Abstract:
Neuroglobin, a heme protein discovered in 2000, is mainly expressed in localised areas of the brain and the retina. The exact function of this protein is still not yet determined, but experiments have shown a protective role of this oxygen-binding heme protein against hypoxia/ischemia in a wide range of brain regions. The intrinsic apoptotic pathway is one of the cell death mediating pathways and neuroglobin has been shown to interfere with this pathway. It has been shown that the ferrous form of neuroglobin has anti-apoptotic roles and it is involved in a futile redox cycle, consisting of oxygen binding to the ferrous form, autoxidation of the ferric form, followed by the cyclic reduction back to the ferrous form. This project aims to investigate the redox activity of human neuroglobin under conditions that more closely resemble the physiological conditions in humans and also the possible mechanism for neuroglobin to provide protection against hypoxia-induced cell death. The stopped-flow apparatus and the UV-VIS spectrophotometer have been used to investigate each of the reactions in the futile redox cycle. The results were used in the GEPASI software to build a mathematical model that may potentially predict the amount of the active, protective form of neuroglobin (Ngb6 2+) in a cell during hypoxic conditions. The results suggest that the level of Ngb6 2+ is low in a normal resting neuron, to prevent tumour formation, whilst allowing physiological apoptosis. The concentration of Ngb6 2+ is increased in hypoxic neurons to protect cells against unwanted apoptosis. Furthermore, this thesis has explored the potential neuroglobin reductants and possible origins of difference in the published p50 values. Overall, the outcome in this thesis provides a good approximation model of the redox response neuroglobin produces upon the onset of hypoxia, as might occur in stroke situations. It could explain the possible mechanism for neuroglobin to not only avoid cancer formation but also provide acute protection against apoptotic cell death. The model could potentially play a role in the future development of reducing drugs, which could be administrated to increase the amount of reduced neuroglobin in stroke patients and protect against hypoxia-induced apoptosis.