Progressive Cardiac Metabolic Defects Accompany Diastolic and Severe Systolic Dysfunction in Spontaneously Hypertensive Rat Hearts.

Background Cardiac metabolic abnormalities are present in heart failure. Few studies have followed metabolic changes accompanying diastolic and systolic heart failure in the same model. We examined metabolic changes during the development of diastolic and severe systolic dysfunction in spontaneously hypertensive rats (SHR). Methods and Results We serially measured myocardial glucose uptake rates with dynamic 2-[18F] fluoro-2-deoxy-d-glucose positron emission tomography in vivo in 9-, 12-, and 18-month-old SHR and Wistar Kyoto rats. Cardiac magnetic resonance imaging determined systolic function (ejection fraction) and diastolic function (isovolumetric relaxation time) and left ventricular mass in the same rats. Cardiac metabolomics was performed at 12 and 18 months in separate rats. At 12 months, SHR hearts, compared with Wistar Kyoto hearts, demonstrated increased isovolumetric relaxation time and slightly reduced ejection fraction indicating diastolic and mild systolic dysfunction, respectively, and higher (versus 9-month-old SHR decreasing) 2-[18F] fluoro-2-deoxy-d-glucose uptake rates (Ki). At 18 months, only few SHR hearts maintained similar abnormalities as 12-month-old SHR, while most exhibited severe systolic dysfunction, worsening diastolic function, and markedly reduced 2-[18F] fluoro-2-deoxy-d-glucose uptake rates. Left ventricular mass normalized to body weight was elevated in SHR, more pronounced with severe systolic dysfunction. Cardiac metabolite changes differed between SHR hearts at 12 and 18 months, indicating progressive defects in fatty acid, glucose, branched chain amino acid, and ketone body metabolism. Conclusions Diastolic and severe systolic dysfunction in SHR are associated with decreasing cardiac glucose uptake, and progressive abnormalities in metabolite profiles. Whether and which metabolic changes trigger progressive heart failure needs to be established.

Evidence That Binding of Cyclic GMP to the Extracellular Domain of NKA (Sodium-Potassium ATPase) Mediates Natriuresis.

BACKGROUND: Extracellular renal interstitial guanosine cyclic 3',5'-monophosphate (cGMP) inhibits renal proximal tubule (RPT) sodium (Na+) reabsorption via Src (Src family kinase) activation. Through which target extracellular cGMP acts to induce natriuresis is unknown. We hypothesized that cGMP binds to the extracellular α1-subunit of NKA (sodium-potassium ATPase) on RPT basolateral membranes to inhibit Na+ transport similar to ouabain-a cardiotonic steroid. METHODS: Urine Na+ excretion was measured in uninephrectomized 12-week-old female Sprague-Dawley rats that received renal interstitial infusions of vehicle (5% dextrose in water), cGMP (18, 36, and 72 µg/kg per minute; 30 minutes each), or cGMP+rostafuroxin (12 ng/kg per minute) or were subjected to pressure-natriuresis±rostafuroxin infusion. Rostafuroxin is a digitoxigenin derivative that displaces ouabain from NKA. RESULTS: Renal interstitial cGMP and raised renal perfusion pressure induced natriuresis and increased phosphorylated SrcTyr416 and Erk 1/2 (extracellular signal-regulated protein kinase 1/2)Thr202/Tyr204; these responses were abolished with rostafuroxin coinfusion. To assess cGMP binding to NKA, we performed competitive binding studies with isolated rat RPTs using bodipy-ouabain (2 µM)+cGMP (10 µM) or rostafuroxin (10 µM) and 8-biotin-11-cGMP (2 µM)+ouabain (10 µM) or rostafuroxin (10 µM). cGMP or rostafuroxin reduced bodipy-ouabain fluorescence intensity, and ouabain or rostafuroxin reduced 8-biotin-11-cGMP staining. We cross-linked isolated rat RPTs with 4-N3-PET-8-biotin-11-cGMP (2 µM); 8-N3-6-biotin-10-cAMP served as negative control. Precipitation with streptavidin beads followed by immunoblot analysis showed that RPTs after cross-linking with 4-N3-PET-8-biotin-11-cGMP exhibited a significantly stronger signal for NKA than non-cross-linked samples and cross-linked or non-cross-linked 8-N3-6-biotin-10-cAMP RPTs. Ouabain (10 µM) reduced NKA in cross-linked 4-N3-PET-8-biotin-11-cGMP RPTs confirming fluorescence staining. 4-N3-PET-8-biotin-11-cGMP cross-linked samples were separated by SDS gel electrophoresis and slices corresponding to NKA molecular weight excised and processed for mass spectrometry. NKA was the second most abundant protein with 50 unique NKA peptides covering 47% of amino acids in NKA. Molecular modeling demonstrated a potential cGMP docking site in the ouabain-binding pocket of NKA. CONCLUSIONS: cGMP can bind to NKA and thereby mediate natriuresis.

