Involvement of TRPM2 in Peripheral Nerve Injury-Induced Infiltration of Peripheral Immune Cells into the Spinal Cord in Mouse Neuropathic Pain Model.

Recent evidence suggests that transient receptor potential melastatin 2 (TRPM2) expressed in immune cells plays an important role in immune and inflammatory responses. We recently reported that TRPM2 expressed in macrophages and spinal microglia contributes to the pathogenesis of inflammatory and neuropathic pain aggravating peripheral and central pronociceptive inflammatory responses in mice. To further elucidate the contribution of TRPM2 expressed by peripheral immune cells to neuropathic pain, we examined the development of peripheral nerve injury-induced neuropathic pain and the infiltration of immune cells (particularly macrophages) into the injured nerve and spinal cord by using bone marrow (BM) chimeric mice by crossing wildtype (WT) and TRPM2-knockout (TRPM2-KO) mice. Four types of BM chimeric mice were prepared, in which irradiated WT or TRPM2-KO recipient mice were transplanted with either WT-or TRPM2-KO donor mouse-derived green fluorescence protein-positive (GFP(+)) BM cells (TRPM2(BM+/Rec+), TRPM2(BM-/Rec+), TRPM2(BM+/Rec-), and TRPM2(BM-/Rec-) mice). Mechanical allodynia induced by partial sciatic nerve ligation observed in TRPM2(BM+/Rec+) mice was attenuated in TRPM2(BM-/Rec+), TRPM2(BM+/Rec-), and TRPM2(BM-/Rec-) mice. The numbers of GFP(+) BM-derived cells and Iba1/GFP double-positive macrophages in the injured sciatic nerve did not differ among chimeric mice 14 days after the nerve injury. In the spinal cord, the number of GFP(+) BM-derived cells, particularly GFP/Iba1 double-positive macrophages, was significantly decreased in the three TRPM2-KO chimeric mouse groups compared with TRPM2(BM+/Rec+) mice. However, the numbers of GFP(-)/Iba1(+) resident microglia did not differ among chimeric mice. These results suggest that TRPM2 plays an important role in the infiltration of peripheral immune cells, particularly macrophages, into the spinal cord, rather than the infiltration of peripheral immune cells into the injured nerves and activation of spinal-resident microglia. The spinal infiltration of macrophages mediated by TRPM2 may contribute to the pathogenesis of neuropathic pain

Involvement of TRPM2 in a wide range of inflammatory and neuropathic pain mouse models.

Recent evidence suggests a role of transient receptor potential melastatin 2 (TRPM2) in immune and inflammatory responses. We previously reported that TRPM2 deficiency attenuated inflammatory and neuropathic pain in some pain mouse models, including formalin- or carrageenan-induced inflammatory pain, and peripheral nerve injury-induced neuropathic pain models, while it had no effect on the basal mechanical and thermal nociceptive sensitivities. In this study, we further explored the involvement of TRPM2 in various pain models using TRPM2-knockout mice. There were no differences in the chemonociceptive behaviors evoked by intraplantar injection of capsaicin or hydrogen peroxide between wildtype and TRPM2-knockout mice, while acetic acid-induced writhing behavior was significantly attenuated in TRPM2-knockout mice. In the postoperative incisional pain model, no difference in mechanical allodynia was observed between the two genotypes. By contrast, mechanical allodynia in the monosodium iodoacetate-induced osteoarthritis pain model and the experimental autoimmune encephalomyelitis model were significantly attenuated in TRPM2-knockout mice. Furthermore, mechanical allodynia in paclitaxel-induced peripheral neuropathy and streptozotocin-induced painful diabetic neuropathy models were significantly attenuated in TRPM2-knockout mice. Taken together, these results suggest that TRPM2 plays roles in a wide range of pathological pain models based on peripheral and central neuroinflammation, rather than physiological nociceptive pain

TRPM2 Contributes to Inflammatory and Neuropathic Pain through the Aggravation of Pronociceptive Inflammatory Responses in Mice.

慢性痛の原因となる神経炎症応答の増悪機構を解明－新しい鎮痛薬開発の可能性－. 京都大学プレスリリース. 2012-03-15.Accumulating evidence suggests that neuroimmune interactions contribute to pathological pain. Transient receptor potential melastatin 2 (TRPM2) is a nonselective Ca(2+)-permeable cation channel that acts as a sensor for reactive oxygen species. TRPM2 is expressed abundantly in immune cells and is important in inflammatory processes. The results of the present study show that TRPM2 plays a crucial role in inflammatory and neuropathic pain. While wild-type and TRPM2 knock-out mice showed no difference in their basal sensitivity to mechanical and thermal stimulation, nocifensive behaviors in the formalin test were reduced in TRPM2 knock-out mice. In carrageenan-induced inflammatory pain and sciatic nerve injury-induced neuropathic pain models, mechanical allodynia and thermal hyperalgesia were attenuated in TRPM2 knock-out mice. Carrageenan-induced inflammation and sciatic nerve injury increased the expression of TRPM2 mRNA in the inflamed paw and around the injured sciatic nerve, respectively. TRPM2 deficiency diminished the infiltration of neutrophils and the production of chemokine (C-X-C motif) ligand-2 (CXCL2), a major chemokine that recruits neutrophils, but did not alter the recruitment of F4/80-positive macrophages in the inflamed paw or around the injured sciatic nerve. Microglial activation after nerve injury was suppressed in the spinal cord of TRPM2 knock-out mice. Furthermore, CXCL2 production and inducible nitric oxide synthase induction were diminished in cultured macrophages and microglia derived from TRPM2 knock-out mice. Together, these results suggest that TRPM2 expressed in macrophages and microglia aggravates peripheral and spinal pronociceptive inflammatory responses and contributes to the pathogenesis of inflammatory and neuropathic pain

