We also confirmed that both the expression and secretion of the MMP1 protein, as analyzed by Western blotting analysis and enzyme-linked immunosorbent assay (ELISA), respectively, were significantly higher in endothelia from ADPKD-iPSCs derived from patients with ICAs compared with those from patients without ICAs (P = 0.029 for protein expression and P = 0.043 for secretion; Fig. 5b–d). This evidence concerns the gene MMP1 and autosomal dominant polycystic kidney disease.