The cGMP-inhibitable phosphodiesterase modulates glucose transport activation by insulin

Salicylate Sodium Suppresses Monocyte Chemoattractant Protein-1 Production by Directly Inhibiting Phosphodiesterase 3B in TNF-α-Stimulated Adipocytes

As a worldwide health issue, obesity is associated with the infiltration of monocytes/macrophages into the adipose tissue causing unresolved inflammation. Monocyte chemoattractant protein-1 (MCP-1) exerts a crucial effect on obesity-related monocytes/macrophages infiltration. Clinically, aspirin and salsalate are beneficial for the treatment of metabolic diseases in which adipose tissue inflammation plays an essential role. Herein, we investigated the effect and precise mechanism of their active metabolite salicylate on TNF-α-elevated MCP-1 in adipocytes. The results indicated that salicylate sodium (SAS) could lower the level of MCP-1 in TNF-α-stimulated adipocytes, which resulted from a previously unrecognized target phosphodiesterase (PDE), 3B (PDE3B), rather than its known targets IKKβ and AMPK. The SAS directly bound to the PDE3B to inactivate it, thus elevating the intracellular cAMP level and activating PKA. Subsequently, the expression of MKP-1 was increased, which led to the decrease in p-EKR and p-p38. Both PDE3B silencing and the pharmacological inhibition of cAMP/PKA compromised the suppressive effect of SAS on MCP-1. In addition to PDE3B, the PDE3A and PDE4B activity was also inhibited by SAS. Our findings identify a previously unrecognized pathway through which SAS is capable of attenuating the inflammation of adipocytes.

Natriuretic peptides promote glucose uptake in a cGMP-dependent manner in human adipocytes

Robust associations between low plasma level of natriuretic peptides (NP) and increased risk of type 2 diabetes (T2D) have been recently reported in humans. Adipose tissue (AT) is a known target of NP. However it is unknown whether NP signalling in human AT relates to insulin sensitivity and modulates glucose metabolism. We here show in two European cohorts that the NP receptor guanylyl cyclase-A (GC-A) expression in subcutaneous AT was down-regulated as a function of obesity grade while adipose NP clearance receptor (NPRC) was up-regulated. Adipose GC-A mRNA level was down-regulated in prediabetes and T2D, and negatively correlated with HOMA-IR and fasting blood glucose. We show for the first time that NP promote glucose uptake in a dose-dependent manner. This effect is reduced in adipocytes of obese individuals. NP activate mammalian target of rapamycin complex 1/2 (mTORC1/2) and Akt signalling. These effects were totally abrogated by inhibition of cGMP-dependent protein kinase and mTORC1/2 by rapamycin. We further show that NP treatment favoured glucose oxidation and de novo lipogenesis independently of significant gene regulation. Collectively, our data support a role for NP in blood glucose control and insulin sensitivity by increasing glucose uptake in human adipocytes. This effect is partly blunted in obesity.

Hypothalamic Phosphodiesterase 3B Pathway Mediates Anorectic and Body Weight-Reducing Effects of Insulin in Male Mice

BACKGROUND

Insulin action in the hypothalamus plays a critical role in the regulation of energy homeostasis, yet the intracellular signaling mechanisms mediating insulin action are incompletely understood. Although phosphodiesterase 3B (PDE3B) mediates insulin action in the adipose tissue and it is highly expressed in the hypothalamic areas implicated in energy homeostasis, its role, if any, in mediating insulin action in the hypothalamus is unknown. We tested the hypothesis that insulin action in the hypothalamus is mediated by PDE3B.

METHODS

Using enzymatic assay, we examined the effects of peripheral or central administration of insulin on hypothalamic PDE3B activity in adult mice. Western blotting and immunohistochemistry also examined p-Akt and p-STAT3 levels in the hypothalamus. Effects of leptin on these parameters were also compared. We injected cilostamide, a PDE3 inhibitor, prior to central injection of insulin and examined the 12- to 24-hour food intake and 24-hour body weight. Finally, we examined the effect of cilostamide on insulin-induced proopiomelanocortin (Pomc), neurotensin (Nt), neuropeptide Y (Npy) and agouti-related peptide (Agrp) gene expression in the hypothalamus by qPCR.

RESULTS

Peripheral or central injection of insulin significantly increased PDE3B activity in the hypothalamus in association with increased p-Akt levels but without any change in p-STAT3 levels. However, leptin-induced increase in PDE3B activity was associated with an increase in both p-Akt and p-STAT3 levels in the hypothalamus. Prior administration of cilostamide reversed the anorectic and body weight-reducing effects as well as stimulatory effect of insulin on hypothalamic Pomc mRNA levels. Insulin did not alter Nt, Npy and Agrp mRNA levels.

