参考文献

The cell-surface straight and branched repeats of N-acetyllactosamine (LacNAc) units,called poly-LacNAc chains,characterize the histo-blood group i and I antigens,respectively. The transition of straight to branched poly-LacNAc chain (i to I) is determined by the I locus,which expresses 3 IGnT transcripts,IGnTA,IGnTB,and IGnTC. Our previous investigation demonstrated that the i-to-I transition in erythroid differentiation is regulated by the transcription factor CCAAT/enhancer binding protein alpha (C/EBPalpha). In the present investigation,the K-562 cell line was used as a model to show that the i-to-I transition is determined by the phosphorylation status of the C/EBPalpha Ser-21 residue,with dephosphorylated C/EBPalpha Ser-21 stimulating the transcription of the IGnTC gene,consequently resulting in I branching. Results from studies using adult erythropoietic and granulopoietic progenitor cells agreed with those derived using the K-562 cell model,with lentiviral expression of C/EBPalpha in CD34(+) hematopoietic cells demonstrating that the dephosphorylated form of C/EBPalpha Ser-21 induced the expression of I antigen,granulocytic CD15,and also erythroid CD71 antigens. Taken together,these results demonstrate that the regulation of poly-LacNAc branching (I antigen) formation in erythropoiesis and granulopoiesis share a common mechanism,with dephosphorylation of the Ser-21 residue on C/EBPalpha playing the critical role. View Publication

The immunodeficiency disorder,X-linked agammaglobulinemia (XLA),results from mutations in the gene encoding Bruton tyrosine kinase (Btk). Btk is required for pre-B cell clonal expansion and B-cell antigen receptor signaling. XLA patients lack mature B cells and immunoglobulin and experience recurrent bacterial infections only partially mitigated by life-long antibody replacement therapy. In pursuit of definitive therapy for XLA,we tested ex vivo gene therapy using a lentiviral vector (LV) containing the immunoglobulin enhancer (Emu) and Igbeta (B29) minimal promoter to drive B lineage-specific human Btk expression in Btk/Tec(-/-) mice,a strain that reproduces the features of human XLA. After transplantation of EmuB29-Btk-LV-transduced stem cells,treated mice showed significant,albeit incomplete,rescue of mature B cells in the bone marrow,peripheral blood,spleen,and peritoneal cavity,and improved responses to T-independent and T-dependent antigens. LV-treated B cells exhibited enhanced B-cell antigen receptor signaling and an in vivo selective advantage in the peripheral versus central B-cell compartment. Secondary transplantation showed sustained Btk expression,viral integration,and partial functional responses,consistent with long-term stem cell marking; and serial transplantation revealed no evidence for cellular or systemic toxicity. These findings strongly support pursuit of B lineage-targeted LV gene therapy in human XLA. View Publication

Clonal analysis is important for many areas of hematopoietic stem cell research,including in vitro cell expansion,gene therapy,and cancer progression and treatment. A common approach to measure clonality of retrovirally transduced cells is to perform integration site analysis using Southern blotting or polymerase chain reaction-based methods. Although these methods are useful in principle,they generally provide a low-resolution,biased,and incomplete assessment of clonality. To overcome those limitations,we labeled retroviral vectors with random sequence tags or barcodes." On integration� View Publication

