Study on the biological characteristics of rat bone marrow mesenchymal stem cells

AIM: To investigate the basic biological characteristics of adult rat bone marrow mesenchymal stem cells(rBMMSCs), and compare to that of human BMMSCs (hBMMSCs). METHODS: rBMMSC and hBMMSCs were separated from bone marrow with the difference of adherence and Ficoll-Paque reagent, and expanded in culture medium in vitro, respectively. The proliferation and growth characteristics of the primary and different passage culture of rBMMSCs and hBMMSCs were analysed. The neural differentiation capacity of rBMMSCs with passages were observed. To detect the surface antigens of rBMMSCs, the labeled cells were analysed on a FACScan flow cytometer. The karyotype of rBMMSCs were detected by blocking cellular fission with colchicines. RESULTS: rBMMSCs and hBMMSCs have a strong self-renewal capacity. Approximately (4-8)×10¹² and (3-4)×10¹² cells were obtained after passage 15 in vitro, respectively. The ability of proliferation, CFU-Fs, and neural differentiation of rBMMSCs and hBMMSCs were decreased gradually with passages, but the ability of proliferation and CFU-Fs of rBMMSCs were higher than that of hBMMSCs at different passage. FACScan result showed rBMMSCs were uniformly positive for CD29 and CD44, and negative for CD11b, CD45, CD61, CD71, CD80, CD86,MHCⅠ and MHCⅡ. rBMMSCs had an normal karyotype, which had an average of 37.0±4.0 to 40.5±2.5 chromosomes. CONCLUSION: Adult rBMMSCs have strong self-renewal and neural differentiation capacity, and have an normal karyotype. So rBMMSCs can be used as the seed cells for tissue engineering.     

Study on Cx43 communication function of cardiomyocyte-like cells derived from rat bone marrow mesenchymal stem cells in vitro

AIM: To approach the gap junction distribution and communication function of cardiomyocyte-like cells derived from rat bone marrow mesenchymal stem cells (MSCs) in vitro.METHODS: MSCs were isolated by extraction of bone marrow specimens,gradient centrifugation and the adherence of culture plates.MSCs were culture in vitro,treated with 5-azacytidine and incubated for 24 h.The induced MSCs,which had been incubated for 2,3 and 4 weeks,were divided into group Ⅰ,Ⅱ and Ⅲ.In addition,the normal cardiomyocyte cells were used as control group.The distribution of connexin 43(Cx43) and the mean fluorescence redistribution rate were detected in every group with the laser scanning confocal microscope.RESULTS: Cx43 protein grain density in induced MSCs was increased with the lasting of incubation by quantitive analysis of Cx43 distribution.After 4 weeks,the Cx43 protein density in induced MSCs was nonsignificant deviation with control group (63.87±12.43,64.87±12.15,P>0.05).The diversify tendency of the mean fluorescence redistribution rate was approximation with the result of Cx43 in every group.The results showed that groupⅠ was 19.59%±6.08%,groupⅡ was 37.17%±3.84%,groupⅢ was 46.82%±2.69%,and control group was 49.71%±5.53%.CONCLUSION: MSCs can be differentiated to cardiomyocyte-like cells,which have been induced and incubated for 4 weeks in vitro.The communicational function of those MSCs is similar to the normal cardiomyocyte cells.     

Age-related changes of bone marrow mesenchymal stem cells in senile osteoporosis

AIM：To investigate the different functions of bone marrow mesenchymal stem cells (BMMSCs) in age-related osteoporosis. METHODS：The senescence-accelerated mice (SAMP6) were used in the experiment. The BMMSCs were isolated from femora and tibiae by flushing. Flow cytometric analysis was performed with MSCs-related monoclonal antibodies. The expression of differentiation genes was tested by real-time RT-PCR. RESULTS：In the progress of age-related osteoporosis, BMMSCs exhibited a decrease in osteogenesis and an increase in adipogenesis. Transforming growth factor β(TGF-β) signaling was significantly changed along with aging in SAMP6 mice. CONCLUSION：The functional changes of BMMSCs may play an important role in senile osteoporosis. The alteration of TGF-β-related gene expression may be the molecular mechanism of dysfunction in BMMSCs.     

