EXPRESSION OF NEURAL CELL-ADHESION MOLECULE (NCAM) CHARACTERIZES A SUBPOPULATION OF TYPE-1 ASTROCYTES IN HUMAN OPTIC-NERVE HEAD

The human optic nerve contains a heterogeneous population of astrocyte s. In situ, a specialized subpopulation of astrocytes was distinguishe d in the adult optic nerve head by expression of neural cell adhesion molecule (NCAM). To further study the biology of astrocytes, we have d eveloped and characterized cells grown from explanted optic nerve head s and myelinated optic nerves as in vitro model systems. Second or thi rd passage cells were processed for immunocytochemistry using antibodi es against glial fibrillary acidic protein (GFAP) and cell surface epi topes: CD56/NCAM, HNK-1/NCAM, A2B5, and O4. Synthesis and gene express ion of NCAM were characterized by Western blot analysis and RNase prot ection assay. Cells grown from myelinated optic nerves expressing GFAP , but not NCAM or A2B5, were identified as type 1A astrocytes, and cel ls expressing GFAP and A2B5, but not NCAM, were identified as type 2 a strocytes. Cells grown from explanted optic nerve head expressing GFAP , NCAM, and O4 were identified as type 1B astrocytes. Expression of NC AM by type 1B astrocytes may provide these cells with adhesion propert ies that allow them specialized responses in their microenvironment. A strocytes from the lamina cribrosa may form a functional barrier to pr event myelination of the retina. In glaucoma, these astrocytes may be exposed to stresses due to fluctuation in intraocular pressure and the refore participate in the optic nerve changes associated with glaucoma tous optic neuropathy. (C) 1997 Wiley-Liss, Inc.