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Hyaluronan Elevates Cell Cycle Regulators P130, E2F4, and P27kip1 in Dormant Human Mesenchymal Stem Cells to Regulate Cell Quiescence

Meei-Ru Lin, Tzyy Yue Wong, Chun-Hsien Wu and Lynn LH Huang

Quiescence conserves the properties of stem cells whilst they are dormant. The mechanisms associated with dormancy involve various cell regulators. Here, the effects of hyaluronan (HA; a polysaccharide associated with the extracellular matrix), on the mesenchymal stem cell cycle and the involvement of p130 and E2F family proteins in mesenchymal stem cell cycle regulation, were evaluated. Placenta-derived mesenchymal stem cells (PDMSCs) were cultured on either a normal tissue culture surface (TCS) or a surface coated with HA. Cell population percentages at the G0/G1, S, and G2/M phases were analyzed 36, 40, 44, 48, and 50 h post-seeding using flow cytometry. At 36 h, HA-treated cells had more PDMSCs in the G0/G1 phase (61.59% versus 43.61% in the TCS group). At and 48 and 50 h for the HA and TCS groups, respectively, PDMSCs had highly similar population distributions in cell cycle phases; thus, these cells were used to study cell cycle regulators. Pocket proteins (p130, p107, and pRb), E2F family proteins (E2F3, E2F4, and E2F5), using sand the binding of p130 to E2F4 and DP1 were analyzed with western blots and coimmunoprecipitation. The HA group at 48 h exhibited increased p130 and E2F4 protein expression compared with the TCS group at 50 h (4.3-fold and 1.5-fold, respectively), and the binding of p130 to E2F4 and DP1 was detected 36, 48, and 50 h post-seeding. In this studyHence, a the HA-regulated formation of a p130/E2F4 complex was observed in PDMSCs, which provides to suggests that the mesenchymal stem cell cycle is regulated by HA as an extracellular matrix.