Changes In Dorsal Root Ganglia Research Articles

Proteomic Analysis of Dorsal Root Ganglia in a Mouse Model of Paclitaxel-Induced Neuropathic Pain.

Paclitaxel is a chemotherapy drug widely used for the treatment of various cancers based on its ability to potently stabilize cellular microtubules and block division in cancer cells. Paclitaxel-based treatment, however, accumulates in peripheral system sensory neurons and leads to a high incidence rate (over 60%) of chemotherapy induced peripheral neuropathy. Using an established preclinical model of paclitaxel-induced peripheral neuropathy (PIPN), we examined proteomic changes in dorsal root ganglia (DRG) of adult male mice that were treated with paclitaxel (8 mg/kg, at 4 injections every other day) relative to vehicle-treated mice. High throughput proteomics based on liquid chromatography electrospray ionization mass spectrometry identified 165 significantly altered proteins in lumbar DRG. Gene ontology enrichment and bioinformatic analysis revealed an effect of paclitaxel on pathways for mitochondrial regulation, axonal function, and inflammatory purinergic signaling as well as microtubule activity. These findings provide insight into molecular mechanisms that can contribute to PIPN in patients.

Proteomic analysis of dorsal root ganglia in a mouse model of paclitaxel-induced neuropathic pain.

Paclitaxel is a chemotherapy drug widely used for the treatment of various cancers based on its ability to potently stabilize cellular microtubules and block division in cancer cells. Paclitaxel-based treatment, however, accumulates in peripheral system sensory neurons and leads to a high incidence rate (over 50%) of chemotherapy induced peripheral neuropathy in patients. Using an established preclinical model of paclitaxel-induced peripheral neuropathy (PIPN), we examined proteomic changes in dorsal root ganglia (DRG) of adult male mice that were treated with paclitaxel (8 mg/kg, at 4 injections every other day) relative to vehicle-treated mice. High throughput proteomics based on liquid chromatography electrospray ionization mass spectrometry identified 165 significantly altered proteins in lumbar DRG. Gene ontology enrichment and bioinformatic analysis revealed an effect of paclitaxel on pathways for mitochondrial regulation, axonal function, and inflammatory purinergic signaling as well as microtubule activity. These findings provide insight into molecular mechanisms that can contribute to PIPN in patients.

Description of Novel Molecular Factors in Lumbar DRGs and Spinal Cord Factors Underlying Development of Neuropathic Pain Component in the Animal Model of Osteoarthritis.

Osteoarthritis (OA) is one of the most common joint disorder, with pain accompanied by functional impairment, as the most pronounced clinical symptom. Currently used pharmacotherapy involves symptomatic treatment that do not always provide adequate pain relief. This may be due to concomitance of central sensitization and development of neuropathic features in OA patients. Here we performed studies in the animal model of OA to investigate of the neuropathic component. Intraarticular injection of monoiodoacetate (MIA, 1mg) was used to induce OA in Wistar male rats. Development of pain phenotype was assessed by behavioral testing (PAM test and von Frey's test), while corresponding changes in dorsal root ganglia (DRGs L3-L5) and spinal cord (SC) gene expression were assessed by means of qRT-PCR technique. We also performed microtomography of OA-affected knee joints to correlate the level of bone degradation with observed behavioral and molecular changes. We observed gradually developing remote allodynia after MIA treatment, indicating the presence of neuropathic component. Our results showed that, among DRGs innervating knee joint, development of central sensitization is most likely due to peripheral input of stimuli through DRG L5. In SC, development of secondary hypersensitivity correlated with increased expression of TAC1 and NPY. Our studies provided molecular records on abnormal activation of pain transmission markers in DRG and SC during development of OA that are responsible for the manifestation of neuropathic features. The obtained results increase insight into molecular changes occurring in the neuronal tissue during OA development and may contribute to readdressing treatment paradigms.

Differences in the Ultrastructure of Neurons in the Spinal Ganglion and Dorsal Rootlet Between Rats Treated with Cisplatin Only versus Co-administration with a Sphingosine 1-Phosphate Receptor 2 Agonist in Attenuating Neuropathy and Allodynia.

