Angiotensin Converting Enzyme-2 Therapy Improves Liver Fibrosis and Glycemic Control in Diabetic Mice With Fatty Liver.

Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease and is frequently associated with type 2 diabetes. However, there is no specific medical therapy to treat this condition. Angiotensin-converting enzyme 2 (ACE2) of the protective renin angiotensin system generates the antifibrotic peptide angiotensin-(1-7) from profibrotic angiotensin II peptide. In this study, we investigated the therapeutic potential of ACE2 in diabetic NAFLD mice fed a high-fat (20%), high-cholesterol (2%) diet for 40 weeks. Mice were given a single intraperitoneal injection of ACE2 using an adeno-associated viral vector at 30 weeks of high-fat, high-cholesterol diet (15 weeks after induction of diabetes) and sacrificed 10 weeks later. ACE2 significantly reduced liver injury and fibrosis in diabetic NAFLD mice compared with the control vector injected mice. This was accompanied by reductions in proinflammatory cytokine expressions, hepatic stellate cell activation, and collagen 1 expression. Moreover, ACE2 therapy significantly increased islet numbers, leading to an increased insulin protein content in ß-cells and plasma insulin levels with subsequent reduction in plasma glucose levels compared with controls. Conclusion: We conclude that ACE2 gene therapy reduces liver fibrosis and hyperglycemia in diabetic NAFLD mice and has potential as a therapy for patients with NAFLD with diabetes.

Casitas b-lineage lymphoma-deficient mice are protected against high-fat diet-induced obesity and insulin resistance.

Casitas b-lineage lymphoma (c-Cbl) is a multiadaptor protein with E3-ubiquitin ligase activity involved in regulating the degradation of receptor tyrosine kinases. We have recently reported that c-Cbl(-/-) mice exhibit a lean phenotype and enhanced peripheral insulin action likely due to elevated energy expenditure. In the study reported here, we examined the effect of a high-fat diet on energy homeostasis and glucose metabolism in these animals. When c-Cbl(-/-) mice were fed a high-fat diet for 4 weeks, they maintained hyperphagia, higher whole-body oxygen consumption (27%), and greater activity (threefold) compared with wild-type animals fed the same diet. In addition, the activity of several enzymes involved in mitochondrial fat oxidation and the phosphorylation of acetyl CoA carboxylase was significantly increased in muscle of high-fat-fed c-Cbl-deficient mice, indicating a greater capacity for fat oxidation in these animals. As a result of these differences, fat-fed c-Cbl(-/-) mice were 30% leaner than wild-type animals and were protected against high-fat diet-induced insulin resistance. These studies are consistent with a role for c-Cbl in regulating nutrient partitioning in skeletal muscle and emphasize the potential of c-Cbl as a therapeutic target in the treatment of obesity and type 2 diabetes.

Low serum PYY is linked to insulin resistance in first-degree relatives of subjects with type 2 diabetes.

Low circulating peptide YY (PYY) levels are reported in obese and type II diabetic subjects and results from PYY knockout animals suggests that PYY deficiency may have a causative role in the etiology of obesity and type 2 diabetes. Here, our aims were to determine whether people with a genetic predisposition to developing type 2 diabetes and obesity differ from otherwise similar subjects without such family history, in fasting or meal-related PYY levels, fasting insulin, insulin secretion (HOMA-B) and insulin sensitivity. We also investigated whether PYY ablation affects the intrinsic ability of islets to secrete insulin, which may be a contributing factor to the hyperinsulinemia observed in PYY knockout mice. Healthy female first-degree relatives of people with type 2 diabetes were matched for age, gender and BMI to control subjects but had significantly lower insulin sensitivity (p<0.05). Relatives also had significantly lower fasting serum PYY levels than controls (p<0.05), but their PYY response to a high fat meal (4250 kJ, 73% fat) was not significantly different. Fasting PYY level correlated positively with glucose infusion rate (r=0.713, p=0.002) and fasting adiponectin (r=0.5, p=0.02). Islets of Langerhans from PYY knockout mice were found to hypersecrete insulin in response to 25 mM glucose (p<0.05). These data demonstrate that lack of PYY enhances insulin secretion from the Islets of Langerhans and that low fasting PYY levels are associated with insulin resistance in humans. Together, these findings suggest that low circulating levels of PYY could contribute to hyperinsulinemia and insulin resistance, and possibly contribute to subsequent development of obesity and type 2 diabetes.

