Col1a1

Western blot analysis was performed as described previously^{35 (link)}. The primary antibodies used in western blot were: Kindlin-2 (Proteintech, 1:1000 dilution), Fibronectin(FN) (Proteintech, 1:1000 dilution), Col1A1 (Boster, 1:400 dilution), α-SMA (Abcam, 1:100 dilution), Smad2/3 (Cell Signaling Technology, 1:1000 dilution), p-Smad2 (Cell Signaling Technology, 1:1000 dilution), p-Smad3 (Cell Signaling Technology, 1:1000 dilution), GAPDH (Abacm, 1:3000 dilution), β-actin (Abacm, 1:3000 dilution), and tubulin (Abcam, 1:3000 dilution). Detection was performed using a chemiluminescent substrate system (Bio-Rad). The gray values were analyzed with ImageJ software.

When the P1 cells reached 100% confluence, cells were fixed with 4% formaldehyde for 30 min and then washed in PBS three times for 5 min each. The fixed cells were then permeabilized with 0.2% Triton X-100 (Solarbio, Beijing, China) for 15 min and then blocked with normal goat serum (Solarbio, Beijing, China) for 30 min at 37°C. After blocking, the cells were incubated with a primary antibody against collagen type I alpha 1 (COL1A1; Boster, Wuhan, China) overnight at 4°C. Afterwards, the cells were then incubated with a DyLight-488 labeled goat-anti-rabbit IgG secondary antibody (Boster, Wuhan, China) for 1 h at 37°C. The cell nuclei were visualized using 4′,6-diamidino-2-phenylindole (DAPI) staining solution (Beyotime, Shanghai, China). Finally, images were captured with a fluorescence microscope (Leica, Wetzlar, Germany) by randomly selecting five fields. The COL1A1-positive cells showed green fluorescence. As for the cell purity, the percentage of COL1A1-positive cells was calculated as (number of COL1A1-positive cells)/(total number of cells in the field) × 100%.