Mitochondrial Respiratory Chain Enzymatic Activities and UCP3 Expression in Muscles of Patients with Hereditary and Sporadic Amyotrophic Lateral Sclerosis (P07.089)

OBJECTIVE: We wished to verify if mitochondrial respiratory chain (RC) dysfunction, decreased SOD1, and elevated UCP3 expression occur in muscles of patients with sporadic and hereditary ALS.BACKGROUND: ALS is characterized by neurodegeneration of motor neurons with an unclear pathogenesis. Dysfunction of the mitochondrial RC has been found in muscles from ALS patients, but the results are controversial. Moreover, a dramatic increase of the mitochondrial uncoupling protein 3 (UCP3) has been reported in muscles of ALS patients by a single study.DESIGN/METHODS: Activities of the RC enzymes (complex I, II, III, IV, I+III, II+III) and of citrate synthase were measured in muscles of controls (n=15), sporadic (n=11) and hereditary ALS patients (2 with a SOD1 and 3 with a c9ORF72 mutation) using optimized spectrophotometric assays. Superoxide dismutase enzymatic activities were also measured. Muscle sections were processed with a combined SDH/COX staining for blinded quantification of COX negative and ragged-blue fibers. Protein expression of UCP3, COX2, and SOD1 was measured by western blotting.RESULTS: The activities of the mitochondrial RC enzymes did not differ between ALS patients and controls except in the coupled assay for complex II+III (p <0.05). The frequence of COX negative and ragged red fibers did not differ between patients and controls. Superoxide dismutase activities were specifically decreased in SOD1 mutant patients, but not in other ALS groups.Expression of the muscle mitochondrial uncoupling protein 3, was very variably expressed in both patients and controls, without any significant difference.CONCLUSIONS: Our data argue against a significant mitochondrial dysfunction as a unifying pathogenetic mechanisms in muscles of sporadic and hereditary ALS patients. UCP3 is not a useful biomarker for ALS. We speculate that the isolated defect of the coupled activities for complex II+III could arise from a secondary reduction in coenzyme Q pools in muscles of ALS patients, warranting further studies.Disclosure: Dr. Spinazzi has nothing to disclose. Dr. Casarin has nothing to disclose. Dr. Salviati has nothing to disclose. Dr. Cima has nothing to disclose. Dr. Gavassini has nothing to disclose. Dr. Pegoraro has received personal compensation for activiteis with BioMarin Pharmaceutical Inc. and MEDA Pharmaceuticals Inc. Dr. Soraru has nothing to disclose. Dr. Angelini has received personal compensation for activities with Genzyme as a member of the Advisory Board.