Identification of new human mesenchymal stem cell biomarker by aptamers / Identificação de novos biomarcadores de células tronco mesenquimais de origem humana por meio de aptâmeros

Stem cells are undifferentiated cells that can be distinguished from others by their ability to self-renew and to differentiate into new specific cell types. Mesenchymal stem cells (MSC) are adult stem cells that can be obtained from different sources, such as adipose tissue, bone marrow, dental pulp, and umbilical cord. They can either replicate, originating new identical cells, or differentiate into cells of mesodermal origin and from other germ layers. MSC have been studied as new tools for regenerative therapy. Although encouraging results have been demonstrated, MSC-based therapies still face a great barrier: the difficulty of isolating these cells from heterogeneous environments. MSC are currently characterized by immunolabelling through a set of multiple surface membrane markers, including CD29, CD73, CD90 and CD105, which are also expressed by other cell types. Hence, the present work aimed to identify new specific biomarkers for the characterization of human MSC using DNA aptamers produced by the SELEX (Systematic Evolution of Ligands by EXponential Enrichment) technique. Our results showed that MSC from different origins bound to DNA candidate aptamers, that is, DNA or RNA oligonucleotides selected from random libraries that bind specifically to biological targets. Aptamer-bound MSC could be isolated by fluorescenceactivated cell sorting (FACS) procedures, enhancing the induction of differentiation into specific phenotypes (chondrocytes, osteocytes and adipocytes) when compared to the whole MSC population. Flow cytometry analyses revealed that candidate aptamers bound to 50% of the MSC population from dental pulp and did not present significant binding rates to human fibroblasts or lymphocytes, both used as negative control. Moreover, immunofluorescence images and confocal analyses revealed staining of MSC by aptamers localized in the surfacemembrane of these cells. The results also showed internal staining of human monocytes by our investigated aptamers. A non-specific control aptamer (CNTR APT) obtained from the random pool was then utilized to compare the specificity of the aptamers bound to the analyzed non-apoptotic cells, showing no staining for MSC. However, 40% of the monocytes bound to the CNTR APT. Normalized data based on the cells bound to candidate aptamers compared to those bound to the CNTR APT, revealed a 10 to 16-fold higher binding rate for MSC against 2-fold for monocytes. Despite its low specificity, monocyte-aptamer binding occurs probably due to the expression of shared markers with MSC, since monocytes are derived from hematopoietic stem cells and are important for the immune system ability to internalize/phagocyte external molecules. Given that, we performed a pull-down assay followed by mass spectrometry analysis to detect which MSC-specific protein or other target epitope not coexpressed by monocytes or the CNTR APT would bind to the candidate aptamer. Distinguishing between MSC and monocyte epitopes is important, as both cells are involved in immunomodulatory effects after MSC transplantations. ADAM17 was found to be a target of the APT10, emerging as a possible biomarker of MSC, since its involvement in the inhibition of the TGF signaling cascade, which is responsible for the differentiation of MSC. Thus, MSC with a higher stemness profile should overexpress the protein ADAM17, which presents a catalytic site with affinity to APT10. Another target of Apt 10 is VAMP3, belonging to a transmembrane protein complex that is involved in endocytosis and exocytosis processes during immune and inflammatory responses. Overall, proteins identified as targets of APT10 may be cell surface MSC biomarkers, with importance for MSC-based cell and immune therapies

