Adenosine A1 receptor activation attenuates neuropathic pain by suppressing microglial ERK/NF-κB-mediated...

Neuropathic pain (NP) is tightly linked to neuroinflammation driven by aberrant activation of spinal microglia; however, the endogenous regulatory mechanisms that limit excessive microglial responses following nerve injury remain incompletely understood. Adenosine (ADO) is widely recognized as a homeostatic mediator released under conditions of tissue damage and stress, and activation of the adenosine A1 receptor (A1R) has been reported to exert antinociceptive effects at both spinal and peripheral levels. Nevertheless, the potential role of A1R as an endogenous modulator of microglial activation in NP, as well as the underlying signaling mechanisms, remains poorly defined. In this study, we found that A1R expression was markedly increased in spinal microglia after nerve injury. Notably, ATPγS-mediated damage-associated molecular pattern (DAMP) stimulation, but not lipopolysaccharide (LPS)-mediated inflammatory stimulation, increased microglial A1R expression. Pharmacological activation of A1R reversed the pro-inflammatory phenotypic shift of microglia and suppressed their excessive proliferation, resulting in significant attenuation of NP behaviors across different injury models. Mechanistically, A1R activation inhibited extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation in microglia, thereby preventing activation and nuclear translocation of the nuclear factor-κB (NF-κB) p65 subunit, reducing the release of pro-inflammatory cytokines (PICs) and alleviating the neuroinflammatory microenvironment in the spinal dorsal horn. Taken together, our findings suggest that injury-associated upregulation of microglial A1R may act as a negative feedback mechanism that restrains microglial activation and neuroinflammation via the ERK/NF-κB signaling axis, providing mechanistic insight into endogenous neuroimmune regulation following nerve injury.