Angiotensin Type-2 Receptors: Transducers of Natriuresis in the Renal Proximal Tubule.

Angiotensin II (Ang II) type-2 receptors (AT2R) are expressed in the adult kidney, prominently in renal proximal tubule cells (RPTCs), and play an important role in opposing renal sodium (Na+) retention induced by Ang II stimulation of Ang II type-1 receptor (AT1R). Natriuresis induced by AT1R blockade is due at least in part to AT2R activation and whole body deletion of AT2Rs reduces the natriuretic response to increased blood pressure (BP). The major endogenous AT2R agonist mediating the natriuretic response is Ang III, the Ang II heptapeptide metabolite generated by aminopeptidase A, and the principal nephron site mediating inhibition of Na+ reabsorption by the AT2R is the renal proximal tubule (RPT). AT2Rs induce natriuresis via a bradykinin, nitric oxide and cyclic GMP (cGMP) signaling cascade. Recent studies demonstrated a key role for protein phosphatase 2A (PP2A) in the AT2R-mediated natriuretic response upstream of cGMP. By inducing natriuresis, AT2Rs lower BP in the Ang II-infusion model of hypertension. PP2A activation and the natriuretic response to AT2R stimulation are defective in spontaneously hypertensive rats, a model of primary hypertension in humans. AT2R agonists are candidates for proximal tubule natriuretic agents in Na+ and fluid retention disorders.

Adipocyte-Specific Modulation of KLF14 Expression in Mice Leads to Sex-Dependent Impacts on Adiposity and Lipid Metabolism.

Genome-wide association studies identified single nucleotide polymorphisms on chromosome 7 upstream of KLF14 to be associated with metabolic syndrome traits and increased risk for type 2 diabetes (T2D). The associations were more significant in women than in men. The risk allele carriers expressed lower levels of the transcription factor KLF14 in adipose tissues than nonrisk allele carriers. To investigate how adipocyte KLF14 regulates metabolic traits in a sex-dependent manner, we characterized high-fat diet-fed male and female mice with adipocyte-specific Klf14 deletion or overexpression. Klf14 deletion resulted in increased fat mass in female mice and decreased fat mass in male mice. Female Klf14-deficient mice had overall smaller adipocytes in subcutaneous fat depots but larger adipocytes in parametrial depots, indicating a shift in lipid storage from subcutaneous to visceral fat depots. They had reduced metabolic rates and increased respiratory exchange ratios consistent with increased use of carbohydrates as an energy source. Fasting- and isoproterenol-induced adipocyte lipolysis was defective in female Klf14-deficient mice, and concomitantly, adipocyte triglycerides lipase mRNA levels were downregulated. Female Klf14-deficient mice cleared blood triglyceride and nonesterified fatty acid less efficiently than wild-type. Finally, adipocyte-specific overexpression of Klf14 resulted in lower total body fat in female but not male mice. Taken together, consistent with human studies, adipocyte KLF14 deficiency in female but not in male mice causes increased adiposity and redistribution of lipid storage from subcutaneous to visceral adipose tissues. Increasing KLF14 abundance in adipocytes of females with obesity and T2D may provide a novel treatment option to alleviate metabolic abnormalities.

Renal AT2 Receptors Mediate Natriuresis via Protein Phosphatase PP2A.

