omic" studies performed at many levels of functionality, from molecules to organelles, cells to organs, and organs to organismal behavior across the life span. The application of chromosomal substitution strategies and development of consomic/congenic rat and mouse strains have greatly expanded our knowledge of genomic variants and their phenotypic relationship to physiological functions and to complex diseases such as hypertension and cancer. © 2020 American Physiological Society. Compr Physiol 10:365-388, 2020.

CCL2 mediates early renal leukocyte infiltration during salt-sensitive hypertension

Studies examining mechanisms of Dahl salt-sensitive (SS) hypertension have implicated the infiltration of leukocytes in the kidneys, which contribute to renal disease and elevated blood pressure. However, the signaling pathways by which leukocytes traffic to the kidneys remain poorly understood. The present study nominated a signaling pathway by analyzing a kidney RNA sequencing data set from SS rats fed either a low-salt (0.4% NaCl) diet or a high-salt (4.0% NaCl) diet. From this analysis, chemokine (C-C motif) ligand 2 (CCL2) and chemokine (C-C motif) receptor 2 (CCR2) were nominated as a potential pathway modifying renal leukocyte infiltration and contributing to SS hypertension. The functional role of the CCL2/CCR2 pathway was tested by daily administration of CCR2 antagonist (RS-102895 at 5 mg·kg^-1·day^-1 in DMSO) or DMSO vehicle for 3 or 21 days by intraperitoneal injections during the high salt challenge. Blood pressure, renal leukocyte infiltration, and renal damage were evaluated. The results demonstrated that RS-102895 treatment ameliorated renal damage (urinary albumin excretion; 43.4 ± 5.1 vs. 114.7 ± 15.2 mg/day in vehicle, P < 0.001) and hypertension (144.3 ± 2.2 vs. 158.9 ± 4.8 mmHg in vehicle, P < 0.001) after 21 days of high-salt diet. It was determined that renal leukocyte infiltration was blunted by day 3 of the high-salt diet (1.4 ± 0.1 vs. 1.9 ± 0.2 in vehicle × 10⁶ CD45⁺ cells/kidney, P = 0.034). An in vitro chemotaxis assay validated the effect of RS-102895 on leukocyte chemotaxis toward CCL2. The results suggest that increased CCL2 in SS kidneys is important in the early recruitment of leukocytes, and blockade of this recruitment by administering RS-102895 subsequently blunted the renal damage and hypertension.

Dietary Protein: Mechanisms Influencing Hypertension and Renal Disease

PURPOSE OF REVIEW

This review will provide an in-depth coverage of the epidemiological and pre-clinical literature surrounding the role of dietary protein in hypertension, with a special emphasis on the history of our work on the Dahl salt-sensitive rat.

RECENT FINDINGS

Our studies have dedicated much effort into understanding the relationship between dietary protein and its effect on the development of salt-sensitive hypertension and renal injury. Our evidence over the last 15 years have demonstrated that both the source and amount of dietary protein can influence the severity of disease, where we have determined mechanisms related to immunity, the maternal environment during pregnancy, and more recently the gut microbiota, which significantly contribute to these diet-induced effects. Deeper understanding of these dietary protein-related mechanisms may provide insight on the plausibility of dietary modifications as future therapeutic avenues for hypertension and renal disease.

Epigenetic Modifications in T Cells: The Role of DNA Methylation in Salt-Sensitive Hypertension

The SS (Dahl salt sensitive) rat is an established model of hypertension and renal damage that is accompanied with immune system activation in response to a high-salt diet. Investigations into the effects of sodium-independent and dependent components of the diet were shown to affect the disease phenotype with SS/MCW (JrHsdMcwi) rats maintained on a purified diet (AIN-76A) presenting with a more severe phenotype relative to grain-fed SS/CRL (JrHsdMcwiCrl) rats. Since contributions of the immune system, environment, and diet are documented to alter this phenotype, this present study examined the epigenetic profile of T cells isolated from the periphery and the kidney from these colonies. T cells isolated from kidneys of the 2 colonies revealed that transcriptomic and functional differences may contribute to the susceptibility of hypertension and renal damage. In response to high-salt challenge, the methylome of T cells isolated from the kidney of SS/MCW exhibit a significant increase in differentially methylated regions with a preference for hypermethylation compared with the SS/CRL kidney T cells. Circulating T cells exhibited similar methylation profiles between colonies. Utilizing transcriptomic data from T cells isolated from the same animals upon which the DNA methylation analysis was performed, a predominant negative correlation was observed between gene expression and DNA methylation in all groups. Lastly, inhibition of DNA methyltransferases blunted salt-induced hypertension and renal damage in the SS/MCW rats providing a functional role for methylation. This study demonstrated the influence of epigenetic modifications to immune cell function, highlighting the need for further investigations.

