Novel role of fumarate metabolism in dahl-salt sensitive hypertension

Proteomic profiling of renal tissue of normo- and hypertensive rats with the renalase peptide RP220 as an affinity ligand

Renalase (RNLS) is a recently discovered protein that plays an important role in the regulation of blood pressure by acting inside and outside cells. Intracellular RNLS is a FAD-dependent oxidoreductase that oxidizes isomeric forms of β-NAD(P)H. Extracellular renalase lacking its N-terminal peptide and cofactor FAD exerts various protective effects via non-catalytic mechanisms. Certain experimental evidence exists in the literature that the RP220 peptide (a 20-mer peptide corresponding to the amino acid sequence RNLS 220-239) reproduces a number of non-catalytic effects of this protein, acting on receptor proteins of the plasma membrane. The possibility of interaction of this peptide with intracellular proteins has not been studied. Taking into consideration the known role of RNLS as a possible antihypertensive factor, the aim of this study was to perform proteomic profiling of the kidneys of normotensive and hypertensive rats using RP220 as an affinity ligand. Proteomic (semi-quantitative) identification revealed changes in the relative content of about 200 individual proteins in the kidneys of hypertensive rats bound to the affinity sorbent as compared to the kidneys of normotensive animals. Increased binding of SHR renal proteins to RP220 over the normotensive control was found for proteins involved in the development of cardiovascular pathology. Decreased binding of the kidney proteins from hypertensive animals to RP220 was noted for components of the ubiquitin-proteasome system, ribosomes, and cytoskeleton.

Renal Epithelial Mitochondria: Implications for Hypertensive Kidney Disease

According to the Centers for Disease Control and Prevention, 1 in 2 U.S. adults have hypertension, and more than 1 in 7 chronic kidney disease. In fact, hypertension is the second leading cause of kidney failure in the United States; it is a complex disease characterized by, leading to, and caused by renal dysfunction. It is well-established that hypertensive renal damage is accompanied by mitochondrial damage and oxidative stress, which are differentially regulated and manifested along the nephron due to the diverse structure and functions of renal cells. This article provides a summary of the relevant knowledge of mitochondrial bioenergetics and metabolism, focuses on renal mitochondrial function, and discusses the evidence that has been accumulated regarding the role of epithelial mitochondrial bioenergetics in the development of renal tissue dysfunction in hypertension. © 2024 American Physiological Society. Compr Physiol 14:5225-5242, 2024.

Fumarate and its downstream signalling pathways in the cardiorenal system: Recent insights and novel expositions in the etiology of hypertension

Hypertension, a risk factor for cardiorenal disease has a huge global health impact. Hence, there is a continuous search for new therapeutic targets and putative antihypertensive ligands. This search has transcended into the realm of mitochondrial metabolism which has been reported to underline the etiology of certain diseases, including hypertension. Recently, genetic alterations in the tricarboxylic acid (TCA) cycle enzyme, fumarase, which converts fumarate to malate, reportedly worsened salt-sensitive hypertension. These novel expositions shifted focus into the activity of TCA in the pathogenesis of hypertension. There is now evidence to show that a mechanistic link exists between blood pressure regulation and intermediaries in the TCA cycle involving fumarate metabolism. Fumarate has been reported to mediate the actions of endogenous ligands such as nitric oxide (NO), and hypoxia inducible factor (HIF)-1α. Similarly, there has been upregulation of protective genes such as nuclear erythroid factor 2 (Nrf2) and reduction in the expression of certain markers like kidney injury molecule 1 (KIM-1). There are reports of interactions with endogenous enzymes such as catalase (CAT) and renin via the activation of GPR91. Fumarate has also been shown to modulate the actions of renal ion channels and by extension, natriuresis. These actions of fumarate have conferred a reno- and cardio-protective effect in hypertension. This review evaluates the role of the TCA cycle, its mechanistic links, and significant contribution to blood pressure regulation with a view to understanding the possibility of a new pathological axis which may be involved in the pathogenesis of hypertension.

Metabolomics reveals serum metabolic signatures in H-type hypertension based on mass spectrometry multi-platform

BACKGROUND

H-type hypertension (HHT) is a disease combined with hyperhomocysteinaemia and hypertension (HT). This study aims to find specific metabolic changes and reveal the pathophysiological mechanism of HHT, which provide the theoretical basis for the early prevention and treatment of HHT.

METHODS

Serum samples from three groups including 53 HHT patients, 36 HT patients and 46 healthy controls (HC) were collected. The targeted and untargeted metabolomics analyses were performed to determine the metabolic changes. Based on multivariate statistical analysis, the serum potential metabolites were screened and different metabolic pathways were explored.

RESULTS

Our results demonstrated that there were 28 important potential metabolites for distinguishing HT from HHT patients. Metabolic pathway analysis showed that the different metabolic pathways between HHT and HC group were arginine biosynthesis, arginine and proline metabolism, and tyrosine metabolism. The changed metabolic pathway of HT and HC group included linoleic acid metabolism. The specific metabolic pathways of HT-HHT comparison group had phenylalanine metabolism; phenylalanine, tyrosine and tryptophan biosynthesis; glycine, serine and threonine metabolism.

CONCLUSIONS

Metabolomics analysis by mass spectrometry multi-platform revealed the differences of metabolic profiles between HHT and HT subjects. This work laid the groundwork for understanding the aetiology of HHT, and these findings may provide the useful information for explaining the HHT metabolic alterations and try to prevent HHT.

Mitochondrial Damage and Hypertension: Another Dark Side of Sodium Excess

PURPOSE OF REVIEW

Essential or primary hypertension (HT) is a worldwide health problem with no definitive cure. Although the exact pathogenesis of HT is not known, genetic factors, increased renin-angiotensin and sympathetic system activity, endothelial dysfunction, oxidative stress, and inflammation play a role in its development. Environmental factors such as sodium intake are also important for BP regulation, and excess sodium intake in the form of salt (NaCl, sodium chloride) increases blood pressure in salt-sensitive people. Excess salt intake increases extracellular volume, oxidative stress, inflammation, and endothelial dysfunction. Recent evidence suggests that increased salt intake also disturbs mitochondrial function both structurally and functionally which is important as mitochondrial dysfunction is associated with HT. In the current review, we have summarized the experimental and clinical data regarding the impact of salt intake on mitochondrial structure and function.

RECENT FINDINGS

Excess salt intake damage mitochondrial structure (e.g., shorter mitochondria with less cristae, increased mitochondrial fission, increased mitochondrial vacuolization). Functionally, high salt intake impairs mitochondrial oxidative phosphorylation and electron transport chain, ATP production, mitochondrial calcium homeostasis, mitochondrial membrane potential, and mitochondrial uncoupling protein function. Excess salt intake also increases mitochondrial oxidative stress and modifies Krebs cycle protein expressions. Studies have shown that high salt intake impairs mitochondrial structure and function. These maladaptive mitochondrial changes facilitate the development of HT especially in salt-sensitive individuals. High salt intake impairs many functional and structural components of mitochondria. These mitochondrial alterations along with increased salt intake promote the development of hypertension.

