Morphology of the mitochondria in heat shock protein 60 deficient fibroblasts from mitochondrial myopathy patients. Effects of stress conditions

We have described two mitochondrial (mt) myopathy patients with reduced activities of various mt enzymes associated with significantly decreased amounts of heat shock protein 60 (hsp60). Experimental evidence suggested that the lack of hsp60 was the primary defect. Since hsp60 is essential for the proper folding of enzyme subunits in the mt matrix a partial deficiency of this protein can explain the observed defects of the mitochondria. Here we report on morphological studies aimed at obtaining more insight into the relation between lack of hsp60 and pathological changes of the mitochondria. Under standard culture conditions mitochondria in the partially hsp60 deficient fibroblasts showed profound morphological aberrations. In contrast, the mitochondria in fibroblasts from a MELAS patient and a cytochrome c oxidase-deficient patient appeared normal. Under stress conditions the integrity of the hsp60 deficient mitochondria declined even further: heat shock induced a temporary collapse of the electrochemical potential across the inner mt membrane, but did not affect the ultrastructure of the mitochondria; prolonged growth in confluent cultures resulted in decrease in mt number. The altered mt morphology in the hsp60 deficient cells is probably indicative of the severely impaired mt metabolism whereas the decreased stress tolerance is likely to be a direct result of paucity of the heat shock protein. Both variables are potentially useful in the diagnosis and molecular characterization of mt disorders with systemic manifestation and multiple enzyme deficiency.