Role Of SGC P2Y12 Receptor In Chronic Neuropathic Pain

Chronic neuropathic pain is hyperalgesia or allodynia caused by peripheral or central nerve injury.Studies have shown that non-nerve cells such as some glial cells are widely involved in the pathogenesis and development of neuropathic pain.P2Y12receptor is a metabotropic receptor that belongs to the Gi class of a group of G protein-coupled purinergic receptor family and is expressed by non-nerve cells that are closely related to the pain pathway,such as microglia and satellite glia cells.It has been known for years that mechanical allodynia was significantly reduced in the P2Y12 knockout mice with neuropathic pain model,comparing to that in wild-type（WT）control mice,suggesting that the P2Y12 receptor plays an important role in the pathogenesis and development of chronic neuropathic pain.However,the cell signaling mechanisms of neuropathic pain mediated by P2Y12 receptor is still unclear.In the central nervous system,P2Y12 receptor is highly expressed in microglia.A large number of studies have shown that microglia play an important role in promoting the formation of neuropathic pain.In peripheral ganglia,P2Y12 receptor is also expressed by satellite glial cells.Satellite glial cells tightly surrounding the neuronal somata,play a decisive role in the microenvironment of the neuronal soma,and participate in the regulation of pain signaling.So,in which type of cells does P2Y12 function and mediate the formation of neuropathic pain?In this study,P2Y12-flox transgenic mice were used,and L4 spinal nerve transection（SNT）was used as a model of chronic neuropathic pain.By observing pain behavior,post-model glial cell activation and changes in P2Y12 expression profiles after knockout P2Y12receptors in whole body,microglia,or satellite glial cells,respectively,we tried to figure out the cell signaling mechanisms of neuropathic pain mediated by P2Y12receptors.Experimental results showed that:1)In P2Y12^flox/flox;CX3CR1^Cre/+mice,which were obtained by crossing CX3CR1-Cre with P2Y12-flox mice,P2Y12 receptors were specifically deleted in microglia.However,the pain behavior of P2Y12^flox/flox;CX3CR1^Cre/+mice after SNT was not different from the WT mice.Meanwhile,there was also no difference for microglial activation in spinal dorsal horn on 7th day after SNT.This indicates that the P2Y12 receptors of microglia are not necessary for the formation of neuropathic pain.2)In P2Y12^flox/flox;Dhh ^Cre/+mice,which were obtained by crossing Dhh-Cre with P2Y12-flox mice,P2Y12 receptors were specifically deleted in satellite glial cells of dorsal root ganglia（DRG）.The P2Y12^flox/flox;Dhh ^Cre/+mice had a significantly higher paw withdrawal mechanical threshold on 3rd day after SNT than WT mice,but the threshold dropped to a level comparable to that of the WT mice on the 5-14 days thereafter.This suggests that P2Y12 receptors of satellite glial cells are involved in the early formation of neuropathic pain,but there are still other cell-derived P2Y12 receptors that play a role thereafter.3)By investigating the expression of P2Y12 receptor after SNT,we found that DRG macrophages that did not express P2Y12 receptor originally began to express the receptors in some cells,suggesting that the P2Y12 receptors from these cells may also play a role in the pathogenesis and development of neuropathic pain.In addition,knockout of the satellite glial P2Y12 receptors did not affect microglial activation of the spinal dorsal horn after SNT.The above results suggest that satellite glia P2Y12 receptors play a key role in the early stage of chronic neuropathic pain,and the activation of P2Y12 expression by macrophages may further promote the formation of neuropathic pain.