Cisplatin is a chemotherapeutic agent for many types of cancer. The neurotoxicity of cisplatin includes neuropathy and allodynia. We aimed to study structural changes by using CYM54-78, attenuates cisplatin-induced neuropathy and blocks the pathogenesis in neurons and promotes axonal regeneration. TEM (Transmission electron microscopy) was used to distinguish ultrastructural changes in dorsal root ganglion (DRG) and dorsal rootlets (DR) between rats treated with cisplatin alone and rats co-treated with cisplatin and sphingosine -1-phosphate receptor2 (S1P2) agonist, CYM-5478. In DRG of rats treated with cisplatin alone, TEM micrographs showed necrosis and apoptotic cells. Neuronal cytoplasm showed numerous vacuole (stage C) and swelling (stage B➔C) mitochondrial degeneration. Neurons in DRG from cisplatin+CYM-5478 group showed a higher percentage of healthy mitochondria (from 5.3% to 75.6%) than those treated with cisplatin alone. DR of cisplatin only group showed abnormal axoplasm, axolemma and focal detached myelin sheaths, especially in Aδ (fast pain) and Aβ (touch) fibers and revealed collateral branches that sprouted from Aβ fibers, which is characteristic of allodynia. Moreover, vasoconstriction was observed in DRG and DR. Rats in cisplatin+CYM-5478 group showed not only fewer abnormal structures than those in cisplatin only group, but also showed Bands of Büngner and onion bulb-like structures, which are characteristic of nerve regeneration. Together with our previous study, showed that CYM-5478 attenuated neuropathy and allodynia in a rat model of cisplatin-induced neuropathy, these results suggest S1P2 agonists as a potential approach for treatment of cancer due to reduction of side-effects of cisplatin. This article is protected by copyright. All rights reserved.

Essential oil of Croton zehntneri prevents electrophysiological alterations in dorsal root ganglia of streptozotocin-induced diabetes mellitus in rats

Croton zehntneri is an aromatic shrub, native to Northeast Brazil, where it is used in folk medicine. The essential oil of C. zehntneri (EOCz) has shown potent antioxidant and anti-inflammatory activities. Our aim was to investigate the beneficial effect of EOCz on electrophysiological changes in dorsal root ganglia (DRG) of rats with streptozotocin-induced diabetes mellitus (DM). DRG excitability and passive and active membrane properties were studied in control and DM-induced rats. Intracellular recording in current-clamp mode with sharp microelectrode was used. For Na+ channel investigation, patch-clamp recording in whole-cell mode was used. DM caused depolarizations (from -60.6 to -55.0 mV) of resting membrane potential without alteration of cell membrane input resistance. Also, it showed a tendency towards a decrease in rheobase and a tendency for increase in excitability, which was confirmed by increase in Na+ current (from -113.6 to -178.3 pF/pA). EOCz did not reverse the hyperglycemia of DM. Regardless of that, upon oral treatment, EOCz prevented neuronal alterations. EOCz was demonstrated to have low toxicity. The preventive effects of EOCz on neuronal changes coupled with its low toxicity make EOCz a potential candidate for a type of treatment of diabetic neuropathy complementary to therapy with hypoglycemic agents.

Chronic constriction injury-induced changes in circular RNA expression profiling of the dorsal root ganglion in a rat model of neuropathic pain

BackgroundThe pathogenesis of neuropathic pain (NP) has not been fully elucidated. Gene changes in dorsal root ganglia (DRG) may contribute to the development of NP. Circular RNAs (circRNAs) are a class of endogenous noncoding RNAs that form covalently closed loop structures and are crucial for genetic and epigenetic regulation. However, little is known about circRNA changes in DRG neurons after peripheral nerve injury.MethodsA sciatic nerve chronic constriction injury (CCI) model was established to induce neuropathic pain. We performed genome-wide circRNA analysis of four paired dorsal root ganglion (DRG) samples (L4–L5) from CCI and negative control (NC) rats using next-generation sequencing technology. The differentially expressed circRNAs (DEcircRNAs) were identified by differential expression analysis, and the expression profile of circRNAs was validated by quantitative PCR. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses were performed to predict the function of DEcircRNAs.ResultsA total of 374 DEcircRNAs were identified between CCI and NC rats using circRNA high-throughput sequencing. Among them, 290 were upregulated and 84 were downregulated in the CCI group. The expression levels of nine DEcircRNAs were validated by qPCR. Functional annotation analysis showed that the DEcircRNAs were mainly enriched in pathways and functions, including ‘dopaminergic synapse,’ ‘renin secretion,’ ‘mitogen-activated protein kinase signaling pathway,’ and ‘neurogenesis.’ Competing endogenous RNA analysis showed that the top 50 circRNAs exhibited interactions with four pain-related microRNAs (miRNAs). Circ:chr2:33950934–33955969 was the largest node in the circRNA–miRNA interaction network.ConclusionsPeripheral nerve injury-induced neuropathic pain led to changes in the comprehensive expression profile of circRNAs in the DRG of rats. DEcircRNAs may advance our understanding of the molecular mechanisms underlying neuropathic pain.

