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Masters Degrees (Physiology)

Permanent URI for this collectionhttps://hdl.handle.net/10413/7046

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Browsing Masters Degrees (Physiology) by Subject "AIDS (Disease)--Complications."

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    HIV-1 transactivator of transcription (TAT) protein causes neurotoxicity via astrocyte activation.
    (2015) Ganga, Yashica.; Daniels, William Mark Uren.; Ramsuran, Duran.
    HIV is most well-known for its negative effects on the immune system and the resulting development of AIDS, however it also has severe damaging effects on the central nervous system. Many infected individuals exhibit neuropsychological and behavioral dysfunctions which are collectively referred to as HIV-associated dementia (HAD). One of the worrying aspects of HAD is the fact that current anti-retroviral therapy, while being effective in managing the onslaughts of HIV on the immune system, is less efficient in addressing the impact of HIV on the CNS. The HIV-1 regulatory protein, transactivator of transcription (Tat), is responsible for the transactivation of viral transcription, and has been identified as a possible etiological factor of HAD. Neurotoxicity caused by HIV-1 is an indirect effect since the virus is unable to infect neurons directly. We subsequently hypothesized that HIV-1 infects non-neuronal cells in the CNS which leads to their activation, resulting in the release of cytokines that are detrimental to neurons. The aims of this study was therefore to (i) determine whether Tat activates astrocytes, (ii) establish whether astrocytes exposed to Tat result in the release of IL-6 and TNF-α, and to (iii) assess whether these cytokines can induce apoptosis of neuronal cells. Our study has shown that Tat does activate astrocytes and that activated astrocytes do indeed release cytokines IL-6 and TNF-α into their growth medium. Tat treated cells release more than double the amount of IL-6 than the control group of untreated astrocytes. We also observed that exogenous administration of these cytokines (individually or collectively) to neurons has the ability to cause neuronal apoptosis. Interestingly in combination, these cytokines show no cooperative effect. Our data also showed that neurons, when exposed to the culture medium of astrocytes that were subjected to Tat, exhibit hallmarks of apoptosis similar to that induced by IL-6 and TNF-α. Our findings led us to conclude that in individuals with HIV-infection, the virus activates astrocytes possibly via the production and release of Tat. This causes the astrocytes to secrete pro-inflammatory cytokines (e.g. TNF- α and IL-6) that may induce apoptotic cell death of neurons. This mechanism may explain the development of HAD.
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    Tat protein induced neurocognitive dysfunction.
    (2013) Makhathini, Khayelihle Brian.; Daniels, William Mark Uren.; Mabandla, Musa Vuyisile.
    Human immunodeficiency virus type 1 (HIV-1) is a major health threat in South Africa. Studies have shown that HIV affects the central nervous system (CNS), and can initiate a progressive neurodegenerative process culminating in HIV associated dementia. Tat protein and gp120 are two viral proteins that have been linked to the neurotoxic effects of HIV. The present study used an animal model to study the effects of tat protein on the brain. The study also investigated the ability of picolinic acid to block the damaging effects of Tat protein. Sprague-Dawley rats were divided into four groups. The control group received a bilateral injection of saline (100μl), and the experimental group received a bilateral injection of tat protein (5μg/100μl) into the hippocampus. The other two groups of rats were treated similarly, but also received picolinic acid at a concentration of 3.36mg/3ml, injected intraperitoneally (i.p) before the intrahippocampal injections. Two tests were performed to assess the cognitive behaviour of all the animals, namely the light/dark box and Morris water maze. After the behavioural tests, the brains of animals were collected for evaluating the activity of the enzyme caspase 3 by various means. Some brains were used to determine caspase 3 mRNA transcriptions by polymerase chain reaction; others were used to measure the expression of caspase 3 protein by Western blotting techniques, while the rest of the brains were used for flow cytometry analysis where a caspase 3 specific staining kit was used. Our behavioural results indicated that tat protein caused impairment in learning and memory in the experimental group, when compared to controls. The group that received both tat protein and picolinic acid showed a significant improvement in learning and memory in Morris water maze test, in comparison to the tat protein treated group. Our gene expression data showed a significant up regulation of caspase 3 gene in the tat protein treated group, compared to controls. This result was supported by the Western blot data that showed significantly increased caspase 3 protein expression in the tat protein treated group. While these increases in caspase 3 expression strongly point to an apoptotic mode of cell death in the hippocampus of animals that were treated with tat protein, our flow cytometry results were less convincing with marginal levels of caspase 3 staining being observed. Both increases in gene and protein expression were inhibited in animals that were pretreated with picolinic acid. Our data led us to conclude that tat protein can cause cognitive abnormalities through toxic sequelae that may include apoptosis. It is therefore likely that this viral protein may be one of the etiological factors of HIV associated neurocognitive impairment. Our results further suggest that picolinic acid may be considered as an adjunct therapy for HAND.