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- ItemOpen AccessEstablishing in vitro models of neuroinflammation to investigate neuroimmune responses in neurocysticercosis(2024) Awala, Amalia Naita; Raimondo, Joseph ValentinoNeurocysticercosis (NCC), a parasitic infection of the central nervous system (CNS) caused by the larvae of the cestode Taenia solium, is the leading cause of adult-acquired epilepsy in the world. A surprising clinical manifestation of NCC is that viable larvae can exist in the brain for extended periods with no symptomatology, but when they die, clinical symptoms develop. Clinical evidence suggests that the hallmark of symptomatic NCC is neuroinflammation; however, the neuroinflammatory mechanisms underlying this disease remain grossly understudied, and how innate immune cells respond to this infection is still debated. One of the reasons for this is that there is a lack of reliable experimental models of inflammation at the level of the brain that allow for cell-type specific tracking of inflammation in innate immune cells. Thus, this thesis's first aim was to establish the rodent-derived organotypic brain slice culture (OBSC) system as an in vitro model for investigating neuroinflammatory signalling and activation of microglia and astrocytes in the brain. To validate this model of neuroinflammation, OBSCs from neonatal mice were treated with the pro-inflammatory stimulant lipopolysaccharide (LPS) for 24 hours and compared to untreated control slices. Inflammatory activation of microglia and astrocytes was measured by tracking the activation of the inflammatory transcription factor nuclear factor for interleukin 6 (NF-IL6), a robust biomarker for tracking neuroinflammation in glial cells. Inflammation was confirmed by measuring the concentrations of pro-inflammatory cytokines IL-6 and TNF-α released by OBSCs in the culture medium. Lastly, we used single-nucleus RNA sequencing to investigate these inflammatory changes at a transcriptomic level. My results show that LPS significantly increased NF-IL6 activation in microglia and astrocytes and increased the release of both IL6 and TNF-α. At the transcriptomic level, I observed an upregulation of major inflammatory genes such as CCL5 and Timp1 in both microglia and astrocytes in response to LPS treatment, further confirming inflammation. Having demonstrated that OBSCs present a robust platform for investigating neuroinflammatory mechanisms in brain infections, the second aim of this thesis sought to use this established model to investigate how viable Taenia larvae modulate neuroinflammation in NCC. The potential immunomodulatory effects of the Taenia larvae on glial activation and inflammation was assessed by concurrently treating OBSCs with both LPS and Taenia larvae homogenate. I found that the co-application of LPS and Taenia larvae homogenate suppressed the LPS-induced microglial and astrocytic activation, proinflammatory cytokine release, and prevented the upregulation of key inflammatory genes. Together, this observed anti-inflammatory effect could explain how Taenia larvae can exist in the human brain without eliciting symptomatology from the host. This thesis's final aim was to set up a comparable translational in vitro human model of neuroinflammation using human II acute and organotypic brain slice cultures (hOBSCs). Using the inflammatory transcription factor NF-IL6 as a marker for glial activation, I found that at baseline, hOBSCs displayed higher levels of microglial and astrocytic activation than human acute slices. Additionally, untreated control and LPS-treated hOBSCs both displayed high levels of NF-IL6 activation. However, cytokine data revealed low concentrations of pro-inflammatory cytokines IL-6 and TNF-α in culture medium in untreated control hOBSCs that increased when slices were exposed to LPS, highlighting an inflammatory reaction. Taken together, these findings provide novel insights into understanding the neuroinflammatory mechanisms underlying NCC and highlight the utility of organotypic brain slice cultures in studying neuroimmune responses in diseases of an inflammatory nature such as NCC.