Unbiased analysis of the dorsal root ganglion after peripheral nerve injury: no neuronal loss, no gliosis, but satellite glial cell plasticity.

Pain syndromes are often accompanied by complex molecular and cellular changes in dorsal root ganglia (DRG). However, the evaluation of cellular plasticity in the DRG is often performed by heuristic manual analysis of a small number of representative microscopy image fields. In this study, we introduce a deep learning-based strategy for objective and unbiased analysis of neurons and satellite glial cells (SGCs) in the DRG. To validate the approach experimentally, we examined serial sections of the rat DRG after spared nerve injury (SNI) or sham surgery. Sections were stained for neurofilament, glial fibrillary acidic protein (GFAP), and glutamine synthetase (GS) and imaged using high-resolution large-field (tile) microscopy. After training of deep learning models on consensus information of different experts, thousands of image features in DRG sections were analyzed. We used known (GFAP upregulation), controversial (neuronal loss), and novel (SGC phenotype switch) changes to evaluate the method. In our data, the number of DRG neurons was similar 14 d after SNI vs sham. In GFAP-positive subareas, the percentage of neurons in proximity to GFAP-positive cells increased after SNI. In contrast, GS-positive signals, and the percentage of neurons in proximity to GS-positive SGCs decreased after SNI. Changes in GS and GFAP levels could be linked to specific DRG neuron subgroups of different size. Hence, we could not detect gliosis but plasticity changes in the SGC marker expression. Our objective analysis of DRG tissue after peripheral nerve injury shows cellular plasticity responses of SGCs in the whole DRG but neither injury-induced neuronal death nor gliosis.

Quantitative proteomic analysis of oxaliplatin induced peripheral neurotoxicity

Oxaliplatin (OXA)-induced peripheral neurotoxicity (OIPN) is a high-incidence and dose-dependent adverse reaction during OXA treatment. Its underlying mechanisms remain unclear, and no effective treatment or prevention therapies are currently available. Here, we employed a data independent acquisition (DIA)-based quantitative proteomic strategy to investigate the global proteome alterations in the dorsal root ganglion (DRG) tissues from mice injected with OXA for different periods. We identified 1128 differentially regulated proteins that were divided into six subclusters according to their alteration trends. Interestingly, these proteins were involved in cellular processes such as cell cycle, ribosomal stress, metabolism, and ion transport. In addition, OXA administration induced abundance changes of ion channels and proteins associated with mitochondrial function and reactive oxygen species production. Furthermore, we investigated the effects of diroximel fumarate (DRF), an FDA-approved oral fumarate drug for the treatment of relapsing forms of multiple sclerosis. Our findings showed that DRF could effectively ameliorate symptoms of OIPN and reduce the level of oxidative stress in mice. Taken together, our study systematically mapped the proteome alteration associated with the neural toxicity of OXA, and the findings could be leveraged to better understand the mechanisms of OIPN and to develop more effect treatment therapies. SignificanceOxaliplatin (OXA)-induced peripheral neurotoxicity (OIPN) is a high-incidence and dose-dependent adverse reaction with unclear mechanism. Here we employed a data independent acquisition (DIA)-based quantitative proteomic strategy to explore the proteome changes in dorsal root ganglion (DRG) tissues from mice treated by OXA. The findings provided novel insights regarding the mechanisms of OIPN. For example, our data showed that OXA induced a broad disturbance in metabolism, particularly in glycolysis and amino acid metabolism. Additionally, we observed abundance changes of many ion channels and proteins associated with mitochondrial function and reactive oxygen species production. Furthermore, this study provided the first evidence for the possibility of repositioning diroximel fumarate (DRF) for treating OIPN.

