Modulation of Cardiac Connexin-43 by Omega-3 Fatty Acid Ethyl-Ester Supplementation Demonstrated in Spontaneously Diabetic Rats

Previous data suggest that type 1 diabetes mellitus leads to the deterioration of myocardial intercellular communication mediated by connexin-43 (Cx43) channels. We therefore aimed to explore Cx43, PKC signaling and ultrastructure in non-treated and omega-3 fatty acid (omega-3) treated spontaneously diabetic Goto-Kakizaki (GK) rats considered as type 2 diabetes model. Four-week-old GK and non-diabetic Wistar-Clea rats were fed omega-3 (200 mg/kg/day) for 2 months and compared with untreated rats. Real-time PCR and immunoblotting were performed to determine Cx43, PKC-epsilon and PKC-delta expression. In situ Cx43 was examined by immunohistochemistry and subcellular alterations by electron microscopy. Omega-3 intake reduced blood glucose, triglycerides, and cholesterol in diabetic rats and this was associated with improved integrity of cardiomyocytes and capillaries in the heart. Myocardial Cx43 mRNA and protein levels were higher in diabetic versus non-diabetic rats and were further enhanced by omega-3. The ratio of phosphorylated (functional) to non-phosphorylated Cx43 was lower in diabetic compared to non-diabetic rats but was increased by omega-3, in part due to up-regulation of PKC-epsilon. In addition, pro-apoptotic PKC-delta expression was decreased. In conclusion, spontaneously diabetic rats at an early stage of disease benefit from omega-3 intake due to its hypoglycemic effect, upregulation of myocardial Cx43, and preservation of cardiovascular ultrastructure. These findings indicates that supplementation of omega-3 may be beneficial also in the management of diabetes in humans.

Differential effects of leptin receptor mutation on male and female BBDR.Gimap5−/Gimap5− spontaneously diabetic rats

Rodents homozygous for autosomal leptin receptor gene mutations not only become obese, insulin resistant, and hyperleptinemic but also develop a dysregulated immune system. Using marker-assisted breeding to introgress the Koletsky rat leptin receptor mutant ( lepr−/lepr−), we developed a novel congenic BBDR. lepr−/lepr− rat line to study the development of obesity and type 2 diabetes (T2D) in the BioBreeding (BB) diabetes-resistant (DR) rat. While heterozygous lepr (−/+) or homozygous (+/+) BBDR rats remained lean and metabolically normal, at 3 wk of age all BBDR. lepr−/lepr− rats were obese without hyperglycemia. Between 45 and 70 days of age, male but not female obese rats developed T2D. We had previously developed congenic BBDR. Gimap5−/Gimap5− rats, which carry an autosomal frameshift mutation in the Gimap5 gene linked to lymphopenia and spontaneous development of type 1 diabetes (T1D) without sex differences. Because the autoimmune-mediated destruction of pancreatic islet β-cells may be affected not only by obesity but also by the absence of leptin receptor signaling, we next generated BBDR. lepr−/lepr−,Gimap5−/Gimap5− double congenic rats carrying the mutation for Gimap5 and T1D as well as the Lepr mutation for obesity and T2D. The hyperleptinemia rescued end-stage islets in BBDR. lepr−/lepr−,Gimap5−/Gimap5− congenic rats and induced an increase in islet size in both sexes, while T1D development was delayed and reduced only in females. These results demonstrate that obesity and T2D induced by introgression of the Koletsky leptin receptor mutation in the BBDR rat result in islet expansion associated with protection from T1D in female but not male BBDR. lepr−/lepr−,Gimap5−/Gimap5− congenic rats. BBDR. lepr−/lepr−,Gimap5−/Gimap5− congenic rats should prove valuable to study interactions between lack of leptin receptor signaling, obesity, and sex-specific T2D and T1D.

Gene expression analysis of hepatic roles in cause and development of diabetes in Goto-Kakizaki rats

Progression of diabetes was studied in male Goto-Kakizaki (GK) spontaneously diabetic rats between 4 and 20 weeks of age, and compared with Wistar-Kyoto (WKY) controls. Five animals from each strain were killed at 4, 8, 12, 16, and 20 weeks of age. Body weight, plasma glucose, and plasma insulin were measured. WKY rats showed a significantly larger weight gain than GK animals from 8 weeks of age onward. Plasma glucose was relatively stable in WKY. By contrast, plasma glucose was higher in GK than WKY even at 4 weeks and continued to increase up to 12 weeks and then maintained a hyperglycemic plateau throughout the remainder of the experiment. Plasma insulin was relatively stable in WKY from 8 weeks onward but was sharply elevated in GK between 4 and 8 weeks. After 8 weeks, insulin declined in GK with GK concentrations lower than WKY at 20 weeks, suggesting β-cell failure. Gene expression in liver was explored using Affymetrix 230-2 gene arrays. Data mining identified 395 probe sets out of more than 31 000 that were differentially regulated. Excluding unidentifiable probe sets and considering duplicate probe sets, there were 311 genes that were expressed differently in the liver of the two strains. A functional analysis of these genes indicated that disruption of lipid metabolism in the liver is a major consequence of the chronic hyperglycemia in the GK strain. In addition, the results suggest that chronic inflammation contributes significantly to the development of diabetes in the GK rats.