Targeting the vascular endothelial growth factor A/neuropilin 1 axis for relief of neuropathic pain

Divergent sex-specific pannexin-1 mechanisms in microglia and T cells underlie neuropathic pain

Chronic pain is a leading cause of disability, affecting more women than men. Different immune cells contribute to this sexual divergence, but the mechanisms, especially in females, are not well defined. We show that pannexin-1 (Panx1) channels on microglia and T cells differentially cause mechanical allodynia, a debilitating symptom of neuropathic pain. In male rodents, Panx1 drives vascular endothelial growth factor-A (VEGF-A) release from microglia. Cell-specific knockdown of microglial Panx1 or pharmacological blockade of the VEGF receptor attenuated allodynia in nerve-injured males. In females, nerve injury increased spinal CD8+ T cells and leptin levels. Leptin release from female-derived CD8+ T cells was Panx1 dependent, and intrathecal leptin-neutralizing antibody injection sex-specifically reversed allodynia. Adoptive transfer of female-derived CD8+ T cells caused robust allodynia, which was prevented by a leptin-neutralizing antibody or leptin small interfering RNA (siRNA) knockdown. Panx1-targeted approaches may alleviate neuropathic pain in both sexes, while T cell- and leptin-directed treatments could have sex-dependent benefits for women.

The dual role of VEGF-A in a complex in vitro model of oxaliplatin-induced neurotoxicity: Pain-related and neuroprotective effects

Vascular endothelial growth factor (VEGF)-A is a main player in the development of neuropathic pain induced by chemotherapy and the pharmacological blockade of VEGF receptor (VEGFR) subtype 1 is a pain killer strategy. Interestingly, VEGF-A has been demonstrated to have also neuroprotective properties. The aim of the study was to investigate the neuroprotective role of VEGF-A against oxaliplatin neurotoxicity, attempting to discriminate pain-related and restorative signaling pathways. We used rat organotypic spinal cord slices treated with oxaliplatin, as an in vitro model to study chemotherapy-induced toxicity. In this model, 10 ​μM oxaliplatin caused a time-dependent release of VEGF-A, which was reduced by the astrocyte inhibitor fluorocitrate. Moreover, glia inhibition exacerbated oxaliplatin-induced cytotoxicity in a VEGF-A sensitive manner. Treatment with VEGF165b, the main isoform of VEGF-A, prevented the oxaliplatin-induced neuronal damage (indicated by NeuN staining) and astrocyte activation (indicated by GFAP staining). In addition, the blockade of VEGFR-2 by the selective antibody DC101 blunted the protective action of VEGF165b. In the same model, VEGF165b increased the release of molecules relevant in pain signaling, like substance P and CGRP, as well as the mRNA expression of glutamate transporters (EAAT1 and EAAT2), similarly to oxaliplatin and these effects were prevented by the selective VEGFR-1 blocker antibody D16F7. In conclusion, VEGF-A plays a dichotomic role in an in vitro model of chemotherapy-induced toxicity, either promoting neuroprotection or triggering pain mediators release, depending on which of its two receptors is activated. The selective management of VEGF-A signaling is suggested as a therapeutic approach.

Exploring protein-protein interactions for the development of new analgesics

The development of new analgesics has been challenging. Candidate drugs often have limited clinical utility due to side effects that arise because many drug targets are involved in signaling pathways other than pain transduction. Here, we explored the potential of targeting protein-protein interactions (PPIs) that mediate pain signaling as an approach to developing drugs to treat chronic pain. We reviewed the approaches used to identify small molecules and peptide modulators of PPIs and their ability to decrease pain-like behaviors in rodent animal models. We analyzed data from rodent and human sensory nerve tissues to build associated signaling networks and assessed both validated and potential interactions and the structures of the interacting domains that could inform the design of synthetic peptides and small molecules. This resource identifies PPIs that could be explored for the development of new analgesics, particularly between scaffolding proteins and receptors for various growth factors and neurotransmitters, as well as ion channels and other enzymes. Targeting the adaptor function of CBL by blocking interactions between its proline-rich carboxyl-terminal domain and its SH3-domain-containing protein partners, such as GRB2, could disrupt endosomal signaling induced by pain-associated growth factors. This approach would leave intact its E3-ligase functions, which are mediated by other domains and are critical for other cellular functions. This potential of PPI modulators to be more selective may mitigate side effects and improve the clinical management of pain.

