Background & Aims

Chronic pain affects almost 30% of the global population, and is a significant health concern, exacerbated by the side effects of widespread opioid use in the last years, emphasizing the urgent need for novel analgesics. Neuropathic pain, resulting from peripheral nerve injury, is a chronic and debilitating condition characterized by increased sensitivity to mechanical stimuli, involving complex molecular signaling pathways. Previous research from our group focused on TrkA signaling mutations, underscored the role of phospholipase c Gamma (PLCg) in TrkA/NGF-mediated inflammatory pain. Building on this, a peptide (TAT-pQYP) from the PLCg anchoring site on TrkA was developed to hinder its interaction with TrkA, crucial for PLCg phosphorylation and subsequent signaling pathways. Experiments demonstrated reduced mechanical sensitivity, suggesting its potential as a novel analgesic. Here with we investigated whether PLCg is involved in increased mechanical sensitivity after nerve injury.

Methods

A chronic neuropathic pain model was induced in mice by partially ligating the sciatic nerve (PSNL), to analyze the effects of TAT-pQYP and PLCg on pain hypersensitivity. Behavioral tests (von Frey) were conducted before surgery, 14 days post-surgery, and 3 hours after peptide application. The peptides and controls were injected intraplantar, in the hind paw ipsilateral to the nerve injury. Reverse transcriptase-polymerase chain reaction (RT-PCR) assessed mRNA expression changes in dorsal root ganglia (DRG) for NTRK1, TRPV1, NGF, BDNF, and PLCgamma. Immunohistochemistry was performed on spinal cord sections in order to analyze the expression of proteins (TRPV1, GFAP, IBA1) involved in pain signaling and cells contributing to pain development and maintenance.

Results

We evaluated the effect of Tat-pQYP 3 hours after its administration in animals that underwent PSNL surgery. Tat-pQYP peptide was successful in reversing the mechanical sensitivity in nerve injured animals. Gene expression levels were analyzed in DRGs after Tat-pQYP administration at 14 days after surgery and 3 hours after peptide injection. A decreased expression of NTRK1 and TRPV1 compared to sham animals was observed after nerve injury which was increased to sham levels after Tat-pQYP peptide administration in PSNL mice. We also observed an increase in TRPV1 expression in the dorsal horn of the spinal cord of treated animals. No difference in the astrocyte the marker GFAP, was observed between control-injected and Tat-pQYP-treated PSNL animals.

Conclusions

Tat-pQYP significantly reversed mechanical sensitivity in a chronic pain model indicating that PLCg signaling is involved in mediating mechanical sensitivity in this neuropathic pain model. In the DRGs, an increase in the expression of NTRK1 and TRPV1 genes were observed in treated animals. These results indicate that inhibiting PLCg may influence the expression of genes associated with neuronal function and pain signaling in nociceptors. Additionally, an increase in TRPV1 expression was also observed in the dorsal horn of the spinal cord of treated animals. TRPV1 is associated with pain perception, and regulation of its expression levels could contribute to the observed effects on mechanical sensitivity. The changes in gene expression levels and protein levels may provide insights into the underlying mechanisms through which Tat-pQYP exerts its effects. These experiments underscore the importance of PLCg in the development of chronic neuropathic pain.

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Presenting Author

Beatriz Caroline de Moraes

Poster Authors

BEATRIZ DE MORAES

PhD student

University of Sao Paulo

Lead Author

Elaine Flamia Toniolo

Department of Anatomy, Institute of Biomedical Sciences, University of Sao Paulo

Lead Author

Carolina Purcell Goes

PhD.

Institute of Biomedical Sciences of University of São Paulo - Brazil

Lead Author

Deborah Schechtman

PhD.

Institute of Chemistry of University of São Paulo - Brazil

Lead Author

Camila Squarzoni Dale

Department of Anatomy, Institute of Biomedical Sciences, University of Sao Paulo

Lead Author

Topics

  • Treatment/Management: Pharmacology: Novel Targets