TRPA1 Is Functionally Expressed Primarily by IB4-Binding, Non-Peptidergic Mouse and Rat Sensory Neurons

Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America.
PLoS ONE (Impact Factor: 3.23). 10/2012; 7(10):e47988. DOI: 10.1371/journal.pone.0047988
Source: PubMed


Subpopulations of somatosensory neurons are characterized by functional properties and expression of receptor proteins and surface markers. CGRP expression and IB4-binding are commonly used to define peptidergic and non-peptidergic subpopulations. TRPA1 is a polymodal, plasma membrane ion channel that contributes to mechanical and cold hypersensitivity during tissue injury, making it a key target for pain therapeutics. Some studies have shown that TRPA1 is predominantly expressed by peptidergic sensory neurons, but others indicate that TRPA1 is expressed extensively within non-peptidergic, IB4-binding neurons. We used FURA-2 calcium imaging to define the functional distribution of TRPA1 among peptidergic and non-peptidergic adult mouse (C57BL/6J) DRG neurons. Approximately 80% of all small-diameter (<27 µm) neurons from lumbar 1-6 DRGs that responded to TRPA1 agonists allyl isothiocyanate (AITC; 79%) or cinnamaldehyde (84%) were IB4-positive. Retrograde labeling via plantar hind paw injection of WGA-Alexafluor594 showed similarly that most (81%) cutaneous neurons responding to TRPA1 agonists were IB4-positive. Additionally, we cultured DRG neurons from a novel CGRP-GFP mouse where GFP expression is driven by the CGRPα promoter, enabling identification of CGRP-expressing live neurons. Interestingly, 78% of TRPA1-responsive neurons were CGRP-negative. Co-labeling with IB4 revealed that the majority (66%) of TRPA1 agonist responders were IB4-positive but CGRP-negative. Among TRPA1-null DRGs, few small neurons (2-4%) responded to either TRPA1 agonist, indicating that both cinnamaldehyde and AITC specifically target TRPA1. Additionally, few large neurons (≥27 µm diameter) responded to AITC (6%) or cinnamaldehyde (4%), confirming that most large-diameter somata lack functional TRPA1. Comparison of mouse and rat DRGs showed that the majority of TRPA1-responsive neurons in both species were IB4-positive. Together, these data demonstrate that TRPA1 is functionally expressed primarily in the IB4-positive, CGRP-negative subpopulation of small lumbar DRG neurons from rodents. Thus, IB4 binding is a better indicator than neuropeptides for TRPA1 expression.

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Available from: Cheryl Stucky, Mar 11, 2014
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    • "These results suggest that Tmem100 is primarily expressed in peptidergic DRG neurons (Figure 1E), many of which are TRPV1 and TRPA1 double positive (Figure 1F) (Bautista et al., 2006; Story et al., 2003). A recent study has shown that TRPA1 is functionally expressed in IB4 + nonpeptidergic neurons (Barabas et al., 2012). The culture conditions of dissociated DRG neurons can influence the expression of TRPA1. "
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    • "Several studies on rat and mouse DRG neurons showed a preferential ASIC expression in IB4-negative neurons (Dirajlal et al., 2003; Liu et al., 2004; Poirot et al., 2006). In mouse, IB4-negative DRG neurons express almost exclusively neuropeptides, while this negative correlation is much weaker in rat (Barabas et al., 2012; Price and Flores, 2007). PcTx1-sensitive currents were found only in 5% of rat DRG neurons in one study (Deval et al., 2008), and in ~ 30% of DRG neurons in our previous study (Poirot et al., 2006). "
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