Malate reduced blood pressure and exerted differential effects on renal hemodynamics; role of the nitric oxide system and renal epithelial sodium channels (ENaC)

Malate regulates blood pressure via nitric oxide production in salt-sensitive rats, a genetic model of hypertension. This study investigated the possible contributions of malate to blood pressure regulation and renal haemodynamics in normotensive rats. Malate (0.1, 0.3 and 1 μg/kg, iv) was injected into rats or L-nitro-arginine methyl ester (L-NAME)-treated rats and mean arterial blood pressure (MABP), cortical blood flow (CBF), and medullary blood flow (MBF), was measured. The clearance study involved infusion of malate at 0.1 μg/kg/h into rats, and MABP, CBF, MBF, glomerular filtration rate (GFR), urine volume (UV) and sodium output (UNaV) were determined. Mechanistic studies to evaluate the role of renal sodium channels involved the treatment with malate (600 mg/kg, po), amiloride (2.5 mg/kg, po) or hydrochlorothiazide (HCTZ) (10 mg/kg, po), and UV and UNaV were determined. Malate elicited significant peak reductions in MABP (124 ± 6.5 vs 105 ± 3.1 mmHg) at 0.1 μg/kg), CBF (231 ± 18.5 vs 205 ± 10.9 PU). L-NAME did not reverse the effect of malate on MABP but tended to blunt the effect on CBF (40%) and MBF (87%) at 0.3 μg/kg. Infusion of malate reduced MABP, CBF, and MBF in a time-dependent manner (p<0.05). Malate exerted a three-fold decrease in GFR in a time-related fashion (p<0.05) as well as increased UV. UNaV increased by 86% in malate-treated-amiloride rats (p<0.05). These data indicate that malate modulates blood pressure and exerts vascular and tubular effects on renal function that may involve epithelial sodium channels (ENaC).

Revealing the Pathogenesis of Salt-Sensitive Hypertension in Dahl Salt-Sensitive Rats through Integrated Multi-Omics Analysis

Salt-induced renal metabolism dysfunction is an important mechanism of salt-sensitive hypertension. Given that the gut-liver axis is the first hit of a high-salt diet (HSD), we aimed to identify the extra-renal mechanism from hepatic metabolism and gut microbiota, and attempted to relieve the salt-induced metabolic dysfunctions by curcumin. Untargeted metabolomics analysis was performed to identify the changes in hepatic metabolic pathways, and integrated analysis was employed to reveal the relationship between hepatic metabolic dysfunction and gut microbial composition. HSD induced significant increase in fumaric acid, l-lactic acid, creatinine, l-alanine, glycine, and l-cysteine levels, and amino acids metabolism pathways associated with glycolysis were significantly altered, including alanine, aspartate, and glutamate metabolism; glycine, serine, and threonine metabolism, which were involved in the regulation of blood pressure. Integrated multi-omics analysis revealed that changes in Paraprevotella, Erysipelotrichaceae, and genera from Clostridiales are associated with metabolic disorders. Gene functional predication analysis based on 16S Ribosomal RNA sequences showed that the dysfunction in hepatic metabolism were correlated with enhanced lipopolysaccharide (LPS) biosynthesis and apoptosis in gut microbes. Curcumin (50 mg/kg/d) might reduce gut microbes-associated LPS biosynthesis and apoptosis, partially reverse metabolic dysfunction, ameliorate renal oxidative stress, and protect against salt-sensitive hypertension.

Effects of fumarate on renal vascular reactivity and the modulation of blood pressure in normotensive rats: Possible contribution of the nitric oxide synthase-nitric oxide system

Introduction: Fumarate, the tricarboxylic acid (TCA) cycle intermediary, has been linked to nitric oxide (NO) production. NO plays a prominent role in the physiological regulation of blood pressure and renal hemodynamics. This study is aimed to investigate any contribution of fumarate to blood pressure and renal hemodynamics in normotensive rats with a possible link to the nitrergic system.

Materials and methods: Fumarate (1, 3 and 10 µmol) was injected into isolated perfused kidneys, pre-constricted with epinephrine (30 µM). The fumarase inhibitor, pyromellitic acid (PMA) (1, 3 and 10 µM), was used to perfuse the isolated kidney and perfusate was collected for nitric oxide and fumarate assays. An acute blood pressure study involved the injection of bolus doses of fumarate (0.1, 0.3 and 1 µg/kg, iv) or PMA (1, 3 and 10 µg/kg, iv) to normotensive rats in the presence of N(ω)-nitro-L-arginine methyl ester (L-NAME) (10 mg/kg, iv) or PMA (1, 3 and 10 µg/kg).

Results and discussion: Fumarate reduced perfusion pressure and elicited a peak reduction at the highest dose. Perfusing the kidney with PMA caused a paradoxical increase in perfusion pressure (70%, p&lt;0.05), compared to baseline. Bolus doses of fumarate reduced blood pressure (-29.3±6.2 mmHg, p&lt;0.05), cortical blood flow (CBF) and increased medullary blood flow (MBF). L-NAME did not abolish the vasodilatory effect of fumarate, but reduced the magnitude of response (50%, p&lt;0.05). PMA did not significantly affect the vasodilatory effect of fumarate (p&gt;0.05).

Conclusion: These data suggest that fumarate exerts a vasodilatory effect on renal and systemic hemodynamics that may partly involve the nitric oxide signaling.

Graphical abstract:

Reduced expression of mitochondrial fumarate hydratase in progressive multiple sclerosis contributes to impaired in vitro mesenchymal stromal cell-mediated neuroprotection

Background:

Cell-based therapies for multiple sclerosis (MS), including those employing autologous bone marrow-derived mesenchymal stromal cells (MSC) are being examined in clinical trials. However, recent studies have identified abnormalities in the MS bone marrow microenvironment.

Objective:

We aimed to compare the secretome of MSC isolated from control subjects (C-MSC) and people with MS (MS-MSC) and explore the functional relevance of findings.

Methods:

We employed high throughput proteomic analysis, enzyme-linked immunosorbent assays and immunoblotting, as well as in vitro assays of enzyme activity and neuroprotection.

Results:

We demonstrated that, in progressive MS, the MSC secretome has lower levels of mitochondrial fumarate hydratase (mFH). Exogenous mFH restores the in vitro neuroprotective potential of MS-MSC. Furthermore, MS-MSC expresses reduced levels of fumarate hydratase (FH) with downstream reduction in expression of master regulators of oxidative stress.

Conclusions:

Our findings are further evidence of dysregulation of the bone marrow microenvironment in progressive MS with respect to anti-oxidative capacity and immunoregulatory potential. Given the clinical utility of the fumaric acid ester dimethyl fumarate in relapsing–remitting MS, our findings have potential implication for understanding MS pathophysiology and personalised therapeutic intervention.

β-Aminoisobutyric acid supplementation attenuated salt-sensitive hypertension in Dahl salt-sensitive rats through prevention of insufficient fumarase

The human Dietary Approaches to Stop Hypertension-Sodium Trial has shown that β-aminoisobutyric acid (BAIBA) may prevent the development of salt-sensitive hypertension (SSHT). However, the specific antihypertensive mechanism remains unclear in the renal tissues of salt-sensitive (SS) rats. In this study, BAIBA (100 mg/kg/day) significantly attenuated SSHT via increased nitric oxide (NO) content in the renal medulla, and it induced a significant increase in NO synthesis substrates (L-arginine and malic acid) in the renal medulla. BAIBA enhanced the activity levels of total NO synthase (NOS), inducible NOS, and constitutive NOS. BAIBA resulted in increased fumarase activity and decreased fumaric acid content in the renal medulla. The high-salt diet (HSD) decreased fumarase expression in the renal cortex, and BAIBA increased fumarase expression in the renal medulla and renal cortex. Furthermore, in the renal medulla, BAIBA increased the levels of ATP, ADP, AMP, and ADP/ATP ratio, thus further activating AMPK phosphorylation. BAIBA prevented the decrease in renal medullary antioxidative defenses induced by the HSD. In conclusion, BAIBA's antihypertensive effect was underlined by the phosphorylation of AMPK, the prevention of fumarase's activity reduction caused by the HSD, and the enhancement of NO content, which in concert attenuated SSHT in SS rats.

