Impact of hepatic HSP72 on insulin signaling.

Heat shock protein 72 (HSP72) is a major inducible molecule in the heat shock response that enhances intracellular stress tolerance. Decreased expression of HSP72 is observed in type 2 diabetes, which may contribute to the development of insulin resistance and chronic inflammation. We used HSP72 knockout (HSP72-KO) mice to investigate the impact of HSP72 on glucose metabolism and endoplasmic reticulum (ER) stress, particularly in the liver. Under a high-fat diet (HFD) condition, HSP72-KO mice showed glucose intolerance, insulin resistance, impaired insulin secretion, and enhanced hepatic gluconeogenic activity. Furthermore, activity of the c-Jun NH2-terminal kinase (JNK) was increased and insulin signaling suppressed in the liver. Liver-specific expression of HSP72 by lentivirus (lenti) in HFD-fed HSP72-KO mice ameliorated insulin resistance and hepatic gluconeogenic activity. Furthermore, increased adipocyte size and hepatic steatosis induced by the HFD were suppressed in HSP72-KO lenti-HSP72 mice. Increased JNK activity and ER stress upon HFD were suppressed in the liver as well as the white adipose tissue of HSP72-KO lenti-HSP72 mice. Thus, HSP72 KO caused a deterioration in glucose metabolism, hepatic gluconeogenic activity, and ß-cell function. Moreover, liver-specific recovery of HSP72 restored glucose homeostasis. Therefore, hepatic HSP72 may play a critical role in the pathogenesis of type 2 diabetes.

Mild Electrical Stimulation with Heat Shock Reduces Visceral Adiposity and Improves Metabolic Abnormalities in Subjects with Metabolic Syndrome or Type 2 Diabetes: Randomized Crossover Trials.

BACKGROUND: The induction of heat shock protein (HSP) 72 by mild electrical stimulation with heat shock (MES + HS), which improves visceral adiposity and insulin resistance in mice, may be beneficial in treating metabolic syndrome (MS) or type 2 diabetes mellitus (T2DM). METHODS: Using open-label crossover trials, 40 subjects with MS or T2DM were randomly assigned using computer-generated random numbers to 12 weeks of therapeutic MES + HS followed by 12 weeks of no treatment, or vice versa. During the intervention period, physical and biochemical markers were measured. FINDINGS: Compared to no treatment, MES + HS treatment was associated with a significant decrease in visceral adiposity (- 7.54 cm(2) (- 8.61%), 95% CI - 8.55 to - 6.53 (p = 0.037) in MS, - 19.73 cm(2) (- 10.89%), 95% CI - 20.97 to - 18.49 (p = 0.003) in T2DM). Fasting plasma glucose levels were decreased by 3.74 mg/dL (- 5.28%: 95% CI - 4.37 to - 3.09 mg/dL, p = 0.029) in MS and by 14.97 mg/dL (10.40%: 95% CI - 15.79 to 14.15 mg/dL, p < 0.001) in T2DM, and insulin levels were also reduced by 10.39% and 25.93%, respectively. HbA1c levels showed a trend toward reduction (- 0.06%) in MS, and was significantly declined by - 0.43% (95% CI - 0.55 to - 0.31%, p = 0.009) in T2DM. HbA1c level of less than 7.0% was achieved in 52.5% of the MES + HS-treated T2DM patients in contrast to 15% of the non-treated period. Several insulin resistance indices, inflammatory cytokines or adipokines, including C-reactive protein, adiponectin, and tumor necrosis factor-α, were all improved in both groups. In isolated monocytes, HSP72 expression was increased and cytokine expression was reduced following MES + HS treatment. Glucose excursions on meal tolerance test were lower after using MES + HS in T2DM. INTERPRETATION: This combination therapy has beneficial impacts on body composition, metabolic abnormalities, and inflammation in subjects with MS or T2DM. Activation of the heat shock response by MES + HS may provide a novel approach for the treatment of lifestyle-related diseases. FUNDING: Funding for this research was provided by MEXT KAKENHI (Grants-in-Aid for Scientific Research from Ministry of Education, Culture, Sports, Science and Technology, Japan).

Effects of combination therapy with vildagliptin and valsartan in a mouse model of type 2 diabetes.

