Molecular phenotyping for analyzing subtle genetic effects in mice: application to an angiotensinogen gene titration

Guanylyl cyclase/natriuretic peptide receptor-A: Identification, molecular characterization, and physiological genomics

The natriuretic peptides (NPs) hormone family, which consists mainly of atrial, brain, and C-type NPs (ANP, BNP, and CNP), play diverse roles in mammalian species, ranging from renal, cardiac, endocrine, neural, and vascular hemodynamics to metabolic regulations, immune responsiveness, and energy distributions. Over the last four decades, new data has transpired regarding the biochemical and molecular compositions, signaling mechanisms, and physiological and pathophysiological functions of NPs and their receptors. NPs are incremented mainly in eliciting natriuretic, diuretic, endocrine, vasodilatory, and neurological activities, along with antiproliferative, antimitogenic, antiinflammatory, and antifibrotic responses. The main locus responsible in the biological and physiological regulatory actions of NPs (ANP and BNP) is the plasma membrane guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA), a member of the growing multi-limbed GC family of receptors. Advances in this field have provided tremendous insights into the critical role of Npr1 (encoding GC-A/NPRA) in the reduction of fluid volume and blood pressure homeostasis, protection against renal and cardiac remodeling, and moderation and mediation of neurological disorders. The generation and use of genetically engineered animals, including gene-targeted (gene-knockout and gene-duplication) and transgenic mutant mouse models has revealed and clarified the varied roles and pleiotropic functions of GC-A/NPRA in vivo in intact animals. This review provides a chronological development of the biochemical, molecular, physiological, and pathophysiological functions of GC-A/NPRA, including signaling pathways, genomics, and gene regulation in both normal and disease states.

Neutrophilic inflammation in gallbladder carcinoma correlates with patient survival: A case-control study

Gallbladder carcinoma is an uncommon malignancy with an overall 5-year survival of less than 5%. Gallbladder carcinoma has been strongly linked with cholelithiasis and chronic inflammation. Case reports and series have described cholecystitis with acute (neutrophilic) inflammation in association with gallbladder carcinoma, although a clear relationship to patient outcome has not been established. Our series included 8 cases of gallbladder carcinoma with high tumor-associated neutrophils (>25 per high power field) that were associated with shorter patient survival (Cox regression coefficient 6.2, p = 0.004) than age- and stage-matched controls. High tumor-associated neutrophils were not associated with gallbladder rupture/perforation or increased bacterial load measured by 16S PCR. Neutrophilic inflammation with gallbladder carcinoma correlates to shorter survival, independent of patient age and stage of carcinoma. The findings suggest that the degree of neutrophilic inflammation may have prognostic significance in specimens from patients with gallbladder carcinoma after cholecystectomy. Further studies with larger case numbers are needed to confirm and generalize these findings.

Importance of the renal ion channel TRPM6 in the circadian secretion of renin to raise blood pressure

Blood pressure has a daily pattern, with higher values in the active period. Its elevation at the onset of the active period substantially increases the risk of fatal cardiovascular events. Renin secretion stimulated by renal sympathetic neurons is considered essential to this process; however, its regulatory mechanism remains largely unknown. Here, we show the importance of transient receptor potential melastatin-related 6 (TRPM6), a Mg²⁺-permeable cation channel, in augmenting renin secretion in the active period. TRPM6 expression is significantly reduced in the distal convoluted tubule of hypotensive Cnnm2-deficient mice. We generate kidney-specific Trpm6-deficient mice and observe a decrease in blood pressure and a disappearance of its circadian variation. Consistently, renin secretion is not augmented in the active period. Furthermore, renin secretion after pharmacological activation of β-adrenoreceptor, the target of neuronal stimulation, is abrogated, and the receptor expression is decreased in renin-secreting cells. These results indicate crucial roles of TRPM6 in the circadian regulation of blood pressure.

Circadian variation of blood pressure, with higher values in the active period, is associated with the risk of fatal cardiovascular events. Here, we show the importance of renal TRPM6, a Magnesium-permeable cation channel, in raising blood pressure by stimulating renin secretion.

CRISPR/Cas9 Mediated Deletion of the Angiotensinogen Gene Reduces Hypertension: A Potential for Cure?

[Figure: see text].

Genetic Ablation and Guanylyl Cyclase/Natriuretic Peptide Receptor-A: Impact on the Pathophysiology of Cardiovascular Dysfunction

Mice bearing targeted gene mutations that affect the functions of natriuretic peptides (NPs) and natriuretic peptide receptors (NPRs) have contributed important information on the pathogenesis of hypertension, kidney disease, and cardiovascular dysfunction. Studies of mice having both complete gene disruption and tissue-specific gene ablation have contributed to our understanding of hypertension and cardiovascular disorders. These phenomena are consistent with an oligogenic inheritance in which interactions among a few alleles may account for genetic susceptibility to hypertension, renal insufficiency, and congestive heart failure. In addition to gene knockouts conferring increased risks of hypertension, kidney disorders, and cardiovascular dysfunction, studies of gene duplications have identified mutations that protect against high blood pressure and cardiovascular events, thus generating the notion that certain alleles can confer resistance to hypertension and heart disease. This review focuses on the intriguing phenotypes of Npr1 gene disruption and gene duplication in mice, with emphasis on hypertension and cardiovascular events using mouse models carrying Npr1 gene knockout and/or gene duplication. It also describes how Npr1 gene targeting in mice has contributed to our knowledge of the roles of NPs and NPRs in dose-dependently regulating hypertension and cardiovascular events.

Characterization of Liver- and Cancer-type-Organic Anion Transporting Polypeptide (OATP) 1B3 Messenger RNA Expression in Normal and Cancerous Human Tissues

BACKGROUND

Membrane transport protein organic anion transporting polypeptide (OATP) 1B3 mediates the cellular uptake of many clinically important drugs including anti-cancer drugs (e.g., paclitaxel). In addition to the well-recognized hepatic expression and function of OATP1B3 [herein named liver-type (Lt) OATP1B3], OATP1B3 also expresses in cancers and has been postulated to play a role in cancer therapy, presumably by facilitating the influx of anti-cancer drugs. Recently, a cancer type (Ct)-OATP1B3 mRNA variant was identified in colon and lung cancer tissues, which encodes truncated Ct-OATP1B3 with negligible transport activity. Other than in colon and lung cancers, reports on mRNA expression of OATP1B3 in other cancers cannot distinguish between the Ltand Ct-OATP1B3.

OBJECTIVE

The current studies were designed to characterize the expression of Lt- and Ct-OATP1B3 mRNA in ovarian, prostate, bladder, breast, and lung tissues.

METHODS

Lt- and Ct-OATP1B3 isoform-specific PCR primers were utilized to determine the mRNA levels of Lt- and Ct-OATP1B3, respectively. An expression vector expressing green fluorescent protein (GFP)-tagged Lt-OATP1B3 was transiently transfected into the ovarian cancer cell line SKOV3. Confocal live-cell microscopy was utilized to determine the localization of GFP-Lt-OATP1B3 in SKOV3 cells.

RESULTS

For the first time, Lt-OATP1B3 mRNA was detected in ovarian, prostate, bladder and breast cancers. The localization of GFP-Lt-OATP1B3 on the plasma membrane of SKOV3 cells after transient transfection was readily detected by confocal microscopy.

CONCLUSION

Our findings are supportive of the potential role of Lt-OATP1B3 in cancer cells.

Characterization of the Hippocampal Neuroimmune Response to Binge-Like Ethanol Consumption in the Drinking in the Dark Model

OBJECTIVES

Alcohol dependence leads to dysregulation of the neuroimmune system, but the effects of excessive alcohol consumption on key players of the neuroimmune response after episodic binge drinking in nondependence has not been readily assessed. These studies seek to determine how the neuroimmune system within the hippocampus responds to binge-like consumption prior to dependence or evidence of brain damage.

METHODS

C57BL/6J mice underwent the drinking in the dark (DID) paradigm to recapitulate binge consumption. Immunohistochemical techniques were employed to determine the effects of ethanol on cytokine and astrocyte responses within the hippocampus. Astrocyte activation was also assessed using qRT-PCR.

RESULTS

Our results indicated that binge-like ethanol consumption resulted in a 3.6-fold increase in the proinflammatory cytokine interleukin (IL)-1β immunoreactivity in various regions of the hippocampus. The opposite effect was seen in the anti-inflammatory cytokine IL-10. Binge-like consumption resulted in a 67% decrease in IL-10 immunoreactivity but had no effect on IL-4 or IL-6 compared with the water-drinking control group. Moreover, astrocyte activation occurred following ethanol exposure as GFAP immunoreactivity was increased over 120% in mice that experienced 3 cycles of ethanol binges. PCR analyses indicated that the mRNA increased by almost 4-fold after one cycle of DID, but this effect did not persist in abstinence.

CONCLUSIONS

Altogether, these findings suggest that binge-like ethanol drinking prior to dependence causes dysregulation to the neuroimmune system. This altered neuroimmune state may have an impact on behavior but could also result in a heightened neuroimmune response that is exacerbated from further ethanol exposure or other immune-modulating events.

