Protein Arginine Methyltransferase 5 Contributes to Paclitaxel-Induced Neuropathic Pain by Activating Transient Receptor Potential Vanilloid 1 Epigenetic Modification in Dorsal Root Ganglion.

BACKGROUND: Paclitaxel (PTX), which is a first-line chemotherapy drug used to treat various types of cancers, exhibits peripheral neuropathy as a common side effect that is difficult to treat. Protein arginine methyltransferase 5 (PRMT 5) is a key regulator of the chemotherapy response, as chemotherapy drugs induce PRMT5 expression. However, little is known about the PRMT5-mediated epigenetic mechanisms involved in PTX-induced neuropathic allodynia. METHODS: Sprague-Dawley rats were intraperitoneally given PTX to induce neuropathic pain. Biochemical analyses were conducted to measure the protein expression levels in the dorsal root ganglion (DRG) of the animals. The von Frey test and hot plate test were used to evaluate nociceptive behaviors. RESULTS: PTX increased the PRMT5 (mean difference [MD]: 0.68, 95% confidence interval [CI], 0.88-0.48; P < .001 for vehicle)-mediated deposition of histone H3R2 dimethyl symmetric (H3R2me2s) at the transient receptor potential vanilloid 1 ( Trpv1 ) promoter in the DRG. PRMT5-induced H3R2me2s recruited WD repeat domain 5 (WDR5) to increase trimethylation of lysine 4 on histone H3 (H3K4me3) at Trpv1 promoters, thus resulting in TRPV1 transcriptional activation (MD: 0.65, 95% CI, 0.82-0.49; P < .001 for vehicle) in DRG in PTX-induced neuropathic pain. Moreover, PTX increased the activity of NADPH oxidase 4 (NOX4) (MD: 0.66, 95% CI, 0.81-0.51; P < .001 for vehicle), PRMT5-induced H3R2me2s, and WDR5-mediated H3K4me3 in the DRG in PTX-induced neuropathic pain. Pharmacological antagonism and the selective knockdown of PRMT5 in DRG neurons completely blocked PRMT5-mediated H3R2me2s, WDR5-mediated H3K4me3, or TRPV1 expression and neuropathic pain development after PTX injection. Remarkably, NOX4 inhibition not only attenuated allodynia behavior and reversed the above-mentioned signaling but also reversed NOX4 upregulation via PTX. CONCLUSIONS: Thus, the NOX4/PRMT5-associated epigenetic mechanism in DRG has a dominant function in the transcriptional activation of TRPV1 in PTX-induced neuropathic pain.

Hsa-miR-409-3p regulates endothelial progenitor senescence via PP2A-P38 and is a potential ageing marker in humans.

We explored the roles of hsa-microRNA (miR)-409-3p in senescence and signalling mechanism of human endothelial progenitor cells (EPCs). Hsa-miR-409-3p was found upregulated in senescent EPCs. Overexpression of miRNA mimics in young EPCs inhibited angiogenesis. In senescent EPCs, compared to young EPCs, protein phosphatase 2A (PP2A) was downregulated, with activation of p38/JNK by phosphorylation. Young EPCs treated with siPP2A caused inhibited angiogenesis with activation of p38/JNK, similar to findings in senescent EPCs. Time series analysis showed, in young EPCs treated with hsa-miR-409-3p mimics, PP2A was steadily downregulated for 72 h, while p38/JNK was activated with a peak at 48 hours. The inhibited angiogenesis of young EPCs after miRNA-409-3p mimics treatment was reversed by the p38 inhibitor. The effect of hsa-miR-409-3p on PP2A signalling was attenuated by exogenous VEGF. Analysis of human peripheral blood mononuclear cells (PBMCs) obtained from healthy people revealed hsa-miR-409-3p expression was higher in those older than 65 years, compared to those younger than 30 years, regardless of gender. In summary, hsa-miR-409-3p was upregulated in senescent EPCs and acted as a negative modulator of angiogenesis via targeting protein phosphatase 2 catalytic subunit alpha (PPP2CA) gene and regulating PP2A/p38 signalling. Data from human PBMCs suggested hsa-miR-409-3p a potential biomarker for human ageing.

Phosphorylated Upstream Frameshift 1-dependent Nonsense-mediated µ-Opioid Receptor mRNA Decay in the Spinal Cord Contributes to the Development of Neuropathic Allodynia-like Behavior in Rats.

