Saposin C mutations in Gaucher disease patients resulting in lysosomal lipid accumulation, saposin C deficiency, but normal prosaposin processing and sorting

Abstract

Gaucher disease (GD) is characterized by accumulation of glucosylceramide (GC) in the cells of monocyte/macrophage system. The degradation of GC is controlled by glucosylceramidase (GCase) and saposin (Sap) C, a member of a family of four small glycoproteins (Saps A, B, C and D), all derived by proteolytic processing of a common precursor, prosaposin (PSAP). Saps contain six cysteine residues, forming three disulfide bridges, that affect their structure and function. Sap C is an essential activator of GCase and its deficit impairs the GCase activity causing GD. In the present study the biological properties of cells from four recently described GD patients carrying mutations in the Sap C domain of the PSAP gene have been characterized. Two patients had mutations involving a cysteine residue, whereas the other two had a L349P mutation. It was found that: (i) in the four Sap C-deficient cells PSAP was normally processed and sorted, the lack of Sap C being mainly due to the Sap C instability in late endosomal/lysosomal environment; (ii) the decrease/absence of Sap C affected the GCase intracellular localization; (iii) the lowest level of Sap C and enhanced autophagy were observed in the cells, which carried a Sap C mutation involving a cysteine residue; (iv) the four Sap C-deficient fibroblasts stored GC, ceramide and cholesterol, the last two lipids being clearly localized in lysosomes; (v) a correlation was observed between the type of Sap C mutation and the Gaucher phenotype: apparently, mutations involving cysteine residues lead to a neurological variant of GD.

Ambroxol-induced rescue of defective glucocerebrosidase is associated with increased LIMP-2 and saposin C levels in GBA1 mutant Parkinson's disease cells

“…GCase activity was assessed in 20 μg of protein lysates for each cell line, using a modification of the protocol described by Vaccaro et al (2010). A reaction mix was prepared (0.1 M sodium citrate phosphate, pH 5.6; 0.1% Triton X-100; 0.25% sodium taurocholate and 2.5 mM 4-methylumbelliferyl-b-D-glucuronide or 4-MUG) and 200 μl were added to each sample.…”

The protective role of prosaposin and its receptors in the nervous system

“…Saposin C deficiency can lead to different forms of Gaucher’s disease in humans, predominantly type 2 and 3, which are known for neuropathological symptoms (Schnabel et al, 1991; Tamargo et al, 2012; Vaccaro et al, 2010). Similarly, the mouse model of saposin C deficiency mimics type 3 Gaucher’s disease (Sun et al, 2010) while the loss of full-length prosaposin (total saposin deficiency) most closely resembles type 2 Gaucher’s disease (Hulkova et al, 2001).…”

The pleiotropic roles of sphingolipid signaling in autophagy

“…88, 89 In GD, the point mutations within the GBA (glucosidase, beta, acid) gene lead to the production of acid β-glucosidase with functional, kinetic, trafficking, and/or stability defects and a resultant decrease in lysosomal function and increase in the accumulation of glucosylceramide and glucosylsphingosine. 76 GD can be classed into three subsets, based on the age of onset and the presence of central nervous system abnormalities.…”