BACKGROUND: Dipeptidyl peptidase-4 (DPP-4) inhibitors modulate incretin hormones and exert anti-diabetic effects in type 2 diabetes mellitus. Treatment with angiotensin II type 1 receptor blockers (ARB) is a proven successful intervention for hypertension with type 2 diabetes. The present study investigated the combined effects of the DPP-4 inhibitor vildagliptin and the ARB valsartan in a mouse model of type 2 diabetes. METHODS: C57BL/6 J mice fed with high-fat diet (HFD) or db/db mice were treated with placebo, phloridzin (PHZ), vildagliptin alone (ViL), valsartan alone (VaL) or ViL with VaL (ViLVaL) for 8 weeks. RESULTS: Glucose metabolism was improved in response to PHZ, ViL and ViLVaL in both HFD and db/db mice. Upon glucose challenge, ViLVaL showed the greatest suppression of blood glucose excursions, with increased insulin secretion, in db/db mice. ViLVaL treatment also showed an improvement of insulin sensitivity in db/db mice. Serum inflammatory cytokines were significantly decreased, and adiponectin was highest, in the ViLVaL group. ViLVaL improved insulin signaling and attenuated stress signaling in liver with amelioration of hepatic steatosis due to activated fatty acid oxidation in db/db mice. Furthermore, immunohistochemical analysis of the pancreas revealed that the combination treatment resulted in an increased expression of insulin and PDX-1, and increased insulin content. CONCLUSIONS: The combination therapy of ViL and VaL improves both pancreatic beta-cell function and insulin sensitivity, with a reduction of the inflammatory and cell stress milieu in mouse models of T2DM. Our results suggest that this combination therapy exerts additive or even synergistic benefits to treat T2DM.

The impact of Ca²âº/calmodulin-dependent protein kinase II on insulin gene expression in MIN6 cells.

Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is expressed in insulin-secreting ß cells. However, the effects of CaMKII on insulin synthesis are unknown. Although Ser133 phosphorylation of cyclic AMP-responsive element-binding protein (CREB) typically increases CREB transcriptional activity, CaMKII phosphorylates CREB at Ser142 and at Ser133 to exert a dominant inhibitory effect. Our objective was to characterize the role of CaMKII in insulin gene expression. In MIN6 cells, insulin gene promoter activity was significantly down-regulated by wild-type (WT) CaMKIIδ2, but was significantly upregulated after small interfering RNA (siRNA) knockdown of CaMKIIδ expression. These results were independent of glucose concentrations and membrane depolarization. Insulin mRNA levels were also decreased by WT CaMKIIδ2 and increased by CaMKIIδ siRNA. Downregulation of insulin gene promoter activity by WT CaMKIIδ2 was partly mediated via cyclic AMP-responsive element 2 (CRE2). WT CaMKIIδ2 significantly increased CREB phosphorylation at Ser142 and significantly decreased binding to CREB binding protein (CBP), whereas kinase dead CaMKIIδ2 did not. Our results indicate that CaMKIIδ2 downregulates insulin gene expression by Ser142 phosphorylation of CREB and reducing binding of CREB to CBP.

Hyperthermia with mild electrical stimulation protects pancreatic ß-cells from cell stresses and apoptosis.

Induction of heat shock protein (HSP) 72 improves metabolic profiles in diabetic model mice. However, its effect on pancreatic ß-cells is not known. The current study investigated whether HSP72 induction can reduce ß-cell stress signaling and apoptosis and preserve ß-cell mass. MIN6 cells and db/db mice were sham-treated or treated with heat shock (HS) and mild electrical stimulation (MES) (HS+MES) to induce HSP72. Several cellular markers, metabolic parameters, and ß-cell mass were evaluated. HS+MES treatment or HSP72 overexpression increased HSP72 protein levels and decreased tumor necrosis factor (TNF)-α-induced Jun NH(2)-terminal kinase (JNK) phosphorylation, endoplasmic reticulum (ER) stress, and proapoptotic signal in MIN6 cells. In db/db mice, HS+MES treatment for 12 weeks significantly improved insulin sensitivity and glucose homeostasis. Upon glucose challenge, a significant increase in insulin secretion was observed in vivo. Compared with sham treatment, levels of HSP72, insulin, pancreatic duodenal homeobox-1, GLUT2, and insulin receptor substrate-2 were upregulated in the pancreatic islets of HS+MES-treated mice, whereas JNK phosphorylation, nuclear translocation of forkhead box class O-1, and nuclear factor-κB p65 were reduced. Apoptotic signals, ER stress, and oxidative stress markers were attenuated. Thus, HSP72 induction by HS+MES treatment protects ß-cells from apoptosis by attenuating JNK activation and cell stresses. HS+MES combination therapy may preserve pancreatic ß-cell volume to ameliorate glucose homeostasis in diabetes.

