Structural and functional study of K453E mutant protective protein/cathepsin A causing the late infantile form of galactosialidosis.

To clarify the molecular basis of the late infantile form of galactosialidosis, we characterized a defective protective protein/cathepsin A (PPCA) gene product with the K453E mutation newly found in an Arabic patient with this disease. Immunocytochemical, expression, and metabolic studies revealed that the precursor PPCA was synthesized but not processed to the mature form, and it was degraded in the mutant. A structural model of the mutant PPCA was constructed by amino acid substitution of 453glutamic acid for lysine in the crystal structure of the wild type PPCA precursor reported. The results show that the K453E mutation is located at the dimer interface of the PPCA and reduces the hydrogen bond formation in the dimer. This structural change may cause instability of the PPCA dimer.

Molecular and structural studies of Japanese patients with sialidosis type 1.

To gain insight into the pathogenesis of sialidosis type 1, we performed molecular investigations of two unrelated Japanese patients. Both of them are compound heterozygotes for base substitutions of 649G-to-A and 727G-to-A, which result in amino acid alterations V217M and G243R, respectively. Using homology modeling, the structure of human lysosomal neuraminidase was constructed and the structural changes caused by these missense mutations were deduced. The predicted change due to V217M was smaller than that caused by G243R, the latter resulting in a drastic, widespread alteration. The overexpressed gene products containing these mutations had the same molecular weight as that of the wild type, although the amounts of the products were moderately decreased. A biochemical study demonstrated that the expressed neuraminidase containing a V217M mutation was partly transported to lysosomes and showed residual enzyme activity, although a G243R mutant was retained in the endoplasmic reticulum/Golgi area and had completely lost the enzyme activity. Considering the data, we surmise that the V217M substitution may be closely associated with the phenotype of sialidosis type 1 with a late onset and moderate clinical course.

Endothelin-1 in the brain of patients with galactosialidosis: its abnormal increase and distribution pattern.

Endothelin-1 is a peptidic substrate in vitro of lysosomal protective protein/cathepsin A (PPCA) with serine carboxypeptidase activity. Endothelin-1-specific immunoreactivity has been demonstrated to be markedly increased and distributed abnormally in the neurons and glial cells within autopsied brain regions, including the cerebellum, hippocampal formation, and spinal cord, of patients affected with galactosialidosis, a human PPCA deficiency. The genetic defect of the endothelin-1 degrading activity of PPCA is suggested to cause some of the neurological abnormalities of this disease.

Stable expression of protective protein/cathepsin A-green fluorescent protein fusion genes in a fibroblastic cell line from a galactosialidosis patient. Model system for revealing the intracellular transport of normal and mutated lysosomal enzymes.

