Brain Region and Gene Specificity of Neuropeptide Gene Expression in Cultured Astrocytes

Abstract

Astrocytes have many neuronal characteristics, such as neurotransmitter receptors, ion channels, and neurotransmitter uptake systems. Cultured astrocytes were shown to express certain neuropeptide genes, with specificity for both the gene expressed and the brain region from which the cells were prepared. Somatostatin messenger RNA and peptides were detected only in cerebellar astrocytes, whereas proenkephalin messenger RNA and enkephalin peptides were present in astrocytes of cortex, cerebellum, and striatum. Cholecystokinin was not expressed in any of the cells. These results support the hypothesis that peptides synthesized in astrocytes may play a role in the development of the central nervous system.

Cellular localization of proenkephalin mRNA and enkephalin peptide products in cultured astrocytes

“…The present results confirm and extend previous reports by localizing proenkephalin mRNA in astrocytes at the cellular level by in situ hybridization, and thereby provide direct evidence that the enkephalin mRNA previously identified in Northern blots is expressed by astrocytes and not by a small number of contaminating non-astrocytic cells which are present in the astrocyte-enriched cultures reported in previous studies 37, 43,52 . In particular, cells double-labeled for both proenkephalin mRNA and GFAP intermediate filaments provide first direct evidence that astrocytes express the proenkephalin gene during development.…”

“…These and other experiments suggest that endogenous opioids are normally available to cells in the developing CNS in sufficient quantities to tonically inhibit growth 17,18,41,[54][55][56] . In support of this hypothesis, opioid peptide levels and opioid binding are greatly increased in the rat cerebellum 48,49 28,32,43,52 . In the present study, proenkephalin (proenkephalin A) mRNA and enkephalin peptide expression were examined by in situ hybridization and immunocytochemistry, respectively, in primary cultures of the developing CNS (i) to identify the specific cellular sites of proenkephalin gene and peptide expression, and (ii) to determine whether opioids are expressed by replicating astrocytes prior to their reaching confluence.…”

“…Proenkephalin mRNA has been previously detected in confluent astrocyte-enriched (95-98% type 1 astrocytes) cultures from the rat cerebral cortex 28,32,43 and cerebellum 43 , or rat striatum 52 by Northern analysis, but not at the cellular level. The present results confirm and extend previous reports by localizing proenkephalin mRNA in astrocytes at the cellular level by in situ hybridization, and thereby provide direct evidence that the enkephalin mRNA previously identified in Northern blots is expressed by astrocytes and not by a small number of contaminating non-astrocytic cells which are present in the astrocyte-enriched cultures reported in previous studies 37,43,52 .…”

“…Recent reports have demonstrated the presence of proenkephalin mRNA by Northern analysis of confluent glial cultures that are enriched in astrocytes (i.e., 95-97% astrocytes) 28,32,43,52 . In the present study, proenkephalin (proenkephalin A) mRNA and enkephalin peptide expression were examined by in situ hybridization and immunocytochemistry, respectively, in primary cultures of the developing CNS (i) to identify the specific cellular sites of proenkephalin gene and peptide expression, and (ii) to determine whether opioids are expressed by replicating astrocytes prior to their reaching confluence.…”

Carboxypeptidase E (enkephalin convertase): mRNA distribution in rat brain by in situ hybridization

“…Vilijn et al (1989) have recently demonstrated that cultured astrocytes can synthesize and secrete CPE. Cultured astrocytes from various brain regions can express peptide genes, including proenkephalin (Vilijn et al, 1988), somatostatin (Shinoda et al, 1989) and angiotensinogen (Stometta et al, 1988). Therefore, CPE may process neuropeptides in both neurons and glia.…”