BACKGROUND: How signals from activated angiotensin type-2 receptors (AT2R) mediate inhibition of sodium ion (Na+) reabsorption in renal proximal tubule cells is currently unknown. Protein phosphatases including PP2A (protein phosphatase 2A) have been implicated in AT2R signaling in tissues other than kidney. We investigated whether inhibition of protein phosphatase PP2A reduced AT2R-mediated natriuresis and evaluated changes in PP2A activity and localization after renal AT2R activation in normal 4- and 10-week-old control Wistar-Kyoto rats and 4-week-old prehypertensive and 10-week-old hypertensive spontaneously hypertensive rats. METHODS AND RESULTS: In Wistar-Kyoto rats, direct renal interstitial administration of selective AT2R nonpeptide agonist Compound-21 (C-21) increased renal interstitial cyclic GMP (cGMP) levels, urine Na+ excretion, and simultaneously increased PP2A activity ≈2-fold in homogenates of renal cortical tubules. The cyclic GMP and natriuretic responses were abolished by concurrent renal interstitial administration of protein phosphatase inhibitor calyculin A. In renal proximal tubule cells in response to C-21, PP2A subunits A, B55α and C, but not B56γ, were recruited to apical plasma membranes together with AT2Rs. Calyculin A treatment abolished C-21-induced translocation of both AT2R and PP2A regulatory subunit B55α to apical plasma membranes. Immunoprecipitation of AT2R solubilized from renal cortical homogenates demonstrated physical association of AT2R with PP2A A, B55α, and C but not B56γ subunits. In contrast, in spontaneously hypertensive rats, administration of C-21 did not alter urine Na+ excretion or PP2A activity and failed to translocate AT2Rs and PP2A subunits to apical plasma membranes. CONCLUSIONS: In renal proximal tubule cells of Wistar-Kyoto rats, PP2A is activated and PP2A subunits AB55αC are recruited to C-21-activated AT2Rs during induction of natriuresis. This response is defective in prehypertensive and hypertensive spontaneously hypertensive rats, presenting a potential novel therapeutic target for treating renal Na+ retention and hypertension.

Knockout of Nephron ATP6AP2 Impairs Proximal Tubule Function and Prevents High-Fat Diet-Induced Obesity in Male Mice.

ATP6AP2 expression is increased in the nephron during high-fat diet (HFD) and its knockout (ATP6AP2 KO) reduces body weight (WT) in mice. We evaluated the contribution of ATP6AP2 to urinary glucose (UG) and albumin (Ualb) handling during HFD. We hypothesized that nephron ATP6AP2 KO increases UG and Ualb and minimizes HFD-induced obesity. Eight-week-old male C57BL/6J mice with inducible nephron-specific ATP6AP2 KO and noninduced controls were fed either normal diet (ND, 12% kcal fat) or HFD (45% kcal fat) for 6 months. ATP6AP2 KO mice on ND had 20% (P < 0.01) lower WT compared with controls. HFD-fed mice had 41% (P < 0.05) greater WT than ND-fed control mice. In contrast, ATP6AP2 KO abrogated the increase in WT induced by HFD by 40% (P < 0.05). Mice on HFD had less caloric intake compared with ND controls (P < 0.01). There were no significant differences in metabolic rate between all groups. UG and Ualb was significantly increased in ATP6AP2 KO mice on both ND and HFD. ATP6AP2 KO showed greater levels of proximal tubule apoptosis and histologic evidence of proximal tubule injury. In conclusion, our results demonstrate that nephron-specific ATP6AP2 KO is associated with glucosuria and albuminuria, most likely secondary to renal proximal tubule injury and/or dysfunction. Urinary loss of nutrients may have contributed to the reduced WT of knockout mice on ND and lack of WT gain in response to HFD. Future investigation should elucidate the mechanisms by which loss of renal ATP6AP2 causes proximal tubule injury and dysfunction.

Adaptive thermogenesis in brown adipose tissue involves activation of pannexin-1 channels.

OBJECTIVE: Brown adipose tissue (BAT) is specialized in thermogenesis. The conversion of energy into heat in brown adipocytes proceeds via stimulation of ß-adrenergic receptor (ßAR)-dependent signaling and activation of mitochondrial uncoupling protein 1 (UCP1). We have previously demonstrated a functional role for pannexin-1 (Panx1) channels in white adipose tissue; however, it is not known whether Panx1 channels play a role in the regulation of brown adipocyte function. Here, we tested the hypothesis that Panx1 channels are involved in brown adipocyte activation and thermogenesis. METHODS: In an immortalized brown pre-adipocytes cell line, Panx1 currents were measured using patch-clamp electrophysiology. Flow cytometry was used for assessment of dye uptake and luminescence assays for adenosine triphosphate (ATP) release, and cellular temperature measurement was performed using a ratiometric fluorescence thermometer. We used RNA interference and expression plasmids to manipulate expression of wild-type and mutant Panx1. We used previously described adipocyte-specific Panx1 knockout mice (Panx1Adip-/-) and generated brown adipocyte-specific Panx1 knockout mice (Panx1BAT-/-) to study pharmacological or cold-induced thermogenesis. Glucose uptake into brown adipose tissue was quantified by positron emission tomography (PET) analysis of 18F-fluorodeoxyglucose (18F-FDG) content. BAT temperature was measured using an implantable telemetric temperature probe. RESULTS: In brown adipocytes, Panx1 channel activity was induced either by apoptosis-dependent caspase activation or by ß3AR stimulation via a novel mechanism that involves Gßγ subunit binding to Panx1. Inactivation of Panx1 channels in cultured brown adipocytes resulted in inhibition of ß3AR-induced lipolysis, UCP-1 expression, and cellular thermogenesis. In mice, adiponectin-Cre-dependent genetic deletion of Panx1 in all adipose tissue depots resulted in defective ß3AR agonist- or cold-induced thermogenesis in BAT and suppressed beigeing of white adipose tissue. UCP1-Cre-dependent Panx1 deletion specifically in brown adipocytes reduced the capacity for adaptive thermogenesis without affecting beigeing of white adipose tissue and aggravated diet-induced obesity and insulin resistance. CONCLUSIONS: These data demonstrate that Gßγ-dependent Panx1 channel activation is involved in ß3AR-induced thermogenic regulation in brown adipocytes. Identification of Panx1 channels in BAT as novel thermo-regulatory elements downstream of ß3AR activation may have therapeutic implications.

