Yoshinori Shimajiri

Cytotoxic T-Lymphocyte Antigen-4 Gene Polymorphisms and Human T-Cell Lymphotrophic Virus-1 Infection: Their Associations with Hashimoto's Thyroiditis in Japanese Patients

Cytotoxic T-lymphocyte antigen-4 (CTLA-4) decreases the immune response of T cells by inactivating the signal that occurs with interaction between CD28 on T cells and B7 on antigen-presenting cells. Gene polymorphisms involving CTLA-4 promoter (-318 C/T), exon 1 (49 A/G), and exon 4 (microsatellite (AT)n) have been linked to Hashimotos thyroiditis (HT) and other autoimmune diseases. HT also has a reported association with human T-cell lymphotrophic virus-1 (HTLV-1) infection. We investigated the occurrence of CTLA-4 polymorphisms in Japanese patients with HT with and without anti-HTLV-1 antibodies (HTLV-1 Ab). DNA samples from 143 patients with HT and 199 controls were subjected to polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis using the restriction enzymes, Bbv 1, Tse 1, and Mse 1. In the HTLV-1 Ab-positive group the exon 1 G allele was more frequent in patients with HT than in controls (67% vs. 53%, p = 0.0377), and in HTLV-1 Ab-negative group it was also frequent in patients with HT than in controls (68% vs. 53%, p = 0.0041). Frequency of the G allele in HT with HTLV-1 Ab was comparable to those without HTLV-1 Ab. Frequency of polymorphism in the promoter did not differ between patients with HT and controls, nor between controls with and without HTLV-1 Ab. HTLV-1 infection is not associated with CTLA-4 polymorphisms in either HT or controls. HTLV-1 infection is not regulated by genetic factor such as CTLA-4, and may affect occurrence of HT as an independent purely environmental factor.

Evidence for a deficient pancreatic β-cell response in a rat model of hyperthyroidism

To clarify mechanism behind the abnormal glucose tolerance, observed in hyperthyroidism, we studied genomic and nongenomic effects of thyroid hormone on insulin secretion using a rat model of hyperthyroidism. Male Sprague-Dawley rats were intraperitoneally injected with vehicle, low (100 microg/kg) or high dose (600 microg/kg) of thyroxin (T(4)) for 2 weeks. Rats treated with high dose, but not low dose, of T(4), showed an increase in serum T(3) levels, and a decrease in body weight as compared to control rats. In rats treated with either dose of T(4), fasting blood glucose levels were increased, but serum insulin levels were similar to those of controls. After an oral glucose load, blood glucose levels were increased in rats treated with high dose, but not low dose, of T(4). Serum insulin levels after the oral glucose load were decreased in rats treated with either dose of T(4). After an intravenous glucose load, blood glucose levels were comparable among groups, but serum insulin levels tended to be low in T(4)-treated rats. Steady-state blood glucose levels were comparable among groups. The insulin secretory responses to high glucose (20mM) or arginine (10mM) of the isolated pancreas was decreased in rats treated with high dose, but not low dose, of T(4). Mean insulin secretory response to glucose and arginine were decreased by 40.1% and by 60.4% in high-dose-T(4)-treated rats. Addition of T(3) in the perfusion medium decreased glucose-induced insulin release. Ratios of proinsulin mRNA levels to beta-actin mRNA were decreased in the islets of T(4)-treated rats (0.45 +/- 0.07 vs control 0.61 +/- 0.03, p < 0.05). Levels of TR (thyroid hormone nuclear receptor) alpha1 + cErb Aalpha2 mRNA, but not TRbeta1, were decreased in the pancreatic islets of T(4)-treated rats. Calculated islet area was increased, but the number of beta-cells determined immunohistochemically was not increased in T(4)-treated rats, nor the volume density of insulin positive islets. We concluded that a deficient pancreatic beta-cell response to glucose, rather than insulin resistance, was responsible for abnormal glucose tolerance in this model of hyperthyroidism. Thyroid hormone causes a decrease in glucose-induced insulin secretion. We observed nongenomic and genomic effects of thyroid hormone on glucose-induced insulin secretion.

Protein kinase B/Akt signalling is required for palmitate-induced β-cell lipotoxicity

Aim:  This study was conducted to clarify cell death and survival signals in pancreatic β‐cell lipotoxicity.

Autophagy protects against human islet amyloid polypeptide‐associated apoptosis

Aims/Introduction:  Islets in type 2 diabetes are characterized by deposition of islet amyloid polypeptide (IAPP) as well as β‐cell dysfunction. The unique amyloidogenic character of human (h)IAPP is associated with cytotoxicity. Autophagy is a ubiquitous system of cellular recycling that contributes to cell survival. Thus, we examined whether autophagy could ameliorate hIAPP‐associated cytotoxicity.