BACKGROUND: Over-expression of aldehyde dehydrogenase and other stem cell markers is characteristic of cells with tumorigenic potential in NOD/SCID mice. Most of these studies have focused on metastatic cells in bone marrow and on solid tumors. There are no studies on correlation of marker expression with ALDH1 expression in cells from human peripheral blood apheresis (HPC-A) samples. METHODS: HPC-A samples from 44 patients were incubated with Aldefluor with or without the presence of aldehyde dehydrogenase inhibitor DEAB. Cells with high aldehyde dehydrogenase expression (ALDH1(bright)) were analyzed for stem/progenitor markers CD34,CD90,CD117,and CD133. Electronic volume measured by Coulter principal in a Quanta flow analyzer was correlated with ALDH1 and marker expression. RESULTS: In ALDH1(bright)/SSC(low) cells,0.13% of the cells had CD34(+) expression and three distinct populations were seen. Expression of CD90 was dim and the frequency of ALDH1(bright)/SSC(low)/CD90(dim) cells amongst the nonlineage depleted samples was 0.04%. CD117(dim-bright) expression was seen in 0.17% of the samples. Three distinct populations of cells with CD133 expression were seen in ALDH1(bright)/SSC(low) nonlineage depleted cells with a frequency of 0.28%. The ALDH1(bright)/CD90(dim) cells had the smallest mean electronic volume of 264.9 microm(3) when compared with cells with CD34(bright) expression (270.2 microm(3)) and ALDH1(dim)/CD90(dim) cells (223 microm(3)). CONCLUSIONS: ALDH1(bright)/SSC(low) cells show heterogeneity in expression of the four stem cell markers studied. The CD90 cells in both the ALDH1(bright) and ALDH1(dim) populations had the smallest mean electronic volume when compared with similar cells with CD117 expression. View Publication

Human embryonic stem (hES) cells have enormous potential for clinical applications. However,one major challenge is to achieve high cell recovery rate after cryopreservation. Understanding how the conventional cryopreservation protocol fails to protect the cells is a prerequisite for developing efficient and successful cryopreservation methods for hES cell lines and banks. We investigated how the stimuli from cryopreservation result in apoptosis,which causes the low cell recovery rate after cryopreservation. The level of reactive oxygen species (ROS) is significantly increased,F-actin content and distribution is altered,and caspase-8 and caspase-9 are activated after cryopreservation. p53 is also activated and translocated into nucleus. During cryopreservation apoptosis is induced by activation of both caspase-8 through the extrinsic pathway and caspase-9 through the intrinsic pathway. However,exactly how the extrinsic pathway is activated is still unclear and deserves further investigation. View Publication

Synthetic materials that promote the growth or differentiation of cells have advanced the fields of tissue engineering and regenerative medicine. Most functional biomaterials are based on a handful of peptide sequences derived from protein ligands for cell surface receptors. Because few proteins possess short peptide sequences that alone can engage cell surface receptors,the repertoire of receptors that can be targeted with this approach is limited. Materials that bind diverse classes of receptors,however,may be needed to guide cell growth and differentiation. To provide access to such new materials,we utilized phage display to identify novel peptides that bind to the surface of pluripotent cells. Using human embryonal carcinoma (EC) cells as bait,approximately 3 x 10(4) potential cell-binding phage clones were isolated. The pool was narrowed using an enzyme-linked immunoassay: 370 clones were tested,and seven cell-binding peptides were identified. Of these,six sequences possess EC cell-binding ability. Specifically,when displayed by self-assembled monolayers (SAMs) of alkanethiols on gold,they mediate cell adhesion. The corresponding soluble peptides block this adhesion,indicating that the identified peptide sequences are specific. They also are functional. Synthetic surfaces displaying phage-derived peptides support growth of undifferentiated human embryonic stem (ES) cells. When these cells were cultured on SAMs presenting the sequence TVKHRPDALHPQ or LTTAPKLPKVTR in a chemically defined medium (mTeSR),they expressed markers of pluripotency at levels similar to those of cells cultured on Matrigel. Our results indicate that this screening strategy is a productive avenue for the generation of materials that control the growth and differentiation of cells. View Publication

Meticulous characterization of human embryonic stem cells (hESC) is critical to their eventual use in cell-based therapies,particularly in view of the diverse methods for derivation and maintenance of these cell lines. However,characterization methods are generally not standardized and many currently used assays are subjective,making dependable and direct comparison of cell lines difficult. In order to address this problem,we selected 10 molecular-based high-resolution assays as components of a panel for characterization of hESC. The selection of the assays was primarily based on their quantitative or objective (rather than subjective) nature. We demonstrate the efficacy of this panel by characterizing 4 hESC lines,derived in two different laboratories using different derivation techniques,as pathogen free,genetically stable,and able to differentiate into derivatives of all three germ layers. Our panel expands and refines a characterization panel previously proposed by the International Stem Cell Initiative and is another step toward standardized hESC characterization and quality control,a crucial element of successful hESC research and clinical translation. View Publication