KLF4 (Kruppel-Like Factor 4)-Dependent Perivascular Plasticity Contributes to Adipose Tissue inflammation.

OBJECTIVE: Smooth muscle cells and pericytes display remarkable plasticity during injury and disease progression. Here, we tested the hypothesis that perivascular cells give rise to Klf4-dependent macrophage-like cells that augment adipose tissue (AT) inflammation and metabolic dysfunction associated with diet-induced obesity (DIO). Approach and Results: Using Myh11-CreERT2 eYFP (enhanced yellow fluorescent protein) mice and flow cytometry of the stromovascular fraction of epididymal AT, we observed a large fraction of smooth muscle cells and pericytes lineage traced eYFP+ cells expressing macrophage markers. Subsequent single-cell RNA sequencing, however, showed that the majority of these cells had no detectable eYFP transcript. Further exploration revealed that intraperitoneal injection of tamoxifen in peanut oil, used for generating conditional knockout or reporter mice in thousands of previous studies, resulted in large increase in the autofluorescence and false identification of macrophages within epididymal AT as being eYFP+; and unintended proinflammatory consequences. Using newly generated Myh11-DreERT2tdTomato mice given oral tamoxifen, we virtually eliminated the problem with autofluorescence and identified 8 perivascular cell dominated clusters, half of which were altered upon DIO. Given that perivascular cell KLF4 (kruppel-like factor 4) can have beneficial or detrimental effects, we tested its role in obesity-associated AT inflammation. While smooth muscle cells and pericytes-specific Klf4 knockout (smooth muscle cells and pericytes Klf4Δ/Δ) mice were not protected from DIO, they displayed improved glucose tolerance upon DIO, and showed marked decreases in proinflammatory macrophages and increases in LYVE1+ lymphatic endothelial cells in the epididymal AT. CONCLUSIONS: Perivascular cells within the AT microvasculature dynamically respond to DIO and modulate tissue inflammation and metabolism in a KLF4-dependent manner.

Adipocyte lipolysis drives acute stress-induced insulin resistance.

Stress hyperglycemia and insulin resistance are evolutionarily conserved metabolic adaptations to severe injury including major trauma, burns, or hemorrhagic shock (HS). In response to injury, the neuroendocrine system increases secretion of counterregulatory hormones that promote rapid mobilization of nutrient stores, impair insulin action, and ultimately cause hyperglycemia, a condition known to impair recovery from injury in the clinical setting. We investigated the contributions of adipocyte lipolysis to the metabolic response to acute stress. Both surgical injury with HS and counterregulatory hormone (epinephrine) infusion profoundly stimulated adipocyte lipolysis and simultaneously triggered insulin resistance and hyperglycemia. When lipolysis was inhibited, the stress-induced insulin resistance and hyperglycemia were largely abolished demonstrating an essential requirement for adipocyte lipolysis in promoting stress-induced insulin resistance. Interestingly, circulating non-esterified fatty acid levels did not increase with lipolysis or correlate with insulin resistance during acute stress. Instead, we show that impaired insulin sensitivity correlated with circulating levels of the adipokine resistin in a lipolysis-dependent manner. Our findings demonstrate the central importance of adipocyte lipolysis in the metabolic response to injury. This insight suggests new approaches to prevent insulin resistance and stress hyperglycemia in trauma and surgery patients and thereby improve outcomes.

Nervonic acid limits weight gain in a mouse model of diet-induced obesity.

