JUN and renal fibrosis: TGF-β1 is the most important inducer of collagen synthesis and EMT and acts through the Smad signaling pathway.[24,25] TGF-β1 has been implicated in renal fibrosis due to its profibrotic properties and is commonly used to induce in vitro renal fibrosis models.[26,27]FOSL2, a protein of the Fos family, belongs to the AP1 transcription complex and may play a critical role in fibrotic diseases.[14] Thus, we investigated the regulatory role of FOSL2 in renal fibrosis in UUO mice and in TGF-β1–treated HK-2 cells.