Exercise reduces pain behavior and pathological changes in dorsal root ganglia induced by systemic inflammation in mice

Emerging research indicates that physical activity can ameliorate chronic pain, but the underlying mechanisms are still largely obscure. In particular, little is known on the mechanisms behind exercise-induced analgesia in the setting of inflammatory pain. In our previous studies on systemic inflammation in mice using lipopolysaccharide (LPS) administration, we characterized satellite glial cells (SGCs) and neurons in dorsal root ganglia (DRG). We found that a week post-LPS injection, the sensitivity to mechanical stimulation was lowered, SGCs were activated and coupling among SGCs increased 3 to 4.5-fold. In the present work, we examined the effects of exercise (free wheel running) on tactile sensitivity and on pathological changes in mouse DRG in the LPS model. We found that exercise prevented tactile hypersensitivity, and also reversed the cellular changes in the DRG induced by LPS that were listed above. We propose that the analgesic effect of exercise is at least partly mediated by reversing the pathological changes in SGCs.

Exercise Reduces Pain and Pathological Changes in Dorsal Root Ganglia Induced by Systemic Inflammation in Mice

Exercise Reduces Pain and Pathological Changes in Dorsal Root Ganglia Induced by Systemic Inflammation in Mice

Suppression of joint pain in transient receptor potential vanilloid 4 knockout rats with monoiodoacetate-induced osteoarthritis.

Transient receptor potential vanilloid 4 (TRPV4) modulates osteoarthritic (OA) pain in animal models. However, the pathophysiological function of TRPV4 in regulating OA pain remains poorly understood. We developed TRPV4-knockout (TRPV4-KO) rats and assessed the effects of Trpv4 gene deficiency in a monoiodoacetate (MIA)-induced OA pain model (MIA rats) by examining pain-related behavior, pathological changes, and electrophysiological changes in dorsal root ganglion (DRG) neurons. The changes detected in TRPV4-KO rats were confirmed in wild-type rats using a TRPV4 antagonist. Transient receptor potential vanilloid 4-KO rats showed the same pain threshold as wild-type rats for thermal or pressure stimuli under normal conditions. Trpv4 gene deletion did not suppress the development of osteoarthritis pathologically in MIA rats. However, the OA-related mechanical pain behaviors observed in MIA rats, including decreased grip strength, increased mechanical allodynia, and reduced weight-bearing on the ipsilateral side, were completely suppressed in TRPV4-KO rats. The DRG neurons in wild-type but not TRPV4-KO MIA rats were depolarized with increased action potentials. Transient receptor potential vanilloid 4 antagonist treatments recapitulated the effects of genetic Trpv4 deletion. Transient receptor potential vanilloid 4 was sensitized in the DRG neurons of MIA rats and played a critical role in the development of OA pain. These results suggest that the inhibition of TRPV4 might be a novel potent analgesic strategy for treating OA pain.

Neuropathological changes in dorsal root ganglia induced by pyridoxine in dogs

BackgroundPyridoxine (PDX; vitamin B6), is an essential vitamin. PDX deficiency induces various symptoms, and when PDX is misused it acts as a neurotoxicant, inducing severe sensory neuropathy.ResultsTo assess the possibility of creating a reversible sensory neuropathy model using dogs, 150 mg/kg of PDX was injected subcutaneously into dogs for 7 days and body weight measurements, postural reaction assessments, and electrophysiological recordings were obtained. In addition, the morphology of dorsal root ganglia (DRG) and changes in glial fibrillary acidic protein (GFAP) immunoreactive satellite glial cells and ionized calcium-binding adapter molecule 1 (Iba-1) immunoreactive microglia/macrophages were assessed at 1 day, 1 week, and 4 weeks after the last PDX treatment. During the administration period, body weight and proprioceptive losses occurred. One day after the last PDX treatment, electrophysiological recordings showed the absence of the H-reflex in the treated dogs. These phenomena persisted over the four post-treatment weeks, with the exception of body weight which recovered to the pre-treatment level. Staining (CV and HE) results revealed significant losses of large-sized neurons in the DRG at 1 day and 1 week after PDX treatment cessation, but the losses were recovered at 4 weeks post-treatment. The Iba-1 and GFAP immunohistochemistry results showed pronounced increases in reactive microglia/macrophage and satellite glial cell at 1 day and 1 week, respectively, after the last PDX treatment, and thereafter, immunoreactivity decreased with increasing time after PDX treatment.ConclusionsThe results suggest that PDX-induced neuropathy is reversible in dogs; thus, dogs can be considered a good experimental model for research on neuropathy.

