Search

OBJECTIVE--Elevated triglyceride (TG) is the major plasma lipid abnormality in obese and diabetic patients and contributes to cardiovascular morbidity in these disorders. We sought to identify novel mechanisms leading to hypertriglyceridemia. Resistance to negative feedback signals from adipose tissue in key central nervous system (CNS) energy homeostatic circuits contributes to the development of obesity. Because triglycerides both represent the largest energy depot in the body and are elevated in both the plasma and adipose in obesity and diabetes, we hypothesized that the same neural circuits that regulate energy balance also regulate the secretion of TGs into plasma. RESEARCH DESIGN AND METHODS--In normal fasting rats, the TG secretion rate was estimated by serial blood sampling after intravascular tyloxapol pretreatment. Neuropeptide Y (NPY) signaling in the CNS was modulated by intracerebroventricular injection of NPY, receptor antagonist, and receptor agonist. RESULTS--A single intracerebroventricular injection of NPY increased TG secretion by 2.5-fold in the absence of food intake, and this was determined to be VLDL by fast performance liquid chromatography (FPLC). This effect was recapitulated by activating NPY signaling in downstream neurons with an NPY-Y5 receptor agouist. An NPY-Y1 receptor antagonist decreased the elevated TGs in the form of VLDL secretion rate by 50% compared with vehicle. Increased TG secretion was due to increased secretion of VLDL particles, rather than secretion of larger particles, because apolipoprotein B100 was elevated in FPLC fractions corresponding to VLDL. CONCLUSIONS--We find that a key neuropeptide system involved in energy homeostasis in the CNS exerts control over VLDL-TG secretion into the bloodstream. Diabetes 57:1482-1490, 2008, Obesity confers significant risk of cardiovascular disease. The major plasma lipid abnormality in obesity is elevated triglycerides (TGs) in the form of VLDL (VLDL-TG) and low HDL cholesterol (rev. in [...]

Glomerular injury plays a pivotal role in the development of diabetic nephropathy. To elucidate molecular mechanisms underlying diabetic glomerulopathy, we compared glomerular gene expression profiles of db/db mice with those of db/m control mice at a normoalbuminuric stage characterized by hyperglycemia and at an early stage of diabetic nephropathy with elevated albuminuria, using cDNA microarray. In db/db mice at the normoalbuminuric stage, hypoxia-inducible factor-1α (HIF-1α), ephrin B2, glomerular epithelial protein 1, and Pod-1, which play key roles in glomerulogenesis, were already upregulated in parallel with an alteration of genes related to glucose metabolism, lipid metabolism, and oxidative stress. Podocyte structure-related genes, actinin 4α and dystroglycan 1 (DG1), were also significantly upregulated at an early stage. The alteration in the expression of these genes was confirmed by quantitative RT-PCR. Through pioglitazone treatment, gene expression of ephrin B2, Pod-1, actinin 4α, and DG1, as well as that of oxidative stress and lipid metabolism, was restored concomitant with attenuation of albuminuria. In addition, HIF-1α protein expression was partially attenuated by pioglitazone. These results suggest that not only metabolic alteration and oxidative stress, but also the alteration of gene expression related to glomerulogenesis and podocyte structure, may be involved in the pathogenesis of early diabetic glomerulopathy in type 2 diabetes., Diabetic nephropathy is the leading cause of end-stage renal disease in the U.S., Japan, and most of Europe (1). Clinical features of diabetic nephropathy are development of albuminuria followed by [...]

Because acetylcholine (ACh) is a recognized potentiator of glucose-stimulated insulin release in the normal β-cell, we have studied ACh's effect on islets of the Goto-Kakizaki (GK) rat, a spontaneous model of type 2 diabetes. We first verified that ACh was able to restore the insulin secretory glucose competence of the GK β-cell. Then, we demonstrated that in GK islets 1) ACh elicited a first-phase insulin release at low glucose, whereas it had no effect in Wistar; 2) total phospholipase C activity, ACh-induced inositol phosphate production, and intracellular free calcium concentration ([[Ca.sup.2+]].sub.i]) elevation were normal; 3) ACh triggered insulin release, even in the presence of thapsigargin, which induced a reduction of the ACh-induced [[Ca.sup.2+]].sub.i] response (suggesting that ACh produces amplification signals that augment the efficacy of elevated [[Ca.sup.2+]].sub.i] on GK exocytosis); 4) inhibition of protein kinase C did not affect [[Ca.sup.2+]].sub.i] nor the insulin release responses to ACh; and 5) inhibition of cAMP-dependent protein kinases (PKAs), adenylyl cyclases, or cAMP generation, while not affecting the [[Ca.sup.2+]].sub.i] response, significantly lowered the insulinotropic response to ACh (at low and high glucose). In conclusion, ACh acts mainly through activation of the cAMP/PKA pathway to potently enhance [Ca.sup.2+]-stimulated insulin release in the GK β-cell and, in doing so, normalizes its defective glucose responsiveness., Cholinergic muscarinic agonists, including the endogenous neurotransmitter acetylcholine (ACh) and the synthetic nonhydrolyzable analog carbachol, are known to enhance glucose-stimulated insulin secretion by the normal β-cell (1). ACh is released [...]

