Membrane protein Nav1.7 contributes to the persistent post-surgical pain regulated by p-p65 in dorsal root ganglion (DRG) of SMIR rats model

Correlative increasing expressions of KIF5b and Nav1.7 in DRG neurons of rats under neuropathic pain conditions

Nav1.7, one of tetrodotoxin-sensitive voltage-gated sodium channels, mainly expressed in the small diameter dorsal root ganglion (DRG) neurons. The expression and accumulation on neuronal membrane of Nav1.7 increased following peripheral tissue inflammation or nerve injury. However, the mechanisms for membrane accumulation of Nav1.7 remained unclear. We report that KIF5b, a highly expressed member of the kinesin-1 family in DRGs, promoted the translocation of Nav1.7 to the plasma membrane in DRG neurons of the rat. Following nociceptive behaviors in rats induced by peripheral spared nerve injury (SNI), synchronously increased KIF5b and Nav1.7 expressions were observed in DRGs. Immunohistochemistry staining demonstrated the co-expressions of KIF5b and Nav1.7 in the same DRG neurons. Immunoprecipitation experiments further confirmed the interactions between KIF5b and Nav1.7. Moreover, intrathecal injections of KIF5b shRNA moderated the SNI-induced both mechanical and thermal hyperalgesia. The rescued analgesic effects also alleviated SNI-induced anxiety-like behaviors. In sum, KIF5b was required for the membrane localizations of Nav1.7, which suggests a novel mechanism for the trafficking of Nav1.7 involved in neuropathic pain.

Genome-Wide Expression Profiling by RNA-Sequencing in Spinal Cord Dorsal Horn of a Rat Chronic Postsurgical Pain Model to Explore Potential Mechanisms Involved in Chronic Pain

Background

Chronic postsurgical pain (CPSP) is common among patients receiving major surgeries. CPSP produces suffering in patients, both physically and mentally. However, the mechanisms underlying CPSP remain elusive. Here, a genome-wide expression profiling of ipsilateral spinal cord dorsal horn (SCDH) was performed to identify potential genes related with CPSP.

Methods

A rat skin/muscle incision and retraction (SMIR) model was established to induce CPSP. Immunostaining was used to study glial cell and neuron activation in ipsilateral SCDH of SMIR model rats. RNA sequencing (RNA-Seq), combined with bioinformatics analysis, was undertaken to explore gene expression profiles. qPCR was applied to validate the expression of some representative genes.

Results

The SMIR model rats developed persistent mechanical allodynia in ipsilateral hindpaw for up to 14 days. Ipsilateral SCDH of SMIR rats showed remarkable glial cell and neuron activation. A number of differentially expressed genes (DEGs) were identified in ipsilateral SCDH of SMIR rats by RNA-Seq. qPCR confirmed expression of some representative DEGs. Bioinformatics indicated that chemical synaptic transmission, sensory perception of pain and neuroactive ligand-receptor interaction were predominant functions. We compared our dataset with human pain-related genes and found that several genes exclusively participate in pain modulation and mechanisms.

Conclusion

Our study provided novel understandings of the molecular mechanisms possibly contributing to CPSP. These findings may offer new targets for future treatment of CPSP.

Nociceptor Overexpression of NaV1.7 Contributes to Chronic Muscle Pain Induced by Early-Life Stress

Adult rats previously submitted to neonatal limited bedding (NLB), a model of early-life stress, display muscle mechanical hyperalgesia and nociceptor hyperexcitability, the underlying mechanism for which is unknown. Since voltage-gated sodium channel subtype 7 (NaV1.7) contributes to mechanical hyperalgesia in several preclinical pain models and is critical for nociceptor excitability, we explored its role in the muscle hyperalgesia exhibited by adult NLB rats. Western blot analyses demonstrated increased NaV1.7 protein expression in L4-L5 dorsal root ganglia (DRG) from adult NLB rats, and antisense oligodeoxynucleotide (AS ODN) targeting NaV1.7 alpha subunit mRNA attenuated the expression of NaV1.7 in DRG extracts. While this AS ODN did not affect nociceptive threshold in normal rats it significantly attenuated hyperalgesia in NLB rats. The selective NaV1.7 activator OD1 produced dose-dependent mechanical hyperalgesia that was enhanced in NLB rats, whereas the NaV1.7 blocker ProTx-II prevented OD1-induced hyperalgesia in control rats and ongoing hyperalgesia in NLB rats. AS ODN knockdown of extracellular signal-regulated kinase 1/2, which enhances NaV1.7 function, also inhibited mechanical hyperalgesia in NLB rats. Our results support the hypothesis that overexpression of NaV1.7 in muscle nociceptors play a role in chronic muscle pain induced by early-life stress, suggesting that NaV1.7 is a target for the treatment of chronic muscle pain. PERSPECTIVE: We demonstrate that early-life adversity, induced by exposure to inconsistent maternal care, produces chronic muscle hyperalgesia, which depends, at least in part, on increased expression of NaV1.7 in nociceptors.

