Endocytosis and transcytosis in growing astrocytes in primary culture. Possible implications in neural development

Endocytosis constitutes an essential process in the regulation of the expre ssion of cell surface molecules and receptors and, therefore, could partici pate in the neural-glial interactions occurring during brain development. H owever, the relationship between endocytic pathways in astroglial cells und er physiological and pathological conditions remains poorly understood. We analyzed the endocytosis and transcytosis processes in growing astrocytes a nd the possible effect of ethanol on these processes. Evidence demonstrates that ethanol affects endocytosis in the liver and we showed that ethanol e xposure during brain development alters astroglial development changing pla sma membrane receptors and surface glycoprotein composition. To study these processes we use several markers for receptor-mediated endocytosis, fluid phase endocytosis and non-specific endocytosis. These markers were labeled for fluorescence microscopy and electron microscopy. 125l-BSA was used to s tudy the effect of ethanol on the internalization and recycling of this mac romolecule. The distribution of several proteins involved in endocytosis (c aveolin, clathrin, rab5 and beta-COP) was analyzed using immunofluorescence , immunoelectron microscopy and immunoblotting. Our results indicate that g rowing astrocytes have a developed endocytic system mainly composed of cave olae, clathrin coated pits and vesicles, tubulo-vesicular and spheric endos omes, multivesicular bodies and lysosomes. Ethanol exposure induces a fragm entation of tubular endosomes, decreases the internalization of 125l-BSA, a lters the processing of internalized BSA, and decreases the levels of caveo lin, clathrin, rab5 and beta-COP. These results indicate that ethanol alter s the endocytosis and transcytosis processes and impairs protein traffickin g in astrocytes, which could perturb astrocyte surface expression of molecu les involved in neuronal migration and maturation during brain development.