Inflammatory mediators and islet β-cell failure: a link between type 1 and type 2 diabetes

Pancreatic islet β-cell death occurs in type 1 and 2 diabetes mellitus, leading to absolute or relative insulin deficiency. β-cell death in type 1 diabetes is due predominantly to autoimmunity. In type 2 diabetes β-cell death occurs as the combined consequence of increased circulating glucose and saturated fatty acids together with adipocyte secreted factors and chronic activation of the innate immune system. In both diabetes types intra-islet inflammatory mediators seem to trigger a final common pathway leading to β-cell apoptosis. Therefore anti-inflammatory therapeutic approaches designed to block β-cell apoptosis could be a significant new development in type 1 and 2 diabete

Obesity‐induced changes in gene expression in feline adipose and skeletal muscle tissue

Indoor-confined cats are prone to developing obesity due to a sedentary life and an energy intake exceeding energy requirements. As in humans, feline obesity decreases insulin sensitivity and increases the risk of developing feline diabetes mellitus, but the pathophysiological mechanisms are currently poorly understood. Human obesity-related metabolic alterations seem to relate to changes in the expression of genes involved in glucose metabolism, insulin action and inflammation. The objective of the current study was to investigate changes in the expression of genes relating to obesity, glucose metabolism and inflammation in cats with non-experimentally induced obesity. Biopsies from the sartorius muscle and subcutaneous adipose tissue were obtained from 73 healthy, neutered, indoor-confined domestic shorthaired cats ranging from lean to obese. Quantification of obesity-related gene expression levels relative to glyceraldehyde-3-phosphate dehydrogenase was performed by quantitative real-time polymerase chain reaction. A negative association between obesity and adiponectin expression was observed in the adipose tissue (mean ± SD; normal weight, 27.30 × 10-3 ± 77.14 × 10-3 ; overweight, 2.89 × 10-3 ± 0.38 × 10-3 and obese, 2.93 × 10-3 ± 4.20 × 10-3 , p < 0.05). In muscle, the expression of peroxisome proliferative activated receptor-γ2 and plasminogen activator inhibitor-1 was increased in the obese compared to the normal-weight cats, and resistin was increased in the normal-weight compared to the overweight cats. There were no detectable obesity-related changes in the messenger RNA levels of inflammatory cytokines. In conclusion, a possible obesity-related low-grade inflammation caused by increased expression of key proinflammatory regulators was not observed. This could imply that the development of feline obesity and ensuing insulin resistance may not be based on tissue-derived inflammation, but caused by several determining factors, many of which still need further investigation

JNK1 Deficient Insulin-Producing Cells Are Protected against Interleukin-1 beta-Induced Apoptosis Associated with Abrogated Myc Expression

The relative contributions of the JNK subtypes in inflammatory β-cell failure and apoptosis are unclear. The JNK protein family consists of JNK1, JNK2, and JNK3 subtypes, encompassing many different isoforms. INS-1 cells express JNK1α1, JNK1α2, JNK1β1, JNK1β2, JNK2α1, JNK2α2, JNK3α1, and JNK3α2 mRNA isoform transcripts translating into 46 and 54 kDa isoform JNK proteins. Utilizing Lentiviral mediated expression of shRNAs against JNK1, JNK2, or JNK3 in insulin-producing INS-1 cells, we investigated the role of individual JNK subtypes in IL-1β-induced β-cell apoptosis. JNK1 knockdown prevented IL-1β-induced INS-1 cell apoptosis associated with decreased 46 kDa isoform JNK protein phosphorylation and attenuated Myc expression. Transient knockdown of Myc also prevented IL-1β-induced apoptosis as well as caspase 3 cleavage. JNK2 shRNA potentiated IL-1β-induced apoptosis and caspase 3 cleavage, whereas JNK3 shRNA did not affect IL-1β-induced β-cell death compared to nonsense shRNA expressing INS-1 cells. In conclusion, JNK1 mediates INS-1 cell death associated with increased Myc expression. These findings underline the importance of differentiated targeting of JNK subtypes in the development of inflammatory β-cell failure and destruction

