Doctoral Degrees (Medical Physiology)

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Browsing Doctoral Degrees (Medical Physiology) by browse.metadata.advisor "Du Plessis, Stefan S."

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    An investigation of obesity as an etiology of male infertility in a rat model
    (Stellenbosch : Stellenbosch University, 2021-03) Skosana, Bongekile Trisha; Du Plessis, Stefan S.; Aboua, Yapo Guillaume; Van der Horst, Gerhard; Marais, Erna; Stellenbosch University. Faculty of Medicine and Health Science. Dept. of Biomedical Sciences: Medical Physiology.
    ENGLISH ABSTRACT: Until recent decades, the inability to produce offspring has been seen as a female-related issue, but better understanding has made it evident that male fertility is l ikewise an essential determinant of couple fertility. Infertility in males has numerous causative factors, including lifestyle factors and obesity. Obesity has been shown to compromise fertility through changes in several aspects of reproductive function, including dysregulation ofhormones (the HPG axis) and changes in the structure of the reproductive organs. There is, however, a great deal that is still unknown about how obesity and infertility interchangeably affect each other. New molecular techniques such as proteomics have been shown to provide insights into disease-causing mechanisms. These techniques may provide an avenue to discover more intrinsic changes that obesity may give rise to; it can also aid in the discovery of mechanisms through which obesity can act to bring about changes in male fertility. The overall aims of this study were: (1) To examine the effects of obesity on male fertility by observing specific macroscopic (anthropometric), microscopic (sperm parameters, histology of the testis and epididymis) and molecular (antioxidant enzyme, reproductive hormones) changes in a diet-induced obesity animal model; (2) To examine changes in protein expression within the reproductive tissues of obese animals, quantify these changes, and identify the affected molecular pathways. This study made use of an animal model of diet-induced obesity (DIO) to assess the effects of obesity on male reproductive organs and sperm parameters. Male Wistar rats (n=40) were randomly and equally divided into control (age-matched) and DIO groups and received standard rat chow or a high caloric diet ad libitum for 54 weeks, respectively. A long-term diet was chosen to mimic the gradual and chronic onset of obesity. At 60 weeks of age, rats were sacrificed by euthanasia. Each animal had their body weight measured and immediately examined post-mortem to determine visceral fat weight, testis weight and non-fasting blood glucose. Blood was collected from the thoracic cavity and used for plasma extraction and haematocrit analysis. Testis and epididymides were excised, weighed and preserved appropriately for subsequent sperm parameter evaluations (morphology and viability), histological analysis (H & E staining), protein determination, antioxidant evaluation (catalase, superoxide dismutase, glutathione, lipid peroxidation), and proteomics analysis (Liquid Chromatography Mass Spectrometry (LC-MS/MS)). The chronic diet elevated body and visceral fat weights significantly in the DIO group compared to controls. Sperm morphology and viability, as well as estradiol production were negatively altered in the DIO group. These changes were associated with alterations in several macroscopic, microscopic and molecular changes including changes in relative testicular weight, histological aberrations, and a reduction in antioxidant enzymes within the testis and epididymis respectively. Interestingly, testosterone was not significantly reduced, as seen in experiments with a shorter DIO feeding duration. This points towards a compensatory mechanism to counteract chronically increased testosterone concentrations. Protein expression profiles of the DIO and control groups suggest that the predominant molecular pathways affected by th treatment were related to metabolism. These seem to be the possible driver of changes in other proteins including those involved in the production of reactive oxygen species (ROS). Some lesser researched antioxidant proteins were increased in expression to counteract ROS. The negative histological changes observed in the DIO group were linked to the underexpression of structural proteins involved in cell-to-cell adhesion. Reproductive proteins including those involved in sperm production, fertilization and the early stages of embryonic development were reduced in expression in the DIO group. These negative changes were possibly instigated by the observed increases in stress proteins, redox and inflammatory proteins. It is therefore evident that long-term obesity can impair male reproductive parameters and could be a contributing factor to the decline in male fertility by affecting sperm and reproductive parameters. Proteomic analysis of the epididymis and sperm showed that proteins essential in metabolism, ROS production, stress, inflammation and in the regulation of reproductive function as well as sperm and epididymis structure were negatively affected. In addition, long-term obesity can mask detrimental changes in physiology due to compensatory mechanisms, making changes in reproductive parameters difficult to explain.