Characterisation of human airway smooth muscle cell lysophosphatidic acid receptors in asthma and health

Lysophosphatidic acid (LPA) is a major serum phospholipid and bioactive lipid mediator that exerts a broad range of effects through its family of cognate G protein-coupled receptors via coupling to multiple G proteins and can affect a variety of cellular functions in a range of tissues and cell-types. LPA is known to affect airway function and a growing body of evidence suggests a role for LPA receptor function in the molecular aetiology of asthma. The aims of this project were to characterise the function of LPA and its receptors in cultured human airway smooth muscle (hASM) cells from asthmatic and control donors. Expression of a broad range of genes related to LPA metabolism/signalling and inflammatory signalling were analysed using both traditional and high throughput RT-qPCR methods. Decreased expression of the genes for a phosphodiesterase, PDE4B, and an LPA metabolising enzyme, LPP2, was detected in hASM cells derived from asthmatic patients compared to control donors. Investigation of LPA receptor pharmacology using a [[superscript 35]S]GTPγS binding assay in a model cell-line showed that LPA species with a range of fatty acid tail lengths and degrees of saturation were active at LPA receptors with varying potencies. LPA exhibited complex modulation of forskolin and isoprenaline induced cAMP responses in hASM cells. Though no differences in the effects of LPA treatment were observed in the two disease-states studied, hASM cells from asthmatics exhibited a significantly higher magnitude of cAMP response compared with those from control donors, which could indicate dysfunctional adenylyl cyclase or PDE activity in disease. These findings confirm that LPA is able to affect hASM cell function in ways pertinent to asthma's pathophysiology, but do not indicate altered LPA receptor expression or function in disease.