Rapid proliferation of bone marrow mesenchymal stem cells enhanced by xanthosine

AIM: To explore the effect of xanthosine (Xs) on proliferation and differentiation of bone marrow mesenchymal stem cells (BMSCs). METHODS: Xs was directly added to the culture system and the effects of Xs on proliferation and differentiation of BMSCs were observed. RESULTS: In the presence of Xs, the growth rate of the 10th passage cells was almost similar to that of the 4th passage cells and no downtrend was observed. However, in control group (without Xs), the growth rate of the 10th passage cells was obviously declined. The BMSCs promoted by Xs still kept up a vigorous capability of differentiation into hepatocytes. CONCLUSION: As an inhibitor of asymmetric cell kinetics, Xs can promote the conversion of BMSCs from asymmetric cell kinetics to symmetric cell kinetics, and keeps synchronously the ability of differentiation from BMSCs into hepatocytes as well. It is helpful for enhancing the proliferation efficiency of BMSCs in vitro, and will have extensive application of clinical practice.     

Microparticles derived from bone marrow mesenchymal stem cells promote angiogenesis in rat myocardial infarction model

AIM: To observe the effects of microparticles derived from bone marrow mesenchymal stem cells (MSC-MPs) on angiogenesis and cardiac function in a rat myocardial infarction model. METHODS: MSCs were obtained from Sprague-Dawley rats. MSCs were treated under serum-free condition in hypoxia for 72 h, and the microparticles were isolated from the supernatants. The phenotypic profile of MSC-MPs was determined by bead-based flow cytometry and the morphology was observed under a transmission electron microscope. The rat myocardial infarction model was established. The cardiac function was evaluated by echocardiography after the intramyocardial injection of MSC-MPs. The myocardial infarct size was observed by Masson staining. The blood vessel density in the peri-infarcted area was measured using immunohistochemical staining for von Willebrand factor and α-smooth muscle actin. The expression of vascular endothelial growth factor (VEGF) was analyzed by real-time PCR. RESULTS: Apoptotic MSCs released a large quantity of microparticles which were phenotypically similar to the parent MSCs and 100~1 000 nm in diameter. The cardiac functions of myocardial infarction rat model were improved at 7 d and 28 d after intramyocardial injection of MSC-MPs compared with control group. The myocardial infarct size was reduced and angiogenesis was promoted significantly in the infarcted heart injected with MSC-MPs 28 d after treatment. MSC-MPs treatment also increased the expression level of VEGF within 7 d.CONCLUSION: MSC-MPs protect cardiac tissue from ischemic injury and improve cardiac function by promoting angiogenesis after myocardial infarction.     

Wnt signaling pathway is involved in catalpol-induced proliferation of rat bone marrow mesenchymal stem cells

AIM：To investigate the changes of Wnt signaling pathway in catalpol-induced proliferation of rat bone marrow mesenchymal stem cells (BMSCs). METHODS：The BMSCs were isolated from SD rats, purified by differential time adherent method and divided into control group and catalpol (1.0 mg/L) group. Flow cytometry was used to detect the proliferation index of BMSCs. The mRNA levels of Wnt3a, Wnt5a, Wnt11 and β-catenin was evaluated by real-time PCR. In addition, the protein expression level of β-catenin was determined by Western blotting. RESULTS：Prolife-ration index was increased from 8.90%±0.46% to 17.93%±1.68% after treatment with catalpol (P<0.01). Compared with control group, the mRNA expression of Wnt5a, Wnt11 and β-catenin was all increased with catalpol treatment. No difference of Wnt3a mRNA expression between control group and catalpol group was observed. Meanwhile, the protein expression of β-catenin was increased in catalpol group compared with control group. CONCLUSION：Catalpol promotes BMSCs going into the cell cycle. Classical and non-classical Wnt signaling pathways are activated in this process.     