Lipid perturbations contribute to detrimental outcomes in obesity. We previously demonstrated that nervonic acid, a C24:1 ω-9 fatty acid, predominantly acylated to sphingolipids, including ceramides, are selectively reduced in a mouse model of obesity. It is currently unknown if deficiency of nervonic acid-sphingolipid metabolites contribute to complications of obesity. Mice were fed a standard diet, a high fat diet, or these diets supplemented isocalorically with nervonic acid. The primary objective was to determine if dietary nervonic acid content alters the metabolic phenotype in mice fed a high fat diet. Furthermore, we investigated if nervonic acid alters markers of impaired fatty acid oxidation in the liver. We observed that a nervonic acid-enriched isocaloric diet reduced weight gain and adiposity in mice fed a high fat diet. The nervonic acid enrichment led to increased C24:1-ceramides and improved several metabolic parameters including blood glucose levels, and insulin and glucose tolerance. Mechanistically, nervonic acid supplementation increased PPARα and PGC1α expression and improved the acylcarnitine profile in liver. These alterations indicate improved energy metabolism through increased ß-oxidation of fatty acids. Taken together, increasing dietary nervonic acid improves metabolic parameters in mice fed a high fat diet. Strategies that prevent deficiency of, or restore, nervonic acid may represent an effective strategy to treat obesity and obesity-related complications.

Metformin Improves Cardiac Metabolism and Function, and Prevents Left Ventricular Hypertrophy in Spontaneously Hypertensive Rats.

Background In spontaneously hypertensive rats (SHR) we observed profound myocardial metabolic changes during early hypertension before development of cardiac dysfunction and left ventricular hypertrophy. In this study, we evaluated whether metformin improved myocardial metabolic abnormalities and simultaneously prevented contractile dysfunction and left ventricular hypertrophy in SHR. Methods and Results SHR and control Wistar-Kyoto rats were treated with metformin from 2 to 5 months of age, when SHR hearts exhibit metabolic abnormalities and develop cardiac dysfunction and left ventricular hypertrophy. We evaluated the effect of metformin on myocardial glucose uptake rates with dynamic 2-[18F] fluoro-2-deoxy-D-glucose positron emission tomography. We used cardiac MRI in vivo to assess the effect of metformin on ejection fraction, left ventricular mass, and end-diastolic wall thickness, and also analyzed metabolites, AMP-activated protein kinase and mammalian target-of-rapamycin activities, and mean arterial blood pressure. Metformin-treated SHR had lower mean arterial blood pressure but remained hypertensive. Cardiac glucose uptake rates, left ventricular mass/tibia length, wall thickness, and circulating free fatty acid levels decreased to normal, and ejection fraction improved in treated SHR. Hearts of treated SHR exhibited increased AMP-activated protein kinase phosphorylation and reduced mammalian target-of-rapamycin activity. Cardiac metabolite profiling demonstrated that metformin decreased fatty acyl carnitines and markers of oxidative stress in SHR. Conclusions Metformin reduced blood pressure, normalized myocardial glucose uptake, prevented left ventricular hypertrophy, and improved cardiac function in SHR. Metformin may exert its effects by normalizing myocardial AMPK and mammalian target-of-rapamycin activities, improving fatty acid oxidation, and reducing oxidative stress. Thus, metformin may be a new treatment to prevent or ameliorate chronic hypertension-induced left ventricular hypertrophy.

Identification of a Primary Renal AT2 Receptor Defect in Spontaneously Hypertensive Rats.

RATIONALE: Previous studies identified a defect in Ang III (angiotensin III [des-aspartyl1-angiotensin II])-elicited AT2R (Ang type-2 receptor)-mediated natriuresis in renal proximal tubule cells of spontaneously hypertensive rats (SHR). OBJECTIVE: This study aimed to delineate in prehypertensive SHR kidneys the receptor or postreceptor defect causing impaired AT2R signaling and renal sodium (Na+) retention by utilizing the selective AT2R agonist compound-21 (C-21). METHODS AND RESULTS: Female 4-week-old Wistar Kyoto and SHR rats were studied after 24-hour systemic AT1R (Ang II type-1 receptor) blockade. Left kidneys received 30-minute renal interstitial infusions of vehicle followed by C-21 (20, 40, and 60 ng/[kg·min], each dose 30 minutes). Right kidneys received vehicle infusions. In Wistar Kyoto, C-21 dose-dependently increased urine Na+ excretion from 0.023±0.01 to 0.064±0.02, 0.087±0.01, and 0.089±0.01 µmol/min (P=0.008, P<0.0001, and P<0.0001, respectively) and renal interstitial fluid levels of AT2R downstream signaling molecule cGMP (cyclic guanosine 3',5' monophosphate) from 0.91±0.3 to 3.1±1.0, 5.9±1.2 and 5.3±0.5 fmol/mL (P=nonsignificant, P<0.0001, and P<0.0001, respectively). In contrast, C-21 did not increase urine Na+ excretion or renal interstitial cGMP in SHR. Mean arterial pressure was slightly higher in SHR but within the normotensive range and unaffected by C-21. In Wistar Kyoto, but not SHR, C-21 induced AT2R translocation to apical plasma membranes of renal proximal tubule cells, internalization/inactivation of NHE-3 (sodium-hydrogen exchanger-3) and Na+/K+ATPase (sodium-potassium-atpase) and phosphorylation of AT2R-cGMP downstream signaling molecules Src (Src family kinase), ERK (extracellular signal-related kinase), and VASP (vasodilator-stimulated phosphoprotein). To test whether cGMP could bypass the natriuretic defect in SHR, we infused 8-bromo-cGMP. This restored natriuresis, Na+ transporter internalization/inactivation, and Src and VASP phosphorylation, but not apical plasma membrane AT2R recruitment. In contrast, 8-bromo-cAMP administration had no effect on natriuresis or AT2R recruitment in SHR. CONCLUSIONS: The results demonstrate a primary renal proximal tubule cell AT2R natriuretic defect in SHR that may contribute to the development of hypertension. Since the defect is abrogated by exogenous intrarenal cGMP, the renal cGMP pathway may represent a viable target for the treatment of hypertension. Visual Overview: An online visual overview is available for this article.

