The catabolism of
ganglioside GM2 is dependent on the lysosomal
enzyme β-
hexosaminidase A and a supporting
lipid transfer protein, the
GM2 activator protein. A genetically based disturbance of GM2 catabolism, leads to several subtypes of the
GM2 gangliosidosis:
Tay-Sachs disease,
Sandhoff disease, the AB-variant and the B1-variant, all of them having GM2 as major lysosomal storage compound. Further on it is known that the
gangliosides GM2 and GM3 accumulate as secondary storage compounds in
mucopolysaccharidoses, especially in Hunter disease,
Hurler disease, Sanfilippo disease and
Sly syndrome, with
chondroitin sulfate as primary storage compound. The exact mechanism of
ganglioside accumulation in mucopolysaccaridoses is still a matter of debate. Here, we show that
chondroitin sulfate strongly inhibits the catabolism of membrane-bound GM2 by β-
hexosaminidase A in presence of
GM2 activator protein in vitro already at low micromolar concentrations. In contrast,
hyaluronan, the major storage compound in
mucopolysaccharidosis IX, a milder disease without secondary
ganglioside accumulation, is a less effective inhibitor. On the other hand, hydrolysis of micellar-bound GM2 by β-
hexosaminidase A without the assistance of GM2AP was not impeded by
chondroitin sulfate implicating that the inhibition of GM2 hydrolysis by
chondroitin sulfate is most likely based on an interaction with GM2AP, the GM2AP-GM2 complex or the GM2-carrying membranes. We also studied the influence of some cationic amphiphilic drugs (
desipramine,
chlorpromazine,
imipramine and
chloroquine), provoking
drug induced phospholipidosis and found that all of them inhibited the hydrolysis of GM2 massively.