Gaucher disease mouse models: point mutations at the acid -glucosidase locus combined with low-level prosaposin expression lead to disease variants

Gaucher disease is a common lysosomal storage disease caused by a defect of acid -glucosidase (GCase). The optimal in vitro hydrolase activity of GCase requires saposin C, an activator protein that derives from a precursor, prosaposin. To develop additional models of Gaucher disease and to test in vivo effects of saposin deficiencies, mice expressing low levels (4–45% of wild type) of prosaposin and saposins (PS-NA) were backcrossed into mice with specific point mutations (V394L/V394L or D409H/D409H) of GCase. The resultant mice were designated 4L/PS-NA and 9H/PS-NA, respectively. In contrast to PS-NA mice, the 4L/PS-NA and 9H/PS-NA mice displayed large numbers of engorged macrophages and nearly exclusive glucosylceramide (GC) accumulation in the liver, lung, spleen, thymus, and brain. Electron microscopy of the storage cells showed the characteristic tubular storage material of Gaucher cells. Compared with V394L/V394L mice, 4L/PS-NA mice that expressed 4–6% of wild-type prosaposin levels had 25–75% decreases in GCase activity and protein in liver, spleen, and fibroblasts. These results imply that reduced saposin levels increased the instability of V394L or D409H GCases and that these additional decreases led to large accumulations of GC in all tissues. These models mimic a more severe Gaucher disease phenotype and could be useful for therapeutic intervention studies. —Sun, Y., B. Quinn, D. P. Witte, and G. A. Grabowski. Gaucher disease mouse models: point mutations at the acid -glucosidase locus combined with low-level prosaposin expression lead to disease variants. J. Lipid Res. 2005. 46: 2102– 2113. Supplementary key words macrophage • lysosomal storage disease • glycosphingolipids Gaucher disease is an autosomal recessive trait and the most common lysosomal storage disorder (1). The defective lysosomal hydrolysis of glucosylceramide (GC) in Gaucher disease is caused by mutations in the gene [human (GBA), mouse ( gba )] encoding acid -glucosidase (GCase), a membrane-associated lysosomal hydrolase (1). More than 200 mutations at the GBA locus have been identified in Gaucher disease patients, and the resultant defective or deficient enzyme activities lead to variable phenotypes (1, 2). The accumulation of GC leads to enlargement of the liver and spleen, bone lesions, and central nervous system (CNS) manifestations in some variants (1, 3–5). The macrophage is the primary cell displaying GC accumulation; nonmacrophage parenchymal cells appear normal in liver, lung, bone marrow, and spleen in Gaucher disease (e.g., hepatocytes, granulocytes, and lymphocytes) (1). The knock out of gba in the mouse leads to lethality in the newborn period (6). Efforts to create animal models of Gaucher disease with a longer life span have included the gba “knock in” of the L444P mutation, but this also led to early death attributable, at least in part, to a defective skin permeability barrier (7). Additional mouse models were designed based on genotype/phenotype correlations in humans (8), as summarized in Table 1 . Homozygosity for N370S in humans results in less severe to asymptomatic phenotypes (1, 9, 10). In comparison, homozygosity for the D409H allele is associated with early-onset, variable disease of the viscera and CNS (11, 12). These patients also can develop characteristic calcific abnormalities of the aortic valves and ascending aorta (13). The V394L allele has been observed only in the heteroallelic state, and when the heteroallele is L444P, the phenotype includes visceral and CNS involvement (11). In contrast, N370S homozygosity in mice was lethal in the neonatal period, V394L homozygosity displayed minor phenotypic abnormalities up to 12 months, and D409H or D409V homozygotes displayed low-grade Gaucher cell formation and GC storage (8). Visceral tisAbbreviations: CNS, central nervous system; gba , gene encoding mouse acid -glucosidase; GC, glucosylceramide; GCase, acid -glucosidase; LacCer, lactosylceramide; 4MU-Glc, 4-methylumbelliferyld -glucopyranoside; WT, wild-type. 1 To whom correspondence should be addressed. e-mail: [email protected] Manuscript received 19 May 2005 and in revised form 15 July 2005. Published, JLR Papers in Press, August 1, 2005. DOI 10.1194/jlr.M500202-JLR200 by gest, on O cber 9, 2017 w w w .j.org D ow nladed fom