- ItemOpen AccessClassical, quantum and numerical aspects of modified theories of gravity(2024) Beckering Vinckers, Ulrich Karoo; De La Cruz, Dombriz Alvaro; Mazumdar, Anupam; Pollney, DenisIn this thesis, we examine some specific aspects of two classes of modified gravity theories: ghostfree infinite-derivative gravity and so-called f(R) gravity. Regarding the former, we consider the four-dimensional theory at the level of the quadratic action and study the single graviton exchange of two massive spin-0 particles. We derive the corresponding gravitational potential energy for the non-static case and show that the quantum correction of the local theory, which is in the form of a Dirac delta function, is smeared out in the non-local theory. It is also shown that the gravitational potential energy associated with the self-interaction of the individual particles is finite. We then examine the quantumgravitational entanglement of two test masses that undergo a spatial splitting that is orthogonal to their separation. For such a set-up, we compute the concurrence and von Neumann entropy for the entanglement and show that an increase in the length scale of nonlocality leads to a decrease in both of the aforementioned quantities. Our attention is then turned to two specific two-dimensional dilaton gravity models; namely the Spherically-Reduced Gravity (SRG) and the Callan-Giddings-Harvey-Strominger (CGHS) theories. The quadratic action for each theory is derived and diagonalised in order to construct ghost-free infinite-derivative modifications. In the case of the SRG theory, we make use of the Schwarzschild-type gauge whereas, for the CGHS theory, we impose the conformal gauge. For each of the two local theories, we construct appropriate source actions that can be used to generate their respective linearised black-hole solutions. We then make use of the same source actions in the linearised non-local theories and obtain non-local modifications to the aforesaid solutions. Lastly, we consider the application of numerical relativity techniques to f(R) gravity models. It is well-known that the Baumgarte-Shapiro-Shibata-Nakamura (BSSN) modification of the Arnowitt-Deser-Misner formulation of General Relativity is suitable for the construction of numerical relativity codes. While a BSSN-like formulation for f(R) gravity exists, it is constructed with Cartesian coordinates in mind. In this thesis, we generalise the formalism to accommodate arbitrary coordinates and then impose spherical symmetry. The description of a numerical relativity code for the Starobinsky gravity model based on this formalism is given before considering a number of scenarios. We first perform the evolution of Schwarzschild Einstein-Rosen bridge initial data using the fourth-order Runge-Kutta method as well as the evolution of a gauge pulse in flat space using the Partially-Implicit-Runge-Kutta scheme. These two cases serve as tests for our code and our results are compared with those presented in the literature. Then, we perform the evolution of a massless scalar field in the context of the Starobinsky gravity model and show that damped oscillations arise for subcritical simulations.
- ItemOpen AccessValerie Desmore s refusal(s): art practice as biomythography(2024) Akoi-Jackson, Nontobeko Ntombela; Makhubu, NomusaThe South African-born British artist and fashion designer Valerie Elizabeth Helene Desmore, who is said to have risen to fame in South Africa in 1942 at the age of sixteen, left South Africa in 1945 to pursue an art career in the United Kingdom. This move was prompted by the infamous South African race bar through which she experienced significant ‘racial persecution'. Feeling rejected, her exile in the United Kingdom resulted in a career change from visual arts to fashion, only to return to visual arts again in her senior years. This oscillation between visual art and fashion culminated in an idiosyncratic body of work that this thesis, through the concepts of refusal and biomythography, examines. This is done by analysing her artworks as they tell her life stories. Argued via a critical consideration of how the artist's work bears rich articulations of selfdetermination, self-writing, and self-enunciation in bold and unapologetic gestures, the dissertation shows patterns of a visual trajectory marked by a series of refusals and her own avant-garde style. Using ‘encumbered methodology' the thesis centres the artist's agency as well as her legacy, as prerequisites for any meaningful undertaking of art-historical writing. As such, the methodology and theoretical framework of refusal and biomythography combined illuminate a multitude of the artist's complex experiences, showing how significant multivocality has become in contemporary art historical practice. In turn, this further reveals how Desmore's choice to reciprocally reject (depart from) that which rejected her (denied her access) disrupted known workings of art historical exclusions. Desmore's audacious gestures complicate and refute the often-simplified understandings of Black South African Modern artists as passive participants and ‘discovered subjects' in the making of their careers. By examining the work of one woman artist, Valerie Desmore, this research asserts a renewed, gendered positionality for Black South African Modern women artists more broadly. The thesis, therefore, presents efforts to re-member and re-assemble the life and work of an artist nearly erased from the art historical canon. Drawing on Black feminist and postcolonial methodologies the thesis lays bare the challenges of researching invisible, disparate and undervalued archival and historical materials.
