Normal human astrocytes (NHAs) in vitro grow slowly at a rate of about 7-10 days for 1 population doubling. ' They showed a limited proliferative lifespan at a maximum of 20 population doubling level (PDL) showing phenotypes of senescent cell such as large and flattened morphology and senescence-associated β-gal expression without apparent telomere shortening. We established lifespan-extended NHAs after introduction of telomerase reverse transcriptase gene (
hTERT).
hTERT-introduced NHAs expressed telomerase activity, maintained telomere size, and proliferated continuously over 100 PDL with normal phenotypes such as growth rate, cell morphology, karyotype, and GFAP (glial fibrillary acidic protein) expression. Senesced normal NHAs at 19 PDL down-regulated the expression of GFAP and upregulated the expressions of PDGF-β, FGF-2, GM-CSF, TGF-α, s100-β, IL-6, NT-4, NGF-β, and M-CSF as compared with those at 10 PDL. Expression level of these genes was recovered in
hTERT-introduced to the level of NHAs at 10 PDL. Expression levels of FGF-1, EGF, IFN-α, CNTF, and NT-3 did not change markedly by senescence or hTERT introduction. These results suggest that NHAs maintained not only proliferative potential but also cellular functions such as cytokine expression by the introduction of hTERT. Proteome analysis revealed overexpression of anti-apoptotic proteins (clusterin, fortilin, and gelsolin) and down-regulation of apoptotic protein (calreticulin) in hTERT-introduced NHAs, although the role of these proteins on lifespan extension was unknown.
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