Extracellular ATP and cAMP signaling promote Piezo2‐dependent mechanical allodynia after trigeminal nerve compression injury

Trigeminal neuralgia (TN) is a type of severe paroxysmal neuropathic pain commonly triggered by mild mechanical stimulation in the orofacial area. Piezo2, a mechanically gated ion channel that mediates tactile allodynia in neuropathic pain, can be potentiated by a cyclic adenosine monophosphate (cAMP)‐dependent signaling pathway that involves the exchange protein directly activated by cAMP 1 (Epac1). To study whether Piezo2‐mediated mechanotransduction contributes to peripheral sensitization in a rat model of TN after trigeminal nerve compression injury, the expression of Piezo2 and activation of cAMP signal‐related molecules in the trigeminal ganglion (TG) were detected. Changes in purinergic P2 receptors in the TG were also studied by RNA‐seq. The expression of Piezo2, cAMP, and Epac1 in the TG of the TN animals increased after chronic compression of the trigeminal nerve root (CCT) for 21 days, but Piezo2 knockdown by shRNA in the TG attenuated orofacial mechanical allodynia. Purinergic P2 receptors P2X4, P2X7, P2Y1, and P2Y2 were significantly up‐regulated after CCT injury. In vitro, Piezo2 expression in TG neurons was significantly increased by exogenous adenosine 5'‐triphosphate (ATP) and Ca2+ ionophore ionomycin. ATP pre‐treated TG neurons displayed elevated [Ca2+]i and faster increase in responding to blockage of Na+/Ca2+ exchanger by KB‐R7943. Furthermore, mechanical stimulation of cultured TG neurons led to sustained elevation in [Ca2+]i in ATP pre‐treated TG neurons, which is much less in naïve TG neurons, or is significantly reduced by Piezo2 inhibitor GsMTx4. These results indicated a pivotal role of Piezo2 in peripheral mechanical allodynia in the rat CCT model. Extracellular ATP, Ca2+ influx, and the cAMP‐to‐Epac1 signaling pathway synergistically contribute to the pathogenesis and the persistence of mechanical allodynia. Chronic compression of the trigeminal nerve root (CCT) increases extracellular ATP level in trigeminal root entry zone (TREZ) and triggers Ca2+ influx into trigeminal ganglion (TG) neurons, stimulating Piezo2 expression along with the expression of multiple P2 receptors. ATP and its metabolite adenosine increase cAMP and exchange protein directly activated by cAMP 1 (Epac1) signaling, promoting the sensitization of Piezo2 channels. Ca2+‐stimulated Piezo2 expression and Piezo2‐mediated Ca2+ influx form a positive feedback loop, together with another likely positive feedback loop between ATP‐induced Ca2+ influx and Ca2+‐induce