TGFβ-induced fibroblast activation requires persistent and targeted HDAC-mediated gene repression.

Tissue fibrosis is a chronic disease driven by persistent fibroblast activation that has recently been linked to epigenetic modifications. Here, we screened a small library of epigenetic small-molecule modulators to identify compounds capable of inhibiting or reversing TGFβ-mediated fibroblast activation. We identified pracinostat, an HDAC inhibitor, as a potent attenuator of lung fibroblast activation and confirmed its efficacy in patient-derived fibroblasts isolated from fibrotic lung tissue. Mechanistically, we found that HDAC-dependent transcriptional repression was an early and essential event in TGFβ-mediated fibroblast activation. Treatment of lung fibroblasts with pracinostat broadly attenuated TGFβ-mediated epigenetic repression and promoted fibroblast quiescence. We confirmed a specific role for HDAC-dependent histone deacetylation in the promoter region of the anti-fibrotic gene PPARGC1A (PGC1α) in response to TGFβ stimulation. Finally, we identified HDAC7 as a key factor whose siRNA-mediated knockdown attenuates fibroblast activation without altering global histone acetylation. Together, these results provide novel mechanistic insight into the essential role HDACs play in TGFβ-mediated fibroblast activation via targeted gene repression.