731: Dorsal Root Ganglion Macrophages Contribute to Ischemic Muscle Hyperalgesia in a Rat Model of PAD

Topic: Basic Science
Subtopic: Pain category (ICD-11), Chronic primary musculoskeletal pain, , , , , , Neuroimmunology, Animal imaging (includes Ca2+ imaging, fluorescence microscopy), Neuroanatomical circuit analysis, , ,

Background and Aims: Patients with peripheral arterial disease (PAD) often suffer from chronic pain symptoms including intermittent claudication. However, pathophysiology of peripheral ischemic pain in PAD has not been fully understood. We have previously demonstrated that P2X3,2/3, ASIC3 regulated by nerve growth factor and Vascular endothelial growth factor (VEGF)-A165a-VEGFR1 signaling may play important roles in ischemic muscle hyperalgesia associated with PAD. It has been reported that there is a significant increase in the number of macrophages in dorsal root ganglion (DRG) after peripheral nerve injury, suggesting the crosstalk between nociceptors and non-neuronal cells such as macrophages in DRG. In this study, we investigated the role of　DRG　macrophages on developing muscle hyperalgesia in a rat model of PAD.

Methods: Under deep anesthesia with intraperitoneal butorphanol, medetomidine, and midazolam, both left common iliac and iliolumbar arteries were ligated respectively, through a midline laparotomy (PAD rats). Sham rats were exposed to the arteries without ligation. Cutaneous blood flow in hindlimb was measured by laser Doppler flowmetry. Von Frey test of the hindpaw and the Randall-Selitto test on the calf were performed. In addition, treadmill test was performed to measure walking distance as an assessment of intermittent claudication. Histological examination of both gastrocnemius muscle (GM) and skin over the muscle were performed on day 4 and 14 after arterial ligation. Effects of successive intrathecal administration of the macrophage depletion agent liposomal clodronate Clophosome-A (LCCA) were evaluated on behavioral responses. Furthermore, to distinguish pro-inflammatory (M1) and anti-inflammatory (M2) macrophage phenotypes, the expressions of Iba1, iNOS and Argnase-1 around DRG neurons innervating GM were examined on day 14 by immunohistochemistry.

Results: Muscle hyperalgesia of the GM was observed for 3 weeks, and reduced walking distance was observed for 12 weeks after ligation in PAD rats. Mechanical allodynia of the hindpaw was observed for 1 week although heat hyperalgesia was not. Reduced cutaneous blood flow was also observed for 6 weeks. Infiltrations of the inflammatory cells and pathological changes of muscle cells (e.g., necrotic cells, central cores) were seen in the GM on day 4 but recovered by day 14. Successive intrathecal administration of macrophage depletion agent LCCA significantly reduces muscle hyperalgesia induced by arterial ligation. Furthermore, the number of iNOS+/Iba1+ cells (M1) was significantly increased around muscle afferent L5 DRG neurons on day 14 after arterial ligation. Although there was no change in the number of Arg-1+/Iba1+ cells (M2).

Conclusions: M1 polarization of DRG macrophages may play a critical role in developing muscle hyperalgesia associated with PAD, revealing that peripheral DRG macrophages could be a potential target for treating ischemic muscle pain in PAD.

References: Hori K. et al. VEGF-A165a-VEGFR1 Signaling Mediates Muscle Hyperalgesia in a Rat Model of PAD. 20th world congress on Pain, FR282, Abstract, 2024
Hori K. et al. Altering VEGF-A165a/VEGF-A165b balance contribute to muscle hyperalgesia in a rat model of peripheral arterial disease. 19th world congress on Pain, PTU237, Abstract, 2022
Hori K. et al. Upregulations of P2X3 and ASIC3 involve in hyperalgesia induced by cisplatin administration in rats. PAIN 2010; 149:393–405.
Okuda H. Hori K. et al. Hedgehog signaling plays a crucial role in hyperalgesia associated with neuropathic pain in mice. Journal of Neurochemistry. 2022; 162:207–220.
Yu X. et al. Dorsal root ganglion macrophages contribute to both the initiation and persistence of neuropathic pain. Nat Commun. 2020; 14;11(1):264
Batbold D. et al. Macrophages in trigeminal ganglion contribute to ectopic mechanical hypersensitivity following inferior alveolar nerve injury in rats. Journal of Neuroinflammation. 2017; 16;14(1):249

Presenting Author: Kiyomi Hori
Submitting Author: Kiyomi Hori

Senior Author: Kiyomi Hori

IASP 2026 Global Year theme of Neuropathic Pain: No

• Yoshitake Shiraishi - Department of Functional Anatomy, Kanazawa University Graduate School of Medical Science
• Tsuneo Nakamura - Department of Functional Anatomy, Kanazawa University Graduate School of Medical Science
• Noriyuki Ozaki: MD. PhD - Department of Functional Anatomy, Kanazawa University Graduate School of Medical Science