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BACKGROUND:Human mesenchymal stem cells (hMSCs) become aging and even die after several passages. Some investigations have shown that telomere has a close correlation with life span of the cells. Whether the ectopic expression of human telomerase reverse transcriptase (hTERT) could induce the activity of the telomerase, maintain the length of telomere, and finally prolong the life cycle of MSCs without losing their multipotent differentiation capacity is still uncertain.OBJECTIVE: To observe the influence of the ectopic expression of hTERT on the telomerase activity and cell life cycles of hMSCs.DESIGN: Repetitive measurement trails.SETTING: Research Center of Stem Cell, Zhengzhou University Medical College.MATERIALS: The experiment was conducted in the Research Center of Stem Cell, Zhengzhou University Medical College from October 2003 to December 2005. hMSCs were obtained from 20 healthy donators from the Department of Pediatric Surgery and Outpatient, the Third and First Affiliated Hospitals of Zhengzhou University. Enhanced green fluorescent protein plasmid (pEGFP-C1) and pEGFP-hTERT were provided by Dr. Chantal Autexier of Canada. DH5α strain provided by Dr. Hou Wei-hong, the Key Molecular Medical Laboratory of Zhengzhou University Medical College.METHODS.: Under sterile condition, 2 mL bone marrow of sternum of healthy donors were harvested, and prepared after centrifugalization,dilution and passage.① Transfection of pEGFP-hTERT into hMSCs and the screening and amplification of resistance cloning:The 5th passage cells were seeded in a 24-well plate,and transfected by pEGFP-hTERT with lipofectamine method.The cells were divided into four groups including untransfected group,lipofectamine group,pEGFP-C1 group and pEGFP-hTERT group. Resistance cloning screen and amplification was performed by G418. ②hTERT mRNA expression and detection of telomerase activity:RT-PCR and PCR-ELISA were used to detect the hTERT mRNA expressions of the fifth passage hMSCs transfected with pEGFP-hTERT, and pEGFP-C1, the untransfected tenth passage hMSCs and K562 cells (positive control), and the telomerase activity of the fifth and thirtieth passage hMSCs transfected with pEGFP-hTERT,the fifth pEGFP-C1-transfected cells and the tenth passage untransfected cells. ③Karyotype analysis of hTERT-transfected MSCs: Chromosome analysis was performed by conventional Giemsa staining.④Inducement of differentiation from telomerase-positive MSCs into neuron-like cells and RE-PCR identification:The transfected MSCs were cultured in a medium containing epidermal growth factor and basic fibroblast growth factor, which could induce the cells differentiate into neuron-like cells. The culture solution was changed every 3 days, and the changes in cell growth condition and morphologic characteristics were observed under an inverted microscope. The microtubule associate protein (MAP2) and neurofliament subunit M (NF-M) were identified by RT-PCR.MAIN OUTCOME MEASURES:①hMSCs transfection with different kathion liposomes and the screening and amplification of resistance cloning; ②hTERT mRNA expressions of each group and detection of telomerase activity; ③Karyotype analysis of pEGFP-hTERT-transfected MSCs; ④ Induction of differentiation from telomerase-positive MSCs into neuron-like cells and RE-PCR identification.RESULTS: ①With the decrease of G418 concentration, the cells in the untransfected and lipofectamine groups died, and stably EGFP expressed MSCs were obtained; after G418 screening, there was a cell clone undergone 35 passages and continued to proliferate, whose appearance and growth characteristics were similar to the untransfected MSCs observed under inverted microscope. ②The fifth passage pEGFP-C1-transfected hMSCs and tenth passage untransfected hMSCs remained telomerase-negative, but the K562 and fifth passage hTERT-transfected cells showed positive telomerase activity. ③The telomerase activity of the fifth and thirtieth passage hTERT-transfected cells was positive. ④The hTERT-MSCs at passage 10, 20 and 30 had 23 pairs of chromosomes, and two X chromosomes. So they were still normal diploid with normal chromosome appearance and number. ⑤Many hTERT-transfected MSCs had the typical appearance of neuron-like cells. RT-PCR analysis showed that th expressions of MAP2 and NF-M were increased.CONCLUSION:Ectopic expression of the hTERT gene is found in hMSCs,and can induce the telomerase activity of hMSCs.The ectopic expression of the hTERT gene in hMSCs could extend the life spans of cells and maintain their multipotent differentiation capacity.