Glucagon antagonism as a potential therapeutic target in type 2 diabetes

Glucagon is a hormone secreted from the alpha cells of the pancreatic islets. Through its effect on hepatic glucose production (HGP), glucagon plays a central role in the regulation of glucose homeostasis. In patients with type 2 diabetes mellitus (T2DM), abnormal regulation of glucagon secretion has been implicated in the development of fasting and postprandial hyperglycaemia. Therefore, new therapeutic agents based on antagonizing glucagon action, and hence blockade of glucagon-induced HGP, could be effective in lowering both fasting and postprandial hyperglycaemia in patients with T2DM. This review focuses on the mechanism of action, safety and efficacy of glucagon antagonists in the treatment of T2DM and discusses the challenges associated with this new potential antidiabetic treatment modality.     

Role and therapeutic potential of microRNAs in diabetes

The discovery in mammalian cells of hundreds of small RNA molecules, called microRNAs, with the potential to modulate the expression of the majority of the protein-coding genes has revolutionized many areas of biomedical research, including the diabetes field. MicroRNAs function as translational repressors and are emerging as key regulators of most, if not all, physiological processes. Moreover, alterations in the level or function of microRNAs are associated with an increasing number of diseases. Here, we describe the mechanisms governing the biogenesis and activities of microRNAs. We present evidence for the involvement of microRNAs in diabetes mellitus, by outlining the contribution of these small RNA molecules in the control of pancreatic β-cell functions and by reviewing recent studies reporting changes in microRNA expression in tissues isolated from diabetes animal models. MicroRNAs hold great potential as therapeutic targets. We describe the strategies developed for the delivery of molecules mimicking or blocking the function of these tiny regulators of gene expression in living animals. In addition, because changes in serum microRNA profiles have been shown to occur in association with different human diseases, we also discuss the potential use of microRNAs as blood biomarkers for prevention and management of diabetes.     

A calcium-dependent protease as a potential therapeutic target for Wolfram syndrome

Wolfram syndrome is a genetic disorder characterized by diabetes and neurodegeneration and considered as an endoplasmic reticulum (ER) disease. Despite the underlying importance of ER dysfunction in Wolfram syndrome and the identification of two causative genes, Wolfram syndrome 1 (WFS1) and Wolfram syndrome 2 (WFS2), a molecular mechanism linking the ER to death of neurons and β cells has not been elucidated. Here we implicate calpain 2 in the mechanism of cell death in Wolfram syndrome. Calpain 2 is negatively regulated by WFS2, and elevated activation of calpain 2 by WFS2-knockdown correlates with cell death. Calpain activation is also induced by high cytosolic calcium mediated by the loss of function of WFS1. Calpain hyperactivation is observed in the WFS1 knockout mouse as well as in neural progenitor cells derived from induced pluripotent stem (iPS) cells of Wolfram syndrome patients. A small-scale small-molecule screen targeting ER calcium homeostasis reveals that dantrolene can prevent cell death in neural progenitor cells derived from Wolfram syndrome iPS cells. Our results demonstrate that calpain and the pathway leading its activation provides potential therapeutic targets for Wolfram syndrome and other ER diseases.The endoplasmic reticulum (ER) takes center stage for protein production, redox regulation, calcium homeostasis, and cell death (1, 2). It follows that genetic or acquired ER dysfunction can trigger a variety of common diseases, including neurodegenerative diseases, metabolic disorders, and inflammatory bowel disease (3, 4). Breakdown in ER function is also associated with genetic disorders such as Wolfram syndrome (5–8). It is challenging to determine the exact effects of ER dysfunction on the fate of affected cells in common diseases with polygenic and multifactorial etiologies. In contrast, we reasoned that it should be possible to define the role of ER dysfunction in mechanistically homogenous patient populations, especially in rare diseases with a monogenic basis, such as Wolfram syndrome (9).Wolfram syndrome (OMIM 222300) is a rare autosomal recessive disorder characterized by juvenile-onset diabetes mellitus and bilateral optic atrophy (7). Insulin-dependent diabetes usually occurs as the initial manifestation during the first decade of life, whereas the diagnosis of Wolfram syndrome is invariably later, with onset of symptoms in the second and ensuing decades (7, 10, 11). Two causative genes for this genetic disorder have been identified and named Wolfram syndrome 1 (WFS1) and Wolfram syndrome 2 (WFS2) (12, 13). It has been shown that multiple mutations in the WFS1 gene, as well as a specific mutation in the WFS2 gene, lead to β cell death and neurodegeneration through ER and mitochondrial dysfunction (5, 6, 14–16). WFS1 gene variants are also associated with a risk of type 2 diabetes (17). Moreover, a specific WFS1 variant can cause autosomal dominant diabetes (18), raising the possibility that this rare disorder is relevant to common molecular mechanisms altered in diabetes and other human chronic diseases in which ER dysfunction is involved.Despite the underlying importance of ER malfunction in Wolfram syndrome, and the identification of WFS1 and WFS2 genes, a molecular mechanism linking the ER to death of neurons and β cells has not been elucidated. Here we show that the calpain protease provides a mechanistic link between the ER and death of neurons and β cells in Wolfram syndrome.     

