Cannabinoid CB2 receptor controls chronic itch by regulating spinal microglial activation and synaptic transmission.

Chronic itch is a devastating clinical condition, and its central mechanisms remain poorly understood. We reported that spinal cannabinoid receptor type 2 (CB2R) activation exerts antipruritic effects and that itch escalates in mice lacking Cnr2 in mouse models of dermatitis and psoriasis. In the spinal cord, CB2R is mainly expressed in microglia, and microglial ablation or inhibition attenuated chronic itch, suggesting that microglial activation contributes to chronic itch. Particularly, conditional Cnr2 deletion in microglia also exacerbated chronic itch in mice. Single-cell RNA sequencing and molecular mechanistic studies suggest that CB2R activation reprogrammed microglia by inducing anti-inflammatory suppressor of cytokine signaling 3 (SOCS3) and reducing itch-related p38 and signal transducer and activator of transcription 1 (STAT1) phosphorylation. Finally, CB2R activation suppressed neuronal excitability and synaptic transmission in gastrin-releasing peptide (GRP)/GRP receptor (GRPR) interneurons and ascending projection neurons by inhibiting microglia-derived cytokines. These findings demonstrate that microglial activation contributes to chronic itch, while CB2R activation in microglia alleviates chronic itch via neuro-immune interactions.