Spinal RyR2 pathway regulated by the RNA-binding protein HuD induces pain hypersensitivity in antiretroviral neuropathy

Sex Differences in the Expression of Neuroimmune Molecules in the Spinal Cord of a Mouse Model of Antiretroviral-Induced Neuropathic Pain

Nucleoside reverse transcriptase inhibitors (NRTIs), drugs used to treat HIV infection, can cause neuropathic pain (NP) and neuroinflammation. An NRTI, 2′-3′-dideoxycytidine (ddC), was reported to induce mechanical allodynia and increase proinflammatory cytokines in the brains of female mice. In some models of NP, microglia activation is important for NP pathophysiology in male mice, while T cells are important in female mice. Age-matched female and male mice (BALB/c strain) treated intraperitoneally once daily with ddC for 5 days developed mechanical allodynia. Treatment with ddC increased Cd11b, H2-Aa, Cd3e, Mapk1, Il1b, Tnf, and Il10 mRNA levels in the spinal cords of female, but not male, mice, whereas there was no alteration found in Gfap and Mapk14 transcripts in both sexes on day 7 after ddC administration. The protein expression of CD11b and phospho-p38 MAPK was significantly increased in the spinal cords of ddC-treated female, but not male, mice, whereas Iba1 protein was elevated in ddC-treated male mice. There was no change in GFAP, CD3e, and phospho-p44/42 MAPK protein levels in both sexes. Thus, changes in neuroimmune cells and molecules in the spinal cords during ddC-induced neuroinflammation were sex-dependent, with female mice being more prone to neuroimmune changes than male mice.

The RNA-Binding Protein HuR Is Integral to the Function of Nociceptors in Mice and Humans

HuR is an RNA-binding protein implicated in RNA processing, stability, and translation. Previously, we examined protein synthesis in dorsal root ganglion (DRG) neurons treated with inflammatory mediators using ribosome profiling. We found that the HuR consensus binding element was enriched in transcripts with elevated translation. HuR is expressed in the soma of nociceptors and their axons. Pharmacologic inhibition of HuR with the small molecule CMLD-2 reduced the activity of mouse and human sensory neurons. Peripheral administration of CMLD-2 in the paw or genetic elimination of HuR from sensory neurons diminished behavioral responses associated with NGF- and IL-6-induced allodynia in male and female mice. Genetic disruption of HuR altered the proximity of mRNA decay factors near a key neurotrophic factor (TrkA). Collectively, the data suggest that HuR is required for local control of mRNA stability and reveals a new biological function for a broadly conserved post-transcriptional regulatory factor.SIGNIFICANCE STATEMENT Nociceptors undergo long-lived changes in excitability, which may contribute to chronic pain. Noxious cues that promote pain lead to rapid induction of protein synthesis. The underlying mechanisms that confer specificity to mRNA control in nociceptors are unclear. Here, we identify a conserved RNA-binding protein called HuR as a key regulatory factor in sensory neurons. Using a combination of genetics and pharmacology, we demonstrate that HuR is required for signaling in nociceptors. In doing so, we report an important mechanism of mRNA control in sensory neurons that ensures appropriate nociceptive responses to inflammatory mediators.

Post-transcriptional control by RNA-binding proteins in diabetes and its related complications

Diabetes mellitus (DM) is a fast-growing chronic metabolic disorder that leads to significant health, social, and economic problems worldwide. Chronic hyperglycemia caused by DM leads to multiple devastating complications, including macrovascular complications and microvascular complications, such as diabetic cardiovascular disease, diabetic nephropathy, diabetic neuropathy, and diabetic retinopathy. Numerous studies provide growing evidence that aberrant expression of and mutations in RNA-binding proteins (RBPs) genes are linked to the pathogenesis of diabetes and associated complications. RBPs are involved in RNA processing and metabolism by directing a variety of post-transcriptional events, such as alternative splicing, stability, localization, and translation, all of which have a significant impact on RNA fate, altering their function. Here, we purposed to summarize the current progression and underlying regulatory mechanisms of RBPs in the progression of diabetes and its complications. We expected that this review will open the door for RBPs and their RNA networks as novel therapeutic targets for diabetes and its related complications.