Parental Dietary Protein Source and the Role of CMKLR1 in Determining the Severity of Dahl Salt-Sensitive Hypertension

Studies from our laboratory have revealed an important role for the maternal diet and the dietary protein source in the development of hypertension and renal injury in Dahl salt-sensitive (SS) rats. The current study sought to compare salt-induced hypertension, renal damage, and immune cell infiltration in the offspring of breeders fed either a casein- or gluten-based diet, with the hypothesis that offspring from gluten-fed breeders would fail to develop these SS phenotypes. When fed identical diets post-weaning, the F1 generation gluten offspring demonstrated lower mean arterial pressure (149.1±3.1 versus 162.5±5.8 mm Hg), albuminuria (166.2±34.6 versus 250.9±27.8 mg/day), and outer medullary protein casting (7.4±0.8% versus 13.1±1.3%) in response to high salt compared with the casein offspring (n=9-11). The gluten offspring also had fewer CD45+ leukocytes, CD11b/c+ monocytes/macrophages, CD3+ T cells, and CD45R+ B cells infiltrating the kidney. Analysis of the F2 generation gluten offspring also exhibited lower mean arterial pressure and renal damage compared with rats born from casein breeders (n=7-9), with no difference in renal immune cell infiltration. CMKLR1-receptor for the novel prohypertensive adipokine chemerin-was found via polymerase chain reaction array to be significantly upregulated (2.99-fold) in renal T cells isolated from F2 offspring of casein-fed versus gluten-fed parents. Furthermore, CMKLR1 inhibition via α-NETA (2-[α-naphthoyl] ethyltrimethylammonium iodide) treatment significantly attenuated renal immune cell infiltration, hypertension, and renal damage in SS rats fed high salt. Together, these data demonstrate the influence of the parental diet in determining the salt-induced hypertension, renal damage, and inflammatory phenotype of the offspring.

Prenatal high-salt diet impaired vasodilatation with reprogrammed renin-angiotensin system in offspring rats

AIMS

High-salt diet is linked to hypertension, and prenatal high-salt diet increases the risk of cardiovascular diseases in the offspring. The present study investigated whether and how prenatal high-salt diet influenced nitric oxide-mediated vasodilatation in the offspring.

METHODS AND RESULTS

Pregnant rats were fed either normal-salt (1% sodium chloride) or high-salt (8% sodium chloride) diet during gestation. Experiments were conducted in 5-month-old male offspring. Sodium nitroprusside (SNP, nitric oxide donor)-induced hypotensive responses (in vivo) and vascular dilatation (in vitro) was significantly attenuated (Emax: 84 ± 2 vs. 51 ± 2, high-salt vs. control, P < 0.001) in the high-salt offspring, indicating reduced vascular relaxations. Pretreatment with Tempol (reactive oxygen species scavenger) alleviated this attenuation. The high-salt offspring showed an increased level of oxidative stress markers in both mesenteric arteries and plasma samples. The antioxidant activity, serum superoxide dismutase and catalase were significantly reduced, whereas malondialdehyde was increased in the high-salt offspring. O2 production, and protein expression of Nox2 and Nox4 in mesenteric arteries was significantly increased in the high-salt offspring whereas Nox1 showed no changes. The local renin-angiotensin system in mesenteric arteries was activated, associated with an increased NADPH oxidase. DNA methylation at the proximal promoter of angiotensin-converting enzyme gene in the lung was significantly increased in the high-salt offspring (P = 0.004).

CONCLUSION

The results suggest that prenatal high-salt diet impairs nitric oxide-mediated vasodilatation because of the increased oxidative stress-affected renin-angiotensin system in the high-salt offspring, providing new information for understanding, and early prevention of cardiovascular diseases in fetal origins.