A comparison of hippocampal microglial responses in aged and young rodents following dependent and non-dependent binge drinking

Alcoholism is a highly visible and prevalent issue in the United States. Although binge-drinking is assumed to be a college-age problem, older adults (ages 65+) consume binge amounts of alcohol and have alcohol use disorders (AUDs). Moreover, individuals with alcohol dependence in their youth often continue to drink as they age. As such, this study tested the hypothesis that the effects of alcohol on hippocampal microglia are exacerbated in aged versus younger rodents in two AUD models. Briefly, adult (2-3 months) and aged (15+ months) Sprague-Dawley rats were administered alcohol or control diet using the Majchrowicz model to study alcohol-induced neurodegeneration. To study the effects of non-dependent binge consumption on microglia, adolescent (6-8 weeks) and aged (18+ months) C57/BL6N were subjected to the Drinking in the Dark paradigm. Microglia number and densitometry were assessed using immunohistochemistry. Hippocampal subregional and model/species-specific effects of alcohol were observed, but overall, aging did not appear to increase the alcohol-induced microglia reactivity as measured by Iba-1 densitometry. However, analysis of microglial counts revealed a significant decrease in the number microglia cells in both the alcohol-induced neurodegeneration and DID model across age groups. In the dentate gyrus, the loss of microglia was exacerbated by aging, particularly in mice after DID, non-dependent model. Using qRT-PCR, the persistence of alcohol and aging effects was assessed following the DID model. Allograft Inflammatory Factor 1 mRNA was increased in both young and aged mice by alcohol exposure; however, only in the aged mice did the alcohol effect persist. Overall, these data imply that the microglial response to alcohol is complex with evidence of depressed numbers of microglia but also increased reactivity with advanced age.

Regulation of glutamate transporter 1 (GLT-1) gene expression by cocaine self-administration and withdrawal

Downregulation of the astroglial glutamate transporter GLT-1 is observed in the nucleus accumbens (NAc) following administration of multiple drugs of abuse. The decrease in GLT-1 protein expression following cocaine self-administration is dependent on both the amount of cocaine self-administered and the length of withdrawal, with longer access to cocaine and longer withdrawal periods leading to greater decreases in GLT-1 protein. However, the mechanism(s) by which cocaine downregulates GLT-1 protein remains unknown. We used qRT-PCR to examine gene expression of GLT-1 splice isoforms (GLT-1A, GLT-1B) in the NAc, prelimbic cortex (PL) and basolateral amygdala (BLA) of rats, following two widely used models of cocaine self-administration: short-access (ShA) self-administration, and the long-access (LgA) self-administration/incubation model. While downregulation of GLT-1 protein is observed following ShA cocaine self-administration and extinction, this model did not lead to a change in GLT-1A or GLT-1B gene expression in any brain region examined. Forced abstinence following ShA cocaine self-administration also was without effect. In contrast, LgA cocaine self-administration and prolonged abstinence significantly decreased GLT-1A gene expression in the NAc and BLA, and significantly decreased GLT-1B gene expression in the PL. No change was observed in NAc GLT-1A gene expression one day after LgA cocaine self-administration, indicating withdrawal-induced decreases in GLT-1A mRNA. In addition, LgA cocaine self-administration and withdrawal induced hypermethylation of the GLT-1 gene in the NAc. These results indicate that a decrease in NAc GLT-1 mRNA is only observed after extended access to cocaine combined with protracted abstinence, and that epigenetic mechanisms likely contribute to this effect.

Interleukin-1 signaling in the basolateral amygdala is necessary for heroin-conditioned immunosuppression

Heroin administration suppresses the production of inducible nitric oxide (NO), as indicated by changes in splenic inducible nitric oxide synthase (iNOS) and plasma nitrate/nitrite. Since NO is a measure of host defense against infection and disease, this provides evidence that heroin can increase susceptibility to pathogens by directly interacting with the immune system. Previous research in our laboratory has demonstrated that these immunosuppressive effects of heroin can also be conditioned to environmental stimuli by repeatedly pairing heroin administration with a unique environmental context. Re-exposure to a previously drug-paired context elicits immunosuppressive effects similar to heroin administration alone. In addition, our laboratory has reported that the basolateral amygdala (BLA) and medial nucleus accumbens shell (mNAcS) are critical neural substrates that mediate this conditioned effect. However, our understanding of the contributing mechanisms within these brain regions is limited. It is known that the cytokine interleukin-1 (IL-1) plays an important role in learning and memory. In fact, our laboratory has demonstrated that inhibition of IL-1β expression in the dorsal hippocampus (DH) prior to re-exposure to a heroin-paired context prevents the suppression of measures of NO production. Therefore, the present studies sought to further investigate the role of IL-1 in heroin-conditioned immunosuppression. Blockade of IL-1 signaling in the BLA, but not in the caudate putamen or mNAcS, using IL-1 receptor antagonist (IL-1Ra) attenuated heroin-conditioned immunosuppression of NO production as measured by plasma nitrate/nitrite and iNOS mRNA expression in spleen tissue. Taken together, these findings suggest that IL-1 signaling in the BLA is necessary for the expression of heroin-conditioned immunosuppression of NO production and may be a target for interventions that normalize immune function in heroin users and patient populations exposed to opiate regimens.

BRG1 and BRM function antagonistically with c-MYC in adult cardiomyocytes to regulate conduction and contractility

RATIONALE

The contractile dysfunction that underlies heart failure involves perturbations in multiple biological processes ranging from metabolism to electrophysiology. Yet the epigenetic mechanisms that are altered in this disease state have not been elucidated. SWI/SNF chromatin-remodeling complexes are plausible candidates based on mouse knockout studies demonstrating a combined requirement for the BRG1 and BRM catalytic subunits in adult cardiomyocytes. Brg1/Brm double mutants exhibit metabolic and mitochondrial defects and are not viable although their cause of death has not been ascertained.

OBJECTIVE

To determine the cause of death of Brg1/Brm double-mutant mice, to test the hypothesis that BRG1 and BRM are required for cardiac contractility, and to identify relevant downstream target genes.

METHODS AND RESULTS

A tamoxifen-inducible gene-targeting strategy utilizing αMHC-Cre-ERT was implemented to delete both SWI/SNF catalytic subunits in adult cardiomyocytes. Brg1/Brm double-mutant mice were monitored by echocardiography and electrocardiography, and they underwent rapidly progressive ventricular dysfunction including conduction defects and arrhythmias that culminated in heart failure and death within 3weeks. Mechanistically, BRG1/BRM repressed c-Myc expression, and enforced expression of a DOX-inducible c-MYC trangene in mouse cardiomyocytes phenocopied the ventricular conduction defects observed in Brg1/Brm double mutants. BRG1/BRM and c-MYC had opposite effects on the expression of cardiac conduction genes, and the directionality was consistent with their respective loss- and gain-of-function phenotypes. To support the clinical relevance of this mechanism, BRG1/BRM occupancy was diminished at the same target genes in human heart failure cases compared to controls, and this correlated with increased c-MYC expression and decreased CX43 and SCN5A expression.

CONCLUSION

BRG1/BRM and c-MYC have an antagonistic relationship regulating the expression of cardiac conduction genes that maintain contractility, which is reminiscent of their antagonistic roles as a tumor suppressor and oncogene in cancer.

Prolactin alters blood pressure by modulating the activity of endothelial nitric oxide synthase

Increased levels of a cleaved form of prolactin (molecular weight 16 kDa) have been associated with preeclampsia. To study the effects of prolactin on blood pressure (BP), we generated male mice with a single-copy transgene (Tg; inserted into the hypoxanthine-guanine phosphoribosyltransferase locus) that enables inducible hepatic production of prolactin and its cleavage product. The Tg is driven by the indole-3-carbinol (I3C)-inducible rat cytochrome P450 1A1 promoter. When the Tg mice were fed normal chow (NC), plasma prolactin concentrations were comparable to those in female WT mice in the last third of pregnancy, and BP was lower than in WT mice (∼95 mm Hg vs. ∼105 mm Hg). When the Tg mice were fed chow containing IC3, plasma prolactin concentrations increased threefold, BP increased to ∼130 mm Hg, and cardiac function became markedly impaired. IC3 chow did not affect the WT mice. Urinary excretion of nitrite/nitrate and the amount of Ser1177-phosphorylated endothelial nitric oxide (NO) synthase (eNOS) were significantly greater in the Tg mice fed NC than in WT mice, as they are during pregnancy. However, when I3C was fed, these indicators of NO production became significantly less in the Tg mice than in WT mice. The effects of increased plasma prolactin were abolished by a genetic absence of eNOS. Thus, a threefold increase in plasma prolactin is sufficient to increase BP significantly and to markedly impair cardiac function, with effects mediated by NO produced by eNOS. We suggest that pregnant women with abnormally high prolactin levels may need special attention.

Influence of Different Levels of Lipoic Acid Synthase Gene Expression on Diabetic Nephropathy

Oxidative stress is implicated in the pathogenesis of diabetic nephropathy (DN) but outcomes of many clinical trials are controversial. To define the role of antioxidants in kidney protection during the development of diabetic nephropathy, we have generated a novel genetic antioxidant mouse model with over- or under-expression of lipoic acid synthase gene (Lias). These models have been mated with Ins2^Akita/+ mice, a type I diabetic mouse model. We compare the major pathologic changes and oxidative stress status in two new strains of the mice with controls. Our results show that Ins2^Akita/+ mice with under-expressed Lias gene, exhibit higher oxidative stress and more severe DN features (albuminuria, glomerular basement membrane thickening and mesangial matrix expansion). In contrast, Ins2^Akita/+ mice with highly-expressed Lias gene display lower oxidative stress and less DN pathologic changes. Our study demonstrates that strengthening endogenous antioxidant capacity could be an effective strategy for prevention and treatment of DN.