Direct Ryanodine Receptor-2 Knockout in Primary Afferent Fibers Modestly Affects Neurological Recovery after Contusive Spinal Cord Injury

Neuronal ryanodine receptors (RyR) release calcium from internal stores and play a key role in synaptic plasticity, learning, and memory. Dysregulation of RyR function contributes to neurodegeneration and negatively impacts neurological recovery after spinal cord injury (SCI). However, the individual role of RyR isoforms and the underlying mechanisms remain poorly understood. To determine whether RyR2 plays a direct role in axonal fate and functional recovery after SCI, we bred Advillin-Cre: tdTomato (Ai9) reporter mice with "floxed" RyR2 mice to directly knock out (KO) RyR2 function in dorsal root ganglion neurons and their spinal projections. Adult 6- to 8-week-old RyR2KO and littermate controls were subjected to a contusive SCI and their dorsal column axons were imaged in vivo using two-photon excitation microscopy. We found that direct RyR2KO in dorsal column primary afferents did not significantly alter secondary axonal degeneration after SCI. We next assessed behavioral recovery after SCI and found that direct RyR2KO in primary afferents worsened open-field locomotor scores (Basso Mouse Scale subscore) compared to littermate controls. However, both TreadScan™ gait analysis and overground kinematic gait analysis tests revealed subtle, but no fundamental, differences in gait patterns between the two groups after SCI. Subsequent removal of spared afferent fibers using a dorsal column crush revealed similar outcomes in both groups. Analysis of primary afferents at the lumbar (L3-L5) level similarly revealed no noticeable differences between groups. Together, our results support a modest contribution of dorsal column primary afferent RyR2 in neurological recovery after SCI.

Fecal transplantation and butyrate improve neuropathic pain, modify immune cell profile, and gene expression in the PNS of obese mice

Obesity affects over 2 billion people worldwide and is accompanied by peripheral neuropathy (PN) and an associated poorer quality of life. Despite high prevalence, the molecular mechanisms underlying the painful manifestations of PN are poorly understood, and therapies are restricted to use of painkillers or other drugs that do not address the underlying disease. Studies have demonstrated that the gut microbiome is linked to metabolic health and its alteration is associated with many diseases, including obesity. Pathologic changes to the gut microbiome have recently been linked to somatosensory pain, but any relationships between gut microbiome and PN in obesity have yet to be explored. Our data show that mice fed a Western diet developed indices of PN that were attenuated by concurrent fecal microbiome transplantation (FMT). In addition, we observed changes in expression of genes involved in lipid metabolism and calcium handling in cells of the peripheral nerve system (PNS). FMT also induced changes in the immune cell populations of the PNS. There was a correlation between an increase in the circulating short-chain fatty acid butyrate and pain improvement following FMT. Additionally, butyrate modulated gene expression and immune cells in the PNS. Circulating butyrate was also negatively correlated with distal pain in 29 participants with varied body mass index. Our data suggest that the metabolite butyrate, secreted by the gut microbiome, underlies some of the effects of FMT. Targeting the gut microbiome, butyrate, and its consequences may represent novel viable approaches to prevent or relieve obesity-associated neuropathies.

Identification of Key Genes and Pathways in Mouse Spinal Cord Involved in ddC-Induced Neuropathic Pain by Transcriptome Sequencing

Highly active antiretroviral therapy (HAART) works effectively in inhibiting HIV replication in patients. However, the use of nucleoside reverse transcriptase inhibitors (NRTIs) often causes side effects of neuropathic pain, and its mechanism remains to be elucidated. Therefore, we aim to explore the mechanism of NRTIs-induced neuropathic pain at the transcriptome level. C57BL/6 J mice were given intraperitoneal injection of zalcitabine (ddC) or saline (control) for 2 weeks, during which the mechanical pain threshold of the mice was detected by von Frey test. Then the L3~L5 spinal segments of the mice were isolated and subsequently used for RNA sequencing (RNA-seq) on the last day of treatment. The mechanical pain threshold of mice given ddC decreased significantly. Compared with the control group, ddC caused significant changes in the expression of 135 genes, of which 66 upregulated and 69 downregulated. Enrichment analysis showed that the functions of these genes are mainly enriched in regulation of transcription, multicellular organism development, and cell differentiation, and the pathway is mainly enriched in the cGMP-PKG signaling pathway and AMPK signaling pathway. Furthermore, key genes such as Gabrd, Kcnd3, Npcd, Insr, Lypd6, Scd2, and Mef2d were also identified. These may serve as drug targets for the prevention or treatment of NRTI-induced neuropathic pain.

