Dysregulation of the endothelial nitric oxide synthase–soluble guanylate cyclase pathway is normalized by insulin in the aorta of diabetic rat

Modified redox signaling in vasculature after chronic infusion of the insulin receptor antagonist, S961

BACKGROUND

Type 2 diabetes and associated vascular complications cause substantial morbidity and mortality. It is important to investigate mechanisms and test therapies in relevant physiological models, yet few animal models adequately recapitulate all aspects of the human condition.

OBJECTIVE

We sought to determine the potential of using an insulin receptor antagonist, S961, in mice for investigating vascular pathophysiology.

METHODS

S961 was infused into mice for 4 weeks. Blood glucose was monitored, and insulin was measured at the end of the protocol. Blood pressure and pressor responses to vasodilators were measured in cannulated mice, and vascular reactive oxygen and nitrogen species were measured in isolated tissue.

RESULTS

S961 infusion-induced hyperglycemia and hyperinsulinemia. There was evidence of increased vascular reactive oxygen and nitrogen species and modification of NO-mediated signaling. Pressor responses to a NO donor were attenuated, but responses to bradykinin were preserved.

CONCLUSIONS

Infusion of S961, an insulin receptor antagonist, results in the production of a mouse model of type 2 diabetes that may be useful for investigating redox signaling in the vasculature of insulin-resistant mice over the short term. It is limited by both the transient nature of the hyperglycemia and incomplete functional analogy to the human condition.

Liraglutide prevents and reverses monocrotaline-induced pulmonary arterial hypertension by suppressing ET-1 and enhancing eNOS/sGC/PKG pathways

Liraglutide, a glucagon-like peptide-1 receptor (GLP-1R) agonist, is widely used to treat diabetes. However, its effect on pulmonary arterial hypertension (PAH) is unknown. In this study, we investigated its effects on rats with monocrotaline (MCT)-induced PAH and mechanisms on rat pulmonary artery smooth muscle cells (PASMCs). Liraglutide was investigated for both prevention and treatment of MCT-induced PAH. The hemodynamic and body weight changes, right heart hypertrophy, lung morphology, immune-reactivity of endothelial nitric oxide synthase (eNOS), endothelin-1 and cyclic guanosine monophosphate (cGMP) levels, protein expressions of eNOS, soluble guanylyl cyclase (sGCα), protein kinase G (PKG) and Rho kinase (ROCK) II pathway were measured in both in vivo and in vitro. Cell migration and cell cycle were also determined. Liraglutide both prevented and reversed MCT-induced PAH, right ventricle hypertrophy and pulmonary vascular wall remodeling. Protein expression of ROCK II was increased while eNOS, sGC and PKG were decreased. Pretreatment with liraglutide inhibited platelet-derived growth factor (PDGF)-BB stimulated PASMCs migration, which were associated with cell-cycle arrest at G₀/G₁ phase. Liraglutide may have both preventive and therapeutic effects on MCT-induced PAH, through the eNOS/sGC/PKG and Rho kinase pathways. Thus, liraglutide may have a therapeutic role in pulmonary vascular remodelling.

Carnitine palmitoyltransferase-1 up-regulation by PPAR-β/δ prevents lipid-induced endothelial dysfunction

Fatty acids cause endothelial dysfunction involving increased ROS (reactive oxygen species) and reduced NO (nitric oxide) bioavailability. We show that in MAECs (mouse aortic endothelial cells), the PPARβ/δ (peroxisome- proliferator-activated receptor β/δ) agonist GW0742 prevented the decreased A23187-stimulated NO production, phosphorylation of eNOS (endothelial nitric oxide synthase) at Ser1177 and increased intracellular ROS levels caused by exposure to palmitate in vitro. The impaired endothelium-dependent relaxation to acetylcholine in mouse aorta induced by palmitate was restored by GW0742. In vivo, GW0742 treatment prevented the reduced aortic relaxation, phosphorylation of eNOS at Ser1177, and increased ROS production and NADPH oxidase in mice fed on a high-fat diet. The PPARβ/δ antagonist GSK0660 abolished all of these protective effects induced by GW0742. This agonist enhanced the expression of CPT (carnitine palmitoyltransferase)-1. The effects of GW0742 on acetylcholine- induced relaxation in aorta and on NO and ROS production in MAECs exposed to palmitate were abolished by the CPT-1 inhibitor etomoxir or by siRNA targeting CPT-1. GW0742 also inhibited the increase in DAG (diacylglycerol), PKCα/βII (protein kinase Cα/βII) activation, and phosphorylation of eNOS at Thr495 induced by palmitate in MAECs, which were abolished by etomoxir. In conclusion, PPARβ/δ activation restored the lipid-induced endothelial dysfunction by up-regulation of CPT-1, thus reducing DAG accumulation and the subsequent PKC-mediated ROS production and eNOS inhibition.