Fibroblastic cell lines derived from a galactosialidosis patient, stably expressing the chimaeric green fluorescent protein variant (EGFP) gene fused to the wild-type and mutant human lysosomal protective protein/cathepsin A (PPCA) cDNA, were first established as a model system for revealing the sorting and processing of lysosomal enzymes and for investigating the molecular bases of their deficiencies. In the cell line expressing the wild-type PPCA-EGFP chimaera gene (EGFP-PPwild), an 81 kDa form (27 kDa EGFP fused to the C-terminus of the 54 kDa PPCA precursor) was produced, then processed into the mature 32/20 kDa two-chain form free of the EGFP domain. The intracellular cathepsin A, alpha-N-acetylneuraminidase and beta-galactosidase activities, which are deficient in the parent fibroblastic cells, could also be significantly restored in the cells. In contrast with the uniform and strong fluorescence throughout the cytoplasm and nucleus in the mock-cell line expressing only EGFP cDNA, weak reticular and punctate fluorescence was distributed throughout the EGFP-PPwild cell line. Bafilomycin A1, a potent inhibitor of vacuolar ATPase and intracellular acidification, induced the distribution of Golgi-like perinuclear fluorescence throughout the living and fixed cells, in which only the 81 kDa product was detected. After removal of the agent, time-dependent transport of the chimaeric protein from the Golgi apparatus to the prelysosomal structure in living cells was monitored with a confocal laser scanning microscope system. Leupeptin caused the distribution of lysosome-like granular fluorescence throughout the cytoplasm in the fixed cells, although it was hardly observed in living cells. The latter agent also dose-dependently induced an increase in the intracellular amount of the 81 kDa product containing the EGFP domain and inhibited the restoration of cathepsin A activity in the EGFP-PPwild cells after the removal of bafilomycin A1. In parallel, both the mature two-chain form and PPCA function disappeared. These results suggested that the chimaera gene product was transported to acidic compartments (endosomes/lysosomes), where proteolytic processing of the PPCA precursor/zymogen, quenching of the fluorescence, and random degradation of the EGFP portion occurred. A cell line stably expressing a chimaeric gene with a mutant PPCA cDNA containing an A1184-->G (Y395C) mutation, commonly detected in Japanese severe early-infantile type of galactosialidosis patients, showed an endoplasmic reticulum (ER)-like reticular fluorescence pattern. The PPCA-immunoreactive gene product was hardly detected in this cell line. The mutant chimaeric product was suggested to be degraded rapidly in the ER before transport to post-ER compartments. A cell line expressing the chimaeric gene with a T746-->A (Y249N) PPCA mutation exhibited both ER-like reticular and granular fluorescence on the reticular structure that was stronger than that in the EGFP-PPwild cells. Some of them contained large fluorescent inclusion-body-like structures. The ineffectiveness of transport inhibitors in the distribution changes in the two mutant chimaeric proteins suggested that they were not delivered to acidic compartments. Therefore this expression system can possibly be applied to the direct analysis of the sorting defects of mutant gene products in living cells and will be useful for the molecular investigation of lysosomal diseases, including galactosialidosis.

Urinary excretion of the vitronectin receptor (integrin alpha V beta 3) in patients with Fabry disease.

A renal disorder is one of the important manifestations of Fabry disease, but the details of the pathogenesis have not been clarified yet. We examined the possibility that the vitronectin receptor (VNR, integrin alpha V beta 3), one of the integrins, is involved in the progression of the renal injury in Fabry disease. We measured the urinary excretion of beta 3 originating from VNR in Fabry patients by immunoblotting analysis and enzyme-linked immunosorbent assay (ELISA). Immunofluorescent microscopic analyses for VNR and globotriaosylceramide were performed on urinary sediments from Fabry patients. Furthermore, beta 3 and vitronectin in kidney tissues were analyzed immunohistochemically. Immunoblotting analysis and ELISA showed that the urinary excretion of beta 3 originating from VNR was significantly increased in the Fabry group compared with both the pathological and healthy control groups. Immunofluorescent microscopy revealed the expression of VNR and accumulation of globotriaosylceramide in urinary sediments from the Fabry patients. Increased expression of beta 3 was observed in glomerular epithelial cells, and in Bowman's capsular epithelial layer and tubular cells, and the amount of vitronectin was moderately increased in the kidney tissues from the Fabry patients. The urinary excretion of VNR was increased, and the expression of VNR was observed in Fabry kidney tissues. The expression of VNR may be involved in the progression of the renal injury in this disease.

GM2 gangliosidosis AB variant: clinical and biochemical studies of a Japanese patient.

OBJECTIVE: To determine the clinical features and biochemical basis of the first Japanese patient with the GM2 gangliosidosis AB variant. METHODS: The clinical manifestations and laboratory findings in the patient were investigated. Cultured fibroblasts from the patient were analyzed by means of immunofluorescence staining with an anti-GM2 ganglioside monoclonal antibody and thin-layer chromatography and immunostaining. GM1 ganglioside catabolism in cultured cells was analyzed by pulse labeling, and the amount of GM2 activator in cells was determined by Western blot analysis. Gene analysis was performed according to standard protocols. RESULTS: The patient showed progressive neurologic manifestations of quite early onset. Muscular weakness and hypotonia became evident by 1 month of age, and the patient then developed a startle reaction, severe psychomotor retardation, and myoclonic seizures. Immunocytochemical analysis clearly revealed the accumulation of GM2 ganglioside in cultured fibroblasts from the patient, and thin-layer chromatography confirmed it. Western blot and metabolic studies showed a complete deficiency of GM2 activator. Gene analysis did not reveal any mutations in the protein coding region of the GM2 activator gene. CONCLUSION: The clinical features and biochemical basis of this Japanese patient with GM2 gangliosidosis AB variant were determined. Immunocytochemical analysis using cultured fibroblasts as samples is available for the diagnosis of this disease.

