1. Tissue-specific effects of saposin A and saposin B on glycosphingolipid degradation in mutant mice
- Author
-
Michael T. Williams, Charles V. Vorhees, Wujuan Zhang, Gregory A. Grabowski, David P. Witte, Sonya Barnes, Ying Sun, Huimin Ran, Matt Zamzow, Brian Quinn, and Kenneth D.R. Setchell
- Subjects
Male ,Mutant ,Motor Activity ,Biology ,Kidney ,Glycosphingolipids ,Saposins ,Mice ,Lactosylceramide ,Galactosylceramidase ,Genetics ,Animals ,Humans ,Beta-galactosidase ,music ,Molecular Biology ,Genetics (clinical) ,Mice, Knockout ,Prosaposin ,music.instrument ,Catabolism ,Autophagy ,Brain ,Kidney metabolism ,Articles ,General Medicine ,beta-Galactosidase ,Molecular biology ,Mice, Inbred C57BL ,Phenotype ,Liver ,Biochemistry ,Organ Specificity ,biology.protein ,Female ,Nervous System Diseases - Abstract
Individual saposin A (A−/−) and saposin B (B−/−)-deficient mice show unique phenotypes caused by insufficient degradation of myelin-related glycosphingolipids (GSLs): galactosylceramide and galactosylsphingosine and sulfatide, respectively. To gain insight into the interrelated functions of saposins A and B, combined saposin AB-deficient mice (AB−/−) were created by knock-in point mutations into the saposins A and B domains on the prosaposin locus. Saposin A and B proteins were undetectable in AB−/− mice, whereas prosaposin, saposin C and saposin D were expressed near wild-type (WT) levels. AB−/− mice developed neuromotor deterioration at >61 days and exhibited abnormal locomotor activity and enhanced tremor. AB−/− mice (∼96 days) lived longer than A−/− mice (∼85 days), but shorter than B−/− mice (∼644 days). Storage materials were observed in Schwann cells and neuronal processes by electron microscopy. Accumulation of p62 and increased levels of LC3-II were detected in the brainstem suggesting altered autophagy. GSL analyses by (liquid chromatography) LC/MS identified substantial increases in lactosylceramide in AB−/− mouse livers. Sulfatide accumulated, but galactosylceramide remained at WT levels, in the AB−/− mouse brains and kidneys. Brain galactosylsphingosine in AB−/− mice was ∼68% of that in A−/− mice. These findings indicate that combined saposins A and B deficiencies attenuated GalCer-β-galactosylceramidase and GM1-β-galactosidase functions in the degradation of lactosylceramide preferentially in the liver. Blocking sulfatide degradation from the saposin B deficiency diminished galactosylceramide accumulation in the brain and kidney and galctosylsphingosine in the brain. These analyses of AB−/− mice continue to delineate the tissue differential interactions of saposins in GSL metabolism.
- Published
- 2013