The Alzheimer's amyloid precursor protein is produced by type I astrocytes in primary cultures of rat neuroglia.

The production of beta-amyloid precursor protein (beta APP) by primary mixed glial cell cultures from cerebral cortex of 2-3 day postnatal rats was examined by Northern and Western blotting and by immunocytochemistry. A single 3.5 kb beta APP RNA transcript was detected using probes recognizing all forms of beta APP messenger RNA. No signal was detected with a probe specific for the alternately spliced Kunitz protease inhibitor (KPI) region. In Western blot analysis of protein extracts, antisera specific for either the cytoplasmic or extracellular parts of beta APP detected several proteins ranging from 105 to 140 kDa. None of these were recognized by an antiserum specific to the KPI insert of the beta APP. Multicolor immunofluorescence showed beta APP immunoreactivity in type I (GFAP+ A2B5-) astrocytes, distributed in a fibrillar pattern like that of glial fibrillary acidic protein (GFAP). No beta APP immunoreactivity was detected in oligodendrocytes (GC+) or in A2B5+ progenitor cells. Moreover, no cultured cells showed immunostaining with an antiserum specific for the KPI sequence of beta APP. We conclude that type I astrocytes in primary culture produce amyloid precursor protein, but that oligodendrocytes and their precursors do not. Moreover, type I astrocytes produce predominantly the beta APP subtypes which lacks the KPI sequence.