WNK2 and lupus nephritis: Since excessive activation of the transforming growth factor (TGF)-β1-mediated MAPK (mitogen-activated protein kinases) signaling pathway is involved in lupus nephritis development in both human and mouse [29, 30], we examined whether the HGC-TAC treatment-induced renoprotection observed in lupus nephritis mice is dependent on the TGF-β1/MAPK signaling pathway.