Methionine Restriction Alleviates Kidney Fibrosis through Epigenetic Repression of the TGF-ß/Smad3/Hoxc8/P-TEFb Axis
Renal fibrosis is a hallmark of chronic kidney diseases (CKDs) and a key driver of disease progression. While low-protein diets have been shown to alleviate fibrosis and slow CKD progression, the specific amino acids responsible for these effects remain unclear, and such diets often lead to malnutrition due to the restriction of essential amino acids. In this study, we evaluated 15 amino acid-restricted diets in a unilateral ureteral obstruction (UUO) mouse model and found that methionine restriction (MetR) most effectively reduced renal fibrosis. We further confirmed the efficacy of MetR in alleviating renal fibrosis in the folic acid nephropathy (FAN) mouse model. Mechanistically, we identified Hoxc8 as a key transcription factor responsive to MetR, mediating TGF-ß-induced fibrotic gene expression. Our findings suggest that TGF-ß-Smad3 signaling activates Hoxc8 during myofibroblast activation, initiating a self-reinforcing feedback loop through Hoxc8 self-activation. Using affinity purification-mass spectrometry, we discovered that Hoxc8 interacts with P-TEFb transcription elongation complex to enhance the expression of fibrotic genes. MetR suppresses Hoxc8 expression by reducing histone modifications, specifically H3K4me3 and H3K36me3, thereby inhibiting the TGF-ß/Smad3/Hoxc8/P-TEFb axis and downregulating fibrosis-related gene expression. Notably, elevated HOXC8 expression was observed in CKD patients with kidney fibrosis, while fibroblast-specific Hoxc8 knockout mice demonstrated significantly reduced fibrosis following UUO surgery. These findings establish the TGF-ß/Smad3/Hoxc8/P-TEFb axis as a crucial regulator of fibrosis and highlight MetR as a promising therapeutic strategy for the treatment of renal fibrosis. Overall design: NRK-49F cellls were treated with TGF-ß  and/or methionine restriction, siHoxc8.