Analysis of Transient Receptor Potential Ankyrin 1 (TRPA1) in Frogs and Lizards Illuminates Both Nociceptive Heat and Chemical Sensitivities and Coexpression with TRP Vanilloid 1 (TRPV1) in Ancestral Vertebrates

Ohkita

Journal of Biological Chemistry

et al. 2016

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Temperature is one of the most critical environmental factors affecting survival, and thus species that inhabit different thermal niches have evolved thermal sensitivities suitable for their respective habitats. During the process of shifting thermal niches, various types of genes expressed in diverse tissues, including those of the peripheral to central nervous systems, are potentially involved in the evolutionary changes in thermosensation. To elucidate the molecular mechanisms behind the evolution of thermosensation, thermal responses were compared between two species of clawed frogs (Xenopus laevis and Xenopus tropicalis) adapted to different thermal environments. X. laevis was much more sensitive to heat stimulation than X. tropicalis at the behavioral and neural levels. The activity and sensitivity of the heat-sensing TRPA1 channel were higher in X. laevis compared with those of X. tropicalis. The thermal responses of another heat-sensing channel, TRPV1, also differed between the two Xenopus species. The species differences in Xenopus TRPV1 heat responses were largely determined by three amino acid substitutions located in the first three ankyrin repeat domains, known to be involved in the regulation of rat TRPV1 activity. In addition, Xenopus TRPV1 exhibited drastic species differences in sensitivity to capsaicin, contained in chili peppers, between the two Xenopus species. Another single amino acid substitution within Xenopus TRPV1 is responsible for this species difference, which likely alters the neural and behavioral responses to capsaicin. These combined subtle amino acid substitutions in peripheral thermal sensors potentially serve as a driving force for the evolution of thermal and chemical sensation.Animals have evolved sophisticated physiological systems for sensing ambient temperatures, as fluctuations in environmental temperature significantly affect various biological processes. Species adapted to different thermal niches are likely to have acquired specific thermal sensitivities suitable for their respective habitats. Recent progress and understanding of the molecular mechanisms behind thermosensation has enabled us to elucidate the molecular basis for the evolution of thermosensation in the process of shifting thermal niches (1-3).In vertebrates, peripheral sensory neurons such as dorsal root ganglion (DRG) 3 and trigeminal ganglion neurons relay temperature information to the central nervous system. During the initiation of signal transduction, thermal stimuli are transduced into electrical signals and a subset of ion channels that are thermally activated plays crucial roles in this process. These ion channels belong to the transient receptor potential (TRP) ion channel superfamily and are called "thermoTRP" (1-3). Animals possess several kinds of thermoTRP channels, which have distinctive temperature ranges for activation. For example, TRPV1 is activated by heat (4 -7), whereas TRPM8 is activated by cold (1-3, 8).Temperature sensitivity among orthologous thermoTRP channels has changed duri...

Section: Behavioral and Sensory Neural Responses To Heat Stimulationmentioning

confidence: 99%

“…The experimental setup for observing nocifensive (jumping) behaviors was established in previous studies (4,11). Briefly, a single frog was put into a glass bowl filled with a small amount of water.…”

Section: Behavioral and Sensory Neural Responses To Heat Stimulationmentioning

confidence: 99%

Evolution of Heat Sensors Drove Shifts in Thermosensation between Xenopus Species Adapted to Different Thermal Niches

Ohkita

Journal of Biological Chemistry

et al. 2016

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“…Amphibians have been used as an alternative model to study pain mechanisms (Stevens, 2004;Stevens et al, 2007;Stevens et al, 2009;Coble et al, 2011;Ohkita et al, 2012;Saito et al, 2012), for several reasons. Stevens (2004) noted that the use of these animals provides a phylogenetic perspective on the mechanisms of pain research.…”