Células tronco são células indiferenciadas que podem ser distinguidas de outros tipos celulares por meio da habilidade de se auto renovarem e de se diferenciarem em novos tipos celulares. Células tronco mesenquimais (MSC) são células tronco adultas encontradas em diferentes tecidos como tecido adiposo, polpa de dente e cordão umbilical. Estas células podem se autodividir em células idênticas ou se diferenciarem em células de origem mesodermal. Estas células têm sido estudadas em novas aplicações que envolvem terapia regenerativas. Embora resultados encorajadores tenham sido demonstrados, terapias que utilizam MSC ainda encontram uma grande barreira: a dificuldade no isolamento destas células a partir de um ambiente heterogêneo. MSC são caracterizadas por populações positivas em ensaios de imunomarcação para os epítopos membranares CD29, CD73, CD90 e CD105, presentes também em outros tipos celulares. Assim, o presente trabalho tem o objetivo de identificar novos biomarcadores de MSC de origem humana, utilizando aptâmeros de DNA produzidos pela técnica SELEX (Systematic Evolution of Ligands by EXponential Enrichment) como ferramenta. Nossos resultados mostraram que MSC de diferentes origens ligam-se a aptâmeros (oligonucleotídeos de DNA ou RNA que atuam como ligantes específicos de alvos moleculares) de DNA candidatos que atuam no isolamento de MSC por meio da técnica FACS de separação celular, promovendo uma maior indução de diferenciação em células específicas (condrócitos, osteócitos e adipócitos) comparada com a população total de MSC. Análises de citometria de fluxo mostraram que os aptâmeros candidatos se ligam a 50% das MSC de polpa de dente e não apresentam taxa de ligação significante para fibroblastos e linfócitos de origem humana - utilizados como controles negativo. Além domais, imagens de imunofluorescência e confocal mostraram ligação na superfície da membrana de MSC e a marcação interna de monócitos a estes aptâmeros. Portanto, um aptâmero controle (CNTR APT) foi utilizado para comparar a especificidade dos aptâmeros ligados a células viáveis, mostrando a não ligação deste aptâmero a MSC. Porém, 40% da população de monócitos ligou-se ao CNTR APT. Uma normalização baseada na comparação entre as taxas de ligação entre células ligadas com aptâmeros candidatos e o aptâmero controle gerou uma taxa de especificidade entre 10-16 vezes maior para MSC contra 2,5 vezes para os monócitos. Deste modo, embora os resultados tenham mostrado uma taxa de ligação entre monócitos e aptâmeros, as MSC ligadas aos aptâmeros candidatos possuem uma maior taxa de especificidade devido a uma maior presença de antígenos que são expressos em ambas as células. Um ensaio de Pull Down seguido de espectrometria de massas foi utilizado para a identificação de biomarcadores que se ligariam aos aptâmeros candidatos, e que não seriam co-expressos por monócitos e por antígenos ligados ao aptâmero controle. Deste modo, a proteína ADAM17 foi identificada nas amostras de APT10 ligadas às MSC. Tal proteína está relacionada à inibição de uma cascata de sinalização da família de proteínas TGF, responsável pela diferenciação de MSC. Assim, MSC com maior potencial tronco deveriam expressar ADAM17 em maior quantidade. Tal proteína apresenta um sítio catalítico que demonstra interagir com o APT10, de acordo com predição Docking entre proteína e DNA. Foi identificada também, a proteína VAMP3, que pertence a um complexo proteico transmembranar responsável pelos processos de endocitose e exocitose, e que podem ter um papel importante na liberação de citocinas e outras moléculas relacionadas às respostas imune e inflamatórias. Deste modo, o APT10 identificou proteínas importantes que devem estar relacionas com a melhora de imunoterapias que utilizam MSC

Cytological study on aptamer selection for bladder cancer through CELL-SELEX / 医学研究生学报

