Purification and Characterization of Novel Genes of Human Fetal Astrocytes

Astrocytes are ubiquitous in the brain and have multiple functions. It is becoming clear that they play an important role in monitoring the neuromicroenvironment, information processing, and signaling in the central nervous system (CNS) in normal conditions and respond to CNS injuries. During the development of the CNS, astrocytes play a key role as a substrate for neuronal migration and axonal growth. To identify genes that could participate in astrocyte maturation, we used the differential display reverse transcription-PCR (DDRT-PCR) method. Human fetal astrocytes were cultured and total RNAs are isolated at intervals of 5 days for 50 days. Using 24 primer combinations, we have identified a set of 18 candidate cDNAs deriving from excised DDRT-PCR bands. DNA sequencing revealed 16 genes that have been described already (HMGCR, thyroid receptor interactor gene, NPM, transglutaminase mRNA, and SPARC etc.). We have also found two novel genes (A3 and C8), which were expressed differently in culture stages. A3 expressed decreasingly and C8 expressed increasingly in accordance with to culture stages. We have analysed these two genes. A3 (3,626 bp) showed 93% homology with the Homo sapiens general transcription factor 3 (GTF3) and C8 (2,401 bp) had 97% homology with the transmembrane receptor Unc5H2. Temporal expression of these two genes in this study suggests that the proteins of these genes may have different roles in maturation of the human fetal astrocytes.

Regulation of TNF - alpha Gene Expression in Human Fetal Astrocytes

Tumor necrosis factor-n (TNF - alpha) involved in the pathogenesis of multiple sclerosis and contribute to the degeneration of oligodendrocytes as well as neurons. TNF - alpha is produced by miocroglia and astrocytes, which also produce hormones and cytokines that influence its biological activity. Astrocytes, the major glial cells in the CNS, are capable of producing TNF - alpha at both the mRNA and protein levels in response to interleukine-1 (IL-1) or TNF - alpha. Two immunosuppressive cytokines, transforming growth factor - beta (TGF - beta) and IL-10, have been shown to influence glial cell function. TGF - beta can modulate the activity of glial cells by inhibiting interferon-gamma (IFN - gamma) induced expression of class II major histocompatibility complex (MHC) molecules on astrocytes and microglia. To explore the role of astrocytes in the production of TNF - alpha, astrocytes were pretreated with IL-10 or TGF - beta and then stimulated with IL-1p to determine their effects on TNF - alpha production. The secretion of TNF - alpha by human fetal astrocytes was markedly inhibited by TGF - beta at a low concentration. In contrast IL-10 had no effect on TNF - alpha mRNA level. These results show that TGF - beta may regulate the expression of TNF - alpha in activated human fetal astrocytes.