Deletion of Acid-Sensing Ion Channel 3 Relieves the Late Phase of Neuropathic Pain by Preventing Neuron Degeneration and Promoting Neuron Repair

Abstract

Neuropathic pain is one type of chronic pain that occurs as a result of a lesion or disease to the somatosensory nervous system. Chronic excessive inflammatory response after nerve injury may contribute to the maintenance of persistent pain. Although the role of inflammatory mediators and cytokines in mediating allodynia and hyperalgesia has been extensively studied, the detailed mechanisms of persistent pain or whether the interactions between neurons, glia and immune cells are essential for maintenance of the chronic state have not been completely elucidated. ASIC3, a voltage-insensitive, proton-gated cation channel, is the most essential pH sensor for pain perception. ASIC3 gene expression is increased in dorsal root ganglion neurons after inflammation and nerve injury and ASIC3 is involved in macrophage maturation. ASIC currents are increased after nerve injury. However, whether prolonged hyperalgesia induced by the nerve injury requires ASIC3 and whether ASIC3 regulates neurons, immune cells or glial cells to modulate neuropathic pain remains unknown. We established a model of chronic constriction injury of the sciatic nerve (CCI) in mice. CCI mice showed long-lasting mechanical allodynia and thermal hyperalgesia. CCI also caused long-term inflammation at the sciatic nerve and primary sensory neuron degeneration as well as increased satellite glial expression and ATF3 expression. ASIC3 deficiency shortened mechanical allodynia and attenuated thermal hyperalgesia. ASIC3 gene deletion shifted ATF3 expression from large to small neurons and altered the M1/M2 macrophage ratio, thereby preventing small neuron degeneration and relieved pain.

Longitudinal intravital imaging nerve degeneration and sprouting in the toes of spared nerve injured mice

“…The alteration of DRG neurons after nerve injury have been approached in previous research. After nerve injury, both large‐ and small‐diameter neurons are partially damaged and lost, and the contributions of large and small neurons are time‐dependent (Kung et al, 2020; Leibovich et al, 2020). The expression of different sub‐populations in small‐diameter neurons (i.e., peptidergic and nonpeptidergic neurons) in DRGs also changed after nerve injury (Yeh et al, 2020).…”

Acid-Sensing Ion Channels and Mechanosensation

“…In studies conducted in ASIC3 −/− mice, a marked reduction in acid-induced pain was noticed, along with a decrease in the ability to prime nociceptors [ 136 ]. Moreover, ASIC3 −/− mice were unable to develop chronic muscle pain, establishing a clear correlation between ASIC3 and nociception [ 137 ]. In mouse DRG neurons, recent experiments have shown that ASIC3 expresses the dual function of mechanosensation and acid-sensation [ 138 ].…”

Acid-sensing ion channels as potential therapeutic targets

“…Despite some of these promising findings, we deem it unlikely that any of these small molecule modulators will prove successful in targeting ASIC-related pain phenotypes due to their lack of specificity. APETx2, rat, IM or IT ~Mechanical sensitivity of paw (FF) [67] RPRFa peptide, mouse, IM ↑ Mechanical sensitivity of paw (FF) ~Mechanical sensitivity of paw (FF) in ASIC3 KO [56] Nociceptive pain via formalin, paw NS383 or Amiloride, rat, IP ↓ Nocifensive flinching behaviors [35] Mambalgin, mouse, IT ↓ Spontaneous pain behaviors [50] PPC-5650, rat, SC ↓ Nocifensive licking behavior [51] Inflammatory hyperalgesia induced by CFA injection into paw Amiloride or A-317567, rat, IP ↓ Thermal sensitivity of paw [38] PcTx1, rat, paw ↓ Inflammation score of paw [47,48] APETx2, rat, paw ↓ Mechanical sensitivity of paw (pinch) [65,67] APETx2, rat, IT ~Mechanical sensitivity of paw (pinch) [67] NS383 or Amiloride, rat, IP ↓ Weight bearing distribution ~Thermal sensitivity of tail Neuropathic pain via CCI NS383 or Amiloride, rat, IP ↓ Mechanical sensitivity of paw (FF) [35] Mambalgin, mouse, IV ↓ Thermal sensitivity of paw ↓ Thermal sensitivity of paw in ASIC1a KO ↓ Mechanical sensitivity of paw (FF) [49] Mambalgin, mouse, IT ↓ Thermal sensitivity of paw ~Thermal sensitivity of paw in ASIC1a KO [49] No treatment, mouse ↓ Mechanical sensitivity of paw (FF) in ASIC3 KO ↓ Thermal sensitivity of paw in ASIC3 KO [58] APETx2, mouse, IT ↓ Mechanical sensitivity of paw (FF) ↓ Thermal sensitivity of paw [58] Osteoarthritis pain via MIA injection into knee Acetylsalicylic acid, rat, oral ↓ Mechanical sensitivity of paw (FF) [43] Compound 10b, rat, IP Better weight bearing distribution ↓ Mechanical sensitivity of paw (FF) [62] Orthodontic force GMQ, rat, periodontal Acidic saline, rat, periodontal ↓ Bite force [60] APETx2, rat, periodontal ↑ Bite force…”

“…In rodents, ASIC3 is predominantly expressed in the PNS and is the most prevalent ASIC isoform in the dorsal root ganglion (DRG) [54]. Numerous in vivo studies therefore focus on its involvement in osteoarthritic pain induced by injection of monosodium iodoacetate (MIA) into the knee [43,62]; neuropathic pain induced by chronic constriction injury of the sciatic nerve [39,49,58]; gastroesophageal reflux disease (GERD), and irritable bowel syndrome (IBS) simulated by local mechanical, thermal, and electrical stimuli via a rectal or esophageal probe, respectively [52,53]; migraine induced either by IP injection of isosorbide dinitrate (ISDN) or nitroglycerine (NTG), or cannulated infusion of inflammatory soup [39,64,68]; inflammatory pain induced by injection of Complete Freund's Adjuvant (CFA), acidic saline, or carrageenan into the gastrocnemius muscle or hind paw [35,38,39,44,[47][48][49][50][51]56,59,62,63,[65][66][67]70,71,100,102]; acid-induced pain through local injection or iontophoresis [36,37,44,66,100,101]. (B) selection of different paradigms to assess pain sensitivity [35][36][37][38]…”

“…Inflammatory muscle pain in mice increased the mRNA levels of ASIC2 and ASIC3 (but not ASIC1) in lumbar DRG neurons [57]. In DRG neurons, ASIC3 gene expression increases after inflammation and nerve injury, and deletion of ASIC3 shortens and reduces mechanical and thermal hyperalgesia in chronic neuropathic pain [58]. ASIC3 KD in mice via miRNA reduces the level of mechanical hyperalgesia in inflammatory pain [59].…”