Immunohistochemical characterization of transgenic mice highly expressing human lysosomal alpha-galactosidase.

Human lysosomal alpha-galactosidase predominantly hydrolyzes ceramide trihexoside. A transgenic mouse line, C57BL/6CrSIc-TgN(GLA) 1951 Rin, highly expressing human alpha-galactosidase, has been established and investigated biochemically and immunohistochemically in order to clarify the distribution of the expressed enzyme proteins and to evaluate it as a donor model of organ transplantation therapy for Fabry disease caused by a genetic defect of alpha-galactosidase. In these transgenic mice, about five copies of the transgene were integrated, and alpha-galactosidase activity was expressed in liver, kidney, heart, spleen, small intestine, submaxillary gland, skeletal muscle, cerebrum, cerebellum, bone marrow cells and serum. The enzyme activity was about 22 to 11,080-fold higher than that in non-transgenic mice. In liver, heart and kidney tissues, which are important organs for transplantation studies, sufficient amounts of alpha-galactosidase mRNAs were transcribed, and the expressed enzymes, with molecular weights of 54-60 kDa, are abundant in the liver (enzyme activity: 53,965 nmol h-1 mg-1 protein) and heart (39,906 nmol h-1 mg-1 protein), followed by in the kidney tissue (9177 nmol h-1 mg-1 protein), respectively. An immunohistochemical microscopic study clearly demonstrated the distribution of the expressed enzyme proteins in kidney and liver tissues. Highly expressed alpha-galactosidase was detected in glomerular cells, tubular cells and hepatocytes. These transgenic mice will be useful as a donor model for experimental organ transplantation, and also it will enable recurrent biopsies and long-term observation. The organ transplantation data on mice will provide us with important information.

Protective protein/cathepsin A loss in cultured cells derived from an early-infantile form of galactosialidosis patients homozygous for the A1184-G transition (Y395C mutation).

Galactosialidosis is a human autosomal recessive lysosomal storage disease caused by a genetic defect of protective protein/cathepsin A (PPCA). The patients in a Japanese family with the severe early-infantile form of galactosialidosis were revealed to be homozygous for the A1184-G transition in the PPCA gene in both alleles, which leads to the Y395C substitution. The acid carboxypeptidase (cathepsin A) and lysosomal neuraminidase activities were markedly decreased in cultured fibroblasts and chorionic villus cells derived from the patients, although the decrease in beta-galactosidase activity was less. Immunoblot and immunocytochemical analyses showed that neither the precursor nor the mature form of the PPCA gene product was present in the cultured cells. The Y395C mutation was revealed to cause the loss of the translated product, that determines the severity of the clinical phenotype.

Adult Sandhoff's disease: R505Q and I207V substitutions in the HEXB gene of the first Japanese case.

We describe a 31-year-old Japanese man with adult Sandhoff s disease presenting as spinocerebellar degeneration. There was a marked cerebellar atrophy on MRI, and proliferation of abundant PAS-positive foamy macrophages in the rectal mucosa. The activities of total beta-Hex, beta-Hex A, and beta-Hex B in leucocytes of the patient were 14%, 15%, and 6% of control values, respectively. However, oligosacchariduria or ultrastructural storage materials in liver tissue were nil. Direct sequencing of cDNA and genomic DNA, and restriction digestion revealed two different homozygous base substitutions in the HEXB gene: the G1514-->A substitution (R505Q) and the A619-->G substitution (1207V). The parents were consanguineous. His healthy mother, an enzymatic heterozygous carrier, was homozygous for 1207V, but heterozygous for R505Q mutation. Thus, the patient is probably homozygous for both base substitutions and a R505Q mutation may be linked to the phenotype of adult Sandhoff's disease.

Stabilizing effect of lysosomal beta-galactosidase on the catalytic activity of protective protein/cathepsin A secreted by human platelets.