Acquisition of heroin conditioned immunosuppression requires IL-1 signaling in the dorsal hippocampus

Opioid users experience increased incidence of infection, which may be partially attributable to both direct opiate-immune interactions and conditioned immune responses. Previous studies have investigated the neural circuitry governing opioid conditioned immune responses, but work remains to elucidate the mechanisms mediating this effect. Our laboratory has previously shown that hippocampal IL-1 signaling, specifically, is required for the expression of heroin conditioned immunosuppression following learning. The current studies were designed to further characterize the role of hippocampal IL-1 in this phenomenon by manipulating IL-1 during learning. Experiment 1 tested whether hippocampal IL-1 is also required for the acquisition of heroin conditioned immunosuppression, while Experiment 2 tested whether hippocampal IL-1 is required for the expression of unconditioned heroin immunosuppression. We found that blocking IL-1 signaling in the dorsal hippocampus with IL-1RA during each conditioning session, but not on interspersed non-conditioning days, significantly attenuated the acquisition of heroin conditioned immunosuppression. Strikingly, we found that the same IL-1RA treatment did not alter unconditioned immunosuppression to a single dose of heroin. Thus, IL-1 signaling is not a critical component of the response to heroin but rather may play a role in the formation of the association between heroin and the context. Collectively, these studies suggest that IL-1 signaling, in addition to being involved in the expression of a heroin conditioned immune response, is also involved in the acquisition of this effect. Importantly, this effect is likely not due to blocking the response to the unconditioned stimulus since IL-1RA did not affect heroin's immunosuppressive effects.

Dietary salt regulates uroguanylin expression and signaling activity in the kidney, but not in the intestine

The peptide uroguanylin (Ugn) is expressed at significant levels only in intestine and kidney, and is stored in both tissues primarily (perhaps exclusively) as intact prouroguanylin (proUgn). Intravascular infusion of either Ugn or proUgn evokes well-characterized natriuretic responses in rodents. Furthermore, Ugn knockout mice display hypertension and salt handling deficits, indicating that the Na(+) excretory mechanisms triggered when the peptides are infused into anesthetized animals are likely to operate under normal physiological conditions, and contribute to electrolyte homeostasis in conscious animals. Here, we provide strong corroborative evidence for this hypothesis, by demonstrating that UU gnV (the rate of urinary Ugn excretion) approximately doubled in conscious, unrestrained rats consuming a high-salt diet, and decreased by ~15% after salt restriction. These changes in UU gnV were not associated with altered plasma proUgn levels (shown here to be an accurate index of intestinal proUgn secretion). Furthermore, enteric Ugn mRNA levels were unaffected by salt intake, whereas renal Ugn mRNA levels increased sharply during periods of increased dietary salt consumption. Together, these data suggest that diet-evoked Ugn signals originate within the kidney, rather than the intestine, thus strengthening a growing body of evidence against a widely cited hypothesis that Ugn serves as the mediator of an entero-renal natriuretic signaling axis, while underscoring a likely intrarenal natriuretic role for the peptide. The data further suggest that intrarenal Ugn signaling is preferentially engaged when salt intake is elevated, and plays only a minor role when salt intake is restricted.

High Elmo1 expression aggravates and low Elmo1 expression prevents diabetic nephropathy

Human genome-wide association studies have demonstrated that polymorphisms in the engulfment and cell motility protein 1 gene (ELMO1) are strongly associated with susceptibility to diabetic nephropathy. However, proof of causation is lacking. To test whether modest changes in its expression alter the severity of the renal phenotype in diabetic mice, we have generated mice that are type 1 diabetic because they have the Ins2(Akita) gene, and also have genetically graded expression of Elmo1 in all tissues ranging in five steps from ∼30% to ∼200% normal. We here show that the Elmo1 hypermorphs have albuminuria, glomerulosclerosis, and changes in the ultrastructure of the glomerular basement membrane that increase in severity in parallel with the expression of Elmo 1. Progressive changes in renal mRNA expression of transforming growth factor β1 (TGFβ1), endothelin-1, and NAD(P)H oxidase 4 also occur in parallel with Elmo1, as do the plasma levels of cystatin C, lipid peroxides, and TGFβ1, and erythrocyte levels of reduced glutathione. In contrast, Akita type 1 diabetic mice with below-normal Elmo1 expression have reduced expression of these various factors and less severe diabetic complications. Remarkably, the reduced Elmo1 expression in the 30% hypomorphs almost abolishes the pathological features of diabetic nephropathy, although it does not affect the hyperglycemia caused by the Akita mutation. Thus, ELMO1 plays an important role in the development of type 1 diabetic nephropathy, and its inhibition could be a promising option for slowing or preventing progression of the condition to end-stage renal disease.

IL-1 receptor signaling in the basolateral amygdala modulates binge-like ethanol consumption in male C57BL/6J mice

Proinflammatory cytokines have been implicated in alcohol-induced neurodegeneration, but the role of the neuroimmune system in alcohol related behaviors has only recently come to the forefront. Herein, the effects of binge-like drinking on IL-1β mRNA and immunoreactivity within the amygdala were measured following the "drinking in the dark" (DID) paradigm, a model of binge-like ethanol drinking in C57BL/6J mice. Moreover, the role of IL-1 receptor signaling in the amygdala on ethanol consumption was assessed. Results indicated that a history of binge-like ethanol drinking promoted a significant increase of IL-1β mRNA expression within the amygdala, and immunohistochemistry analyses revealed that the basolateral amygdala (BLA), but not central amygdala (CeA), exhibited significantly increased IL-1β immunoreactivity. However, Fluoro-Jade® C labeling indicated that multiple cycles of the DID paradigm were not sufficient to elicit neuronal death. Bilateral infusions of IL-1 receptor antagonist (IL-1Ra) reduced ethanol consumption when infused into the BLA but not the CeA. These observations were specific to ethanol drinking as the IL-1Ra did not alter either sucrose drinking or open-field locomotor activity. The current findings highlight a specific role for IL-1 receptor signaling in modulating binge-like ethanol consumption and indicate that proinflammatory cytokines can be induced prior to dependence or any evidence of neuronal cell death. These findings provide a framework in which to understand how neuroimmune adaptations may alter ethanol consumption and therein contribute to alcohol abuse.

Fenofibrate unexpectedly induces cardiac hypertrophy in mice lacking MuRF1

The muscle-specific ubiquitin ligase muscle ring finger-1 (MuRF1) is critical in regulating both pathological and physiological cardiac hypertrophy in vivo. Previous work from our group has identified MuRF1's ability to inhibit serum response factor and insulin-like growth factor-1 signaling pathways (via targeted inhibition of cJun as underlying mechanisms). More recently, we have identified that MuRF1 inhibits fatty acid metabolism by targeting peroxisome proliferator-activated receptor alpha (PPARα) for nuclear export via mono-ubiquitination. Since MuRF1-/- mice have an estimated fivefold increase in PPARα activity, we sought to determine how challenge with the PPARα agonist fenofibrate, a PPARα ligand, would affect the heart physiologically. In as little as 3 weeks, feeding with fenofibrate/chow (0.05% wt/wt) induced unexpected pathological cardiac hypertrophy not present in age-matched sibling wild-type (MuRF1+/+) mice, identified by echocardiography, cardiomyocyte cross-sectional area, and increased beta-myosin heavy chain, brain natriuretic peptide, and skeletal muscle α-actin mRNA. In addition to pathological hypertrophy, MuRF1-/- mice had an unexpected differential expression in genes associated with the pleiotropic effects of fenofibrate involved in the extracellular matrix, protease inhibition, hemostasis, and the sarcomere. At both 3 and 8 weeks of fenofibrate treatment, the differentially expressed MuRF1-/- genes most commonly had SREBP-1 and E2F1/E2F promoter regions by TRANSFAC analysis (54 and 50 genes, respectively, of the 111 of the genes >4 and <-4 log fold change; P ≤ .0004). These studies identify MuRF1's unexpected regulation of fenofibrate's pleiotropic effects and bridges, for the first time, MuRF1's regulation of PPARα, cardiac hypertrophy, and hemostasis.

Reductively Responsive Hydrogel Nanoparticles with Uniform Size, Shape, and Tunable Composition for Systemic siRNA Delivery in Vivo

To achieve the great potential of siRNA based gene therapy, safe and efficient systemic delivery in vivo is essential. Here we report reductively responsive hydrogel nanoparticles with highly uniform size and shape for systemic siRNA delivery in vivo. "Blank" hydrogel nanoparticles with high aspect ratio were prepared using continuous particle fabrication based on PRINT (particle replication in nonwetting templates). Subsequently, siRNA was conjugated to "blank" nanoparticles via a disulfide linker with a high loading ratio of up to 18 wt %, followed by surface modification to enhance transfection. This fabrication process could be easily scaled up to prepare large quantity of hydrogel nanoparticles. By controlling hydrogel composition, surface modification, and siRNA loading ratio, siRNA conjugated nanoparticles were highly tunable to achieve high transfection efficiency in vitro. FVII-siRNA conjugated nanoparticles were further stabilized with surface coating for in vivo siRNA delivery to liver hepatocytes, and successful gene silencing was demonstrated at both mRNA and protein levels.

Metabolomics Reveals a Key Role for Fumarate in Mediating the Effects of NADPH Oxidase 4 in Diabetic Kidney Disease

The NADPH oxidase (NOX) isoform NOX4 has been linked with diabetic kidney disease (DKD). However, a mechanistic understanding of the downstream effects of NOX4 remains to be established. We report that podocyte-specific induction of NOX4 in vivo was sufficient to recapitulate the characteristic glomerular changes noted with DKD, including glomerular hypertrophy, mesangial matrix accumulation, glomerular basement membrane thickening, albuminuria, and podocyte dropout. Intervention with a NOX1/NOX4 inhibitor reduced albuminuria, glomerular hypertrophy, and mesangial matrix accumulation in the F1 Akita model of DKD. Metabolomic analyses from these mouse studies revealed that tricarboxylic acid (TCA) cycle-related urinary metabolites were increased in DKD, but fumarate levels were uniquely reduced by the NOX1/NOX4 inhibitor. Expression of fumarate hydratase (FH), which regulates urine fumarate accumulation, was reduced in the diabetic kidney (in mouse and human tissue), and administration of the NOX1/NOX4 inhibitor increased glomerular FH levels in diabetic mice. Induction of Nox4 in vitro and in the podocyte-specific NOX4 transgenic mouse led to reduced FH levels. In vitro, fumarate stimulated endoplasmic reticulum stress, matrix gene expression, and expression of hypoxia-inducible factor-1α (HIF-1α) and TGF-β. Similar upregulation of renal HIF-1α and TGF-β expression was observed in NOX4 transgenic mice and diabetic mice and was attenuated by NOX1/NOX4 inhibition in diabetic mice. In conclusion, NOX4 is a major mediator of diabetes-associated glomerular dysfunction through targeting of renal FH, which increases fumarate levels. Fumarate is therefore a key link connecting metabolic pathways to DKD pathogenesis, and measuring urinary fumarate levels may have application for monitoring renal NOX4 activity.