Diabetes enhances the intrahepatic vascular response to endothelin-1 in cirrhotic rats: association with the ETA receptor and pERK up-regulation

BACKGROUND & AIMS

Cirrhosis is characterized by increased intrahepatic vascular resistance and enhanced vasocontractile responsiveness that impedes portal inflow and elevates portal pressure, in which endothelin-1 (ET-1) plays a role. Diabetes and glucose influence vasoresponsiveness but their impact on the intrahepatic vascular bed in cirrhosis is unknown. To investigate intrahepatic ET-1 vasoresponsiveness in cirrhotic rats with and without diabetes and to explore the underlying mechanisms.

METHODS

Spraque-Dawley rats received common bile-duct ligation (BDL) to induce cirrhosis. Streptozotocin was injected to induce diabetes in the BDL rats (BDL/STZ). In situ liver perfusion was performed to obtain the ET-1 concentration-response curves. The basic hemodynamics and hepatic protein expressions of ET-1 receptors, pERK, ERK, pAkt, Akt, iNOS, eNOS, peNOS and calmodulin were evaluated. The circulating concentrations of N-terminal pro-brain natriuretic peptide (NT-ProBNP), blood urea nitrogen (BUN) and creatinine were also determined.

RESULTS

Body weight, mean arterial pressure, heart rate and survival rate were significantly decreased in the BDL/STZ rats. The perfusion pressure changes in response to ET-1 were higher in the BDL/STZ group for all perfusates. ETA receptor and pERK expressions were enhanced in the BDL/STZ group. The circulating concentrations of NT-ProBNP, BUN and creatinine, as well as SMA flow, were not significantly different between the BDL and BDL/STZ groups.

CONCLUSION

Cirrhotic rats with diabetes showed higher intrahepatic ET-1 vasoresponsiveness than normoglycemic cirrhotic rats. This effect is not affected by changes in perfused glucose concentration and may be related, at least in part, to intrahepatic ETA R receptor and pERK over-expression.

Berberine protects against palmitate-induced endothelial dysfunction: involvements of upregulation of AMPK and eNOS and downregulation of NOX4

Endothelial dysfunction is a critical factor during the initiation of cardiovascular complications in diabetes. Berberine can ameliorate endothelial dysfunction induced by diabetes. However, the underlying mechanisms remain unclear. The aim of this study was to investigate the protective effect and mechanism of berberine on palmitate-induced endothelial dysfunction in human umbilical vein endothelial cells (HUVECs). The cell viability of HUVECs was determined by MTT assays. Nitric oxide (NO) level and production of reactive oxygen species (ROS) were determined in supernatants or in the cultured HUVECs. The mRNA level of endothelial nitric oxide synthase (eNOS) was measured by RT-PCR, and the protein levels of eNOS, p-eNOS, Akt, p-Akt, AMPK, p-AMPK, and NADPH oxidase (NOX4) were analyzed. The results demonstrated that berberine significantly elevated NO levels and reduced the production of ROS. The expressions of eNOS were significantly increased, while NOX4 protein expression was decreased in berberine-treated HUVECs. Moreover, berberine upregulated the protein expression of AMPK and p-AMPK in palmitate-treated HUVECs, but had no effect on the levels of Akt. Therefore, berberine ameliorates palmitate-induced endothelial dysfunction by upregulating eNOS expression and downregulating expression of NOX4. This regulatory effect of berberine may be related to the activation of AMPK.