Fumarate exerted an antihypertensive effect and reduced kidney injury molecule (KIM)-1 expression in deoxycorticosterone acetate-salt hypertension

Background: The tricarboxylic (TCA) acid cycle provides the energy needed for regulatory functions in the cardio-renal system. Recently, a genetic defect in the TCA cycle enzyme, fumarase hydratase, altered L-arginine metabolism and exacerbated hypertension in salt-sensitive rats. This study evaluated the effect of fumarate and its possible link to L-arginine metabolism in deoxycorticosterone (DOCA)-salt hypertension, a non-genetic model of hypertension.Method: Hypertension was induced with DOCA (25 mg/kg s.c, twice weekly) + 1% NaCL in uninephrectomised rats placed on fumarate (1 g/L, ad libitum). Blood pressure was measured in conscious rats via carotid cannulation. Biochemical and western blot analyses were carried out on kidney fractions.Results: Fumarate reduced mean blood pressure (198 ± 5 vs 167 ± 7 mmHg, p < .01), increased nitric oxide levels in the renal cortex (36.1 ± 2 vs 61.3 ± 4 nM/µg) and medulla (27.4 ± 1 vs 54.1 ± 2 nM/µg) of DOCA-salt rats (p < .01). Consistent with this, arginase activity was reduced (threefold) in the renal medulla but not cortex of DOCA-salt rats. Fumarate increased superoxide dismutase activity in the medulla (p < .001) of DOCA-hypertensive rats. However, catalase activity was exacerbated by fumarate in both renal cortex (4.5 ± 1 vs 11.2 ± 1) and medulla (3.7 ± 1 vs 16.3 ± 1 units/mg) of DOCA-salt rats (p < .001). Proteinuria (64.6%), kidney injury molecule-1 expression and kidney weight were reduced in DOCA-hypertensive rats treated with fumarate (p< .05). However, there was a paradoxical increase in TGF-β expression in fumarate-treated DOCA-salt rats. Conclusion: These data show that fumarate attenuated hypertension, renal injury and improved the redox state of the kidney in DOCA/salt hypertension by mechanisms involving selective reduction of L-arginine metabolism.

Microbiota and Metabolites as Factors Influencing Blood Pressure Regulation

The study of microbes has rapidly expanded in recent years due to a surge in our understanding that humans host a plethora of commensal microbes, which reside in their bodies and depending upon their composition, contribute to either normal physiology or pathophysiology. This article provides a general foundation for learning about host-commensal microbial interactions as an emerging area of research. The article is divided into two sections. The first section is dedicated to introducing commensal microbiota and its known effects on the host. The second section is on metabolites, which are biochemicals that the host and the microbes use for bi-directional communication with each other. Together, the sections review what is known about how microbes interact with the host to impact cardiovascular physiology, especially blood pressure regulation. © 2021 American Physiological Society. Compr Physiol 11:1731-1757, 2021.

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.

Protective effect of oral histidine on hypertension in Dahl salt-sensitive rats induced by high-salt diet

AIMS

Salt-sensitive hypertension is a risk factor for cardiovascular disease. Previous studies have shown that insufficient arginine in the kidney caused by metabolic imbalance is an important factor in salt-sensitive hypertension. Whether the high nitrogen content of histidine can affect the balance of nitrogen metabolism in Dahl salt-sensitive (SS) rats. This article aimed to study the effects of oral histidine on salt-sensitive hypertension, kidney damage and metabolic patterns of high-salt diet in SS rats.

MAIN METHODS

Adult rats were divided into four groups, and blood pressure was measured using a non-invasive tail-cuff system. Gas chromatography-mass spectrometry analyzed metabolites in serum and kidney tissues.

KEY FINDINGS

High-salt diet significantly increased the blood pressure of rats and aggravated kidney damage. Of note, histidine can attenuate salt-sensitive hypertension and kidney damage by improving metabolic pattern, reducing Reactive Oxygen Species (ROS) and increasing nitric oxide levels in SS rats.

SIGNIFICANCE

These results suggest that histidine could be a potential adjuvant to prevent and control salt-sensitive hypertension.

High salt diet contributes to hypertension by weakening the medullary tricarboxylic acid cycle and antioxidant system in Dahl salt-sensitive rats

High salt diet (HSD, 8% NaCl) contributes to salt-sensitive hypertension, this study aimed to determine the effect of HSD on salt-sensitive hypertension by combining proteomic with metabolomics methods. Salt-sensitive rats were fed on HSD and normal salt diet (NSD, 0.4% NaCl) for two weeks before further analysis. Proteomic analysis showed the differential expression proteins (DEPs) were primarily mapped in the tricarboxylic acid (TCA)-cycle, glycolysis/gluconeogenesis, and other pathways associated with multiple amino acids. HSD decreased the medullary activities and protein expression level of two key enzymes of TCA-cycle, MDH and NADP⁺-IDH. Metabolomics showed three serous TCA-cycle-associated compounds, including decreased malic acid, decreased citric acid, and increased fumaric acid were differentially detected, which resulted in a decrease in NO content and an increase in H₂O₂ content in serum. The content of GSH, GSH/GSSG ratio, and synthesis substrates of GSH-cysteine and glycine, were significantly decreased by HSD, thus attenuated the antioxidant system in the renal medulla. HSD enhanced the medullary pentose phosphate pathway, which finally increased the concentration of NADPH and NADP⁺, NADPH/NADP^+, and the activity of NADPH oxidase in the renal medulla. Additionally, HSD enhanced the glycolysis pathway in the renal medulla. In summary, HSD significantly weakened the TCA cycle, and attenuated the antioxidant system in the renal medulla, which finally contributed to salt-sensitive hypertension.

Endogenous miR-204 Protects the Kidney against Chronic Injury in Hypertension and Diabetes

BACKGROUND

Aberrant microRNA (miRNA) expression affects biologic processes and downstream genes that are crucial to CKD initiation or progression. The miRNA miR-204-5p is highly expressed in the kidney but whether miR-204-5p plays any role in the development of chronic renal injury is unknown.

METHODS

We used real-time PCR to determine levels of miR-204 in human kidney biopsies and animal models. We generated Mir204 knockout mice and used locked nucleic acid-modified anti-miR to knock down miR-204-5p in mice and rats. We used a number of physiologic, histologic, and molecular techniques to analyze the potential role of miR-204-5p in three models of renal injury.

RESULTS

Kidneys of patients with hypertension, hypertensive nephrosclerosis, or diabetic nephropathy exhibited a significant decrease in miR-204-5p compared with controls. Dahl salt-sensitive rats displayed lower levels of renal miR-204-5p compared with partially protected congenic SS.13^BN26 rats. Administering anti-miR-204-5p to SS.13^BN26 rats exacerbated interlobular artery thickening and renal interstitial fibrosis. In a mouse model of hypertensive renal injury induced by uninephrectomy, angiotensin II, and a high-salt diet, Mir204 gene knockout significantly exacerbated albuminuria, renal interstitial fibrosis, and interlobular artery thickening, despite attenuation of hypertension. In diabetic db/db mice, administering anti-miR-204-5p exacerbated albuminuria and cortical fibrosis without influencing blood glucose levels. In all three models, inhibiting miR-204-5p or deleting Mir204 led to upregulation of protein tyrosine phosphatase SHP2, a target gene of miR-204-5p, and increased phosphorylation of signal transducer and activator of transcription 3, or STAT3, which is an injury-promoting effector of SHP2.

CONCLUSIONS

These findings indicate that the highly expressed miR-204-5p plays a prominent role in safeguarding the kidneys against common causes of chronic renal injury.

Exposure to Amoxicillin in Early Life Is Associated With Changes in Gut Microbiota and Reduction in Blood Pressure: Findings From a Study on Rat Dams and Offspring

Background

Pediatric hypertension is recognized as an emerging global health concern. Although new guidelines are developed for facilitating clinical management, the reasons for the prevalence of hypertension in children remain unknown. Genetics and environmental factors do not fully account for the growing incidence of pediatric hypertension. Because stable bacterial flora in early life are linked with health outcomes later in life, we hypothesized that reshaping of gut microbiota in early life affects blood pressure (BP) of pediatric subjects.

