Diacylglycerol kinase ζ is a positive insulin secretion regulator in pancreatic β-cell line MIN6.

Some isoforms of diacylglycerol (DAG) kinase (DGK), an enzyme converting DAG into phosphatidic acid, i.e., DGKα, γ and δ, have been reportedly involved in the regulation of pancreatic β-cell function.

Mouse liver blood flow is regulated by hepatic stellate cells in response to the sympathetic neurotransmitter norepinephrine.

Background: There is no clear information on the regulation of liver blood flow by the autonomic nervous system. We conducted this study to investigate whether quiescent hepatic stellate cells (qHSCs) regulate liver blood flow in response to the sympathetic neurotransmitter norepinephrine (NE).

Methods: qHSCs isolated from mice were cultured in Dulbecco's modified Eagle medium without fetal bovine serum for 1 day on collagen gel.

Oral ingestion of Shiikuwasha extract suppresses diabetes progression in mice by preserving β-cell mass.

Introduction: Nobiletin is a polymethoxyflavonoid abundant in citrus peels and has been reported to have various bioactive effects. We have previously reported that nobiletin inhibits endoplasmic reticulum stress-induced apoptosis in the pancreatic β-cell line INS-1 and that continuous subcutaneous administration of nobiletin suppresses the progression of diabetes by protecting β-cells in type 2 diabetic mice. In the present study, we investigated effects of oral ingestion of Shiikuwasha extract rich in nobiletin on the pathogenesis of type 2 diabetes in mice.

GDP-bound Rab27a regulates clathrin disassembly through HSPA8 after insulin secretion.

Clathrin-dependent endocytosis is a key process for secretory cells, in which molecules on the plasma membrane are both degraded and recycled in a stimulus-dependent manner. There are many reports showing that disruption of endocytosis is involved in the onset of various diseases. Recently, it has been reported that such disruption in pancreatic β-cells causes impaired insulin secretion and might be associated with the pathology of diabetes mellitus.

Development of Therapeutic Agents with a Novel Mechanism of Action Targeting Pancreatic β-Cells for Diabetes.

Although diabetes is associated with an increased risk of various diseases, including cancer and infectious diseases, no definitive cure has yet been found. Long-term treatment for blood glucose control significantly reduces the QOL. Pancreatic β-cells are the only cells that can lower blood glucose levels by secreting insulin.

Apigenin Alleviates Endoplasmic Reticulum Stress-Mediated Apoptosis in INS-1 β-Cells.

The improvement of type 2 diabetes mellitus induced by naturally occurring polyphenols, known as flavonoids, has received considerable attention. However, there is a dearth of information regarding the effect of the trihydroxyflavone apigenin on pancreatic β-cell function. In the present study, the anti-diabetic effect of apigenin on pancreatic β-cell insulin secretion, apoptosis, and the mechanism underlying its anti-diabetic effects, were investigated in the INS-ID β-cell line.

Asymmetric dimethylarginine accumulation under hyperglycemia facilitates β-cell apoptosis via inhibiting nitric oxide production.

Low concentrations of nitric oxide (NO) produced by constitutive NO synthase (cNOS) has been shown to suppress apoptosis in pancreatic β-cells. In the present study, the influence of asymmetric dimethylarginine (ADMA), the major endogenous inhibitor of NOS, on the apoptosis-suppressive effect of NO was investigated. The expression of dimethylarginine dimethylaminohydrolase 2 (DDAH2), an ADMA-metabolizing enzyme, in INS-1 β-cells and in mouse pancreatic islets was drastically reduced by in vitro exposure to high-concentration glucose (20 mM) and by in vivo treatment of mice with the insulin receptor blocker S661, which resulted in hyperglycemia, respectively.

[Involvement of Diacylglycerol Kinase on the Regulation of Insulin Secretion in Pancreatic β-Cells during Type 2 Diabetes].

Depression of lipid metabolism in β-cells has been indicated to be one of the causes of impaired insulin secretion in type 2 diabetes. Diacylglycerol (DAG) is an important lipid mediator and is known to regulate insulin secretion in pancreatic β-cells. Intracellular DAG accumulation is involved in β-cell dysfunction in the pathogenesis of type 2 diabetes; thus, the regulation of intracellular DAG levels is likely important for maintaining the β-cell function.

Harmine suppresses collagen production in hepatic stellate cells by inhibiting DYRK1B.

Liver fibrosis is a major consequence of chronic liver disease, where excess extracellular matrix is deposited, due caused by the activation of hepatic stellate cells (HSCs). The suppression of collagen production in HSCs is therefore regarded as a therapeutic target of liver fibrosis. The present study investigated effects of harmine, which is a β-carboline alkaloid and known as an inhibitor of dual-specificity tyrosine-regulated kinases (DYRKs), on the production of collagen in HSCs.