BACKGROUND: Nonsense-mediated messenger RNA (mRNA) decay increases targeted mRNA degradation and has been implicated in the regulation of gene expression in neurons. The authors hypothesized that nonsense-mediated µ-opioid receptor mRNA decay in the spinal cord is involved in the development of neuropathic allodynia-like behavior in rats. METHODS: Adult Sprague-Dawley rats of both sexes received spinal nerve ligation to induce neuropathic allodynia-like behavior. The mRNA and protein expression contents in the dorsal horn of animals were measured by biochemical analyses. Nociceptive behaviors were evaluated by the von Frey test and the burrow test. RESULTS: On Day 7, spinal nerve ligation significantly increased phosphorylated upstream frameshift 1 (UPF1) expression in the dorsal horn (mean ± SD; 0.34 ± 0.19 in the sham ipsilateral group vs. 0.88 ± 0.15 in the nerve ligation ipsilateral group; P < 0.001; data in arbitrary units) and drove allodynia-like behaviors in rats (10.58 ± 1.72 g in the sham ipsilateral group vs. 1.19 ± 0.31 g in the nerve ligation ipsilateral group, P < 0.001). No sex-based differences were found in either Western blotting or behavior tests in rats. Eukaryotic translation initiation factor 4A3 (eIF4A3) triggered SMG1 kinase (0.06 ± 0.02 in the sham group vs. 0.20 ± 0.08 in the nerve ligation group, P = 0.005, data in arbitrary units)-mediated UPF1 phosphorylation, leading to increased nonsense-mediated mRNA decay factor SMG7 binding and µ-opioid receptor mRNA degradation (0.87 ± 0.11-fold in the sham group vs. 0.50 ± 0.11-fold in the nerve ligation group, P = 0.002) in the dorsal horn of the spinal cord after spinal nerve ligation. Pharmacologic or genetic inhibition of this signaling pathway in vivo ameliorated allodynia-like behaviors after spinal nerve ligation. CONCLUSIONS: This study suggests that phosphorylated UPF1-dependent nonsense-mediated µ-opioid receptor mRNA decay is involved in the pathogenesis of neuropathic pain.

Phosphate NIMA-Related Kinase 2-Dependent Epigenetic Pathways in Dorsal Root Ganglion Neurons Mediates Paclitaxel-Induced Neuropathic Pain.

BACKGROUND: The microtubule-stabilizing drug paclitaxel (PTX) is an important chemotherapeutic agent for cancer treatment and causes peripheral neuropathy as a common side effect that substantially impacts the functional status and quality of life of patients. The mechanistic role for NIMA-related kinase 2 (NEK2) in the progression of PTX-induced neuropathic pain has not been established. METHODS: Adult male Sprague-Dawley rats intraperitoneally received PTX to induce neuropathic pain. The protein expression levels in the dorsal root ganglion (DRG) of animals were measured by biochemical analyses. Nociceptive behaviors were evaluated by von Frey tests and hot plate tests. RESULTS: PTX increased phosphorylation of the important microtubule dynamics regulator NEK2 in DRG neurons and induced profound neuropathic allodynia. PTX-activated phosphorylated NEK2 (pNEK2) increased jumonji domain-containing 3 (JMJD3) protein, a histone demethylase protein, to specifically catalyze the demethylation of the repressive histone mark H3 lysine 27 trimethylation (H3K27me3) at the Trpv1 gene, thereby enhancing transient receptor potential vanilloid subtype-1 (TRPV1) expression in DRG neurons. Moreover, the pNEK2-dependent PTX response program is regulated by enhancing p90 ribosomal S6 kinase 2 (RSK2) phosphorylation. Conversely, intrathecal injections of kaempferol (a selective RSK2 activation antagonist), NCL 00017509 (a selective NEK2 inhibitor), NEK2-targeted siRNA, GSK-J4 (a selective JMJD3 inhibitor), or capsazepine (an antagonist of TRPV1 receptor) into PTX-treated rats reversed neuropathic allodynia and restored silencing of the Trpv1 gene, suggesting the hierarchy and interaction among phosphorylated RSK2 (pRSK2), pNEK2, JMJD3, H3K27me3, and TRPV1 in the DRG neurons in PTX-induced neuropathic pain. CONCLUSIONS: pRSK2/JMJD3/H3K27me3/TRPV1 signaling in the DRG neurons plays as a key regulator for PTX therapeutic approaches.

A novel naphthalimide derivative reduces platelet activation and thrombus formation via suppressing GPVI.