Mechanisms of catalpol-induced osteogenic differentiation in SD rat bone marrow mesenchymal stem cells

AIM: To investigate the mechanisms for catalpol-induced osteogenic differentiation of SD rat bone marrow mesenchymal stem cells (BMSCs) in vitro. METHODS: The cells were divided into control group, osteoinduction group and catalpol group. The activity of alkaline phosphatase (ALP) was measured at 7 d, 14 d and 21 d after catapol treatment, meanwhile ALP positive cell numbers and calcium nodes were counted at 14 d and 21 d after catapol treatment,respectively. The mRNA expression of Runx2, osteocalcin, Wnt3a, β-catenin, Wnt5a and Wnt11 was detected at 7 d, 14 d and 21 d after catapol treatment by real-time PCR. RESULTS: Catalpol at 2.0 mg/L increased ALP activity and ALP positive cell numbers significantly(P<0.05), meanwhile, it also increased calcium nodes numbers in cultured BMSCs (P<0.05). Compared with control group, catalpol increased the mRNA expression of Runx2 significantly at 14 d, but not at the 7 d and 21 d. Catapol also promoted the mRNA expression of osteocalcin significantly from 7 d to 21 d. Compared with control group, the mRNA expression of Wnt3a and β-catenin in catalpol group was increased at 14 d and 21 d. In addition, the mRNA expression of Wnt5a and Wnt11 in catalpol group was higher than that in control group at 14 d, but that was decreased at 21 d. CONCLUSION: Catalpol induces differentiation of BMSCs into osteoblast by increasing the mRNA expression of Runx2, and promotes the differentiation and mature of these osteoblasts by increasing ALP secretion, osteocalcin mRNA expression and calcium deposition. The activation of Wnt signaling pathway may be involved in this pro-osteogenic differentiation process.     

Effects of azathioprine on proliferation,cell cycles and apoptosis of me-senchymal stem cells from rat bone marrow in vitro

AIM: To investigate the effects of azathioprine (AZA) on the proliferation, cell cycle and apoptosis of mesenchymal stem cells (MSCs) from the bone marrow of Sprague-Dawley rats in vitro. METHODS: MSCs were cultured in low-glucose DMEM containing 10% FBS,and treated with AZA at concentrations of 50 mg/L, 100 mg/L, 200 mg/L and 300 mg/L for 24 h, 48 h and 72 h. The effects of AZA on the growth curve and proliferation of MSCs were tested by cell counter under microscope. The apoptosis and cell cycle was determined by flow cytometry. RESULTS: Pure MSCs were gained by 3 times of passages. No significant effect of AZA at concentration of less than 100 mg/L on the proliferation, cell cycle and apoptosis of MSCs was observed (P>0.05). Under the condition of more than 200 mg/L for 72 h, AZA inhibited the growth of MSCs.The inhibitory rate was more than 66%, and the rate of apoptosis was increased (P<0.05). However, at the concentration of 300 mg/L for 72 h, AZA decreased the apoptotic rate and the necrotic rate of MSCs was obviously increased (P<0.05). Using AZA at concentration of more than 200 mg/L, as the action time prolonged, the MSCs in G₀/G₁ phase were increased, and those in S phase were decreased (P<0.05). CONCLUSION: At some concentrations, AZA significantly affects the proliferation, apoptosis and cell cycle of MSCs. Large dose of AZA may cause MSCs to death.     