ObjectiveThe methods based on bladder cancer markers which could be applied to early diagnosis and postoperative recurrence monitoring of bladder cancer were current research hotspots. This study aims to screen aptamers that specifically recognize human bladder cancer cell lines (EJ, T24, BIU87) through cell-based systematic evolution of ligand by exponential enrichment (CELL-SELEX).MethodsFor CELL-SELEX screening, bladder cancer cell lines EJ, T24, and BIU87 were used as positive control cells. HCV 29 (human normal urothelial cell line), 293T (human embryonic kidney cell line), huh7 (human hepatocellular carcinoma cell line) were used as negative control cells. PCR upstream primers were labeled with FITC, downstream primer was labeled with Biotin. ssDNA fragments collected from each round were amplified by PCR, and the amplified product was then purified using a DNA purification Kit. The biotin-streptavidin magnetic separation methods were used to isolate the PCR product to obtain secondary FITC-ssDNA for the next CELL-SELEX round. The screening process was monitored by flow cytometry. ssDNA pool with the highest binding rates to bladder cancer cell lines(EJ, T24, and BIU87) was selected to PCR amplification, product purification, molecular cloning, and sequencing. According to the sequencing results, the secondary structure of the aptamer was pre-simulated by Dnaman software. Aptamer labeled with FITC was synthesized in vitro, flow cytometry was used to detect the binding rate of the aptamer to bladder cancer cell lins (EJ, T24 and BIU87).ResultsWith the advance of the CELL-SELEX process, the binding rate of FITC-ssDNA to bladder cancer cell lins (EJ, T24, and BIU87) increased gradually. By the 15th round, the binding rate of FITC-ssDNA to EJ cells reached the highest level. The apt1 had the highest enrichment among the 15th round ssDNA pool. By the 18th round, the binding rate of FITC-ssDNA to T24 or BIU87 cells reached the highest level. The apt2 and apt3 had the highest enrichment among the 18th round ssDNA pool. DNA structure prediction showed that the secondary structure of apt1, apt2, and apt3 was mainly stem-loop structure. Flow cytometry showed that the highest binding rate was FITC-apt1 to EJ cells, FITC-apt2 to T24 cells, and FITC-apt3 to BIU87 cells, respectively. There is no significant combination between these aptamers with the negative cells.ConclusionIn this study, three kinds of aptamers with high specificity for bladder cancer cell lines were successfully screened by CELL-SELEX. The apt1 can specifically recognize EJ cells, apt2 can specifically recognize T24 cells and apt3 can specifically recognize BIU87 cells, all of which provide experimental evidence for early diagnosis and targeted therapy technology research of bladder cancer.

Aptamers from Cell-based Selection for Bioanalysis and Bioimaging / 分析化学

Aptamers are single-stranded oligonucleotides ( DNA or RNA ) selected through a technology termed "Systematic evolution of ligands by exponential enrichment" ( SELEX ) . In addition to high affinity and high specificity for their target molecules, aptamers have some advantages such as low molecular weight, easy synthesis, high chemical stability, low immunogenicity, and convenient modification. Based on the Cell-SELEX technique, a panel of aptamers which can specifically recognize target cell lines has been generated. By targeting specific membrane proteins in their native state, these aptamers can identify subtle molecular differences among different cell lines, thus have attracted a broad interest in biomedical research. In this review, we summarized the development of aptamers and their use in detection, profiling and imaging of tumor cells. Also, their perspectives were discussed.

Selection and identification of aptamers for mesenchymal stem cells from different species / 军事医学

Objective To screen an ssDNA aptamer for rabbit mesenchymal stem cells (MSCs) and to identify the ability of the aptamer to recognize MSCs of a variety of species origin.Methods MSCs were isolated from the thigh bone of immature rabbits and identified by induced osteogenic and adipogenic differentiation,respectively.Aptamers were screened by cell SELEX (systematic evolution of ligands by exponential enrichment) technique targeting to isolated MSCs.Enrichment of the 5th pool was evaluated through binding assay of FAM modified pool to MSCs by confocal microscopy.The enriched 5th pool was then cloned into pGE-T vector and the cloned sequences were determined randomly.The candidates were chosen based on primary sequence conservation and predicted secondary structure by RNA structure and MEME online analysis.Flow cytometry analysis was used to identify the aptamers binding to MSCs of rabbit, rat, and human origin.Results The isolated MSCs had the potential of osteogenic differentiation and adipogenic differentiation under certain conditions.Aptamer 5-1-12 from 5th enriched pool was characterized as MSCs recognizing aptamer binding to MSCs of rabbit, rat and human origin.Conclusion Aptamer 5-1-12 that recognizes MSCs of different species origin is obtained through live cell-SELEX.