Intrathecally Administered Apelin-13 Alleviated Complete Freund’s Adjuvant-Induced Inflammatory Pain in Mice

Shuangyu Lv,Xinchun Wang,Xiaomei Zhang,Yuchen Zhou,Yanjie Yang,Yu Feng

doi:10.3389/fphar.2020.01335

Shuangyu Lv, Xinchun Wang + Show 4 more

Open Access

https://doi.org/10.3389/fphar.2020.01335

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Abstract

Apelin is the endogenous ligand for APJ, a G-protein-coupled receptor. Apelin gene and protein are widely distributed in the central nervous system and peripheral tissues. The role of apelin in chronic inflammatory pain is still unclear. In the present study, a mouse model of complete Freund’s adjuvant (CFA)-induced inflammatory pain was utilized, and the paw withdrawal latency/threshold in response to thermal stimulation and Von Frey ﬁlament stimulation were recorded after intrathecal (i.t.) injection of apelin-13 (0.1, 1, and 10 nmol/mouse). The mRNA and protein expression, concentration of glutamic acid (Glu), and number of c-Fos immunol staining in lumbar spinal cord (L4/5) were determined. The results demonstrated that Apln gene expression in the lumbar spinal cord was down-regulated in the CFA pain model. Apelin-13 (10 nmol/mouse, i.t.) alleviated CFA-induced inflammatory pain, and it exhibited a more potent antinociceptive effect than apelin-36 and (pyr)apelin-13. The antinociception of apelin-13 could be blocked by APJ antagonist apelin-13(F13A). I.T. apelin-13 attenuated the increased levels of Aplnr, Grin2b, Camk2d, and c-Fos genes expression, Glu concentration, and NMDA receptor 2B (GluN2B) protein expression caused by CFA. Apelin-13 significantly reduced the number of Fos-positive cells in laminae III and IV/V of the dorsal horn. This study indicated that i.t. apelin-13 exerted an analgesic effect against inflammatory pain, which was mediated by activation of APJ, and inhibition of Glu/GluN2B function and neural activity of the spinal dorsal horn.

Highlights

Apelin, an endogenous peptide, was identified as the natural ligand of the orphan receptor APJ (Tatemoto et al, 1998)
Our result demonstrated complete Freund’s adjuvant (CFA) injection upregulated FBJ osteosarcoma oncogene (Fos) mRNA expression in lumbar spinal cord and increased Fos-positive staining of laminae III and IV/V of the dorsal horn compared with the vehicle control, which was consistent with previous studies (Bao et al, 2017; Choi et al, 2018)
We found that i.t. apelin-13 reduced the increased Fos mRNA level in lumbar spinal cord and the number of Foslike immunoreactive (FLI) cells located in laminae III and IV/V, suggesting that the inhibitory effect of apelin-13 on inflammatory pain was related to the reduction of neuronal activity in spinal dorsal horn

Summary

Introduction

An endogenous peptide, was identified as the natural ligand of the orphan receptor APJ (Tatemoto et al, 1998). Apelin is generated from a 77-amino-acid precursor, named preproapelin, which can be hydrolyzed by endopeptidases into several active biological fragments, including apelin-36 (apelin42–77), apelin-17 (apelin61–77), apelin-16 (apelin62–77), apelin-13 (apelin65– 77), and apelin-12 (apelin66–77) and pyroglutaminated apelin13 [(pyr)apelin-13] (Kawamata et al, 2001). Preproapelin contains N and C termini with potential proteolytic cleavage sites, and the sequence of 23 amino acids between tryptophan 55 and phenylalanine 77 is fully conserved among different species (Medhurst et al, 2003). Apelin-13 is the most potent activator for APJ expressed in cell lines, and apelin-13 and apelin-36 are the most widely studied (Tatemoto et al, 1998; Habata et al, 1999; Kawamata et al, 2001)

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