Methods and Results

To test this hypothesis, we administered amoxicillin, the most commonly prescribed pediatric antibiotic, to alter gut microbiota of young, genetically hypertensive rats (study 1) and dams during gestation and lactation (study 2) and recorded their BP. Reshaping of microbiota with reductions in Firmicutes/Bacteriodetes ratio were observed. Amoxicillin treated rats had lower BP compared with untreated rats. In young rats treated with amoxicillin, the lowering effect on BP persisted even after antibiotics were discontinued. Similarly, offspring from dams treated with amoxicillin showed lower systolic BP compared with control rats. Remarkably, in all cases, a decrease in BP was associated with lowering of Veillonellaceae, which are succinate‐producing bacteria. Elevated plasma succinate is reported in hypertension. Accordingly, serum succinate was measured and found lower in animals treated with amoxicillin.

Conclusions

Our results demonstrate a direct correlation between succinate‐producing gut microbiota and early development of hypertension and indicate that reshaping gut microbiota, especially by depleting succinate‐producing microbiota early in life, may have long‐term benefits for hypertension‐prone individuals.

Identification of Activators of Human Fumarate Hydratase by Quantitative High-Throughput Screening

Fumarate hydratase (FH) is a metabolic enzyme that is part of the Krebs cycle and reversibly catalyzes the hydration of fumarate to malate. Mutations of the FH gene have been associated with fumarate hydratase deficiency (FHD), hereditary leiomyomatosis and renal cell cancer (HLRCC), and other diseases. Currently, there are no high-quality small-molecule probes for studying human FH. To address this, we developed a quantitative high-throughput screening (qHTS) FH assay and screened a total of 57,037 compounds from in-house libraries in dose-response. While no inhibitors of FH were confirmed, a series of phenyl-pyrrolo-pyrimidine-diones were identified as activators of human FH. These compounds were not substrates of FH, were inactive in a malate dehydrogenase counterscreen, and showed no detectable reduction-oxidation activity. The binding of two compounds from the series to human FH was confirmed by microscale thermophoresis. The low hit rate in this screening campaign confirmed that FH is a "tough target" to modulate, and the small-molecule activators of human FH reported here may serve as a starting point for further optimization and development into cellular probes of human FH and potential drug candidates.

MiR-192-5p in the Kidney Protects Against the Development of Hypertension

MicroRNA miR-192-5p is one of the most abundant microRNAs in the kidney and targets the mRNA for ATP1B1 (β1 subunit of Na⁺/K⁺-ATPase). Na⁺/K⁺-ATPase drives renal tubular reabsorption. We hypothesized that miR-192-5p in the kidney would protect against the development of hypertension. We found miR-192-5p levels were significantly lower in kidney biopsy specimens from patients with hypertension (n=8) or hypertensive nephrosclerosis (n=32) compared with levels in controls (n=10). Similarly, Dahl salt-sensitive (SS) rats showed a reduced abundance of miR-192-5p in the renal cortex compared with congenic SS.13^BN26 rats that had reduced salt sensitivity (n=9; P<0.05). Treatment with anti-miR-192-5p delivered through renal artery injection in uninephrectomized SS.13^BN26 rats exacerbated hypertension significantly. Mean arterial pressure on a 4% NaCl high-salt diet at day 14 post anti-miR-192-5p treatment was 16 mm Hg higher than in rats treated with scrambled anti-miR (n=8 and 6; P<0.05). Similarly, Mir192 knockout mice on the high-salt diet treated with Ang II (angiotensin II) for 14 days exhibited a mean arterial pressure 22 mm Hg higher than wild-type mice (n=9 and 5; P<0.05). Furthermore, protein levels of ATP1B1 were higher in Dahl SS rats than in SS.13^BN26 rats. Na⁺/K⁺-ATPase activity increased in the renal cortex of SS.13^BN26 rats 9 days posttreatment with anti-miR-192-5p compared with that of control anti-miR treated rats. Intrarenal knockdown of ATP1B1 attenuated hypertension in SS.13^BN26 rats with intrarenal knockdown of miR-192-5p. In conclusion, miR-192-5p in the kidney protects against the development of hypertension, which is mediated, at least in part, by targeting Atp1b1.

The role of mitochondrial oxidative stress in the metabolic alterations in diet-induced obesity in rats

The impact of the mitochondria-targeted antioxidant MitoQ was evaluated in the metabolic alterations and the adipose tissue remodeling associated with obesity. Male Wistar rats were fed either a high-fat diet (HFD; 35% fat) or a standard diet (3.5% fat) for 7 wk and treated with MitoQ (200 µM). A proteomic analysis of visceral adipose tissue from patients with obesity and patients without obesity was performed. MitoQ partially prevented the increase in body weight, adiposity, homeostasis model assessment index, and adipose tissue remodeling in HFD rats. It also ameliorated protein level changes of factors involved in insulin signaling observed in adipose tissue of obese rats: reductions in adiponectin and glucose transporter 4 (GLUT 4) and increases in dipeptidylpeptidase 4, suppressor of cytokine signaling 3 (SOCS3), and insulin receptor substrate 1 phosphorylation. MitoQ prevented down-regulation of adiponectin and GLUT 4 and increases in SOCS3 levels in a TNF-α-induced insulin-resistant 3T3-L1 adipocyte model. MitoQ also ameliorated alterations in mitochondrial proteins observed in obese rats: increases in cyclophylin F and carnitine palmitoyl transferase 1A and reductions in mitofusin1, peroxiredoxin 4, and fumarate hydratase. The proteomic analysis of the visceral adipose tissue from patients with obesity show alterations in mitochondrial proteins similar to those observed in obese rats. Therefore, the data show the beneficial effect of MitoQ in the metabolic dysfunction induced by obesity.-Marín-Royo, G., Rodríguez, C., Le Pape, A., Jurado-López, R., Luaces, M., Antequera, A., Martínez-González, J., Souza-Neto, F. V., Nieto, M. L., Martínez-Martínez, E., Cachofeiro, V. The role of mitochondrial oxidative stress in the metabolic alterations in diet-induced obesity in rats.

Fumarase Overexpression Abolishes Hypertension Attributable to endothelial NO synthase Haploinsufficiency in Dahl Salt-Sensitive Rats

Human blood pressure salt sensitivity is associated with changes in urinary metabolites related to fumarase (Fh) and nitric oxide (NO) metabolism, and fumarase promotes NO production through an arginine regeneration pathway. We examined the role of the fumarase-NO pathway in the development of hypertension using genetically engineered rat models. Dahl salt-sensitive (SS) rats with heterozygous mutation of eNOS (endothelial NO synthase or Nos3; SS-Nos3^+/-) were bred with SS rats with a hemizygous Fh transgene. SS-Nos3^+/- rats without the Fh transgene (SS-Nos3^+/-/Fh^0/0) developed substantial hypertension with a mean arterial pressure of 134.2±3.7 mm Hg on a 0.4% NaCl diet and 178.0±3.5 mm Hg after 14 days on a 4% NaCl diet. Mean arterial pressure decreased remarkably to 123.1±1.4 mm Hg on 0.4% NaCl, and 143.3±1.5 mm Hg on 4% NaCl in SS-Nos3^+/- rats with a Fh transgene (SS-Nos3^+/-/Fh^0/1), and proteinuria, renal fibrosis, and tubular casts were attenuated in SS-Nos3^+/-/Fh^0/1 rats compared with SS-Nos3^+/-/Fh^0/0 rats. eNOS protein abundance decreased in rats with the Nos3 heterozygous mutation, which was not influenced by Fh overexpression in rats on the 0.4% NaCl diet. However, the decrease in NO metabolite in the renal outer medulla of SS-Nos3^+/-/Fh^0/0 rats on the 0.4% NaCl diet was reversed in SS-Nos3^+/-/Fh^0/1 rats, and levels of L-arginine, but not the other 12 amino acids analyzed, were significantly higher in SS-Nos3^+/-/Fh^0/1 rats than in SS-Nos3^+/+/Fh^0/0 rats. In conclusion, fumarase has potent effects in restoring NO production and blunting the development of hypertension attributable to eNOS haploinsufficiency.

