BPS2026 – Copine-3 regulates sensitivity of peripheral somatosensory neurons to mechanical pressure

Copines are a family of calcium-sensitive phospholipid-binding proteins with functions associated with membrane dynamics, trafficking, and intracellular signaling. Out of nine mammalian copine isoforms, Copine-3, -4, and -6 are highly expressed in the peripheral somatosensory neurons. Recently we demonstrated that in the rodent dorsal root ganglion (DRG) neurons, Copine-6 functions as a TRPM3 escort protein: it promotes TRPM3 insertion into the plasma membrane in an activity-dependent manner, thus controlling the sensitivity of sensory neurons to noxious heat. The roles of other copines in somatosensory physiology are currently unknown. Here, we investigated function of Copine-3. We found that this isoform is expressed in the mouse DRG at much higher levels than in the brain or spinal cord. DRG-specific shRNA knockdown of the Copine-3 gene, Cpne3 , potently and selectively enhanced sensitivity to noxious mechanical stimulation (von Frey, Randall-Selitto tests) in vivo, while sensitivity to heat (Hargreaves test and tail flick test) and cold (dry ice test) was largely unaffected. Copine-3 expression was significantly downregulated after neuropathic injury in rats (spinal nerve injury SNI model ) and viral overexpression of Copine-3 in the DRG significantly alleviated mechanical, but not thermal hyperalgesia, induced by the SNI model. On the cellular level, conditional knockout of Cpne3 in mouse somatosensory neurons resulted in overexcitable neurons with significantly depolarized resting membrane potential (−59 ± 1.3 mV; n = 28 in control vs. −52.1 ± 1.6 mV, n = 28 in the Cpne3 KD neurons; p = 0.001) and increased firing frequency in response to 300 pA depolarizing current injection (20.5 ± 1.4 Hz, n = 28 in control vs. 27.6 ± 1.8 Hz, n = 28 in the Cpne3 KD neurons; p=0.003). Molecular mechanisms for these effects are currently being elucidated and may include trafficking or regulation of a potassium channel. Taken together, these findings establish a novel molecular player for determining the sensitivity of somatosensory neurons to mechanical pressure.