Naphthalimide derivatives have multiple biological activities, including antitumour and anti-inflammatory activities. We previously synthesized several naphthalimide derivatives; of them, compound 5 was found to exert the strongest inhibitory effect on human DNA topoisomerase II activity. However, the effects of naphthalimide derivatives on platelet activation have not yet been investigated. Therefore, the mechanism underlying the antiplatelet activity of compound 5 was determined in this study. The data revealed that compound 5 (5-10 µM) inhibited collagen- and convulxin- but not thrombin- or U46619-mediated platelet aggregation, suggesting that compound 5 is more sensitive to the inhibition of glycoprotein VI (GPVI) signalling. Indeed, compound 5 could inhibit the phosphorylation of signalling molecules downstream of GPVI, followed by the inhibition of calcium mobilization, granule release and GPIIb/IIIa activation. Moreover, compound 5 prevented pulmonary embolism and prolonged the occlusion time, but tended to prolong the bleeding time, indicating that it can prevent thrombus formation but may increase bleeding risk. This study is the first to demonstrate that the naphthalimide derivative compound 5 exerts antiplatelet and antithrombotic effects. Future studies should modify compound 5 to synthesize more potent and efficient antiplatelet agents while minimizing bleeding risk, which may offer a therapeutic potential for cardiovascular diseases.

Effect of phenylurea hydroxamic acids on histone deacetylase and VEGFR-2.

A series of phenylurea hydroxamic acids incorporating pharmacophores of inhibitors of HDAC inhibitors and VEGFR-2 has been designed. Most of the compounds show antiproliferative activity comparable to that of Vorinostat and Sorafenib, and better EPC inhibitory activity. Enzymatic assays and Western blotting results indicated that compound 14 not only inhibits HDAC but also has slight VEGFR-2 inhibitory activity. A docking study revealed that the polar hydroxamic acid retains the interaction with HDAC through a zinc ion and also interacts with some residues of the active site of VEGFR-2. Despite 14 displaying a weaker VEGFR-2 activity, a possible route to develop potent HDAC/VEGFR-2 inhibitors is suggested.

Dihydrolipoic acid-coated gold nanocluster bioactivity against senescence and inflammation through the mitochondria-mediated JNK/AP-1 pathway.

Cellular senescence is the progressive impairment of function and proliferation in response to various regulators. Dihydrolipoic acid-coated gold nanoclusters (DHLA-Au NCs), which are molecular clusters with covalently linked dihydroxyl lipoic acid, preserve cellular activities for long-term incubation. DHLA-Au NC delivery was characterized, and we determined the role of growth supplements on internalization, allowing the optimization of DHLA-Au NC bioactivity. In the optimized medium, DHLA-Au NCs attenuated the levels of the senescence-associated phenotype. Molecular mechanism analysis further indicated that during DHLA-Au NC treatment, the activation of the stress signal JNK and its downstream c-Jun were impaired under LPS induction, which led to a decline in AP-1-mediated TNF-α transactivation. Confocal microscopy and subcellular fractionation analysis suggested that DHLA-Au NCs interacted with mitochondria through their lipid moiety and attenuated mitochondria-derived reactive oxygen species. With adequate treatment, DHLA-Au NCs show protection against cellular senescence and inflammation in vitro and in vivo.

Phospholipase D1 and D2 Synergistically Regulate Thrombus Formation.

Previously, we reported that phospholipase D1 (PLD1) and PLD2 inhibition by selective PLD1 and PLD2 inhibitors could prevent platelet aggregation in humans, but not in mice. Moreover, only the PLD1 inhibitor, but not PLD2 inhibitor, could effectively prevent thrombus formation in mice, indicating that PLD might play different roles in platelet function in humans and mice. Although PLD1 and PLD2 were reported to be implicated in thrombotic events, the role of PLD in mice remains not completely clear. Here, we investigated the role of PLD1 and PLD2 in acute pulmonary thrombosis and transient middle cerebral artery occlusion-induced brain injury in mice. The data revealed that inhibition of PLD1, but not of PLD2, could partially prevent pulmonary thrombosis-induced death. Moreover, concurrent PLD1 and PLD2 inhibition could considerably increase survival rate. Likewise, inhibition of PLD1, but not PLD2, partially improved ischemic stroke and concurrent inhibition of PLD1, and PLD2 exhibited a relatively better protection against ischemic stroke, as evidenced by the infarct size, brain edema, modified neurological severity score, rotarod test, and the open field test. In conclusion, PLD1 might play a more important role than PLD2, and both PLD1 and PLD2 could act synergistically or have partially redundant functions in regulating thrombosis-relevant events.

Spinal RNF20-Mediated Histone H2B Monoubiquitylation Regulates mGluR5 Transcription for Neuropathic Allodynia.