Low TGFβ1 expression prevents and high expression exacerbates diabetic nephropathy in mice

Nephropathy develops in many but not all patients with long-standing type 1 diabetes. Substantial efforts to identify genotypic differences explaining this differential susceptibility have been made, with limited success. Here, we show that the expression of the transforming growth factor β1 gene (Tgfb1) affects the development of diabetic nephropathy in mice. To do this we genetically varied Tgfb1 expression in five steps, 10%, 60%, 100%, 150%, and 300% of normal, in mice with type 1 diabetes caused by the Akita mutation in the insulin gene (Ins2(Akita)). Although plasma glucose levels were not affected by Tgfb1 genotype, many features of diabetic nephropathy (mesangial expansion, elevated plasma creatinine and urea, decreased creatinine clearance and albuminuria) were progressively ameliorated as Tgfb1 expression decreased and were progressively exacerbated when expression was increased. The diabetic 10% hypomorphs had comparable creatinine clearance and albumin excretion to wild-type mice and no harmful changes in renal morphology. The diabetic 300% hypermorphs had ∼1/3 the creatinine clearance of wild-type mice, >20× their albumin excretion, ∼3× thicker glomerular basement membranes and severe podocyte effacement, matching human diabetic nephropathy. Switching Tgfb1 expression from low to high in the tubules of the hypomorphs increased their albumin excretion more than 10-fold but creatinine clearance remained high. Switching Tgfb1 expression from low to high in the podocytes markedly decreased creatinine clearance, but minimally increased albumin excretion. Decreasing expression of Tgfb1 could be a promising option for preventing loss of renal function in diabetes.

The role of brain interleukin-1 in stress-enhanced fear learning

Posttraumatic stress disorder (PTSD) has been shown to be associated with pro-inflammatory markers, including elevated plasma levels of interleukin-1β (IL-1β). However, the precise role of neuroinflammation and central immune signaling on the development of this debilitating psychological disorder is not known. Here, we used stress-enhanced fear learning (SEFL), an animal model of the disorder, to examine the role of central IL-1β in PTSD. The results show that the severe stressor in SEFL induces a time-dependent increase in IL-1β immunoreactivity and mRNA expression within the dentate gyrus of the dorsal hippocampus (DH). There was no increase in IL-1β in the basolateral amygdala or the perirhinal cortex. Moreover, blocking the action of IL-1β following the severe stressor with IL-1 receptor antagonist (10 μg, intracerebroventricular (i.c.v.), 24 and 48 h after the stressor) prevented the development of SEFL. To provide further support for the role of IL-1β in the development of SEFL, we show that systemic morphine, a treatment which is known to reduce both PTSD and SEFL, also reduces IL-1β expression in the DH induced by the severe stressor. These studies provide the first evidence that IL-1 is involved SEFL and suggest that IL-1 signaling in the brain may have a critical role in the development of PTSD.

Dexamethasone promotes hypertension by allele-specific regulation of the human angiotensinogen gene

The human angiotensinogen (hAGT) gene has polymorphisms in its 2.5-kb promoter that form two haplotype (Hap) blocks: -6A/G (-1670A/G, -1562C/T, and -1561T/C) and -217A/G (-532T/C, -793A/G, -1074T/C, and -1178G/A). Hap -6A/-217A is associated with human hypertension, whereas Hap -6G/-217G reduces cardiovascular risk. Hap -6A/-217A has increased promoter activity with enhanced transcription factor binding, including to the glucocorticoid receptor (GR). Glucocorticoid therapy frequently causes hypertension, the mechanisms for which are incompletely understood. We have engineered double transgenic (TG) mice containing the human renin gene with either Hap of the hAGT gene and examined the physiological significance of glucocorticoid-mediated allele-specific regulation of the hAGT gene. We have also studied the consequential effects on the renin angiotensin system and blood pressure. TG mice with Hap -6A and -6G were treated with and without a low dose of a GR agonist, dexamethasone (2.5 μg/ml), for 72 h. We found greater chromatin-GR binding with increased GR agonist-induced hAGT expression in liver and renal tissues of Hap -6A mice. Additionally, dexamethasone treatment increased circulating hAGT and angiotensin II levels in Hap -6A mice, as compared with -6G mice. Importantly, GR agonist significantly increased blood pressure and redox markers in TG mice with Hap-6A of the hAGT gene. Taken together, our results show, for the first time, that glucocorticoids affect hAGT expression in a haplotype-dependent fashion with SNPs in Hap -6A favoring agonist-induced GR binding. This leads to increased expression of the hAGT, up-regulation of the renin angiotensin system, and increased blood pressure and oxidative stress in Hap -6A mice.

Novel mechanism of impaired function of organic anion-transporting polypeptide 1B3 in human hepatocytes: post-translational regulation of OATP1B3 by protein kinase C activation

The organic anion-transporting polypeptide (OATP) 1B3 is a membrane transport protein that mediates hepatic uptake of many drugs and endogenous compounds. Currently, determination of OATP-mediated drug-drug interactions in vitro is focused primarily on direct substrate inhibition. Indirect inhibition of OATP1B3 activity is under-appreciated. OATP1B3 has putative protein kinase C (PKC) phosphorylation sites. Studies were designed to determine the effect of PKC activation on OATP1B3-mediated transport in human hepatocytes using cholecystokinin-8 (CCK-8), a specific OATP1B3 substrate, as the probe. A PKC activator, phorbol-12-myristate-13-acetate (PMA), did not directly inhibit [(3)H]CCK-8 accumulation in human sandwich-cultured hepatocytes (SCH). However, pretreatment with PMA for as little as 10 minutes rapidly decreased [(3)H]CCK-8 accumulation. Treatment with a PKC inhibitor bisindolylmaleimide (BIM) I prior to PMA treatment blocked the inhibitory effect of PMA, indicating PKC activation is essential for downregulating OATP1B3 activity. PMA pretreatment did not affect OATP1B3 mRNA or total protein levels. To determine the mechanism(s) underlying the indirect inhibition of OATP1B3 activity upon PKC activation, adenoviral vectors expressing FLAG-Myc-tagged OATP1B3 (Ad-OATP1B3) were transduced into human hepatocytes; surface expression and phosphorylation of OATP1B3 were determined by biotinylation and by an anti-phosphor-Ser/Thr/Tyr antibody, respectively. PMA pretreatment markedly increased OATP1B3 phosphorylation without affecting surface or total OATP1B3 protein levels. In conclusion, PKC activation rapidly decreases OATP1B3 transport activity by post-translational regulation of OATP1B3. These studies elucidate a novel indirect inhibitory mechanism affecting hepatic uptake mediated by OATP1B3, and provide new insights into predicting OATP-mediated drug interactions between OATP substrates and kinase modulator drugs/endogenous compounds.

Guanylyl cyclase/natriuretic peptide receptor-A signaling antagonizes phosphoinositide hydrolysis, Ca(2+) release, and activation of protein kinase C

Thus far, three related natriuretic peptides (NPs) and three distinct sub-types of cognate NP receptors have been identified and characterized based on the specific ligand binding affinities, guanylyl cyclase activity, and generation of intracellular cGMP. Atrial and brain natriuretic peptides (ANP and BNP) specifically bind and activate guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA), and C-type natriuretic peptide (CNP) shows specificity to activate guanylyl cyclase/natriuretic peptide receptor-B (GC-B/NPRB). All three NPs bind to natriuretic peptide receptor-C (NPRC), which is also known as clearance or silent receptor. The NPRA is considered the principal biologically active receptor of NP family; however, the molecular signaling mechanisms of NP receptors are not well understood. The activation of NPRA and NPRB produces the intracellular second messenger cGMP, which serves as the major signaling molecule of all three NPs. The activation of NPRB in response to CNP also produces the intracellular cGMP; however, at lower magnitude than that of NPRA, which is activated by ANP and BNP. In addition to enhanced accumulation of intracellular cGMP in response to all three NPs, the levels of cAMP, Ca²⁺ and inositol triphosphate (IP₃) have also been reported to be altered in different cells and tissue types. Interestingly, ANP has been found to lower the concentrations of cAMP, Ca²⁺, and IP₃; however, NPRC has been proposed to increase the levels of these metabolic signaling molecules. The mechanistic studies of decreased and/or increased levels of cAMP, Ca²⁺, and IP₃ in response to NPs and their receptors have not yet been clearly established. This review focuses on the signaling mechanisms of ANP/NPRA and their biological effects involving an increased level of intracellular accumulation of cGMP and a decreased level of cAMP, Ca²⁺, and IP₃ in different cells and tissue systems.

