There is evidence that the excitotoxin quinolinic acid (QUIN) synthesized through the kynurenine pathway (KP) by activated microglia may play a role in the pathogenesis of several major neuroinflammatory diseases and more particularly in Alzheimer??s disease (AD). The hypothesis of this project is QUIN affects the function and morphology of astrocytes. In this study I used human foetal astrocytes stimulated with AD associated cytokines including IFN-gamma, TNF-alpha, TGF-alpha and different concentrations of QUIN ranging from low physiological to high excitotoxic concentrations. I found that QUIN induces IL-1beta expression in human astrocytes and subsequently, contribute to the inflammatory cascade that is present in AD pathology. Glial fibrillary acid protein (GFAP) and vimentin protein expression were complementary in expression to each other after 24 hr stimulation with different QUIN doses. However, there were marked increases in GFAP levels and reduction in vimentin levels compared to controls with QUIN treatment indicating that QUIN can trigger astrogliosis in human astrocytes. Glutamine synthetase (GS) activity was used as a functional metabolic test for astrocytes and I found a dose-dependent inhibition of GS activity by QUIN. This inhibition was inversely correlated with iNOS expression whereby reduced GS activity is accompanied with an increase expression of iNOS in human astrocytes. These results suggest that reduction in GS activity can lead to accumulation of extracellular glutamate then leading to exacerbated excitotoxicity via NMDA receptor over-activation and ultimately neuronal death. PCR array results showed that at least four different pathways were activated with pathological concentration of QUIN including p38 MAPK that is associated with pro-inflammatory cytokine production, ERK/MAPK growth and differentiation that can modulate structural proteins, mitochondrial-induced apoptotic cascade and cell cycle control pathway. QUIN-induced astrogliosis and excitotoxicity could lead to glial scar formation and prevention of axonal growth thus exacerbation of neurodegeneration via synaptosomal NMDA receptor over-activation. All together, this study showed that, in the context of AD, QUIN is an important factor for astroglial activation, dysregulation and death, which can be mediated by the previously mentioned pathways.
| Identifer | oai:union.ndltd.org:ADTP/257792 |
| Date | January 2008 |
| Creators | Ting, Ka Ka, Clinical School - St Vincent's Hospital, Faculty of Medicine, UNSW |
| Publisher | Publisher:University of New South Wales. Clinical School - St Vincent's Hospital |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://unsworks.unsw.edu.au/copyright, http://unsworks.unsw.edu.au/copyright |
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