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.

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.

A role for fumarate hydratase in mediating oxidative effects of galectin-3 in human cardiac fibroblasts

AIMS

Galectin-3 (Gal-3), a β-galactoside-binding lectin involved in cardiac inflammation and fibrosis, could regulate oxidative stress, although the mechanisms have not been elucidated. We herein investigated the changes in oxidative stress-related mediators induced by Gal-3 in human cardiac fibroblasts and in pathological animal and human models of cardiac diseases.

RESULTS

Using quantitative proteomics and immunodetection approaches, we have identified that Gal-3 down-regulated fumarate hydratase (FH) in human cardiac fibroblasts. In parallel, Gal-3 increased fumarate production in a time-dependent manner. Gal-3 treatment enhanced carbonylated proteins detected through OxyBlot technique. Interestingly, treatment of cells with fumarate induced oxidative stress, enhanced fibroblast activation markers and increased collagen and interleukin-6 secretion. In Gal-3-silenced cells and in heart from Gal-3 knock-out mice, FH was increased and fumarate was decreased. In myocardial biopsies from patients with aortic stenosis (AS, n=26), FH levels were decreased as compared to Controls (n=13). Cardiac Gal-3 inversely correlated with FH levels in myocardial biopsies. In an experimental model of AS rats, pharmacological inhibition of Gal-3 restored cardiac FH, decreased fumarate concentration and improved oxidative status.

CONCLUSION

In human cardiac fibroblasts, Gal-3 decreased FH expression increasing fumarate concentration and promoting oxidative stress. In human AS, cardiac levels of Gal-3 inversely associated with FH. Gal-3 blockade restored FH and improved fumarate and oxidative stress status in AS rats. FH is therefore a key molecule mediating Gal-3-induced oxidative stress in cardiac cells.

MicroRNA-214-3p in the Kidney Contributes to the Development of Hypertension

BACKGROUND

In spite of extensive study, the mechanisms for salt sensitivity of BP in humans and rodent models remain poorly understood. Several microRNAs (miRNAs) have been associated with hypertension, but few have been shown to contribute to its development.

METHODS

We examined miRNA expression profiles in human kidney biopsy samples and rat models using small RNA deep sequencing. To inhibit an miRNA specifically in the kidney in conscious, freely moving rats, we placed indwelling catheters to allow both renal interstitial administration of a specific anti-miR and measurement of BP. A rat with heterozygous disruption of the gene encoding endothelial nitric oxide synthase (eNOS) was developed. We used bioinformatic analysis to evaluate the relationship between 283 BP-associated human single-nucleotide polymorphisms (SNPs) and 1870 human miRNA precursors, as well as other molecular and cellular methods.

RESULTS

Compared with salt-insensitive SS.13BN26 rats, Dahl salt-sensitive (SS) rats showed an upregulation of miR-214-3p, encoded by a gene in the SS.13BN26 congenic region. Kidney-specific inhibition of miR-214-3p significantly attenuated salt-induced hypertension and albuminuria in SS rats. miR-214-3p directly targeted eNOS. The effect of miR-214-3p inhibition on hypertension and albuminuria was abrogated in SS rats with heterozygous loss of eNOS. Human kidney biopsy specimens from patients with hypertension or hypertensive nephrosclerosis showed upregulation of miR-214-3p; the gene encoding miR-214-3p was one of several differentially expressed miRNA genes located in proximity to human BP-associated SNPs.

CONCLUSIONS

Renal miR-214-3p plays a functional and potentially genetic role in the development of hypertension, which might be mediated in part by targeting eNOS.

Transcriptomic analysis reveals inflammatory and metabolic pathways that are regulated by renal perfusion pressure in the outer medulla of Dahl-S rats

Studies exploring the development of hypertension have traditionally been unable to distinguish which of the observed changes are underlying causes from those that are a consequence of elevated blood pressure. In this study, a custom-designed servo-control system was utilized to precisely control renal perfusion pressure to the left kidney continuously during the development of hypertension in Dahl salt-sensitive rats. In this way, we maintained the left kidney at control blood pressure while the right kidney was exposed to hypertensive pressures. As each kidney was exposed to the same circulating factors, differences between them represent changes induced by pressure alone. RNA sequencing analysis identified 1,613 differently expressed genes affected by renal perfusion pressure. Three pathway analysis methods were applied, one a novel approach incorporating arterial pressure as an input variable allowing a more direct connection between the expression of genes and pressure. The statistical analysis proposed several novel pathways by which pressure affects renal physiology. We confirmed the effects of pressure on p-Jnk regulation, in which the hypertensive medullas show increased p-Jnk/Jnk ratios relative to the left (0.79 ± 0.11 vs. 0.53 ± 0.10, P < 0.01, n = 8). We also confirmed pathway predictions of mitochondrial function, in which the respiratory control ratio of hypertensive vs. control mitochondria are significantly reduced (7.9 ± 1.2 vs. 10.4 ± 1.8, P < 0.01, n = 6) and metabolomic profile, in which 14 metabolites differed significantly between hypertensive and control medullas ( P < 0.05, n = 5). These findings demonstrate that subtle differences in the transcriptome can be used to predict functional changes of the kidney as a consequence of pressure elevation.

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.

Mitochondrial Dysfunction and Altered Renal Metabolism in Dahl Salt-Sensitive Rats

BACKGROUND/AIMS

The kidney plays a critical role in the control of blood pressure and its elevation in salt-induced hypertension. Mitochondrial dysfunction, especially in energy metabolism, has been associated with hypertension. Here, we aimed to investigate mitochondrial function and metabolic features in renal mitochondria of Dahl salt-sensitive (SS) rats to gain further insight into the relationship between mitochondrial metabolism and predisposition to hypertension.

METHODS

In this study, SS rats fed low-salt (LS) or high-salt (HS) diets were used to investigate mitochondrial function and metabolism including mitochondrial enzyme activities, pyridine nucleotides, metabolites, and oxidative stress by biochemical analysis and gas chromatography-mass spectrometer (GC-MS).

RESULTS

Significantly lower activity levels of fumarase, isocitrate dehydrogenase and succinyl-CoA synthetase were observed in renal mitochondria of SS rats compared with SS.13BN control rats fed LS diets. Intra-mitochondrial pyridine nucleotide content and mitochondrial metabolism were adversely affected in SS rats. In accordance with this, reduced ATP production, Δψm, and superoxide dismutase (SOD) activity were also observed in mitochondria of the renal medulla and cortex of SS rats. Moreover, ATP production was further impaired and oxidative stress was increased, confirming that the mitochondria of SS rats fed HS diets were dysfunctional compared to those of rats fed LS diets.

CONCLUSIONS

Our data demonstrated that the renal mitochondria of SS rats exhibited complicated metabolic alteration and dysfunction in low-salt diets, and high-salt diets aggravated these dysfunctions. Thus, these results may be associated with renal dysfunction, which, in turn, would help in understanding the development of salt-sensitive hypertension.

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.

Renal Tumor Necrosis Factor α Contributes to Hypertension in Dahl Salt-Sensitive Rats

Tumor necrosis factor α (TNFα) is a major proinflammatory cytokine and its level is elevated in hypertensive states. Inflammation occurs in the kidneys during the development of hypertension. We hypothesized that TNFα specifically in the kidney contributes to the development of hypertension and renal injury in Dahl salt-sensitive (SS) rats, a widely used model of human salt-sensitive hypertension and renal injury. SS rats were chronically instrumented for renal interstitial infusion and blood pressure measurement in conscious, freely moving state. Gene expression was measured using real-time PCR and renal injury assessed with histological analysis. The abundance of TNFα in the renal medulla of SS rats, but not the salt-insensitive congenic SS.13^BN26 rats, was significantly increased when rats had been fed a high-salt diet for 7 days (n = 6 or 9, p < 0.01). The abundance of TNFα receptors in the renal medulla was significantly higher in SS rats than SS.13^BN26 rats. Renal interstitial administration of Etanercept, an inhibitor of TNFα, significantly attenuated the development of hypertension in SS rats on a high-salt diet (n = 7–8, p < 0.05). Glomerulosclerosis and interstitial fibrosis were also significantly ameliorated. These findings indicate intrarenal TNFα contributes to the development of hypertension and renal injury in SS rats.

