Diacylglycerol Kinase Inhibition Reduces Airway Contraction by Negative Feedback Regulation of Gq-signaling.

Exaggerated airway smooth muscle (ASM) contraction regulated by the Gq family of G protein-coupled receptors (GPCRs) causes airway hyperresponsiveness (AHR) in asthma. Activation of Gq-coupled GPCRs leads to phospholipase C (PLC)-mediated generation of inositol triphosphate (IP3) and diacylglycerol (DAG). DAG signaling is terminated by the action of DAG kinase (DGK) that converts DAG into phosphatidic acid (PA). Our previous study demonstrated that DGKα and ζ isoform knockout mice are protected from the development of allergen-induced AHR. Here we aimed at determining the mechanism by which DGK regulates ASM contraction. Activity of DGK isoforms was inhibited in human ASM cells by siRNA-mediated knockdown of DGKα and ζwhile pharmacological inhibition was achieved by pan DGK inhibitor I (R59022). Effects of DGK inhibition on contractile agonist-induced activation of PLC and myosin light chain (MLC) kinase, elevation of IP3, and calcium levels were assessed. Further, we employed human precision-cut lung slices and assessed the role of DGK in agonist-induced bronchoconstriction. DGK inhibitor I attenuated histamine- and methacholine-induced bronchoconstriction. DGKα and ζ knockdown or pre-treatment with DGK inhibitor I resulted in attenuated agonist-induced phosphorylation of MLC and myosin light chain phosphatase in ASM cells. Further, DGK inhibition decreased Gq agonist-induced calcium elevation, generation of IP3, and increased histamine-induced production of PA. Finally, DGK inhibition or treatment with DAG analog resulted in attenuation of activation of PLC in human ASM cells. Our findings suggest that DGK inhibition perturbed the DAG:PA ratio resulting in inhibition of Gq-PLC activation in a negative feedback manner, resulting in protection against ASM contraction.