Protocol for Flow Cytometric Sorting of Enriched Neuronal Cultures from iPSCs

Surface molecule profiles undergo dynamic changes in physiology and pathology, serve as markers of cellular state and phenotype and can be exploited for cell selection strategies and diagnostics. The isolation of well-defined cell subsets is needed for in vivo and in vitro applications in stem cell biology. In this technical report, the authors present an approach for defining a subset of interest in a mixed cell population by flow cytometric detection of intracellular antigens. They have developed a fully validated protocol that enables the co-detection of cluster of differentiation (CD) surface antigens on fixed, permeabilized neural cell populations defined by intracellular staining. Determining the degree of co-expression of surface marker candidates with intracellular target population markers (nestin, MAP2, doublecortin, TUJ1) on neuroblastoma cell lines (SH-SY5Y, BE(2)-M17) yielded a combinatorial CD49f^-/CD200^high surface marker panel. Its application in fluorescence-activated cell sorting (FACS) generated enriched neuronal cultures from differentiated cell suspensions derived from human induced pluripotent stem cells. Our data underlines the feasibility of using the described co-labeling protocol and co-expression analysis for quantitative assays in mammalian neurobiology and for screening approaches to identify much needed surface markers in stem cell biology: Turaç G, Hindley CJ, Thomas R, Davis JA, Deleidi M, et al. (2013) Combined Flow Cytometric Analysis of Surface and Intracellular Antigens Reveals Surface Molecule Markers of Human Neuropoiesis. PLoS ONE 8(6): e68519. doi:10.1371/journal.pone.0068519

Figure 1. Experimental outline. Schematic illustrating the research strategy of identifying novel surface marker combinations on a target population in neural and other stem cell differentiation systems for which intracellular, standard immunocytochemical markers are well established. Following harvesting, the resulting single cell suspension is subject to surface antigen candidate staining, followed by gentle fixation, permeabilization and subsequent co-staining with known intracellular markers. CD markers co-labeling the target population serve as positive markers, those absent on the target population serve as negative markers. In a separate, subsequent step, a combination of the identified positive and/or negative CD markers enables the flow cytometric enrichment of the viable population of interest from a heterogeneous cell suspension for further study and biomedical applications. doi:10.1371/journal.pone.0068519.g001.

Figure 2. Accurate detection of intracellular antigens with optimized fixation-permeabilization conditions preserving surface antigens. Flow cytometric detection of TUJ1, MAP2 and nestin antigens in BJ fibroblasts and the neural SH-SY5Y cell line (A). TUJ1 and nestin are present in both cell lines, while the mature neuronal marker MAP2 was only detected in SH-SY5Y cells (arrows). Note stable fluorescent levels of the negative population, indicating low background staining using this protocol. Representative experiment of three independent repeats shown. (B) Corresponding validation by immunofluorescence analysis. (C) Quantitation of TUJ1, MAP2 and nestin intracellular antigen detection (n=3). Error bars indicate standard deviation. (D) Response of TUJ1 and MAP2 intracellular antigen expression to 6 DIV of 10 µM retinoic acid (RA) treatment of SH-SY5Y cells. Note disappearance/reduction of subsets negative for these markers (upward shift, green arrows), as well as a shift toward CD184low expression with differentiation (blue arrows). doi:10.1371/journal.pone.0068519.g003.

Please note: In addition to the our Human Mouse Monoclonal Nestin Antibody used in the study, we have an extensive catalog of stem cell solutions. I will continue to post highlights of new applications.