Absence of major accumulation of mitochondrial ND5 mutations in Parkinson patient muscle

Abstract

The pathogenesis of the selective loss of dopaminergic neurons in idiopathic Parkinson's disease (PD) has not been understood up to now. Respiratory chain dysfunction and accumulation of mitochondrial DNA deletions to biochemically relevant levels have been observed in the dopaminergic neurons. However, respiratory chain defects have also been reported in other tissues, pointing to a generalized component of oxidative stress in PD. Recently, somatic point mutations in a narrow region of the complex I polypeptide ND5 (codons 120 - 150) were suggested to separate PD patients from age-matched controls, using frontal cortex homogenates. The present study intended to analyze whether those recently described ND5 mutations may also generally occur in skeletal muscle tissue of PD patients, in which complex I dysfunction had been measured earlier with biochemical approaches. Skeletal muscle biopsy samples of 5 PD individuals with a previously characterized biochemical complex I defect and of 5 age-matched controls were used. DNA was extracted from the muscle samples. The relevant ND5 region was PCR-cloned using a high fidelity Pfu polymerase and a low number of PCR cycles (15). Amean number of 96 clones were randomly selected from the ampicillin plates and sequenced by the dye terminator method to allow the detection of low abundance mutations with a sensitivity around 1%. Mutations between codons 120 and 150 were only slightly more frequent in PD versus controls (60 versus 40% of samples affected), while this ratio had been 100 versus 12.5% in frontal cortex. In contrast to results reported for PD frontal cortex, low-level ND5 mutations between codons 120 and 150 do not accumulate severely in biochemically affected skeletal muscle samples of PD patients.