A novel Flp reporter mouse shows that TRPA1 expression is largely limited to sensory neuron subsets.

Transient receptor potential ankyrin 1 (TRPA1) is a polymodal cation channel that is activated by electrophilic irritants, oxidative stress, cold temperature and GPCR signaling. TRPA1 expression has been primarily identified in subsets of nociceptive sensory afferents and is considered a target for future analgesics. Nevertheless, TRPA1 has been implicated in other cell types including keratinocytes, epithelium, enterochromaffin cells, endothelium, astrocytes and CNS neurons. Here, we developed a knock-in mouse which expresses the recombinase Flp O in TRPA1-expressing cells. We crossed the TRPA1 Flp mouse with the R26 ai65f mouse that expresses tdTomato in a Flp-sensitive manner. We found tdTomato expression correlated well with TRPA1 mRNA expression and sensitivity to TRPA1 agonists in subsets of TRPV1-expressing neurons in the vagal ganglia and dorsal root ganglia (DRG), although tdTomato expression efficiency was limited in DRG. We observed tdTomato-expressing afferent fibers centrally (in the medulla and spinal cord) and peripherally in the esophagus, gut, airways, bladder and skin. Furthermore, chemogenetic activation of TRPA1-expressing nerves in the paw evoked flinching behavior. tdTomato expression was very limited in other cell types. We found tdTomato in subepithelial cells in the gut mucosa but not in enterochromaffin cells. tdTomato was also observed in supporting cells within the cochlea, but not in hair cells. Lastly, tdTomato was occasionally observed in neurons in the somatomotor cortex and the piriform area, but not in astrocytes or vascular endothelium. Thus this novel mouse strain may be useful for mapping and manipulating TRPA1-expressing cells, and deciphering TRPA1's role in physiological and pathophysiological processes. Significance Statement The ion channel TRPA1 is activated by oxidative stress, pollutants, cold and downstream of GPCR. TRPA1 is expressed on some nociceptive sensory afferent nerves, and its activation evokes pain and nocifensive reflexes. However, there is disagreement regarding the extent of TRPA1 expression, both within specific afferent subsets and in non-afferent cells. We developed a TRPA1 Flp mouse that expresses Flp recombinase in TRPA1-expressing cells, allowing for their identification and manipulation. TRPA1 was reported in vagal and DRG subsets, and their chemogenetic activation in the skin evoked pain. TRPA1 was also reported in gut subepithelial cells, cochleal supporting cells and some cortical neurons. We found no evidence of TRPA1 reporting in enterochromaffin cells, epithelium, endothelium, keratinocytes, Schwann cells, smooth muscle or astrocytes.