Lentivirus-mediated calcitonin gene-related peptide transfection enhances endothelial differentiation of rat bone marrow mesenchymal stem cells

AIM：To study the effect of calcitonin gene-related peptide (CGRP) gene transfection mediated by lentivirus on the differentiation of rat bone marrow mesenchymal stem cells (MSCs) to endothelial cells. METHODS：Rat bone marrow MSCs were isolated by density gradient centrifugation combined with adherence method. Recombinant lentivirus vector carrying CGRP gene (Lenti-CGRP) was transfected into the MSCs. The secretion of CGRP in culture supernatants of the transfected MSCs was detected using ELISA method. The cells at passage 3 were divided into three groups: CGRP group (MSCs transfected with Lenti-CGRP), CGRP+CGRP8-37 (an antagonist of CGRP receptor) group and control group (MSCs transfected with PBS). The differentiation of the MSCs was detected by immunocytochemical staining for CD31 and factor Ⅷ-related antigen. The proliferation of the cells was measured by cell counting, and the angiogenic ability of the cells was analyzed using Matrigel assay. RESULTS：The proportion of CD31-and factor Ⅷ-related antigen-positive cells in CGRP and CGRP+CGRP8-37 groups was larger than that in control group (P<0.05). The numbers of the cells in CGRP and CGRP+CGRP8-37 groups were significantly increased compared with control group (P<0.05). Lumen-like structures were observed in CGRP and CGRP+CGRP8-37 groups. The above indexes in CGRP+CGRP8-37 group were reduced compared with CGRP group. CONCLUSION: Transfection with CGRP gene induces rat bone marrow MSCs to differentiate into endothelial cells and enhances their proliferation, suggesting that CGRP may play a role in the regulation of angiogenesis.     

Effects of naringin on MAPK signal pathway in rat bone marrow mesenchymal stem cells during osteogenic differentiation

AIM: To study the effects of Chinese herbal monomer naringin (NG) on the MAPK signal pathway in bone marrow mesenchymal stem cells (MSCs) derived from SD rats during the differentiation into osteoblasts in vitro . METHODS: The changes of evaluating indicators alkaline phosphatase (ALP), bone gla protein (BGP) and type I collagen (Col I) in MSCs were observed under the conditions of normal, adding p38 pathway inhibitor SB203580, adding extracellular signal-regulated kinase (ERK) pathway inhibitor PD98059, adding c-Jun N-terminal kinase (JNK) pathway inhibitor SP600125, and adding SB203580, PD98059 and SP600125 together. The protein phosphorylation of p38, ERK1/2 and JNK was measured by Western blotting. The mRNA expression levels of transforming growth factor beta 1 (TGF-β₁), bone morphogenetic protein 2 (BMP-2) and core binding factor α1 (Cbfα1) were measured by fluorescence quantitative PCR. RESULTS: The most effective concentration of NG to promote the differentiation of MSCs into osteoblasts was 10^-7 mol/L. The highest expression levels of both ALP and BGP were observed in NG group (P<0.05), while the expression of Col I did not reveal significant difference (P>0.05). Compared with NG group, the expression levels of ALP, BGP and Col I decreased differently after adding different inhibitors. Compared with control group, the protein phosphorylation of JNK was increased (P<0.05), and the phosphorylation of p38 was decreased (P<0.05), while the phosphorylation of ERK1/2 did not reveal significant difference (P>0.05) in NG group. Compared with NG group, the protein phosphorylation of p38, ERK1/2 and JNK showed fluctuation with some increasing and others decreasing. Compared with control group, the expression of BMP-2 was increased (P<0.05), and the expression of Cbfα1 was decreased(P<0.05), while the expression of TGF-β₁ did not reveal significant difference (P>0.05) in NG group. Compared with NG group, the mRNA expression levels of TGF-β₁, BMP-2 and Cbfα1 decreased differently after adding different inhibitors. CONCLUSION: Activation of ERK/JNK signaling and up-regulation of BMP-2 expression may be the main mechanism of NG to promote the differentiation of MSCs into osteoblasts. NG has strong impact on p38 pathway to improve the expression of BMP-2 in MSCs.     

