Combined saposin C and D deficiencies in mice lead to a neuronopathic phenotype, glucosylceramide and alpha-hydroxy ceramide accumulation, and altered prosaposin trafficking.
Saposins (A, B, C and D) are approximately 80 amino acid stimulators of glycosphingolipid (GSL) hydrolases that derive from a single precursor, prosaposin. In both humans and mice, prosaposin/saposin deficiencies lead to severe neurological deficits. The CD-/- mice with saposin C and D combined deficiencies were produced by introducing genomic point mutations into a critical cysteine in each of these saposins. These mice develop a severe neurological phenotype with ataxia, kyphotic posturing and hind limb paralysis. Relative to prosaposin null mice ( approximately 30 days), CD-/- mice had an extended life span ( approximately 56 days). Loss of Purkinje cells was evident after 6 weeks, and storage bodies were present in neurons of the spinal cord, brain and dorsal root ganglion. Electron microscopy showed well-myelinated fibers and axonal inclusions in the brain and sciatic nerve. Marked accumulations of glucosylceramides and alpha-hydroxy ceramides were present in brain and kidney. Minor storage of lactosylceramide (LacCer) was observed when compared with tissues from the prosaposin null mice, suggesting a compensation in LacCer degradation by saposin B for the saposin C deficiency. Skin fibroblasts and tissues from CD-/- mice showed an increase of intracellular prosaposin, impaired prosaposin secretion, deficiencies of saposins C and D and decreases in saposins A and B. In addition, the deficiency of saposin C in CD-/- mice resulted in cellular decreases of acid beta-glucosidase activity and protein. This CD null mouse model provides a tool to explore the in vivo functional interactions of saposins in GSL metabolism and lysosomal storage diseases, and prosaposin's physiological effects.
Sun
Ying
Y
Division of Human Genetics, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA.
Witte
David P
DP
Zamzow
Matt
M
Ran
Huimin
H
Quinn
Brian
B
Matsuda
Junko
J
Grabowski
Gregory A
GA
D000818:Animals; D002478:Cells, Cultured; D002518:Ceramides / Q000378:metabolism*; D005776:Gaucher Disease / Q000235:genetics* / Q000401:mortality / Q000473:pathology; D005786:Gene Expression Regulation; D005963:Glucosylceramides / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008954:Models, Biological; D004676:Myelin Basic Protein / Q000235:genetics; D010641:Phenotype; D011499:Protein Processing, Post-Translational; D021381:Protein Transport; D049231:Saposins / Q000235:genetics* / Q000378:metabolism
D002518:Ceramides; D005963:Glucosylceramides; D004676:Myelin Basic Protein; C483344:Psap protein, mouse; D049231:Saposins