Distribution of acid-sensing ion channel subunits in human sensory neurons contrasts with that in rodents

Genetic Risk Factors for Bortezomib-induced Neuropathic Pain in an Asian Population: A Genome-wide Association Study in South Korea

Bortezomib-induced neuropathic pain (BINP) poses a challenge in multiple myeloma (MM) treatment. Genetic factors play a key role in BINP susceptibility, but research has predominantly focused on Caucasian populations. This research explored novel genetic risk loci and pathways associated with BINP development in Korean MM patients while evaluating the reproducibility of variants from Caucasians. Clinical data and buffy coat samples from 185 MM patients on bortezomib were collected. The cohort was split into discovery and validation cohorts through random stratification of clinical risk factors for BINP. Genome-wide association study was performed on the discovery cohort (n = 74) with Infinium Global Screening Array-24 v3.0 BeadChip (654,027 single nucleotide polymorphism [SNPs]). Relevant biological pathways were identified using the pathway scoring algorithm. The top 20 SNPs were validated in the validation cohort (n = 111). Previously reported SNPs were validated in the entire cohort (n = 185). Pathway analysis of the genome-wide association study results identified 31 relevant pathways, including immune systems and endosomal vacuolar pathways. Among the top 20 SNPs from the discovery cohort, 16 were replicated, which included intronic variants in ASIC2 and SMOC2, recently implicated in nociception, as well as intergenic variants or long noncoding RNAs. None of the 17 previously reported SNPs remained significant in our cohort (rs2274578, P = .085). This study represents the first investigation of novel genetic loci and biological pathways associated with BINP occurrence. Our findings, in conjunction with existing Caucasian studies, expand the understanding of personalized risk prediction and disease mechanisms. PERSPECTIVE: This article is the first to explore novel genetic loci and pathways linked to BINP in Korean MM patients, offering novel insights beyond the existing research focused on Caucasian populations into personalized risk assessment and therapeutic strategies of BINP.

Satellite Glial Cells in Human Disease

Satellite glial cells (SGCs) are the main type of glial cells in sensory ganglia. Animal studies have shown that these cells play essential roles in both normal and disease states. In a large number of pain models, SGCs were activated and contributed to the pain behavior. Much less is known about SGCs in humans, but there is emerging recognition that SGCs in humans are altered in a variety of clinical states. The available data show that human SGCs share some essential features with SGCs in rodents, but many differences do exist. SGCs in DRG from patients suffering from common painful diseases, such as rheumatoid arthritis and fibromyalgia, may contribute to the pain phenotype. It was found that immunoglobulins G (IgG) from fibromyalgia patients can induce pain-like behavior in mice. Moreover, these IgGs bind preferentially to SGCs and activate them, which can sensitize the sensory neurons, causing nociception. In other human diseases, the evidence is not as direct as in fibromyalgia, but it has been found that an antibody from a patient with rheumatoid arthritis binds to mouse SGCs, which leads to the release of pronociceptive factors from them. Herpes zoster is another painful disease, and it appears that the zoster virus resides in SGCs, which acquire an abnormal morphology and may participate in the infection and pain generation. More work needs to be undertaken on SGCs in humans, and this review points to several promising avenues for better understanding disease mechanisms and developing effective pain therapies.

Genetic exploration of roles of acid-sensing ion channel subtypes in neurosensory mechanotransduction including proprioception

Although acid-sensing ion channels (ASICs) are proton-gated ion channels responsible for sensing tissue acidosis, accumulating evidence has shown that ASICs are also involved in neurosensory mechanotransduction. However, in contrast to Piezo ion channels, evidence of ASICs as mechanically gated ion channels has not been found using conventional mechanoclamp approaches. Instead, ASICs are involved in the tether model of mechanotransduction, with the channels gated via tethering elements of extracellular matrix and intracellular cytoskeletons. Methods using substrate deformation-driven neurite stretch and micropipette-guided ultrasound were developed to reveal the roles of ASIC3 and ASIC1a, respectively. Here we summarize the evidence supporting the roles of ASICs in neurosensory mechanotransduction in knockout mouse models of ASIC subtypes and provide insight to further probe their roles in proprioception.