Antidiabetic treatment restores adiponectin serum levels and APPL1 expression, but does not improve adiponectin-induced vasodilation and endothelial dysfunction in Zucker diabetic fatty rats

Background

Adiponectin is able to induce NO-dependent vasodilation in Zucker lean (ZL) rats, but this effect is clearly alleviated in their diabetic littermates, the Zucker diabetic fatty (ZDF) rats. ZDF rats also exhibit hypoadiponectinemia and a suppressed expression of APPL1, an adaptor protein of the adiponectin receptors, in mesenteric resistance arteries. Whether an antidiabetic treatment can restore the vasodilatory effect of adiponectin and improve endothelial function in diabetes mellitus type 2 is not known.

Methods

During our animal experiment from week 11 to 22 in each case seven ZDF rats received an antidiabetic treatment with either insulin (ZDF+I) or metformin (ZDF+M). Six normoglycemic ZL and six untreated ZDF rats served as controls. Blood glucose was measured at least weekly and serum adiponectin levels were quantified via ELISA in week 11 and 22. The direct vasodilatory response of their isolated mesenteric resistance arteries to adiponectin as well as the endothelium-dependent and -independent function was evaluated in a small vessel myograph. Additionally, the expression of different components of the adiponectin signaling pathway in the resistance arteries was quantified by real-time RT-PCR.

Results

In ZDF rats a sufficient blood glucose control could only be reached by treatment with insulin, but both treatments restored the serum levels of adiponectin and the expression of APPL1 in small resistance arteries. Nevertheless, both therapies were not able to improve the vasodilatory response to adiponectin as well as endothelial function in ZDF rats. Concurrently, a downregulation of the adiponectin receptors 1 and 2 as well as endothelial NO-synthase expression was detected in insulin-treated ZDF rats. Metformin-treated ZDF rats showed a reduced expression of adiponectin receptor 2.

Conclusions

An antidiabetic treatment with either insulin or metformin in ZDF rats inhibits the development of hypoadiponectinemia and downregulation of APPL1 in mesenteric resistance arteries, but is not able to improve adiponectin induced vasodilation and endothelial dysfunction. This is possibly due to alterations in the expression of adiponectin receptors and eNOS.

Activation of peroxisome proliferator-activated receptor-β/-δ (PPARβ/δ) prevents endothelial dysfunction in type 1 diabetic rats

Endothelial dysfunction plays a key role in the pathogenesis of diabetic vascular disease. Herein, we have analyzed if the peroxisome proliferator-activated receptor-β/-δ (PPARβ/δ) agonist GW0742 exerts protective effects on endothelial function in type 1 diabetic rats. The rats were divided into 4 groups: control, control-treated (GW0742, 5 mg kg(-1)day(-1) for 5 weeks), diabetic (streptozotocin injection), and diabetic-treated. GW0742 administration in diabetic rats did not alter plasma glucose, systolic blood pressure, or heart rate, but reduced plasma triglyceride levels. The vasodilatation induced by acetylcholine was decreased in aortas from diabetic rats. GW0742 restored endothelial function, increasing eNOS phosphorylation. Superoxide production, NADPH oxidase activity, and mRNA expression of prepro endothelin-1, p22(phox), p47(phox), and NOX-1 were significantly higher in diabetic aortas, and GW0742 treatment prevented these changes. In addition, GW0742 prevented the endothelial dysfunction and the upregulation of prepro endothelin-1 and p47(phox) after the in vitro incubation of aortic rings with high glucose and these effects were prevented by the PPARβ/δ antagonist GSK0660. PPARβ/δ activation restores endothelial function in type 1 diabetic rats. This effect seems to be related to an increase in nitric oxide bioavailability as a result of reduced NADPH oxidase-driven superoxide production and downregulation of prepro endothelin-1.

Glucagon-like peptide-2 (GLP-2) modulates the cGMP signalling pathway by regulating the expression of the soluble guanylyl cyclase receptor subunits in cultured rat astrocytes

