Munehide Matsuhisa

Possible novel therapy for diabetes with cell-permeable JNK-inhibitory peptide

The JNK pathway is known to be activated in several tissues in the diabetic state, and is possibly involved in the development of insulin resistance and suppression of insulin biosynthesis. Here we show a potential new therapy for diabetes using cell-permeable JNK-inhibitory peptide. Intraperitoneal administration of the peptide led to its transduction into various tissues in vivo, and this treatment markedly improved insulin resistance and ameliorated glucose tolerance in diabetic mice. These data indicate that the JNK pathway is critically involved in diabetes and that the cell-permeable JNK-inhibitory peptide may have promise as a new therapeutic agent for diabetes.

Role of Reactive Oxygen Species in the Progression of Type 2 Diabetes and Atherosclerosis

Type 2 diabetes is the most prevalent and serious metabolic disease all over the world, and its hallmarks are pancreatic β-cell dysfunction and insulin resistance. Under diabetic conditions, chronic hyperglycemia and subsequent augmentation of reactive oxygen species (ROS) deteriorate β-cell function and increase insulin resistance which leads to the aggravation of type 2 diabetes. In addition, chronic hyperglycemia and ROS are also involved in the development of atherosclerosis which is often observed under diabetic conditions. Taken together, it is likely that ROS play an important role in the development of type 2 diabetes and atherosclerosis.

The Forkhead Transcription Factor Foxo1 Bridges the JNK Pathway and the Transcription Factor PDX-1 through Its Intracellular Translocation

It has been shown that oxidative stress and activation of the c-Jun N-terminal kinase (JNK) pathway induce the nucleocytoplasmic translocation of the pancreatic transcription factor PDX-1, which leads to pancreatic β-cell dysfunction. In this study, we have shown that the forkhead transcription factor Foxo1/FKHR plays a role as a mediator between the JNK pathway and PDX-1. Under oxidative stress conditions, Foxo1 changed its intracellular localization from the cytoplasm to the nucleus in the pancreatic β-cell line HIT-T15. The overexpression of JNK also induced the nuclear localization of Foxo1, but in contrast, suppression of JNK reduced the oxidative stress-induced nuclear localization of Foxo1, suggesting the involvement of the JNK pathway in Foxo1 translocation. In addition, oxidative stress or activation of the JNK pathway decreased the activity of Akt in HIT cells, leading to the decreased phosphorylation of Foxo1 following nuclear localization. Furthermore, adenovirus-mediated Foxo1 overexpression reduced the nuclear expression of PDX-1, whereas repression of Foxo1 by Foxo1-specific small interfering RNA retained the nuclear expression of PDX-1 under oxidative stress conditions. Taken together, Foxo1 is involved in the nucleocytoplasmic translocation of PDX-1 by oxidative stress and the JNK pathway.

Oxidative stress, ER stress, and the JNK pathway in type 2 diabetes

Pancreatic β-cell dysfunction and insulin resistance are observed in type 2 diabetes. Under diabetic conditions, oxidative stress and ER stress are induced in various tissues, leading to activation of the JNK pathway. This JNK activation suppresses insulin biosynthesis and interferes with insulin action. Indeed, suppression of the JNK pathway in diabetic mice improves insulin resistance and ameliorates glucose tolerance. Thus, the JNK pathway plays a central role in pathogenesis of type 2 diabetes and may be a potential target for diabetes therapy.

A Crucial Role of MafA as a Novel Therapeutic Target for Diabetes

MafA, a recently isolated pancreatic β-cell-specific transcription factor, is a potent activator of insulin gene transcription. In this study, we show that MafA overexpression, together with PDX-1 (pancreatic and duodenal homeobox factor-1) and NeuroD, markedly increases insulin gene expression in the liver. Consequently, substantial amounts of insulin protein were induced by such combination. Furthermore, in streptozotocin-induced diabetic mice, MafA overexpression in the liver, together with PDX-1 and NeuroD, dramatically ameliorated glucose tolerance, while combination of PDX-1 and NeuroD was much less effective. These results suggest a crucial role of MafA as a novel therapeutic target for diabetes.

