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The thesis describes experiments on the role of Epidermal Growth Factor receptor (ErbB1) in limiting axonal regeneration. Pharmacological inhibitors of ErbB1 are known to improve neurite outgrowth from neurons grown in vitro on various inhibitory substrates such as CNS myelin, chondroitin sulphate proteoglycans (CSPGs) and fibrinogen (Koprivica et al., 2005). However, the hypothesis that ErbB1 is involved in the signalling mechanisms from various CNS inhibitory molecules has been challenged in papers form the Logan laboratory (Ahmed et al., 2010) which concluded that pharmacological blockers disinhibit neurite outgrowth by acting off-target to ErbB1. The first stage of this project was to use primary sensory neurons from ErbB1 knockout mice to test the hypothesis that ErbB1 is involved in inhibition of neurite outgrowth in vitro in the presence of CNS myelin, a Toll-Like Receptor 3 ligand (Poly I:C) and CSPGs. Through a series of experiments that have been described in this thesis, it was shown that ErbB1 antagonists act on-target and that ErbB1 signalling causes inhibition of neurite outgrowth of neurons cultured in the presence of Poly I:C, CNS myelin or CSPGs. Moreover, buffering calcium was shown to abolish the inhibitory effects caused by ErbB1 signalling, indicating that calcium is essential for the activation of the receptor. Other molecules that may be associated with ErbB1 signalling leading to inhibition of neurite outgrowth include PTEN and novel Sulfatase enzymes- Sulf1 and Sulf2. Using immunohistochemistry, Sulf1 and Sulf2 were shown to be expressed by a large variety of neurons. Also, ErbB1 expression detected immunohistochemically was predominantly localised to neurons. The thesis also describes preliminary observations on the efficacy of an ErbB1 antagonist or a dominant-negative ErbB1 lentivirus in improving axonal regeneration following an optic nerve crush or spinal cord injury in adult rats. In conclusion, ErbB1 signalling following injury is associated with regeneration failure. |