Peptidomimetic inhibitors of the VEGF-A165/NRP-1 complex obtained by modification of the C-terminal arginine

Inhibitors of the interaction between Neuropilin-1 (NRP-1) and Vascular Endothelial Growth Factor-A165 (VEGF-A165) hold significant promise as therapeutic and diagnostic agents directed against cancers overexpressing NRP-1. In our efforts in this field, a few series of strong and fairly stable peptide-like inhibitors of the general formula Lys(Har)1-Xaa2-Xaa3-Arg4 have been previously discovered. In the current work, we focused on Lys(Har)-Dap/Dab-Pro-Arg sequence. The aim was to examine whether replacing C-terminal Arg with its homologs and mimetics would yield more stable yet still potent inhibitors. Upon considering the results of modelling and other factors, ten novel analogues with Xaa4 = homoarginine (Har), 2-amino-4-guanidino-butyric acid (Agb), 2-amino-3-guanidino-propionic acid (Agp), citrulline (Cit), 4-aminomethyl-phenylalanine [Phe(4-CH2-NH2)] were designed, synthesized and evaluated. Two of the proposed modifications resulted in inhibitors with activity slightly lower [e.g. IC50 = 14.3 μM for Lys(Har)-Dab-Pro-Har and IC50 = 19.8 μM for Lys(Har)-Dab-Pro-Phe(4-CH2-NH2)] than the parent compounds [e.g. IC50 = 4.7 μM for Lys(Har)-Dab-Pro-Arg]. What was a surprise to us, the proteolytic stability depended more on position two of the sequence than on position four. The Dab2-analogues exhibited half-life times beyond 60 h. Our results build up the knowledge on the structural requirements that effective VEGF-A165/NRP-1 inhibitors should fulfil.

The role of neuropilin in bone/cartilage diseases

Bone remodeling is the balance between osteoblasts and osteoclasts. Bone diseases such as osteoporosis and osteoarthritis are associated with imbalanced bone remodeling. Skeletal injury leads to limited motor function and pain. Neurophilin was initially identified in axons, and its various ligands and roles in bone remodeling, angiogenesis, neuropathic pain and immune regulation were later discovered. Neurophilin promotes osteoblast mineralization and inhibits osteoclast differentiation and its function. Neuropolin-1 provides channels for immune cell chemotaxis and cytokine diffusion and leads to pain. Neuropolin-1 regulates the proportion of T helper type 17 (Th17) and regulatory T cells (Treg cells), and affects bone immunity. Vascular endothelial growth factors (VEGF) combine with neuropilin and promote angiogenesis. Class 3 semaphorins (Sema3a) compete with VEGF to bind neuropilin, which reduces angiogenesis and rejects sympathetic nerves. This review elaborates on the structure and general physiological functions of neuropilin and summarizes the role of neuropilin and its ligands in bone and cartilage diseases. Finally, treatment strategies and future research directions based on neuropilin are proposed.

Genetic overlap and causality between COVID-19 and multi-site chronic pain: the importance of immunity

Background

The existence of chronic pain increases susceptibility to virus and is now widely acknowledged as a prominent feature recognized as a major manifestation of long-term coronavirus disease 2019 (COVID-19) infection. Given the ongoing COVID-19 pandemic, it is imperative to explore the genetic associations between chronic pain and predisposition to COVID-19.

Methods

We conducted genetic analysis at the single nucleotide polymorphism (SNP), gene, and molecular levels using summary statistics of genome-wide association study (GWAS) and analyzed the drug targets by summary data-based Mendelian randomization analysis (SMR) to alleviate the multi-site chronic pain in COVID-19. Additionally, we performed a latent causal variable (LCV) method to investigate the causal relationship between chronic pain and susceptibility to COVID-19.

Results

The cross-trait meta-analysis identified 19 significant SNPs shared between COVID-19 and chronic pain. Coloc analysis indicated that the posterior probability of association (PPH4) for three loci was above 70% in both critical COVID-19 and COVID-19, with the corresponding top three SNPs being rs13135092, rs7588831, and rs13135092. A total of 482 significant overlapped genes were detected from MAGMA and CPASSOC results. Additionally, the gene ANAPC4 was identified as a potential drug target for treating chronic pain (P=7.66E-05) in COVID-19 (P=8.23E-03). Tissue enrichment analysis highlighted that the amygdala (P=7.81E-04) and prefrontal cortex (P=8.19E-05) as pivotal in regulating chronic pain of critical COVID-19. KEGG pathway enrichment further revealed the enrichment of pleiotropic genes in both COVID-19 (P=3.20E-03,Padjust=4.77E-02,hsa05171) and neurotrophic pathways (P=9.03E-04,Padjust =2.55E-02,hsa04621). Finally, the latent causal variable (LCV) model was applied to find the genetic component of critical COVID-19 was causal for multi-site chronic pain (P=0.015), with a genetic causality proportion (GCP) of was 0.60.

Conclusions

In this study, we identified several functional genes and underscored the pivotal role of the inflammatory system in the correlation between the paired traits. Notably, heat shock proteins emerged as potential objective biomarkers for chronic pain symptoms in individuals with COVID-19. Additionally, the ubiquitin system might play a role in mediating the impact of COVID-19 on chronic pain. These findings contribute to a more comprehensive understanding of the pleiotropy between COVID-19 and chronic pain, offering insights for therapeutic trials.