Haploinsufficiency of the brain-derived neurotrophic factor gene is associated with reduced pain sensitivity

The differentiation of glial precursors into neuronal-like cells through the Wnt and Neurotrophin signaling pathways via Ctnnβ1

Glial precursor cells are among the major types of glia in the dorsal root ganglias (DRGs) of the peripheral nervous system. Previous studies have shown that the transdifferentiation of DRGs-derived glial precursor cells contributes to peripheral neurogenesis. In the present study, we investigated the mRNA expression profiles and examined the effects of differential expression mRNAs (DEMs) during the differentiation of glial precursor cells derived from the rat DRGs. We characterized glial precursor cells derived from rat DRGs explants using immunofluorescence. Sequencing was subsequently conducted, followed by enrichment analysis utilizing gene ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. The identified genes were subsequently subjected to protein-protein interaction (PPI) network analysis during the differentiation process of glial precursor cells derived from the rat DRGs. The establishment of a sciatic nerve injury (SNI) model was followed by the detection of the expression of key genes in the Wnt and Neurotrophin pathways in the DRGs of SNI rats via qRT-PCR. Additionally, the terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay was employed to assess apoptosis in the DRGs. We detected the mRNA expression profiles during the neuronal differentiation of rat DRGs-derived glial precursor cells. More DEMs and GO terms were detected on the third day of DRGs-derived glial precursor cells transdifferentiation, accompanied by morphological alterations in the cells; that is, some cells presented neuronal-like phenotypic characteristics (the early neuronal marker Tuj1 was positive). KEGG enrichment and PPI network analyses revealed that Wnt and Neurotrophin pathways play crucial roles in the process of glial precursor cell differentiation into neuronal-like cells. After knocking down cadherin-associated protein beta 1 (Ctnnβ1) in the SNI model, the number of apoptotic cells was significantly reduced, and the expression of Wnt4 and Ntrk3 was significantly increased. The Ctnnβ1 gene may be a crosstalk factor between the Wnt and Neurotrophin pathways that negatively regulates the differentiation of glial precursor cells.

The Genetics of Obesity

Understanding the genetic causes of obesity permits anticipatory guidance and targeted treatments. Children with hyperphagia and severe early-onset obesity should receive genetic testing for rare monogenic and syndromic disorders caused by pathogenic variants involving a single gene or single chromosomal region. Gene panels covering the leptin pathway, the key regulator of energy balance, are becoming more widely available and at lower cost. Polygenic obesity is much more common and involves multiple genes throughout the genome, although the overlap in genes for rare and common disorders suggests a spectrum of severity and the potential of shared precision medicine approaches for treatment.

An improved conflict avoidance assay reveals modality-specific differences in pain hypersensitivity across sexes

ABSTRACT

Abnormal encoding of somatosensory modalities (ie, mechanical, cold, and heat) are a critical part of pathological pain states. Detailed phenotyping of patients' responses to these modalities have raised hopes that analgesic treatments could one day be tailored to a patient's phenotype. Such precise treatment would require a profound understanding of the underlying mechanisms of specific pain phenotypes at molecular, cellular, and circuitry levels. Although preclinical pain models have helped in that regard, the lack of a unified assay quantifying detailed mechanical, cold, and heat pain responses on the same scale precludes comparing how analgesic compounds act on different sensory phenotypes. The conflict avoidance assay is promising in that regard, but testing conditions require validation for its use with multiple modalities. In this study, we improve upon the conflict avoidance assay to provide a validated and detailed assessment of all 3 modalities within the same animal, in mice. We first optimized testing conditions to minimize the necessary amount of training and to reduce sex differences in performances. We then tested what range of stimuli produce dynamic stimulus-response relationships for different outcome measures in naive mice. We finally used this assay to show that nerve injury produces modality-specific sex differences in pain behavior. Our improved assay opens new avenues to study the basis of modality-specific abnormalities in pain behavior.