Probucol preserves pancreatic β-cell function through reduction of oxidative stress in type 2 diabetes

Oxidative stress is induced under diabetic conditions and causes various forms of tissue damage in patients with diabetes. Recently, pancreatic beta-cells have emerged as a putative target of oxidative stress-induced tissue damage and this seems to explain in part the progressive deterioration of beta-cell function in type 2 diabetes. As a step toward clinical trial of antioxidant for type 2 diabetes, we investigated the possible anti-diabetic effects of probucol, an antioxidant widely used as an anti-hyperlipidemic agent, on preservation of beta-cell function in diabetic C57BL/KsJ-db/db mice. Probucol-containing diet was given to mice from 6 to 16 weeks of age. Immunostaining for oxidative stress markers such as 4-hydroxy-2-nonenal (HNE)-modified proteins and heme oxygenase-1 revealed that probucol treatment decreased reactive oxygen species (ROS) in pancreatic islets of diabetic animals. Oxidative stress is known to enhance apoptosis of beta-cells and to suppress insulin biosynthesis, but probucol treatment led to preservation of beta-cell mass and the insulin content. According to intraperitoneal glucose tolerance tests, the probucol treatment preserved glucose-stimulated insulin secretion and improved glucose tolerance at 10 and 16 weeks: insulin, 280+/-82 vs. 914+/-238 pmol/l (120 min, at 16 weeks; P<0.05); glucose, 44.6+/-2.4 vs. 35.2+/-2.6 mmol/l (120 min, at 16 weeks; P<0.05). Thus, our present observations demonstrate the potential usefulness of probucol for treatment of type 2 diabetes.

Oxidative stress induces p21 expression in pancreatic islet cells: possible implication in beta-cell dysfunction

Aims/hypothesis. Prolonged poor glycaemic control in patients with Type II (non-insulin-dependent) diabetes mellitus often causes pancreatic beta-cell dysfunction accompanied by decreases in insulin biosynthesis and beta-cell proliferation. This is well known as a clinical concept called glucose toxicity. Whereas oxidative stress is provoked under diabetic conditions, we examined the possible implication of cyclin-dependent kinase (Cdk) inhibitor p21 (WAF1/CIP1/Sdi1) in beta-cell dysfunction mediated by oxidative stress. Methods. Oxidative stress was induced in isolated rat pancreatic islet cells by treatment with H2O2 and mRNA expression of p21 and insulin was examined by northern blot analyses. Also, the expression of p21 and insulin mRNA was examined in Zucker diabetic fatty rat. In islet cells p21 was overexpressed using adenovirus and its effect on insulin gene transcription was examined. Results. When oxidative stress was charged on isolated rat pancreatic islet cells, p21 mRNA expression was induced whereas insulin mRNA was decreased. Also, when diabetes developed in Zucker diabetic fatty rats, p21 expression was induced and the insulin mRNA expression was reduced. As support for the implication of p21 in impairment of beta-cell function, the p21 overexpression in the islet cells suppressed the insulin gene transcription. Conclusions/interpretation. The expression of cyclin-dependent kinase inhibitor p21, which can be induced by oxidative stress, increases in pancreatic islet cells upon development of diabetes. By suppressing cell proliferation and insulin biosynthesis, the p21 induction is likely to be implicated in the beta-cell glucose toxicity. [Diabetologia (1999) 42: 1093–1097}

Serum endogenous secretory RAGE level is an independent risk factor for the progression of carotid atherosclerosis in type 1 diabetes