Proliferation and differentiation of bone marrow mesenchymal stem cells in process of bone loss in ovariectomized rats

AIM: To study the function of proliferation and differentiation of bone marrow mesenchymal stem cells (BMSCs) for bone loss in the pathogenesis of osteoporosis (OP) in ovariectomized rats. METHODS: Animal model of OP was established by ovariectomy (OVX,bilateral ovarian resection) in 10-week-old healthy female Sprague-Dawley (SD) rats.BMSCs were isolated, cultured and purified by the combination of density gradient centrifugation, adhesion separation and limited dilution method, and cultured in vitro to the 3rd~4th passage in all experiments. The BMSCs phenotype appraisal was studied by flow cytometry. Colony-forming assay was applied to detect the BMSCs proliferation ability. The MTT method was used to analyze the growth curves of BMSCs. After adipogenic induction (ADI), lipid drops were observed by oil red O staining to compare the adipogenic potential between the 2 kinds of BMSCs. After osteogenic induction (OSI), calcium nodules were observed by alizarin red staining (ARS). The mRNA expression levels of BMSCs osteogenesis-related proteins, for instance, Runx2, osteocalcin (OCN) and osteopontin (OPN) were measured by RT-PCR. RESULTS: Compared with sham group, the colony-forming ability of BMSCs in OVX group became decreased, the proliferation capacity was declined, the osteogenic potential was decreased, and the adipogenic potential was increased(P<0.05). CONCLUSION: In ovariectomized OP rats, the proliferation and osteogenesis of BMSCs decrease, and the adipogenesis of BMSCs increases, which may cause rapid bone loss and play an important role in the pathogenesis of OP.     

Effects of lentivirus-mediated caspase-3 silencing on proliferation and apoptosis of rat bone marrow mesenchymal stem cells

AIM：To investigate the effects of caspase-3 gene silencing on proliferation, cell cycle and apoptosis of rat bone marrow mesenchymal stem cells (MSCs). METHODS：A lentiviral vector expressing caspase-3 shRNA was constructed and transfected into rat bone marrow MSCs．The expression of caspase-3 at mRNA and protein levels was detected by real-time PCR and Western blotting, respectively. Cell proliferation and cell cycle were evaluated by MTS assay and flow cytometry, respectively. The expression of bcl-2 and bax mRNA was detected by real-time PCR. The apoptosis of the cells was evaluated by Hoechst 33258 staining. RESULTS：Recombinant lentivirus was successfully transfected into MSCs. The proliferation of the MSCs transfected with caspase-3 shRNA was significantly promoted (P<0.05) and the proportion of the cells in S phase was increased to (52.66±0.30) %. Compared with control groups, caspase-3 silencing up-regulated the mRNA level of bcl-2 and down-regulated the mRNA level of bax, and the ratio of bcl-2 to bax increased (P<0.05). The apoptotic rate in MSCs-shRNA group was (15.01±1.73) %, which was significantly lower than those in MSCs and MSCs-vector group ［(23.67±1.16) % and (25.67±3.05) %, respectively; P<0.05］. CONCLUSION: Caspase-3 silencing regulates cell cycle, promotes the proliferation and attenuates the apoptosis of rat bone marrow MSCs.     

Effect of lentiviral vector of microRNA-9-1 on differentiation of mouse bone marrow mesenchymal stem cells into neurons