Pain research and children and adolescents with severe intellectual disability: ethical challenges and imperatives

Children with severe intellectual disabilities encounter inequities in pain-related care, yet little pain research involves this population. A considerable issue with pain research in this population is its ethical complexity. This Viewpoint delineates the ethical challenges of pain research involving children (aged 2-12 years) and adolescents (aged 13-21 years) with severe intellectual disabilities. There are two main issues. First, some of the standard methods for assessing pain and pain sensitivity are not suitable for individuals with severe intellectual disability, who are often non-verbal and unable to understand or follow instructions. Second, children and adolescents with severe intellectual disability cannot provide informed consent or assent to participate in pain research, and their dissent is not always recognised. The existing ethical guidelines for pain research by the International Association for the Study of Pain provide helpful, but general, guidance. This Viewpoint supplements these guidelines and uses a well established framework for assessing the ethics of clinical research to highlight points relevant to designing, doing, reviewing, and evaluating research involving children and adolescents with severe intellectual disability, focusing on issues that are unaddressed in existing guidance.

Transcriptional Activation, Deactivation and Rebound Patterns in Cortex, Hippocampus and Amygdala in Response to Ketamine Infusion in Rats

Ketamine, an N-methyl-D-aspartate (NMDA)-receptor antagonist, is a recently revitalized treatment for pain and depression, yet its actions at the molecular level remain incompletely defined. In this molecular-pharmacological investigation in the rat, we used short- and longer-term infusions of high dose ketamine to stimulate neuronal transcription processes. We hypothesized that a progressively stronger modulation of neuronal gene networks would occur over time in cortical and limbic pathways. A continuous intravenous administration paradigm for ketamine was developed in rat consisting of short (1 h) and long duration (10 h, and 10 h + 24 h recovery) infusions of anesthetic concentrations to activate or inhibit gene transcription in a pharmacokinetically controlled fashion. Transcription was measured by RNA-Seq in three brain regions: frontal cortex, hippocampus, and amygdala. Cellular level gene localization was performed with multiplex fluorescent in situ hybridization. Induction of a shared transcriptional regulatory network occurred within 1 h in all three brain regions consisting of (a) genes involved in stimulus-transcription factor coupling that are induced during altered synaptic activity (immediate early genes, IEGs, such as c-Fos, 9–12 significant genes per brain region, p < 0.01 per gene) and (b) the Nrf2 oxidative stress-antioxidant response pathway downstream from glutamate signaling (Nuclear Factor Erythroid-Derived 2-Like 2) containing 12–25 increasing genes (p < 0.01) per brain region. By 10 h of infusion, the acute results were further reinforced and consisted of more and stronger gene alterations reflecting a sustained and accentuated ketamine modulation of regional excitation and plasticity. At the cellular level, in situ hybridization localized up-regulation of the plasticity-associated gene Bdnf, and the transcription factors Nr4a1 and Fos, in cortical layers III and V. After 24 h recovery, we observed overshoot of transcriptional processes rather than a smooth return to homeostasis suggesting an oscillation of plasticity occurs during the transition to a new phase of neuronal regulation. These data elucidate critical molecular regulatory actions during and downstream of ketamine administration that may contribute to the unique drug actions of this anesthetic agent. These molecular investigations point to pathways linked to therapeutically useful attributes of ketamine.

Sex differences in choice-based thermal nociceptive tests in adult rats

Interest in the role of sex as a biological variable has increased, including a mandate for the study of both sexes in NIH-funded research. As sex differences exist in both human chronic pain conditions and rodent models of nociception, it is critical to understand the impact of sex in nociceptive assays. Choice-based thermal nociceptive tests permit the study of avoidance responses to thermal stimuli compared to traditional nociceptive assays, which measure nocifensive reactions. However, to date no comparison of male and female responses to choice-based tests has been published. Herein, we examined the effect of sex on two choice-based thermal nociceptive tests, the thermal gradient test and the temperature place preference test, in adult rats. The activation of a 10 °C-to-47 °C thermal gradient results in an increase in time spent in the 10 °C zone in females, compared to a reduction in males. Additionally, in a temperature place preference test pairing a surface temperature of 22 °C with either 5 °C, 10 °C, 47 °C, or 50 °C, females appeared to have overall greater tolerance for non-ambient temperatures. Males spent less than 50% of their time in every non-22 °C zone, whereas in females this was only observed when testing 5 °C and 50 °C. Together, these results suggest that male rats show more avoidance behavior than females to both hot and cold non-ambient temperatures when given free access to multiple zones, including at milder temperatures than those typically used to evoke a nociceptive response in traditional hot and cold plate tests.