The aim of this work was to study the effect of glucagon-like peptide-2 (GLP-2) on the cyclic guanosine monophosphate (cGMP) signalling pathway and whether insulin or epidermal growth factor (EGF) might modulate the effects of GLP-2. GLP-2 produced a dose-dependent decrease in intracellular sodium nitroprusside-induced cGMP production. However, insulin induced an increase in the levels of cGMP that was dose-dependently decreased by the addition of GLP-2. By contrast, EGF induced a decrease in cGMP production, which was further reduced by the addition of GLP-2. To assess whether variations in cGMP production might be related with changes in some component of soluble guanylyl cyclase (sGC), the expression of the α1, α2, and β1 subunits were determined by Western blot analysis. At 1 h, GLP-2 produced a decrease in the expression of both α1 and β1 in the cytosolic fraction, but at 24 h only β1was reduced. As expected, insulin induced an increase in the expression of both subunits after 1 h of incubation; this was decreased by the addition of GLP-2. Likewise, incubation with EGF for 24 h produced a decrease in the expression of both subunits that was maximal when GLP-2 was added. In addition, incubation with insulin for 1 h produced an increase in the expression of the α2 subunit, which was reduced by the addition of GLP-2. These results suggest that GLP-2 inhibits cGMP production by decreasing the cellular content of at least one subunit of the heterodimeric active form of the sGC, independently of the presence of insulin or EFG. This may open new insights into the actions of this neuropeptide.

Gustatory perception and fat body energy metabolism are jointly affected by vitellogenin and juvenile hormone in honey bees

Honey bees (Apis mellifera) provide a system for studying social and food-related behavior. A caste of workers performs age-related tasks: young bees (nurses) usually feed the brood and other adult bees inside the nest, while older bees (foragers) forage outside for pollen, a protein/lipid source, or nectar, a carbohydrate source. The workers' transition from nursing to foraging and their foraging preferences correlate with differences in gustatory perception, metabolic gene expression, and endocrine physiology including the endocrine factors vitellogenin (Vg) and juvenile hormone (JH). However, the understanding of connections among social behavior, energy metabolism, and endocrine factors is incomplete. We used RNA interference (RNAi) to perturb the gene network of Vg and JH to learn more about these connections through effects on gustation, gene transcripts, and physiology. The RNAi perturbation was achieved by single and double knockdown of the genes ultraspiracle (usp) and vg, which encode a putative JH receptor and Vg, respectively. The double knockdown enhanced gustatory perception and elevated hemolymph glucose, trehalose, and JH. We also observed transcriptional responses in insulin like peptide 1 (ilp1), the adipokinetic hormone receptor (AKHR), and cGMP-dependent protein kinase (PKG, or "foraging gene" Amfor). Our study demonstrates that the Vg-JH regulatory module controls changes in carbohydrate metabolism, but not lipid metabolism, when worker bees shift from nursing to foraging. The module is also placed upstream of ilp1, AKHR, and PKG for the first time. As insulin, adipokinetic hormone (AKH), and PKG pathways influence metabolism and gustation in many animals, we propose that honey bees have conserved pathways in carbohydrate metabolism and conserved connections between energy metabolism and gustatory perception. Thus, perhaps the bee can make general contributions to the understanding of food-related behavior and metabolic disorders.

Stabilization of cGMP-dependent protein kinase G (PKG) expression in vascular smooth muscle cells: contribution of 3'UTR of its mRNA

The type-I cGMP-dependent protein kinase (PKG-I) expression regulation is not yet completely understood. In this study, we examined the role of 3'-untranslated region (3'UTR)-PKG-I messenger RNA (mRNA) in the control of PKG-I expression in vascular smooth muscle cells (VSMCs). Using a 3'-rapid amplification of cDNA ends (RACE) for the amplification of complementary DNA (cDNA) ends, we generated and cloned a 1.2-kb-3'UTR mRNA PKG-I in pGL3 control vector downstream of the luciferase reporter gene. Serial deletions and functional studies revealed that among the deleted constructs, only the 1.2-kb-3'UTR PKG-I mRNA possesses the highest activity in transfected VSMC. Kinetic luciferase assays in the presence of actinomycin D showed that this construct stabilizes luciferase activity compared to the control vector. Sequence analysis of 3'UTR-PKG-I mRNA revealed the existence of four AU-rich regions (AU1 through AU4) in addition to a potential poly(A) site. Different riboprobes were generated either by 5'-end-labelling of designed ribonucleotides, containing individual AU-rich regions or by in vitro transcription assay using cloned 1.2-kb cDNA as a template. RNA-electrophoretic mobility shift assay (EMSA) and ultra-violet cross-linking (UV-CL) assays showed that AU1, AU3, AU4 and 1.2-kb probes were able to retard cytosolic and nuclear proteins. Taken together, these data suggest that PKG-I expression is subjected to post-transcriptional regulation in VSMC through the 3'UTR of its mRNA.