Dietary Effects on Dahl Salt-Sensitive Hypertension, Renal Damage, and the T Lymphocyte Transcriptome

The Dahl salt-sensitive (SS) rat is an established model of SS hypertension and renal damage. In addition to salt, other dietary components were shown to be important determinants of hypertension in SS rats. With previous work eliminating the involvement of genetic differences, grain-fed SS rats from Charles River Laboratories (SS/CRL; 5L2F/5L79) were less susceptible to salt-induced hypertension and renal damage compared with purified diet-fed SS rats bred at the Medical College of Wisconsin (SS/MCW; 0.4% NaCl, AIN-76A). With the known role of immunity in hypertension, the present study characterized the immune cells infiltrating SS/MCW and SS/CRL kidneys via flow cytometry and RNA sequencing in T-cells isolated from the blood and kidneys of rats maintained on their respective parental diet or on 3 weeks of high salt (4.0% NaCl, AIN-76A). SS/CRL rats were protected from salt-induced hypertension (116.5±1.2 versus 141.9±14.4 mm Hg), albuminuria (21.7±3.5 versus 162.9±22.2 mg/d), and renal immune cell infiltration compared with SS/MCW. RNA-seq revealed >50% of all annotated genes in the entire transcriptome to be significantly differentially expressed in T-cells isolated from blood versus kidney, regardless of colony or chow. Pathway analysis of significantly differentially expressed genes between low and high salt conditions demonstrated changes related to inflammation in SS/MCW renal T-cells compared with metabolism-related pathways in SS/CRL renal T-cells. These functional and transcriptomic T-cell differences between SS/MCW and SS/CRL show that dietary components in addition to salt may influence immunity and the infiltration of immune cells into the kidney, ultimately impacting susceptibility to salt-induced hypertension and renal damage.

Low Birth Weight, Blood Pressure and Renal Susceptibility

PURPOSE OF THE REVIEW

The purpose of this review is to highlight the clinical significance of increased renal risk that has its origins in fetal life. This review will also discuss the critical need to identify therapeutic interventions for use in a pregnancy complicated by placental dysfunction and intrauterine growth restriction that can mitigate the developmental origins of kidney disease without inflicting additional harm on the developing fetus.

RECENT FINDINGS

A reduction in nephron number is a contributory factor in the pathogenesis of hypertension and kidney disease in low birth weight individuals. Reduced nephron number may heighten susceptibility to a secondary renal insult, and recent studies suggest that perinatal history including birth weight should be considered in the assessment of renal risk in kidney donors. This review highlights current findings related to placental dysfunction, intrauterine growth restriction, increased risk for renal injury and disease, and potential therapeutic interventions.

The complement system in hypertension and renal damage in the Dahl SS rat

Evidence indicates the immune system is important in development of hypertension and kidney disease. In the Dahl Salt-Sensitive (SS) rat model, lymphocytes play a role in development of hypertension and kidney damage after increased sodium intake. Recent transcriptomic analyses demonstrate upregulation of the innate immune complement system in the kidney of Dahl SS rat fed a high-salt diet, leading us to hypothesize that inhibition of complement activation would attenuate development of hypertension and kidney damage. Male Dahl SS rats on a low salt (0.4% NaCl) diet were instrumented with telemeters for continuous monitoring of arterial blood pressure. Animals received saline vehicle (Control) or sCR1, a soluble form of endogenous Complement Receptor 1 (CR1; CD35) that inhibits complement activation. At Day 0, rats were switched to high salt (4.0% NaCl) diet and assigned to sCR1 (15 mg/kg per day) or Control groups with daily ip injections either days 1-7 or days 14-18. Urine was collected overnight for determination of albumin excretion. Treatment with sCR1, either immediately after high-salt diet was initiated, or at days 14-18, did not alter development of hypertension or albuminuria. The sCR1 dose effectively inhibited total hemolytic complement activity as well as C3a generation. High salt caused an increase in message for complement regulator Cd59, with minimal change in Crry that controls the C3 convertase. Thus, innate immune complement activation in the circulation is not critical for development of hypertension and kidney damage due to increased sodium intake, and therapeutic manipulation of the complement system is not indicated in salt-sensitive hypertension.

Thick Ascending Limb Sodium Transport in the Pathogenesis of Hypertension

The thick ascending limb plays a key role in maintaining water and electrolyte balance. The importance of this segment in regulating blood pressure is evidenced by the effect of loop diuretics or local genetic defects on this parameter. Hormones and factors produced by thick ascending limbs have both autocrine and paracrine effects, which can extend prohypertensive signaling to other structures of the nephron. In this review, we discuss the role of the thick ascending limb in the development of hypertension, not as a sole participant, but one that works within the rich biological context of the renal medulla. We first provide an overview of the basic physiology of the segment and the anatomical considerations necessary to understand its relationship with other renal structures. We explore the physiopathological changes in thick ascending limbs occurring in both genetic and induced animal models of hypertension. We then discuss the racial differences and genetic defects that affect blood pressure in humans through changes in thick ascending limb transport rates. Throughout the text, we scrutinize methodologies and discuss the limitations of research techniques that, when overlooked, can lead investigators to make erroneous conclusions. Thus, in addition to advancing an understanding of the basic mechanisms of physiology, the ultimate goal of this work is to understand our research tools, to make better use of them, and to contextualize research data. Future advances in renal hypertension research will require not only collection of new experimental data, but also integration of our current knowledge.