Evidence of the Importance of Nox4 in Production of Hypertension in Dahl Salt-Sensitive Rats

This study reports the consequences of knocking out NADPH (nicotinamide adenine dinucleotide phosphate) oxidase 4 (Nox4) on the development of hypertension and kidney injury in the Dahl salt-sensitive (SS) rat. Zinc finger nuclease injection of single-cell SS embryos was used to create an 8 base-pair frame-shift deletion of Nox4, resulting in a loss of the ≈68 kDa band in Western blot analysis of renal cortical tissue of the knock out of Nox4 in the SS rat (SS(Nox4-/-)) rats. SS(Nox4-/-) rats exhibited a significant reduction of salt-induced hypertension compared with SS rats after 21 days of 4.0% NaCl diet (134±5 versus 151±3 mm Hg in SS) and a significant reduction of albuminuria, tubular casts, and glomerular injury. Optical fluorescence 3-dimensional cryoimaging revealed significantly higher redox ratios (NADH/FAD [reduced nicotinamide adenine dinucleotide/flavin adenine dinucleotide]) in the kidneys of SS(Nox4-/-) rats even when fed the 0.4% NaCl diet, indicating greater levels of mitochondrial electron transport chain metabolic activity and reduced oxidative stress compared with SS rats. Before the development of hypertension, RNA expression levels of Nox subunits Nox2, p67(phox), and p22(phox) were found to be significantly lower (P<0.05) in SS(Nox4-/-) compared with SS rats in the renal cortex. Thus, the mutation of Nox4 seems to modify transcription of several genes in ways that contribute to the protective effects observed in the SS(Nox4-/-) rats. We conclude that the reduced renal injury and attenuated blood pressure response to high salt in the SS(Nox4-/-) rat could be the result of multiple pathways, including gene transcription, mitochondrial energetics, oxidative stress, and protein matrix production impacted by the knock out of Nox4.

Evidence for a link between gut microbiota and hypertension in the Dahl rat

The gut microbiota plays a critical role in maintaining physiological homeostasis. This study was designed to evaluate whether gut microbial composition affects hypertension. 16S rRNA genes obtained from cecal samples of Dahl salt-sensitive (S) and Dahl salt-resistant (R) rats were sequenced. Bacteria of the phylum Bacteroidetes were higher in the S rats compared with the R rats. Furthermore, the family S24-7 of the phylum Bacteroidetes and the family Veillonellaceae of the phylum Firmicutes were higher in the S rats compared with the R rats. Analyses of the various phylogenetic groups of cecal microbiota revealed significant differences between S and R rats. Both strains were maintained on a high-salt diet, administered antibiotics for ablation of microbiota, transplanted with S or R rat cecal contents, and monitored for blood pressure (BP). Systolic BP of the R rats remained unaltered irrespective of S or R rat cecal transplantation. Surprisingly, compared with the S rats given S rat cecal content, systolic BP of the S rats given a single bolus of cecal content from R rats was consistently and significantly elevated during the rest of their life, and they had a shorter lifespan. A lower level of fecal bacteria of the family Veillonellaceae and increased plasma acetate and heptanoate were features associated with the increased BP observed in the S rats given R rat microbiota compared with the S rats given S rat microbiota. These data demonstrate a link between microbial content and BP regulation and, because the S and R rats differ in their genomic composition, provide the necessary basis to further examine the relationship between the host genome and microbiome in the context of BP regulation in the Dahl rats.

Renalase contributes to the renal protection of delayed ischaemic preconditioning via the regulation of hypoxia-inducible factor-1α

Ischaemic preconditioning (IPC) attenuates acute kidney injury (AKI) from renal ischaemia reperfusion. Renalase, an amine oxidase secreted by the proximal tubule, not only degrades circulating catecholamines but also protects against renal ischaemia reperfusion injury. Here, it has been suggested that the renoprotective effect of renal IPC is partly mediated by renalase. In a model of brief intermittent renal IPC, the increased cortex renalase expression was found to last for 48 hrs. IPC significantly reduced renal tubular inflammation, necrosis and oxidative stress following renal ischaemia reperfusion injury. Such effects were attenuated by blocking renalase with an anti-renalase monoclonal antibody. We further demonstrated that renalase expression was up-regulated by hypoxia in vitro via an hypoxia-inducible factor (HIF)-1α mechanism. The IPC-induced up-regulation of renalase in vivo was also reduced by pre-treatment with an HIF-1α inhibitor, 3-(5′-Hydroxymethyl-2′-furyl)-1-benzyl indazole. In summary, the renoprotective effect of IPC is partly dependent on the renalase expression, which may be triggered by hypoxia via an HIF-1α mechanism. Endogenous renalase shows potential as a therapeutic agent for the prevention and treatment of AKI.

Reconstruction and analysis of correlation networks based on GC-MS metabolomics data for young hypertensive men

The awareness, treatment, and control rates of hypertension for young adults are much lower than average. It is urgently needed to explore the variances of metabolic profiles for early diagnosis and treatment of hypertension. In current study, we applied a GC-MS based metabolomics platform coupled with a network approach to analyze plasma samples from young hypertensive men and age-matched healthy controls. Our findings confirmed distinct metabolic footprints of young hypertensive men. The significantly altered metabolites between two groups were enriched for the biological module of amino acids biosynthesis. The correlations of GC-MS metabolomics data were then visualized as networks based on Pearson correlation coefficient (threshold=0.6). The plasma metabolites identified by GC-MS and the significantly altered metabolites (P<0.05) between patients and controls were respectively included as nodes of a network. Statistical and topological characteristics of the networks were studied in detail. A few amino acids, glycine, lysine, and cystine, were screened as hub metabolites with higher values of degree (k), and also obtained highest scores of three centrality indices. The short average path lengths and high clustering coefficients of the networks revealed a small-world property, indicating that variances of these amino acids have a major impact on the metabolic change in young hypertensive men. These results suggested that disorders of amino acid metabolism might play an important role in predisposing young men to developing hypertension. The combination of metabolomics and network methods would provide another perspective on expounding the molecular mechanism underlying complex diseases.

Reactive oxygen species as important determinants of medullary flow, sodium excretion, and hypertension

The physiological evidence linking the production of superoxide, hydrogen peroxide, and nitric oxide in the renal medullary thick ascending limb of Henle (mTAL) to regulation of medullary blood flow, sodium homeostasis, and long-term control of blood pressure is summarized in this review. Data obtained largely from rats indicate that experimentally induced elevations of either superoxide or hydrogen peroxide in the renal medulla result in reduction of medullary blood flow, enhanced Na(+) reabsorption, and hypertension. A shift in the redox balance between nitric oxide and reactive oxygen species (ROS) is found to occur naturally in the Dahl salt-sensitive (SS) rat model, where selective reduction of ROS production in the renal medulla reduces salt-induced hypertension. Excess medullary production of ROS in SS rats emanates from the medullary thick ascending limbs of Henle [from both the mitochondria and membrane NAD(P)H oxidases] in response to increased delivery and reabsorption of excess sodium and water. There is evidence that ROS and perhaps other mediators such as ATP diffuse from the mTAL to surrounding vasa recta capillaries, resulting in medullary ischemia, which thereby contributes to hypertension.

