RESUMEN
BACKGROUND: beta-Mannosidosis (OMIM 248510) is a rare inborn lysosomal storage disorder caused by the deficient activity of beta-mannosidase, an enzyme encoded by a single gene (MANBA) located on chromosome 4q22-25. To date, only 20 cases of this autosomal recessive disorder have been described and 14 different MANBA mutations were incriminated in the disease. These are all null mutations or missense mutations that abolish beta-mannosidase activity. In this study, we characterized the molecular defect of a new case of beta-mannosidosis, presenting with a severe neurological disorder. METHODS: Genomic DNA was isolated from peripheral blood leukocytes of the patient to allow MANBA sequencing. The identified mutation was engineered by site-directed mutagenesis and the mutant protein was expressed through transient transfection in HEK293T cells. The beta-mannosidase expression and activity were respectively assessed by Western blot and fluorometric assay in both leukocytes and HEK293T cells. RESULTS: A missense disease-associated mutation, c.1922G>A (p.Arg641His), was identified for which the patient was homozygous. In contrast to previously described missense mutations, this substitution does not totally abrogate the enzyme activity but led to a residual activity of about 7% in the patient's leukocytes, 11% in lymphoblasts and 14% in plasma. Expression studies in transfected cells also resulted in 7% residual activity. CONCLUSION: Correlations between MANBA mutations, residual activity of beta-mannosidase and the severity of the ensuing neurological disorder are discussed. Whether the c.1922G>A mutation is responsible for a yet undescribed pseudodeficiency of beta-mannosidase is also discussed.
Asunto(s)
Mutación Missense , beta-Manosidasa/genética , beta-Manosidosis/genética , Western Blotting , Línea Celular , Niño , Análisis Mutacional de ADN , Demencia Vascular/complicaciones , Demencia Vascular/genética , Femenino , Expresión Génica , Humanos , Masculino , Mutagénesis Sitio-Dirigida , Linaje , Transfección , beta-Manosidasa/deficiencia , beta-Manosidosis/complicacionesRESUMEN
Two families of Greek patients with subclinical to severe cardiomyopathy are presented. The diagnosis of Danon disease was supported by a total lack of LAMP2 immunostaining in cultured skin fibroblasts and muscle biopsies. The LAMP2 mutation carried by one patient (c.928G>A) has already been reported but with different symptoms. The second patient had a novel point deletion. This has not been described previously, but it could be detected easily by restriction analysis. This mutation was also found in the patient's brother, and it was associated with severe cardiomyopathy leading to heart failure. Surprisingly, the proband also had partial reduction of alpha-galactosidase A activity, despite the absence of characteristic clinical features of Fabry disease. A substitution in the GLA gene (c.937G>T) was found, and its involvement in the cardiac disease is discussed.
Asunto(s)
Cardiomiopatías/diagnóstico , Cardiomiopatías/genética , Predisposición Genética a la Enfermedad/genética , Enfermedad por Depósito de Glucógeno de Tipo IIb/diagnóstico , Enfermedad por Depósito de Glucógeno de Tipo IIb/genética , Proteínas de Membrana de los Lisosomas/metabolismo , Sustitución de Aminoácidos/genética , Secuencia de Bases/genética , Cardiomiopatías/fisiopatología , Células Cultivadas , Niño , Preescolar , Análisis Mutacional de ADN , Exones/genética , Femenino , Eliminación de Gen , Marcadores Genéticos/genética , Genotipo , Enfermedad por Depósito de Glucógeno de Tipo IIb/fisiopatología , Humanos , Intrones/genética , Proteína 2 de la Membrana Asociada a los Lisosomas , Proteínas de Membrana de los Lisosomas/análisis , Proteínas de Membrana de los Lisosomas/genética , Masculino , Mutación/genética , Linaje , alfa-Galactosidasa/genéticaRESUMEN
The lipid mediator sphingosine 1-phosphate (S1P) may alter the proliferation of mesangial cells during pathophysiological processes. Here, S1P stimulated proliferation of rat mesangial cells and phosphorylation of MAPKs at subconfluent cell density. Both effects were inhibited by pertussis toxin treatment. Mesangial cells expressed several S1P receptors of the endothelial differentiation gene family: EDG-1, -3, -5, and -8. Conversely, S1P induced apoptosis at low cell density (2 x 10(4) cells/cm(2)), which was demonstrated by flow cytometry and Hoechst staining. Apoptosis was observed also in quiescent or growing cells and was not reverted by lysophosphatidic acid or platelet-derived growth factor. S1P enhanced phosphorylation of SAPKs. Incubation with [(33)P]S1P, [(3)H]S1P, and [(3)H]sphingosine demonstrated increased S1P hydrolysis, resulting in enhanced intracellular sphingosine levels and decreased S1P levels. A rise in total ceramide levels was also observed; however, ceramide did not originate from [(3)H]sphingosine, and S1P-induced apoptosis was not inhibited by fumonisin B, precluding involvement of de novo ceramide synthesis in apoptosis. Therefore, we suggest that sphingosine accumulation and decreased S1P are primarily responsible for S1P-induced apoptosis. In conclusion, incubation of low-density mesangial cells with S1P results in apoptosis, presumably due to increased S1P hydrolysis.