- ItemOpen AccessExploring the relationship between shifts in high-density lipoprotein (HDL) particle subclass distribution/functionality and cardiac function in doxorubicin (DOX)-induced cardiotoxicity(2024) Abrahams, Carmelita Bianca; Lecour, Sandrine; Woudberg, NicholasIntroduction: Elucidating the mechanisms involved in cardiotoxicity that develops in cancer patients receiving doxorubicin (DOX) chemotherapy is key to identify potential cardioprotective strategies and early biomarkers in these patients. Both breast cancer and DOX treatment are associated with dyslipidaemia, however changes in high-density lipoprotein (HDL) particle subclass distribution, composition and functionality are unknown. We therefore aimed to investigate whether changes in HDL particle subclass distribution, composition and functionality in breast cancer patients and tumour bearing mice receiving DOX chemotherapy may contribute to cardiac dysfunction. Methods: Blood samples were collected in 34 female breast cancer patients (18-65 years old with no co-morbidities) prior (B) to and after completion (E) of DOX chemotherapy (6 cycles every 3 weeks). Breast cancer was induced in female C57/Bl6 mice (6-8 weeks old) by subcutaneous injection of the E0771 cell line. Once a palpable tumour formed, DOX (5 mg/kg, i.p.) was given weekly for 5 weeks. The following groups were considered: Control (C, n=17), DOX (D, n=17), Tumour (T, n=20) and DOX+Tumour (DT, n=17). Cardiac function was measured with echocardiography, and serum was collected at baseline (B) and at endpoint (E). In serum, HDL subclass distribution was measured using the Lipoprint® system. HDL anti-oxidative functionality was assessed by measuring paraoxonase-1 (PON1) activity. The ability of isolated HDL particles to protect against DOX-induced cytotoxicity was assessed in H9C2 cells and measured using the adenosine-triphosphate (ATP) assay. Results: DOX-induced subclinical cardiotoxicity was observed in 9 breast cancer patients. DOX therapy reduced the intermediate HDL subclasses [52.5±1.0% (B) vs 48.6±0.9% (E), p<0.001], an effect that correlated with cardiac dysfunction in patients (r =+0.29, p<0.05). In the mouse model, DOX induced cardiac alterations by reducing radial strain of the left ventricular anterior wall [D: 49.96±2.3% (B) vs 21.8±2.9% (E), p<0.0001 and DT: 46.7±2.7% (B) vs 31.7±4.4% (E), p<0.01]. In mice, breast cancer reduced the intermediate HDL subclasses (D: 74.8±1.2% vs DT: 67.7±2.4%, p<0.001) and increased the large HDL subclasses (D: 24.0±1.2% vs DT: 30.9±2.3%, p<0.001), while DOX treatment increased the small HDL subclasses (T: 0.3±0.2% vs DT: 0.9±0.5%, p<0.05). DOX treatment in breast cancer mice was associated with reduced PON1 activity (C: 0.4±0.0% vs DT: 0.2±0.0%, p<0.05). Interestingly, a reduction in the intermediate HDL subclass, HDL-4, and PON1 activity were associated with a reduction in radial strain of the left ventricular anterior wall (r=+0.41, p<0.05 and r=+0.44, p<0.05, respectively). Most importantly, HDL particles isolated from breast cancer or DOX treated mice could not protect against DOX-induced cytotoxicity in H9C2 cells compared to HDL particles isolated from control mice (C: 100.0±16.6 ATP% vs D: 49.3±11.9 ATP% or T: 52.44±19.8 ATP%, p<0.05 vs C). Conclusion: In breast cancer patients and in tumour bearing mice, a treatment with DOX was associated with a shift in HDL subclass distribution and functionality that correlated with cardiac alterations. This change in HDL particle dynamic caused it to lose its cardioprotective functionality against DOXinduced cardiotoxicity, thus suggesting that HDL particles may play a key role in the development of cardiotoxicity associated with DOX chemotherapy. Our data therefore highlight HDL particles as a potential therapeutic target to limit DOX-induced cardiotoxicity. Our study also improves upon prior research by including a cancer environment in our mouse model of DOX-induced cardiotoxicity and highlights the contribution of the cancer to the pathophysiological changes observed.
