Doctoral Degrees (Medical Physiology)

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Browsing Doctoral Degrees (Medical Physiology) by Subject "Aspalathus"

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    Characterisation of high fat, high sugar diet-induced epigenetic changes in skeletal muscle of wistar rats and metabolic effects of an aspalathin-rich rooibos extract
    (Stellenbosch : Stellenbosch University, 2021-12) Myataza, Asive; Carmen, Pheiffer; Tarryn, Willmer; Shantal, Windvogel; Rabia, Johnson; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Biomedical Sciences: Medical Physiology.
    Background Animal models are widely used to elucidate the pathophysiological mechanisms that underlie obesity and to test the efficacy of anti-obesity therapeutics. However, these models have been largely biased towards males, partly due to the complexity of hormonal fluctuations in females. The primary aim of this study was to elucidate DNA methylation profiles and gene regulatory networks that are altered in the skeletal muscle during the development of obesity in female and male Wistar rats, and to explore whether Afriplex-GRT™ could prevent aberrant DNA methylation patterns and the progression of metabolic disease. Methods Different animal models were employed where female and/or male Wistar rats were fed a standard or a high fat, high sugar (HFHS) diet for 12, 3 or 9 months. The effect of rooibos was investigated in the latter model, where 60 mg/kg of bodyweight Afriplex-GRTTM was co-administered with the diets. Parameters measured included food and water intake, bodyweight, and glucose, insulin, lipid and cytokine concentrations. Skeletal muscle was harvested for histology, gene expression measured using RT2 Profiler™ PCR arrays and Taqman® assays and global and gene-specific DNA methylation were quantified using pyrosequencing. To further explore the effects of DNA methylation, high glucose and fatty acids on skeletal muscle, C2C12 myocytes were differentiated with 7 μM 5-azacytidine, a global DNA methylation inhibitor, 33 mM glucose and 0.5 mM palmitate. Mitochondrial activity and oxidative stress were measured using appropriate assays. Myoblast differentiation and the expression of myoblast determination protein 1 (MyoD), myosin heavy chain 1 (Myh1), insulin growth factor 2 (Igf2), sterol regulatory element binding transcription factor 1 (Srebf1) and DNA methyltransferase 1 (Dnmt1) were assessed. Results The HFHS diet induced visceral adiposity and hypertriglyceridaemia in both male and female rats, while hyperinsulinaemia and significant bodyweight gain was observed in male rats, and systemic inflammation in females only. These changes were accompanied by increased expression of Igf2 and decreased expression of Srebfb1 and Dnmt1 in skeletal muscle of male, but not female rats. No differences in DNA methylation patterns were observed. Treatment with Afriplex-GRT™ did not ameliorate HFHS diet-induced metabolic dysregulation. In C2C12 cells, treatment with 5-azacytidine induced myoblast differentiation and MyoD and Myh1 expression, while palmitate inhibited differentiation and decreased the expression of MyoD, Myh1, Igf2 and Srebf1, which was restored by 5-azacytidine. High glucose increased Igf2 expression but did not affect Srebf1 expression, while a combination of high glucose and 5- azacytidine decreased Srebf1 and Dnmt1 expression. Conclusion The HFHS diet induced different metabolic responses and gene expression patterns in females and males. In general, females exhibited a dampened metabolic response, which we presume may be due to the intrinsic protective effects of female reproductive hormones. Afriplex-GRTTM did not prevent HFHS diet-induced weight gain, which contrasts previous findings where treatment with 60 mg/kg Afriplex-GRTTM decreased bodyweight in obese male rats, suggesting that Afriplex-GRTTM may be better targeted as a therapeutic than a preventative nutraceutical. This study provides novel information on how molecular differences in skeletal muscle may contribute to sex differences in response to HFHS feeding and may have important implications for the identification of therapeutic targets.