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Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Slovak Research and Development under the contract no. 21-0410 (APVV) and 20-0411 (APVV) and VEGA grant no. 2/0006/23 Introduction Type 2 Diabetes Mellitus (T2DM), the most common metabolic disorder in human population is caused by defective insulin secretion and reduced tissue responsiveness to insulin. T2DM is characterized by hyperglycaemia accompanied by oxidative stress and inflammation that results in organopathy. The Zucker diabetic fatty rats (ZDF) are established animal model for research of T2DM associated with obesity, and for efficacy of novel treatments. Myocardial electrical coupling protein, connexin43 (Cx43) is one of the key factors affecting heart function and arrhythmogenesis. We have previously shown upregulation of Cx43 in type 1 DM rats that was associated with reduced susceptibility to malignant arrhythmias. However, it is not known whether T2DM affects Cx43 expression and/or function in the heart as well as in brown adipose tissue (BAT). The purpose of our study was to examine expression of Cx43 in heart and BAT as well as the effect of treatment with highly selective and efficient aldose reductase inhibitor enriched with antioxidant activity, Cemtirestat. Methods: Forty 4-month-old male ZDF rats (fa/+ and fa/fa) were divided into 4 groups: 1) untreated control lean rats (fa/+), 2) control lean rats treated with Cemtirestat, 3) untreated diabetic fatty rats (fa/fa), 4) diabetic fatty rats treated with Cemtirestat (2,55 mg/kg/day). After 6 months of treatment, biometric parameters were registered and left ventricle (LV) + BAT were used for Western blot analysis of Cx43, PKCɛ (phosphorylates Cx43) and PKCδ (implicated in proapoptotic signaling). BAT and LV tissue sections were also used for immunolabeling of Cx43 to examine its topology. Results: Increase of body weight, heart weight, LV weight, adiposity, plasma triglycerides, cholesterol and blood glucose were registered in ZDF fa/fa rats. T2DM resulted in altered localisation of Cx43 that was not affected by treatment with Cemtirestat. Expression of Cx43 was significantly decreased in LV of fa/fa rats and restored with Cemtirestat. Moreover, BAT exhibited significantly lower expression of total Cx43 in fa/fa rats, that was moderately increased by Cemtirestat. The expression of PKCɛ was significantly decreased in both, LV and BAT of fa/fa rats with mild elevation of PKCɛ in LV of treated fa/fa rats. Cemtirestat slightly normalized increased expression of PKCδ in LV of fa/fa rats, but had no effect on lower PKCδ levels in BAT of fa/fa rats. Echocardiographic examination did not show significant difference between treated and untreated groups of rats and showed mild differences between diabetic and control rats. In conclusions, findings point out that T2DM downregulates Cx43 in the heart and BAT, however further studies are necessary for understanding the mechanisms implicated in every step in the development of T2DM cardiopathy and arrhythmogenesis as well as BAT alterations. Further research is required to determine factors involved in cardioprotective effects of Cemtirestat.
Beňová et al. (Wed,) studied this question.