EFFECTS OF WILD-TYPE AND MUTATED COPPER ZINC SUPEROXIDE-DISMUTASE ON NEURONAL SURVIVAL AND L-DOPA-INDUCED TOXICITY IN POSTNATAL MIDBRAIN CULTURE/

Mutations in the free radical-scavenging enzyme copper/zinc superoxide dismutase (Cu/Zn-SOD) are associated with neuronal death in humans an d mice. Here, we examine the effects of human wild-type (WT SOD) and m utant (Gly(93) --> Ala; G93A) Cu/Zn-SOD enzyme on the fate of postnata l midbrain neurons. One-week-old cultures from transgenic mice express ing WT SOD enzyme had significantly more midbrain neurons and fewer ne crotic and apoptotic neurons than nontransgenic cultures, In contrast, 1-week-old cultures from transgenic G93A mice expressing mutant SOD e nzyme had significantly fewer midbrain neurons and more necrotic and a poptotic neurons than nontransgenic cultures. To subject postnatal mid brain neurons to oxidative stress, cultures were incubated with L-DOPA . L-DOPA at 200 mu M caused similar to 50% loss of tyrosine hydroxylas e (TH)-positive neurons in nontransgenic cultures and even greater los s in transgenic G93A cultures; no alterations were noted in GABA neuro n numbers. in contrast, 200 mu M L-DOPA did not cause any significant reductions in TH-positive or GABA neuron numbers in transgenic WT SOD cultures. L-DOPA at 50 mu M had opposite effects, in that it significa ntly increased TH-positive, but not GABA neuron numbers in transgenic WT SOD and G93A and in nontransgenic cultures. These results indicate that increased amounts of WT SOD enzyme promote cell survival and prot ect against L-DOPA-induced dopaminergic neurotoxicity, whereas increas ed amounts of mutated Cu/Zn-SOD enzyme have inverse effects. As the sp ontaneous loss and L-DOPA-induced loss of postnatal dopaminergic midbr ain neurons appear to be mediated by free radicals, our study supports the view that mutated Cu/Zn-SOD enzyme kills cells by oxidative stres s.