Ca²⁺-binding protein NECAB2 facilitates inflammatory pain hypersensitivity

Painful signals are transmitted by mutisynaptic glutamatergic pathways. Their first synapse between primary nociceptors and excitatory spinal interneurons gates sensory load. Glutamate release herein is orchestrated by Ca²⁺ sensor proteins with neuronal calcium-binding protein 2 (NECAB2) being particularly abundant. However, neither the importance of NECAB2⁺ neuronal contingents in dorsal root ganglia (DRG) and spinal cord nor function-determination by NECAB2 has been defined. A combination of histochemistry and single-cell RNA-seq showed NECAB2 in small/medium-sized C- and Aδ D-hair low threshold mechanoreceptors in DRG, as well as in protein kinase γ-positive excitatory spinal interneurons. NECAB2 was downregulated by peripheral nerve injury, offering the hypothesis that NECAB2 loss-of-funtion could limit pain sensation. Indeed, Necab2^–/– mice reached a pain-free state significantly faster after peripheral inflammation than wild-type littermates. Genetic access to transiently-activated neurons revealed that a mediodorsal cohort of NECAB2⁺ neurons mediates inflammatory pain in mouse spinal dorsal horn. Here, besides dampening excitatory transmission in spinal interneurons, NECAB2 limited pronociceptive brain-derived neurotrophic factor release from sensory afferents. Hox8b-dependent reinstatement of NECAB2 expression in Necab2^–/– mice then demonstrated that spinal/DRG NECAB2 alone could control inflammation-induced sensory hyperensitivity. Overall, we identify NECAB2 as a critical component of pro-nociceptive pain signaling whose inactivation offers substantial pain relief.

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