Diacylglycerol kinase δ functions as a proliferation suppressor in pancreatic β-cells.

Although an aberrant reduction in pancreatic β-cell mass contributes to the pathogenesis of diabetes, the mechanism underlying the regulation of β-cell mass is poorly understood. Here, we show that diacylglycerol kinase δ (DGKδ) is a key enzyme in the regulation of β-cell mass. DGKδ expression was detected in the nucleus of β-cells.

[Citrus flavonoids as a target for the prevention of pancreatic β-cells dysfunction in diabetes.].

The number of patients with type 2 diabetes mellitus (T2DM) has rapidly increased, especially in East and Southeast Asia. In these areas, in general, people have especially vulnerable β-cells and insulin secretion deficiency and reduced β-cell mass are the primary cause of T2DM. Therefore, the alleviation of such β-cell dysfunction would provide therapeutic approaches to prevent the development of T2DM.

The sialidase inhibitor 2,3-dehydro-2-deoxy-N-acetylneuraminic acid is a glucose-dependent potentiator of insulin secretion.

Sialidase cleaves sialic acid residues from a sialoglycoconjugate: oligosaccharides, glycolipids and glycoproteins that contain sialic acid. Histochemical imaging of the mouse pancreas using a benzothiazolylphenol-based sialic acid derivative (BTP3-Neu5Ac), a highly sensitive histochemical imaging probe used to assess sialidase activity, showed that pancreatic islets have intense sialidase activity. The sialidase inhibitor 2,3-dehydro-2-deoxy-N-acetylneuraminic acid (DANA) remarkably enhances glutamate release from hippocampal neurons.

Dual effect of reduced type I diacylglycerol kinase activity on insulin secretion from MIN6 β-cells.

The role of type I diacylglycerol kinases (DGKs) in the regulation of insulin secretion was investigated in MIN6 β-cells. In intracellular Ca concentration ([Ca]) measurement experiments, 1 μM R59949, a type I DGK inhibitor, and 10 μM DiC, a diacylglycerol (DAG) analog, amplified 22.2 mM glucose-induced [Ca] oscillations in a protein kinase C (PKC)-dependent manner, whereas 10 μM R59949 and 100 μM DiC decreased [Ca] independent of PKC.

TRPV2 channels mediate insulin secretion induced by cell swelling in mouse pancreatic β-cells.

β-Cell swelling induces membrane depolarization, which has been suggested to be caused at least partly by the activation of cation channels. Here, we show the identification of the cation channels. In isolated mouse pancreatic β-cells, the exposure to 30% hypotonic solution elicited an increase in cytosolic Ca concentration ([Ca]).

[Development and Analysis of Novel Therapeutic Targets to Improve Pancreatic β-Cell Function in Type 2 Diabetes].

Pancreatic β-cell dysfunction is a major feature of type 2 diabetes. Therefore maintenance of β-cell function is essential to preventing the onset and progression of type 2 diabetes. To elucidate the mechanisms underlying the regulation of insulin secretion and β-cell survival, we particularly focused on the roles of gasotransmitters in pancreatic β-cells.

[Regulation of Lipid Metabolism by Diacylglycerol Kinases in Pancreatic β-cells].

The appropriate secretion of insulin from pancreatic β-cells is essential for regulating blood glucose levels. Glucose-stimulated insulin secretion (GSIS) involves the following steps: Glucose uptake by pancreatic β-cells is metabolized to produce ATP. Increased ATP levels result in the closure of ATP-sensitive K(+) (KATP) channels, resulting in membrane depolarization that activates voltage-dependent Ca(2+) channels to subsequently trigger insulin secretion.

Obligatory Role of Early Ca(2+) Responses in H2O2-Induced β-Cell Apoptosis.

Our previous study using apoptosis analysis suggested that Ca(2+) release through inositol 1,4,5-trisphosphate (IP3) receptors and the subsequent Ca(2+) influx through store-operated channels (SOCs) constitute a triggering signal for H2O2-induced β-cell apoptosis. In the present study, we further examined the obligatory role of early Ca(2+) responses in β-cell apoptosis induction. H2O2 induced elevation of the cytosolic Ca(2+) concentration ([Ca(2+)]c) consisting of two phases: an initial transient [Ca(2+)]c elevation within 30 min and a slowly developing one thereafter.

Structure-dependent inhibitory effects of green tea catechins on insulin secretion from pancreatic β-cells.

The effects of green tea catechins on glucose-stimulated insulin secretion (GSIS) were investigated in the β-cell line INS-1D. Epigallocatechin gallate (EGCG) at 10 µM or gallocatechin gallate (GCG) at 30 µM caused significant inhibitory effects on GSIS, and each of these at 100 µM almost abolished it. In contrast, epicatechin (EC) or catechin (CA) had no effect on GSIS at concentrations up to 100 µM.