Fluorescent- and tagged-protoxin II peptides: potent markers of the Nav 1.7 channel pain target

BACKGROUND AND PURPOSE

Protoxin II (ProTx II) is a high affinity gating modifier that is thought to selectively block the Na_v 1.7 voltage-dependent Na⁺ channel, a major therapeutic target for the control of pain. We aimed at producing ProTx II analogues entitled with novel functionalities for cell distribution studies and biochemical characterization of its Na_v channel targets.

EXPERIMENTAL APPROACH

We took advantage of the high affinity properties of the peptide, combined to its slow off rate, to design a number of new tagged analogues useful for imaging and biochemistry purposes. We used high-throughput automated patch-clamp to identify the analogues best matching the native properties of ProTx II and validated them on various Na_v -expressing cells in pull-down and cell distribution studies.

KEY RESULTS

Two of the produced ProTx II analogues, Biot-ProTx II and ATTO488-ProTx II, best emulate the pharmacological properties of unlabelled ProTx II, whereas other analogues remain high affinity blockers of Na_v 1.7. The biotinylated version of ProTx II efficiently works for the pull-down of several Na_v isoforms tested in a concentration-dependent manner, whereas the fluorescent ATTO488-ProTx II specifically labels the Na_v 1.7 channel over other Na_v isoforms tested in various experimental conditions.

CONCLUSIONS AND IMPLICATIONS

The properties of these ProTx II analogues as tools for Na_v channel purification and cell distribution studies pave the way for a better understanding of ProTx II channel receptors in pain and their pathophysiological implications in sensory neuronal processing. The new fluorescent ProTx II should also be useful in the design of new drug screening strategies.

NGF-Induced Nav1.7 Upregulation Contributes to Chronic Post-surgical Pain by Activating SGK1-Dependent Nedd4-2 Phosphorylation

At present, chronic post-surgical pain (CPSP) is difficult to prevent and cure clinically because of our lack of understanding of its mechanisms. Surgical injury induces the upregulation of voltage-gated sodium channel Nav1.7 in dorsal root ganglion (DRG) neurons, suggesting that Nav1.7 is involved in the development of CPSP. However, the mechanism leading to persistent dysregulation of Nav1.7 is largely unknown. Given that nerve growth factor (NGF) induces a long-term increase in the neuronal hyperexcitability after injury, we hypothesized that NGF might cause the long-term dysregulation of Nav1.7. In this study, we aimed to investigate whether Nav1.7 regulation by NGF is involved in CPSP and thus contributes to the specific mechanisms involved in the development of CPSP. Using conditional nociceptor-specific Nav1.7 knockout mice, we confirmed the involvement of Nav1.7 in NGF-induced pain and identified its role in the maintenance of pain behavior during long-term observations (up to 14 days). Using western blot analyses and immunostaining, we showed that NGF could trigger the upregulation of Nav1.7 expression and thus support the development of CPSP in rats. Using pharmacological approaches, we showed that the increase of Nav1.7 might be partly regulated by an NGF/TrkA-SGK1-Nedd4-2-mediated pathway. Furthermore, reversing the upregulation of Nav1.7 in DRG could alleviate spinal sensitization. Our results suggest that the maintained upregulation of Nav1.7 triggered by NGF contributes to the development of CPSP. Attenuating the dysregulation of Nav1.7 in peripheral nociceptors may be a strategy to prevent the transition from acute post-surgical pain to CPSP.

Age-related molecular changes in the lumbar dorsal root ganglia of mice: Signs of sensitization, and inflammatory response

Aging is a major risk factor for numerous painful, inflammatory, and degenerative diseases including disc degeneration. A better understanding of how the somatosensory nervous system adapts to the changing physiology of the aging body will be of great significance for our expanding aging population. Previously, we reported that chronological aging of mouse lumbar discs is pathological and associated with behavioral changes related to pain. It is established that with age and degeneration the lumbar discs become inflammatory and innervated. Here we analyze the aging lumbar dorsal root ganglia (DRGs) and spinal cord dorsal horn (SCDH) in mice between 3 and 24 months of age for age-related somatosensory adaptations. We observe that as mice age there are signs of peripheral sensitization, and response to inflammation at the molecular and cellular level in the DRGs. From 12 months onwards the mRNA expression of vasodilator and neurotransmitter, Calca (CGRP); stress (and survival) marker, Atf3; and neurotrophic factor, Bdnf, increases linearly with age in the DRGs. Further, while the mRNA expression of neuropeptide, Tac1, precursor of Substance P, did not change at the transcriptional level, TAC1 protein expression increased in 24-month-old DRGs. Additionally, elevated expression of NFκB subunits, Nfkb1 and Rela, but not inflammatory mediators, Tnf, Il6, Il1b, or Cox2, in the DRGs suggest peripheral nerves are responding to inflammation, but do not increase the expression of inflammatory mediators at the transcriptional level. These results identify a progressive, age-related shift in the molecular profile of the mouse somatosensory nervous system and implicates nociceptive sensitization and inflammatory response.

