As periostin is known to increase cell proliferation in ADPKD cyst epithelial cells [24], we estimated in vitro the physiological relevance of the periostin cleavage by MMP9 by quantifying the proliferation of IMCD-3 cell line, which do not produce MMP9 (S1A Fig). This evidence concerns the gene POSTN and autosomal dominant polycystic kidney disease.