The 32/20-kDa two-chain form of protective protein/cathepsin A (CathA) secreted by human platelets was thermostable in the aggregation supernatant at acidic pH, but was denatured at neutral pH. Leupeptin partly protected the CathA against denaturation, which was not observed in the supernatant after depletion of the cosecreted lysosomal acid beta-galactosidase (beta-Gal) by affinity separation with p-aminophenylthiogalactose (PATG)-agarose beads even at pH 4.8. The purified recombinant human beta-Gal proteins, the 84-kDa precursor and 64-kDa mature-like enzyme (the tryptic product of the 84-kDa precursor), also protected the CathA against denaturation at neutral pH in part. Biospecific interaction analysis revealed that the CathA secreted by platelets dose dependently bound to the immobilized recombinant beta-Gal proteins. The association rate constant of CathA with the 64-kDa mature-like beta-Gal was 4.0 x 10(6) (M-1 s-1) at acidic pH, which was three times larger than that with the 84-kDa beta-Gal precursor. The calculated affinity constants for the enzyme molecules at acidic pH were approximately 1 x 10(9) (M-1), and those at neutral pH were two orders lower. These results first demonstrated that beta-Gal stabilizes the catalytic activity of CathA through direct binding in vitro. The affinity was shown to increase with removal of the carboxy-terminal domain of the beta-Gal precursor.

Generation and characterization of transgenic mice expressing a human mutant alpha-galactosidase with an R301Q substitution causing a variant form of Fabry disease.

Transgenic mice expressing a human mutant alpha-galactosidase with an R301Q substitution, which was found in a patient with a variant form of Fabry disease, were established. The mice transcribed a sufficient amount of alpha-galactosidase mRNA, but the steady-state levels of the enzyme protein were decreased in liver, kidney and heart, only residual activity being detected in these tissues. The mice will be useful for the clarification of the defective regulation of the structurally altered enzyme protein expressed by the mutant gene at the organ or individual level as well as for the evaluation of drugs that stabilize and/or activate the mutant alpha-galactosidase.

Screening and detection of gene mutations in Japanese patients with Fabry disease by non-radioactive single-stranded conformation polymorphism analysis.

We have applied non-radioactive polymerase chain reaction (PCR)-single-stranded conformation polymorphism (SSCP) to the detection of gene mutations causing Fabry disease. Nineteen of 22 known mutations were detected as electrophoretic mobility shifts on PCR-SSCP analysis. Then, DNA from newly diagnosed Japanese patients with the classical form of Fabry disease was subjected to PCR-SSCP analysis, and 4 novel mutations (1 small deletion, 1 nonsense mutation and 2 missense mutations) and 1 neutral polymorphism were identified. Furthermore, identification of an asymptomatic heterozygote and a hemizygote with moderate clinical manifestations was successfully achieved by application of this method to a family with the variant form of Fabry disease. PCR-SSCP is useful for the gene diagnosis of etiologically heterogeneous Fabry disease.

Molecular form and subcellular distribution of acid beta-galactosidase in fibroblasts from patients with GM1 gangliosidosis, Morquio B disease and galactosialidosis.

The molecular form and subcellular distribution of acid beta-galactosidase in cultured fibroblasts from patients with beta-galactosidase deficiency (GM1-gangliosidosis, Morquio B disease and galactosialidosis) were studied, using antibodies against three different forms of the human enzyme: a high-molecular-weight multienzymic complex, a recombinant 84-kDa precursor, and a 64-kDa tryptic product of the precursor. The mature enzyme from normal fibroblasts was immunoprecipitated by the anti-complex and anti-64-kDa protein antibodies, but not by the anti-84-kDa precursor one. immunofluorescence staining of normal fibroblasts revealed the granular (lysosomal) distribution with anti-64-kDa protein antibody and the perinuclear reticular distribution with anti-84-kDa precursor antibody, probably representing the Golgi apparatus. Both patterns were demonstrated in Morquio B disease, but the residual enzyme activity was exclusively due to the mature enzyme. In Type 1 galactosialidosis, most of the expressed enzyme was detected as the precursor form with a perinuclear reticular distribution. In type 2 galactosialidosis, more than half of the enzyme activity was due to the mature form with a lysosomal distribution. Fibroblasts from a patient with GM1 gangliosidosis, expressing no beta-galactosidase mRNA, did not react against either anti-64-kDa protein antibody or anti-84-kDa precursor antibody. The combined use of immunoprecipitation and immunostaining was useful for analysing the pathophysiology of the intracellular processing and transport of the mutant beta-galactosidase.