To date, histone H2B monoubiquitination (H2Bub), a mark associated with transcriptional elongation and ongoing transcription, has not been linked to the development or maintenance of neuropathic pain states. Here, using male Sprague Dawley rats, we demonstrated spinal nerve ligation (SNL) induced behavioral allodynia and provoked ring finger protein 20 (RNF20)-dependent H2Bub in dorsal horn. Moreover, SNL provoked RNF20-mediated H2Bub phosphorylated RNA polymerase II (RNAPII) in the promoter fragments of mGluR5, thereby enhancing mGluR5 transcription/expression in the dorsal horn. Conversely, focal knockdown of spinal RNF20 expression reversed not only SNL-induced allodynia but also RNF20/H2Bub/RNAPII phosphorylation-associated spinal mGluR5 transcription/expression. Notably, TNF-α injection into naive rats and specific neutralizing antibody injection into SNL-induced allodynia rats revealed that TNF-α-associated allodynia involves the RNF20/H2Bub/RNAPII transcriptional axis to upregulate mGluR5 expression in the dorsal horn. Collectively, our findings indicated TNF-α induces RNF20-drived H2B monoubiquitination, which facilitates phosphorylated RNAPII-dependent mGluR5 transcription in the dorsal horn for the development of neuropathic allodynia.SIGNIFICANCE STATEMENT Histone H2B monoubiquitination (H2Bub), an epigenetic post-translational modification, positively correlated with gene expression. Here, TNF-α participated in neuropathic pain development by enhancing RNF20-mediated H2Bub, which facilitates phosphorylated RNAPII-dependent mGluR5 transcription in dorsal horn. Our finding potentially identified neuropathic allodynia pathophysiological processes underpinning abnormal nociception processing and opens a new avenue for the development of novel analgesics.

Mitochondrial fission protein 1 up-regulation ameliorates senescence-related endothelial dysfunction of human endothelial progenitor cells.

BACKGROUND: We investigated the contribution of mitochondrial dysfunction to the senescence of human endothelial progenitor cells (EPCs) expanded in vitro and the underlying molecular mechanism. METHODS AND RESULTS: Serial passage increased cell doubling time and those cells reaching the doubling time for more than 100% were defined as senescent EPCs, of which the activity of therapeutic angiogenesis was attenuated in mouse ischemic hindlimbs. The senescent cells, in medium free of glucose and bicarbonate, showed impaired activity in migration and tube formation. Flow cytometry indicated increased content of reactive oxygen species, mitochondria, and calcium, while bioenergetic analysis showed increased oxygen consumption and reduced ATP content. Examination of mitochondrial network showed that senescence increased the length of the network and ultrastructure analysis exhibited elongated mitochondria. Immunoblotting of the senescent EPCs demonstrated decreased expression level of fission protein1 (Fis1). In rat EPCs, the Fis1 level was decreased in the animals aged 24 months or older, compared to those of 3 months. Silencing of Fis1 in the young EPCs using Fis1-specific siRNA leads to appearance of phenotype resembling those of senescent cells, including elevated oxidative stress, disturbed mitochondrial network, reduced mitochondria membrane potential, decreasing ATP content, lower proliferation activity, and loss of therapeutic potential in ischemic hindlimbs. Fis1 over-expression in senescent EPCs reduced the oxidative stress, increased the proliferation, and restored the cobble stone-like morphology, senescence, bioenergetics, angiogenic potential, and therapeutic activity. CONCLUSION: In human EPCs, down-regulation of Fis1 is involved in mitochondrial dysfunction and contributes to the impaired activity of EPCs during the senescence process. Enhanced expression of Fis1 in senescent EPCs restores the youthful phenotype.

Spinal Fbxo3-Dependent Fbxl2 Ubiquitination of Active Zone Protein RIM1α Mediates Neuropathic Allodynia through CaV2.2 Activation.

UNLABELLED: Spinal plasticity, a key process mediating neuropathic pain development, requires ubiquitination-dependent protein turnover. Presynaptic active zone proteins have a crucial role in regulating vesicle exocytosis, which is essential for synaptic plasticity. Nevertheless, the mechanism for ubiquitination-regulated turnover of presynaptic active zone proteins in the progression of spinal plasticity-associated neuropathic pain remains unclear. Here, after research involving Sprague Dawley rats, we reported that spinal nerve ligation (SNL), in addition to causing allodynia, enhances the Rab3-interactive molecule-1α (RIM1α), a major active zone protein presumed to regulate neural plasticity, specifically in the synaptic plasma membranes (SPMs) of the ipsilateral dorsal horn. Spinal RIM1α-associated allodynia was mediated by Fbxo3, which abates Fbxl2-dependent RIM1α ubiquitination. Subsequently, following deubiquitination, enhanced RIM1α directly binds to CaV2.2, resulting in increased CaV2.2 expression in the SPMs of the dorsal horn. While exhibiting no effect on Fbxo3/Fbxl2 signaling, the focal knockdown of spinal RIM1α expression reversed the SNL-induced allodynia and increased spontaneous EPSC (sEPSC) frequency by suppressing RIM1α-facilitated CaV2.2 expression in the dorsal horn. Intrathecal applications of BC-1215 (a Fbxo3 activity inhibitor), Fbxl2 mRNA-targeting small-interfering RNA, and ω-conotoxin GVIA (a CaV2.2 blocker) attenuated RIM1α upregulation, enhanced RIM1α expression, and exhibited no effect on RIM1α expression, respectively. These results confirm the prediction that spinal presynaptic Fbxo3-dependent Fbxl2 ubiquitination promotes the subsequent RIM1α/CaV2.2 cascade in SNL-induced neuropathic pain. Our findings identify a role of the presynaptic active zone protein in pain-associated plasticity. That is, RIM1α-facilitated CaV2.2 expression plays a role in the downstream signaling of Fbxo3-dependent Fbxl2 ubiquitination/degradation to promote spinal plasticity underlying the progression of nociceptive hypersensitivity following neuropathic injury. SIGNIFICANCE STATEMENT: Ubiquitination is a well known process required for protein degradation. Studies investigating pain pathology have demonstrated that ubiquitination contributes to chronic pain by regulating the turnover of synaptic proteins. Here, we found that the spinal presynaptic active zone protein Rab3-interactive molecule-1α (RIM1α) participates in neuropathic pain development by binding to and upregulating the expression of CaV2.2. In addition, Fbxo3 modifies this pathway by inhibiting Fbxl2-mediated RIM1α ubiquitination, suggesting that presynaptic protein ubiquitination makes a crucial contribution to the development of neuropathic pain. Research in this area, now in its infancy, could potentially provide a novel therapeutic strategy for pain relief.