Inhibition of CaMKII does not attenuate cardiac hypertrophy in mice with dysfunctional ryanodine receptor

In cardiac muscle, the release of calcium ions from the sarcoplasmic reticulum through ryanodine receptor ion channels (RyR2s) leads to muscle contraction. RyR2 is negatively regulated by calmodulin (CaM) and by phosphorylation of Ca²⁺/CaM-dependent protein kinase II (CaMKII). Substitution of three amino acid residues in the CaM binding domain of RyR2 (RyR2-W3587A/L3591D/F3603A, RyR2^ADA) impairs inhibition of RyR2 by CaM and results in cardiac hypertrophy and early death of mice carrying the RyR2^ADA mutation. To test the cellular function of CaMKII in cardiac hypertrophy, mutant mice were crossed with mice expressing the CaMKII inhibitory AC3-I peptide or the control AC3-C peptide in the myocardium. Inhibition of CaMKII by AC3-I modestly reduced CaMKII-dependent phosphorylation of RyR2 at Ser-2815 and markedly reduced CaMKII-dependent phosphorylation of SERCA2a regulatory subunit phospholamban at Thr-17. However the average life span and heart-to-body weight ratio of Ryr2^ADA/ADA mice expressing the inhibitory peptide were not altered compared to control mice. In Ryr2^ADA/ADA homozygous mice, AC3-I did not alter cardiac morphology, enhance cardiac function, improve sarcoplasmic reticulum Ca²⁺ handling, or suppress the expression of genes implicated in cardiac remodeling. The results suggest that CaMKII was not required for the rapid development of cardiac hypertrophy in Ryr2^ADA/ADA mice.

Local renal circadian clocks control fluid-electrolyte homeostasis and BP

The circadian timing system is critically involved in the maintenance of fluid and electrolyte balance and BP control. However, the role of peripheral circadian clocks in these homeostatic mechanisms remains unknown. We addressed this question in a mouse model carrying a conditional allele of the circadian clock gene Bmal1 and expressing Cre recombinase under the endogenous Renin promoter (Bmal1(lox/lox)/Ren1(d)Cre mice). Analysis of Bmal1(lox/lox)/Ren1(d)Cre mice showed that the floxed Bmal1 allele was excised in the kidney. In the kidney, BMAL1 protein expression was absent in the renin-secreting granular cells of the juxtaglomerular apparatus and the collecting duct. A partial reduction of BMAL1 expression was observed in the medullary thick ascending limb. Functional analyses showed that Bmal1(lox/lox)/Ren1(d)Cre mice exhibited multiple abnormalities, including increased urine volume, changes in the circadian rhythm of urinary sodium excretion, increased GFR, and significantly reduced plasma aldosterone levels. These changes were accompanied by a reduction in BP. These results show that local renal circadian clocks control body fluid and BP homeostasis.

Programmable mechanobioreactor for exploration of the effects of periodic vibratory stimulus on mesenchymal stem cell differentiation

A programmable bioreactor using a voice-coil actuator was developed to enable research on the effects of periodic vibratory stimulus on human and porcine mesenchymal stem cells (MSCs). We hypothesized that low frequency vibrations would result in a cartilage phenotype and higher frequency vibrations would result in a bone phenotype. The mechanical stimulation protocol is adjusted from a computer external to the incubator via a USB cable. Once programmed, the embedded microprocessor and sensor system on the bioreactor execute the protocol independent of the computer. In each test, a sinusoidal stimulus was applied to a culture plate in 1-min intervals with a 15-min rest following each, for a total of 15 h per day for 10 days. Frequencies of 1 and 100 Hz were applied to cultures of both human and porcine umbilical cord–derived MSCs. Chondrogenesis was determined by Alcian blue staining for glycosaminoglycans and an increased differentiation index (ratio of mRNA for collagen II and collagen I). Osteogenic differentiation was indicated with Alizarin red for calcium staining and increased bone morphogenetic protein 2 mRNA. One-hertz stimulation resulted in a cartilage phenotype for both human and porcine MSCs, while 100-Hz stimulation resulted in a bone phenotype.

An experimental approach to evaluate the impact of impaired transport function on hepatobiliary drug disposition using Mrp2-deficient TR- rat sandwich-cultured hepatocytes in combination with Bcrp knockdown

Breast cancer resistance protein (BCRP) and multidrug resistance-associated protein 2 (MRP2) are members of the ATP binding cassette (ABC) transporter family located in the canalicular membrane of hepatocytes that mediate biliary excretion of many drugs and endogenous compounds. BCRP and MRP2 have overlapping substrate profiles. Predicting drug disposition in the setting of altered transport function has important clinical significance. This investigation was designed to establish an in vitro model system to evaluate the impact of impaired Mrp2 and Bcrp function on hepatobiliary drug disposition. To achieve Bcrp knockdown by RNA interference (RNAi), sandwich-cultured hepatocytes (SCH) from Mrp2-deficient (TR(-)) and wild-type (WT) rats were infected with adenoviral vectors to express shRNA targeting Bcrp (Ad-siBcrp) at multiplicity of infection (MOI) of 1-10. MOI of 5 was identified as optimal. At MOI of 5, viral infection as well as WT or TR(-) status was statistically significant predictors of the rosuvastatin (RSV) biliary excretion index (BEI), consistent with the known role of Bcrp and Mrp2 in the biliary excretion of RSV in vivo in rats. Relative to WT rat SCH, marginal mean BEI (%) of RSV in TR(-) rat SCH decreased by 28.6 (95% CI: 5.8-51.3). Ad-siBcrp decreased marginal mean BEI (%) of RSV by 13.3 (7.5-9.1) relative to SCH infected with adenoviral vectors expressing a nontargeting shRNA (Ad-siNT). The BEI of RSV was almost ablated in TR(-) rat SCH with Bcrp knockdown (5.9 ± 3.0%) compared to Ad-siNT-infected WT rat SCH (45.4 ± 6.6%). These results demonstrated the feasibility of Bcrp knockdown in TR(-) rat SCH as an in vitro system to assess the impact of impaired Bcrp and Mrp2 function. At MOI of 5, viral infection had minimal effects on RSV total accumulation, but significantly decreased marginal mean taurocholate total accumulation (pmol/mg of protein) and BEI (%) by 9.9 (7.0-12.8) and 7.5 (3.7-11.3), respectively, relative to noninfected SCH. These findings may be due to off-target effects on hepatic bile acid transporters, even though no changes in protein expression levels of the hepatic bile acid transporters were observed. This study established a strategy for optimization of the knockdown system, and demonstrated the potential use of RNAi in SCH as an in vitro tool to predict altered hepatobiliary drug disposition when canalicular transporters are impaired.

RGS21, a regulator of taste and mucociliary clearance?

OBJECTIVES/HYPOTHESIS

Motile cilia of airway epithelial cells help to expel harmful inhaled material. Activation of bitterant-responsive G protein-coupled receptors (GPCRs) is believed to potentiate cilia beat frequency and mucociliary clearance. In this study, we investigated whether regulator of G protein signaling-21 (RGS21) has the potential to modulate signaling pathways connected to airway mucociliary clearance, given that RGS proteins modulate GPCR signaling by acting as GTPase-accelerating proteins (GAPs) for the Gα subunits of heterotrimeric G proteins.

STUDY DESIGN

This is a pilot investigation to determine if RGS21, a potential tastant specific RGS gene, is expressed in sinonasal mucosa, and to determine its specific Gα substrate using in vitro biochemical assays with purified proteins.

METHODS

Rgs21 expression in sinonasal mucosa was determined using quantitative, real-time PCR and a transgenic mouse expressing RFP from the Rgs21 promoter. Rgs21 was cloned, over-expressed, and purified using multistep protein chromatography. Biochemical and biophysical assays were used to determine if RGS21 could bind and accelerate the hydrolysis of GTP on heterotrimeric Gα subunits.

RESULTS

Rgs21 was expressed in sinonasal mucosa and lingual epithelium. Purified recombinant protein directly bound and accelerated GTP hydrolysis on Gα subunits.

CONCLUSIONS

Rgs21 is expressed in sinonasal mucosa, is amenable to purification as a recombinant protein, and can bind to Gα(i/o/q) subunits. Furthermore, RGS21 can accelerate the hydrolysis rate of GTP on Gαi subunits. This provides evidence that RGS21 may be a negative regulator of bitterant responses. Future studies will be needed to determine the physiological role of this protein in mucociliary clearance.

Connective tissue growth factor (CTGF) expression modulates response to high glucose

Connective tissue growth factor (CTGF) is an important mediator of fibrosis; emerging evidence link changes in plasma and urinary CTGF levels to diabetic kidney disease. To further ascertain the role of CTGF in responses to high glucose, we assessed the consequence of 4 months of streptozotocin-induced diabetes in wild type (+/+) and CTGF heterozygous (+/−) mice. Subsequently, we studied the influence of glucose on gene expression and protein in mice embryonic fibroblasts (MEF) cells derived from wildtype and heterozygous mice. At study initiation, plasma glucose, creatinine, triglyceride and cholesterol levels were similar between non-diabetic CTGF+/+ and CTGF+/− mice. In the diabetic state, plasma glucose levels were increased in CTGF+/+ and CTGF+/− mice (28.2 3.3 mmol/L vs 27.0 3.1 mmol/L), plasma triglyceride levels were lower in CTGF+/− mice than in CTGF+/+ (0.7 0.2 mmol/L vs 0.5 0.1 mmol/L, p<0.05), but cholesterol was essentially unchanged in both groups. Plasma creatinine was higher in diabetic CTGF+/+ group (11.7±1.2 vs 7.9±0.6 µmol/L p<0.01), while urinary albumin excretion and mesangial expansion were reduced in diabetic CTGF+/− animals. Cortices from diabetic mice (both CTGF +/+ and CTGF +/−) manifested higher expression of CTGF and thrombospondin 1 (TSP1). Expression of nephrin was reduced in CTGF +/+ animals; this reduction was attenuated in CTGF+/− group. In cultured MEF from CTGF+/+ mice, glucose (25 mM) increased expression of pro-collagens 1, IV and XVIII as well as fibronectin and thrombospondin 1 (TSP1). In contrast, activation of these genes by high glucose was attenuated in CTGF+/− MEF. We conclude that induction of Ctgf mediates expression of extracellular matrix proteins in diabetic kidney. Thus, genetic variability in CTGF expression directly modulates the severity of diabetic nephropathy.

