The role of src kinases in controlling neutrophil function in acute inflammation

Abstract

The src family kinases are key cellular regulators of acute neutrophilic inflammation. When uncontrolled, this causes numerous inflammatory disorders, including the acute respiratory distress syndrome (ARDS). This is associated with an unacceptably high 90-day mortality and prolonged hospital admissions. ARDS currently has no effective pharmacological treatment. The work contained in this thesis aimed to characterise the anti-inflammatory, pro-resolutionary effects of src kinase inhibition on various neutrophil functions, using novel in vitro and in vivo models of acute inflammation and resolution. Results show that the src kinase inhibitors, PP1 and dasatinib, attenuate in vitro neutrophil extracellular degranulation in response to stimulation with formylated peptide, lipopolysaccharide and live bacteria. They also exert additional effects on integrin-dependent neutrophil functions, but have no effect on neutrophil fate or bacterial killing efficiency. Src kinase inhibition of neutrophils also attenuates in vitro epithelial cell damage and promotes a pro-resolutionary environment, with improved macrophage efferocytosis of apoptotic neutrophils, by inhibiting the release of an unidentified soluble factor believed to be a product of neutrophil degranulation. Extending these findings to in vivo murine models of bacteria- and acid-induced experimental lung inflammation, dasatinib exerts an inhibitory effect on markers of neutrophil degranulation in each model, at doses of 1mg/kg and 5mg/kg, respectively. At 10mg/kg, a detrimental effect is observed, as evidenced by reduced bacterial clearance, increased alveolar leak and extrapulmonary toxicity in the infection model and increased neutrophil influx, degranulation and alveolar haemorrhage in the acid model. These findings highlight a possible therapeutic role of src kinase inhibition in inflammatory conditions driven by neutrophil influx and degranulation that is worthy of further study in other models of lung inflammation. Future work should focus on developing more specific inhibitors to offer selective control over neutrophil granule processing, and careful dosing to avoid undesired effects on bacterial killing mechanisms.