Epigenetic BET inhibitor apabetalone counters inflammatory and fibrotic processes in activated cardiac fibroblasts providing insight into reduced hospitalizations for heart failure in BETonMACE trial

Abstract Background After myocardial infarction (MI), sustained crosstalk between monocytes and cardiac fibroblasts (CFs) promotes chronic inflammation and interstitial fibrosis that can contribute to heart failure (HF). Resident and myocardium-infiltrating immune cells produce proinflammatory cytokines IL-1β and TNFα that stimulate CFs to produce monocyte chemoattractants. Monocytes secrete TGF-β1 that transforms CFs into contractile myofibroblasts overproducing the extracellular matrix (ECM) responsible for cardiac fibrosis. Epigenetic BET inhibitors (BETi) reduce CF transdifferentiation to prevent cardiac fibrosis and HF in animal models. In patients with cardiovascular disease, type 2 diabetes and recent MI, administration of the BETi apabetalone (APA) resulted in less hospitalization due to HF vs. placebo (BETonMACE phase 3 trial; hazard ratio 0.59, p=0.03). Purpose To examine APA’s in vitro effects on inflammatory and profibrotic processes in CFs associated with cardiac fibrosis and HF. Methods Immortalized and primary human CFs were stimulated with cytokines (10ng/mL IL-1β, TNFα, TGF-β1) or with conditioned media from 10ng/mL IFNγ and 100ng/mL lipopolysaccharide-treated THP-1 macrophages ± 5μM APA on plastic or in 3D collagen gels. Gene expression was analyzed by PCR, protein levels by FACS or ELISA, collagen deposition with picrosirius red, THP-1 monocyte migration in Boyden chambers, and CF contraction with 3D collagen gels. Results IL-1β or TNFα stimulation of CFs upregulated monocyte chemoattractant 1 (CCL2) and vascular cell adhesion protein 1 (VCAM1) expression, promoting THP-1 cell migration and adhesion to CFs. APA treatment reduced cytokine-induced CCL2 (>20%) and VCAM1 (>70%) gene expression as well as THP-1 cell migration and adhesion to stimulated CFs (>60%). TGF-β1 treatment induced CF transdifferentiation into myofibroblasts as shown by increased expression of α smooth muscle actin (α-SMA) protein, and secretion of ECM proteins fibronectin and periostin. APA treatment reduced myofibroblast mRNA and protein expression of α-SMA (~30%), fibronectin (~30%) and periostin (97%). Myofibroblast-mediated collagen deposition was also reduced by APA by ~20%. α-SMA-dependent CF contraction can be visualized in attached 3D collagen gels. TGF-β1, IL-1β, TNFα or macrophage-conditioned media promoted CF-mediated gel contraction by 2.5, 1.4, 2.1, or 1.8-fold, respectively. APA treatment countered gel contraction by 30-60%, thereby reducing the myofibroblast-like behaviour in organotypic cultures. Conclusions In vitro, APA treatment reduced proinflammatory crosstalk between monocytes and CFs, resulting in less monocyte migration, monocyte - CF adhesion and CF contraction. APA also reduced signaling by TGF-β1, thus reducing profibrotic and contractile behaviour of CFs responsible for cardiac fibrosis. Since fibrosis contributes to HF, this data provides insight into the observed reduction in hospitalization due to HF in the BETonMACE trial.