Ryanodine Receptor to Mitochondrial Reactive Oxygen Species Pathway Plays an Important Role in Chronic Human Immunodeficiency Virus gp120MN-Induced Neuropathic Pain in Rats

BACKGROUND

Chronic pain is one of the most common complaints in patients with human immunodeficiency virus (HIV)-associated sensory neuropathy. Ryanodine receptor (RyR) and mitochondrial oxidative stress are involved in neuropathic pain induced by nerve injury. Here, we investigated the role of RyR and mitochondrial superoxide in neuropathic pain induced by repeated intrathecal HIV glycoprotein 120 (gp120) injection.

METHODS

Recombinant HIV glycoprotein gp120MN was intrathecally administered to induce neuropathic pain. Mechanical threshold was tested using von Frey filaments. Peripheral nerve fiber was assessed by the quantification of the intraepidermal nerve fiber density in the skin of the hindpaw. The expression of spinal RyR was examined using Western blots. Colocalization of RyR with neuronal nuclei (NeuN; neuron marker), glial fibrillary acidic protein (GFAP; astrocyte marker), or ionizing calcium-binding adaptor molecule 1 (Iba1; microglia marker) in the spinal cord was examined using immunohistochemistry. MitoSox-positive profiles (a mitochondrial-targeted fluorescent superoxide indicator) were examined. The antiallodynic effects of intrathecal administration of RyR antagonist, dantrolene (a clinical drug for malignant hyperthermia management), or selective mitochondrial superoxide scavenger, Mito-Tempol, were evaluated in the model.

RESULTS

We found that repeated but not single intrathecal injection of recombinant protein gp120 induced persistent mechanical allodynia. Intraepidermal nerve fibers in repeated gp120 group was lower than that in sham at 2 weeks, and the difference in means (95% confidence interval) was 8.495 (4.79-12.20), P = .0014. Repeated gp120 increased expression of RyR, and the difference in means (95% confidence interval) was 1.50 (0.504-2.495), P = .007. Repeated gp120 also increased mitochondrial superoxide cell number in the spinal cord, and the difference in means (95% confidence interval) was 6.99 (5.99-8.00), P < .0001. Inhibition of spinal RyR or selective mitochondrial superoxide scavenger dose dependently reduced mechanical allodynia induced by repeated gp120 injection. RyR and mitochondrial superoxide were colocalized in the neuron, but not glia. Intrathecal injection of RyR inhibitor lowered mitochondrial superoxide in the spinal cord dorsal horn in the gp120 neuropathic pain model.

CONCLUSIONS

These data suggest that repeated intrathecal HIV gp120 injection induced an acute to chronic pain translation in rats, and that neuronal RyR and mitochondrial superoxide in the spinal cord dorsal horn played an important role in the HIV neuropathic pain model. The current results provide evidence for a novel approach to understanding the molecular mechanisms of HIV chronic pain and treating chronic pain in patients with HIV.

Cancer the'RBP'eutics-RNA-binding proteins as therapeutic targets for cancer

RNA-binding proteins (RBPs) play a critical role in the regulation of various RNA processes, including splicing, cleavage and polyadenylation, transport, translation and degradation of coding RNAs, non-coding RNAs and microRNAs. Recent studies indicate that RBPs not only play an instrumental role in normal cellular processes but have also emerged as major players in the development and spread of cancer. Herein, we review the current knowledge about RNA binding proteins and their role in tumorigenesis as well as the potential to target RBPs for cancer therapeutics.