Microglia and brain angiotensin type 1 receptors are involved in desensitising baroreflex by intracerebroventricular hypertonic saline in male Sprague-Dawley rats

High salt diet alters cardiovascular control by increasing concentration of sodium ions (Na⁺) in cerebrospinal fluid (CSF) and is a risk factor for hypertension. Hypernatremic conditions activate microglia and upregulate renin-angiotensin system in the brain. Thus, we checked if chronic elevation of CSF Na⁺ affects neural control of circulatory system via microglia and brain angiotensin type 1 receptors (AT1Rs). Normotensive adult male Sprague-Dawley rats received two-week intracerebroventricular (ICV) infusion of either isoosmotic saline (0.9% NaCl); hyperosmotic saline (5% NaCl); 5% NaCl with minocycline - inhibitor of microglia; 5% NaCl with losartan - AT1R blocker. Fluid intake, urine output, and urinary Na⁺ excretion were measured before and during ICV infusions. At the end of ICV infusions, blood pressure and heart rate were recorded in awake rats at rest, in response to acute air jet stressor, during pharmacological evaluation of baroreflex, and after autonomic ganglia blockade. CSF and blood were collected for evaluation of Na⁺ concentration. Baroreflex was blunted in rats ICV infused with 5% NaCl. ICV treatment with losartan or minocycline prevented decrease in baroreflex sensitivity. Hemodynamic parameters at rest, in response to acute stressor and autonomic ganglia blockade were similar in all groups. Neither treatment affected water intake, urine output and urinary Na⁺ excretion. ICV infusion of 5% NaCl resulted in higher concentration of Na⁺ in CSF than in control group (0.9% NaCl) and in plasma. Our results indicate that chronic ICV infusion of hyperosmotic saline blunts baroreflex in normotensive rats and this desensitization is mediated by microglia and AT1Rs.

Role of gut metabolism of adrenal corticosteroids and hypertension: clues gut-cleansing antibiotics give us

Intestinal bacteria can metabolize sterols, bile acids, steroid hormones, dietary proteins, fiber, foodstuffs, and short chain fatty acids. The metabolic products generated by some of these intestinal bacteria have been linked to a number of systemic diseases including obesity with Type 2 diabetes mellitus, some forms of inflammation, and more recently, systemic hypertension. In this review, we primarily focus on the potential role selected gut bacteria play in metabolizing the endogenous glucocorticoids corticosterone and cortisol. Those generated steroid metabolites, when reabsorbed in the intestine back into the circulation, produce biological effects most notably as inhibitors of 11β-hydroxysteroid dehydrogenase (11β-HSD) types 1 and 2. Inhibition of the dehydrogenase actions of 11β-HSD, particularly in kidney and vascular tissue, allows both corticosterone and cortisol the ability to bind to and activate mineralocorticoid receptors with attended changes in sodium handling and vascular resistance leading to increases in blood pressure. In several animal models of hypertension, administration of gut-cleansing antibiotics results in transient resolution of hypertension and transfer of intestinal contents from a hypertensive animal to a normotensive animal produces hypertension in the recipient. Moreover, fecal samples from hypertensive humans transplanted into germ-free mice resulted in hypertension in the recipient mice. Thus, it appears that the intestinal microbiome may not just be an innocent bystander but certain perturbations in the type and number of bacteria may directly or indirectly affect hypertension and other diseases.

Uteroplacental insufficiency temporally exacerbates salt-induced hypertension associated with a reduced natriuretic response in male rat offspring

