SPP1 and chronic kidney disease: Although vascular calcification was undetectable in these CKD mice at the histological level, expression levels of markers for vascular calcification such as osteopontin, but not runt-related transcription factor-2 (Runx2) and osteocalcin, were increased in aorta both in wild-type CKD mice and Fgf21−/− CKD mice to the similar extent (Fig. 1g–i).