Islet cell autoimmunity and mitochondrial DNA mutation in Korean subjects with typical and atypical Type I diabetes

Mitochondrial regulation in human pluripotent stem cells during reprogramming and β cell differentiation

Mitochondria are the powerhouse of the cell and dynamically control fundamental biological processes including cell reprogramming, pluripotency, and lineage specification. Although remarkable progress in induced pluripotent stem cell (iPSC)-derived cell therapies has been made, very little is known about the role of mitochondria and the mechanisms involved in somatic cell reprogramming into iPSC and directed reprogramming of iPSCs in terminally differentiated cells. Reprogramming requires changes in cellular characteristics, genomic and epigenetic regulation, as well as major mitochondrial metabolic changes to sustain iPSC self-renewal, pluripotency, and proliferation. Differentiation of autologous iPSC into terminally differentiated β-like cells requires further metabolic adaptation. Many studies have characterized these alterations in signaling pathways required for the generation and differentiation of iPSC; however, very little is known regarding the metabolic shifts that govern pluripotency transition to tissue-specific lineage differentiation. Understanding such metabolic transitions and how to modulate them is essential for the optimization of differentiation processes to ensure safe iPSC-derived cell therapies. In this review, we summarize the current understanding of mitochondrial metabolism during somatic cell reprogramming to iPSCs and the metabolic shift that occurs during directed differentiation into pancreatic β-like cells.

Biodistribution of Insulin Following Massive Insulin Subcutaneous Injection

A man in his 30s injected insulin several times into his abdomen and was found dead several hours later. Micropathological findings showed alveolar injury with hemorrhaging and cerebral parietal lobe nerve cell edema. Biochemical examinations showed that the blood insulin level was high, significantly so at the insulin injection sites. The blood glucose and C-peptide levels were low. The insulin level in the kidneys was low. In forensic medicine, a postmortem diagnosis of insulin subcutaneous injection is often difficult. When insulin injection is suspected, particularly high insulin levels can be expected at the insulin injection site, rather than in the blood.

β-cell mitochondria in diabetes mellitus: a missing puzzle piece in the generation of hPSC-derived pancreatic β-cells?

Diabetes mellitus (DM), currently affecting 463 million people worldwide is a chronic disease characterized by impaired glucose metabolism resulting from the loss or dysfunction of pancreatic β-cells with the former preponderating in type 1 diabetes (T1DM) and the latter in type 2 diabetes (T2DM). Because impaired insulin secretion due to dysfunction or loss of pancreatic β-cells underlies different types of diabetes, research has focused its effort towards the generation of pancreatic β-cells from human pluripotent stem cell (hPSC) as a potential source of cells to compensate for insulin deficiency. However, many protocols developed to differentiate hPSCs into insulin-expressing β-cells in vitro have generated hPSC-derived β-cells with either immature phenotype such as impaired glucose-stimulated insulin secretion (GSIS) or a weaker response to GSIS than cadaveric islets. In pancreatic β-cells, mitochondria play a central role in coupling glucose metabolism to insulin exocytosis, thereby ensuring refined control of GSIS. Defects in β-cell mitochondrial metabolism and function impair this metabolic coupling. In the present review, we highlight the role of mitochondria in metabolism secretion coupling in the β-cells and summarize the evidence accumulated for the implication of mitochondria in β-cell dysfunction in DM and consequently, how targeting mitochondria function might be a new and interesting strategy to further perfect the differentiation protocol for generation of mature and functional hPSC-derived β-cells with GSIS profile similar to human cadaveric islets for drug screening or potentially for cell therapy.

The spectrum of clinical presentation, diagnosis, and management of mitochondrial forms of diabetes

Primary mitochondrial diseases refer to a group of heterogeneous and complex genetic disorders affecting 1:5000 people. The true prevalence is anticipated to be even higher because of the complexity of achieving a diagnosis in many patients who present with multisystemic complaints ranging from infancy to adulthood. Diabetes is a prominent feature of several of these disorders which might be overlooked by the endocrinologist. We here review mitochondrial disorders and describe the phenotypic and pathogenetic differences between mitochondrial diabetes mellitus (mDM) and other more common forms of diabetes mellitus.