The role of protein kinase C (PKC) in glucose-stimulated insulin secretion (GSIS) is controversial. Using recombinant adenoviruses for overexpression of PKCα and PKCδ, in both wild-type (WT) and kinase-dead (KD) forms, we here demonstrate that activation of these two PKCs is neither necessary nor sufficient for GSIS from batch-incubated, rat pancreatic islets. In contrast, responses to the pharmacologic activator 12-O-tetradecanoylphorbol-13-acetate (TPA) were reciprocally modulated by overexpression of the PKCαWT or PKCαKD but not the corresponding PKCδ adenoviruses. The kinetics of the secretory response to glucose (monitored by perifusion) were not altered in either cultured islets overexpressing PKCαKD or freshly isolated islets stimulated in the presence of the conventional PKC (cPKC) inhibitor Go6976. However, the latter did inhibit the secretory response to TPA. Using phosphorylation state-specific antisera for consensus PKC phosphorylation sites, we also showed that (compared with TPA) glucose causes only a modest and transient functional activation of PKC (maximal at 2-5 min). However, glucose did promote a prolonged (15 min) phosphorylation of PKC substrates in the presence of the phosphatase inhibitor okadaic acid. Overall, the results demonstrate that glucose does stimulate PKCα in pancreatic islets but that this makes little overall contribution to GSIS., The protein kinase C (PKC) family of serine and threonine kinases has 10 members that are characterized by their molecular structure and activation requirements. The subfamilies consist of the conventional [...]

Whereas the loss of ATP-sensitive [K.sup.+] channel ([K.sub.ATP] channel) activity in human pancreatic β-cells causes severe hypoglycemia in certain forms of hyperinsulinemic hypoglycemia, similar channel loss in sulfonylurea receptor-1 (SUR1) and Kir6.2 null mice yields a milder phenotype that is characterized by normoglycemia, unless the animals are stressed. While investigating potential compensatory mechanisms, we found that incretins, specifically glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP), can increase the cAMP content of Sur1KO islets but do not potentiate glucose-stimulated insulin release. This impairment is secondary to a restriction in the ability of Sur1KO β-cells to sense cAMP correctly. Potentiation does not appear to require cAMP-activated protein kinase (PKA) because H-89 (N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide) and KT5720, inhibitors of PKA, do not affect stimulation by GLP-1, GIP, or exendin-4 in wild-type islets, although they block phosphorylation of cAMP-response element-binding protein. The impaired incretin response in Sur1KO islets is specific; the stimulation of insulin release by other modulators, including mastoparan and activators of protein kinase C, is conserved. The results suggest that the defect responsible for the loss of cAMP-induced potentiation of insulin secretion is PKA independent. We hypothesize that a reduced release of insulin in response to incretins may contribute to the unexpected normoglycemic phenotype of Sur1KO mice versus the pronounced hypoglycemia seen in neonates with loss of [K.sub.ATP] channel activity., Insulin secretion is a unique example of exocytosis controlled by metabolic, ionic, and hormonal pathways. An imbalance in insulin release due to disruption of these pathways can produce the profound [...]

The fast component (mode 1) of [Ca.sup.2+]-dependent exocytosis in pancreatic β-cells, unlike that in adrenal chromaffin cells, is regulated by cytosolic ATP in a concentration-dependent manner. This action of ATP [...]

Recent genome searches suggest a putative linkage of many loci to susceptibility to type I diabetes. The chromosome 2q31-35 region is reported to be linked to susceptibility to type I [...]

Glucose induces biphasic insulin secretion by the islet β-cell. Based on recent knowledge on glucose signaling in the β-cell, the underlying mechanisms for this biphasicity could be envisaged as follows. [...]

Leptin resistance has recently been confirmed not only in animal obese models but in human obesity. Evidence is rapidly emerging that suggests that activation of histamine signaling in the hypothalamus [...]

Histamine neurons are widely distributed in the brain and suppress food intake through the histamine [H.sub.1] receptor ([H.sub.1]-R) in the hypothalamus. To examine the role of neuronal histamine in leptin [...]

Type 2 diabetes is characterized by impaired Β-cell function, hyperglycemia, and islet amyloid deposition. The primary constituent of islet amyloid is the 37-amino acid Β-cell product called islet amyloid polypeptide [...]

We have shown previously that continuous (6 days) intracerebroventricular (ICV) leptin infusion in normal rats resulted in decreases in food intake and body weight. A reduction of food intake imposed [...]

Polymorphic markers within the CTLA4 gene on chromosome 2q33 have been shown to be associated with type 1 diabetes. Therefore, a gene responsible for the disease (IDDM12) most likely lies [...]