A compendium of validated pain genes

The development of novel pain therapeutics hinges on the identification and rigorous validation of potential targets. Model organisms provide a means to test the involvement of specific genes and regulatory elements in pain. Here we provide a list of genes linked to pain-associated behaviors. We capitalize on results spanning over three decades to identify a set of 242 genes. They support a remarkable diversity of functions spanning action potential propagation, immune response, GPCR signaling, enzymatic catalysis, nucleic acid regulation, and intercellular signaling. Making use of existing tissue and single-cell high-throughput RNA sequencing datasets, we examine their patterns of expression. For each gene class, we discuss archetypal members, with an emphasis on opportunities for additional experimentation. Finally, we discuss how powerful and increasingly ubiquitous forward genetic screening approaches could be used to improve our ability to identify pain genes. This article is categorized under: Neurological Diseases > Genetics/Genomics/Epigenetics Neurological Diseases > Molecular and Cellular Physiology.

The Persistent Pain Transcriptome: Identification of Cells and Molecules Activated by Hyperalgesia

During persistent pain, the dorsal spinal cord responds to painful inputs from the site of injury, but the molecular modulatory processes have not been comprehensively examined. Using transcriptomics and multiplex in situ hybridization, we identified the most highly regulated receptors and signaling molecules in rat dorsal spinal cord in peripheral inflammatory and post-surgical incisional pain models. We examined a time course of the response including acute (2 hours) and longer term (2 day) time points after peripheral injury representing the early onset and instantiation of hyperalgesic processes. From this analysis, we identify a key population of superficial dorsal spinal cord neurons marked by somatotopic upregulation of the opioid neuropeptide precursor prodynorphin, and 2 receptors: the neurokinin 1 receptor, and anaplastic lymphoma kinase. These alterations occur specifically in the glutamatergic subpopulation of superficial dynorphinergic neurons. In addition to specific neuronal gene regulation, both models showed induction of broad transcriptional signatures for tissue remodeling, synaptic rearrangement, and immune signaling defined by complement and interferon induction. These signatures were predominantly induced ipsilateral to tissue injury, implying linkage to primary afferent drive. We present a comprehensive set of gene regulatory events across 2 models that can be targeted for the development of non-opioid analgesics. PERSPECTIVE: The deadly impact of the opioid crisis and the need to replace morphine and other opioids in clinical practice is well recognized. Embedded within this research is an overarching goal of obtaining foundational knowledge from transcriptomics to search for non-opioid analgesic targets. Developing such analgesics would address unmet clinical needs.

A Role for Global DNA Methylation Level and IL2 Expression in the Transition From Acute to Chronic Low Back Pain

Objectives: The transition from acute low back pain (aLBP) to chronic LBP (cLBP) results from a variety of factors, including epigenetic modifications of DNA. The aim of this study was to (1) compare global DNA (gDNA) methylation and histone acetylation at LBP onset between the aLBP and cLBP participants, (2) compare mRNA expression of genes with known roles in the transduction, maintenance, and/or modulation of pain between the aLBP and cLBP participants, (3) compare somatosensory function and pain ratings in our participants, and (4) determine if the aforementioned measurements were associated.

Methods: A total of 220 participants were recruited for this prospective observational study following recent onset of an episode of LBP. We retained 45 individuals whose gDNA was of sufficient quality for analysis. The final sample included 14 participants whose pain resolved within 6 weeks of onset (aLBP),15 participants that reported pain for 6 months (cLBP), and 16 healthy controls. Participants were subjected to quantitative sensory testing (QST), blood was drawn via venipuncture, gDNA isolated, and global DNA methylation and histone acetylation, as well as mRNA expression of 84 candidate genes, were measured.

Results: Individuals that develop cLBP display multimodal somatosensory hypersensitivity relative to aLBP participants. cLBP participants also had significantly lower global DNA methylation, which was negatively correlated with interleukin-2 (IL2) mRNA expression.

