Characterization of gana-1, a Caenorhabditis elegans gene encoding a single ortholog of vertebrate α-galactosidase and α-N-acetylgalactosaminidase

BACKGROUND: Human α-galactosidase A (α-GAL) and α-N-acetylgalactosaminidase (α-NAGA) are presumed to share a common ancestor. Deficiencies of these enzymes cause two well-characterized human lysosomal storage disorders (LSD) – Fabry (α-GAL deficiency) and Schindler (α-NAGA deficiency) diseases. Caenorhabditis elegans was previously shown to be a relevant model organism for several late endosomal/lysosomal membrane proteins associated with LSDs. The aim of this study was to identify and characterize C. elegans orthologs to both human lysosomal luminal proteins α-GAL and α-NAGA. RESULTS: BlastP searches for orthologs of human α-GAL and α-NAGA revealed a single C. elegans gene (R07B7.11) with homology to both human genes (α-galactosidase and α-N-acetylgalactosaminidase) – gana-1. We cloned and sequenced the complete gana-1 cDNA and elucidated the gene organization. Phylogenetic analyses and homology modeling of GANA-1 based on the 3D structure of chicken α-NAGA, rice α-GAL and human α-GAL suggest a close evolutionary relationship of GANA-1 to both human α-GAL and α-NAGA. Both α-GAL and α-NAGA enzymatic activities were detected in C. elegans mixed culture homogenates. However, α-GAL activity on an artificial substrate was completely inhibited by the α-NAGA inhibitor, N-acetyl-D-galactosamine. A GANA-1::GFP fusion protein expressed from a transgene, containing the complete gana-1 coding region and 3 kb of its hypothetical promoter, was not detectable under the standard laboratory conditions. The GFP signal was observed solely in a vesicular compartment of coelomocytes of the animals treated with Concanamycin A (CON A) or NH(4)Cl, agents that increase the pH of the cellular acidic compartment. Immunofluorescence detection of the fusion protein using polyclonal anti-GFP antibody showed a broader and coarsely granular cytoplasmic expression pattern in body wall muscle cells, intestinal cells, and a vesicular compartment of coelomocytes. Inhibition of gana-1 by RNA interference resulted in a decrease of both α-GAL and α-NAGA activities measured in mixed stage culture homogenates but did not cause any obvious phenotype. CONCLUSIONS: GANA-1 is a single C. elegans ortholog of both human α-GAL and α-NAGA proteins. Phylogenetic, homology modeling, biochemical and GFP expression analyses support the hypothesis that GANA-1 has dual enzymatic activity and is localized in an acidic cellular compartment

Replacement of α-galactosidase A in Fabry disease: effect on fibroblast cultures compared with biopsied tissues of treated patients

The function and intracellular delivery of enzyme therapeutics for Fabry disease were studied in cultured fibroblasts and in the biopsied tissues of two male patients to show diversity of affected cells in response to treatment. In the mutant fibroblasts cultures, the final cellular level of endocytosed recombinant α-galactosidases A (agalsidases, FabrazymeTM, and ReplagalTM) exceeded, by several fold, the amount in control fibroblasts and led to efficient direct intra-lysosomal hydrolysis of (3H)Gb3Cer. In contrast, in the samples from the heart and some other tissues biopsied after several months of enzyme replacement therapy (ERT) with FabrazymeTM, only the endothelial cells were free of storage. Persistent Gb3Cer storage was found in cardiocytes (accompanied by increase of lipopigment), smooth muscle cells, fibroblasts, sweat glands, and skeletal muscle. Immunohistochemistry of cardiocytes demonstrated, for the first time, the presence of a considerable amount of the active enzyme in intimate contact with the storage compartment. Factors responsible for the limited ERT effectiveness are discussed, namely post-mitotic status of storage cells preventing their replacement by enzyme supplied precursors, modification of the lysosomal system by longstanding storage, and possible relative lack of Sap B. These observations support the strategy of early treatment for prevention of lysosomal storage