Murine ß-galactosidase stability is not dependent on temperature or protective protein/cathepsin A.

GM1 gangliosidosis, a neurodegenerative disorder, and Morquio B disease, a skeletal disorder, are lysosomal storage disorders caused by inherited defects in the enzyme ß-galactosidase (GLB1; EC 3.1.2.23; MIM #611458). Enzyme replacement therapy (ERT), a standard of care for a number of non-neuronopathic lysosomal storage disorders, is not yet available for GLB1 deficiency. Although functionally active recombinant human and feline GLB1 precursors have been purified, ERT has not yet been demonstrated in GM1 gangliosidosis or Morquio B disease models. A major obstacle to developing effective therapy may be the stability of human GLB1. We show here that mouse GLB1 has greater stability when compared to human GLB1, and that human GLB1 activity is temperature and protective-dependent on protein cathepsin A, while that of mouse GLB1 is not. These findings may impact on the eventual development of ERT for GLB1 deficiency. Despite our attempts to improve the extracellular stability of human GLB1 through sequence modification and the use of chemical chaperone N-butyldeoxygalactonojirimycin, the specific enzyme activity remained well below that of mGLB1.

Structural alterations of epididymal epithelial cells in cathepsin A-deficient mice affect the blood-epididymal barrier and lead to altered sperm motility.

Past studies have shown that the epithelial lining of the epididymis in adult mice deficient in protective protein cathepsin A (PPCA -/-) becomes swollen and vacuolated as a result of an accumulation of pale lysosomes, some very large, in addition to the presence of an abundance of macrophages infiltrating the intertubular spaces. The purpose of this study was to assess the integrity of the epididymal epithelial-blood barrier in these altered mice by characterizing the distribution of claudins (Cldns) and the leakiness of tight junctions to lanthanum nitrate. A second goal was to characterize sperm motility behavior in PPCA -/- mice using computer-assisted sperm analyses (CASA). The results indicated that lanthanum nitrate penetrated apical junctional complexes between adjacent epithelial cells and entered the epididymal lumen in PPCA -/- mice but not in control PPCA +/+ mice. Immunostaining for Cldns 1, 3, 8, and 10 revealed unique patterns of expression based on cell type and region specificity in PPCA +/+ mice, which were much different in PPCA -/- mice. PPCA -/- mice showed reduced intensities of immunoreactions, complete absence of immunoreactions, and appearance of atypical cytoplasmic immunoreactions. CASA indicated that sperm counts in the PPCA -/- mice were 70% reduced, and among other problems, there was a fourfold higher percentage of static sperm in PPCA -/- mice compared with controls. These results suggest that PPCA deficiency causes structural changes to the blood-epididymal barrier as evidenced by lanthanum nitrate and Cldns expression that affects the luminal environment of the epididymis, resulting in altered sperm motility.

Elastogenesis in cultured dermal fibroblasts from patients with lysosomal beta-galactosidase, protective protein/cathepsin A and neuraminidase-1 deficiencies.

The human GLB1 gene encodes a lysosomal beta-galactosidase (beta-Gal) and an elastin-binding protein (EBP). Defect of the EBP as a chaperon for tropoelastin and a component of receptor complex among neuraminidase-1 (NEU1) and protective protein/cathepsin A (PPCA) is suggested responsible for impaired elastogenesis in autosomal recessive beta-Gal, PPCA and NEU1 deficiencies. The purpose of this study is to determine effects of GLB1, PPCA and NEU1 gene mutations on elastogenesis in skin fibroblasts. Elastic fiber formation and the EBP mRNA expression were examined by immunofluorescence with an anti-tropoelastin antibody and RT-PCR selective for EBP in skin fibroblasts with these lysosomal enzyme deficiencies. Apparently normal elastogenesis and EBP mRNA expression were observed for fibroblasts from Morquio B disease cases with the GLB1 gene alleles (W273L/W273L, W273L/R482H and W273L/W509C substitutions, respectively), a galactosialidosis case with the PPCA allele (IVS7+3A/IVS7+3A) and a sialidosis case with the NEU1 allele (V217M/G243R) as well as normal subject. In this study, the W273L substitution in the EBP could impossibly cause the proposed defect of elastogenesis, and the typical PPCA splicing mutation and the V217M/G243R substitutions in the NEU1 might hardly have effects on elastic fiber formation in the dermal fibroblasts.

New mutations in the PPBG gene lead to loss of PPCA protein which affects the level of the beta-galactosidase/neuraminidase complex and the EBP-receptor.

We describe the clinical findings, and the molecular and biochemical studies in an Italian family with recurrent hydrops fetalis due to galactosialidosis (GS). GS is a rare lysosomal storage disorder caused by a deficiency of the protective protein/cathepsin A (PPCA). This protein forms a high-molecular-weight complex with the hydrolases beta-galactosidase (GLB1) and neuraminidase (NEU1). By virtue of this association these two enzymes are correctly compartmentalized in lysosomes and protected against rapid proteolytic degradation. Controversial data show that PPCA is also present in a second complex, including the Elastin Binding Protein (EBP) the EBP-receptor, which is involved in elastogenesis, and NEU1. We investigated the potential role of the PPCA in both complexes. Two new genetic lesions (c60delG and IVS2+1 G > T) that lead to a frameshift and a premature stop codon were detected in the PPCA cDNA and genomic DNA of the patient. The deleterious effect of such mutations was confirmed by the complete absence of the PPCA protein on Western blots. Thus, we examined the effect of the loss of PPCA on the two protein complexes in the patient's fibroblasts. Interestingly, a reduced amount of both GLB1 and EBP proteins was detected. These data confirm that PPCA is present in two functional complexes one with GLB1 and NEU1 in the lysosomal lumen and the other with EBP at the cell surface. The reduction in GLB1 and EBP confirms that PPCA is essential for their integrity.

Characterization of cell- and region-specific abnormalities in the epididymis of cathepsin A deficient mice.

Cathepsin A (PPCA), a lysosomal carboxypeptidase that functions as a protective protein for alpha-neuraminidase and beta-galactosidase in a multi-enzyme complex, has been shown to be expressed in the epithelial cells of the epididymis. In the present study, the epididymis of PPCA-/- mice from 2 to 10 months of age was compared with those of their wild-type counterparts. Major accumulations of pale vacuoles, corresponding to lysosomes, were noted in principal and narrow/apical cells in PPCA-/- mice, and clear cells also appearing highly vacuolated, were grossly enlarged in size. This was especially evident in the caput and corpus regions, where quantitative analyses confirmed that the epithelium of the tubules in these regions was expanding in profile area. In addition, the base of the epithelium in these regions was often greatly vacuolated, corresponding to cells that presented no identifiable features and appeared to be degenerating. Halo cells dispersed at various levels in the epithelium also appeared to be abnormal, accumulating pale lysosomes. Furthermore, numerous macrophages were observed in the intertubular space of the entire duct, presenting a large size and plethora of pale lysosomes. Taken together, the present data indicate major lysosomal abnormalities in the epididymis of PPCA-/- mice in a cell type and region specific manner. In addition, it is suggested that the compromised halo cells, due to PPCA deficiency within their lysosomes, cannot function properly and as a result there is a recruitment of macrophages in the intertubular space.