A Placebo-Controlled Study on the Effects of the Glucagon-Like Peptide-1 Mimetic, Exenatide, on Insulin Secretion, Body Composition and Adipokines in Obese, Client-Owned Cats

Glucagon-like Peptide-1 mimetics increase insulin secretion and reduces body weight in humans. In lean, healthy cats, short-term treatment has produced similar results, whereas the effect in obese cats or with extended duration of treatment is unknown. Here, prolonged (12 weeks) treatment with the Glucagon-like Peptide-1 mimetic, exenatide, was evaluated in 12 obese, but otherwise healthy, client-owned cats. Cats were randomized to exenatide (1.0 μg/kg) or placebo treatment twice daily for 12 weeks. The primary endpoint was changes in insulin concentration; the secondary endpoints were glucose homeostasis, body weight, body composition as measured by dual-energy x-ray absorptiometry and overall safety. An intravenous glucose tolerance test (1 g/kg body weight) was conducted at week 0 and week 12. Exenatide did not change the insulin concentration, plasma glucose concentration or glucose tolerance (P>0.05 for all). Exenatide tended to reduce body weight on continued normal feeding. Median relative weight loss after 12 weeks was 5.1% (range 1.7 to 8.4%) in the exenatide group versus 3.2% (range -5.3 to 5.7%) in the placebo group (P = 0.10). Body composition and adipokine levels were unaffected by exenatide (P>0.05). Twelve weeks of exenatide was well-tolerated, with only two cases of mild, self-limiting gastrointestinal signs and a single case of mild hypoglycemia. The long-term insulinotropic effect of exenatide appeared less pronounced in obese cats compared to previous short-term studies in lean cats. Further investigations are required to fully elucidate the effect on insulin secretion, glucose tolerance and body weight in obese cats

The Lysine Demethylase KDM5B Regulates Islet Function and Glucose Homeostasis

Aims. Posttranslational modifications of histones and transcription factors regulate gene expression and are implicated in beta-cell failure and diabetes. We have recently shown that preserving H3K27 and H3K4 methylation using the lysine demethylase inhibitor GSK-J4 reduces cytokine-induced destruction of beta-cells and improves beta-cell function. Here, we investigate the therapeutic potential of GSK-J4 to prevent diabetes development and examine the importance of H3K4 methylation for islet function. Materials and Methods. We used two mouse models of diabetes to investigate the therapeutic potential of GSK-J4. To clarify the importance of H3K4 methylation, we characterized a mouse strain with knockout (KO) of the H3K4 demethylase KDM5B. Results. GSK-J4 administration failed to prevent the development of experimental diabetes induced by multiple low-dose streptozotocin or adoptive transfer of splenocytes from acutely diabetic NOD to NODscid mice. KDM5B-KO mice were growth retarded with altered body composition, had low IGF-1 levels, and exhibited reduced insulin secretion. Interestingly, despite secreting less insulin, KDM5B-KO mice were able to maintain normoglycemia following oral glucose tolerance test, likely via improved insulin sensitivity, as suggested by insulin tolerance testing and phosphorylation of proteins belonging to the insulin signaling pathway. When challenged with high-fat diet, KDM5B-deficient mice displayed similar weight gain and insulin sensitivity as wild-type mice. Conclusion. Our results show a novel role of KDM5B in metabolism, as KDM5B-KO mice display growth retardation and improved insulin sensitivity.Fil: Backe, Marie Balslev. Universidad de Copenhagen; DinamarcaFil: Jin, Chunyu. Universidad de Copenhagen; DinamarcaFil: Andreone, Luz. Universidad Austral. Facultad de Ciencias Biomédicas. Instituto de Investigaciones en Medicina Traslacional. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones en Medicina Traslacional; ArgentinaFil: Sankar, Aditya. Universidad de Copenhagen; Dinamarca. The Novo Nordisk Foundation Center for Stem Cell Biology; DinamarcaFil: Agger, Karl. Universidad de Copenhagen; Dinamarca. The Novo Nordisk Foundation Center for Stem Cell Biology; DinamarcaFil: Helin, Kristian. Universidad de Copenhagen; Dinamarca. The Novo Nordisk Foundation Center for Stem Cell Biology; DinamarcaFil: Madsen, Andreas N.. Universidad de Copenhagen; DinamarcaFil: Poulsen, Steen S.. Universidad de Copenhagen; DinamarcaFil: Bysani, Madhusudhan. Lund University; SueciaFil: Bacos, Karl. Lund University; SueciaFil: Ling, Charlotte. Lund University; SueciaFil: Perone, Marcelo Javier. Universidad de Copenhagen; Dinamarca. Universidad Austral. Facultad de Ciencias Biomédicas. Instituto de Investigaciones en Medicina Traslacional. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones en Medicina Traslacional; ArgentinaFil: Holst, Birgitte. Universidad de Copenhagen; DinamarcaFil: Mandrup Poulsen, Thomas. Universidad de Copenhagen; Dinamarc