CONCLUSION

Insulin induction of hypothalamic PDE3B activity and the reversal of the anorectic and body weight-reducing effects and stimulatory effect of insulin on hypothalamic Pomc gene expression by cilostamide suggest that activation of PDE3B is a novel mechanism of insulin signaling in the hypothalamus.

From PDE3B to the regulation of energy homeostasis

The incidence of obesity in the developed world is increasing at an alarming rate. Concurrent with the increase in the incidence of obesity is an increase in the incidence of type 2 diabetes. Cyclic AMP (cAMP) and cGMP are key second messengers in all cells; for example, when it comes to processes of relevance for the regulation of energy metabolism, cAMP is a key mediator in the regulation of lipolysis, glycogenolysis, gluconeogenesis and pancreatic β cell insulin secretion. PDE3B, one of several enzymes which hydrolyze cAMP and cGMP, is expressed in cells of importance for the regulation of energy homeostasis, including adipocytes, hepatocytes, hypothalamic cells and β cells. It has been shown, using PDE3 inhibitors and gene targeting approaches in cells and animals, that altered levels of PDE3B result in a number of changes in the regulation of glucose and lipid metabolism and in overall energy homeostasis. This article highlights the complexity involved in the regulation of PDE3B by hormones, and in the regulation of downstream metabolic effects by PDE3B in several interacting tissues.

Coordinated regulation of esterification and lipolysis by palmitate, H2O2 and the anti-diabetic sulfonylurea drug, glimepiride, in rat adipocytes

Inhibition of lipolysis by palmitate, H2O2 and the anti-diabetic sulfonylurea drug, glimepiride, in isolated rat adipocytes has previously been shown to rely on the degradation of cyclic adenosine monophosphate by the phosphodiesterase, Gce1, and the 5'-nucleotidase, CD73. These glycosylphosphatidylinositol (GPI)-anchored proteins are translocated from plasma membrane lipid rafts to intracellular lipid droplets upon H2O2-induced activation of a GPI-specific phospholipase C (GPI-PLC) in response to palmitate and glimepiride in intact adipocytes and, as demonstrated here, in cell-free systems as well. The same agents are also known to stimulate the incorporation of fatty acids into triacylglycerol. Here the involvement of H2O2 production, GPI-PLC activation and translocation of Gce1 and CD73 in the agent-induced esterification and accompanying lipid droplet formation was tested in rat adipocytes using relevant inhibitors. The results demonstrate that upregulation of the esterification and accumulation of triacylglycerol by glimepiride depends on the sequential H2O2-induced GPI-PLC activation and GPI-protein translocation as does inhibition of lipolysis. In contrast, stimulation of the esterification and triacylglycerol accumulation by palmitate relies on insulin-independent tyrosine phosphorylation and thus differs from its anti-lipolytic mechanism. As expected, insulin regulates lipid metabolism via typical insulin signalling independent of H2O2 production, GPI-PLC activation and GPI-protein translocation, albeit these processes are moderately stimulated by insulin. In conclusion, triacylglycerol and lipid droplet formation in response to glimepiride and H2O2 may involve the hydrolysis of cyclic adenosine monophosphate by lipid droplet-associated Gce1 and CD73 which may regulate lipid droplet-associated triacylglycerol-synthesizing and hydrolyzing enzymes in coordinated and inverse fashion.

Alterations in regulation of energy homeostasis in cyclic nucleotide phosphodiesterase 3B-null mice

Cyclic nucleotide phosphodiesterase 3B (PDE3B) has been suggested to be critical for mediating insulin/IGF-1 inhibition of cAMP signaling in adipocytes, liver, and pancreatic beta cells. In Pde3b-KO adipocytes we found decreased adipocyte size, unchanged insulin-stimulated phosphorylation of protein kinase B and activation of glucose uptake, enhanced catecholamine-stimulated lipolysis and insulin-stimulated lipogenesis, and blocked insulin inhibition of catecholamine-stimulated lipolysis. Glucose, alone or in combination with glucagon-like peptide-1, increased insulin secretion more in isolated pancreatic KO islets, although islet size and morphology and immunoreactive insulin and glucagon levels were unchanged. The beta(3)-adrenergic agonist CL 316,243 (CL) increased lipolysis and serum insulin more in KO mice, but blood glucose reduction was less in CL-treated KO mice. Insulin resistance was observed in KO mice, with liver an important site of alterations in insulin-sensitive glucose production. In KO mice, liver triglyceride and cAMP contents were increased, and the liver content and phosphorylation states of several insulin signaling, gluconeogenic, and inflammation- and stress-related components were altered. Thus, PDE3B may be important in regulating certain cAMP signaling pathways, including lipolysis, insulin-induced antilipolysis, and cAMP-mediated insulin secretion. Altered expression and/or regulation of PDE3B may contribute to metabolic dysregulation, including systemic insulin resistance.

