EPO and chronic kidney disease: In CKD, renal EPO-producing (REP) fibroblasts, but not fibroblasts derived from injured tubular epithelial cells through epithelial-mesenchymal transition, transdifferentiate into myofibroblasts and predominantly contribute to fibrosis, with concomitant disruption of hypoxia-PHD-HIFa (HPH) signaling, resulting in loss of EPO production (Asada et al. 2011; Kobayashi et al. 2022).