Centre for Neuroscience - Theses
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ItemDifferential responses to neural injury and disease in EphA4 knockout mice( 2011)Promoting repair and regeneration of the injured and diseased central nervous system is among the most critical fields in research today, and would improve the quality of life of people suffering from traumatic brain and spinal cord injury, multiple sclerosis and many other conditions. Mice lacking the developmental axon guidance molecule EphA4 demonstrate extensive axonal outgrowth and functional recovery following spinal cord injury (Goldshmit et al., 2004), and a greater understanding of the mechanisms orchestrating this regenerative response is the focus of this thesis. To identify differentially expressed genes which may contribute to axonal regeneration, RNA collected from adult EphA4 knockout and wild-type mice 4 days following lumbar spinal cord hemisection or laminectomy only was hybridised to Affymetrix All-Exon Array 1.0 GeneChipsTM. Microarray analysis indicated attenuated or otherwise altered expression of a number of inflammatory genes in injured EphA4 knockout spinal cords. These included inflammatory phospholipid-related genes lysophosphatidic acid receptor 1 (LPAR1, p=0.002), a receptor for lysophosphatidic acid, and alkaline ceramidase 2 (ACER2, p=0.006), a regulator of sphingosine production. In both genotypes at 4 days post-injury, LPAR1 was localised to reactive astrocytes surrounding the spinal cord lesion and ACER2 was predominantly localised to macrophages / activated microglia within the lesion. Microarray results also indicated arginase 1 (ARG1) was lower in injured EphA4 knockout compared to wild-type mice (p=0.014 and fold difference=3.17 between injured groups) and a lower proportion of ARG1-immunoreactive macrophages / activated microglia in EphA4 knockout spinal cords was confirmed histologically at 4 days post-injury. However there was no difference in the overall number or spread of macrophages / activated microglia in injured EphA4 knockout compared to wild-type mice at 2, 4 or 14 days post-injury. To further investigate whether a subtly altered neuroinflammatory response contributes to the regenerative phenotype of injured EphA4 knockout mice, the response of EphA4 knockout compared to wild-type mice was examined using a model of neural injury caused by inflammation, experimental autoimmune encephalomyelitis. In this animal model of multiple sclerosis, EphA4 knockout mice had less severe neurological symptoms compared to wild-type mice, indicating less neural injury. The proportion of ARG1-immunoreactive macrophages / microglia was not altered in experimental autoimmune encephalomyelitis-affected EphA4 knockout mice at 20 days post-immunisation, and whether the attenuated response to disease symptoms seen in EphA4 knockout mice is primarily due to differences in immune or central nervous system parenchymal cells remains to be determined. In summary, EphA4 knockout mice not only display regeneration following spinal cord injury but also have a less severe response to experimental autoimmune encephalomyelitis, a model of multiple sclerosis. Alterations in the neuroinflammatory response of injured EphA4 knockout mice may contribute to their improved outcomes to models of CNS disease and injury. Investigations in this thesis have also resulted in the localisation of two inflammatory phospholipid-related genes, LPAR1 and ACER2, previously uncharacterised in the injured CNS.