Discussion: cLBP is characterized by somatosensory hypersensitivity, lower global DNA methylation, and higher IL2 expression level compared to those whose pain will resolve quickly (aLBP). These results suggest potential diagnostic and therapeutic relevance for global DNA methylation and IL2 expression in the pathology underlying the transition from acute to chronic LBP.

Antiplexin D1 Antibodies Relate to Small Fiber Neuropathy and Induce Neuropathic Pain in Animals

OBJECTIVES

To assess the prevalence of antiplexin D1 antibodies (plexin D1-immunoglobulin G [IgG]) in small fiber neuropathy (SFN) and the effects of these antibodies in vivo.

METHODS

We developed an ELISA for plexin D1-IgG using a recombinant extracellular domain of human plexin D1 containing the major epitope and sera from 58 subjects previously studied with a standard tissue-based indirect immunofluorescence assay (TBA). We screened 63 patients with probable SFN and 55 healthy controls (HCs) for serum plexin D1-IgG using ELISA. The results were confirmed by TBA. IgG from 3 plexin D1-IgG-positive patients, 2 plexin D1-IgG-negative inflammatory disease controls, and 2 HCs was intrathecally injected into mice, which were assessed for mechanical and thermal hypersensitivity 24 and 48 hours after injection.

RESULTS

The ELISA had 75% sensitivity and 100% specificity using the TBA as a standard, and the coincidence rate of ELISA to TBA was 96.6% (56/58). The frequency of plexin D1-IgG was higher in patients with SFN than in HCs (12.7% [8/63] vs 0.0% [0/55], p = 0.007). Purified IgG from all 3 plexin D1-IgG-positive patients, but not 2 plexin D1-IgG-negative patients, induced significant mechanical and/or thermal hypersensitivity compared with IgG from HCs. In mice injected with plexin D1-IgG-positive but not D1-IgG-negative patient IgG, phosphorylated extracellular signal-regulated protein kinase immunoreactivity, an activation marker, was confined to small dorsal root ganglion neurons and was significantly more abundant than in mice injected with HC IgG.

CONCLUSIONS

Plexin D1-IgG is pathogenic but with low prevalence and is a potential biomarker for immunotherapy in SFN.

Gene Transcript Alterations in the Spinal Cord, Anterior Cingulate Cortex, and Amygdala in Mice Following Peripheral Nerve Injury

Chronic neuropathic pain caused by nerve damage is a most common clinical symptom, often accompanied by anxiety- and depression-like symptoms. Current treatments are very limited at least in part due to incompletely understanding mechanisms underlying this disorder. Changes in gene expression in the dorsal root ganglion (DRG) have been acknowledged to implicate in neuropathic pain genesis, but how peripheral nerve injury alters the gene expression in other pain-associated regions remains elusive. The present study carried out strand-specific next-generation RNA sequencing with a higher sequencing depth and observed the changes in whole transcriptomes in the spinal cord (SC), anterior cingulate cortex (ACC), and amygdala (AMY) following unilateral fourth lumbar spinal nerve ligation (SNL). In addition to providing novel transcriptome profiles of long non-coding RNAs (lncRNAs) and mRNAs, we identified pain- and emotion-related differentially expressed genes (DEGs) and revealed that numbers of these DEGs displayed a high correlation to neuroinflammation and apoptosis. Consistently, functional analyses showed that the most significant enriched biological processes of the upregulated mRNAs were involved in the immune system process, apoptotic process, defense response, inflammation response, and sensory perception of pain across three regions. Moreover, the comparisons of pain-, anxiety-, and depression-related DEGs among three regions present a particular molecular map among the spinal cord and supraspinal structures and indicate the region-dependent and region-independent alterations of gene expression after nerve injury. Our study provides a resource for gene transcript expression patterns in three distinct pain-related regions after peripheral nerve injury. Our findings suggest that neuroinflammation and apoptosis are important pathogenic mechanisms underlying neuropathic pain and that some DEGs might be promising therapeutic targets.