Flow cytometry analysis of BM-derived cells in WT/TRPM2-KO BM chimeric mice.

<p>Representative histograms of GFP⁺ cells in WT mice (A; negative control), GFP-transgenic mice (B; positive control), TRPM2^BM+/Rec+ mice (C), TRPM2^BM–/Rec+ mice (D), TRPM2^BM+/Rec– mice (E), and TRPM2^BM-/Rec– mice (F). In all examined chimeric mice, more than 90% of the BM-derived cells were GFP⁺.</p

The numbers of Iba1⁺ and GFP⁺ cells around the injured sciatic nerve.

<p>The numbers of Iba1⁺ and GFP⁺ cells around the injured sciatic nerve.</p

The numbers of Iba1⁺ and GFP⁺ cells in the spinal dorsal horn.

<p>The numbers of Iba1⁺ and GFP⁺ cells in the spinal dorsal horn.</p

Peripheral nerve injury-induced mechanical allodynia in WT/TRPM2-KO BM chimeric mice.

<p>In the pSNL model of neuropathic pain, the 50% withdrawal threshold to mechanical stimuli was determined in the ipsilateral (<b>A</b>) and contralateral paws (<b>B</b>) of TRPM2^BM+/Rec+, TRPM2^BM–/Rec+, TRPM2^BM+/Rec–, and TRPM2^BM+/Rec+ mice. *<i>p</i> < 0.05; **<i>p</i> < 0.01; ***<i>p</i> < 0.001, compared with TRPM2^BM+/Rec+ mice. ^#<i>p</i> <0.05;^##<i>p</i> <0.01, compared with Day 0 in each BM chimeric mouse group. <i>n</i> = 5–7. Data are expressed as the mean ± SEM.</p

Infiltration of GFP⁺ BM-derived cells into the spinal cord in WT/TRPM2-KO BM chimeric mice.

<p>(<b>A, B</b>) GFP⁺ cells and Iba1⁺ cells were visualized by GFP fluorescence (green) and immunostaining with Iba1 antibody (red), respectively, in the spinal cord sections 14 days after pSNL surgery. Iba1⁺/GFP⁺ cells were visualized as a yellow signal in merged images. (<b>A</b>) Representative microphotographs in WT-BM and WT chimeric mice are shown (scale bars = 200 µm). (<b>B</b>) Representative microphotographs in selected regions of contralateral and ipsilateral spinal dorsal horn (defined by the rectangular area in A) are shown (scale bars = 100 µm). (<b>C</b>) The numbers of Iba1^-/GFP⁺ cells, Iba1⁺/GFP^-cells, and Iba1⁺/GFP⁺ cells within the selected regions were counted in the contralateral (left panel) and ipsilateral (right panel) spinal dorsal horn. <i>n</i> = 3–6. Data are expressed as the mean ± SEM.</p

The effect of emotional valence in searching Knanji-combination words

Attention is influenced by mood, stimulus characteristics, and personality traits. Many studies have reported on the tendency to attend to negative stimuli, which is elicited by the induction of a negative mood. However, few studies have compared the effects of negative, positive, and neutral stimuli on this attention bias. The different effect of inducing positive and negative moods on visual-search performance for Kanji-combination words was investigated. Participants listened to negative or positive music to induce the mood and then choose negative, positive or neutral Kanji-combination words from scrambled Kanji grids. The result showed that music had no effect on mood induction; however, participants choose more emotional than neutral words, regardless of their mood. These findings suggest that emotional words are more likely to be chosen than neutral Kanji-combination words, regardless of the mood induced by music

感情価の異なる漢字二字熟語の検出に及ぼす気分状態の影響

Attention is influenced by mood, stimulus characteristics, and personality traits. Many studies have reported on the tendency to attend to negative stimuli, which is elicited by the induction of a negative mood. However, few studies have compared the effects of negative, positive, and neutral stimuli on this attention bias. The different effect of inducing positive and negative moods on visual-search performance for Kanji-combination words was investigated. Participants listened to negative or positive music to induce the mood and then choose negative, positive or neutral Kanji-combination words from scrambled Kanji grids. The result showed that music had no effect on mood induction; however, participants choose more emotional than neutral words, regardless of their mood. These findings suggest that emotional words are more likely to be chosen than neutral Kanji-combination words, regardless of the mood induced by music