KEY POINTS

Low weight at birth increases the risk of developing chronic diseases in adulthood A diet that is high in salt is known to elevate blood pressure, which is a major risk factor for cardiovascular and kidney diseases The present study demonstrates that growth restricted male rats have a heightened sensitivity to high dietary salt, in the context of raised systolic blood pressure, reduced urinary sodium excretion and stiffer mesenteric resistance vessels Other salt-induced effects, such as kidney hyperfiltration, albuminuria and glomerular damage, were not exacerbated by being born small The present study demonstrates that male offspring born small have an increased cardiovascular susceptibility to high dietary salt, such that that minimizing salt intake is probably of particular benefit to this at-risk population ABSTRACT: Intrauterine growth restriction increases the risk of developing chronic diseases in adulthood. Lifestyle factors, such as poor dietary choices, may elevate this risk. We determined whether being born small increases the sensitivity to a dietary salt challenge, in the context of hypertension, kidney disease and arterial stiffness. Bilateral uterine vessel ligation or sham surgery (offspring termed Restricted and Control, respectively) was performed on 18-day pregnant Wistar Kyoto rats. Male offspring were allocated to receive a diet high in salt (8% sodium chloride) or remain on standard rat chow (0.52% sodium chloride) from 20 to 26 weeks of age for 6 weeks. Systolic blood pressure (tail-cuff), renal function (24 h urine excretions) and vascular stiffness (pressure myography) were assessed. Restricted males were born 15% lighter than Controls and remained smaller throughout the study. Salt-induced hypertension was exacerbated in Restricted offspring, reaching a peak systolic pressure of ∼175 mmHg earlier than normal weight counterparts. The natriuretic response to high dietary salt in Restricted animals was less than in Controls and may explain the early rise in arterial pressure. Growth restricted males allocated to a high salt diet also had increased passive arterial stiffness of mesenteric resistance arteries. Other aspects of renal function, including salt-induced hyperfiltration, albuminuria and glomerular damage, were not exacerbated by uteroplacental insufficiency. The present study demonstrates that male offspring exposed to uteroplacental insufficiency and born small have an increased sensitivity to salt-induced hypertension and arterial remodelling.

Role of DNA De Novo (De)Methylation in the Kidney in Salt-Induced Hypertension

Numerous adult diseases involving tissues consisting primarily of nondividing cells are associated with changes in DNA methylation. It suggests a pathophysiological role for de novo methylation or demethylation of DNA, which is catalyzed by DNA methyltransferase 3 and ten-eleven translocases. However, the contribution of DNA de novo (de)methylation to these diseases remains almost completely unproven. Broad changes in DNA methylation occurred within days in the renal outer medulla of Dahl SS rats fed a high-salt diet, a classic model of hypertension. Intrarenal administration of anti-DNA methyltransferase 3a/ten-eleven translocase 3 GapmeRs attenuated high salt-induced hypertension in SS rats. The high-salt diet induced differential expression of 1712 genes in the renal outer medulla. Remarkably, the differential expression of 76% of these genes was prevented by anti-DNA methyltransferase 3a/ten-eleven translocase 3 GapmeRs. The genes differentially expressed in response to the GapmeRs were involved in the regulation of metabolism and inflammation and were significantly enriched for genes showing differential methylation in response to the GapmeRs. These data indicate a significant role of DNA de novo (de)methylation in the kidney in the development of hypertension in SS rats. The findings should help to shift the paradigm of DNA methylation research in diseases involving nondividing cells from correlative analysis to functional and mechanistic studies.

Influence of dietary protein on Dahl salt-sensitive hypertension: a potential role for gut microbiota

High blood pressure affects 1.39 billion adults across the globe and is the leading preventable cause of death worldwide. Hypertension is a multifaceted disease with known genetic and environmental factors contributing to its progression. Our studies utilizing the Dahl salt-sensitive (SS) rat have demonstrated the remarkable influence of dietary protein and maternal environment on the development of hypertension and renal damage in response to high salt. There is growing interest in the relationship between the microbiome and hypertension, with gut dysbiosis being correlated to a number of pathologies. This review summarizes the current literature regarding the interplay among dietary protein, the gut microbiota, and hypertension. These studies may provide insight into the effects we have observed between diet and hypertension in Dahl SS rats and, we hope, lead to new perspectives where potential dietary interventions or microbiota manipulations could serve as plausible therapies for hypertension.

Salt-sensitive (Rapp) rats from Envigo spontaneously develop accelerated hypertension independent of ovariectomy on a low-sodium diet

