Among the most prominently reduced CI subunits validated in a series of quantitative RT-PCR experiments (Fig. 1e and Extended Data Fig. 1c–e), we focused on Ndufs4, an accessory 18 kDa subunit of the CI, for further analysis since its mRNA and protein levels were consistently reduced not only in podocytes of type 1 (Ins2Akita/+) and type 2 (Leprdb/db) diabetic mouse models but also in glomeruli of subjects with DKD (Fig. 1e–g and Extended Data Fig. 1c–e). Here, NDUFS4 is linked to diabetic kidney disease.