DRG神経におけるホメオボックス遺伝子DRGXの神経障害性疼痛への関与

Neuropathic pain is caused by lesions or diseases of the somatosensory system and is less responsive to pain medications. Transcriptomic changes in dorsal root ganglion (DRG) neurons are involved in initiation and maintenance of neuropathic pain. Dorsal Root Ganglia Homeobox (DRGX) is a paired-like homeodomain transcription factor crucial for the development of nociceptive DRG neurons. However, roles for DRGX after development are almost unclarified. Here, we report that DRGX downregulation in DRG neurons due to nerve injury in the post-developmental stage is involved in neuropathic pain in rats. DRGX expression was persistently decreased in DRG neurons in neuropathic pain model rats produced by spinal nerve ligation. DRGX protein was mainly downregulated in nuclei of small-to-medium DRG neurons after the nerve injury. Additionally, DRGX downregulation using an adeno-associated viral vector expressing short hairpin RNA induced mechanical allodynia and thermal hyperalgesia in intact rats, while DRGX overexpression suppressed neuropathic pain. DRGX regulated mRNA expression of matrix metalloproteinase-9 and prostaglandin E receptor 2 in the DRG. These results suggest that DRGX downregulation after development contributes to neuropathic pain through transcriptional modulation of pain-related genes in DRG neurons.

Cutaneous inflammation differentially regulates the expression and function of Angiotensin-II types 1 and 2 receptors in rat primary sensory neurons.

Neuropathic and inflammatory pain results from cellular and molecular changes in dorsal root ganglion (DRG) neurons. The type-2 receptor for Angiotensin-II (AT2R) has been involved in this type of pain. However, the underlying mechanisms are poorly understood, including the role of the type-1 receptor for Angiotensin-II (AT1R). Here, we used a combination of immunohistochemistry and immunocytochemistry, RT-PCR and in vitro and in vivo pharmacological manipulation to examine how cutaneous inflammation affected the expression of AT1R and AT2R in subpopulations of rat DRG neurons and studied their impact on inflammation-induced neuritogenesis. We demonstrated that AT2R-neurons express C- or A-neuron markers, primarily IB4, trkA, and substance-P. AT1R expression was highest in small neurons and co-localized significantly with AT2R. In vitro, an inflammatory soup caused significant elevation of AT2R mRNA, whereas AT1R mRNA levels remained unchanged. In vivo, we found a unique pattern of change in the expression of AT1R and AT2R after cutaneous inflammation. AT2R increased in small neurons at 1day and in medium size neurons at 4days. Interestingly, cutaneous inflammation increased AT1R levels only in large neurons at 4days. We found that in vitro and in vivo AT1R and AT2R acted co-operatively to regulate DRG neurite outgrowth. In vivo, AT2R inhibition impacted more on non-peptidergic C-neurons neuritogenesis, whereas AT1R blockade affected primarily peptidergic nerve terminals. Thus, cutaneous-induced inflammation regulated AT1R and AT2R expression and function in different DRG neuronal subpopulations at different times. These findings must be considered when targeting AT1R and AT2R to treat chronic inflammatory pain. Cover Image for this issue: doi: 10.1111/jnc.14737.

Multiplex Epigenome Editing of Dorsal Root Ganglion Neuron Receptors Abolishes Redundant Interleukin 6, Tumor Necrosis Factor Alpha, and Interleukin 1β Signaling by the Degenerative Intervertebral Disc.

