Browsing by Author "Nyawo, Thembeka Amanda"

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    Evaluation of mitochondrial and molecular derangements in cardiac adipose tissue during type 2 diabetes and relationship with cardiovascular risk
    (Stellenbosch : Stellenbosch University, 2023-06) Nyawo, Thembeka Amanda; Pheiffer, Carmen; Mazibuko-Mbeje, Sithandiwe; Phiwayinkosi, Dludla; Hanel, Sadie Van Gijsen; Hans, Strijdom; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Biomedical Sciences. Division of Medical Physiology.
    ENGLISH ABSTRACT: Cardiovascular disease (CVD) affects hundreds of millions of people globally, and 18.6 million deaths were attributed to CVD during 2019 alone. Type 2 diabetes (T2D) and obesity contribute significantly towards the increasing prevalence of CVD. Ageing and adipose tissue dysfunction are important mechanisms in the pathology of these metabolic diseases and their downstream cardiovascular complications. The roles of visceral (VAT) and subcutaneous (SAT) adipose depots in T2D and CVD development have been well documented; however, there is limited evidence on the pathological contribution of cardiac fat (CF) to CVD. The aim of this study was to elucidate the role of CF, in comparison to retroperitoneal (RF) and inguinal (IF) fat depots, representatives of VAT and SAT, respectively, in the development and progression of CVD in an experimental mouse model of obesity and diabetes. The study used male obese, diabetic db/db mice and their lean db/+ counterparts to explore morphological features of CF, gene expression signatures, mitochondrial bioenergetics, and associations with CVD risk factors. Briefly, mice were monitored for 8, 12 and 18 weeks, during which body weight and fasting blood glucose concentrations were measured weekly. Glucose tolerance was assessed using the oral glucose tolerance test one week prior to euthanasia. Blood and tissue samples of the heart, CF, RF, and IF were collected for assessment of biochemical markers, histological examination using Haematoxylin and Eosin staining, and gene expression analysis using quantitative real time PCR. In addition, CF, RF and IF were harvested for the assessment of mitochondrial function in adipose-derived stromal cells (ADSCs). Phenotypic and metabolic parameters deteriorated with disease and age, where db/db mice displayed conditions of hyperglycaemia, hyperinsulinaemia, hyperlipidaemia and glucose intolerance with ageing. In addition, an age-related increase in adiponectin serum levels were observed in db/+ mice, while in db/db mice, adiponectin levels decreased with age. Furthermore, histological analysis showed that adipocyte size in all depots increased over time in both the non-diabetic and diabetic state. Adipose depot-, disease- and age-related changes in gene expression signatures in CF, RF and IF were observed, with RF and IF in db/db mice exhibiting upregulation of genes involved in inflammation and oxidative stress, while CF appears to possess increased expression of genes representing thermogenic capacity. Disease- and age-related differential regulation of circulating CVD risk markers were observed. Dysregulation of markers such as metalloproteinase 9 (MMP9), intercellular adhesion molecule 1 (ICAM1), platelet endothelial cell adhesion molecule 1 (Pecam1) and Thrombomodulin (THBD) suggested vascular remodelling and dysfunction during CVD progression. Moreover, circulating levels of MMP9, ICAM and P-Selectin positively correlated with CF adipocyte size. In heart tissue, signs of histological myocardial changes with microarchitecture disruption and the presence of intramyocardial lipid droplets in db/db mice were observed in with ageing. Moreover, gene expression analysis in heart tissue revealed a disease- and age- related downregulation of brain natriuretic peptide (BNP) levels in db/db mice. Furthermore, ADSCs from CF had higher mitochondrial bioenergetics parameters compared to ADSCs from RF. This may be attributed to the higher uncoupling protein 1 (UCP1) expression in CF which reportedly decreases oxidative phosphorylation through thermogenesis. In conclusion, the positive correlation between CVD risk markers with CF adipocyte size in the diabetic state indicates a relationship with CF, supporting the notion that increased CF adiposity is associated with increased CVD risk. Importantly, CF, unlike RF and IF, displays beige-like adipocytes and thermogenic capacity, which may help mitigate the harmful effects of diabetes and its cardiovascular complications.
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    Fingerprinting and molecular characterisation of ARC's apricot and plum collection
    (Stellenbosch : Stellenbosch University, 2017-12) Nyawo, Thembeka Amanda; Roodt-Wilding, R.; Tobutt, K. R; Louw, Esme D.; Stellenbosch University. Faculty of AgriSciences. Dept. of Genetics.
    ENGLISH ABSTRACT: In South Africa apricot (Prunus armeniaca) and plum (Prunus salicina) production forms part of the economically important stone fruit industry, which is mainly situated in the Western Cape, Northern Cape and the Eastern Cape. Cultivars of main importance to the industry are primarily supplied by the Cultivar Development Division of the Agricultural Research Council Infruitec-Nietvoorbij. The ARC produces new and improved apricots and plums through the breeding of cultivars and selections maintained in the stone fruit germplasms held at Bien Donne experimental farm in the Western Cape. Visual inspection of the gene banks has revealed mislabelling/mis-identification of cultivars and inefficient record keeping of the genetic information of the available cultivars. It is therefore essential to fingerprint and characterise the gene banks on a molecular level, in order to confirm trueness to type of the cultivars and to confirm parentages. A set of microsatellite primers designed from peach were used for fingerprinting 106 apricot and 95 plum accessions. Ten (in apricot) and eight (in plum) of the microsatellite primers were grouped into four multiplexes and were successfully used to determine the fingerprints. The obtained data was used as a starting point for comparing fingerprints of apricot and plum cultivars. In apricot, all reported parentages were confirmed to be true; however in plum one accession was found not to be related to the reported parents. Trueness to type was determined by evaluating the genetic relationship using UPGMA cluster analysis, where by four apricot cultivars were identified as false. The self-incompatibility genotypes of the apricot and plum collections were evaluated through the first and second intron amplification of the S-RNase gene using consensus primers. Furthermore, allele-specific SFB primers were used to distinguish self-compatible cultivars. In apricot, 14 PCR products were amplified corresponding to 14 previously published S-alleles. In plum, amplification of nine S-alleles was observed. Self-compatible apricots displaying the Sc allele were confirmed in 70 accessions. The self-compatibility S-allele (Se) in plum was identified in 39 accessions. Two cultivars were also observed that were self-compatible but which did not have the Se allele; indicating the possibility of another source of the self-compatibility phenotype. The findings of this study, which confirmed trueness to type as well as parentages of the cultivars, provides confidence for the breeders when planning crosses. The molecular fingerprints identified in this study also have the potential of being used as a database for cultivar comparison. In terms of the SI genotypes identified, the findings provide some level of certainty for the commercial farmers to expect good yield and provides information which assists in orchard planning, provided that they plant cultivars with different SI genotypes or self-compatible cultivars.