Enhanced harm detection following maternal separation: Transgenerational transmission and reversibility by inhaled amiloride

Early-life adversities are associated with altered defensive responses. Here, we demonstrate that the repeated cross-fostering (RCF) paradigm of early maternal separation is associated with enhancements of distinct homeostatic reactions: hyperventilation in response to hypercapnia and nociceptive sensitivity, among the first generation of RCF-exposed animals, as well as among two successive generations of their normally reared offspring, through matrilineal transmission. Parallel enhancements of acid-sensing ion channel 1 (ASIC1), ASIC2, and ASIC3 messenger RNA transcripts were detected transgenerationally in central neurons, in the medulla oblongata, and in periaqueductal gray matter of RCF-lineage animals. A single, nebulized dose of the ASIC-antagonist amiloride renormalized respiratory and nociceptive responsiveness across the entire RCF lineage. These findings reveal how, following an early-life adversity, a biological memory reducible to a molecular sensor unfolds, shaping adaptation mechanisms over three generations. Our findings are entwined with multiple correlates of human anxiety and pain conditions and suggest nebulized amiloride as a therapeutic avenue.

Acidosis-related pain and its receptors as targets for chronic pain

Sensing acidosis is an important somatosensory function in responses to ischemia, inflammation, and metabolic alteration. Accumulating evidence has shown that acidosis is an effective factor for pain induction and that many intractable chronic pain diseases are associated with acidosis signaling. Various receptors have been known to detect extracellular acidosis and all express in the somatosensory neurons, such as acid sensing ion channels (ASIC), transient receptor potential (TRP) channels and proton-sensing G-protein coupled receptors. In addition to sense noxious acidic stimulation, these proton-sensing receptors also play a vital role in pain processing. For example, ASICs and TRPs are involved in not only nociceptive activation but also anti-nociceptive effects as well as some other non-nociceptive pathways. Herein, we review recent progress in probing the roles of proton-sensing receptors in preclinical pain research and their clinical relevance. We also propose a new concept of sngception to address the specific somatosensory function of acid sensation. This review aims to connect these acid-sensing receptors with basic pain research and clinical pain diseases, thus helping with better understanding the acid-related pain pathogenesis and their potential therapeutic roles via the mechanism of acid-mediated antinociception.

Persistent nociceptor hyperactivity as a painful evolutionary adaptation

Chronic pain caused by injury or disease of the nervous system (neuropathic pain) has been linked to persistent electrical hyperactivity of the sensory neurons (nociceptors) specialized to detect damaging stimuli and/or inflammation. This pain and hyperactivity are considered maladaptive because both can persist long after injured tissues have healed and inflammation has resolved. While the assumption of maladaptiveness is appropriate in many diseases, accumulating evidence from diverse species, including humans, challenges the assumption that neuropathic pain and persistent nociceptor hyperactivity are always maladaptive. We review studies indicating that persistent nociceptor hyperactivity has undergone evolutionary selection in widespread, albeit selected, animal groups as a physiological response that can increase survival long after bodily injury, using both highly conserved and divergent underlying mechanisms.

Group II metabotropic glutamate receptor activation attenuates acid-sensing ion channel currents in rat primary sensory neurons

Acid-sensing ion channels (ASICs) play an important role in pain associated with tissue acidification. Peripheral inhibitory group II metabotropic glutamate receptors (mGluRs) have analgesic effects in a variety of pain conditions. Whether there is a link between ASICs and mGluRs in pain processes is still unclear. Herein, we show that the group II mGluR agonist LY354740 inhibited acid-evoked ASIC currents and action potentials in rat dorsal root ganglia neurons. LY354740 reduced the maximum current response to protons, but it did not change the sensitivity of ASICs to protons. LY354740 inhibited ASIC currents by activating group II mGluRs. We found that the inhibitory effect of LY354740 was blocked by intracellular application of the G_i/o protein inhibitor pertussis toxin and the cAMP analogue 8-Br-cAMP and mimicked by the protein kinase A (PKA) inhibitor H-89. LY354740 also inhibited ASIC3 currents in CHO cells coexpressing mGluR2 and ASIC3 but not in cells expressing ASIC3 alone. In addition, intraplantar injection of LY354740 dose-dependently alleviated acid-induced nociceptive behavior in rats through local group II mGluRs. Together, these results suggested that activation of peripheral group II mGluRs inhibited the functional activity of ASICs through a mechanism that depended on G_i/o proteins and the intracellular cAMP/PKA signaling pathway in rat dorsal root ganglia neurons. We propose that peripheral group II mGluRs are an important therapeutic target for ASIC-mediated pain.