PAX4 mutation (R121W) as a prodiabetic variant in Okinawans.

We previously reported that a missense mutation at codon 121 (CGG(Arg) to TGG(Trp), R121W) of PAX4 may be associated with the onset of type 2 diabetes in Japanese. In this study, we determined the frequency of the R121W mutation of PAX4 and characterized the prodiabetic phenotype in a population-based study. Healthy 372 residents participated in annual health check-ups in Nishihara (Okinawa, Japan) and unrelated 193 type 2 diabetic patients from the outpatient clinic of Ryukyu University Hospital were enrolled. Diagnosis of diabetes was based on the 1997 American Diabetes Association criteria. The R121W mutation in PAX4 was genotyped by PCR-RFLP analysis. In healthy residents, R121W mutation was detected in 12 of 372 residents (3.1%). The prevalence of newly diagnosed type 3 diabetes (25% vs. 5%, p=0.004) and HbA(1c) (5.6+/-1.9 vs. 5.1+/-0.7, p=0.026) was higher in the variants than in the wild-types. The odds ratio of diabetes in the R121W variants was 5.98 with 95% confidence interval from 1.50 to 23.9. The R121W mutation was observed in 12 of the 193 type 2 diabetic patients (6.2%). Onset-ages of diabetes were earlier (37+/-10 vs. 47+/-13 years, p=0.010) and the rate of insulin user was two times higher (83% vs. 41%, p=0.005) in the variants. The R121W mutation in PAX4 is a predisposing factor for the development of type 2 diabetes in Okinawans.

Identification of three new mutations of the HNF-1 α gene in Japanese MODY families

Abstract Aim/hypothesis. We analysed Japanese MODY patients for mutations in the HNF-1α gene. Methods. Fifty unrelated Japanese patients with early-onset diabetes (diagnosed at 25 years of age or younger) or with a strong family history of diabetes were screened for mutations in the HNF-1α gene. Functional studies of the mutant HNF-1α were carried out. Results. We identified three new mutations in the HNF-1α gene in the families with a strong family history for diabetes. One mutation (L518P519fsTCC→A) was identified in three unrelated families, while the other two mutations (T521I and V617I) were identified in one family. We also identified the A site of the promoter (+102G-to-C), which was reported previously. We examined the functional properties of the mutant HNF-1α. By increasing the amount of L518P519fsTCC→A-HNF-1α, increasing inhibition of the transcription of human transthyretin (TTR) was observed (up to 61% of the control). Increasing amounts of T521I-HNF-1α or V617I-HNF-1α mutant proteins increased TTR promoter transcription up to 4.3-fold and 2.4-fold, respectively, whereas both increased transcription up to 12.4-fold of the control. Conclusion/interpretation. The L518P519fsTCC→A was identified for the first time and this mutation might be a common cause of Japanese MODY3 in Okinawa area. In addition, both the T521I and V617I mutations were present in two patients in the same family. Since the prevalence of these mutations is relatively high (10%, 5/50), the HNF-1α gene needs to be screened for mutations in patients either with early-onset diabetes or with a strong family history for diabetes.

Chronic kidney disease has a more powerful impact on peripheral arterial disease than metabolic syndrome in Japanese type 2 diabetic patients.

BACKGROUND Chronic kidney disease (CKD) and metabolic syndrome have been recognized as risk factors for cardiovascular disease. However, there is no information comparing their impact on macroangiopathy in diabetic patients. Thus, we studied the prevalence of CKD and metabolic syndrome in Japanese type 2 diabetic patients and then compared their impact on peripheral arterial disease (PAD) in type 2 diabetic patients. METHODS This study focused on Japanese type 2 diabetic patients without hemodialysis (n = 1014). Patients with albuminuria, including microalbuminuria and/or an estimated glomerular filtration rate less than 60 mL/min/1.73(2), were diagnosed as having CKD. PAD was defined as ankle-brachial blood pressure index less than 0.9. RESULTS The prevalence of CKD and metabolic syndrome was 47.1% and 39.6%, respectively. In four age- and duration-matched groups classified by the presence or absence of CKD and metabolic syndrome, the prevalence of PAD was significantly higher in groups with CKD alone than those with metabolic syndrome alone, and the high prevalence in the groups with CKD was not influenced by the coexistence with metabolic syndrome. CONCLUSIONS This study indicates that CKD has more powerful impact on PAD than metabolic syndrome in type 2 diabetic patients.

Kir6.2 E23K polymorphism is related to secondary failure of sulfonylureas in non-obese patients with type 2 diabetes

The Kir6.2 E23K polymorphism was studied with a special reference to secondary sulfonylurea (SU) failure in non‐obese patients with type 2 diabetes.