Bone marrow-derived mesenchymal stem cells (BM-MSCs) can be induced to differentiate into myogenic cells. Despite their potential,previous studies have not been successful in producing a high percentage of cardiac-like cells with a muscle phenotype. We hypothesized that cardiac lineage development in BM-MSC is related to cell passage,culture milieu,and enrichment for specific cell subtypes before and during differentiation. Our study demonstrated that Lin(-) BM-MSC at an intermediate passage (IP; P8-P12) expressed cardiac troponin T (cTnT) after 21 days in culture. Cardiac TnT expression was similar whether IP cells were differentiated in media containing 5-azacytidine+2% FBS (AZA; 14%) or 2% FBS alone (LS; 12%) and both were significantly higher than AZA+5% FBS. This expression was potentiated by first enriching for CD117/Sca-1 cells followed by differentiation (AZA,39% and LS,28%). A second sequential enrichment for the dihydropyridine receptor subunit alpha2delta1 (DHPR-alpha2) resulted in cardiac TnT expressed in 54% of cultured cells compared to 28% of cells after CD117/Sca-1(+) enrichment. Cells enriched for CD117/Sca-1 and subjected to differentiation displayed spontaneous intracellular Ca(2+) transients with an increase in transient frequency and a 60% decrease in the transient duration amplitude between days 14 and 29. In conclusion,IP CD117/Sca-1(+) murine BM-MSCs display robust cardiac muscle lineage development that can be induced independent of AZA but is diminished under higher serum concentrations. Furthermore,temporal changes in calcium kinetics commensurate with increased cTnT expression suggest progressive maturation of a cardiac muscle lineage. Enrichment with CD117/Sca-1 to establish lineage commitment followed by DHPR-alpha2 in lineage developing cells may enhance the therapeutic potential of these cells for transplantation. View Publication

Hematopoietic stem cells (HSCs) are enriched for aldehyde dehydrogenase (ALDH) activity and ALDH is a selectable marker for human HSCs. However,the function of ALDH in HSC biology is not well understood. We sought to determine the function of ALDH in regulating HSC fate. Pharmacologic inhibition of ALDH with diethylaminobenzaldehyde (DEAB) impeded the differentiation of murine CD34(-)c-kit(+)Sca-1(+)lineage(-) (34(-)KSL) HSCs in culture and facilitated a ninefold expansion of cells capable of radioprotecting lethally irradiated mice compared to input 34(-)KSL cells. Treatment of bone marrow (BM) 34(-)KSL cells with DEAB caused a fourfold increase in 4-week competitive repopulating units,verifying the amplification of short-term HSCs (ST-HSCs) in response to ALDH inhibition. Targeted siRNA of ALDH1a1 in BM HSCs caused a comparable expansion of radioprotective progenitor cells in culture compared to DEAB treatment,confirming that ALDH1a1 was the target of DEAB inhibition. The addition of all trans retinoic acid blocked DEAB-mediated expansion of ST-HSCs in culture,suggesting that ALDH1a1 regulates HSC differentiation via augmentation of retinoid signaling. Pharmacologic inhibition of ALDH has therapeutic potential as a means to amplify ST-HSCs for transplantation purposes. View Publication

Since their derivation 11 years ago,human embryonic stem (hES) cells have become a powerful tool in both basic biomedical research and developmental biology. Their capacity for self-renewal and differentiation into any tissue type has also brought interest from fields such as cell therapy and drug screening. We conducted an extensive analysis of 750 papers (51% of the total published about hES cells between 1998 and 2008) to present a spectrum of hES cell research including culture protocols developed worldwide. This review may stimulate discussions about the importance of having unvarying methods to culture hES cells,in order to facilitate comparisons among data obtained by research groups elsewhere,especially concerning preclinical studies. Moreover,the description of the most widely used cell lines,reagents,and procedures adopted internationally will help newcomers on deciding the best strategies for starting their own studies. Finally,the results will contribute with the efforts of stem cell researchers on comparing the performance of different aspects related to hES cell culture methods. View Publication