METTL3 Potentiates M2 Macrophage-Driven MMT to Aggravate Renal Allograft Fibrosis via the TGF-β1/Smad3 Pathway.

METTL3, a key enzyme in N6-methyladenosine (m6A) modification, plays a crucial role in the progression of renal fibrosis, particularly in chronic active renal allograft rejection (CAR). This study explored the mechanisms by which METTL3 promotes renal allograft fibrosis, focusing on its role in the macrophage-to-myofibroblast transition (MMT). Using a comprehensive experimental approach, including TGF-β1-induced MMT cell models, METTL3 conditional knockout (METTL3 KO) mice, and renal biopsy samples from patients with CAR, the study investigates the involvement of METTL3/Smad3 axis in driving MMT and renal fibrosis during the episodes of CAR. We found that elevated m6A modification and METTL3 levels strongly correlated with enhanced MMT and increased fibrotic severity. METTL3 knockout (METTL3 KO) significantly increased the m6A modification of Smad3, decreased Smad3 expression, and inhibited M2-driven MMT. Smad3 knockdown with siRNA (siSmad3) further inhibited M2-driven MMT, while Smad3 overexpression rescued the inhibitory effects of METTL3 silencing, restoring M2-driven MMT and fibrotic tissue damage. Additionally, the METTL3 inhibitor STM2457 effectively reversed M2-driven MMT and alleviated fibrotic tissue damage in CAR. These findings highlight that METTL3 enhances M2-driven MMT in renal fibrosis during CAR by promoting the TGF-β1/Smad3 axis, suggesting that METTL3 is a promising therapeutic target for mitigating renal fibrosis in CAR.