Expression of constitutively active cGMP-dependent protein kinase inhibits glucose-induced vascular smooth muscle cell proliferation

Previously, we have demonstrated that cGMP-dependent protein kinase (PKG) activity is downregulated in vessels from diabetic animals or in vascular smooth muscle cells (VSMCs) exposed to high-glucose conditions, contributing to diabetes-associated vessel dysfunction. However, whether decreased PKG activity plays a role in hyperglycemia-induced proliferation of VSMCs is unknown. In this report, high-glucose-mediated decreased PKG activity in VSMCs was restored by transfection of cells with expression vector for the catalytic domain of PKG-I (PKG-CD, constitutive active PKG). The effect of glucose on cell proliferation was determined. Our data demonstrated that high glucose exposure stimulated VSMC proliferation and G1 to S phase progression of the cell cycle, which was inhibited by restoration of PKG activity. Expression of constitutively active PKG inhibited G1 phase exit in VSMCs under high glucose conditions, which was accompanied by an inhibition of retinoblastoma protein (Rb) phosphorylation (a key switch for G1 to S phase cell cycle progression). Glucose-induced cyclin E expression and cyclin E-cyclin-dependent kinase 2 activity was also reduced by expression of PKG-CD in VSMCs. Moreover, expression of PKG-CD suppressed glucose-induced p27 degradation. These data demonstrate that restoring the high-glucose-mediated decrease in PKG activity in VSMCs inhibits glucose-induced abnormal VSMC proliferation occurring upstream of Rb phosphorylation. Our work provides the first direct evidence linking decreased PKG activity to high glucose-induced proliferation and cell cycle progression in VSMCs, suggesting that strategies to increase PKG activity might be useful in preventing abnormal VSMC proliferation in diabetic patients and might provide treatments for diabetes-associated proliferative vascular diseases.

cGMP-dependent protein kinase: linking foraging to energy homeostasis

Successful foraging is necessary for procurement of nutritional resources essential for an animal’s survival. Maintenance of foraging and food acquisition is dependent on the ability to balance food intake and energy expenditure. This review examines the role of cGMP-dependent protein kinase (PKG) as a regulator of foraging behaviour, food acquisition, and energy balance. The role of PKG in food-related behaviours is highly conserved among worms, flies, bees, ants, and mammals. A growing body of literature suggests that PKG plays an integral role in the component behaviours and physiologies underlying foraging behaviour. These include energy acquisition, nutrient absorption, nutrient allocation, nutrient storage, and energy use. New evidence suggests that PKG mediates both neural and physiological mechanisms underlying these processes. This review illustrates how investigating the role of PKG in energy homeostasis in a diversity of organisms can offer a broad perspective on the mechanisms mediating energy balance.

Natural variation in plasticity of glucose homeostasis and food intake

Balancing the acquisition, allocation and storage of energy during periods of food deprivation is critical for survival. We show that natural variation in the foraging (for) gene, which encodes a cGMP-dependent protein kinase (PKG) in the fruit fly Drosophila melanogaster, affects behavioral and physiological responses to short-term food deprivation. Rover and sitter, natural allelic variants of for, differ in their stored carbohydrate reserves as well as their response to short-term deprivation. Fewer carbohydrates are stored in the fat body of rovers compared with sitters, and more labeled glucose is allocated to lipid stores compared with carbohydrate stores during a short feeding bout. Short-term food deprivation decreases hemolymph glucose levels in rovers but not in sitters. After food deprivation, rovers increase their food intake more slowly than sitters, and rover hemolymph levels take longer to respond to re-feeding. Finally, rovers have lower adipokinetic hormone (akh) mRNA levels than sitters. Our data suggest that for mediates larval responses to short-term food deprivation by altering food intake and blood glucose levels.

