Cuproenzyme dysfunction in the pathogenesis of amyotrophic lateral sclerosis and multiple sclerosis
Document TypePhD thesis
Access StatusOpen Access
© 2016 Dr. James Benjamin William Hilton
Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterised by the selective death of motor neurons within the spinal cord and brain. Although the aetiology of the disease is not well understood, inherited genetic mutations account for a small proportion of cases, with Cu,Zn-superoxide dismutase (SOD1) mutations being the most extensively studied. Effective treatment options for ALS do not exist, however, pre-clinical outcomes indicate that therapeutically modulating copper bioavailability in the central nervous system (CNS) may be a feasible treatment strategy for ALS. Therefore, the initial objective of this study was to investigate the significance of copper dyshomeostasis in the progression of a mutant SOD1 mouse model of ALS. We hypothesised that age-related changes to cuproenzymes progress with disease symptoms in SOD1G37R mice compared to age-matched non-transgenic littermates and mice overexpressing wild-type human SOD1. To test this hypothesis, locomotor performance was assessed to track disease progression, then CNS and peripheral tissues were collected at distinct stages of disease for biochemical analyses. Data presented in Chapter 3 provide evidence for copper malfunction in the CNS of ALS mice and indicate that copper malfunction is an early feature of the disease which worsens as symptoms progress. Specifically, a disconnect exists between the abundance and copper-dependent activity of cuproenzymes SOD1 and ceruloplasmin. Next, the therapeutic significance of these changes to SOD1 and ceruloplasmin were assessed. In Chapter 4, data show that overexpressing CTR1 or treating ALS model mice with the copper compound CuII(atsm) extends survival and improves copper bioavailability to SOD1 and ceruloplasmin in the CNS. To ascertain the relevance of outcomes in a broader disease context, we next assessed human cases of sporadic ALS. Data presented in Chapter 5 show that SOD1 and ceruloplasmin dysfunction detected in mice is also evident in sporadic ALS. Significantly, changes to ceruloplasmin are associated with changes to iron homeostasis, where diminished copper- dependent ceruloplasmin activity may contribute to iron overload in the ALS-affected motor cortex and decreased transferrin bound iron in the cerebrospinal fluid. As such, we propose that changes to copper-dependent ceruloplasmin activity in ALS may be the mechanistic basis for two ALS biomarkers and represent the first biochemical evidence for the feasibility of treating ALS, including sporadic ALS, by therapeutically improving copper bioavailability to CNS cuproenzymes. Multiple sclerosis (MS) is a disease characterised by CNS demyelination, with evidence suggesting a link between demyelination and limited copper bioavailability. This is supported by data presented in Chapter 7 from both ALS model mice and MS-affected CNS tissue. We also show that changes to copper, SOD1, ceruloplasmin and myelin-associated proteins are common to ALS and MS, and that modulating copper bioavailability may provide a therapeutic intervention. Overall, data presented in this thesis indicate that: copper malfunction is a feature of ALS and MS; copper malfunction evident in sporadic cases of ALS are recapitulated in mutant SOD1 mouse models of familial ALS; and perturbations to the copper-dependent ceruloplasmin activity may be important to iron accumulation in the ALS-affected motor cortex. The therapeutic implications of these observations are discussed.
Keywordsamyotrophic lateral sclerosis; multiple sclerosis; copper; cuproenzymes; superoxide dismutase; neurodegeneration; therapeutics; iron; ceruloplasmin; cytochrome c oxidase; biomarkers
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- Pathology - Theses