Study of pathogenesis in twitcher mouse, an enzymatically authentic model of Krabbe's disease.

The twitcher mouse was investigated by examining in vivo synthesis of galactosylceramide (Galcer) and galactosylsphingosine (Galsph) in a sciatic nerve culture, and in vitro enzymic activities for synthesis of Galcer and Galsph in the spinal cord from normal and affected mice. For the in vivo study, the sciatic nerve was incubated for 24 h in medium containing [3H]galactose, or [3H]-sphingosine-labeled Galcer or Galsph. With [3H]galactose, reduced synthesis of Galcer was found as early as 1 week of age and synthesis decreased to about 15% of normal value at 4 weeks. Increased Galsph was detected after 7 days of feeding with galactose. In a study of [3H]sphingosine-labeled Galcer and Galsph feeding, Galcer did not induce Galsph synthesis in either normal or affected mice, and synthesis of Galcer from Galsph was found only in normal mice, suggesting that Galcer was synthesized from sphingosine after hydrolysis of Galsph. In vitro, the activities of UDP-galactose: ceramide galactosyltransferase and UDP-galactose: sphingosine galactosyltransferase were reduced to less than 50% of control after 2 weeks of age in affected mice. We conclude that (1) decreased Galcer was due to impaired synthesis of Galcer, (2) Galsph was synthesized from galactose and not from deacylation of Galcer, and (3) Galsph accumulation was due not to increased synthesis but to decreased hydrolysis.