Analysis of metabolites in plasma reveals distinct metabolic features between Dahl salt-sensitive rats and consomic SS.13(BN) rats

Salt-sensitive hypertension is a major risk factor for cardiovascular disorders. Our previous proteomic study revealed substantial differences in several proteins between Dahl salt-sensitive (SS) rats and salt-insensitive consomic SS.13(BN) rats. Subsequent experiments indicated a role of fumarase insufficiency in the development of hypertension in SS rats. In the present study, a global metabolic profiling study was performed using gas chromatography/mass spectrometry (GC/MS) in plasma of SS rats (n=9) and SS.13(BN) rats (n=8) on 0.4% NaCl diet, designed to gain further insights into the relationship between alterations in cellular intermediary metabolism and predisposition to hypertension. Principal component analysis of the data sets revealed a clear clustering and separation of metabolic profiles between SS rats and SS.13(BN) rats. 23 differential metabolites were identified (P<0.05). Higher levels of five TCA cycle metabolites, fumarate, cis-aconitate, isocitrate, citrate and succinate, were observed in SS rats. Pyruvate, which connects TCA cycle and glycolysis, was also increased in SS rats. Moreover, lower activity levels of fumarase, aconitase, α-ketoglutarate dehydrogenase and succinyl-CoA synthetase were detected in the heart, liver or skeletal muscles of SS rats. The distinct metabolic features in SS and SS.13(BN) rats indicate abnormalities of TCA cycle in SS rats, which may play a role in predisposing SS rats to developing salt-sensitive hypertension.

Characterization of biological pathways associated with a 1.37 Mbp genomic region protective of hypertension in Dahl S rats

The goal of the present study was to narrow a region of chromosome 13 to only several genes and then apply unbiased statistical approaches to identify molecular networks and biological pathways relevant to blood-pressure salt sensitivity in Dahl salt-sensitive (SS) rats. The analysis of 13 overlapping subcongenic strains identified a 1.37 Mbp region on chromosome 13 that influenced the mean arterial blood pressure by at least 25 mmHg in SS rats fed a high-salt diet. DNA sequencing and analysis filled genomic gaps and provided identification of five genes in this region, Rfwd2, Fam5b, Astn1, Pappa2, and Tnr. A cross-platform normalization of transcriptome data sets obtained from our previously published Affymetrix GeneChip dataset and newly acquired RNA-seq data from renal outer medullary tissue provided 90 observations for each gene. Two Bayesian methods were used to analyze the data: 1) a linear model analysis to assess 243 biological pathways for their likelihood to discriminate blood pressure levels across experimental groups and 2) a Bayesian graphical modeling of pathways to discover genes with potential relationships to the candidate genes in this region. As none of these five genes are known to be involved in hypertension, this unbiased approach has provided useful clues to be experimentally explored. Of these five genes, Rfwd2, the gene most strongly expressed in the renal outer medulla, was notably associated with pathways that can affect blood pressure via renal transcellular Na(+) and K(+) electrochemical gradients and tubular Na(+) transport, mitochondrial TCA cycle and cell energetics, and circadian rhythms.

Ultrastructure of mitochondria and the endoplasmic reticulum in renal tubules of Dahl salt-sensitive rats

Metabolic and functional abnormalities in the kidney precede or coincide with the initiation of overt hypertension in the Dahl salt-sensitive (SS) rat. However, renal histological injury in SS rats is mild before the development of overt hypertension. We performed electron microscopy analysis in 7-wk-old SS rats and salt-insensitive consomic SS.13(BN) rats and Sprague-Dawley (SD) rats fed a 4% NaCl diet for 7 days. Long mitochondria (>2 μm) accounted for a significantly smaller fraction of mitochondria in medullary thick ascending limbs in SS rats (4% ± 1%) than in SS.13(BN) rats (8% ± 1%, P < 0.05 vs. SS rats) and SD rats (9% ± 1%, P < 0.01 vs. SS rats), consistent with previous findings of mitochondrial functional insufficiency in the medulla of SS rats. Long mitochondria in proximal tubules, however, were more abundant in SS rats than in SS.13(BN) and SD rats. The width of the endoplasmic reticulum, an index of endoplasmic reticulum stress, was significantly greater in medullary thick ascending limbs of SS rats (107 ± 1 nm) than in SS.13(BN) rats (95 ± 2 nm, P < 0.001 vs. SS rats) and SD rats (74 ± 3 nm, P < 0.01 vs. SS or SS.13(BN) rats). The tubules examined were indistinguishable between rat strains under light microscopy. These data indicate that ultrastructural abnormalities occur in the medullary thick ascending limbs of SS rats before the development of histological injury in renal tubules, providing a potential structural basis contributing to the subsequent development of overt hypertension.

Base-resolution maps of 5-methylcytosine and 5-hydroxymethylcytosine in Dahl S rats: effect of salt and genomic sequence

Analysis of 5-hydroxymethylcytosine (5hmC) at single-base resolution has been largely limited to studies of stem cells or developmental stages. Given the potential importance of epigenetic events in hypertension, we have analyzed 5hmC and 5-methylcytosine (5mC) at single-base resolution in the renal outer medulla of the Dahl salt-sensitive rat and examined the effect of disease-relevant genetic or environmental alterations on 5hmC and 5mC patterns. Of CpG sites that fell within CpG islands, 11% and 1% contained significant 5mC and 5hmC, respectively. 5mC levels were substantially higher for genes with lower mRNA abundance and showed a prominent nadir around the transcription start site. In contrast, 5hmC levels were higher in genes with higher expression. Substitution of a 12.9-Mbp region of chromosome 13, which attenuates the hypertensive and renal injury phenotypes in salt-sensitive rats, or exposure to a high-salt diet, which accelerates the disease phenotypes, was associated with differential 5mC or 5hmC in several hundred CpG islands. Nearly 80% of the CpG islands that were differentially methylated in response to salt and associated with differential mRNA abundance were intragenic CpG islands. The substituted genomic segment had significant cis effects on mRNA abundance but not on DNA methylation. The study established base-resolution maps of 5mC and 5hmC in an in vivo model of disease and revealed several characteristics of 5mC and 5hmC important for understanding the role of epigenetic modifications in the regulation of organ systems function and complex diseases.

Increased mitochondrial activity in renal proximal tubule cells from young spontaneously hypertensive rats

Renal proximal tubule cells from spontaneously hypertensive rats (SHR), compared with normotensive Wistar-Kyoto rats (WKY), have increased oxidative stress. The contribution of mitochondrial oxidative phosphorylation to the subsequent hypertensive phenotype remains unclear. We found that renal proximal tubule cells from SHR, relative to WKY, had significantly higher basal oxygen consumption rates, ATP synthesis-linked oxygen consumption rates, and maximum and reserve respiration. These bioenergetic parameters indicated increased mitochondrial function in renal proximal tubule cells from SHR compared with WKY. Pyruvate dehydrogenase complex activity was consistently higher in both renal proximal tubule cells and cortical homogenates from SHR than WKY. Treatment for 6 days with dichloroacetate, an inhibitor of pyruvate dehydrogenase kinase, significantly increased renal pyruvate dehydrogenase complex activity and systolic blood pressure in 3-week old WKY and SHR. Therefore, mitochondrial oxidative phosphorylation is higher in renal proximal tubule cells from SHR compared with WKY. Thus the pyruvate dehydrogenase complex is a determinant of increased mitochondrial metabolism that could be a causal contributor to the hypertension in SHR.

miR-29c is downregulated in renal interstitial fibrosis in humans and rats and restored by HIF-α activation

Treatment with L-mimosine, which activates hypoxia-inducible factor-α (HIF-α), attenuates renal tubulointerstitial injury and improves renal function in a rat remnant kidney model. The miR-29 family of microRNAs directly targets a large number of extracellular matrix genes and reduces renal interstitial fibrosis. We analyzed microRNA expression profiles in rat remnant kidneys with or without treatment with L-mimosine. The expression of miR-29c was downregulated in rat remnant kidneys compared with sham control and significantly restored by the L-mimosine treatment. In cultured human kidney epithelial HK2 cells, cobalt chloride activated HIF-α and upregulated miR-29c expression. The upregulation of miR-29c expression was significantly attenuated by knockdown of HIF-1α or HIF-2α. Downregulation of miR-29c was associated with significant increases in interstitial fibrosis, collagen type II α1 (COL2A1) protein, and tropomyosin 1α (TPM1) protein in rat remnant kidneys and in kidneys from IgA nephropathy patients. The increases in rat remnant kidneys were attenuated by the L-mimosine treatment. COL2A1 and TPM1 were confirmed to be new, direct targets of miR-29c. In conclusion, miR-29c, an antifibrotic microRNA, is upregulated by HIF-α activation. MiR-29c is downregulated in renal interstitial fibrosis in humans and rats and restored by activation of HIF-α that attenuates fibrosis.