Bromodomain-containing Protein 4 Activates Voltage-gated Sodium Channel 1.7 Transcription in Dorsal Root Ganglia Neurons to Mediate Thermal Hyperalgesia in Rats.

BACKGROUND: Bromodomain-containing protein 4 binds acetylated promoter histones and promotes transcription; however, the role of bromodomain-containing protein 4 in inflammatory hyperalgesia remains unclear. METHODS: Male Sprague-Dawley rats received hind paw injections of complete Freund's adjuvant to induce hyperalgesia. The dorsal root ganglia were examined to detect changes in bromodomain-containing protein 4 expression and the activation of genes involved in the expression of voltage-gated sodium channel 1.7, which is a key pain-related ion channel. RESULTS: The intraplantar complete Freund's adjuvant injections resulted in thermal hyperalgesia (4.0 ± 1.5 s; n = 7). The immunohistochemistry and immunoblotting results demonstrated an increase in the bromodomain-containing protein 4-expressing dorsal root ganglia neurons (3.78 ± 0.38 fold; n = 7) and bromodomain-containing protein 4 protein levels (2.62 ± 0.39 fold; n = 6). After the complete Freund's adjuvant injection, histone H3 protein acetylation was enhanced in the voltage-gated sodium channel 1.7 promoter, and cyclin-dependent kinase 9 and phosphorylation of RNA polymerase II were recruited to this area. Furthermore, the voltage-gated sodium channel 1.7-mediated currents were enhanced in neurons of the complete Freund's adjuvant rats (55 ± 11 vs. 19 ± 9 pA/pF; n = 4 to 6 neurons). Using bromodomain-containing protein 4-targeted antisense small interfering RNA to the complete Freund's adjuvant-treated rats, the authors demonstrated a reduction in the expression of bromodomain-containing protein 4 (0.68 ± 0.16 fold; n = 7), a reduction in thermal hyperalgesia (7.5 ± 1.5 s; n = 7), and a reduction in the increased voltage-gated sodium channel 1.7 currents (21 ± 4 pA/pF; n = 4 to 6 neurons). CONCLUSIONS: Complete Freund's adjuvant triggers enhanced bromodomain-containing protein 4 expression, ultimately leading to the enhanced excitability of nociceptive neurons and thermal hyperalgesia. This effect is likely mediated by the enhanced expression of voltage-gated sodium channel 1.7.

Growth Arrest and DNA-damage-inducible Protein 45ß-mediated DNA Demethylation of Voltage-dependent T-type Calcium Channel 3.2 Subunit Enhances Neuropathic Allodynia after Nerve Injury in Rats.

