Hypoxia-inducible factor-1α–mediated upregulation of CD99 promotes the proliferation of placental mesenchymal stem cells by regulating ERK1/2

Figure 4 Effect of CD99 expression on human placenta-derived mesenchymal stem cells proliferation under hypoxia. A: Proliferation of human placenta-derived mesenchymal stem cells (hP-MSCs) cultured under hypoxia after pretreatment with CD99-specific small interfering RNAs (siCD99#1). Data are means ± SD (n = 4); B: Cell cycle phase distribution of hP-MSCs cultured under hypoxia after pretreatment with siCD99#1 and assayed by flow cytometry; C: Graph of the cell cycle distribution. Data are means ± SD (n = 3); Student’s t-test; D: Western blotting of CD99, cyclin E1, cyclin A2, CDK2, and p21 in hP-MSCs cultured under hypoxia for 48 h after pretreatment with siCD99#1; E: Expression levels of CD99, cyclin E1, cyclin A2, CDK2, and p21 normalized against that of glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Data are means ± SD (n = 3). ^aP < 0.05 and ^bP < 0.01. NC: Negative control; OD: Optical density.