Differentiation of iPSCs into insulin-producing cells via adenoviral transfection of PDX-1, NeuroD1 and MafA

Aims

The aim of this study was to evaluate the effect of PDX-1 (pancreatic and duodenal homeobox-1), NeuroD1 (neurogenic differentiation-1) and MafA (V-maf musculoaponeurotic fibrosarcoma oncogene homolog A) in the differentiation of induced pluripotent stem cells (iPSCs) into insulin-producing cells and to explore this new approach of cell transplantation therapy for type 1 diabetes in mice.

Methods

iPSCs were infected with adenovirus (Ad-Mouse PDX-1-IRES-GFP, Ad-Mouse NeuroD1-IRES-GFP and Ad-Mouse Mafa-IRES-GFP) and then differentiated into insulin-producing cells in vitro. RT-PCR was applied to detect insulin gene expression, immunofluorescence to identify insulin protein, and mouse insulin enzyme-linked immunosorbent assay (ELISA) was used to evaluate the amount of insulin at different concentration of glucose. Insulin-producing cells were transplanted into the liver parenchyma of diabetic mice. Immunohistochemistry, intraperitoneal glucose tolerance test (IPGTT) and fasting blood glucose (FBG) were performed to assess the function of insulin-producing cells.

Results

Insulin biosynthesis and secretion were induced in iPSCs and insulin-producing cells were responsive to glucose in a dose-dependent manner. Gene expression of the three-gene-modified embryoid bodies (EBs) was similar to the mouse pancreatic β cell line MIN6. Transplantation of insulin-producing cells into type I diabetic mice resulted in hyperglycemia reversal.

Conclusions

The insulin-producing cells we obtained from three-gene-modified EBs may be used as seed cells for tissue engineering and may represent a cell replacement strategy for the production of β cells for the treatment of type 1 diabetes.     

Epsilon protein kinase C as a potential therapeutic target for the ischemic heart

Ischemic heart disease is the leading cause of morbidity and mortality in the western world. Ischemic damage can occur by acute myocardial infarction, stable angina, cardiac stunning, and myocardial hibernation. In addition, 'scheduled' ischemic events, occurring during cardiac surgery, heart transplantation, and elective angioplasty, can also result in cardiac damage. Ischemic or pharmacological preconditioning can decrease the extent of damage to the myocardium. Although the mechanism of preconditioning-mediated cardioprotection is not fully understood, epsilonPKC has been implicated as a critical mediator of this process in animal studies. The use of isozyme-specific pharmacological tools has permitted a better elucidation of the upstream stimuli and the downstream transducers of epsilonPKC in the pathways leading to cardioprotection. While little is known about the role of epsilonPKC in these pathways in humans, animal studies suggest a potential therapeutic role of epsilonPKC. This review will focus on the role of epsilonPKC in cardiac protection and on the signal transduction cascades that have been implicated in this protection.     