The implication of transient receptor potential canonical 6 in BDNF-induced mechanical allodynia in rat model of diabetic neuropathic pain

AIMS

Brain-derived neurotrophic factor (BDNF) is vital in the pathogenesis of mechanical allodynia with a paucity of reports available regarding diabetic neuropathy pain (DNP). Herein we identified the involvement of BDNF in driving mechanical allodynia in DNP rats via the activation of transient receptor potential canonical 6 (TRPC6) channel.

MATERIALS AND METHODS

The DNP rat model was established via streptozotocin (STZ) injection, and allodynia was assessed by paw withdrawal mechanical threshold (PWMT) and paw withdrawal thermal latency (PWTL). The expression profiles of BDNF and TRPC6 in dorsal root ganglia (DRG) and spinal cord were illustrated by immunofluorescence and Western blotting. Intrathecal administration of K252a or TrkB-Fc was performed to inhibit BNDF/TrkB expression, and respective injection of GsMTX-4, BTP2 and TRPC6 antisense oligodeoxynucleotides (TRPC6-AS) was likewise conducted to inhibit TRPC6 expression in DNP rats. Calcium influx in DRG was monitored by calcium imaging.

KEY FINDINGS

The time-dependent increase of BDNF and TRPC6 expression in DRG and spinal cord was observed since the 7th post-STZ day, correlated with the development of mechanical allodynia in DNP rats. Intrathecal administration of K252a, TrkB-Fc, GsMTX-4 and BTP2 prevented mechanical allodynia in DNP rats. Pre-treatment of TRPC6-AS reversed the BDNF-induced pain-like responses in DNP rats rather than the naïve rats. In addition, the TRPC6-AS reversed BDNF-induced increase of calcium influx in DRG neurons in DNP rats.

SIGNIFICANCE

The intrathecal inhibition of TRPC6 alleviated the BDNF-induced mechanical allodynia in DNP rat model. This finding may validate the application of TRPC6 antagonists as interesting strategy for DNP management.

Comparative Analysis of Dorsal Root, Nodose and Sympathetic Ganglia for the Development of New Analgesics

Interoceptive and exteroceptive signals, and the corresponding coordinated control of internal organs and sensory functions, including pain, are received and orchestrated by multiple neurons within the peripheral, central and autonomic nervous systems. A central aim of the present report is to obtain a molecularly informed basis for analgesic drug development aimed at peripheral rather than central targets. We compare three key peripheral ganglia: nodose, sympathetic (superior cervical), and dorsal root ganglia in the rat, and focus on their molecular composition using next-gen RNA-Seq, as well as their neuroanatomy using immunocytochemistry and in situ hybridization. We obtained quantitative and anatomical assessments of transmitters, receptors, enzymes and signaling pathways mediating ganglion-specific functions. Distinct ganglionic patterns of expression were observed spanning ion channels, neurotransmitters, neuropeptides, G-protein coupled receptors (GPCRs), transporters, and biosynthetic enzymes. The relationship between ganglionic transcript levels and the corresponding protein was examined using immunohistochemistry for select, highly expressed, ganglion-specific genes. Transcriptomic analyses of spinal dorsal horn and intermediolateral cell column (IML), which form the termination of primary afferent neurons and the origin of preganglionic innervation to the SCG, respectively, disclosed pre- and post-ganglionic molecular-level circuits. These multimodal investigations provide insight into autonomic regulation, nodose transcripts related to pain and satiety, and DRG-spinal cord and IML-SCG communication. Multiple neurobiological and pharmacological contexts can be addressed, such as discriminating drug targets and predicting potential side effects, in analgesic drug development efforts directed at the peripheral nervous system.

The physiology of regulated BDNF release

The neurotrophic factor BDNF is an important regulator for the development of brain circuits, for synaptic and neuronal network plasticity, as well as for neuroregeneration and neuroprotection. Up- and downregulations of BDNF levels in human blood and tissue are associated with, e.g., neurodegenerative, neurological, or even cardiovascular diseases. The changes in BDNF concentration are caused by altered dynamics in BDNF expression and release. To understand the relevance of major variations of BDNF levels, detailed knowledge regarding physiological and pathophysiological stimuli affecting intra- and extracellular BDNF concentration is important. Most work addressing the molecular and cellular regulation of BDNF expression and release have been performed in neuronal preparations. Therefore, this review will summarize the stimuli inducing release of BDNF, as well as molecular mechanisms regulating the efficacy of BDNF release, with a focus on cells originating from the brain. Further, we will discuss the current knowledge about the distinct stimuli eliciting regulated release of BDNF under physiological conditions.