Back pain is the leading cause of disability worldwide and contributes to significant socioeconomic impacts. It has been hypothesized that the degenerative intervertebral disc (IVD) contributes to back pain by sensitizing nociceptive neurons innervating the IVD to stimuli that would not be painful to healthy patients. However, the inflammatory signaling networks mediating this sensitization remain poorly understood. A better understanding of the underlying mechanisms of degenerative IVD-induced changes in nociception is required to improve the understanding and treatment of back pain. Toward these ends, a novel in vitro model was developed to investigate degenerative IVD-induced changes in dorsal root ganglion (DRG) neuron activation by measuring DRG neuron activity following neuron seeding on human degenerative IVD tissue collected from patients undergoing surgical treatment for back pain. Lentiviral clustered regularly interspaced palindromic repeat (CRISPR) epigenome editing vectors were built to downregulate the inflammatory receptors TNFR1, IL1R1, and IL6st in DRG neurons in single- and multiplex. Multiplex CRISPR epigenome editing of inflammatory receptors demonstrated that degenerative IVD tissue drives thermal sensitization through the simultaneous and redundant signaling of interleukin (IL)-6, tumor necrosis factor alpha (TNF-α), and IL-1β. This work elucidates redundant signaling pathways in neuron interactions with the degenerative IVD and suggests the need for multiplex targeting of IL-6, TNF-α, and IL-1β for pain modulation in the degenerative IVD.

Antiallodynic effects of the selective NaV1.7 inhibitor Pn3a in a mouse model of acute postsurgical pain: evidence for analgesic synergy with opioids and baclofen.

Pain is the leading cause of disability in the developed world but remains a poorly treated condition. Specifically, postsurgical pain continues to be a frequent and undermanaged condition. Here, we investigate the analgesic potential of pharmacological NaV1.7 inhibition in a mouse model of acute postsurgical pain, based on incision of the plantar skin and underlying muscle of the hind paw. We demonstrate that local and systemic treatment with the selective NaV1.7 inhibitor μ-theraphotoxin-Pn3a is effectively antiallodynic in this model and completely reverses mechanical hypersensitivity in the absence of motor adverse effects. In addition, the selective NaV1.7 inhibitors ProTx-II and PF-04856264 as well as the clinical candidate CNV1014802 also reduced mechanical allodynia. Interestingly, co-administration of the opioid receptor antagonist naloxone completely reversed analgesic effects of Pn3a, indicating an involvement of endogenous opioids in the analgesic activity of Pn3a. In addition, we found superadditive antinociceptive effects of subtherapeutic Pn3a doses not only with the opioid oxycodone but also with the GABAB receptor agonist baclofen. Transcriptomic analysis of gene expression changes in dorsal root ganglia of mice after surgery did not reveal any changes in mRNA expression of endogenous opioids or opioid receptors; however, several genes involved in pain, including Runx1 (Runt related transcription factor 1), Cacna1a (CaV2.1), and Cacna1b (CaV2.2), were downregulated. In summary, these findings suggest that pain after surgery can be successfully treated with NaV1.7 inhibitors alone or in combination with baclofen or opioids, which may present a novel and safe treatment strategy for this frequent and poorly managed condition.

DNMT3a-triggered downregulation of K2p 1.1 gene in primary sensory neurons contributes to paclitaxel-induced neuropathic pain.

Antineoplastic drugs induce dramatic transcriptional changes in dorsal root ganglion (DRG) neurons, which may contribute to chemotherapy-induced neuropathic pain. K2p 1.1 controls neuronal excitability by setting the resting membrane potential. Here, we report that systemic injection of the chemotherapy agent paclitaxel time-dependently downregulates the expression of K 2p 1.1 mRNA and its coding K2p 1.1 protein in the DRG neurons. Rescuing this downregulation mitigates the development and maintenance of paclitaxel-induced mechanical allodynia and heat hyperalgesia. Conversely, in the absence of paclitaxel administration, mimicking this downregulation decreases outward potassium current and increases excitability in the DRG neurons, leading to the enhanced responses to mechanical and heat stimuli. Mechanically, the downregulation of DRG K 2p 1.1 mRNA is attributed to paclitaxel-induced increase in DRG DNMT3a, as blocking this increase reverses the paclitaxel-induced the decrease of DRG K2p 1.1 and mimicking this increase reduces DRG K2p 1.1 expression. In addition, paclitaxel injection increases the binding of DNMT3a to the K 2p 1.1 gene promoter region and elevates the level of DNA methylation within this region in the DRG. These findings suggest that DNMT3a-triggered downregulation of DRG K2p 1.1 may contribute to chemotherapy-induced neuropathic pain.