RNA control in pain: Blame it on the messenger

mRNA function is meticulously controlled. We provide an overview of the integral role that posttranscriptional controls play in the perception of painful stimuli by sensory neurons. These specialized cells, termed nociceptors, precisely regulate mRNA polarity, translation, and stability. A growing body of evidence has revealed that targeted disruption of mRNAs and RNA-binding proteins robustly diminishes pain-associated behaviors. We propose that the use of multiple independent regulatory paradigms facilitates robust temporal and spatial precision of protein expression in response to a range of pain-promoting stimuli. This article is categorized under: RNA in Disease and Development > RNA in Disease Translation > Translation Regulation RNA Turnover and Surveillance > Regulation of RNA Stability.

RNA-Binding Proteins HuB, HuC, and HuD are Distinctly Regulated in Dorsal Root Ganglia Neurons from STZ-Sensitive Compared to STZ-Resistant Diabetic Mice

The neuron-specific Elav-like Hu RNA-binding proteins were described to play an important role in neuronal differentiation and plasticity by ensuring the post-transcriptional control of RNAs encoding for various proteins. Although Elav-like Hu proteins alterations were reported in diabetes or neuropathy, little is known about the regulation of neuron-specific Elav-like Hu RNA-binding proteins in sensory neurons of dorsal root ganglia (DRG) due to the diabetic condition. The goal of our study was to analyze the gene and protein expression of HuB, HuC, and HuD in DRG sensory neurons in diabetes. The diabetic condition was induced in CD-1 adult male mice with single-intraperitoneal injection of streptozotocin (STZ, 150 mg/kg), and 8-weeks (advanced diabetes) after induction was quantified the Elav-like proteins expression. Based on the glycemia values, we identified two types of responses to STZ, and mice were classified in STZ-resistant (diabetic resistant, glycemia < 260 mg/dL) and STZ-sensitive (diabetic, glycemia > 260 mg/dL). Body weight measurements indicated that 8-weeks after STZ-induction of diabetes, control mice have a higher increase in body weight compared to the diabetic and diabetic resistant mice. Moreover, after 8-weeks, diabetic mice (19.52 ± 3.52 s) have longer paw withdrawal latencies in the hot-plate test than diabetic resistant (11.36 ± 1.92 s) and control (11.03 ± 1.97 s) mice, that correlates with the installation of warm hypoalgesia due to the diabetic condition. Further on, we evidenced the decrease of Elav-like gene expression in DRG neurons of diabetic mice (Elavl2, 0.68 ± 0.05 fold; Elavl3, 0.65 ± 0.01 fold; Elavl4, 0.53 ± 0.07 fold) and diabetic resistant mice (Ealvl2, 0.56 ± 0.07 fold; Elavl3, 0.32 ± 0.09 fold) compared to control mice. Interestingly, Elav-like genes have a more accentuated downregulation in diabetic resistant than in diabetic mice, although hypoalgesia was evidenced only in diabetic mice. The Elav-like gene expression changes do not always correlate with the Hu protein expression changes. To detail, HuB is upregulated and HuD is downregulated in diabetic mice, while HuB, HuC, and HuD are downregulated in diabetic resistant mice compared to control mice. To resume, we demonstrated HuD downregulation and HuB upregulation in DRG sensory neurons induced by diabetes, which might be correlated with altered post-transcriptional control of RNAs involved in the regulation of thermal hypoalgesia condition caused by the advanced diabetic neuropathy.

HuD Is a Neural Translation Enhancer Acting on mTORC1-Responsive Genes and Counteracted by the Y3 Small Non-coding RNA

The RNA-binding protein HuD promotes neurogenesis and favors recovery from peripheral axon injury. HuD interacts with many mRNAs, altering both stability and translation efficiency. We generated a nucleotide resolution map of the HuD RNA interactome in motor neuron-like cells, identifying HuD target sites in 1,304 mRNAs, almost exclusively in the 3' UTR. HuD binds many mRNAs encoding mTORC1-responsive ribosomal proteins and translation factors. Altered HuD expression correlates with the translation efficiency of these mRNAs and overall protein synthesis, in a mTORC1-independent fashion. The predominant HuD target is the abundant, small non-coding RNA Y3, amounting to 70% of the HuD interaction signal. Y3 functions as a molecular sponge for HuD, dynamically limiting its recruitment to polysomes and its activity as a translation and neuron differentiation enhancer. These findings uncover an alternative route to the mTORC1 pathway for translational control in motor neurons that is tunable by a small non-coding RNA.

