Cytoplasmic restoration and persistence of glucose-6-phosphate dehydrogenase activity in stable hybrid myotubes

In previous experiments, we obtained an in vitro restoration of a cytosolic enzyme glucose-6-phosphate dehydrogenase (G6PD) in hybrid myotubes formed between G6PD-deficient and human or murine myoblasts. In the present series of experiments, the degree of restoration was observed and the persistence of the restored activity was evaluated in the hybrids formed. Quantitative measurements of enzymatic activity in single human-human or human-mouse myotubes, identified by using either fluorescent latex microspheres or Hoechst stain 33258, were made by using a computer-controlled Leitz photometer. Histospectrophotometry and statistical analysis showed a 50% restoration of enzymatic activity in human-human hybrids compared to deficient and normal myotubes. The restored activity was uniformly distributed throughout the cytoplasm and persisted in long-term cultures. No nuclear domain was observed for G6PD. Knowledge of the degree of restoration, of the extent of distribution of the products of "competent" nuclei and the demonstration that the correction is not a transitory event in vitro, supports the potential usefulness of myoblast transfer therapy for this type of myopathy.