Plasma membrane cyclic nucleotide phosphodiesterase 3B (PDE3B) is associated with caveolae in primary adipocytes

Caveolae, plasma membrane invaginations particularly abundant in adipocytes, have been suggested to be important in organizing insulin signalling. Insulin-induced activation of the membrane bound cAMP degrading enzyme, phosphodiesterase 3B (PDE3B) is a key step in insulin-mediated inhibition of lipolysis and is also involved in the regulation of insulin-mediated glucose uptake and lipogenesis in adipocytes. The aim of this work was to evaluate whether PDE3B is associated with caveolae. Subcellular fractionation of primary rat and mouse adipocytes demonstrated the presence of PDE3B in endoplasmic reticulum and plasma membrane fractions. The plasma membrane PDE3B was further analyzed by detergent treatment at 4 degrees C, which did not solubilize PDE3B, indicating an association of PDE3B with lipid rafts. Detergent-treated plasma membranes were studied using Superose-6 chromatography which demonstrated co-elution of PDE3B with caveolae and lipid raft markers (caveolin-1, flotillin-1 and cholesterol) at a Mw of >4000 kDa. On sucrose density gradient centrifugation of sonicated plasma membranes, a method known to enrich caveolae, PDE3B co-migrated with the caveolae markers. Immunoprecipitation of caveolin-1 using anti caveolin-1 antibodies co-immunoprecipitated PDE3B and immunoprecipitation of flag-PDE3B from adipocytes infected with a flag-PDE3B adenovirus resulted in co-immunoprecipitation of caveolin-1. Studies on adipocytes with disrupted caveolae, using either caveolin-1 deficient mice or treatment of adipocytes with methyl-beta-cyclodextrin, reduced the membrane associated PDE3B activity. Furthermore, inhibition of PDE3 in primary rat adipocytes resulted in reduced insulin stimulated glucose transporter-4 translocation to caveolae, isolated by immunoprecipitation using caveolin-1 antibodies. Thus, PDE3B, a key enzyme in insulin signalling, appears to be associated with caveolae in adipocytes and this localization seems to be functionally important.

Role of PDE3B in insulin-induced glucose uptake, GLUT-4 translocation and lipogenesis in primary rat adipocytes

In adipocytes, phosphorylation and activation of PDE3B is a key event in the antilipolytic action of insulin. The role of PDE4, another PDE present in adipocytes, is not yet known. In this work we investigate the role of PDE3B and PDE4 in insulin-induced glucose uptake, GLUT-4 translocation and lipogenesis. Inhibition of PDE3 (OPC3911, milrinone) but not PDE4 (RO 20-1724) lowered insulin-induced glucose uptake and lipogenesis, especially in the presence of isoproterenol (a general beta-adrenergic agonist), CL316243, a selective beta3-adrenergic agonist, and pituitary adenylate cyclase-activating peptide. The inhibitory effect of OPC3911 was associated with reduced translocation of GLUT-4 from the cytosol to the plasma membrane. Both OPC3911 and RO 20-1724 increased protein kinase A (PKA) activity and lipolysis. H89, a PKA inhibitor, did not affect OPC3911-mediated inhibition of insulin-induced glucose uptake and lipogenesis, whereas 8-pCPT-2'-O-Me-cAMP, an Epac agonist which mediates PKA independent cAMP signaling events, mimicked all the effects of OPC3911. Insulin-mediated activation of protein kinase B, a kinase involved in insulin-induced glucose uptake, was apparently not altered by OPC3911. In summary, our data suggest that PDE3B, but not PDE4, contributes to the regulation of insulin-induced glucose uptake, GLUT-4 translocation, and lipogenesis presumably by regulation of a cAMP/Epac signalling mechanisms.