Defective Renal Angiotensin III and AT2 Receptor Signaling in Prehypertensive Spontaneously Hypertensive Rats.

Background Previous studies demonstrated that angiotensin (Ang) III , not Ang II , is the predominant endogenous agonist for Ang type-2 receptor ( AT 2R)-induced natriuresis in normal rats, and that hypertensive 12-week-old spontaneously hypertensive rats ( SHR ) lack natriuretic responses to Ang III . This study tested whether prehypertensive SHR already have defective Ang III -induced natriuresis and determined possible mechanisms. Methods and Results Female and male normotensive 4-week-old SHR and Wistar Kyoto rats were studied after 24-hour systemic AT 1R blockade. Left kidneys received 30 minute renal interstitial infusions of vehicle followed by Ang III (3.5, 7.0, 14, and 28 nmol/kg per min; each dose for 30 minutes). Right kidneys received vehicle infusions. In 4-week-old Wistar Kyoto rats, renal interstitial Ang III increased urine sodium (Na+) excretion but failed to induce natriuresis in 4-week-old SHR . Renal Ang III levels were similar between Wistar Kyoto rats and SHR , making increased Ang III degradation as a possible cause for defective natriuresis in SHR unlikely. In Wistar Kyoto rats, renal interstitial Ang III induced translocation of AT 2Rs to apical plasma membranes of renal proximal tubule cells. Simultaneously, Ang III induced retraction of the major Na+ transporter Na+-H+ exchanger-3 ( NHE -3) from apical membranes and internalization of Na+/K+ ATP ase ( NKA ) from basolateral membranes of renal proximal tubule cells. Consistent with NHE -3 and NKA retraction, Ang III increased pS er552- NHE -3 and decreased pS er23- NKA . In contrast, in SHR , intrarenal Ang III failed to induce AT 2R translocation, NHE -3 or NKA retraction, pS er552- NHE -3 phosphorylation, or pS er23- NKA dephosphorylation. Conclusions These results indicate impaired Ang III / AT 2R signaling as a possible primary defect in prehypertensive SHR .

Metabolic Changes in Spontaneously Hypertensive Rat Hearts Precede Cardiac Dysfunction and Left Ventricular Hypertrophy.

Background Sustained pressure overload leads to changes in cardiac metabolism, function, and structure. Both time course and causal relationships between these changes are not fully understood. Therefore, we studied spontaneously hypertensive rats (SHR) during early hypertension development and compared them to control Wistar Kyoto rats. Methods and Results We serially evaluated myocardial glucose uptake rates (Ki) with dynamic 2-[18F] fluoro-2-deoxy-D-glucose positron emission tomography, and ejection fraction and left ventricular mass to body weight ratios with cardiac magnetic resonance imaging in vivo, determined glucose uptake and oxidation rates in isolated perfused hearts, and analyzed metabolites, mammalian target of rapamycin activity and endoplasmic reticulum stress in dissected hearts. When compared with Wistar Kyoto rats, SHR demonstrated increased glucose uptake rates (Ki) in vivo, and reduced ejection fraction as early as 2 months of age when hypertension was established. Isolated perfused SHR hearts showed increased glucose uptake and oxidation rates starting at 1 month. Cardiac metabolite analysis at 2 months of age revealed elevated pyruvate, fatty acyl- and branched chain amino acid-derived carnitines, oxidative stress, and inflammation. Mammalian target of rapamycin activity increased in SHR beginning at 2 months. Left ventricular mass to body weight ratios and endoplasmic reticulum stress were elevated in 5 month-old SHR. Conclusions Thus, in a genetic hypertension model, chronic cardiac pressure overload promptly leads to increased myocardial glucose uptake and oxidation, and to metabolite abnormalities. These coincide with, or precede, cardiac dysfunction while left ventricular hypertrophy develops only later. Myocardial metabolic changes may thus serve as early diagnostic markers for hypertension-induced left ventricular hypertrophy.

