High β-galactosidase and ganglioside GM1 levels in the human parotid gland

Background: Ganglioside G(M1) is a membrane glycolipid typical of nerve cell membranes, where it partakes in neurotransmitter release and is catabolized by the lysosomal alpha -galactosidase (GM1ase) (EC 3.2.1.23). After demonstrating a novel degenerative disease of the parotid gland in mice deficient in GM1ase, mimicking the human storage disease GM(1) gangliosidosis, we studied GM1ase and ganglioside G-(M1) content in the human parotid glands. Study Design: Levels of GM1ase and ganglioside GM(1) were determined in samples of parotid tissues and neighboring muscle (as a negative control) for 3 subjects. Tissues were also processed for histochemical demonstration of GM1ase. Results: The mean specific activity of GM1ase was more than 6-fold higher in the healthy human parotid tissues (1.4 +/-0.5 nmol of 4-methylumbelliferone per minute per milligram of protein) relative to the neighboring muscle tissue (0.23 +/- 0.07 nmol of 4-methylumbelliferone per minute permilligram of protein). Activity, of GM1ase was histochemically localized mainly to striated duct and acinar cells of the parotid gland. Ganglioside G(M1) content in the parotid gland was on average 30-fold higher relative to muscle. Conclusions: Our results are consistent with previous findings reported in the mouse and the rabbit, and probably reflect a general property of the mammalian parotid glands. The novel mechanism we previously proposed for the mouse parotid saliva secretion, mimicking neurotransmitter release in ganglioside G(M1)-containing nerve cells, is probably applicable also to the human parotid gland. Similarly, the human parotid gland is probably also severely affected in GM(1) gangliosidosis.