A human protective protein gene partially overlaps the gene encoding phospholipid transfer protein on the complementary strand of DNA.

The entire human protective protein gene has been cloned, and structural analysis revealed that the gene spans 7.5kb and comprises 15 exons. Furthermore, it partially overlaps on the opposite strand with the gene encoding phospholipid transfer protein. This region of DNA on chromosome 20 appears to encode two distinct mRNAs expressing defined functional products, and the mRNAs overlap by 58 nucleotides at their 3'-untranslated ends.

Protective protein as an endogenous endothelin degradation enzyme in human tissues.

An enzyme hydrolyzing the carboxyl terminus of endothelin-1 was detected in control human tissues but was deficient in tissues from a patient with galactosialidosis, a metabolic disease caused by the protective protein gene mutation. It was proportional to the amount of immunologically estimated mature protective protein. An antibody against the lysosomal protective protein/beta-galactosidase complex precipitated the enzyme activity almost completely. Transfection of the human cDNA for protective protein resulted in high expression of the enzyme activity in transformed fibroblasts from a galactosialidosis patient. These results indicated that the mature protective protein is a major soluble endogenous endothelin degradation enzyme in human tissues.

Distribution of lysosomal protective protein in human tissues.

We raised two polyclonal antibodies against synthetic oligopeptides comprising amino acid sequences in the human lysosomal protective protein. The first antibody recognized the 54-kDa precursor and the N-terminal sequence of the 32-kDa mature protein subunit, and the second one recognized the precursor and the C-terminal sequence of the 20-kDa subunit. In normal fibroblasts, mature protective protein was detected on immunoblotting with these antibodies. Considerable amounts of mature protective protein also were detected in kidney, lung, liver, and spleen, but not in brain from a patient with Gaucher disease. Neither the precursor nor the mature protective protein was detected in cultured fibroblasts, liver or cerebrum from a galactosialidosis patient with protective protein deficiency.

Brain- and muscle-type promoters of the dystrophin gene are selected in peripheral lymphocytes and Epstein Barr virus-transformed lymphoblastoid [correction of lymphoplastoid] cells.

Promoter-specific transcripts of the dystrophin gene in peripheral lymphocytes and Epstein Barr virus-transformed lymphoblastoid cells were analysed using reverse transcription-nested polymerase chain reaction. Two DNA fragments, corresponding to the alternative first exons transcribed from either brain- or muscle-type promoters, were both amplified from cDNA prepared from normal lymphocytes and lymphoblastoid cells. The nucleotide sequences of the amplified products were 100% homologous to the 5' termini of the cDNA of brain- and muscle-type dystrophins, respectively. Neither fragment was amplified from the lymphoblastoid cells of a patient with Duchenne muscular dystrophy, who has a partial deletion involving the brain- and muscle-type promoters in the dystrophin gene. These findings showed that the brain-type as well as the muscle-type promoter of the dystrophin gene was active in lymphocytes and lymphoblastoid cells.

Protective protein gene mutations in galactosialidosis.

Four different protective protein cDNA mutations, 146A-->G (Q49R), 193T-->C (W65R), 268-269TC-->CT (S90L), and 1184A-->G (Y395C), were identified in six Japanese galactosialidosis patients with various phenotypic manifestations, and another mutation, 746T-->A (Y249N), in a patient of French-German origin with an atypical clinical course. Y395C was a common mutation in four Japanese patients in infancy and childhood; two juvenile patients were compound heterozygotes of Y395C and another common mutation, SpDEx7, and the other two infants were compound heterozygotes of Y395C and mutant alleles other than SpDEx7. We confirmed these mutations in genomic DNA by direct-sequence analysis or restriction-site analysis. The mutant cDNA clones, transiently expressed in a transformed galactosialidosis cell line, did not restore the secondarily deficient beta-galactosidase or alpha-neuraminidase activity except for the Y249N mutation that expressed some carboxypeptidase activity and restored the two lysosomal enzyme activities. Pulse-chase analysis detected a small amount of the mature form, as well as the precursor, in the cells transfected with the Y249N cDNA. Only precursor proteins were detected, mature proteins not appearing for the other mutant cDNAs.