Correction: Biologically anchored knowledge expansion approach uncovers KLF4 as a novel insulin signaling regulator.

[This corrects the article DOI: 10.1371/journal.pone.0204100.].

Biologically anchored knowledge expansion approach uncovers KLF4 as a novel insulin signaling regulator.

One of the biggest challenges in analyzing high throughput omics data in biological studies is extracting information that is relevant to specific biological mechanisms of interest while simultaneously restricting the number of false positive findings. Due to random chances with numerous candidate targets and mechanisms, computational approaches often yield a large number of false positives that cannot easily be discerned from relevant biological findings without costly, and often infeasible, biological experiments. We here introduce and apply an integrative bioinformatics approach, Biologically Anchored Knowledge Expansion (BAKE), which uses sequential statistical analysis and literature mining to identify highly relevant network genes and effectively removes false positive findings. Applying BAKE to genomic expression data collected from mouse (Mus musculus) adipocytes during insulin resistance progression, we uncovered the transcription factor Krueppel-like Factor 4 (KLF4) as a regulator of early insulin signaling. We experimentally confirmed that KLF4 controls the expression of two key insulin signaling molecules, the Insulin Receptor Substrate 2 (IRS2) and Tuberous Sclerosis Complex 2 (TSC2).

Module Anchored Network Inference: A Sequential Module-Based Approach to Novel Gene Network Construction from Genomic Expression Data on Human Disease Mechanism.

Different computational approaches have been examined and compared for inferring network relationships from time-series genomic data on human disease mechanisms under the recent Dialogue on Reverse Engineering Assessment and Methods (DREAM) challenge. Many of these approaches infer all possible relationships among all candidate genes, often resulting in extremely crowded candidate network relationships with many more False Positives than True Positives. To overcome this limitation, we introduce a novel approach, Module Anchored Network Inference (MANI), that constructs networks by analyzing sequentially small adjacent building blocks (modules). Using MANI, we inferred a 7-gene adipogenesis network based on time-series gene expression data during adipocyte differentiation. MANI was also applied to infer two 10-gene networks based on time-course perturbation datasets from DREAM3 and DREAM4 challenges. MANI well inferred and distinguished serial, parallel, and time-dependent gene interactions and network cascades in these applications showing a superior performance to other in silico network inference techniques for discovering and reconstructing gene network relationships.

Acute low-dose endotoxin treatment results in improved whole-body glucose homeostasis in mice.

BACKGROUND: Obese individuals present with an increased inflammatory tone as compared to healthy, normal-weight individuals, which is associated with insulin resistance. One factor hypothesized to contribute to increased inflammation in obese and diabetic states is elevated blood endotoxin levels, a condition known as metabolic endotoxemia. In non-obese and insulin sensitive individuals, circulating endotoxin concentrations fluctuate over the course of the day with elevations in the post-prandial state that return to baseline levels in the post-absorptive state. Evidence suggests that high-fat feeding alters these fluctuations causing endotoxin levels to remain high throughout the day. The effects of alterations in endotoxin levels on glucose metabolism are not clearly understood. PURPOSE/PROCEDURES: The goal of this study was to determine the effects of both short-term and long-term increases in endotoxin (lipopolysaccharide, LPS) of a low magnitude on the glucose tolerance and insulin signaling in a human primary cell line as well as the effects of short-term endotoxin treatments on glucose homeostasis in a C57/Bl6 mouse model. First, we tested the hypothesis that short-term low-dose endotoxin treatments would augment insulin signaling and glycogen synthesis while long-term treatments would be disruptive in the cell culture model. Second, we examined if these short-term low dose treatments of endotoxin would contribute to similar improvements in whole-body glucose homeostasis in a mouse model. MAIN FINDINGS: Contrary to our initial hypothesis, short-term endotoxin treatment had no effect on insulin signaling or glycogen synthesis, however long-term treatment indeed decreased glycogen synthesis (P<.05). Interestingly, short-term endotoxin treatment resulted in significant improvements in glucose homeostasis in the mouse model (P<.01); which is believed to be at least partly attributed to an inhibitory action of LPS on liver glucose production. CONCLUSIONS: This research shows that low-magnitude, short-term changes in LPS can have significant effects on whole body glucose metabolism and this likely occurs through its direct actions on the liver. Additional studies are necessary to understand the mechanisms responsible for altered glucose metabolism in response to low magnitude changes in LPS levels.