Influence of androgenic blockade with flutamide on pain behaviour and expression of the genes that encode the NaV1.7 and NaV1.8 voltage-dependent sodium channels in a rat model of postoperative pain

Background

Experimental studies suggest that testosterone reduces the nociceptive response after inflammatory and neuropathic stimuli, however the underlying mechanisms have not been fully elucidated. The aims of this study were to evaluate the effect of peripheral blockade of testosterone on pain behaviour and on expression levels of the genes that encode the NaV1.7 and NaV1.8 channels, in dorsal root ganglia in an acute postoperative pain model, as well as the influence of androgen blockade on the expression of these genes.

Methods

Postoperative pain was induced by a plantar incision and the study group received flutamide to block testosterone receptor. The animals were submitted to behavioural evaluation preoperatively, 2 h after incision, and on the 1st, 2nd, 3rd and 7th postoperative days. Von Frey test was used to evaluate paw withdrawal threshold after mechanical stimuli and the guarding pain test to assess spontaneous pain. The expression of the genes encoding the sodium channels at the dorsal root ganglia was determined by real time quantitative polymerase chain reaction.

Results

Animals treated with flutamide presented lower paw withdrawal threshold at the 1st, 2nd, 3rd, and 7th postoperative days. The guarding pain test showed significant decrease in the flutamide group at 2 h and on the 3rd and 7th postoperative days. No difference was detected between the study and control groups for the gene expression.

Conclusions

Our data suggest an antinociceptive effect of androgens following plantar incision. The expression of genes that encode voltage-gated sodium channels was not influenced by androgen blockade.

Voltage-gated sodium channel 1.7 expression decreases in dorsal root ganglia in a spinal nerve ligation neuropathic pain model

The role of the voltage-gated sodium channel 1.7 (Nav1.7) is unclear in models of neuropathic pain induced by nerve injury. In the present study, we measured expression levels of Nav1.7 in two distinct neuropathic pain models: spinal nerve ligation (SNL) and chronic constriction injury (CCI). In the SNL model, both mRNA and protein levels of Nav1.7 were markedly lower in the L5 dorsal root ganglia (DRG) but were significantly higher in the L4 DRG. Nav1.7 protein levels were notably higher in both L4 and L5 DRGs under CCI conditions. We found that excessive damage of L5 nerves such as SNL reduced expression levels of Nav1.7 in the injured L5 DRG and activated the adjacent uninjured DRG, resulting in Nav1.7 level increases in the adjacent L4 DRG. We confirmed again that Nav1.7 was closely related to neuropathic pain induced by nerve injury. More importantly, our results suggest that tracing the molecular changes exclusively in the L5 DRG in SNL model may not completely explain the pain mechanism; it is necessary to study the adjacent uninjured L4 DRG.

Mechanisms of acute and chronic pain after surgery: update from findings in experimental animal models

PURPOSE OF REVIEW

Management of postoperative pain is still a major issue and relevant mechanisms need to be investigated. In preclinical research, substantial progress has been made, for example, by establishing specific rodent models of postoperative pain. By reviewing most recent preclinical studies in animals related to postoperative, incisional pain, we outline the currently available surgical-related pain models, discuss assessment methods for pain-relevant behavior and their shortcomings to reflect the clinical situation, delineate some novel clinical-relevant mechanisms for postoperative pain, and point toward future needs.

RECENT FINDINGS

Since the development of the first rodent model of postoperative, incisional pain almost 20 years ago, numerous variations and some procedure-specific models have been emerged including some conceivably relevant for investigating prolonged, chronic pain after surgery. Many mechanisms have been investigated by using these models; most recent studies focussed on endogenous descending inhibition and opioid-induced hyperalgesia. However, surgical models beyond the classical incision model have so far been used only in exceptional cases, and clinical relevant behavioral pain assays are still rarely utilized.

SUMMARY

Pathophysiological mechanisms of pain after surgery are increasingly discovered, but utilization of pain behavior assays are only sparsely able to reflect clinical-relevant aspects of acute and chronic postoperative pain in patients.

Arthropod toxins and their antinociceptive properties: From venoms to painkillers

The complex process of pain control commonly involves the use of systemic analgesics; however, in many cases, a more potent and effective polypharmacological approach is needed to promote clinically significant improvement. Additionally, considering side effects caused by current painkillers, drug discovery is once more turning to nature as a source of more efficient therapeutic alternatives. In this context, arthropod venoms contain a vast array of bioactive substances that have evolved to selectively bind to specific pharmacological targets involved in the pain signaling pathway, playing an important role as pain activators or modulators, the latter serving as promising analgesic agents. The current review explores how the pain pathway works and surveys neuroactive compounds obtained from arthropods' toxins, which function as pain modulators through their interaction with specific ion channels and membrane receptors, emerging as promising candidates for drug design and development.