Diabetes induces pulmonary artery endothelial dysfunction by NADPH oxidase induction

Recent data suggest that diabetes is a risk factor for pulmonary hypertension. The aim of the present study was to analyze whether diabetes induces endothelial dysfunction in pulmonary arteries and the mechanisms involved. Male Sprague-Dawley rats were randomly divided into a control (saline) and a diabetic group (70 mg/kg(-1) streptozotocin). After 6 wk, intrapulmonary arteries were mounted for isometric tension recording, and endothelial function was tested by the relaxant response to acetylcholine. Protein expression and localization were measured by Western blot and immunohistochemistry and superoxide production by dihydroethidium staining. Pulmonary arteries from diabetic rats showed impaired relaxant response to acetylcholine and reduced vasoconstrictor response to the nitric oxide (NO) synthase inhibitor L-NAME, whereas the response to nitroprusside and the expression of endothelial NO synthase remained unchanged. Endothelial dysfunction was reversed by addition of superoxide dismutase or the NADPH oxidase inhibitor apocynin. An increase in superoxide production and increased expression of the NADPH oxidase regulatory subunit p47(phox) were also found in pulmonary arteries from diabetic rats. In conclusion, the pulmonary circulation is a target for diabetes-induced endothelial dysfunction via enhanced NADPH oxidase-derived superoxide production.

Palmitic and linoleic acids impair endothelial progenitor cells by inhibition of Akt/eNOS pathway

BACKGROUND

Endothelial progenitor cells (EPCs) are involved in adult neovasculogenesis and maintenance of vascular integrity. Scarce data have been provided for the individual effect of elevated free fatty acids (FFAs) on EPCs. This study was designed to investigate the association between Akt/eNOS signal pathway changes and the proliferation/function of EPCs in the presence of palmitic and linoleic acids.

METHODS

After 14-day culture, EPCs were stimulated with different concentrations of palmitic and linoleic acids, with or without SNP, L-NAME, or LY294002. The proliferation and ability of adhesion, migration and tube structure formation of EPCs were observed and the level of phosphorylated Akt protein expression and eNOS protein expression were assayed.

RESULTS

Incubation with palmitic and linoleic acids at concentrations of 0.2 muM or higher inhibited EPCs proliferation, significantly reduced migratory rate, reduced adhesion to fibronectin and impaired ability of EPCs to form tube structure in a dose-dependent manner. A simultaneous dose-dependent NO generation and Akt phosphorylation decrease as well as eNOS expression reduction at protein levels were also observed. However, all of the detrimental effects were attenuated by pretreating EPCs with SNP, NO donor. AKT and eNOS inhibitor, LY294002 and L-NAME, respectively, augmented palmitic and linoleic acids inhibitory effects on EPCs.

CONCLUSIONS

These findings suggest that palmitic and linoleic acids downregulated AKT/eNOS signal pathway, which contributed to overall poor function and decrease proliferation of EPCs. These changes induced by palmitic and linoleic acids in signaling offer a novel explanation for the overall poor function of EPCs in diabetes mellitus.

Mechanisms underlying recoupling of eNOS by HMG-CoA reductase inhibition in a rat model of streptozotocin-induced diabetes mellitus

OBJECTIVE

HMG-CoA reductase inhibitors have been shown to upregulate GTP cyclohydrolase I (GTPCH-I), the key enzyme for tetrahydrobiopterin de novo synthesis and to normalize tetrahydrobiopterin levels in hyperglycemic endothelial cells. We sought to determine whether in vivo treatment with the HMG-CoA reductase inhibitor atorvastatin is able to upregulate the GTPCH-I, to recouple eNOS and to normalize endothelial dysfunction in an experimental model of diabetes mellitus.

METHODS AND RESULTS

In male Wistar rats, diabetes was induced by streptozotocin (STZ, 60 mg/kg). In STZ rats, atorvastatin feeding (20 mg/kg/d, 7 weeks), normalized vascular dysfunction as analyzed by isometric tension studies, levels of circulating endothelial progenitor cells (FACS-analysis), superoxide formation (assessed by lucigenin-enhanced chemiluminescence and dihydroethidium staining), vascular levels of the phosphorylated vasodilator-stimulated phosphoprotein (P-VASP), tyrosine nitration of the prostacyclin synthase, expression of GTPCH-I, dihydrofolate reductase and eNOS, translocation of regulatory NADPH oxidase subunits rac1, p47phox and p67phox (assessed by Western blot) and vascular tetrahydrobiopterin levels as measured by HPLC. Dihydroethidine staining revealed that the reduction of vascular superoxide was at least in part due to eNOS recoupling.

CONCLUSION

HMG-CoA reductase inhibition normalizes endothelial function and reduces oxidative stress in diabetes by inhibiting activation of the vascular NADPH oxidase and by preventing eNOS uncoupling due to an upregulation of the key enzyme of tetrahydrobiopterin synthesis, GTPCH-I.