Protein kinase C in cardiac disease and as a potential therapeutic target

Protein kinase C (PKC) is a member of a large family of serine/threonine kinases that plays an integral role in many of the signaling cascades that govern cellular behavior. As such, it is intricately involved in the processes that mediate disease pathogenesis. Strategies that serve to alter PKC function may prove to be useful in the treatment of numerous disease states. This article reviews the various roles PKC may play in cardiovascular disease, specifically with regard to ischemic heart disease, cardiac hypertrophy, heart failure, hypertension, and atherosclerosis, and suggests the potential for developing therapeutic approaches that can target PKC activity.     

IDO and TDO as a potential therapeutic target in different types of depression

Depression is highly prevalent worldwide and a leading cause of disabilty. However, the medications currently available to treat depression fail to adequately relieve depressive symptoms for a large number of patients. Research into the aberrant overactivation of the kynurenine pathway and the production of various active metabolites has brought new insight into the progression of depression. IDO and TDO are the first and rate-limiting enzymes in the kynurenine pathway and regulate the production of active metabolites. There is substantial evidence that TDO and IDO enzyme are activated during depression, and therefore, IDO and TDO inhibitors have been identified as ideal therapeutic targets for depressive disorder. Hence, this review will focus on the kynurenine branch of tryptophan metabolism and describe the role of IDO and TDO in the pathology of depression. In addition, this review will compare the relative imbalance between KYNA and neurotoxic kynurenine metabolites in different psychiatric disorders. Finally, this review is also directed toward assessing whether IDO and TDO are potential therapeutic target in depression associated with other diseases such as diabetes and/or cancer, as well as the development of potent IDO and TDO inhibitors.     

Protein kinase C: A potential therapeutic target for endothelial dysfunction in diabetes

Protein kinase C (PKC) is a family of serine/threonine protein kinases that play an important role in many organs and systems and whose activation contributes significantly to endothelial dysfunction in diabetes. The increase in diacylglycerol (DAG) under high glucose conditions mediates PKC activation and synthesis, which stimulates oxidative stress and inflammation, resulting in impaired endothelial cell function. This article reviews the contribution of PKC to the development of diabetes-related endothelial dysfunction and summarizes the drugs that inhibit PKC activation, with the aim of exploring therapeutic modalities that may alleviate endothelial dysfunction in diabetic patients.     

Role of TGF-beta in proliferative vitreoretinal diseases and ROCK as a therapeutic target

Cicatricial contraction of preretinal fibrous membrane is a cause of severe vision loss in proliferative vitreoretinal diseases such as proliferative diabetic retinopathy (PDR) and proliferative vitreoretinopathy (PVR). TGF-β is overexpressed in the vitreous of patients with proliferative vitreoretinal diseases and is also detectable in the contractile membranes. Therefore, TGF-β is presumed to contribute to the cicatricial contraction of the membranes, however, the underlying mechanisms and TGF-β's importance among various other factors remain to be elucidated. Vitreous samples from PDR or PVR patients caused significantly larger contraction of hyalocyte-containing collagen gels, compared with nonproliferative controls. The contractile effect was strongly correlated with the vitreal concentration of activated TGF-β2 (r = 0.82, P < 0.0001). PDR or PVR vitreous promoted expression of α-smooth muscle actin (α-SMA) and phosphorylation of myosin light chain (MLC), a downstream mediator of Rho-kinase (ROCK), both of which were dramatically but incompletely suppressed by TGF-β blockade. In contrast, fasudil, a potent and selective ROCK inhibitor, almost completely blocked the vitreous-induced MLC phosphorylation and collagen gel contraction. Fasudil disrupted α-SMA organization, but it did not affect its vitreal expression. In vivo, fasudil significantly inhibited the progression of experimental PVR in rabbit eyes without affecting the viability of retinal cells by electroretinographic and histological analyses. These results elucidate the critical role of TGF-β in mediating cicatricial contraction in proliferative vitreoretinal diseases. ROCK, a key downstream mediator of TGF-β and other factors might become a unique therapeutic target in the treatment of proliferative vitreoretinal diseases.