Inbred salt-sensitive (SS) rats developed by John Rapp and distributed by Harlan (SS/JrHsd) were shown to model ovariectomy-induced hypertension because on a low-sodium (LS) diet, ovariectomized SS (SS-OVX) animals became hypertensive in contrast to their sham-operated (SS-SHAM) normotensive littermates. After Harlan merged with Envigo in 2015, inconsistencies in the LS normotensive phenotype were reported. To further investigate these inconsistencies, we studied the effects of ovariectomy on SS and salt-resistant (SR) rats purchased from Envigo (SS/JrHsd/Env) between 2015 and 2017. The mean arterial pressure (MAP) in SS rats on a LS diet exceeded 160 mmHg at 7 mo old. Ovariectomy at 3 mo had no detectable effect on MAP from 4 to 7 mo, nor did ovariectomy at 1.5 mo significantly affect MAP at 10 mo in either strain; only strain differences in MAP were observed [MAP: SR-SHAM ( n = 7 rats), 102 ± 3 mmHg; SR-OVX ( n = 6 rats), 114 ± 1 mmHg; SS-SHAM ( n = 7 rats), 177 ± 6 mmHg; SS-OVX ( n = 5 rats), 190 ± 12 mmHg; where P < 0.0001 vs. SR, same ovarian-status for SS-SHAM and SS-OVX, respectively]. Whole genome sequencing revealed more genomic variants of SS/JrHsd/Env, including single nucleotide and insertion deletion polymorphisms and higher heterozygous/homozygous ratios compared with the reference genome, than for SS/JrHsd/Mcwi and SS/Jr rats maintained in Milwaukee, WI and Toledo, OH, respectively, and which still exhibit normal blood pressure on a LS diet. These findings demonstrate that the female SS/JrHsd/Env rat has genetically diverged from the original phenotype, which was normotensive on a LS diet when the ovaries were intact but rapidly developed hypertension when the ovaries were removed. Nonetheless, the SS/JrHsd/Env rat could be a valuable model that complements other animal models of spontaneous hypertension used to investigate mechanisms of essential hypertension.

Sodium bicarbonate loading limits tubular cast formation independent of glomerular injury and proteinuria in Dahl salt-sensitive rats

Sodium bicarbonate (NaHCO₃) slows the decline in kidney function in patients with chronic kidney disease (CKD), yet the mechanisms mediating this effect remain unclear. The Dahl salt-sensitive (SS) rat develops hypertension and progressive renal injury when fed a high salt diet; however, the effect of alkali loading on kidney injury has never been investigated in this model. We hypothesized that NaHCO₃ protects from the development of renal injury in Dahl salt-sensitive rats via luminal alkalization which limits the formation of tubular casts, which are a prominent pathological feature in this model. To examine this hypothesis, we determined blood pressure and renal injury responses in Dahl SS rats drinking vehicle (0.1 M NaCl) or NaHCO₃ (0.1 M) solutions as well as in Dahl SS rats lacking the voltage-gated proton channel (Hv1). We found that oral NaHCO₃ reduced tubular NH₄⁺ production, tubular cast formation, and interstitial fibrosis in rats fed a high salt diet for 2 weeks. This effect was independent of changes in blood pressure, glomerular injury, or proteinuria and did not associate with changes in renal inflammatory status. We found that null mutation of Hv1 also limited cast formation in Dahl SS rats independent of proteinuria or glomerular injury. As Hv1 is localized to the luminal membrane of TAL, our data suggest that alkalization of the luminal fluid within this segment limits cast formation in this model. Reduced cast formation, secondary to luminal alkalization within TAL segments may mediate some of the protective effects of alkali loading observed in CKD patients.

Stability of global methylation profiles of whole blood and extracted DNA under different storage durations and conditions

AIM

To test whether DNA samples stored for a prolonged period (20 years) under various storage conditions could be used for comparative methylation studies using reduced representation bisulfite sequencing.

PATIENTS & METHODS

Five groups of human blood DNA samples (n = 5-6/group) were compared. The groupings were based on the anticoagulant used and storage temperature and duration.

RESULTS

Methylation profiles of defined genomic regions in the DNA or blood samples archived for 20 years were similar across all storage temperatures, including 4°C. The level of intersample similarity in archived samples was not significantly different than that in recently collected samples.

CONCLUSION

Archived samples, including DNA stored at 4°C for 20 years, are suitable for comparative studies of DNA methylation.

Urinary Metabolites Associated with Blood Pressure on a Low- or High-Sodium Diet

Dietary salt intake has significant effects on arterial blood pressure and the development of hypertension. Mechanisms underlying salt-dependent changes in blood pressure remain poorly understood, and it is difficult to assess blood pressure salt-sensitivity clinically. Methods: We examined urinary levels of metabolites in 103 participants of the Dietary Approaches to Stop Hypertension (DASH)-Sodium trial after nearly 30 days on a defined diet containing high sodium (targeting 150 mmol sodium intake per day) or low sodium (50 mmol per day). Targeted chromatography/mass spectrometry analysis was performed in 24 h urine samples for 47 amino metabolites and 10 metabolites related to the tricarboxylic acid cycle. The effect of an identified metabolite on blood pressure was examined in Dahl salt-sensitive rats. Results: Urinary metabolite levels improved the prediction of classification of blood pressure salt-sensitivity based on race, age and sex. Random forest and generalized linear mixed model analyses identified significant (false discovery rate <0.05) associations of 24 h excretions of β-aminoisobutyric acid, cystine, citrulline, homocysteine and lysine with systolic blood pressure and cystine with diastolic blood pressure. The differences in homocysteine levels between low- and high-sodium intakes were significantly associated with the differences in diastolic blood pressure. These associations were significant with or without considering demographic factors. Treatment with β-aminoisobutyric acid significantly attenuated high-salt-induced hypertension in Dahl salt-sensitive rats. Conclusion: These findings support the presence of new mechanisms of blood pressure regulation involving metabolic intermediaries, which could be developed as markers or therapeutic targets for salt-sensitive hypertension.