Mitochondrial metabolism and diabetes

The oversupply of calories and sedentary lifestyle has resulted in a rapid increase of diabetes prevalence worldwide. During the past two decades, lines of evidence suggest that mitochondrial dysfunction plays a key role in the pathophysiology of diabetes. Mitochondria are vital to most of the eukaryotic cells as they provide energy in the form of adenosine triphosphate by oxidative phosphorylation. In addition, mitochondrial function is an integral part of glucose-stimulated insulin secretion in pancreatic β-cells. In the present article, we will briefly review the major functions of mitochondria in regard to energy metabolism, and discuss the genetic and environmental factors causing mitochondrial dysfunction in diabetes. In addition, the pathophysiological role of mitochondrial dysfunction in insulin resistance and β-cell dysfunction are discussed. We argue that mitochondrial dysfunction could be the central defect causing the abnormal glucose metabolism in the diabetic state. A deeper understanding of the role of mitochondria in diabetes will provide us with novel insights in the pathophysiology of diabetes. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2010.00047.x, 2010).

α-helix to β-hairpin transition of human amylin monomer

The human islet amylin polypeptide is produced along with insulin by pancreatic islets. Under some circumstances, amylin can aggregate to form amyloid fibrils, whose presence in pancreatic cells is a common pathological feature of Type II diabetes. A growing body of evidence indicates that small, early stage aggregates of amylin are cytotoxic. A better understanding of the early stages of the amylin aggregation process and, in particular, of the nucleation events leading to fibril growth could help identify therapeutic strategies. Recent studies have shown that, in dilute solution, human amylin can adopt an α-helical conformation, a β-hairpin conformation, or an unstructured coil conformation. While such states have comparable free energies, the β-hairpin state exhibits a large propensity towards aggregation. In this work, we present a detailed computational analysis of the folding pathways that arise between the various conformational states of human amylin in water. A free energy surface for amylin in explicit water is first constructed by resorting to advanced sampling techniques. Extensive transition path sampling simulations are then employed to identify the preferred folding mechanisms between distinct minima on that surface. Our results reveal that the α-helical conformer of amylin undergoes a transformation into the β-hairpin monomer through one of two mechanisms. In the first, misfolding begins through formation of specific contacts near the turn region, and proceeds via a zipping mechanism. In the second, misfolding occurs through an unstructured coil intermediate. The transition states for these processes are identified. Taken together, the findings presented in this work suggest that the inter-conversion of amylin between an α-helix and a β-hairpin is an activated process and could constitute the nucleation event for fibril growth.

Clinical features, diagnosis and management of maternally inherited diabetes and deafness (MIDD) associated with the 3243A>G mitochondrial point mutation

Maternally inherited diabetes and deafness (MIDD) affects up to 1% of patients with diabetes but is often unrecognized by physicians. It is important to make an accurate genetic diagnosis, as there are implications for clinical investigation, diagnosis, management and genetic counselling. This review summarizes the range of clinical phenotypes associated with MIDD; outlines the advances in genetic diagnosis and pathogenesis of MIDD; summarizes the published prevalence data and provides guidance on the clinical management of these patients and their families.

Effects of structured hospital-based care compared with standard care for Type 2 diabetes-The Asker and Baerum Cardiovascular Diabetes Study, a randomized trial

AIMS

Few studies have compared structured vs. standard care on the effects of modifying several cardiovascular (CV) risk factors in subjects with Type 2 diabetes. Because of the complexity of the disease, we hypothesized that structured care with a multi-interventional approach is necessary to effectively reach treatment goals and to reduce CV risk.

METHODS

An open 2-year parallel-group study in 120 patients (age 59 +/- 10 years, 31 females) with Type 2 diabetes (median duration 4 years) was conducted. The patients were randomized to standard care (follow-up by their general practitioner) or to structured care at a hospital outpatient clinic consisting of an initial 6 months' lifestyle programme followed by targeted intensified pharmacological treatment to reach prespecified goals for glycaemic, lipid and blood pressure (BP) control. The primary outcome was change in the estimated 10-year absolute risk for fatal coronary heart disease (CHD).