AIM: To investigate the role of microRNA-9 in inducing bone marrow mesenchymal stem cell(MSCs) differentiation into neurons.METHODS: The lentiviral vector of microRNA-9-1(microRNA-9-1-LV) was constructed and transfected into mouse MSCs. The cells were divided into non-transfected group, transfected group(transfected with microRNA-9-1-LV) and negative control group(transfected with FU-RNAi-NC-LV). MSCs were treated with β-mercaptoethanol(β-ME) as an inducer for triggering the cells to differentiate into neurons. The fluorescence expressed by transfected MSCs were observed under inverted fluorescence microscope. The mRNA expression of microtublin-associated protein 2(MAP-2) was detected by RT-PCR. The expression of neuron-specific markers,neuron-specific enolase(NSE), MAP-2 and glial fibrillary acidic protein(GFAP), were measured by immunocytochemical method. The viability of MSCs was determined by MTT method. RESULTS: The results of PCR confirmed successful construction of mouse microRNA-9-1-LV. The virus titer was 1×10¹² TU/L(TU, transduction unit). The best transfection efficiency(up to 91.3%±4.2%) and survival rate appeared when multiply of infection(MOI)was 20 and on 4th day. β-ME induced MSCs to differentiate into neurons and the best efficiency of the induction was observed in transfected group. The expression levels of NSE and MAP-2 in transfected cells were higher than those in the cells of other group(P<0.05).CONCLUSION: MicroRNA-9-1-LV has high transfection efficiency in mouse MSCs. Higher differentiation rate from mouse MSCs to neurons is induced by β-ME after the cells are transfected with microRNA-9-1-LV.     

Differentiation of mesenchymal stem cells derived from human umbilical cord

AIM: To explore an ideal method to induce the differen-tiation of human umbilical cord mesenchymal stem cells(hUCMSCs) into neuron-like cells and to provide some evidence for the transplantation of hUCMSCs for spinal cord injury. METHODS: The hUCMSCs were isolated from human umbilical cord digested with collagenase Ⅱ. The hUCMSCs was verified by flow cytometry analysis. The passage 5 cells were randomly divided into 4 groups. The differentiation of hUCMSCs was induced by bFGF in group A, bFGF and BDNF in group B, or BHA, bFGF and BDNF in group C, while the cells in group D served as a control group cultured with DMEM-F12 and 10% FBS. Two weeks later, the expression of nestin, neurofilament protein H(NEFH) and glial fibrillary acidic protein(GFAP) was detected by real-time PCR and immunocytochemistry. The morphological changes of cells were observed under an atomic force microscope. RESULTS: Mesenchymal stem cells were isolated and cultured from human umbilical cord by enzyme digestion. hUCMSCs expressed CD29, CD44 and CD105, but no CD34, CD45 or HLA-DR. After cultured with inducing medium for 2 weeks, the cells were successfully induced into neuron-like cells. The appearance of the cells had great change. The induced hUCMSCs developed round cell bodies with multiple neurite-like extensions observed under an atomic force microscope. The result of real-time PCR showed that nestin was positive in A, B and C groups, and NEFH was positive in A and B groups, but GFAP was negative in 4 groups. The difference of nestin and NEFH expression among the induced groups was significant(P<0.05). CONCLUSION: Mesenchymal stem cells were isolated and cultured from human umbilical cord by enzyme digestion in vitro, and all the hUCMACs presented stable biological properties. Moreover, hUCMSCs were induced to differentiate into neuron-like cells in vitro via bFGF combined with BDNF.     

Differentiation potential of human placenta derived mesenchymal stem cells into vascular endothelial cells

AIM: To investigate the differentiation potential of human placenta derived mesenchymal stem cells (PDMSCs) into endothelial cells (ECs) in vitro. METHODS: PDMSCs were isolated from human placenta tissues, characterized by flow cytometry and induced to differentiate into endothelial cells with 50 μg/L VEGF and 10 μg/L bFGF. To detect the specific markers of ECs during the process of differentiation, the method of immunocytochemistry was performed. The specific structure and function of endothelial cells were observed by transmission electron microscopy and in vitro angiogenesis assay kit, respectively. RESULTS: CD105 and CD106 were positive in PDMSCs, while CD34,CD45 and CD31 were negative.The ECs differentiated from PDMSCs showed cobblestone-like morphology, and expressed early endothelial marker of Flk-1/KDR and mature endothelial markers of CD31, vWF and CD144/VE-cadherin in a time-dependent manner during the endothelial cell differentiation (0 day, 4 days, 8 days and 12 days). The endothelial specific structure, Weibel-palade body, was observed under transmission electron microscope. The inoculation of ECs on the extra cellular matrix gel formed capillary-like structures. CONCLUSION: Plentiful PDMSCs can be isolated from placenta, and differentiate into the cells with functional characteristics of ECs in vitro, indicating that the placenta tissues will become optimal source of seed cells for vascular engineering and regenerative medicine.     