Section: Introductionmentioning

confidence: 99%

Effects of sciatic nerve transection on glucose uptake in the presence and absence of lactate in the frog dorsal root ganglia and spinal cord

et al. 2014

Frogs have been used as an alternative model to study pain mechanisms because the simplicity of their nervous tissue and the phylogenetic aspect of this question. One of these models is the sciatic nerve transection (SNT), which mimics the clinical symptoms of "phantom limb", a condition that arises in humans after amputation or transverse spinal lesions. In mammals, the SNT increases glucose metabolism in the central nervous system, and the lactate generated appears to serve as an energy source for nerve cells. An answerable question is whether there is elevated glucose uptake in the dorsal root ganglia (DRG) after peripheral axotomy. As glucose is the major energy substrate for frog nervous tissue, and these animals accumulate lactic acid under some conditions, bullfrogs Lithobates catesbeianus were used to demonstrate the effect of SNT on DRG and spinal cord 1-[ C-2-DG uptake was lower when lactate was added to the incubation medium. No change was found in glucose and lactate oxidation after SNT, but lactate and glucose levels in the blood were reduced. Thus, our results showed that SNT increased the glucose metabolism in the frog DRG and spinal cord. The effect of lactate on this uptake suggests that glucose is used in glycolytic pathways after SNT. Efeito da secção do nervo isquiático sobre a captação de glicose na presença e ausência de lactato em gânglio da raiz dorsal e medula espinhal de rãs ResumoAs rãs são usadas como modelos experimentais alternativos no estudo da nocicepção, tanto pela simplicidade do seu tecido nervoso como por permitirem uma abordagem filogenética sobre o tema. Um desses modelos é a secção do nervo isquiático (SNI), o qual simula os sintomas clínicos do "membro fantasma", uma condição que ocorre nos humanos após amputação ou secção completa da medula espinal. Em mamíferos, a SNI aumenta o metabolismo da glicose no sistema nervoso central, e o lactato é uma fonte energética para as células nervosas. Porém é desconhecido se essa é a situação em gânglio da raiz dorsal (GRD). Como a glicose é o principal substrato energético para o tecido nervoso de rãs, e a concentração plasmática de lactato está aumentada nesses animais em distintas situações, a rã-touro Lithobates catesbeianus foi usada para demonstrar os efeitos da SNI sobre a captação de 1-[ 14 C] 2-deoxi-D-glicose ( 14 C-2-DG), na presença e ausência de lactato, em GRD e medula espinal. Foram demonstrados ainda os efeitos dessa condição experimental sobre a formação de 14 CO 2 a partir de 14 C-glicose e 14 C-L-lactato, e a concentração plasmática de glicose e lactato. A captação de 3-O-[14 C] metil-D-glicose ( 14 C-3-OMG) foi usada para demonstrar a relação tecido/meio estável da glicose nessas condições. A captação de 14 C-2-DG aumentou três dias após a SNI, sem qualquer alteração na captação de 14 C-3-OMG. O aumento foi reduzido quando o lactato foi acrescentado ao meio de incubação. A taxa de oxidação da glicose e do lactato não modificou após SNI, mas houve redução na concentração plasmática de glicose e lactato. Ass...

“…In some experiments, expression vectors for western clawed frog TRPA1, green anole TRPA1, and mouse TRPA1 were used (16,31). Single amino acid mutants of human TRPA1 were made using a PrimeSTAR mutagenesis basal kit (Takara) with the primer sets containing the specific mutations shown in Table 1.…”

Section: Methodsmentioning

confidence: 99%

Molecular Basis Determining Inhibition/Activation of Nociceptive Receptor TRPA1 Protein

Banzawa

Journal of Biological Chemistry

Imagawa

et al. 2014

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Background: Nociceptive TRPA1 is an important drug discovery target for identification of analgesics. Results: A967079, one of the most potent mammalian TRPA1 antagonists, showed marked species differences. Conclusion: A single amino acid was responsible for inhibitory/stimulatory actions of A967079. Significance: The present data provide novel insight in the search for analgesics targeting TRPA1.