Undernutrition upregulates fumarate hydratase in the rat nucleus accumbens

Previous comparative studies of fumarate hydratase (FH) protein density revealed that the enzyme was overexpressed in the striatum of rodents that are less influenced by rewarding stimuli, from cocaine to food. Therefore, we recently proposed FH as a potential striatal biomarker of brain reward deficiency and addiction vulnerability. This work has been focused to investigate FH activity in the Nucleus Accumbens (NAc) of undernourished rats, taking into account that malnutrition has been related to increased responsiveness to food and drug reward. To this end, we have studied adult female Wistar rats severely food restricted from the 16th day of intrauterine life until adulthood. Animals were sacrificed to dissect the NAc and obtain mitochondrial and cytosolic fractions after homogenisation and centrifugation. FH activity was measured by conversion of malate to fumarate, and protein levels were compared by Western blot analysis when fractions showed differences in activity. Undernutrition did not change cytosolic FH activity but led to a marked increase of mitochondrial FH activity (72 %) and protein content (50 %) in the NAc. This change was in the opposite direction that one would predict if it was related to addiction vulnerability of some kind, but strongly suggests that mitochondrial FH needs to be at some optimal level for normal reward responsiveness.

MicroRNAs contribute to the maintenance of cell-type-specific physiological characteristics: miR-192 targets Na+/K+-ATPase β1

MicroRNAs (miRNAs) play important roles in biological development and disease. Much less is known about their role in normal adult physiology. The proximal convoluted tubule (PCT) and the medullary thick ascending limb (mTAL) in the kidney consist of epithelial cells with different transport activities. We identified 55 possible miRNA-target pairs of which the miRNAs and their predicted target proteins, many of which are involved in epithelial transport, were inversely enriched in PCT and mTAL. Some miRNAs appeared to have synergistic effects on shared targets. miR-192 and its predicted target the β-1 subunit of Na⁺/K⁺-ATPase (Atp1b1), an enzyme providing the driving force for tubular transport, were inversely enriched in kidney regions. In mice, knockdown of miR-192 led to up-regulation of Atp1b1 protein. When mice were fed with a high-salt diet, knockdown of miR-192 blunted the adaptational increase of urine output. Interestingly, miR-192 appeared to target Atp1b1 through the 5′-, rather than 3′-untranslated region. The study suggests a novel physiological mechanism in which miR-192 suppresses Na⁺/K⁺-ATPase and contributes to renal handling of fluid balance. It supports an important role of miRNAs in determining cellular characteristics that may appear subtle yet are physiologically critical.

Increased proliferative cells in the medullary thick ascending limb of the loop of Henle in the Dahl salt-sensitive rat

Studies of transcriptome profiles have provided new insights into mechanisms underlying the development of hypertension. Cell type heterogeneity in tissue samples, however, has been a significant hindrance in these studies. We performed a transcriptome analysis in medullary thick ascending limbs of the loop of Henle isolated from Dahl salt-sensitive rats. Genes differentially expressed between Dahl salt-sensitive rats and salt-insensitive consomic SS.13(BN) rats on either 0.4% or 7 days of 8.0% NaCl diet (n=4) were highly enriched for genes located on chromosome 13, the chromosome substituted in the SS.13(BN) rat. A pathway involving cell proliferation and cell cycle regulation was identified as one of the most highly ranked pathways based on differentially expressed genes and by a Bayesian model analysis. Immunofluorescent analysis indicated that just 1 week of a high-salt diet resulted in a severalfold increase in proliferative medullary thick ascending limb cells in both rat strains, and that Dahl salt-sensitive rats exhibited a significantly greater proportion of medullary thick ascending limb cells in a proliferative state than in SS.13(BN) rats (15.0±1.4% versus 10.1±0.6%; n=7-9; P<0.05). The total number of cells per medullary thick ascending limb section analyzed was not different between the 2 strains. The study revealed alterations in regulatory pathways in Dahl salt-sensitive rats in tissues highly enriched for a single cell type, leading to the unexpected finding of a greater increase in the number of proliferative medullary thick ascending limb cells in Dahl salt-sensitive rats on a high-salt diet.

Mitochondrial proteomic analysis reveals deficiencies in oxygen utilization in medullary thick ascending limb of Henle in the Dahl salt-sensitive rat

The renal medullary thick ascending limb (mTAL) of the Dahl salt-sensitive (SS) rat is the site of enhanced NaCl reabsorption and excess superoxide production. In the present studies we isolated mitochondria from mTAL of SS and salt-resistant control strain SS.13(BN) rats on 0.4 and 8% salt diet for 7 days and performed a proteomic analysis. Purity of mTAL and mitochondria isolations exceeded 93.6 and 55%, respectively. Using LC/MS spectral analysis techniques we identified 96 mitochondrial proteins in four biological mTAL mitochondria samples, run in duplicate, as defined by proteins with a false discovery rate <5% and scan count ≥2. Seven of these 96 proteins, including IDH2, ACADM, SCOT, Hsp60, ATPA, EFTu, and VDAC2 were differentially expressed between the two rat strains. Oxygen consumption and high-resolution respirometry analyses showed that mTAL cells and the mitochondria in the outer medulla of SS rats fed high-salt diet exhibited lower rates of oxygen utilization compared with those from SS.13(BN) rats. These studies advance the conventional proteomic paradigm of focusing exclusively upon whole tissue homogenates to a focus upon a single cell type and specific subcellular organelle. The results reveal the importance of a largely unexplored role for deficiencies of mTAL mitochondrial metabolism and oxygen utilization in salt-induced hypertension and renal medullary oxidative stress.

Delayed ischemic preconditioning contributes to renal protection by upregulation of miR-21

Delayed ischemic preconditioning effectively protects kidneys from ischemia-reperfusion injury but the mechanism underlying renal protection remains poorly understood. Here we examined the in vivo role of microRNA miR-21 in the renal protection conferred by delayed ischemic preconditioning in mice. A 15 minute renal ischemic preconditioning significantly increased the expression of miR-21 by 4 hours and substantially attenuated ischemia-reperfusion injury induced 4 days later. A locked nucleic acid-modified anti-miR-21 given at the time of ischemic preconditioning knocked down miR-21 and significantly exacerbated subsequent ischemia-reperfusion injury in the mouse kidney. Knockdown of miR-21 resulted in significant upregulation of programmed cell death protein 4, a pro-apoptotic target gene of miR-21, and substantially increased tubular cell apoptosis. Hypoxia inducible factor-1α in the kidney was activated after ischemic preconditioning and blockade of its activity with a decoy abolished the up-regulation of miR-21 in cultured human renal epithelial cells treated with the inducer cobalt chloride. In the absence of ischemic preconditioning, knockdown of miR-21 alone did not significantly affect ischemia-reperfusion injury in the mouse kidney. Thus, upregulation of miR-21 contributes to the protective effect of delayed ischemic preconditioning against subsequent renal ischemia-reperfusion injury.