Ketamine does not produce relief of neuropathic pain in mice lacking the β-common receptor (CD131)

Neuropathic pain (NP) is a debilitating condition associated with traumatic, metabolic, autoimmune and neurological etiologies. Although the triggers for NP are diverse, there are common underlying pathways, including activation of immune cells in the spinal cord and up-regulation of the N-methyl-D-aspartate receptor (NMDAR). Ketamine, a well-known NDMAR antagonist, reduces neuropathic pain in a sustained manner. Recent study has shown that the novel 11-amino acid peptide erythropoietin derivative ARA290 produces a similar, long-lasting relief of NP. Here, we show that both drugs also have similar effects on the expression of mRNA of the NMDAR, as well as that of microglia, astrocytes and chemokine (C-C motif) ligand 2, all-important contributors to the development of NP. Although the effects of ketamine and ARA 290 on NP and its molecular mediators suggest a common mechanism of action, ARA 290 has no affinity for the NMDAR and acts specifically via the innate repair receptor (IRR) involved in tissue protection. We speculated therefore, that the IRR might be critically involved in the action of ketamine on neuropathic pain. To evaluate this, we studied the effects of ketamine and ARA 290 on acute pain, side effects, and allodynia following a spared nerve injury model in mice lacking the β-common receptor (βcR), a structural component of the IRR. Ketamine (50 mg/kg) and ARA 290 (30 µg/kg) produced divergent effects on acute pain: ketamine produced profound antinociception accompanied with psychomotor side effects, but ARA290 did not, in both normal and knock out mice. In contrast, while both drugs were antiallodynic in WT mice, they had no effect on NP in mice lacking the βcR. Together, these results show that an intact IRR is required for the effective treatment of NP with either ketamine or ARA 290, but is not involved in ketamine’s analgesic and side effects.

Codelivery of VEGF siRNA and gemcitabine monophosphate in a single nanoparticle formulation for effective treatment of NSCLC

There is an urgent need for new therapeutics for the treatment of aggressive and metastatic refractory human non-small-cell lung cancer (NSCLC). Antiangiogenesis therapy and chemotherapy are the two major treatment options. Unfortunately, both types of therapies when used individually have their disadvantages. Integrating antiangiogenesis therapy with chemotherapy is expected to target the tumor's vascular endothelial cells and the tumor cells simultaneously. In this study, we coformulated Vascular endothelial growth factor (VEGF) siRNA targeting VEGFs and gemcitabine monophosphate (GMP) into a single cell-specific, targeted lipid/calcium/phosphate (LCP) nanoparticle formulation. Antitumor effect of the combination therapy using LCP loaded with both VEGF siRNA and GMP was evaluated in both subcutaneous and orthotopic xenograft models of NSCLC with systemic administration. The improved therapeutic response, as compared with either VEGF siRNA or GMP therapy alone, was supported by the observation of 30-40% induction of tumor cell apoptosis, eightfold reduction of tumor cell proliferation and significant decrease of tumor microvessel density (MVD). The combination therapy led to dramatic inhibition of tumor growth, with little in vivo toxicity. In addition, the current studies demonstrated the possibility of incorporating multiple nucleic acid molecules and phosphorylated small-molecule drugs, targeting to different pathways, into a single nanoparticle formulation for profound therapeutic effect.

MicroRNA-22 and promoter motif polymorphisms at the Chga locus in genetic hypertension: functional and therapeutic implications for gene expression and the pathogenesis of hypertension

Hypertension is a common hereditary syndrome with unclear pathogenesis. Chromogranin A (Chga), which catalyzes formation and cargo storage of regulated secretory granules in neuroendocrine cells, contributes to blood pressure homeostasis centrally and peripherally. Elevated Chga occurs in spontaneously hypertensive rat (SHR) adrenal glands and plasma, but central expression is unexplored. In this report, we measured SHR and Wistar-Kyoto rat (control) Chga expression in central and peripheral nervous systems, and found Chga protein to be decreased in the SHR brainstem, yet increased in the adrenal and the plasma. By re-sequencing, we systematically identified five promoter, two coding and one 3'-untranslated region (3'-UTR) polymorphism at the SHR (versus WKY or BN) Chga locus. Using HXB/BXH recombinant inbred (RI) strain linkage and correlations, we demonstrated genetic determination of Chga expression in SHR, including a cis-quantitative trait loci (QTLs) (i.e. at the Chga locus), and such expression influenced biochemical determinants of blood pressure, including a cascade of catecholamine biosynthetic enzymes, catecholamines themselves and steroids. Luciferase reporter assays demonstrated that the 3'-UTR polymorphism (which disrupts a microRNA miR-22 motif) and promoter polymorphisms altered gene expression consistent with the decline in SHR central Chga expression. Coding region polymorphisms did not account for changes in Chga expression or function. Thus, we hypothesized that the 3'-UTR and promoter mutations lead to dysregulation (diminution) of Chga in brainstem cardiovascular control nuclei, ultimately contributing to the pathogenesis of hypertension in SHR. Accordingly, we demonstrated that in vivo administration of miR-22 antagomir to SHR causes substantial (∼18 mmHg) reductions in blood pressure, opening a novel therapeutic avenue for hypertension.

Cardiac hypertrophy associated with impaired regulation of cardiac ryanodine receptor by calmodulin and S100A1

The cardiac ryanodine receptor (RyR2) is inhibited by calmodulin (CaM) and S100A1. Simultaneous substitution of three amino acid residues (W3587A, L3591D, F3603A; RyR2ADA) in the CaM binding domain of RyR2 results in loss of CaM inhibition at submicromolar (diastolic) and micromolar (systolic) Ca²⁺, cardiac hypertrophy, and heart failure in Ryr2ADA/ADA mice. To address whether cardiac hypertrophy results from the elimination of CaM and S100A1 inhibition at diastolic or systolic Ca²⁺, a mutant mouse was generated with a single RyR2 amino acid substitution (L3591D; RyR2D). Here we report that in single-channel measurements RyR2-L3591D isolated from Ryr2D/D hearts lost CaM inhibition at diastolic Ca²⁺ only, whereas S100A1 regulation was eliminated at both diastolic and systolic Ca²⁺. In contrast to the ~2-wk life span of Ryr2ADA/ADA mice, Ryr2D/D mice lived longer than 1 yr. Six-month-old Ryr2D/D mice showed a 9% increase in heart weight-to-body weight ratio, modest changes in cardiac morphology, and a twofold increase in atrial natriuretic peptide mRNA levels compared with wild type. After 4-wk pressure overload with transverse aortic constriction, heart weight-to-body weight ratio and atrial natriuretic peptide mRNA levels increased and echocardiography showed changes in heart morphology of Ryr2D/D mice compared with sham-operated mice. Collectively, the findings indicate that the single RyR2-L3591D mutation, which distinguishes the effects of diastolic and systolic Ca²⁺, alters heart size and cardiac function to a lesser extent in Ryr2D/D mice than the triple mutation in Ryr2ADA/ADA mice. They further suggest that CaM inhibition of RyR2 at systolic Ca²⁺ is important for maintaining normal cardiac function.

Mefloquine exposure induces cell cycle delay and reveals stage-specific expression of the pfmdr1 gene

Drug-resistant Plasmodium falciparum malaria is a major public health problem. An elevated pfmdr1 gene copy number (CN) is known to decrease parasite sensitivity to the commonly used antimalarial mefloquine (MFQ). To understand the relationship between pfmdr1 CN and mefloquine resistance, we evaluated pfmdr1 transcript levels in three P. falciparum strains with different CNs in the presence and absence of MFQ. Parasite strains with multiple pfmdr1 gene copies exhibited higher relative transcript levels than single-copy parasites, and MFQ induced pfmdr1 expression above the levels without treatment in all three strains evaluated. Concomitant morphology analyses of the sampled cultures revealed that MFQ treatment of synchronized ring-stage parasites induced a delay in parasite maturation through the intraerythrocytic cycle. pfmdr1 expression peaks in the ring stage, and MFQ could be causing increased transcription by delaying parasite maturation. However, pretreatment with mefloquine did not affect the artemisinin in vitro half-maximal inhibitory concentration (IC(50)). These results suggest that MFQ-induced increases in pfmdr1 expression are the direct result of the maturation delay at the ring stage but that this change in expression does not affect the antimalarial activity of artemisinin.

Lack of association of A-6G polymorphism of AGT gene with essential hypertension in the Chinese population

BACKGROUND

The angiotensinogen (AGT) A-6G gene polymorphism has been indicated to be related to the susceptibility of essential hypertension. However, the results are still unclear.

OBJECTIVE AND METHODS

To survey the relationship between AGT A-6G gene polymorphism and essential hypertension, 18 separate studies with 9306 patients were analyzed through meta-analysis. The random-effect model was used to calculate the pooled odds ratio (OR) and its corresponding 95% confidence interval (CI).

RESULTS

In this AGT A-6G gene polymorphism and essential hypertension meta-analysis of the Chinese population, the distribution of the G-allele frequency was 0.23 for the essential hypertension group and 0.21 for the control group. The association between the AGT A-6G gene polymorphism and essential hypertension in the entire sample population was not significant. The pooled OR for the frequency of the G allele was 1.10 (95% CI 0.96 to 1.27, Pheterogeneity < 0.00001, P = 0.17). In the stratified analysis by ethnicity, a significant association in Li and Mongolian ethnicities (P ≤ 0.05) was achieved. However, no significant association was found in other ethnicities such as Han, Tibetan, Kazakh, Bai and Yi (P > 0.05).

