Figure 4. COL13A1 and COL15A1 knockdown induced senescence in hDPCs. (A) hDPCs (P5) were transfected with COL13A1 (siCOL13A1), COL15A1 (siCOL15A1), or control (siCont) siRNAs for 48 h, after which the amounts of COL13A1 (left) and COL15A1 (right) mRNA were determined by qRT-PCR. (B) Quantification and representative images of SA-β-gal-positive cells in control, COL13A1, and COL15A1 siRNA-treated hDPCs (P5). Scale bar, 200 μm. p16 (C) and p21 (D) mRNA expression by qRT-PCR after siRNA transfection for 48 h. (E) hDPCs (P4) were transfected with COL13A1- or COL15A1-specific siRNA for 24 h and then grown in 3D for another 24 h. Representative images for hDPC spheroids transfected with control, COL13A1, or COL15A1 siRNA. Scale bar, 200 μm. (F) Cell numbers after COL13A1 and COL15A1 siRNA transfection for 48 h. All quantitative data are shown as the mean ± SD of three independent experiments. *p < 0.05; **p < 0.01; ***p < 0.005. Asterisk indicates Student's t-test.