BACKGROUND: Growth arrest and DNA-damage-inducible protein 45ß reactivates methylation-silenced neural plasticity-associated genes through DNA demethylation. However, growth arrest and DNA-damage-inducible protein 45ß-dependent demethylation contributes to neuropathic allodynia-associated spinal plasticity remains unclear. METHODS: Adult male Sprague-Dawley rats (654 out of 659) received a spinal nerve ligation or a sham operation with or without intrathecal application of one of the following: growth arrest and DNA-damage-inducible protein 45ß messenger RNA-targeted small interfering RNA, lentiviral vector expressing growth arrest and DNA-damage-inducible protein 45ß, Ro 25-6981 (an NR2B-bearing N-methyl-D-aspartate receptor antagonist), or KN-93 (a calmodulin-dependent protein kinase II antagonist) were used for behavioral measurements, Western blotting, immunofluorescence, dot blots, detection of unmodified cytosine enrichment at cytosine-phosphate-guanine site, chromatin immunoprecipitation quantitative polymerase chain reaction analysis, and slice recordings. RESULTS: Nerve ligation-enhanced growth arrest and DNA-damage-inducible protein 45ß expression (n = 6) in ipsilateral dorsal horn neurons accompanied with behavioral allodynia (n = 7). Focal knockdown of growth arrest and DNA-damage-inducible protein 45ß expression attenuated ligation-induced allodynia (n = 7) by reducing the binding of growth arrest and DNA-damage-inducible protein 45ß to the voltage-dependent T-type calcium channel 3.2 subunit promoter (n = 6) that decreased expression of and current mediated by the voltage-dependent T-type calcium channel 3.2 subunit (both n = 6). In addition, NR2B-bearing N-methyl-D-aspartate receptors and calmodulin-dependent protein kinase II act in an upstream cascade to increase growth arrest and DNA-damage-inducible protein 45ß expression, hence enhancing demethylation at the voltage-dependent T-type calcium channel 3.2 subunit promoter and up-regulating voltage-dependent T-type calcium channel 3.2 subunit expression. Intrathecal administration of Ro 25-6981, KN-93, or a growth arrest and DNA-damage-inducible protein 45ß-targeting small interfering RNA (n = 6) reversed the ligation-induced enrichment of unmodified cytosine at the voltage-dependent T-type calcium channel 3.2 subunit promoter by increasing the associated 5-formylcytosine and 5-carboxylcytosine levels. CONCLUSIONS: By converting 5-formylcytosine or 5-carboxylcytosine to unmodified cytosine, the NR2B-bearing N-methyl-D-aspartate receptor, calmodulin-dependent protein kinase II, or growth arrest and DNA-damage-inducible protein 45ß pathway facilitates voltage-dependent T-type calcium channel 3.2 subunit gene demethylation to mediate neuropathic allodynia.

Melatonin impedes Tet1-dependent mGluR5 promoter demethylation to relieve pain.

Melatonin (N-acetyl-5-methoxytryptamine)/MT2 receptor-dependent epigenetic modification represents a novel pathway in the treatment of neuropathic pain. Because spinal ten-eleven translocation methylcytosine dioxygenase 1 (Tet1)-dependent epigenetic demethylation has recently been linked to pain hypersensitivity, we hypothesized that melatonin/MT2-dependent analgesia involves spinal Tet1-dependent demethylation. Here, we showed that spinal Tet1 gene transfer by intrathecal delivery of Tet1-encoding vectors to naïve rats produced profound and long-lasting nociceptive hypersensitivity. In addition, enhanced Tet1 expression, Tet1-metabotropic glutamate receptor subtype 5 (mGluR5) promoter coupling, demethylation at the mGluR5 promoter, and mGluR5 expression in dorsal horn neurons were observed. Rats subjected to spinal nerve ligation and intraplantar complete Freund's adjuvant injection displayed tactile allodynia and behavioral hyperalgesia associated with similar changes in the dorsal horn. Notably, intrathecal melatonin injection reversed the protein expression, protein-promoter coupling, promoter demethylation, and pain hypersensitivity induced by Tet1 gene transfer, spinal nerve ligation, and intraplantar complete Freund's adjuvant injection. All the effects caused by melatonin were blocked by pretreatment with a MT2 receptor-selective antagonist. In conclusion, melatonin relieves pain by impeding Tet1-dependent demethylation of mGluR5 in dorsal horn neurons through the MT2 receptor. Our findings link melatonin/MT2 signaling to Tet1-dependent epigenetic demethylation of nociceptive genes for the first time and suggest melatonin as a promising therapy for the treatment of pain.

VPS26A-SNX27 Interaction-Dependent mGluR5 Recycling in Dorsal Horn Neurons Mediates Neuropathic Pain in Rats.

