Intracellular binding of fukutin and alpha-dystroglycan: relation to glycosylation of alpha-dystroglycan.

The functions of fukutin, a gene product responsible for Fukuyama type congenital muscular dystrophy, still remain unclear, although a relation to the glycosylation of alpha-dystroglycan is presumed. To investigate the functions of fukutin, immunohistochemistry, examination using cultured astrocytes, enzyme-linked immunosorbent assay (ELISA)-based binding assay and immunoprecipitation were performed using control muscle and central nervous system tissues. Immunohistochemistry showed that alpha-dystroglycan and fukutin were co-expressed, especially in the glial cytoplasm and glia limitans of the central nervous system. An anti-fukutin antibody added to the culture medium did not bring about any changes in the astrocytes cultured on laminin-coated dishes. Together with the immunohistochemical results, the intracellular function of fukutin is considered. ELISA-based binding assay and immunoprecipitation may suggest the direct binding of fukutin and alpha-dystroglycan, at least in part. Fukutin seems to bind to both the hypoglycosylated and fully glycosylated form of alpha-dystroglycan, and seems bind to the core area rather than the sugar chain of alpha-dystroglycan. Fukutin may directly interact with alpha-dystroglycan during glycosylation, but further examinations are needed to confirm these details.

Fukutin expression in glial cells and neurons: implication in the brain lesions of Fukuyama congenital muscular dystrophy.

Expression and localization of fukutin, a gene responsible for Fukuyama congenital muscular dystrophy (FCMD), was studied in the central nervous system by in situ hybridization and immunohistochemistry. In control cases, glial cells expressed fukutin and the expression continued from fetuses to adults. Double immunostaining revealed that some of these cells were astrocytes. The glia limitans was stained by immunohistochemistry. In contrast, neuronal expression was decreased with neuronal maturation. The glia limitans formed by endfeet of astrocytes is abnormal in the brain of fetal to adult FCMD cases. These findings suggest an important role of astrocytes for the genesis of FCMD brain, although immature neurons expressed fukutin. In FCMD cases, expression of fukutin looked decreased. In the brain of fetal FCMD cases, decreased expression of fukutin is considered to provoke the disruption of glia limitans. In post-natal FCMD cases, prominent superficial gliosis is observed in the cerebral surface, where fukutin was weakly positive. Reactive increase of astrocytes may be required to maintain the glia limitans for compensating the decrease of fukutin expression in individual astrocytes. In the cerebellum, Bergmann glia, which did not express fukutin in control cases, elongated their cytoplasmic processes to the surface to form glia limitans even in the polymicrogyric area.

Oxidative stress in the human fetal brain: an immunohistochemical study.

Because accumulation of oxidative modification products seems to relate to aging and has not been fully studied in fetal brains, an immunohistochemical examination was performed on nine brains ranging from 22-40 weeks of gestation. These brains did not demonstrate lesions except hypoxic-ischemic changes. Advanced glycation end products and 4-hydroxynonenal are generally reported to be negative in neurons of normal young brains, but, in the present study, distinct positive immunoreaction was observed in neurons of fetal brains. Positive immunoreaction appeared earlier in the medulla oblongata than in the cerebrum, and 4-hydroxynonenal began to accumulate earlier than advanced glycation end products. As for glial cells, advanced glycation end products and 4-hydroxynonenal were positive in reactive astrocytes in mid- to late gestation. Because hypoxic-ischemic changes were observed in most of the patients, it is possible that oxidative stress caused by hypoxic-ischemic may be involved in the accumulation of these products in the fetal brain. 8-Hydroxy-2'-deoxyguanosine was negative even in patients demonstrating positive reaction for advanced glycation end products and 4-hydroxynonenal. In the fetal brain, DNA might be strongly protected from oxidative damage. 4-Hydroxynonenal is generally positive in the cytoplasm but was positive in the nucleus of immature neurons and glial cells in the present study, suggesting a unique metabolism of the fetal brain.