- ItemOpen AccessEssays on water resources management in the agricultural sector of South Africa: the role of technology, policy and institutions in mitigating farm level water scarcity(2024) Apio, Alfred Tunyire; Thiam Djiby, Thiam; Dinar, ArielSouth Africa is a water-stressed country prone to multi-year droughts and water shortages, with varying impacts on several sectors, including agriculture. Agriculture, as the largest user of the country's freshwater resources, is the most sensitive sector to water scarcity and would be the hardest hit by intensifying climate change, droughts, and water shortages. Yet the agricultural sector has the largest potential to make adjustments and take actions to promote resilience to water scarcity by implementing water conservation, water quality regulation, legitimate allocation, and an appropriate management response in the face of growing water scarcity. This thesis, therefore, provides an understanding of how the agricultural sector of South Africa is responding to the water scarcity problem. Its general objective is to further the stock of knowledge in natural resources management, with special emphasis on water resources management in the agricultural sector. It consists of three core chapters (chapters 2, 3, and 4), alongside the introduction (chapter 1) and conclusion (chapter 5). The first core chapter (Chapter 2) examines the factors that drive farmers' multiple adoption of six water conservation practices (WCPs) and the intensity of their adoption. Using survey data from 555 farmers in the Limpopo River Basin (LRB) of South Africa, a multivariate probit model is estimated to determine these factors, and for the intensity of their adoption, an ordered probit model is estimated. The results show that gender, age, education, and farm size, among other factors, influence the probability and extent of adoption of WCPs. Furthermore, combinations like drip and/or sprinkler irrigations and cover cropping, drip and/or sprinkler irrigations, and intercropping, among other practices, are complements, suggesting the bundling of these WCPs. This chapter provides a clear framework in agriculture not only to prepare farmers to be resilient in the midst of intensifying climate change, droughts, and water shortages but also to enhance their water conservation efforts. This would help farmers become better acclimatized to the growing realities of water scarcity and enhance the sustainability of the resource, enabling them to continue to make meaningful contributions to economic growth. The second core chapter (Chapter 3) employs a discrete choice methodology to investigate farmers' willingness to accept compensation to control agricultural nonpoint source (agNPS) pollution in the LRB. The LRB is highly polluted, yet it is important for agriculture, mining, and industry, which contribute to employment, income, and poverty alleviation. Reducing this pollution is part of the restoration and protection plan for the basin. However, because agNPS pollution does not easily lend itself to traditional forms of regulation, monetary incentives that induce farmers to adjust their farming practices to reduce agriculture's impact on water quality are seen as an effective means of controlling it, hence this chapter. Conditional logit and restricted latent class models are used to estimate the survey data of 552 farmers. This chapter identified one random choice class and three preference classes of farmers (low, moderate, and high resistance) with dissimilar compensation requirements to improve water quality. The chapter offers new insights to enrich the efficient design of tailored water quality improvementrelated agri-environmental schemes for more persistent environmental benefits that would ultimately result in positive externalities beyond benefits to farmers and the environment. The third core chapter (Chapter 4) presents a meta-analysis of the empirical literature that investigates the performance of water institutions. This chapter synthesized and quantified the overall water institution-performance effect using data extracted from 23 original studies that reported the effect of water institutions on the performance of the water sector in various regions of the world. The results from the bivariate and multivariate meta-regressions suggest the presence of a publication selection bias that favours a positive impact of water institutions on performance. Also, a genuine positive empirical effect of water institutions on the performance of the water sector is found. In addition, the variations in the primary studies are attributable to differences in the way the primary studies capture water institutions, the dependent variables used to capture performance, and the estimation strategy/methodology, among others. The main novelty of this chapter is its use of meta-analysis to increase the statistical power of this set of literature, which covers different methodologies, geographic and environmental conditions under which water institutions performed compared to single studies. This thesis concludes by underscoring forcefully that farmers need sustainable supplies of water but must also manage the impact of agriculture on water resources to ensure sufficient quantity and quality of water for production, but robust water management institutions are key. In terms of policy recommendations, this thesis offers several of them, including but not limited to the fact that WCPs are interdependent, and therefore, the design of any effective strategy(ies) aimed at increasing their uptake rate must take this interdependence into consideration. It also advocates the promotion and use of monetary incentives to induce farmers to lessen agriculture's impact on water quality. Finally, it recommends that to engender water sector reforms and/or for the further development, facilitation, and strengthening of water institutions, there is the need to incorporate and strengthen the water law and/or the water policy in policy formulation and reforms for successful water resource management and governance.