Adherent culture conditions enrich the side population obtained from the cochlear modiolus-derived stem/progenitor cells

Objectives: Previously, our group reported that sphere-forming cells derived from the organ of Corti represent the stem/progenitor cells (SPCs) of the cochlea due to their properties of self-renewal and multipotency. However, long-term propagation of sphere-forming cells under suspension culture conditions may fail to maintain the characteristic sternness of these cells. Therefore, this study investigated whether an adherent culture system would be beneficial in terms of preserving more stem-like cells for long-term manipulations in vitro. Methods: Isolated modiolus-derived SPCs were placed on poly-D-lysine-coated petri dishes to form the so-called "adherent" culture system. Results: Modiolus SPCs cultured under adherent conditions exhibited a significantly increased percentage of cells with the side population (SP) phenotype (18.6%) compared with cells cultured under conventional suspension culture conditions (0.8%). Even after repeated passages, modiolus SPCs cultured under adherent culture conditions preserved more SP phenotype cells. In comparison with the non-SP phenotype cells, the sorted SP cells exhibited more stem-like but less differentiated properties, with an upregulated expression of the ATP-binding cassette subfamily G member 2 (ABCG2), Nestin, Sox2, and Nanog proteins. Furthermore, Retinoic acid (RA) treatment confirmed the expression of the multipotent differentiation markers in the SP cells, including TUJ1, pancytokeratin, glial fibrillary acidic protein (GFAP), and p27(Kip1). Conclusion: Employment of an adherent culture system, instead of a suspension culture system, resulted in the enrichment of the SP cells from SPCs while retaining their stemness and multipotency. (C) 2013 Elsevier Ireland Ltd. All rights reserved.