Photochemical control of cold-sensitive TRPA1 ion channel gating for modulation of pain sensation

As a polymodal biosensor, the TRPA1 ion channel undergoes rapid opening and closing, a dynamic process known as gating that defines the fundamental function and modulation of ion channels. TRPA1 gating is primarily regulated by chemical and mechanical stimuli. However, whether and how TRPA1 gating transduces the biological function of pain sensation is poorly understood.

A series of photoswitchable TRPA1 probes (PSTRAPs1-4) were designed and synthesized. Whole-cell patch clamp recordings of hTRPA1 channels expressed in CHO cells were performed to test whether PSTRAPs could optically switch TRPA1 channel function. Site-directed mutagenesis was conducted to identify the binding site of PSTRAPs on the extracellular surface of TRPA1. In a mouse model of cheek pain, intracutaneous injection of PSTRAPs elicited pain sensation in response to photoswitching.

PSTRAP-2 and PSTRAP-4 reversibly modulate TRPA1 channel function with spatiotemporal resolution. These azobenzene photoswitches can activate and deactivate TRPA1 currents expressed in CHO cells upon switching between blue light and darkness. Structural-activity relationship (SAR) analysis of PSTRAPs1-4 combined with site-directed mutagenesis revealed a residue Y926 between the pore helix 1 and 2 critical for the interaction between the PSTRAPs and TRPA1. In a mouse cheek pain model, photochemical gating of TRPA1 by intracutaneous injections of photoswitchable PSTRAP-2 and PSTRAP-4 induced pain perception in response to photoswitching cycles.

Our identification of these photoswitches not only provides small molecule tools for probing and understanding TRPA1 channel gating but also holds developmental potential for pain modulation.