Manganese superoxide dismutase levels are elevated in a proportion of amyotrophic lateral sclerosis patient cell lines

The most frequent genetic causes of amyotrophic lateral sclerosis (ALS) det ermined so far are mutations occurring in the gene for copper/zinc superoxi de dismutase (CuZnSOD), The mechanism may involve inappropriate formation o f hyroxyl radicals, peroxynitrite or malfunctioning of the SOD protein. We hypothesized that undiscovered genetic causes of sporadically occurring amy otrophic lateral sclerosis might be found in the mechanisms that create and destroy oxygen free radicals within the cell. After determining that there were no CuZnSOD mutations present, we measured superoxide production from mitochondria and manganese superoxide dismutase (MnSOD), glutathione peroxi dase, NF kappa B, Bcl-2 and Bax by immunoblot, Of the ten sporadic patients we tested we found three patients with significantly increased concentrati ons of MnSOD. These patients also had lower levels of superoxide production from mitochondria and decreased expression of Bcl-2, No mutations were fou nd in the cDNA sequence of either MnSOD in any of the sporadic patients. A patient with a CuZnSOD mutation (G82R) used as a positive control showed no ne of these abnormalities. The patients displaying the MnSOD aberrations sh owed no specific distinguishing features. This result suggests that the cau se of ALS in a subgroup of ALS patients (30%) is genetic in origin and can be identified by these markers. The alteration in MnSOD and Bcl-2 are likel y epiphenomena resulting from the primary genetic defect. It suggests also that the oxygen free radicals are part of the cause in this subgroup and th at dysregulation of MnSOD or increased endogenous superoxide production mig ht be responsible. (C) 2000 Academic Press.