In in vitro experiments with cultured mouse mesangial cells, the TZDs, rosiglitazone and pioglitazone, but not insulin, decreased AngII-induced OPN expression, while recombinant OPN upregulated TGF-β, ERK/MAPK, and JNK/MAPK signaling, which have been shown to be involved in the pathology of DKD. Here, MAPK8 is linked to diabetic kidney disease.