Investigation into the underlying mechanisms of diabetic cardiomyopathy using a mouse model ofdiabetes

Abstract

Diabetes Mellitus (DM) is one of the most common metabolic disorders in theworld with an estimated prevalence of over 415 million patients. Heart failure(HF) is the most common cardiovascular complication of diabetes. Theprevalence of diabetes in patients with HF is reported at approximately 30%.However, the molecular mechanisms that contribute to the development ofheart failure in diabetic patients remain uncertain.To study this, a genetic mouse model of diabetes (GENA348) with a pointmutation in the glucokinase gene was used. Glucokinase is a glucose sensorthat controls insulin release. This mutation in the glucokinase is similar to thatfound in Maturity Onset Diabetes of the Young Type 2 (MODY2) in humans.Our group has previously shown that GENA348 mice exhibit a diabeticphenotype. At 6 months, the mice developed a diabetic cardiomyopathyanalogous to that seen in clinical practice with the development of cardiachypertrophy and diastolic dysfunction, which progressed to dilatation of the leftventricle and systolic dysfunction at 12 months.The aim of the project was to examine the molecular and pathophysiologicalmechanisms that contribute to development of this cardiac phenotype indiabetic GENA348 mice in the setting of hypertension and at baseline.To study the mice under hypertensive stress conditions, 6 month old-GENA348HO and WT mice were infused with angiotensin II (ANG II) via minipump. AfterANG II treatment, HO and WT GENA348 mice showed a significantly greaterincrease in systolic and diastolic blood pressure compared to untreatedcontrols. It was evident that ANG II treatment resulted in cardiac hypertrophywith the same level observed in both HO and WT mice. The diastolic functionwas generally preserved in the WT and HO mice following the ANG II treatment.Our data indicates that the HO mice have had a blunted hypertrophic responseto the hypertension induced by ANG II.At baseline, two hypothesis-generating methods were used. Firstly, gaschromatography-mass spectrometry (GC-MS) and ultra performance liquidchromatography-mass spectrometry (UPLC-MS) were used on 12-month-oldGENA348 mice heart and serum samples. Secondly, diabetes PCR array plateswere used on 6- and 12-month-old GENA348 mice heart samples. For the GCMSand UPLC-MS, there were 43 differences in metabolites from tissuesamples and 93 from serum samples. The main altered metabolites from tissuesamples were sugars and fatty acids. However, fatty acids, phospholipids andsphingolipids were the main altered metabolites from serum samples.After the validation of the array plates the most apparent observation was thatonly two up-regulated genes, Phosphoenolpyruvate carboxykinase 1 (Pck1)and Glucose-6-Phosphatase, Catalytic Subunit (G6pc) showed a comparablepattern as the array results. Pck1 and G6pc are the main enzymes that play akey role in gluconeogenesis regulation. We also looked at the expression level of one of the main transcriptional regulators of gluconeogenesis, Forkhead boxprotein O1 (FoxO1). It was found that the expression was altered at 12 months.In conclusion, it was clear that hyperglycaemia altered gene expression and themetabolites profiles in 12 month old HO mice, with evident alterations detectedin genes involved in the metabolic regulation of the heart. In addition, this studymay provide preliminary insight into pathophysiological alterations in the cardiacmetabolism that may contribute to the development of diabetic cardiomyopathy.

Date of Award	31 Dec 2016
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Mamas Mamas (Supervisor) & Elizabeth Cartwright (Supervisor)