The objective of the proposed studies is to determine the in vivo effects of prosaposin (PS)-derived sphingolipid activator protein (saposins A, B, C and D) deficiencies on the control of glycosphingolipid (GSL) metabolism. The hypothesis is that GSL catabolism is modulated by the interactions of these saposins in the metabolic pathway, and that this represents an example of intragenic epistasis. Furthermore, we propose that saposin B is the key modulator that controls flow through this pathway. These studies are based on the observations that the rare, not fully detailed, human (B and C) and mouse (A) isolated saposin deficiencies have significantly different phenotypes (both clinically and biochemically), than simultaneous deficiency (PS-/-) of all four PS-derived saposins. Similarly, the PS-/- genotype leads to new phenotypes by masking the GSL storage of isolated B, C or A deficiency. We postulate that these altered phenotypes result from the interactions and redundancies of the saposins at specific steps in the GSL catabolic pathway, suggested by in vitro/ex vivo analyses. For these studies, mice with mono- or di- saposin deficiencies will be created by targeted introduction of specific point mutations that, based on human and mouse models, have produced functionally intact prosaposin and """"""""non-mutated saposins,"""""""" and isolated deficiencies of the saposins. The mutations will disrupt the conserved disulfide structure of the saposins by substitution of Phe or Ser for Cys at selected residues: ex vivo expression analyses will evaluate the overall effects of these mutations on PS and saposin stability prior to ES cell targeting. Mono-saposin B, C or D deficiencies will be created first and the resultant phenotypes characterized at the clinical, histologic and biochemical [in vivo and in vitro (e.g., cultured fibroblasts, neurons, hepatocytes)] levels: Saposin A deficient mice are available to us. Disaposin deficiencies of saposins A and B, and B and C will be created to evaluate the interactions at specific steps in GSL catabolism: e.g., the proposed need of saposins B and C for lactosylceramide degradation and the """"""""rescue"""""""" of the saposin A deficient phenotype by inclusion of saposin B deficiency. These studies have implications for GSL metabolism, and lysosomal storage disease phenotypic expression and therapy.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Research Project (R01)
Project #
Application #
Study Section
Medical Biochemistry Study Section (MEDB)
Program Officer
Tagle, Danilo A
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Children's Hospital Med Ctr (Cincinnati)
United States
Zip Code
León, Luis; Tatituri, Raju V V; Grenha, Rosa et al. (2012) Saposins utilize two strategies for lipid transfer and CD1 antigen presentation. Proc Natl Acad Sci U S A 109:4357-64
Sun, Ying; Liou, Benjamin; Xu, You-Hai et al. (2012) Ex vivo and in vivo effects of isofagomine on acid ?-glucosidase variants and substrate levels in Gaucher disease. J Biol Chem 287:4275-87
Xu, Y H; Sun, Y; Ran, H et al. (2011) Accumulation and distribution of ?-synuclein and ubiquitin in the CNS of Gaucher disease mouse models. Mol Genet Metab 102:436-47
Pearse, Bradley R; Tamura, Taku; Sunryd, Johan C et al. (2010) The role of UDP-Glc:glycoprotein glucosyltransferase 1 in the maturation of an obligate substrate prosaposin. J Cell Biol 189:829-41
Campeau, Philippe M; Rafei, Moutih; Boivin, Marie-Noelle et al. (2009) Characterization of Gaucher disease bone marrow mesenchymal stromal cells reveals an altered inflammatory secretome. Blood 114:3181-90
Grabowski, Gregory A (2008) Phenotype, diagnosis, and treatment of Gaucher's disease. Lancet 372:1263-71
Sun, Ying; Quinn, Brian; Xu, You-Hai et al. (2006) Conditional expression of human acid beta-glucosidase improves the visceral phenotype in a Gaucher disease mouse model. J Lipid Res 47:2161-70
Sun, Ying; Quinn, Brian; Witte, David P et al. (2005) Gaucher disease mouse models: point mutations at the acid beta-glucosidase locus combined with low-level prosaposin expression lead to disease variants. J Lipid Res 46:2102-13
Sun, Ying; Qi, Xiaoyang; Grabowski, Gregory A (2003) Saposin C is required for normal resistance of acid beta-glucosidase to proteolytic degradation. J Biol Chem 278:31918-23
Sun, Ying; Witte, David P; Jin, Peng et al. (2003) Analyses of temporal regulatory elements of the prosaposin gene in transgenic mice. Biochem J 370:557-66

Showing the most recent 10 out of 15 publications