Retromer, which crucially contributes to endosomal sorting machinery through the retrieval and recycling of signaling receptors away from degradation, has been identified as a critical element for glutamatergic-receptor-dependent neural plasticity at excitatory synapses. We observed it accompanied by behavioral allodynia; neuropathic injury time-dependently enhanced VPS26A and SNX27 expression; VPS26A-SNX27 coprecipitation; and VPS26A-positive, SNX27-positive, and VPS26A-SNX27 double-labeled immunoreactivity in the dorsal horn of Sprague Dawley rats that were all sufficiently ameliorated through the focal knock-down of spinal VPS26A expression. Although the knock-down of spinal SNX27 expression exhibited similar effects, spinal nerve ligation (SNL)-enhanced VPS26A expression remained unaffected. Moreover, SNL also increased membrane-bound and total mGluR5 abundance, VPS26A-bound SNX27 and mGluR5 and mGluR5-bound VPS26A and SNX27 coprecipitation, and mGluR5-positive and VPS26A/SNX27/mGluR5 triple-labeled immunoreactivity in the dorsal horn, and these effects were all attenuated through the focal knock-down of spinal VPS26A and SNX27 expression. Although administration with MPEP adequately ameliorated SNL-associated allodynia, mGluR5 expression, and membrane insertion, SNL-enhanced VPS26A and SNX27 expression were unaffected. Together, these results suggested a role of spinal VPS26A-SNX27-dependent mGluR5 recycling in the development of neuropathic pain. This is the first study that links retromer-associated sorting machinery with the spinal plasticity underlying pain hypersensitivity and proposes the possible pathophysiological relevance of endocytic recycling in pain pathophysiology through the modification of glutamatergic mGluR5 recycling. SIGNIFICANCE STATEMENT: VPS26A-SNX27-dependent mGluR5 recycling plays a role in the development of neuropathic pain. The regulation of the VPS26A-SNX27 interaction that modifies mGluR5 trafficking and expression in the dorsal horn provides a novel therapeutic strategy for pain relief.

Melatonin relieves neuropathic allodynia through spinal MT2-enhanced PP2Ac and downstream HDAC4 shuttling-dependent epigenetic modification of hmgb1 transcription.

Melatonin (MLT; N-acetyl-5-methoxytryptamine) exhibits analgesic properties in chronic pain conditions. While researches linking MLT to epigenetic mechanisms have grown exponentially over recent years, very few studies have investigated the contribution of MLT-associated epigenetic modification to pain states. Here, we report that together with behavioral allodynia, spinal nerve ligation (SNL) induced a decrease in the expression of catalytic subunit of phosphatase 2A (PP2Ac) and enhanced histone deacetylase 4 (HDAC4) phosphorylation and cytoplasmic accumulation, which epigenetically alleviated HDAC4-suppressed hmgb1 gene transcription, resulting in increased high-mobility group protein B1 (HMGB1) expression selectively in the ipsilateral dorsal horn of rats. Focal knock-down of spinal PP2Ac expression also resulted in behavioral allodynia in association with similar protein expression as observed with SNL. Notably, intrathecal administration with MLT increased PP2Ac expression, HDAC4 dephosphorylation and nuclear accumulation, restored HDAC4-mediated hmgb1 suppression and relieved SNL-sensitized behavioral pain; these effects were all inhibited by spinal injection of 4P-PDOT (a MT2 receptor antagonist, 30 minutes before MLT) and okadaic acid (OA, a PP2A inhibitor, 3 hr after MLT). Our findings demonstrate a novel mechanism by which MLT ameliorates neuropathic allodynia via epigenetic modification. This MLT-exhibited anti-allodynia is mediated by MT2-enhanced PP2Ac expression that couples PP2Ac with HDAC4 to induce HDAC4 dephosphorylation and nuclear import, herein increases HDAC4 binding to the promoter of hmgb1 gene and upregulates HMGB1 expression in dorsal horn neurons.

Association of Single Nucleotide Polymorphisms with Atrial Fibrillation and the Outcome after Catheter Ablation.

BACKGROUND: The association of gene variants with atrial fibrillation (AF) type and the recurrence of AF after catheter ablation in Taiwan is still unclear. In this study, we aimed to investigate the relationships between gene variants, AF type, and the recurrence of AF. METHODS: In our investigation, we examined 383 consecutive patients with AF (61.9 ± 14.0 years; 63% men); of these 383 patients, 189 underwent catheter ablation for drug-refractory AF. Thereafter, the single nucleotide polymorphisms rs2200733, and rs7193343 were genotyped using real-time polymerase chain reaction. RESULTS: The rs7193343 variant was independently associated with non-paroxysmal AF (non-PAF). In the PAF group, the rs7193343 variant was independently associated with AF recurrence after catheter ablation. However, the rs2200733 variant was not associated with AF recurrence in this group. The combination of the rs7193343 and rs2200733 risk alleles was associated with a better predictive power in the PAF patients. In contrast, in the non-PAF group, the SNPs were not associated with recurrence. The rs7193343 and rs2200733 variants were not associated with different atrial voltage and activation times. CONCLUSIONS: The rs7193343 variants were associated with AF recurrence after catheter ablation in PAF patients but not in non-PAF patients. The rs7193343 CC variant was independently associated with non-PAF.

Reduction of connexin43 in human endothelial progenitor cells impairs the angiogenic potential.