CONCLUSIONS

The current meta-analysis suggested that AGT A-6G gene polymorphism might not be related to the increased risk of essential hypertension in the entire Chinese population. However, the G-allele of AGT A-6G might predispose to essential hypertension in the Li and Mongolian ethnicities.

Human thrombomodulin knock-in mice reveal differential effects of human thrombomodulin on thrombosis and atherosclerosis

OBJECTIVE

We sought to develop a murine model to examine the antithrombotic and antiinflammatory functions of human thrombomodulin in vivo.

METHODS AND RESULTS

Knock-in mice that express human thrombomodulin from the murine thrombomodulin gene locus were generated. Compared with wild-type mice, human thrombomodulin knock-in mice exhibited decreased protein C activation in the aorta (P<0.01) and lung (P<0.001). Activation of endogenous protein C following infusion of thrombin was decreased by 90% in knock-in mice compared with wild-type mice (P<0.05). Carotid artery thrombosis induced by photochemical injury occurred more rapidly in knock-in mice (12±3 minutes) than in wild-type mice (31±6 minutes; P<0.05). No differences in serum cytokine levels were detected between knock-in and wild-type mice after injection of endotoxin. When crossed with apolipoprotein E-deficient mice and fed a Western diet, knock-in mice had a further decrease in protein C activation but did not exhibit increased atherosclerosis.

CONCLUSION

Expression of human thrombomodulin in place of murine thrombomodulin produces viable mice with a prothrombotic phenotype but unaltered responses to systemic inflammatory or atherogenic stimuli. This humanized animal model will be useful for investigating the function of human thrombomodulin under pathophysiological conditions in vivo.

Reduced expression of lipoic acid synthase accelerates diabetic nephropathy

Oxidative stress contributes to the pathogenesis of diabetic nephropathy. In mitochondria, lipoic acid synthase produces α-lipoic acid, an antioxidant and an essential cofactor in α-ketoacid dehydrogenase complexes, which participate in glucose oxidation and ATP generation. Administration of lipoic acid abrogates diabetic nephropathy in animal models, but whether lower production of endogenous lipoic acid promotes diabetic nephropathy is unknown. Here, we crossed mice heterozygous for lipoic acid synthase deficiency (Lias(+/-)) with Ins2(Akita/+) mice, a well characterized model of type 1 diabetes. Double mutant mice had more overt diabetic nephropathy, including microalbuminuria, glomerular basement thickening, mesangial matrix expansion, and hypertension, compared with Lias(+/+)Ins2(Akita/+) controls. We also identified proximal tubules as a major site for generation of superoxide anions during diabetic nephropathy. Mitochondria in proximal tubular cells were particularly sensitive to damage in diabetic mice with reduced lipoic acid production. These results suggest that lipoic acid synthase deficiency increases oxidative stress and accelerates the development of diabetic nephropathy.

AMPK mediates the initiation of kidney disease induced by a high-fat diet

The mechanisms underlying the association between obesity and progressive renal disease are not well understood. Exposure to a high-fat diet decreases levels of the cellular energy sensor AMPK in many organs, including the kidney, but whether AMPK contributes to the pathophysiology of kidney disease induced by a high-fat diet is unknown. In this study, we randomly assigned C57BL/6J mice to a standard or high-fat diet. After 1 week, mice fed a high-fat diet exhibited an increase in body weight, renal hypertrophy, an increase in urine H(2)O(2) and urine MCP-1, and a decrease in circulating adiponectin levels and renal AMPK activity. Urine ACR progressively increased after 4 weeks of a high-fat diet. After 12 weeks, kidneys of mice fed a high-fat diet demonstrated a marked increase in markers of fibrosis and inflammation, and AMPK activity remained significantly suppressed. To determine whether inhibition of AMPK activity explained these renal effects, we administered an AMPK activator along with a high-fat diet for 1 week. Although AMPK activation did not abrogate the weight gain, it reduced the renal hypertrophy, urine H(2)O(2), and urine and renal MCP-1. In vitro, AMPK activation completely inhibited the induction of MCP-1 by palmitic acid in mesangial cells. In conclusion, these data suggest that the energy sensor AMPK mediates the early renal effects of a high-fat diet.

Analysis of human auricular cartilage to guide tissue-engineered nanofiber-based chondrogenesis: implications for microtia reconstruction

OBJECTIVE

Nanofiber-supported, in vitro-generated cartilage may represent an optimal starting material for the development of a cartilage implant for use in microtia reconstruction. To do so, the authors aim to first characterize the molecular composition of endogenous auricular cartilage and determine if human umbilical cord mesenchymal stem cells (hUCMSCs) can be differentiated into cartilage in vitro.

STUDY DESIGN

Prospective, controlled.

SETTING

Academic research laboratory.

SUBJECTS AND METHODS

Human ear cartilage from normal adults, pediatric patients with microtia, and pediatric patients with preauricular appendages (n = 2) was analyzed for collagens I, II, and X and elastin expression. In parallel, hUCMSCs were cultured on either polycaprolactone (PCL) or D, L-lactide-co-glycolic acid (PLGA) nanofiber scaffolds for 21 days under chondrogenic conditions. Cells were harvested for histologic, biochemical, and quantitative polymerase chain reaction analysis. Control cells were grown under both chondrogenic and nonchondrogenic conditions in the absence of nanofiber scaffolds.

RESULTS

Histological analysis of human ear cartilage revealed similar levels and distribution of collagens I and X and elastin. Collagen II was not highly expressed in the microtia samples. hUCMSC cultures stained positively for glycosaminosglycans (GAG) and sulfated proteoglycans. Compared to control cells, hUCMSCs grown on PLGA nanofiber scaffolds had a higher differentiation index (P ≤ .012) and higher levels of collagen X mRNA expression (P ≤ .006).

CONCLUSION

These data provide information regarding the composition of endogenous ear cartilage and suggest that hUCMSCs grown on PLGA nanofiber scaffolds may represent an optimal starting material for the development of a cartilage implant for use in microtia reconstruction.

A major role for the EP4 receptor in regulation of renin

Prostaglandins have been implicated as paracrine regulators of renin secretion, but the specific pathways and receptor(s) carrying out these functions have not been fully elucidated. To examine the contributions of prostanoid synthetic pathways and receptors to regulation of renin in the intact animal, we used a panel of mice with targeted disruption of several key genes: cyclooxygenase-2 (COX-2), microsomal PGE synthases 1 and 2 (mPGES1, mPGES2), EP2 and EP4 receptors for PGE(2), and the IP receptor for PGI(2). To activate the macula densa signal for renin stimulation, mice were treated with furosemide over 5 days and renin mRNA levels were determined by real-time RT-PCR. At baseline, there were no differences in renin mRNA levels between wild-type and the various strains of mutant mice. Furosemide caused marked stimulation of renin mRNA expression across all groups of wild-type control mice. This response was completely abrogated in the absence of COX-2, but was unaffected in mice lacking mPGES1 or mPGES2. The absence of G(s)/cAMP-linked EP2 receptors had no effect on stimulation of renin by furosemide and there was only a modest, insignificant reduction in renin responses in mice lacking the IP receptor. By contrast, renin stimulation in EP4(-/-) mice was significantly reduced by ∼70% compared with wild-type controls. These data suggest that stimulation of renin by the macula densa mechanism is mediated by PGE(2) through a pathway requiring COX-2 and the EP4 receptor, but not EP2 or IP receptors. Surprisingly, mPGES1 or mPGES2 are not required, suggesting other alternative mechanisms for generating PGE(2) in response to macula densa stimulation.

Role of the USF1 transcription factor in diabetic kidney disease

The predominant transcription factors regulating key genes in diabetic kidney disease have not been established. The transcription factor upstream stimulatory factor 1 (USF1) is an important regulator of glucose-mediated transforming growth factor (TGF)-β1 expression in mesangial cells; however, its role in the development of diabetic kidney disease has not been evaluated. In the present study, wild-type (WT; USF1 +/+), heterozygous (USF1 +/-), and homozygous (USF1 -/-) knockout mice were intercrossed with Akita mice (Ins2/Akita) to induce type 1 diabetes. Mice were studied up to 36 wk of age. The degree of hyperglycemia and kidney hypertrophy were similar in all groups of diabetic mice; however, the USF1 -/- diabetic mice had significantly less albuminuria and mesangial matrix expansion than the WT diabetic mice. TGF-β1 and renin gene expression and protein were substantially increased in the WT diabetic mice but not in USF1 -/- diabetic mice. The underlying pathway by which USF1 is regulated by high glucose was investigated in mesangial cell culture. High glucose inhibited AMP-activated protein kinase (AMPK) activity and increased USF1 nuclear translocation. Activation of AMPK with AICAR stimulated AMPK activity and reduced nuclear accumulation of USF1. We thus conclude that USF1 is a critical transcription factor regulating diabetic kidney disease and plays a critical role in albuminuria, mesangial matrix accumulation, and TGF-β1 and renin stimulation in diabetic kidney disease. AMPK activity may play a key role in high glucose-induced regulation of USF1.

STT3A, C1orf24, TFF3: putative markers for characterization of follicular thyroid neoplasms from fine-needle aspirates

OBJECTIVES/HYPOTHESIS

The goals of this study were to characterize gene expression using fine-needle aspirates (FNAs) from follicular neoplasms to distinguish follicular adenomas (FAs) from follicular thyroid carcinomas (FTCs) and follicular variant of papillary thyroid carcinomas (FVPTCs); and to use FNA material to distinguish benign from malignant follicular neoplasms.

STUDY DESIGN

Retrospective expression analysis of diagnosed follicular neoplasms (level of evidence 2b); prospective cohort of FNA from the operating room after thyroid lobectomy (level of evidence 1b).

