Evidence is steadily accumulating that oxygen free radical damage plays a major role in age-related neurodegenerative disease. Humans or experimental animals with altered expression of Cu/Zn superoxide dismutase (SOD-1), a key enzyme in the oxygen free radical scavenging system, exhibit either accelerated or delayed degenerative changes in the CNS. For example, transgenic mice with increased expression of SOD-1 are resistant to drug-induced neurodegeneration, and humans carrying a variety of point mutations in the SOD-1 gene are subject to familial, autosomal dominant amyotrophic lateral sclerosis (FALS), an age-related degenerative disease that mainly involves motor neurons. In this grant we propose to modify the SOD-1 locus of mice in order to study the effects of such engineered modifications on neurodegeneration. In our preliminary results we show that an altered murine SOD-1 gene corresponding to one of the human mutations associated with FALS, when expressed in transgenic mice, is associated with a profound, age-related loss of motor function. We propose to study these animals to characterize their deficits, as well as introduce other such mutant constructs into transgenic mice using the native SOD-1 promoter as has already been done, or the neuron-specific human Thy-1 promoter. Similarly, homologous recombination will be used to either delete the SOD-1 locus or replace it with one or more mutant genes that correspond to the human FALS mutants. The phenotypes of these animals will be followed with age and correlated with periodic histopathological analyses. In addition, in order to determine if altered SOD-1 expression affects mutation accumulation, some animals of the same inbred genetic background will be microinjected with a second transgene, a lacZ reporter construct that can serve as a sensitive monitor of mutation accumulation in vivo. Finally, the effects of altered SOD-1 genes on overall activity of SOD-1 and related enzymes in the oxygen free radical scavenging pathway will be studied in order to clarify the relationship between the expression of modified SOD-1 genes and free radical management in vivo. These experiments are likely, based on our preliminary observations, to provide important new murine models of neurodegenerative disease. Not only could these models clarify the role of SOD-1 in neurodegenerative disease, the experiments could provide definitive information concerning the hypothesized relationship between oxygen free radical scavenging and protection against mutations of DNA.
