ASIC3 inhibition modulates inflammation-induced changes in the activity and sensitivity of Aδ and C fiber sensory neurons that innervate bone

Abstract

The Acid Sensing Ion Channel 3 (ASIC3) is a non-selective cation channel that is activated by acidification, and is known to have a role in regulating inflammatory pain. It has pro-algesic roles in a range of conditions that present with bone pain, but the mechanism for this has not yet been demonstrated. We aimed to determine if ASIC3 is expressed in Aδ and/or C fiber bone afferent neurons, and to explore its role in the activation and sensitization of bone afferent neurons after acute inflammation. A combination of retrograde tracing and immunohistochemistry was used to determine expression of ASIC3 in the soma of bone afferent neurons. A novel, in vivo, electrophysiological bone-nerve preparation was used to make recordings of the activity and sensitivity of bone afferent neurons in the presence of carrageenan-induced inflammation, with and without the selective ASIC3 inhibitor APET×2. A substantial proportion of bone afferent neurons express ASIC3, including unmyelinated (neurofilament poor) and small diameter myelinated (neurofilament rich) neurons that are likely to be C and Aδ nerve fibers respectively. Electrophysiological recordings revealed that application of APET×2 to the marrow cavity inhibited carrageenan-induced spontaneous activity of C and Aδ fiber bone afferent neurons. APET×2 also inhibited carrageenan-induced sensitization of Aδ and C fiber bone afferent neurons to mechanical stimulation, but had no effect on the sensitivity of bone afferent neurons in the absence of inflammation. This evidence supports a role for ASIC3 in the pathogenesis of pain associated with inflammation of the bone.

Antibody-induced pain-like behavior and bone erosion: links to subclinical inflammation, osteoclast activity, and acid-sensing ion channel 3–dependent sensitization

“… 80 Acid-sensing ion channel 3, expressed by peripheral nociceptors, becomes activated at pH ≈ 7.2 and is likely important in the nonadapting pain caused by tissue acidosis, particularly because it has the ability to sensitize nociceptors to other types of stimuli. 18 As preclinical evidence suggests a key role of ASIC3 in inflammatory 36 , 65 , 100 and noninflammatory pain with bone pathology, such as osteoarthritis 39 and osteoporosis, 20 , 31 we examined whether B02/B09-induced mechanical hypersensitivity was dependent on ASIC3 activation. Using APETx2, an inhibitor of ASIC3-containing channels, as well as a global, functional ASIC3 knockout, we identified ASIC3 signaling as a critical component of B02/B09-induced hypersensitivity.…”

Piezo2 Knockdown Inhibits Noxious Mechanical Stimulation and NGF-Induced Sensitization in A-Delta Bone Afferent Neurons

“…We have recently developed a novel in vivo electrophysiological bone-nerve preparation that allows us to record, for the first time, the activity of different populations of bone afferent neurons in response to noxious mechanical stimulation Nencini et al, , 2018Nencini et al, , 2019Morgan et al, 2019;Morgan et al, 2020). In the present study, we use this approach to determine how Piezo2 knockdown affects the ability of bone afferent neurons to respond to noxious mechanical stimulation applied to the bone.…”

Commentary: Pharmacological Validation of ASIC1a as a Druggable Target for Neuroprotection in Cerebral Ischemia Using an Intravenously Available Small Molecule Inhibitor

“…C5b is similarly nonselective due to its inhibition of ASIC3 in DRG neurons ( Buta et al, 2015 ), so it could have effects on pain throughout the entire body. Anthopleura elagantissima toxin 2 (APETx2) inhibits ASIC3 and ASIC3-containing channels in afferent bone sensory neurons and has been used to treat inflammatory bone pain ( Morgan et al, 2020 ). By looking at drugs with similar inhibitory properties as C5b, there is a possibility that C5b could produce effects on various systems, and this will require further study.…”