MAPK8 and liver dysplastic nodule: In cultured mouse mesangial cells, the TZDs but not insulin, decreased angiotensin II-induced OPN expression, while recombinant OPN upregulated TGF-β, ERK/mitogen-activated protein kinases (MAPK), and Jun N-terminal kinase (JNK)/MAPK signaling, which have been shown to be involved in the pathology of DN.