RNA-binding proteins as targets for pain therapeutics

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Post-transcriptional regulation is linked to the development of pain hypersensitivity.

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A growing body of evidence indicates that RNA-binding proteins are involved in pain.

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RNA-based inhibitors are a potential new source of pain therapeutics.

RNA-protein interactions permeate biology. Transcription, translation, processing, and mRNA decay all hinge on widespread use of regulatory information decoded by RNA-binding proteins. The final committed step of protein synthesis, translation, is intimately linked to nociceptor excitability. Understanding the factors that control translation is essential as nociceptor plasticity is a hallmark of persistent pain. Here, we review the growing body of evidence for widespread involvement of RNA-binding proteins in pain. Many of the relevant factors have been implicated in post-transcriptional and translational mechanisms of mRNA control. We propose that recent advances in the development of RNA-based therapeutics provide a potential means to exploit our current understanding of liaisons between RNAs and proteins for therapeutic purposes.

Phosphorylated CCAAT/Enhancer Binding Protein β Contributes to Rat HIV-Related Neuropathic Pain: In Vitro and In Vivo Studies

Chronic pain is increasingly recognized as an important comorbidity of HIV-infected patients, however, the exact molecular mechanisms of HIV-related pain are still elusive. CCAAT/enhancer binding proteins (C/EBPs) are expressed in various tissues, including the CNS. C/EBPβ, one of the C/EBPs, is involved in the progression of HIV/AIDS, but the exact role of C/EBPβ and its upstream factors are not clear in HIV pain state. Here, we used a neuropathic pain model of perineural HIV envelope glycoprotein gp120 application onto the rat sciatic nerve to test the role of phosphorylated C/EBPβ (pC/EBPβ) and its upstream pathway in the spinal cord dorsal horn (SCDH). HIV gp120 induced overexpression of pC/EBPβ in the ipsilateral SCDH compared with contralateral SCDH. Inhibition of C/EBPβ using siRNA against C/EBPβ reduced mechanical allodynia. HIV gp120 also increased TNFα, TNFRI, mitochondrial superoxide (mtO₂^·-), and pCREB in the ipsilateral SCDH. ChIP-qPCR assay showed that pCREB enrichment on the C/EBPβ gene promoter regions in rats with gp120 was higher than that in sham rats. Intrathecal TNF soluble receptor I (functionally blocking TNFα bioactivity) or knockdown of TNFRI using antisense oligodeoxynucleotide against TNFRI reduced mechanical allodynia, and decreased mtO₂^·-, pCREB and pC/EBPβ. Intrathecal Mito-tempol (a mitochondria-targeted O₂^·-scavenger) reduced mechanical allodynia and decreased pCREB and pC/EBPβ. Knockdown of CREB with antisense oligodeoxynucleotide against CREB reduced mechanical allodynia and lowered pC/EBPβ. These results suggested that the pathway of TNFα/TNFRI-mtO₂^·--pCREB triggers pC/EBPβ in the HIV gp120-induced neuropathic pain state. Furthermore, we confirmed the pathway using both cultured neurons treated with recombinant TNFα in vitro and repeated intrathecal injection of recombinant TNFα in naive rats. This finding provides new insights in the understanding of the HIV neuropathic pain mechanisms and treatment.SIGNIFICANCE STATEMENT Painful HIV-associated sensory neuropathy is a neurological complication of HIV infection. Phosphorylated C/EBPβ (pC/EBPβ) influences AIDS progression, but it is still not clear about the exact role of pC/EBPβ and the detailed upstream factors of pC/EBPβ in HIV-related pain. In a neuropathic pain model of perineural HIV gp120 application onto the sciatic nerve, we found that pC/EBPβ was triggered by TNFα/TNFRI-mtO₂^·--pCREB signaling pathway. The pathway was confirmed by using cultured neurons treated with recombinant TNFα in vitro, and by repeated intrathecal injection of recombinant TNFα in naive rats. The present results revealed the functional significance of TNFα/TNFRI-mtO₂^·--pCREB-pC/EBPβ signaling in HIV neuropathic pain, and should help in the development of more specific treatments for neuropathic pain.

