Saposins (sphingolipid activator proteins) in the twitcher mutant mouse

Area of Science:

• Biochemistry
• Genetics
• Neuroscience

Background:

• Krabbe disease, a lysosomal storage disorder, is modeled by the twitcher mouse.
• This model exhibits a deficiency in galactosylceramide beta-galactosidase activity.
• Saposin A and C are known activators of galactosylceramide beta-galactosidase.

Purpose of the Study:

• To investigate the role of saposin A and C in the twitcher mouse model of Krabbe disease.
• To determine if the twitcher mutation impacts saposin levels or function.

Main Methods:

• Preparation of boiled supernatant fractions from twitcher and control tissues (brain, liver, kidney, spleen).
• Assay of galactosylceramide beta-galactosidase and glucosylceramide beta-glucosidase activities.
• Testing the effect of purified saposin A and C on enzyme activity in twitcher and control homogenates.

Main Results:

• Saposin-containing preparations from twitcher tissues showed similar effects on glucosylceramide beta-glucosidase activity compared to controls.
• Authentic saposin A and C exhibited similar stimulatory effects on galactosylceramide beta-galactosidase and glucosylceramide beta-glucosidase in twitcher and control tissues.
• The twitcher mutation did not alter the interaction between saposins A/C and their target enzymes.

Conclusions:

• The twitcher mutation does not appear to affect the concentration or function of saposin A or C.
• Saposin deficiency is unlikely to be the primary cause of galactosylceramide beta-galactosidase deficiency in the twitcher mouse model.
• Further research is needed to identify the precise molecular defect in the twitcher mouse model.