Immunolabelling of mitochondrial superoxide dismutase and of Hsp60 in muscles harbouring a respiratory chain deficiency

In mitochondrial encephalomyopathies, impairment of the electron transfer c hain may lead to overproduction of reduced oxygen species because oxygen co nsumption is decreased. Whether heat shock proteins (Hsp) are induced or no t in mitochondria against oxidative stress is questionable. Muscle ragged-r ed fibres are the histological hallmark of most respiratory chain deficienc ies in humans. They exhibit abnormal mitochondria which accumulate mainly u nder their sarcolemma. Within these fibres, immunolabelling demonstrated st rong expression of mitochondrial manganese-dependent superoxide dismutase a nd a lack of expression of mitochondrial Hsp60 within the subsarcolemmal sp aces. In contrast, Hsp60 was overexpressed within the intermyofibrillar mit ochondria These findings suggest enhanced generation and dismutation of sup eroxide anions and that processing and integration of imported precursor pr oteins is impaired within the subsarcolemmal mitochondrial aggregates of ra gged-red fibres, whereas protein import and assembly may still be efficient in the intermyofibrillar mitochondria of these fibres. (C) 2000 Elsevier S cience B.V. All rights reserved.