Biological characteristics of long passaging rat mesenchymal stem cells

AIM:To investigate multi-potential of rat bone marrow mesenchymal stem cells (rBMMSC) and mutation inclination, the rBMMSC were long passaged in vitro. METHODS:Cellular cycles of different passages were assayed by FACSan flow cytometry and karyotypes of passage 6, passage 25 and passage 45 were compared by G-binding analysis. RESULTS:The early passages and long-term passages all showed strong proliferation; passage 6, passage 25 and passage 45 all showed normal karyotype. CONCLUSION:Long-term culture and passage of rBMMSC still remains strong proliferation. With this capability, the mutation inclination is not enhanced.     

Lentivirus mediated CCN1 gene on growth and migration of rat bone marrow mesenchymal stem cells

AIM：To investigate the role of cysteine-rich 61 (Cyr61/CNN1) in proliferation and migration of bone marrow mesenchymal stem cells (BMSCs). METHODS：The lentiviral vector carrying CCN1 (Lenti-GFP-CCN1) was constructed and then transfected into the rat BMSCs. The cells were divided into non-transfection group, transfection group (transfected with Lenti-GFP-CCN1) and negative control group (Lenti-GFP). The fluorescence intensity of the transfected BMSCs was observed under inverted fluorescence microscope. The effects of CCN1 on the proliferation and migration of BMSCs were detected by MTT assay and scratch wound healing assay. RESULTS：The proliferation of BMSCs transfected with Lenti-GFP CCN1 had no significant difference compared with negative control group and control group. The width/thickness ratio of migrated BMSCs in wound healing was significantly higher in Lenti-GFP-CCN1 group than that in negative control group and control group (P<0.05). CONCLUSION：Exogenous CCN1 promotes the migration of BMSCs.     

Mechanism of telomere mainteance in human bone marrow mesenchymal stem cells

AIM： To study the telomere maintenance mechanism in mesenchymal stem calls (MSCs).〖WT5"HZ〗 METHODS：MSCs were isolated from healthy human bone marrow by their adherence to plastic and then were checked with CD14-FITC,CD45-FITC,CD44-FITC,HLA-DR-FITC,CD34-PE,CD29-PE and CD166-PE.Telomere length and ECTR DNA in MSCs were detected by Southern blotting.The localization of TRF1 and promyelocytic leukemia (PML) in MSCs were detected with immunofluorescence staining.TRAP protocol was performed to detect the telomerase activity in MSCs and MSCs-derived adipocytes.Western blotting and TRAP protocol were applied to measure telomerase activity of MSCs,which were synchronized by serum starvation and aphidicolin treatment.〖WT5"HZ〗RESULTS：The telomere in length seemed shorter and relatively more homogeneous in MSCs and HeLa cells than that in WI-38-2RA cells.TRF1 did not concide with PML nuclear body in MSCs and HeLa cells while it exclusively did in WI-38-2RA cells.ECTR DNA was negative in MSCs and HeLa cells but positive in WI-38-2RA cells.Telomerase was negative in MSCs but it was positive in MSCs-derived adipocytes detected by TRAP.Moreover,a cell cycle-dependent expression profile of telomerase was found in MSCs when they were synchronized by serum starvation and aphidicolin treatment.Untreated MSCs expressed very low level of telomerase probed by Western blotting with 2C4 mAb,but the telomerase level had significantly increased when these cells were trapped in S phase.〖WT5"HZ〗CONCLUSION：The telomere of MSCs is maintained by telomerase pathway instead of alternative lengthing of telomere(ALT) and the level of telomerase expression is associated with cell cycle stage.