The regulation of proenkephalin expression in a distinct population of glial cells

The expression of opioid genes was examined in isolated populations of glial cells in primary culture. Northern blot analysis of purified type I astrocytes, oligodendrocytes and mixed oligodendrocyte-type-2-astrocyte lineage cells derived from cerebral cortex demonstrated robust expression of proenkephalin mRNA exclusively in type I astrocytes. The expression of proenkephalin mRNA was stimulated by the beta-adrenergic agonist isoproterenol, and 8-(4-chlorophenyl thio)adenosine 3'-5'-cyclic monophosphate (cpt-cAMP). Both of these compounds regulated a proenkephalin-chloramphenicol acetyltransferase fusion gene transiently transfected into type I astrocytes. HPLC and immunoassay of the cell culture media revealed significant levels of unprocessed proenkephalin secreted by the cell and this secretion was stimulated by isoproterenol and cpt-cAMP. The relatively high levels of proenkephalin expressed suggest that enhanced expression in astrocytes may be important during neural development, in trauma-induced gliosis and in neuroimmune interactions.