Epigenetic histone methylation modulates fibrotic gene expression

Area of Science:

• Nephrology
• Epigenetics
• Molecular Biology

Background:

• Transforming growth factor-beta 1 (TGF-β1) is crucial in chronic kidney disease pathogenesis, particularly diabetic nephropathy, by inducing extracellular matrix (ECM) gene expression.
• The precise mechanisms by which nuclear chromatin modulates TGF-β1-induced ECM gene expression remain incompletely understood.
• Epigenetic modifications, specifically histone H3 lysine methylation (H3Kme), are implicated but their role in this context requires elucidation.

Purpose of the Study:

• To investigate the role of epigenetic chromatin marks, particularly histone H3 lysine methylation (H3Kme), in mediating TGF-β1-induced extracellular matrix (ECM) gene expression.
• To examine these epigenetic changes in rat mesangial cells under both normal and high-glucose (HG) conditions.
• To identify key enzymes and their recruitment to gene promoters involved in these TGF-β1-driven epigenetic alterations.

Main Methods:

• Treatment of rat mesangial cells with TGF-β1 under normal and high-glucose (HG) conditions.
• Analysis of extracellular matrix (ECM) gene expression (CTGF, COL1A1, PAI-1) using quantitative methods.
• Chromatin immunoprecipitation (ChIP) assays to assess levels of specific histone H3 lysine methylation marks (H3K4me1/2/3, H3K9me2/3) and the methyltransferase SET7/9 at gene promoters.
• Gene silencing of SET7/9 using small interfering RNAs (siRNAs).
• Inhibition of TGF-β1 signaling using a TGF-β1 antibody.

Main Results:

• TGF-β1 significantly upregulated the expression of ECM genes, including connective tissue growth factor (CTGF), collagen-α1[Ι] (COL1A1), and plasminogen activator inhibitor-1 (PAI-1).
• These gene expression changes were associated with increased active epigenetic marks (H3K4me1, H3K4me2, H3K4me3) and decreased repressive marks (H3K9me2, H3K9me3) at the target gene promoters.
• TGF-β1 elevated the expression and promoter recruitment of the H3K4 methyltransferase SET7/9; SET7/9 silencing attenuated ECM gene induction, and TGF-β1 antibody blocked or reversed HG-induced changes.
• These findings demonstrate a functional role for H3Kme in TGF-β1-mediated ECM gene expression in mesangial cells.

Conclusions:

• Epigenetic chromatin modifications, specifically histone H3 lysine methylation, are critical mediators of TGF-β1-induced extracellular matrix (ECM) gene expression in rat mesangial cells.
• The methyltransferase SET7/9 plays a key role in these TGF-β1-driven epigenetic changes and subsequent ECM gene upregulation.
• Targeting and reversing these epigenetic modifications, particularly H3Kme, presents a potential therapeutic strategy for renoprotection in diabetic nephropathy.