Oxidative stress and the viability of osteoblasts and cerebellar granule neurones

Fatokun, Amos Akintayo (2006) Oxidative stress and the viability of osteoblasts and cerebellar granule neurones. PhD thesis, University of Glasgow.

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Abstract

L-Glutamate is the major excitatory neurotransmitter in the CNS, where it activates both its ionotropic and metabotropic receptors. Excessive levels of glutamate lead to increased intracellular free calcium concentrations, which activate calcium-dependent events resulting in the production of reactive oxygen species (ROS) such as nitric oxide, superoxide and hydrogen peroxide. Glutamate-induced neuronal damage in stroke and neurodegenerative diseases may be mediated by these ROS, which are known to promote oxidative stress. Glutamate receptors are also expressed in non-neuronal peripheral tissues such as bone, where osteoblasts actively secrete glutamate and express glutamate receptors showing striking electrophysiological, biochemical and molecular similarities to those found in the CNS. The responses of osteoblastic and neuronal cultures to culture conditions, glutamate and ROS-generated oxidative stress were therefore the focus of this study. Further experiments focussed on ROS, especially H2O2, which produced concentration- and time-dependent viability reductions in the two cell types that correlated well with morphological damage, although the osteoblasts were less sensitive to its effect. The more differentiated (switch) osteoblast cultures proved more sensitive to peroxide damage than the less differentiated (non-switch) cultures. An attempt to probe whether mitochondrial impairment underlies the differences in sensitivities of MC3T3-E1 and CGN cultures to oxidative damage revealed that the integrity of the osteoblasts was not significantly compromised in the presence of the mitochondrial poisons: potassium cyanide (KCN) and 3-nitropropionic acid (3-NPA) (except for 24 h application of 3-NPA at 100?M and 1mM). The neurones "succumbed" to lower concentrations and shorter exposures to the poisons. The neurotoxic effects of the poisons were mediated by the NMDA receptor, since they were blocked by the antagonist D-AP5. Thus, while neurones depend critically on mitochondrial oxidative phosphorylation for energy production (ATP synthesis), the osteoblasts might follow preferentially the glycolytic pathway. The stable adenosine analogue, 2-chloroadenosine (2-ClA), and the A1 and A2A receptor agonists, CPA and CGS21680, respectively, each conferred partial but significant protection against H2O2 damage to osteoblasts, while the respective A1 and A2A antagonists, DPCPX and ZM241385 had no effect. Glutamate- and H2O2-induced damage to CGNs were significantly prevented by CPA and ZM241385, but not by DPCPX or CGS21680. Therefore, while osteoblasts and neurones may be similar in terms of glutamate receptor expression, they exhibit differences in their manner of responses and the degree of sensitivity to toxic agents. Further elucidation of underlying mechanisms may be furnished through molecular biology-based approaches.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: T W Stone
Keywords: Neurosciences
Date of Award: 2006
Depositing User: Enlighten Team
Unique ID: glathesis:2006-71380
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 10 May 2019 10:49
Last Modified: 10 May 2019 10:49
URI: http://theses.gla.ac.uk/id/eprint/71380

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