NPY signalling in early osteoblasts controls glucose homeostasis.

OBJECTIVE: The skeleton has recently emerged as an additional player in the control of whole-body glucose metabolism; however, the mechanism behind this is not clear. METHODS: Here we employ mice lacking neuropeptide Y, Y1 receptors solely in cells of the early osteoblastic lineage (Y1f3.6Cre), to examine the role of osteoblastic Y1 signalling in glycaemic control. RESULTS: Y1f3.6Cre mice not only have a high bone mass phenotype, but importantly also display altered glucose homeostasis; significantly decreased pancreas weight, islet number and pancreatic insulin content leading to elevated glucose levels and reduced glucose tolerance, but with no effect on insulin induced glucose clearance. The reduced glucose tolerance and elevated bone mass was corrected in Y1f3.6Cre mice by bone marrow transplant from wildtype animals, reinforcing the osteoblastic nature of this pathway. Importantly, when fed a high fat diet, Y1f3.6Cre mice, while equally gaining body weight and fat mass compared to controls, showed significantly improved glucose and insulin tolerance. Conditioned media from Y1f3.6Cre osteoblastic cultures was unable to stimulate insulin expression in MIN6 cells compared to conditioned media from wildtype osteoblast, indicating a direct signalling pathway. Importantly, osteocalcin a secreted osteoblastic factor previously identified as a modulator of insulin secretion was not altered in the Y1f3.6Cre model. CONCLUSION: This study identifies the existence of other osteoblast-derived regulators of pancreas function and insulin secretion and illustrates a mechanism by which NPY signalling in bone tissue is capable of regulating pancreatic function and glucose homeostasis.

Contribution of Intronic miR-338-3p and Its Hosting Gene AATK to Compensatory ß-Cell Mass Expansion.

The elucidation of the mechanisms directing ß-cell mass regeneration and maintenance is of interest, because the deficit of ß-cell mass contributes to diabetes onset and progression. We previously found that the level of the microRNA (miRNA) miR-338-3p is decreased in pancreatic islets from rodent models displaying insulin resistance and compensatory ß-cell mass expansion, including pregnant rats, diet-induced obese mice, and db/db mice. Transfection of rat islet cells with oligonucleotides that specifically block miR-338-3p activity increased the fraction of proliferating ß-cells in vitro and promoted survival under proapoptotic conditions without affecting the capacity of ß-cells to release insulin in response to glucose. Here, we evaluated the role of miR-338-3p in vivo by injecting mice with an adeno-associated viral vector permitting specific sequestration of this miRNA in ß-cells. We found that the adeno-associated viral construct increased the fraction of proliferating ß-cells confirming the data obtained in vitro. miR-338-3p is generated from an intron of the gene coding for apoptosis-associated tyrosine kinase (AATK). Similarly to miR-338-3p, we found that AATK is down-regulated in rat and human islets and INS832/13 ß-cells in the presence of the cAMP-raising agents exendin-4, estradiol, and a G-protein-coupled Receptor 30 agonist. Moreover, AATK expression is reduced in islets of insulin resistant animal models and selective silencing of AATK in INS832/13 cells by RNA interference promoted ß-cell proliferation. The results point to a coordinated reduction of miR-338-3p and AATK under insulin resistance conditions and provide evidence for a cooperative action of the miRNA and its hosting gene in compensatory ß-cell mass expansion.

MicroRNAs contribute to compensatory ß cell expansion during pregnancy and obesity.

Pregnancy and obesity are frequently associated with diminished insulin sensitivity, which is normally compensated for by an expansion of the functional ß cell mass that prevents chronic hyperglycemia and development of diabetes mellitus. The molecular basis underlying compensatory ß cell mass expansion is largely unknown. We found in rodents that ß cell mass expansion during pregnancy and obesity is associated with changes in the expression of several islet microRNAs, including miR-338-3p. In isolated pancreatic islets, we recapitulated the decreased miR-338-3p level observed in gestation and obesity by activating the G protein-coupled estrogen receptor GPR30 and the glucagon-like peptide 1 (GLP1) receptor. Blockade of miR-338-3p in ß cells using specific anti-miR molecules mimicked gene expression changes occurring during ß cell mass expansion and resulted in increased proliferation and improved survival both in vitro and in vivo. These findings point to a major role for miR-338-3p in compensatory ß cell mass expansion occurring under different insulin resistance states.