Pharmacological Targeting of BET Bromodomains Inhibits Lens Fibrosis via Downregulation of MYC Expression.

Purpose: Lens fibrosis involves aberrant growth, migration, and transforming growth factorβ (TGFβ)-induced epithelial-mesenchymal transition (EMT) of lens epithelial cells (LECs). In this study, we investigated the role of the bromo- and extra-terminal domain (BET) inhibitor in lens fibrotic disorder to identify drug-based therapies.
Methods: Rat lens explants, rabbit primary lens epithelial cells (rLECs), human lens explants and human SRA01/04 cells were treated with TGFβ2 in the presence or absence of the BET bromodomain inhibitor JQ1 or the MYC inhibitor 10058-F4. Proliferation was determined by MTS assay. Cell migration was measured by wound healing and transwell assays. The expression levels of fibronectin (FN), α-smooth muscle actin (α-SMA), E-cadherin, and phosphorylated downstream Smads were analyzed by Western blot, qRT-PCR, and immunocytochemical experiments. Transcriptome analysis was conducted to explore the molecular mechanism.
Results: Blockage of BET bromodomains with JQ1 significantly suppressed rLECs proliferation by inducing G1 cell cycle arrest. Furthermore, JQ1 attenuated TGFβ2-dependent upregulation of mesenchymal gene expression and phosphorylation of Smad2/3 during the progression of EMT, whereas E-cadherin expression was preserved. JQ1 repressed MYC expression, which was dose- and time-dependently upregulated by TGFβ2. Inhibiting MYC with either the small-molecule inhibitor 10058-F4 or genetic knockdown phenocopied the effects of JQ1 treatment. MYC overexpression partially reversed the JQ1-regulated EMT-related alteration of gene expression. Both JQ1 and 10058-F4 blocked the expression of TGFβ receptor II and integrin αv in rLECs and abolished TGFβ2-induced opacification and subcapsular plaque formation in rat lens explants.
Conclusions: Our results demonstrate the antifibrotic role of JQ1 in maintaining the epithelial characteristics of LECs and blocking TGFβ2-induced EMT, possibly by downregulating MYC, thereby providing new avenues for treating lens fibrosis.