Heat shock response regulates insulin sensitivity and glucose homeostasis: pathophysiological impact and therapeutic potential.

A large and increasing number of people in all over the world suffer from obesity, metabolic syndrome (MS) and type 2 diabetes mellitus (T2DM). Attenuation of the heat shock response (HSR), which was originally identified as a cellular defense mechanism, is one of the key factors involved in the deterioration of metabolic abnormalities. On the other hand, activating the HSR increases heat shock protein 72 (HSP72) expression and improves insulin resistance and glucose homeostasis in rodents and humans, possibly by inhibiting the activation of stress kinases such as c-jun terminal kinase (JNK) and inhibitor of kappa B kinase ß (IKKß). These approaches may also reduce inflammatory cytokine production and prevent the onset of atherogenic complications. This review focuses on the physiological effects of HSR in regulating insulin sensitivity and hyperglycemia, and the potential to target the HSR system for the treatment of MS and T2DM, as well as other cellular stress-related diseases.

Heat shock treatment with mild electrical stimulation safely reduced inflammatory markers in healthy male subjects.

OBJECTIVE: Obesity induces chronic inflammation, which contributes to the development and progression of insulin resistance, diabetes and atherosclerosis. We have recently shown that induction of heat shock protein 72 by mild electric current and thermo (MET) treatment in mouse model of type 2 diabetes ameliorated glucose homeostasis and insulin resistance accompanied by reduced adiposity. For clinical application of MET, we confirmed its safety in healthy subjects. METHODS: MET was applied for 10 healthy Japanese male (12 V, 55 pulses/s, 30 min at 42 °C) twice a week for 8 weeks. Fat volume was measured by CT scan and several parameters were investigated. RESULTS: MET did not induce any adverse effects nor muscle contraction/pain. There were no significant alterations in glucose homeostasis or insulin resistance. Visceral and subcutaneous fat volume showed a trend of decrease without significant difference (-3.9% and -4.3%, respectively), which were restored 8 weeks after withdrawal of MET. Interestingly, serum tumor necrosis factor-α (TNF-α: 0.91 ± 0.05 pg/mL vs. 0.67 ± 0.06 pg/mL; p = 0.006) and high sensitivity C-reactive protein (hs-CRP: 521.9 ± 73.9 ng/mL vs. 270.8 ± 43.7 ng/mL; p = 0.023) levels, both of which are associated with chronic inflammation, were significantly decreased. CONCLUSION: MET may be beneficial for the reduction of an inflammatory response observed in diabetes and metabolic syndrome.

A case of ectopic adrenocorticotropic hormone-producing pancreatic neuroendocrine tumor with multiple liver metastases.

Ectopic adrenocorticotropic hormone (ACTH) production by the pancreatic neuroendocrine tumor (p-NET) is relatively rare, and patients with this tumor show poor prognosis. In this study, we present the case of a 64-year-old woman who presented with ectopic ACTH syndrome due to p-NET with multiple liver metastases. Computed tomography revealed that she had multiple masses in the liver and a solid mass in the head of the pancreas. Endocrinological examinations revealed markedly elevated plasma ACTH (735.0 pg/mL) and cortisol (34.7 microg/dL) levels associated with hypokalemia (2.7 mEq/L), diabetes and typical Cushingoid features. Histological examinations by needle biopsy of liver tumors in S5 and S8 indicated metastatic ACTH-producing NET, which was also confirmed by venous sampling. The metastatic live tumor was somatostatin receptor (SSTR)-2a- and SSTR-5-positive as revealed by immunohistochemical staining, and reverse transcription polymerase chain reaction revealed divergent expression patterns of SSTRs, pro-opiomelanocortin, and gastrin mRNA. To avoid complications of hypercortisolemia, metyrapone was first administered to reduce the cortisol levels. After near-normalization of cortisol levels, transarterial chemoembolization and somatostatin analogue treatment were performed. The combination of these treatments effectively decreased ACTH and cortisol levels and also ameliorated hyperglycemia. We have achieved controlled hormone secretion and prevented tumor growth in this patient for more than 20 months, suggesting that highly individualized treatment for NET should be undertaken because of its divergent and heterogeneous characteristics.