Altered DNA‐Damage/BRD4 Signaling Pathways in the Lungs of Patients with Pulmonary Hypertension Can Propagate to the Coronary Vasculature and Induce Coronary Artery Disease
Authors: Meloche Jolyane , Nadeau Valerie , Tremblay Eve , Potus Francois , Chabot Sophie , Charbonneau Eric , Provencher Steeve , Bonnet Sebastien 
Published: November 2023

BackgroundPulmonary arterial hypertension (PAH) is a devastating vasculopathy. Recent progress in understanding its pathogenesis led to an increase in patients’ quality of life. With ageing, PAH patients now develop comorbidities including coronary artery diseases (CAD), further challenging their therapeutic management. Interestingly, studies reported that CAD prevalence in PAH is 4 times higher (28.4%) compared to the global population (7.3%), suggesting a predisposition of the PAH population to develop CAD. We thus speculated that the activation of pathophysiological pathways in PAH contribute to CAD development in these patients. In both CAD and PAH, the inflammatory dependent pro‐proliferative/anti‐apoptotic phenotype of vascular smooth muscle cells (SMCs) is, at least in part, attributable to cytokines‐dependent activation of DNA damage signaling pathways including the epigenetic reader Bromodomain‐containing protein 4 (BRD4). We hypothesized that sustained DNA damage‐dependent BRD4 activation in the lungs of PAH patients contributes to CAD development by promoting coronary VSMC proliferation and resistance to apoptosis through a similar pathophysiological pathwayMethods and ResultsWe demonstrated in distal pulmonary arteries of PAH patients a significant increase in both DNA damage and BRD4 expression. Interestingly, coronary arteries from PAH patients, even without CAD, also exhibit increased BRD4 levels and enhanced DNA damage to a level comparable to the one observed in coronary arteries from CAD patients with no PAH (n=10–15, p<0.05). At the cellular levels, this phenotype is also observed in coronary artery SMCs (CoASMCs) of PAH and CAD patients compared to control CoASMCs (n=5, p<0.05). Proliferation (Ki67) and apoptosis (AnnexinV) assays revealed that, similarly to CAD patients’ CoASMCs (with no PAH), CoASMCs isolated from PAH patients are more proliferative (n=4, p<0.05) and resistant to apoptosis (n=4, p<0.05) in a BRD4‐dependent manner, as JQ1 (a BRD4 inhibitor) reverses this phenotype (n=4 p<0.05). Finally, we provide evidence that PAH‐CoASMCs are sensitive to TNF and IL‐6, as these cytokines further increase DNA damage (g‐H2AX) and BRD4 expression, thus promoting the proliferation/apoptosis imbalance, which may consequently lead to CAD. Interestingly, in vivo models of PAH also exhibit increased coronary artery remodeling and this process seems to be subsequent to PAH development. In a carotid injury model in MCT‐induced PAH rats, we demonstrated that BRD4 inhibition decreases neointima formation (n=4).ConclusionComorbidities in PAH such as CAD has become a major clinical problem. Thus, targeting mechanisms implicated in both PAH and subsequent comorbidities is warranted. To this aim, we propose that BRD4 represents an attractive target and since BRD4 inhibitors are presently in clinical trials further potentiates its use in PAH.Support or Funding InformationA “Fonds de recherche Québec‐Santé” scholarship to Jolyane Meloche and Canadian Institutes of Health Research grants to Dr. Bonnet supported this work.