Nitric oxide production by glomerular podocytes

Nitric Oxide (NO), a potent vasodilator and vital signaling molecule, has been shown to contribute to the regulation of glomerular ultrafiltration. However, whether changes in NO occur in podocytes during the pathogenesis of salt-sensitive hypertension has not yet been thoroughly examined. We showed here that podocytes produce NO, and further hypothesized that hypertensive animals would exhibit reduced NO production in these cells in response to various paracrine factors, which might contribute to the damage of glomeruli filtration barrier and development of proteinuria. To test this, we isolated glomeruli from the kidneys of Dahl salt-sensitive (SS) rats fed a low salt (LS; 0.4% NaCl) or high salt (HS; 4% NaCl, 3 weeks) diets and loaded podocytes with either a combination of NO and Ca²⁺ fluorophores (DAF-FM and Fura Red, respectively) or DAF-FM alone. Changes in fluorescence were observed with confocal microscopy in response to adenosine triphosphate (ATP), angiotensin II (Ang II), and hydrogen peroxide (H₂O₂). Application of Ang II resulted in activation of both NO and intracellular calcium ([Ca²⁺]_i) transients. In contrast, ATP promoted [Ca²⁺]_i transients, but did not have any effects on NO production. SS rats fed a HS diet for 3 weeks demonstrated impaired NO production: the response to Ang II or H₂O₂ in podocytes of glomeruli isolated from SS rats fed a HS diet was significantly reduced compared to rats fed a LS diet. Therefore, glomerular podocytes from hypertensive rats showed a diminished NO release in response to Ang II or oxidative stress, suggesting that podocytic NO signaling is dysfunctional in this condition and likely contributes to the development of kidney injury.

Essential role of Kir5.1 channels in renal salt handling and blood pressure control

Supplementing diets with high potassium helps reduce hypertension in humans. Inwardly rectifying K+ channels Kir4.1 (Kcnj10) and Kir5.1 (Kcnj16) are highly expressed in the basolateral membrane of distal renal tubules and contribute to Na+ reabsorption and K+ secretion through the direct control of transepithelial voltage. To define the importance of Kir5.1 in blood pressure control under conditions of salt-induced hypertension, we generated a Kcnj16 knockout in Dahl salt-sensitive (SS) rats (SSKcnj16-/-). SSKcnj16-/- rats exhibited hypokalemia and reduced blood pressure, and when fed a high-salt diet (4% NaCl), experienced 100% mortality within a few days triggered by salt wasting and severe hypokalemia. Electrophysiological recordings of basolateral K+ channels in the collecting ducts isolated from SSKcnj16-/- rats revealed activity of only homomeric Kir4.1 channels. Kir4.1 expression was upregulated in SSKcnj16-/- rats, but the protein was predominantly localized in the cytosol in SSKcnj16-/- rats. Benzamil, but not hydrochlorothiazide or furosemide, rescued this phenotype from mortality on a high-salt diet. Supplementation of high-salt diet with increased potassium (2% KCl) prevented mortality in SSKcnj16-/- rats and prevented or mitigated hypertension in SSKcnj16-/- or control SS rats, respectively. Our results demonstrate that Kir5.1 channels are key regulators of renal salt handling in SS hypertension.

Beyond gut feelings: how the gut microbiota regulates blood pressure

Hypertension is the leading risk factor for heart disease and stroke, and is estimated to cause 9.4 million deaths globally every year. The pathogenesis of hypertension is complex, but lifestyle factors such as diet are important contributors to the disease. High dietary intake of fruit and vegetables is associated with reduced blood pressure and lower cardiovascular mortality. A critical relationship between dietary intake and the composition of the gut microbiota has been described in the literature, and a growing body of evidence supports the role of the gut microbiota in the regulation of blood pressure. In this Review, we describe the mechanisms by which the gut microbiota and its metabolites, including short-chain fatty acids, trimethylamine N-oxide, and lipopolysaccharides, act on downstream cellular targets to prevent or contribute to the pathogenesis of hypertension. These effects have a direct influence on tissues such as the kidney, the endothelium, and the heart. Finally, we consider the role of the gut microbiota in resistant hypertension, the possible intergenerational effect of the gut microbiota on blood pressure regulation, and the promising therapeutic potential of gut microbiota modification to improve health and prevent disease.