OBJECTIVE Advanced glycation end-products (AGEs) and the receptor for AGEs (RAGE) system plays an important role in the development of atherosclerosis. It has been recently reported that endogenous secretory RAGE (esRAGE) and total soluble RAGE (sRAGE) levels are associated with diabetic complications. The aim of the present study is to longitudinally evaluate the association between esRAGE and sRAGE levels and the progression of carotid intima-media thickness (IMT), a surrogate marker of atherosclerosis. METHODS AND RESULTS Japanese type 1 diabetic patients (n=47, aged 24.0+/-3.1 years) were enrolled into a 4-year follow-up study and annual measurements of serum esRAGE and sRAGE levels and IMTs were performed. At baseline, mean-IMT was inversely correlated with circulating esRAGE levels (r=-0.317, p=0.0292), whereas there was not statistical significance between mean-IMT and sRAGE levels. Mean-IMT significantly increased during the follow-up period (from 0.63+/-0.10 to 0.67+/-0.10mm, p=0.0022). Annual increase in mean-IMT (=(mean-IMT after 4 years-mean-IMT at baseline)/4) was positively correlated with the arithmetic average of systolic blood pressure (r=0.310, p=0.0332) and triglyceride (r=0.337, p=0.0201), and inversely correlated with circulating esRAGE levels (r=-0.360, p=0.0124) and sRAGE levels (r=-0.406, p=0.0042) during the follow-up period. Furthermore, stepwise multivariate regression analyses revealed that continuous low levels of circulating esRAGE and sRAGE were determinants of the progression of mean-IMT independently of conventional risk factors. CONCLUSIONS Circulating esRAGE level as well as sRAGE level was an independent risk factor for the progression of carotid IMT in type 1 diabetic subjects.

Antiplatelet Drugs Attenuate Progression of Carotid Intima-Media Thickness in Subjects with Type 2 Diabetes

The intima-media thickness of the carotid artery has been established as a surrogate of definite atherosclerosis in subjects with high risk of vascular events. This study was done to evaluate the effectiveness of long-term antiplatelet therapy in attenuating progression of the intima-media thickness of the carotid artery of subjects with type 2 diabetes. Subjects who had an intima-media thickness over the threshold of the normal subjects but showed no symptoms of vascular events were randomly divided into groups given antiplatelet drugs [ticlopidine (n = 34) or a small dose of aspirin (n = 40)] or no drugs (n = 74). For the follow-up period (3.0+/-0.06 years), the subjects not given antiplatelet drugs showed a significantly higher progression of intima-media thickness (0.067+/-0.009 mm/year) than those given ticlopidine (0.034+/-0.013 mm/year) or aspirin (0.033+/-0.010 mm/year). Stepwise multivariant regression analysis showed that long-term administration of ticlopidine or aspirin significantly reduced the progression of intima-media thickness of diabetic subjects by 0.041 mm/year or 0.032 mm/ year, respectively. These data indicated that despite differences of their pharmacological mechanisms, antiplatelet drugs could attenuate the progression of intima-media thickness of the carotid artery wall of asymptomatic type 2 diabetics who had early-stage carotid atherosclerosis.

Regulation of MafA Expression in Pancreatic β-cells in db/db Mice with Diabetes

OBJECTIVE Islet β-cells loose their ability to synthesize insulin under diabetic conditions, which is at least partially due to the decreased activity of insulin transcription factors such as MafA. Although an in vitro study showed that reactive oxygen species (ROS) decrease MafA expression, the underlying mechanism still remains unclear. In this study, we examined the effects of c-Jun, which is known to be upregulated by ROS, on the expression of MafA under diabetic conditions. RESEARCH DESIGN AND METHODS To examine the protein levels of MafA and c-Jun, we performed histological analysis and Western blotting using diabetic db/db mice. In addition, to evaluate the possible effects of c-Jun on MafA expression, we performed adenoviral overexpression of c-Jun in the MIN6 β-cell line and freshly isolated islets. RESULTS MafA expression was markedly decreased in the islets of db/db mice, while in contrast c-Jun expression was increased. Costaining of these factors in the islets of db/db mice clearly showed that MafA and insulin levels are decreased in c-Jun–positive cells. Consistent with these results, overexpression of c-Jun significantly decreased MafA expression, accompanied by suppression of insulin expression. Importantly, MafA overexpression restored the insulin promoter activity and protein levels that were suppressed by c-Jun. These results indicate that the decreased insulin biosynthesis induced by c-Jun is principally mediated by the suppression of MafA activity. CONCLUSIONS It is likely that the augmented expression of c-Jun in diabetic islets decreases MafA expression and thereby reduces insulin biosynthesis, which is often observed in type 2 diabetes.