Gene expression changes in dorsal root ganglia following peripheral nerve injury: roles in inflammation, cell death and nociception.

Subsequent to a peripheral nerve injury, there are changes in gene expression within the dorsal root ganglia in response to the damage. This review selects factors which are well-known to be vital for inflammation, cell death and nociception, and highlights how alterations in their gene expression within the dorsal root ganglia can affect functional recovery. The majority of studies used polymerase chain reaction within animal models to analyse the dynamic changes following peripheral nerve injuries. This review aims to highlight the factors at the gene expression level that impede functional recovery and are hence are potential targets for therapeutic approaches. Where possible the experimental model, specific time-points and cellular location of expression levels are reported.

Peripheral pain is enhanced by insulin-like growth factor 1 and its receptors in a mouse model of type 2 diabetes mellitus.

Insulin-like growth factor 1 (IGF1) is a neurotrophic factor with many actions, including a possible hyperalgesic effect. This study investigated the effects of IGF1 on the overall behavior of diabetic mice and explored the possible mechanisms underlying IGF1-induced pain. Mice were divided into five groups (db/m, db/db, vehicle-treated db/db, IGF1-treated db/db, and IGF1 + JB1-treated db/db mice). Behavioral studies were conducted using the hot plate and Von Frey tests after intraplantar injection of recombinant (r) IGF1 (50 μg/kg) and the IGF1 receptor (IGF1R) antagonist JB1 (6 μg/mouse). Morphological changes in dorsal root ganglia (DRG) were evaluated using electron microscopy. Immunofluorescence was used to detect IGF1R expression and colocalisation with pain mediators in the DRG. Changes in the expression of IGF1R, extracellular signal-regulated kinase (ERK), and ras-associated factor-1 (c-raf) in the DRG were evaluated using western blotting. Intraplantar injection of rIGF1 resulted in a hyperalgesic effect after 2 hours. This IGF1-induced hypersensitivity was attenuated by prior intraplantar injection of the IGF1R antagonist. There was no significant change in neuronal structure in the db/m group, whereas neuronal structure was impaired in the other four groups. Moreover, IGF1R was colocalised with pain mediators in the DRG of mice. Intraplantar injection of rIGF1 resulted in increased IGF1R, phosphorylated (p-) ERK, and c-raf expression in the DRG; prior intraplantar injection of the IGF1R antagonist attenuated rIGF1-induced increases in p-ERK and c-raf. The results indicate that IGF1-induced acute hyperalgesia may be associated with the IGF1R/c-raf/ERK pathway. The IGF1-induced hypersensitivity was attenuated by an IGF1R antagonist.

Transcription factor networks involved in cell death in the dorsal root ganglia following peripheral nerve injury.

The peripheral nervous system has the potential to regenerate after nerve injury owing to the intrinsic regrowth ability of neurons and the permissive microenvironment. The regenerative process involves numerous gene expression changes, in which transcription factors play a critical role. Previously, we profiled dysregulated genes in dorsal root ganglion neurons at different time points (0, 3 and 9 hours, and 1, 4 and 7 days) after sciatic nerve injury in rats by RNA sequencing. In the present study, we investigated differentially expressed transcription factors following nerve injury, and we identified enriched molecular and cellular functions of these transcription factors by Ingenuity Pathway Analysis. This analysis revealed the dynamic changes in the expression of transcription factors involved in cell death at different time points following sciatic nerve injury. In addition, we constructed regulatory networks of the differentially expressed transcription factors in cell death and identified some key transcription factors (such as STAT1, JUN, MYC and IRF7). We confirmed the changes in expression of some key transcription factors (STAT1 and IRF7) by quantitative reverse transcription-polymerase chain reaction. Collectively, our analyses provide a global overview of transcription factor changes in dorsal root ganglia after sciatic nerve injury and offer insight into the regulatory transcription factor networks involved in cell death.