Natural variation in food acquisition mediatedviaaDrosophilacGMP-dependent protein kinase

In natural environments where food abundance and quality can change drastically over time, animals must continuously alter their food acquisition strategies. Although genetic variation contributes to this plasticity, the specific genes involved and their interactions with the environment are poorly understood. Here we report that natural variation in the Drosophilagene, foraging (for), which encodes a cGMP-dependent protein kinase (PKG), affects larval food acquisition in an environmentally dependent fashion. When food is plentiful, the wild-type rover(forR) allele confers lower food intake and higher glucose absorption than both the wild-type sitter (fors) allele and the mutant fors2 allele. When food is scarce, forR, fors and fors2 larvae increase food intake to a common maximal level, but forRlarvae retain their increased absorption efficiency. Changes in forexpression can induce corrective behavioral modifications in response to food deprivation. When reared in environments with low food levels, forR larvae have higher survivorship and faster development than fors and fors2larvae. Together, these results show that natural variation in forhas far reaching implications affecting a suite of phenotypes involved in the regulation of food acquisition.

Glucose down-regulation of cGMP-dependent protein kinase I expression in vascular smooth muscle cells involves NAD(P)H oxidase-derived reactive oxygen species

Reduced levels of cGMP-dependent protein kinase I (PKG-I) in vasculature have been shown to contribute to diabetic vascular dysfunctions. However, the underlying mechanisms remain unknown. In this report, using primary rat aortic smooth muscle cells (VSMC), we investigated the mechanisms of glucose-mediated regulation of PKG-I expression. Our data showed that high glucose (30 mM glucose) exposure significantly reduced PKG-I production (protein and mRNA levels) as well as PKG-I activity in cultured VSMC. Glucose-mediated decreases in PKG-I levels were inhibited by a superoxide scavenger (tempol) or NAD(P)H oxidase inhibitors (diphenylene iodonium or apocynin). High glucose exposure time-dependently increased superoxide production in VSMC, which was abolished by tempol or apocynin treatment, but not by other inhibitors of superoxide-producing enzymes (L-NAME, rotenone, or oxypurinol). Total protein levels and phosphorylated levels of p47phox (an NADPH oxidase subunit) were increased in VSMC after high glucose exposure. Transfection of cells with siRNA-p47phox abolished glucose-induced superoxide production and restored PKG-I protein levels in VSMC. Treatment of cells with PKC inhibitor prevented glucose-induced p47phox expression/phosphorylation and superoxide production and restored the PKG-I levels. Decreased PKG-I protein levels were also found in femoral arteries from diabetic mice, which were associated with the decreased DEA-NONOate-induced vasorelaxation. Taken together, the present results suggest that glucose-mediated down-regulation of PKG-I expression in VSMC occurs through PKC-dependent activation of NAD(P)H oxidase-derived superoxide production, contributing to diabetes-associated vessel dysfunctions.

Increased eNOS accounts for changes in connexin expression in renal arterioles during diabetes

Previous studies have shown that connexin (Cx) expression is considerably higher in the preglomerular compared to postglomerular vasculature and that these differences are accentuated during diabetes. Since nitric oxide (NO) has been reported to alter Cx expression in endothelial cells and muscle cells and NO bioavailability is altered in diabetes, we hypothesized that NO may be responsible for the changes during diabetes. Cx expression was studied using immunohistochemistry in mice in which eNOS expression was either upregulated (eNOS transgenic) or downregulated (eNOS knockout). Diabetes was induced intraperitoneally with a single dose of alloxan or multiple low doses of streptozotocin. Expression of Cx40 in smooth muscle cells of afferent arterioles was increased, while expression of Cx43 in endothelial cells of efferent arterioles was absent in eNOS transgenic mice, similar to the changes occurring in wild-type mice during diabetes. Expression of Cx40 and Cx43 in eNOS knockout mice was not different from control; however, induction of diabetes in eNOS knockout mice failed to produce any changes in Cx40 or Cx43 in either afferent or efferent arterioles. Immunohistochemistry showed that eNOS expression was increased in the endothelium of renal arterioles in wild-type diabetic and eNOS transgenic mice, but absent from arterioles of eNOS knockout mice. We conclude that changes occurring in Cx expression in afferent and efferent arterioles during diabetes may result from increased eNOS.