AT2 Receptor Activation Prevents Sodium Retention and Reduces Blood Pressure in Angiotensin II-Dependent Hypertension.

RATIONALE: Compound 21 (C-21) is a highly selective nonpeptide angiotensin AT2 receptor (AT2R) agonist. OBJECTIVE: To test the hypothesis that chronic AT2R activation with C-21 induces natriuresis via an action at the renal proximal tubule (RPT) and lowers blood pressure (BP) in experimental angiotensin II (Ang II)-dependent hypertension. METHODS AND RESULTS: In rats, Ang II infusion increased both sodium (Na(+)) retention and BP on day 1, and BP remained elevated throughout the 7-day infusion period. Either intrarenal or systemic administration of C-21 prevented Ang II-mediated Na(+) retention on day 1, induced continuously negative cumulative Na(+) balance compared with Ang II alone, and reduced BP chronically. The effects of C-21 are likely to be mediated by action on the RPT as acute systemic C-21-induced natriuresis was additive to that induced by chlorothiazide and amiloride. At 24 hours of Ang II infusion, AT2R activation with C-21, both intrarenally and systemically, translocated AT2Rs from intracellular sites to the apical plasma membranes of RPT cells without altering the total cellular pool of AT2Rs and internalized/inactivated major RPT Na(+) transporters Na(+)-H(+)-exchanger-3 and Na(+)/K(+)ATPase. C-21 lowered BP to a similar degree whether administered before or subsequent to the establishment of Ang II-dependent hypertension. CONCLUSIONS: Chronic AT2R activation initiates and sustains receptor translocation to RPT apical plasma membranes, internalizes/inactivates Na(+)-H(+)-exchanger-3 and Na(+)/K(+)ATPase, prevents Na(+) retention resulting in negative cumulative Na(+) balance, and lowers BP in experimental Ang II-induced hypertension. Acting uniquely at the RPT, C-21 is a promising candidate for the treatment of hypertension and Na(+)-retaining states in humans.

Rab GAPs AS160 and Tbc1d1 play nonredundant roles in the regulation of glucose and energy homeostasis in mice.

The related Rab GTPase-activating proteins (Rab GAPs) AS160 and Tbc1d1 regulate the trafficking of the glucose transporter GLUT4 that controls glucose uptake in muscle and fat cells and glucose homeostasis. AS160- and Tbc1d1-deficient mice exhibit different adipocyte- and skeletal muscle-specific defects in glucose uptake, GLUT4 expression and trafficking, and glucose homeostasis. A recent study analyzed male mice with simultaneous deletion of AS160 and Tbc1d1 (AS160(-/-)/Tbc1d1(-/-) mice). Herein, we describe abnormalities in male and female AS160(-/-)/Tbc1d1(-/-) mice on another strain background. We confirm the earlier observation that GLUT4 expression and glucose uptake defects of single-knockout mice join in AS160(-/-)/Tbc1d1(-/-) mice to affect all skeletal muscle and adipose tissues. In large mixed fiber-type skeletal muscles, changes in relative basal GLUT4 plasma membrane association in AS160(-/-) and Tbc1d1(-/-) mice also combine in AS160(-/-)/Tbc1d1(-/-) mice. However, we found different glucose uptake abnormalities in isolated skeletal muscles and adipocytes than reported previously, resulting in different interpretations of how AS160 and Tbc1d1 regulate GLUT4 translocation to the cell surface. In support of a larger role for AS160 in glucose homeostasis, in contrast with the previous study, we find similarly impaired glucose and insulin tolerance in AS160(-/-)/Tbc1d1(-/-) and AS160(-/-) mice. However, in vivo glucose uptake abnormalities in AS160(-/-)/Tbc1d1(-/-) skeletal muscles differ from those observed previously in AS160(-/-) mice, indicating additional defects due to Tbc1d1 deletion. Similar to AS160- and Tbc1d1-deficient mice, AS160(-/-)/Tbc1d1(-/-) mice show sex-specific abnormalities in glucose and energy homeostasis. In conclusion, our study supports nonredundant functions for AS160 and Tbc1d1.