CRITICAL SIGNALING EVENTS IN THE MECHANOACTIVATION OF HUMAN MAST CELLS VIA P.C492Y-ADGRE2.

A role for the adhesion G-protein coupled receptor ADGRE2 (EMR2) in mechanosensing was revealed by the finding of a missense substitution (p.C492Y) associated with familial vibratory urticaria (VU). In these patients, friction of the skin induces mast cell hyper-degranulation through p.C492Y-ADGRE2, causing localized hives, flushing and hypotension. We have now characterized the responses and intracellular signals elicited by mechanical activation in human mast cells expressing p.C492Y-ADGRE2 and attached to dermatan sulfate, a ligand for ADGRE2. The presence of p.C492Y-ADGRE2 reduced the threshold to activation and increased the extent of degranulation along with the percentage of mast cells responding. Vibration caused PLC activation, transient increases in cytosolic calcium, and downstream activation of PI3K and ERK1/2 by Gbetagamma, Galphaq/11 and Galphai/o-independent mechanisms. Degranulation induced by vibration was dependent on PLC pathways, including calcium, PKC and PI3K but not ERK1/2 pathways, along with pertussis toxin (PTX)-sensitive signals. In addition, mechanoactivation of mast cells stimulated the synthesis and release of PGD2, a previously unreported mediator in VU, and ERK1/2 activation was required for this response together with calcium, PKC and, to some extent, PI3K. Our studies thus identify critical molecular events initiated by mechanical forces and potential therapeutic targets for patients with VU.