Interleukin-1 Stimulates β-Cell Necrosis and Release of the Immunological Adjuvant HMGB1

BACKGROUND: There are at least two phases of β-cell death during the development of autoimmune diabetes: an initiation event that results in the release of β-cell-specific antigens, and a second, antigen-driven event in which β-cell death is mediated by the actions of T lymphocytes. In this report, the mechanisms by which the macrophage-derived cytokine interleukin (IL)-1 induces β-cell death are examined. IL-1, known to inhibit glucose-induced insulin secretion by stimulating inducible nitric oxide synthase expression and increased production of nitric oxide by β-cells, also induces β-cell death. METHODS AND FINDINGS: To ascertain the mechanisms of cell death, the effects of IL-1 and known activators of apoptosis on β-cell viability were examined. While IL-1 stimulates β-cell DNA damage, this cytokine fails to activate caspase-3 or to induce phosphatidylserine (PS) externalization; however, apoptosis inducers activate caspase-3 and the externalization of PS on β-cells. In contrast, IL-1 stimulates the release of the immunological adjuvant high mobility group box 1 protein (HMGB1; a biochemical maker of necrosis) in a nitric oxide-dependent manner, while apoptosis inducers fail to stimulate HMGB1 release. The release of HMGB1 by β-cells treated with IL-1 is not sensitive to caspase-3 inhibition, while inhibition of this caspase attenuates β-cell death in response to known inducers of apoptosis. CONCLUSIONS: These findings indicate that IL-1 induces β-cell necrosis and support the hypothesis that macrophage-derived cytokines may participate in the initial stages of diabetes development by inducing β-cell death by a mechanism that promotes antigen release (necrosis) and islet inflammation (HMGB1 release)

A Systematic Comparison of Purification and Normalization Protocols for Quantitative MicroRNA Expressional Profiling in Insulin-Producing Cells

As microRNAs (miRs) are gaining increasing attention as key regulators of cellular processes, expressional quantification is widely applied. However, in the processing of relatively quantified data, the importance of testing the stability of several reference mRNAs and/or miRs and choosing among these for normalization is often overlooked, potentially leading to biased results. Here, we have optimized the purification of miR-enriched total RNA from pancreatic insulin-producing INS-1 cells. Additionally, we optimized and analyzed miR expression by a qPCR-based microarray and by specific qPCR and tested the stability of candidate reference mRNAs and miRs. Hence, this study gives a widely applicable example on how to easily and systematically test and decide how to normalize miR quantification. We suggest that caution in the interpretation of miR quantification studies that do not comprise stability analysis should be exerted