Effect of GPR4 inhibition in a murine tobacco smoke model of chronic obstructive pulmonary disease

Puneeta Nath, Christopher Stevenson, Mark Freeman, Chris Poll, Katharine Banner, Thomas Suply, Alexandre Triffilief, Carol Jones

Novartis, Horsham, UK

GPR4 is a de-orphanised G-protein coupled receptor (GPCR), highly expressed on lung tissue (Yang et al 2007), that belongs to a novel family of pH sensing GPCRs and is activated by the interaction of protons with histidine residues situated at the extracellular surface of the receptor (Ludwig et al 2003). Recently, airway pH has been shown to be significantly reduced in chronic obstructive pulmonary disease (COPD) and has been correlated with increased inflammatory cell numbers (Kostikas et al 2002). To examine the role of GPR4 in COPD, we investigated the effect of GPR4 gene deletion using GPR4-/- mice in a tobacco smoke exposure model. Male and female GPR4-/- and Balb/c wild-type mice, weighing 20-26g, were exposed to 5 x 1R3F cigarettes per day, for either three days, two weeks or six months (n=6/8 mice per group). Forty Eight hours following three days smoke exposure there was a significant increase in bronchoalveolar lavage (BAL) fluid neutrophils in both wild-type and GPR4-/- mice compared to sham controls (29.3±4.4 versus 0.3±0.1 x 104 cells ml-1; P<0.001 and 15.4±2.6 versus 0.8±0.6 x 104 cells ml-1; P<0.001 respectively). Resolution of airway inflammation was accelerated in GPR4-/- mice compared to wild-type mice as observed by a significant reduction in BAL fluid neutrophils at 72 hours following smoke exposure (5.1±1.3 versus 15.2±3.4 x 104 cells ml-1; P<0.05 respectively). In the two weeks smoke exposure model a significant reduction in BAL cell neutrophils was observed in GPR4-/- mice compared to wild-type mice at 24 hours following smoke exposure (6.5±0.8 versus 12.7±1.9 x 104 cells ml-1; P<0.01 respectively ). A similar trend was observed in the six month smoke exposure model with BAL cell neutrophils significantly reduced in GPR4-/- mice compared to wild-type mice at two weeks following the last smoke exposure (3.0±0.7 versus 6.2±0.9 x 104 cells ml-1; P<0.05). Taken together this data suggests that depleting GPR4 signalling enhances neutrophil resolution in a tobacco smoke induced model of airway inflammation and thus GPR4 may represent a novel therapeutic anti-inflammatory target for COPD.

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