Increased P2 purinergic signalling in circulating monocytes of patients with progressive pulmonary fibrosis

Background: Idiopathic pulmonary fibrosis (IPF) and other forms of progressive pulmonary fibrosis (PPF) are interstitial lung diseases (ILD) with unknown aetiology and poor prognosis. The P2 receptor family, including G protein-coupled receptors (P2Y) and ATP-gated ion channels (P2X), are upregulated in ILD, although their role remains unclear. We hypothesised that dysregulated P2 receptor expression of resident pulmonary immune cells and circulating monocytes triggers inflammatory mechanisms, resulting in fibrosis. Methods: Blood samples and bronchoalveolar lavage (BAL) were collected from patients with PPF and healthy individuals. ATP levels in plasma and BAL were measured via bioluminescence. Gene expression was assessed by RT-qPCR. IL-1? was quantified by ELISA. Results: Elevated ATP levels were recorded in plasma (p=<0.0001) and BAL (p=0.0015) of PPF patients (n=12). Increased mRNA expression of P2X4R (p=0.0001), P2X7R (p=0.016), P2Y4R (p=0.03), P2Y6R (p=0.0008), P2Y12R (p=0.0005) and P2Y13R (p=0.004) were detected in PPF monocytes. Increased IL-1? levels in plasma and BAL correlated significantly with ATP levels (p=0.02 and p=0.005, respectively). ATP stimulated PPF monocytes released increased cytokines, an effect reduced by P2X4 and P2X7 inhibitors. Conclusion: P2 purinergic signalling is implicated in PPF, with ATP activation of monocyte P2X4 and P2X7 receptors a driver of inflammation. These findings provide insights into the role of circulating immune cells in the pathogenesis of PPF and suggest novel targets for therapeutic intervention.