Our previous work showed that arsenic trioxide down-regulated Cx43 and attenuated the angiogenic potential of human late endothelial progenitor cells (EPC). However, the relation between Cx43 and angiogenic activity of the EPC remained unclear. In the study, human late EPC were treated with siRNA specific to Cx43 (Cx43siRNA). The expression profiles as well as activity of the treated cells were examined. In parallel, the angiogenic potential of human EPC treated with Cx43siRNA was evaluated using murine hind limb ischemic model. The results showed that, in the EPC treated with Cx43siRNA, the activity of migration, proliferation, and angiogenic potential were attenuated, accompanied by reduction in vascular endothelial growth factor (VEGF) expression. In hind limb ischemia mice, EPC treated with Cx43siRNA lost the therapeutic angiogenic potential. VEGF supplementation partially recovered the activity impaired by Cx43 down-regulation. In conclusion, reduced Cx43 expression per se in the EPC causes decreased expression of VEGF and impaired angiogenic potential of the cells. Prevention of Cx43 reduction is a potential target to maintain the angiogenic potential of the EPC.

Functional characterization of atrial electrograms in a pacing-induced heart failure model of atrial fibrillation: importance of regional atrial connexin40 remodeling.

INTRODUCTION: Heart failure (HF) increases the susceptibility to atrial fibrillation (AF) and is associated with altered cardiomyocyte connexin. The regional remodeling of connexin(s) may contribute to the spatiotemporal organization of AF. This study sought to investigate the regional differences in connexin(s) and fibrosis in specific atrial regions and correlate that with the electrogram properties. METHODS AND RESULTS: Biatrial electroanatomic mapping during sinus rhythm (electrogram voltage and velocity) and AF (dominant frequency, DF) was performed in 6 ventricular pacing-induced HF dogs (at 252 beats/minute for 6 weeks) and 6 controls. Atrial tissues were sampled from 7 specific sites for analysis of the connexin and fibrosis. HF caused marked atrial dilatation, and increased the induced AF duration (P < 0.001). Remodeled connexins, including a lower expression and more lateralization of both connexin40 (Cx40) and Cx43 as well as increased regional dispersion of Cx40, in the presence of diffuse enhanced atrial fibrosis, characterized the atrial substrate of the HF dogs (P < 0.01). Regional analysis showed abnormal velocity and low electrogram voltage in the areas with downregulated Cx40 and Cx43 was enhanced in the presence of marked atrial fibrosis (>30% of area, P < 0.01). During AF, lower expression of the Cx40 was associated with higher DF in areas of less and more fibrosis, respectively (R = 0.67 and 0.58, P < 0.01). CONCLUSIONS: An altered expression of connexins correlated with the electrogram properties in the existence of diffuse enhanced atrial fibrosis associated with HF. The regional remodeling of Cx40 is likely an important factor in the maintenance of AF in HF.

Melatonin Relieves Paclitaxel-Induced Neuropathic Pain by Regulating pNEK2-Dependent Epigenetic Pathways in DRG Neurons.

The neurohormone melatonin (MLT) demonstrates promising potential in ameliorating neuropathic pain induced by paclitaxel (PTX) chemotherapy. However, little is known about its protective effect on dorsal root ganglion (DRG) neurons in neuropathic pain resulting from the chemotherapeutic drug PTX. Here, PTX-treated rats revealed that intrathecal administration of MLT dose-dependently elevated hind paw withdrawal thresholds and latency, indicating that MLT significantly reversed PTX-induced neuropathic pain. Mechanistically, the analgesic effects of MLT were found to be mediated via melatonin receptor 2 (MT2), as pretreatment with an MT2 receptor antagonist inhibited these effects. Moreover, intrathecal MLT injection reversed the pNEK2-dependent epigenetic program induced by PTX. All of the effects caused by MLT were blocked by pretreatment with an MT2 receptor-selective antagonist, 4P-PDOT. Remarkably, multiple MLT administered during PTX treatment (PTX+MLTs) exhibited not only rapid but also lasting reversal of allodynia/hyperalgesia compared to single-bolus MLT administered after PTX treatment (PTX+MLT). In addition, PTX+MLTs exhibited greater efficacy in reversing PTX-induced alterations in pRSK2, pNEK2, JMJD3, H3K27me3, and TRPV1 expression and interaction in DRG neurons than PTX+MLT. These results indicated that MLT administered during PTX treatment reduced the incidence and/or severity of neuropathy and had a better inhibitory effect on the pNEK2-dependent epigenetic program compared to MLT administered after PTX treatment. In conclusion, MLT/MT2 is a promising therapy for the treatment of pNEK2-dependent painful neuropathy resulting from PTX treatment. MLT administered during PTX chemotherapy may be more effective in the prevention or reduction of PTX-induced neuropathy and maintaining quality.