[Learning from the studies of twitcher mouse]

Twitcher mouse is a naturally occurring mouse model for human Krabbe disease, a lysosomal galactosyl-ceramidase deficiency. Therefore, this mouse provides us an excellent experimental model for studying the pathogenesis and effective therapies for Krabbe disease. First, we succeeded to clone cDNA of human galactosylceramidase from lymphocytes, and determined its sequence. Consequently, many mutations of Krabbe disease have been discovered. For the trial of gene therapy for twitcher mouse, a recombinant retrovirus vector containing human galactosylceramidase cDNA was constructed and targeted to bone marrow cells ex vivo. These cells were transplanted intraperitoneally into twitcher neonates. This protocol resulted in slightly better weight gain and increase in the enzymatic activity in the peripheral nerve in the gene therapy group, but the survival period was prolonged. These results suggest that the efficacy of viral transfection is critical for the gene therapy. In addition, in order to understand the pathogenesis of demyelinating process and to evaluate the gene therapy more precisely, we examined the pathophysiology of oligodendrocytes and their related cells in the nervous system of twitcher mouse. We introduced pi-glutathione-S-transferase immunostaining for the specific identification of oligodendrocytes. Using this method, the oligodendrocytes with multiple varicose processes were recognized in the early stages. With the progression of the disease, these cells became shrunk showing the ultrastructural and biochemical characteristics of apoptosis. This may provide a key to the future treatment of Krabbe disease.