Journal of Pain Research (Aug 2021)
TLR4 Antagonism Reduces Movement-Induced Nociception and ATF-3 Expression in Experimental Osteoarthritis
Abstract
Joana Ferreira-Gomes,1,2 Miguel M Garcia,3– 5 Diana Nascimento,1,2 Lígia Almeida,1,2 Ernesto Quesada,3,5 José Manuel Castro-Lopes,1,2 David Pascual,3– 5 Carlos Goicoechea,3– 5 Fani Lourença Neto1,2 1i3S - Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal; 2Departamento de Biomedicina, Faculdade de Medicina da Universidade do Porto, Porto, Portugal; 3Area of Pharmacology, Nutrition and Bromatology, Department of Basic Health Sciences, Universidad Rey Juan Carlos, Unidad Asociada I+D+i Instituto de Química Médica (IQM) CSIC-URJC, Madrid, Spain; 4High Performance Experimental Pharmacology research group, Universidad Rey Juan Carlos (PHARMAKOM), Alcorcón, Spain; 5Grupo de Excelencia Investigadora URJC-Banco de Santander-Grupo multidisciplinar de investigación y tratamiento del dolor (i+DOL), Alcorcón, SpainCorrespondence: Joana Ferreira-GomesDepartamento de Biomedicina – Unidade de Biologia Experimental 5º piso, Faculdade de Medicina da Universidade do Porto, Rua Dr. Plácido da Costa, Porto, 4200-450, PortugalTel +351 220426740Email [email protected]: Toll-like receptor 4 (TLR4) is a pattern recognition receptor involved in the detection of pathogen-associated molecular patterns (PAMPs), but also a “danger-sensing” receptor that recognizes host-derived endogenous molecules called damage-associated molecular patterns (DAMPs). The involvement of TLR4 in rheumatic diseases is becoming evident, as well as its potential role as a target for therapeutic intervention. Moreover, increasing evidence also suggests that TLR4 is implicated in chronic pain states. Thus, in this study, we evaluated whether a systemic administration of a synthetic antagonist of TLR4 (TLR4-A1) could decrease nociception and cartilage degradation in experimental osteoarthritis (OA). Furthermore, as the activation transcription factor (ATF)-3 serves as a negative regulator for TLR4-stimulated inflammatory response, we also evaluated the effect of TLR4 inhibition on ATF-3 expression in primary afferent neurons at the dorsal root ganglia (DRG).Methods: OA was induced in adult male Wistar rats through an intra-articular injection of 2 mg of sodium mono-iodoacetate (MIA) into the left knee. From days 14 to 28 after OA induction, animals received an intraperitoneal injection of either TLR4-A1 (10 mg/kg) or vehicle. Movement- and loading-induced nociception was evaluated in all animals, by the Knee-Bend and CatWalk tests, before and at several time-points after TLR4-A1/vehicle administration. Immunofluorescence for TLR4 and ATF-3 was performed in L3-L5 DRG. Knee joints were processed for histopathological evaluation.Results: Administration of TLR4-A1 markedly reduced movement-induced nociception in OA animals, particularly in the Knee-Bend test. Moreover, the increase of ATF-3 expression observed in DRG of OA animals was significantly reduced by TLR4-A1. However, no effect was observed in cartilage loss nor in the neuronal cytoplasmic expression of TLR4 upon antagonist administration.Conclusion: The TLR4 antagonist administration possibly interrupts the TLR4 signalling cascade, thus decreasing the neurotoxic environment at the joint, which leads to a reduction in ATF-3 expression and in nociception associated with experimental OA.Keywords: osteoarthritis, TLR4, Knee-Bend, CatWalk, ATF-3, DRG