Analysis of the insulin-sensitive phosphodiesterase 3B gene in type 2 diabetes

We screened for mutations in the gene of insulin-sensitive phosphodiesterase 3B (PDE3B), which regulates antilipolytic actions of insulin via reduction of intracellular cyclic AMP levels, in Japanese patients with type 2 diabetes mellitus and lipoatrophic diabetes mellitus using single-stranded conformation polymorphism analysis and Southern analysis and investigated frequencies of variable number of tandem repeats. A silent polymorphism at the Arg463 codon (AGG-->AGA) in exon 4 was identified after examining all 16 exons and exon-intron splicing junctions of the gene. This polymorphism was found in 53 of 100 subjects with type 2 diabetes mellitus, 2 of 5 lipoatrophic diabetic patients and 24 of 50 control subjects, without any significant difference in allele frequency between groups. An EcoRI restriction fragment length polymorphism was identified in patients with type 2 diabetes mellitus and control subjects, again with no differences in occurrence. The allelic distribution of two polymorphic tandem repeats sequences in introns 5 and 12 of the gene did not differ significantly between patients with type 2 diabetes mellitus and control subjects. In conclusion, alterations in the PDE3B gene are unlikely to contribute importantly to the pathogenesis of type 2 diabetes mellitus or lipoatrophic diabetes mellitus in Japan.

Cyclic nucleotide phosphodiesterases: relating structure and function

Cyclic nucleotide phosphodiesterases (PDEs) comprise a superfamily of metallophosphohydrolases that specifically cleave the 3',5'-cyclic phosphate moiety of cAMP and/or cGMP to produce the corresponding 5'-nucleotide. PDEs are critical determinants for modulation of cellular levels of cAMP and/or cGMP by many stimuli. Eleven families of PDEs with varying selectivities for cAMP or cGMP have been identified in mammalian tissues. Within these families, multiple isoforms are expressed either as products of different genes or as products of the same gene through alternative splicing. Regulation of PDEs is important for controlling myriad physiological functions, including the visual response, smooth muscle relaxation, platelet aggregation, fluid homeostasis, immune responses, and cardiac contractility. PDEs are critically involved in feedback control of cellular cAMP and cGMP levels. Activities of the various PDEs are highly regulated by a panoply of processes, including phosphorylation events, interaction with small molecules such as cGMP or phosphatidic acid, subcellular localization, and association with specific protein partners. The PDE superfamily continues to be a major target for pharmacological intervention in a number of medically important maladies.

L-arginine but not D-arginine stimulates insulin-mediated glucose uptake

Our study aims at investigating a possible role for L-arginine and D-arginine in insulin-mediated glucose uptake. Twelve lean healthy subjects volunteered for the study and were submitted to three euglycemic-hyperinsulinemic glucose clamps to investigate the effect of L-arginine (0.5 g/min in the last 60 minutes of the clamp), D-arginine (0.5 g/min in the last 60 minutes of the clamp), and saline 0.9% NaCl on insulin-mediated glucose uptake. All tests were made in random order. In study 1, L-arginine versus saline infusion was associated with a significant increase in blood flow (131% +/- 7% v 87% +/- 5%, P < .001) and whole-body glucose disposal ([WBGD] 61.4 +/- 4.4 v 41.3 +/- 3.5 mumol/kg fat-free mss [FFM].min, P < .001). Analysis of substrate oxidation demonstrated that both oxidative and nonoxidative glucose metabolism was improved by L-arginine delivery. After adjustment for the change in blood flow, WBGD was still greater after L-arginine than after saline infusion. Along with L-arginine infusion and independently of the change in blood flow, the percent change in WBGD correlated with the percent change in plasma cGMP (r = .55, P < .05). D-Arginine infusion did not affect insulin-mediated glucose uptake. In particular, WBGD (42.1 +/- 3.4 v 41.3 +/- 3.5 mumol/kg FFM.min, P = NS) was similar in both experimental conditions. Basal levels (2.8 +/- 0.2 v 2.7 +/- 0.3 nmol/L, P = NS) and the insulin-mediated increase (43% +/- 5% v 39% +/- 4%, P = NS) in plasma cGMP were also superimposable along with insulin plus D-arginine and insulin alone, respectively. Finally, blood flow (224 +/- 29 v 230 +/- 35 mL/min, P = NS) was not different at baseline and was similarly stimulated (84% +/- 4% v 87% +/- 5%, P = NS) by insulin infusion. In conclusion, L-arginine but not D-arginine stimulates insulin-mediated glucose uptake. Nitric oxide (NO), the metabolic mediator for L-arginine, potentiates insulin-mediated glucose uptake through the increase in blood flow. Nevertheless, an independent effect of intracellular cGMP on WBGD cannot be ruled out.