RESULTS

One hundred and six patients completed the study. Improvements were greater among patients receiving structured rather than standard care for systolic BP, triglycerides, glucose and glycated haemoglobin (HbA(1c)) (P < 0.05), as well as for the estimated 10-year CHD-risk (17.9% to 14.5% vs. 18.3% to 19.6%) and the prevalence of a CHD risk >or= 20% (38% to 22% vs. 39% to 45%). Most of the reduction in estimated CHD risk (77%) in the structured care group was obtained during the period (6-24 months) with intensified pharmacological treatment (P < 0.01).

CONCLUSIONS

This study shows that 2 years of structured care combining lifestyle and pharmacological interventions improved several CV risk factors and reduced the estimated 10-year absolute risk for CHD in patients with Type 2 diabetes.

Exercise training protects the renal circulation against high glucose challenge

It has been shown previously that high glucose causes direct and acute endothelial dysfunction in non-diabetic isolated rabbit kidney. This study assessed whether exercise training is able to maintain normal renal vascular endothelial function despite high glucose exposure. Animals were pen confined (SED) or treadmill trained over a 12-week period (ExT). Kidneys isolated from SED and ExT rabbits were continuously perfused ex vivo during 3 h with Krebs-Henseleit solutions containing normal (5.5 mm) or high (15 mm) concentrations of d-glucose. In the SED 5.5 group, acetylcholine (ACh) induced dose-related vasodilator responses, reaching the maximum of 41+/- 2% (n=10; P<0.05). In the kidneys perfused with high concentrations of glucose (SED 15), endothelium-dependent vasodilation was significantly blunted. Maximal relaxation in the presence of 15 mm glucose was of 19 +/- 2%, which was significantly different from the SED 5.5 group (41+/- 2%, n=10, P<0.01). In the ExT 5.5 group, ACh-induced vasodilation was significantly enhanced when compared with the SED 5.5 group, reaching the maximum of (52+/- 2%, n=10, P<0.05). Moreover, the exposure of the renal circulation of ExT animals to high glucose did not change endothelium-dependent vasodilation induced by ACh (46+/- 3%, n=6), when compared with the ExT 5.5 group. Finally, exercise training prevented the deleterious effects of high glucose on endothelial-dependent renal vasodilation (SED 15: 19+/- 2% vs. ExT 15: 46+/- 3%; P<0.05). It is concluded that exercise training protects the rabbit renal circulation against endothelial dysfunction elicited by acute exposure to moderately elevated glucose levels, corresponding to the postprandial glycemia of diabetes type 2 patients under treatment. The enhanced renal vasodilator reserve elicited by exercise training turns out to be a response that protects the kidney from the deleterious effects of glycemic peaks.

Glucose levels observed in daily clinical practice induce endothelial dysfunction in the rabbit macro- and microcirculation

We investigated whether different concentrations of elevated glucose - corresponding to levels observed in patients with type 2 diabetes under routine care (post-prandial mean and maximum values) and those used for diagnosing diabetes - induce impairment of vascular reactivity of the macro- and microcirculation in non-diabetic rabbits. Aortic rings and isolated perfused kidneys from normal rabbits were acutely exposed (3 h) to normal (5.5 mm) or high (7-25 mM) D-glucose concentrations. Vascular reactivity was evaluated with endothelium-dependent [acetylcholine (ACh) and bradykinin (BK)] and independent [sodium nitroprusside (SNP)] vasodilating agents. Endothelium-dependent relaxation of the thoracic aorta induced by ACh or BK was significantly attenuated after a 3-h exposure to high D-glucose (15-25 mM) but not after corresponding increased osmolarity with mannitol solutions. Relaxation induced by SNP (endothelium-independent) was not affected by high D-glucose concentrations. Moreover, endothelium-dependent but not independent vasodilation of the isolated rabbit kidney was also impaired after 3-h perfusion with high D-glucose (11.1-25 mM). Perfusion with mannitol solutions (15-25 mM) partially blunted endothelium-dependent renal vasodilation. It is concluded that acute hyperglycemia corresponding to post-prandial levels in patients with type 2 diabetes induces endothelial dysfunction of conduit vessels as well as of the renal circulation of non-diabetic rabbits.