Browsing by Author "Erasmus, Melisse"

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    Investigating aberrant DNA methylation patterns in LOXL2 as a potential predictor of diabetes-induced cardiac dysfunction
    (Stellenbosch : Stellenbosch University, 2021-04) Erasmus, Melisse; Johnson, Rabia; Samodien, Ebrahim; Maarman, Gerald; Pheiffer, Carmen; Stellenbosch University. Faculty of Science. Dept. of Physiological Sciences.
    ENGLISH ABSTRACT: Cardiovascular disease (CVD) remains the leading cause of mortality worldwide, with 17.9 million deaths annually. CVD pathophysiology is often characterized by increased stiffening of the heart muscle due to fibrosis, thus resulting in diminished cardiac function. Fibrosis can be caused by increased oxidative stress and inflammation, which is strongly linked to lifestyle and the environment. Diets rich in fat and sugar have been implicated as one of the prominent risk factors for the occurrence of CVD including associated risk factors such as obesity and insulin resistance. These diets are known to induce an inflammatory response that promotes myocardial stiffening due to increased cardiac fibrosis. Recently, Lysyl oxidase-like 2 (LOXL2), an enzyme required for collagen and elastin cross-linking in the myocardium, has been proposed to have a profound role in cardiac fibrosis and mechanical dysfunction of stressed hearts. Despite acknowledging the crucial role of LOXL2 as an early marker of cardiac fibrosis, there is a paucity of data on LOXL2 regulation and its role in CVD. Additionally, there is a definite need to investigate if LOXL2 regulation may be mediated by epigenetic mechanisms. This would greatly aid in identifying a means to control and manipulate LOXL2, particularly in humans, thereby developing novel therapeutics to combat this worldwide CVD problem. As such, this study aims to gain insight into (1) the mechanisms by which LOXL2 and its downstream effectors are regulated in physiological conditions responsible for CVD development, (2) whether LOXL2 expression in male and female rats is regulated by DNA methylation, and (3) if a pharmaceutical grade of green rooibos (AfriplexGRTTM) can prevent altered gene expression. Furthermore, in search of new therapeutic targets, this study also aimed to investigate the ameliorative effects of AfriplexGRTTM on high glucose and palmitate (HG+PAL)-induced stress in an in vitro H9c2 and in vivo obesogenic diet-induced cardiac fibrosis using a Wistar rat model. Methods: For the in vitro model, H9c2 cells were treated with HG+PAL for 24 hours, followed by further 6-hour treatment with AfriplexGRTTM, or its bioactive compound Aspalathin. The effect of stress induction was investigated by studying ATP production, ROS generation, mitochondrial bioenergetics, mitochondrial membrane potential and apoptosis. Cells were also harvested for mRNA expression analysis. To establish a model of diet-induced fibrosis in vivo, Wistar rats were fed different obesogenic diets, including a high-fat, high-sugar (HFHS) diet, and obesogenic 1 (OB1) diet, or an obesogenic 2 diet (OB2), over a set period with or without supplementation with AfriplexGRTTM. Bodyweight, food intake and fasting blood glucoses were monitored over the study period, after which blood was collected for serum analysis of lipids, triglycerides, insulin levels as well as serum LOXL2 levels. Heart tissue was collected for DNA methylation profile (HFHS diet only), mRNA, and protein expression analysis. Results: Results from the in vitro study showed that HG+PAL treatment induced an inflammatory response, increased oxidative stress and reduced mitochondrial membrane potential, increased apoptosis. It, however, could not induce a significant change in gene expression levels of various fibrotic markers including LOXL2. AfriplexGRTTM and Aspalathin treatments were unable to ameliorate the detrimental effects induced by HG+PAL treatment. Results from the in vivo studies indicated that the obesogenic diets were able to increase animal bodyweights, serum insulin levels, triglyceride levels and serum LOXL2, with no significant differences were observed at a gene expression or DNA methylation level. However, enhanced protein expression levels correlated with increased serum levels of LOXL2 in male Wistar rats. Therefore, it has been postulated that early events of cardiac fibrosis might have been activated, that require further validation in future studies. Conclusion: This study demonstrated that an obesogenic diet can induce alterations in metabolic parameters that are gender-specific. These findings also indicated that LOXL2 regulation may have been driven by a mechanism independent of DNA methylation and that AfriplexGRTTM was unable to mitigate LOXL2-induced fibrosis or cardiac perturbations in these diet-induced obesity Wistar rat models.
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    Linking LOXL2 to Cardiac Interstitial Fibrosis
    (MDPI, 2020-08) Erasmus, Melisse; Samodien, Ebrahim; Lecour, Sandrine; Cour, Martin; Lorenzo, Oscar; Dludla, Phiwayinkosi; Pheiffer, Carmen; Johnson, Rabia
    Cardiovascular diseases (CVDs) are the leading causes of death worldwide. CVD pathophysiology is often characterized by increased stiffening of the heart muscle due to fibrosis, thus resulting in diminished cardiac function. Fibrosis can be caused by increased oxidative stress and inflammation, which is strongly linked to lifestyle and environmental factors such as diet, smoking, hyperglycemia, and hypertension. These factors can affect gene expression through epigenetic modifications. Lysyl oxidase like 2 (LOXL2) is responsible for collagen and elastin cross-linking in the heart, and its dysregulation has been pathologically associated with increased fibrosis. Additionally, studies have shown that, LOXL2 expression can be regulated by DNA methylation and histone modification. However, there is a paucity of data on LOXL2 regulation and its role in CVD. As such, this review aims to gain insight into the mechanisms by which LOXL2 is regulated in physiological conditions, as well as determine the downstream effectors responsible for CVD development.