METHODS

Gene expression analysis via reverse-transcription polymerase chain reaction (rt-PCR) of nine genes previously noted to be differentially expressed in follicular neoplasms was performed on formalin-fixed, paraffin-embedded archived normal thyroid tissue (n = 63) and follicular neoplasms as diagnosed on preoperative FNA: FA (n = 16), FTC (n = 13), FVPTC (n = 24), and papillary thyroid carcinomas (PTCs) (n = 10). All cases were originally read as follicular neoplasms on preoperative FNA. To determine if these results could be translated into fresh tissue, ex vivo FNA was performed on follicular neoplasms (n = 17) in the operating room after thyroidectomy.

RESULTS

Quantitative gene analysis detected differential TFF3 expression in FA versus FTC, FVPTC, and PTC (P = .02). Rt-PCR of FNA samples demonstrated that malignant nodules overexpress STT3A as compared with benign disease (P = .046). The combination of STT3A overexpression/Clorf24 underexpression identified malignant disease (P = .03) on FNA samples.

CONCLUSIONS

Gene-expression data suggest a difference in expression between STT3A, Clorf24, and TFF3 in FAs versus carcinomas that may be detected from an FNA sample. Findings must be validated from preoperative FNAs in larger numbers.

Systems biology and heart failure: concepts, methods, and potential research applications

Dramatic advances in molecular biology dominated twentieth century biomedical science and delineated the function of individual genes and molecules in exquisite detail. However, biological processes cannot be fully understood based on the properties of individual genes and molecules alone, since these elements act in concert to enable the specific functions that make for living cells and organisms. The discipline of systems biology provides a novel conceptual framework for understanding biological phenomenon. Systems biology synthesizes information concerning the interactions of genes and molecules and allows characterization of the supramolecular networks and functional modules that represent the most essential aspects of cell organization and physiology.

Dysfunctional ryanodine receptor and cardiac hypertrophy: role of signaling molecules

Mice with three amino acid mutations in the calmodulin binding domain of type-2 ryanodine receptor ion channel (Ryr2(ADA/ADA) mice) have impaired intracellular Ca(2+) handling and cardiac hypertrophy with death at an early age. In this report, the role of signaling molecules implicated in cardiac hypertrophy of Ryr2(ADA/ADA) mice was investigated. Calcineurin A-β (CNA-β) and nuclear factor of activated T cell (NFAT) signaling were monitored in mice carrying either luciferase transgene driven by NFAT-dependent promoter or knockout of CNA-β. NFAT transcriptional activity in Ryr2(ADA/ADA) hearts was not markedly upregulated at embryonic day 16.5 compared with wild-type but significantly increased at postnatal days 1 and 10. Ablation of CNA-β extended the life span of Ryr2(ADA/ADA) mice and enhanced cardiac function without improving sarcoplasmic reticulum Ca(2+) handling or suppressing the expression of genes implicated in cardiac hypertrophy. Embryonic day 16.5 Ryr2(ADA/ADA) mice had normal heart weights with no major changes in Akt1 and class II histone deacetylase phosphorylation and myocyte enhancer factor-2 activity. In contrast, phosphorylation levels of Erk1/2, p90 ribosomal S6 kinases (p90RSKs), and GSK-3β were increased in hearts of embryonic day 16.5 homozygous mutant mice. The results indicate that an impaired calmodulin regulation of RyR2 was neither associated with an altered CNA-β/NFAT, class II histone deacetylase (HDAC)/MEF2, nor Akt signaling in embryonic day 16.5 hearts; rather increased Erk1/2 and p90RSK phosphorylation levels likely leading to reduced GSK-3β activity were found to precede development of cardiac hypertrophy in mice expressing dysfunctional ryanodine receptor ion channel.

The rat kidney contains high levels of prouroguanylin (the uroguanylin precursor) but does not express GC-C (the enteric uroguanylin receptor)

The peptide uroguanylin (Ugn) regulates enteric and renal electrolyte transport. Previous studies have shown that Ugn and its receptor GC-C (a ligand-activated guanylate cyclase) are abundant in the intestine. Less is known about Ugn and GC-C expression in the kidney. Here, we identify a 9.4-kDa polypeptide in rat kidney extracts that appears, based on its biochemical and immunological properties, to be authentic prouroguanylin (proUgn). This propeptide is relatively plentiful in the kidney (~16% of intestinal levels), whereas its mRNA is marginally present (<1% of intestinal levels), and free Ugn peptide levels are below detection limits (<0.4% of renal proUgn levels). The paucity of preproUgn-encoding mRNA and free Ugn peptide raises the possibility that the kidney might absorb intact proUgn from plasma, where the concentration of propeptide greatly exceeds that of Ugn. However, immunocytochemical analysis reveals that renal proUgn is found exclusively in distal tubular segments, sites previously shown not to accumulate radiolabeled proUgn after intravascular infusions. Thus proUgn appears to be synthesized within the kidney, but the factors that determine its abundance (rates of transcription, translation, processing, and secretion) must be balanced quite differently than in the gut. Surprisingly, we also find negligible expression of GC-C in the rat kidney, a result confirmed both by RT-PCR and by functional assays that measure Ugn-activated cGMP synthesis. Taken together, these data provide evidence for an intrarenal Ugn system that differs from the well-described intestinal system in its regulatory mechanisms and in the receptor targeted by the peptide.

Decreased hepatic breast cancer resistance protein expression and function in multidrug resistance-associated protein 2-deficient (TR⁻) rats

Multidrug resistance-associated protein (Mrp) 2-deficient (TR(-)) Wistar rats have been used to elucidate the role of Mrp2 in drug disposition. Decreased breast cancer resistance protein (Bcrp) levels were reported in sandwich-cultured hepatocytes (SCH) from TR(-) rats compared with those from wild-type (WT) rats. This study was designed to characterize hepatic Bcrp expression and function in TR(-) rats, using nitrofurantoin and pitavastatin as substrates. Bcrp was knocked down by RNA interference in rat SCH. Antibody BXP53, but not BXP21, specifically detected Bcrp knockdown in SCH. Bcrp protein levels were decreased markedly in TR(-) but not Mrp2-deficient Sprague-Dawley [Eisai hyperbilirubinemic rats (EHBR)] rats. Bcrp mRNA levels were decreased significantly in TR(-) livers as determined by TaqMan real-time reverse transcriptase-polymerase chain reaction. Biliary excretion of nitrofurantoin, a specific Bcrp substrate, was decreased significantly in SCH and isolated perfused livers from TR(-) rats compared with those from WT controls, indicating that hepatic Bcrp function is decreased in TR(-) rats. In Bcrp knockdown SCH, the biliary excretion index and in vitro biliary clearance of pitavastatin were decreased significantly to ∼ 58 and ∼ 52% of control, respectively, indicating that Bcrp plays a role in pitavastatin biliary excretion. Pitavastatin biliary excretion was decreased significantly in perfused livers from TR(-) compared with those from WT rats. In conclusion, expression and function of hepatic Bcrp are decreased significantly in TR(-) rats. The potential role of both Bcrp and Mrp2 should be considered when data generated in TR(-) rats are interpreted. TR(-) and EHBR rats in combination may be useful in differentiating the role of Mrp2 and Bcrp in drug/metabolite disposition.

Renal actions of RGS2 control blood pressure

G protein-coupled receptors (GPCRs) have key roles in cardiovascular regulation and are important targets for the treatment of hypertension. GTPase-activating proteins, such as RGS2, modulate downstream signaling by GPCRs. RGS2 displays regulatory selectivity for the Gαq subclass of G proteins, and mice lacking RGS2 develop hypertension through incompletely understood mechanisms. Using total body RGS2-deficient mice, we used a kidney crosstransplantation strategy to examine separately the contributions of RGS2 actions in the kidney from those in extrarenal tissues with regard to BP regulation. Loss of renal RGS2 was sufficient to cause hypertension, whereas the absence of RGS2 from all extrarenal tissues including the peripheral vasculature did not significantly alter BP. Accordingly, these results suggest that RGS2 acts within the kidney to modulate BP and prevent hypertension. These data support a critical role for the renal epithelium and/or vasculature as the final determinants of the intra-arterial pressure in hypertension.

RNA interference screen for RGS protein specificity at muscarinic and protease-activated receptors reveals bidirectional modulation of signaling

Regulator of G protein signaling (RGS) proteins are considered key modulators of G protein-coupled receptor (GPCR)-mediated signal transduction. These proteins act directly on Galpha subunits in vitro to increase their intrinsic rate of GTP hydrolysis; this activity is central to the prevailing view of RGS proteins as negative regulators of agonist-initiated GPCR signaling. However, the specificities of action of particular RGS proteins toward specific GPCRs in an integrated cellular context remain unclear. Here, we developed a medium-throughput assay to address this question in a wholly endogenous context using RNA interference. We performed medium-throughput calcium mobilization assays of agonist-stimulated muscarinic acetylcholine and protease-activated receptors in human embryonic kidney 293 (HEK293) cells transfected with individual members of a "pooled duplex" short interfering RNA library targeting all conventional human RGS transcripts. Only knockdown of RGS11 increased both carbachol-mediated calcium mobilization and inositol phosphate accumulation. Surprisingly, we found that knockdown of RGS8 and RGS9, but not other conventional RGS proteins, significantly decreased carbachol-mediated calcium mobilization, whereas only RGS8 knockdown decreased protease-activated receptor-1 (PAR-1)-mediated calcium mobilization. Loss of responsiveness toward carbachol and PAR-1 agonist peptide upon RGS8 knockdown appears due, at least in part, to a loss in respective receptor cell surface expression, although this is not the case for RGS9 knockdown. Our data suggest a cellular role for RGS8 in the stable surface expression of M3 muscarinic acetylcholine receptor and PAR-1, as well as a specific and opposing set of functions for RGS9 and RGS11 in modulating carbachol responsiveness similar to that seen in Caenorhabditis elegans.