SPP1 and chronic kidney disease: Furthermore, transcripts encoding kidney injury biomarkers Lcn2 (protein; Ngal) and Spp1 (protein; osteopontin (OPN)) (Viau et al. 2010, Kaleta 2019), as well as Fgf23, were increased in CKD mice, whereas Slc34a1 (protein; NaPi-2a) expression was decreased (Supplementary Fig. 3A).