Advances in transgenic animal models and techniques

On May 11th and 12th 2017 was held in Nantes, France, the international meeting "Advances in transgenic animal models and techniques" ( http://www.trm.univ-nantes.fr/ ). This biennial meeting is the fifth one of its kind to be organized by the Transgenic Rats ImmunoPhenomic (TRIP) Nantes facility ( http://www.tgr.nantes.inserm.fr/ ). The meeting was supported by private companies (SONIDEL, Scionics computer innovation, New England Biolabs, MERCK, genOway, Journal Disease Models and Mechanisms) and by public institutions (International Society for Transgenic Technology, University of Nantes, INSERM UMR 1064, SFR François Bonamy, CNRS, Région Pays de la Loire, Biogenouest, TEFOR infrastructure, ITUN, IHU-CESTI and DHU-Oncogeffe and Labex IGO). Around 100 participants, from France but also from different European countries, Japan and USA, attended the meeting.

MicroRNA-21 regulates peroxisome proliferator-activated receptor alpha, a molecular mechanism of cardiac pathology in Cardiorenal Syndrome Type 4

Cardiovascular events are the leading cause of death in patients with chronic kidney disease (CKD), although the pathological mechanisms are poorly understood. Here we longitudinally characterized left ventricle pathology in a 5/6 nephrectomy rat model of CKD and identify novel molecular mediators. Next-generation sequencing of left ventricle mRNA and microRNA (miRNA) was performed at physiologically distinct points in disease progression, identifying alterations in genes in numerous immune, lipid metabolism, and inflammatory pathways, as well as several miRNAs. MiRNA miR-21-5p was increased in our dataset and has been reported to regulate many identified pathways. Suppression of miR-21-5p protected rats with 5/6 nephrectomy from developing left ventricle hypertrophy and improved left ventricle function. Next-generation mRNA sequencing revealed that miR-21-5p suppression altered gene expression in peroxisome proliferator-activated receptor alpha (PPARα) regulated pathways in the left ventricle. PPARα, a miR-21-5p target, is the primary PPAR isoform in the heart, importantly involved in regulating fatty acid metabolism. Therapeutic delivery of low-dose PPARα agonist (clofibrate) to rats with 5/6 nephrectomy improved cardiac function and prevented left ventricle dilation. Thus, comprehensive characterization of left ventricle molecular changes highlights the involvement of numerous signaling pathways not previously explored in CKD models and identified PPARα as a potential therapeutic target for CKD-related cardiac dysfunction.

Elevation of fumarase attenuates hypertension and can result from a nonsynonymous sequence variation or increased expression depending on rat strain

The activity of fumarase, an enzyme in the tricarboxylic acid cycle, is lower in Dahl salt-sensitive SS rats compared with SS.13^BN rats. SS.13^BN rats have a Brown Norway (BN) allele of fumarase and exhibit attenuated hypertension. The SS allele of fumarase differs from the BN allele by a K481E sequence variation. It remains unknown whether higher fumarase activities can attenuate hypertension and whether the mechanism is relevant without the K481E variation. We developed SS-TgFh1 transgenic rats overexpressing fumarase on the background of the SS rat. Hypertension was attenuated in SS-TgFh1 rats. Mean arterial pressure in SS-TgFh1 rats was 20 mmHg lower than transgene-negative SS littermates after 12 days on a 4% NaCl diet. Fumarase overexpression decreased H₂O₂, while fumarase knockdown increased H₂O₂ Ectopically expressed BN form of fumarase had higher specific activity than the SS form. However, sequencing of more than a dozen rat strains indicated most rat strains including salt-insensitive Sprague-Dawley (SD) rats had the SS allele of fumarase. Despite that, total fumarase enzyme activity in the renal medulla was still higher in SD rats than in SS rats, which was associated with higher expression of fumarase in SD. H₂O₂ can suppress the expression of fumarase. Renal medullary interstitial administration of fumarase siRNA in SD rats resulted in higher blood pressure on the high-salt diet. These findings indicate elevation of total fumarase activity attenuates the development of hypertension and can result from a nonsynonymous sequence variation in some rat strains and higher expression in other rat strains.