Influences of UGT2B7 rs7439366 and rs12233719 Polymorphisms on Fentanyl Sensitivity in Chinese Gynecologic Patients

Background

This study discussed potential influences of UDP glucuronosyltransferase family 2 member B7 (UGT2B7) rs7439366 and rs12233719 polymorphisms on fentanyl sensitivity among Chinese gynecologic patients.

Material/Methods

UGT2B7 polymorphisms were genotyped by polymerase chain reaction (PCR) and direct sequencing. Before surgery, baseline latency to pain perception (PPLpre) and pain perception latency of the dominant hand (PPLpost) at 3 minutes after injecting fentanyl were measured by cold pressor-induced pain test. Perioperative fentanyl adoption referred to the total of fentanyl administration during and after operation. Intensity of spontaneous pain was appraised adopting 100-mm visual analog scale (VAS). Factorial analysis was performed by Mann-Whitney U test and Kruskal-Wallis H test.

Results

Significant differences of PPLpost (CC/CT/TT, P=0.038) and preoperative analgesic effect (CC/CT/TT, P=0.028) were discovered between the rs7439366 genotypes. PPLpost was significantly different between the CT and TT groups (P=0.009) and the CC+CT and TT groups (P=0.026). Preoperative analgesic effect was significantly different between the CT and TT groups (P=0.007) and the CC+CT and TT groups (P=0.009). All of the clinical features studied had no close association with rs12233719 SNP.

Conclusions

Gynecologic patients with rs7439366 TT genotype had significantly lower fentanyl sensitivity than the other 2 genotype carriers.

Targeting neurotrophic factors: Novel approaches to musculoskeletal pain

Chronic pain represents a substantial unmet medical need globally. In recent years, the quest for a new generation of novel, safe, mechanism-based analgesic treatments has focused on neurotrophic factors, a large group of secreted proteins that control the growth and survival of different populations of neurons, but that postnatally are involved in the genesis and maintenance of pain, with biological activity in both the periphery and the central nervous system. In this narrative review, we discuss the two families of neurotrophic proteins that have been extensively studied for their role in pain: first, the neurotrophins, nerve growth factor (NGF) and brain-derived growth factor (BDNF), and secondly, the GDNF family of ligands (GFLs). We provide an overview of the pain pathway, and the pain-producing effects of these different proteins. We summarize accumulating preclinical and clinical findings with a focus on musculoskeletal pain, and on osteoarthritis in particular, because the musculoskeletal system is the most prevalent source of chronic pain and of disability, and clinical testing of these novel agents - often biologics- is most advanced in this area.

Mallotus oblongifolius extracts ameliorate ischemic nerve damage by increasing endogenous neural stem cell proliferation through the Wnt/β-catenin signaling pathway

Mallotus oblongifolius (MO), an edible medicinal plant from Hainan in China, shows a wide range of bioactivities. The daily consumption of MO or its extracts has been observed to ameliorate ischemic nerve injury. However the mechanisms remain unclear. In this study, the effects of MO both in vitro and in vivo were investigated. The results indicated that MO improved the motor ability, neurosensory ability, balance and grasping ability of mice with ischemic injuries, induced by bilateral common carotid artery ligation (BCCAL). In addition, MO improved the morphology of neurons, resisted the loss of neurons, and enhanced the content of the nestin protein in the cerebral cortex and subgranular zone (SGZ) area. Furthermore, in the oxygen-glucose deprivation and reperfusion (OGD/R) treated cell model, MO could effectively activate the Wnt/β-catenin signaling pathway and promote the proliferation of neural stem cells (NSCs) and increase the protein expression levels of β-catenin and CyclinD1. Our results suggest that Mallotus oblongifolius may be used as nutraceuticals or functional foods to alleviate ischemic nerve damage and promote recovery from ischemic stroke.