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

Abstract

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.

Calcium Signaling in the Ventricular Myocardium of the Goto-Kakizaki Type 2 Diabetic Rat

“…Following a glucose challenge, in the fasted state, blood glucose is significantly elevated at 30, 60, and 120 min [ 29 , 37 – 40 , 44 , 46 , 48 – 50 ] in the GK rat indicating end organ resistance to the action of insulin ( Table 2 ). Blood cholesterol is increased [ 29 , 35 , 43 , 44 ] whilst high-density lipoprotein cholesterol may be either unaltered [ 31 ] or increased [ 44 ] and low-density lipoprotein cholesterol is unaltered [ 31 , 44 ] in the GK rat compared to controls. Blood free fatty acids are either unaltered [ 11 , 31 ] or increased [ 38 , 45 ] in the GK rats compared to controls.…”

“…Blood free fatty acids are either unaltered [ 11 , 31 ] or increased [ 38 , 45 ] in the GK rats compared to controls. Triglycerides are either increased [ 38 , 43 – 45 ] or unaltered [ 2 , 30 , 45 ] in the GK rats compared to controls ( Table 3 ). Part of the variability in blood chemistry may be attributed to the age of the animals and dietary regime.…”

Myocyte membrane and microdomain modifications in diabetes: determinants of ischemic tolerance and cardioprotection

“…In cultured myocytes CX-43 expression is suppressed by hyperglycemia [ 436 ], potentially involving PKC-dependent miR-1/206 expression [ 437 ]; and by the AGE-RAGE system, potentially involving PKC and ERK signaling [ 438 ]. In STZ-dependent T1DM in rats an increased SA nodal expression of CX-43 (and -40 and -45) is associated with nodal conduction delay [ 439 ], while ventricular expression is reportedly unaltered [ 440 ], reduced [ 435 ] or increased [ 441 , 442 ]. Olsen et al [ 426 ] observe reduced lateralization of CX-43 in hearts from ZDF rats exhibiting reduced conduction velocity.…”

“…Olsen et al [ 426 ] observe reduced lateralization of CX-43 in hearts from ZDF rats exhibiting reduced conduction velocity. Phosphorylation of atrial and ventricular CX-43 declines in models of DM [ 439 , 442 , 443 ], potentially as a result of impaired PKCε expression [ 444 ], though these investigators also report increased PKCε mediated CX-43 phosphorylation in DM myocardium, which may promote proteolytic degradation [ 435 ]. The extent of cardiac CX-43 phosphorylation reportedly declines with progression of DM while protein nitration increases [ 443 ].…”

Identification of Protein Kinase C Isoforms Involved in Type 1 Diabetic Encephalopathy in Mice

“…The expression of cPKC β II increases in the renal tissues of diabetic rats on 21 days after STZ injection [ 28 ]. The nPKC ε level increases in the skeletal muscle of nutritionally induced diabetic rats in 3 weeks [ 29 ] and vessels of spontaneously diabetic rats [ 30 ]. And the expression of cPKC γ is also found to increase in the trigeminal spinal nucleus of T1DM mice on 14 days after STZ injection [ 21 ].…”