Ferreira-Gomes Joana, Garcia Miguel M, Nascimento Diana, Almeida Lígia, Quesada Ernesto, Castro-Lopes José Manuel, Pascual David, Goicoechea Carlos, Neto Fani Lourença
i3S - Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal.
Departamento de Biomedicina, Faculdade de Medicina da Universidade do Porto, Porto, Portugal.
J Pain Res. 2021 Aug 24;14:2615-2627. doi: 10.2147/JPR.S317877. eCollection 2021.
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).
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.
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.
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.
Toll样受体4（TLR4）是一种模式识别受体，参与病原体相关分子模式（PAMPs）的检测，也是一种“危险感知”受体，可识别称为损伤相关分子模式（DAMPs）的宿主来源内源性分子。TLR4在风湿性疾病中的作用日益明显，其作为治疗干预靶点的潜在作用也日益凸显。此外，越来越多的证据还表明TLR4与慢性疼痛状态有关。因此，在本研究中，我们评估了全身给予TLR4的合成拮抗剂（TLR4-A1）是否能减轻实验性骨关节炎（OA）中的伤害感受和软骨降解。此外，由于激活转录因子（ATF）-3作为TLR4刺激的炎症反应的负调节因子，我们还评估了TLR4抑制对背根神经节（DRG）初级传入神经元中ATF-3表达的影响。
通过向成年雄性Wistar大鼠左膝关节腔内注射2mg单碘乙酸钠（MIA）诱导OA。在OA诱导后第14天至28天，动物接受腹腔注射TLR4-A1（10mg/kg）或赋形剂。在给予TLR4-A1/赋形剂之前和之后的几个时间点，通过屈膝和CatWalk试验评估所有动物的运动和负荷诱导的伤害感受。在L3-L5 DRG中进行TLR4和ATF-3的免疫荧光检测。对膝关节进行组织病理学评估。
给予TLR4-A1显著降低了OA动物的运动诱导伤害感受，尤其是在屈膝试验中。此外，TLR4-A1显著降低了OA动物DRG中观察到的ATF-3表达的增加。然而，给予拮抗剂后，在软骨损失或TLR4的神经元细胞质表达方面未观察到影响。
给予TLR4拮抗剂可能会中断TLR4信号级联反应，从而减少关节处的神经毒性环境，导致ATF-3表达降低以及与实验性OA相关的伤害感受降低。
