Activation of Drosophila melanogaster TRPA1 Isoforms by Citronellal and Menthol

Abstract

Background: The transient receptor potential ankyrin 1 (TRPA1) cation channels function as broadly-tuned sensors of noxious chemicals in many species. Recent studies identified four functional TRPA1 isoforms in Drosophila melanogaster (dTRPA1(A) to (D)), but their responses to non-electrophilic chemicals are yet to be fully characterized. Methods: We determined the behavioral responses of adult flies to the mammalian TRPA1 non-electrophilic activators citronellal and menthol, and characterized the effects of these compounds on all four dTRPA1 channel isoforms using intracellular Ca2+ imaging and whole-cell patch-clamp recordings. Results: Wild type flies avoided citronellal and menthol in an olfactory test and this behavior was reduced in dTrpA1 mutant flies. Both compounds activate all dTRPA1 isoforms in the heterologous expression system HEK293T, with the following sensitivity series: dTRPA1(C) = dTRPA1(D) > dTRPA1(A) ≫ dTRPA1(B) for citronellal and dTRPA1(A) > dTRPA1(D) > dTRPA1(C) > dTRPA1(B) for menthol. Conclusions: dTrpA1 was required for the normal avoidance of Drosophila melanogaster towards citronellal and menthol. All dTRPA1 isoforms are activated by both compounds, but the dTRPA1(B) is consistently the least sensitive. We discuss how these findings may guide further studies on the physiological roles and the structural bases of chemical sensitivity of TRPA1 channels.

Drosophila as a Model to Study the Mechanism of Nociception

“…In addition to participating in the response to harmful temperature stimuli, dTRPA1 has also been detected in chemical stimuli ( Tracey et al, 2003 ; Im and Galko, 2012 ). Boonen et al (2021) found that wild-type flies avoid citronellal and menthol in olfactory tests, while dTRPA1 mutant flies have reduced this behavior. dTRPA1 channel mediates chemical avoidance in gustatory receptor neurons (GRNs), in which know down of dTRPA1 in GRNs significantly reduced the aversive response to aristolochic acid ( Kim et al, 2010 ).…”

“…The Drosophila genome contains genes encoding 13 TRP channels, and encodes four TRPA homologs: dTRPA1 , painless , pyrexia , and water witch ( Fowler and Montell, 2013 ). TRPA channels have been the most widely studied for their roles in temperature-sensing behavior in flies ( Goodman, 2003 ; Xu et al, 2006 ; Neely et al, 2011 ; Bellemer, 2015 ) and also play important roles in chemical and mechanical sensing ( Mandel et al, 2018 ; Boonen et al, 2021 ). TRPA1 has been implicated as a mammal noxious cold receptor, which is activated by extremely cold temperatures (below < 15°C) ( Kwan and Corey, 2009 ).…”

“…dTRPA1 was first identified as a heat-activated channel in flies ( Rosenzweig et al, 2005 ; Kwon et al, 2008 ). It is 32% identical and 54% similar to its mammalian orthology by amino acid identity, and is activated in response to high temperature, reactive chemicals and downstream of intracellular signaling pathways ( Neely et al, 2011 ; Bellemer, 2015 ; Boonen et al, 2021 ). The dTRPA1 channel is expressed in the multiple groups of central neurons and several classes of peripheral sensory neurons ( Hamada et al, 2008 ; Kang et al, 2010 ; Kim et al, 2010 ).…”

“…TRP, Piezo and other ion channels have been identified as key pain receptors ( Hwang and Oh, 2007 ; Volkers et al, 2015 ). Among these channels, TRPV1, TRPA1, Piezo1 and Piezo2 are expressed in nociceptors ( Liedtke, 2007 ; Flood et al, 2013 ; Volkers et al, 2015 ; Himmel and Cox, 2017 ; Boonen et al, 2021 ). They serve as detectors and sensors for cold, heat, chemical and mechanical stimuli in nociceptors.…”