Integrins Regulate Mouse Embryonic Stem Cell Self-Renewal

¹ Department of Life Sciences (Biology), Graduate School of Arts and Sciences, The University of Tokyo, Tokyo 153-8902, Japan
² Department of Biochemistry and Molecular Biology, and Oral Health Research Center, Kanagawa Dental College, Yokosuka 253-8980, Japan
³ Department of Molecular Oral Medicine and Maxillofacial Surgery, Division of Frontier Medical Sciences, Graduate Science School of Biomedical Sciences, Hiroshima University, Hiroshima 734-8553, Japan
⁴ Department of Biological Science, Graduate School of Science, The University of Tokyo, Tokyo 153-8902, Japan
⁵ Mount Desert Island Biological Laboratory, Salisbury Cove, ME, 04672, USA
⁶ Department of Life Sciences (Biology), Graduate School of Arts and Sciences, and Department of Biological Science, Graduate School of Science, The University of Tokyo, Tokyo 153-8902, Japan; International Cooperative Research Project (ICORP)/Japan Science and Technology Agency (JST), Tokyo 153-8902, Japan

^* To whom correspondence should be addressed. E-mail: mihofuru{at}kdcnet.ac.jp.

	Abstract

Extracellular matrix (ECM) components regulate stem-cell behavior although the exact effects elicited in embryonic stem (ES) cells are poorly understood. We previously developed a simple, defined, serum-free culture medium that contains leukemia inhibitory factor (LIF) for propagating pluripotent mouse ES (mES) cells in the absence of feeder cells. In this study, we determined the effects of ECM components as culture substrata on mES cell self-renewal in this culture medium, comparing conventional culture conditions that contain serum and LIF with gelatin as a culture substratum. mES cells remained undifferentiated when cultured on Type I and IV collagen or poly-D-lysine. However, they differentiated when cultured on laminin or fibronectin as indicated by altered morphologies, the activity of alkaline phosphatase decreased, Fgf5 expression increased, and Nanog and SSEA1 expression decreased. Under these conditions, the activity of STAT3 and Akt/PKB, which maintain cell self-renewal, decreased. In contrast, the ERK1/2 activity, which negatively controls cell self-renewal, increased. In the defined conditions, mES cells did not express collagen-binding integrin subunits, but they expressed laminin- and fibronectin-binding integrin subunits. The expression of some collagen-binding integrin subunits was downregulated in a LIF concentration-dependent manner. Blocking the interactions between ECM and integrins inhibited this differentiation. Conversely, the stimulation of ECM–integrins interactions by overexpressing collagen-binding integrin subunits induced differentiation of mES cells cultured on Type I collagen. The results of the study indicated that inactivation of the integrin signaling is crucial in promoting mouse embryonic stem cell self-renewal.

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