Increase of neurofilament-H protein in sensory neurons in antiretroviral neuropathy: Evidence for a neuroprotective response mediated by the RNA-binding protein HuD

Nucleoside reverse transcriptase inhibitors (NRTIs) are key components of HIV/AIDS treatment to reduce viral load. However, antiretroviral toxic neuropathy has become a common peripheral neuropathy among HIV/AIDS patients leading to discontinuation of antiretroviral therapy, for which the underlying pathogenesis is uncertain. This study examines the role of neurofilament (NF) proteins in the spinal dorsal horn, DRG and sciatic nerve after NRTI neurotoxicity in mice treated with zalcitabine (2',3'-dideoxycitidine; ddC). ddC administration up-regulated NF-M and pNF-H proteins with no effect on NF-L. The increase of pNF-H levels was counteracted by the silencing of HuD, an RNA binding protein involved in neuronal development and differentiation. Sciatic nerve sections of ddC exposed mice showed an increased axonal caliber, concomitantly to a pNF-H up-regulation. Both events were prevented by HuD silencing. pNF-H and HuD colocalize in DRG and spinal dorsal horn axons. However, the capability of HuD to bind NF mRNA was not demonstrated, indicating the presence of an indirect mechanism of control of NF expression by HuD. RNA immunoprecipitation experiments showed the capability of HuD to bind the BDNF mRNA and the administration of an anti-BDNF antibody prevented pNF-H increase. These data indicate the presence of a HuD - BDNF - NF-H pathway activated as a regenerative response to the axonal damage induced by ddC treatment to counteract the antiretroviral neurotoxicity. Since analgesics clinically used to treat neuropathic pain are ineffective on antiretroviral neuropathy, a neuroregenerative strategy might represent a new therapeutic opportunity to counteract neurotoxicity and avoid discontinuation or abandon of NRTI therapy.

Spinal CPEB-mtROS-CBP signaling pathway contributes to perineural HIV gp120 with ddC-related neuropathic pain in rats

Human immunodeficiency virus (HIV) patients treated with nucleoside reverse transcriptase inhibitors (NRTIs), have been known to develop neuropathic pain. While there has been a major shift away from some neurotoxic NRTIs in current antiretroviral therapy, a large number of HIV patients alive today have previously received them, and many have developed painful peripheral neuropathy. The exact mechanisms by which HIV with NRTIs contribute to the development of neuropathic pain are not known. Previous studies suggest that cytoplasmic polyadenylation element-binding protein (CPEB), reactive oxygen species (ROS), and cAMP-response element-binding protein (CREB)-binding protein (CBP), are involved in the neuroimmunological diseases including inflammatory/neuropathic pain. In this study, we investigated the role of CPEB, mitochondrial ROS (mtROS), or CBP in neuropathic pain induced by HIV envelope protein gp120 combined with antiretroviral drug. The application of recombinant gp120 into the sciatic nerve plus systemic ddC (one of NRTIs) induced mechanical allodynia. Knockdown of CPEB or CBP using intrathecal antisense oligodeoxynucleotide (AS-ODN) reduced mechanical allodynia. Intrathecal mitochondrial superoxide scavenger mito-tempol (Mito-T) increased mechanical withdrawal threshold. Knockdown of CPEB using intrathecal AS-ODN, reduced the up-regulated mitochondrial superoxide in the spinal dorsal horn in rats with gp120 combined with ddC. Intrathecal Mito-T lowered the increased expression of CBP in the spinal dorsal horn. Immunostaining studies showed that neuronal CPEB positive cells were co-localized with MitoSox positive profiles, and that MitoSox positive profiles were co-localized with neuronal CBP. Our studies suggest that neuronal CPEB-mtROS-CBP pathway in the spinal dorsal horn, plays an important role in the gp120/ddC-induced neuropathic pain in rats.