Pulpal inflammation is known to be mediated by multiple signaling pathways. However, whether melatonin plays regulatory roles in pulpal inflammation remains unclear. This study aimed at elucidating an in situ expression of melatonin and its receptors in human pulpal tissues, and the contribution of melatonin on the antagonism of lipopolysaccharide (LPS)-infected pulpal fibroblasts. Melatonin expression in pulpal tissues harvested from healthy teeth was investigated by immunohistochemical staining. Its receptors, melatonin receptor 1 (MT1) and melatonin receptor 2 (MT2), were also immunostained in pulpal tissues isolated from healthy teeth and inflamed teeth diagnosed with irreversible pulpitis. Morphometric analysis was subsequently performed. After LPS infection of cultured pulpal fibroblasts, cyclo-oxygenase (COX) and interleukin-1 β (IL-1 β) transcripts were examined by using reverse transcription-polymerase chain reaction (RT-PCR). Analysis of mRNA expression was performed to investigate an antagonism of LPS stimulation by melatonin via COX and IL-1 β induction. Mann-Whitney U test and One-way ANOVA were used for statistical analysis to determine a significance level. Melatonin was expressed in healthy pulpal tissue within the odontoblastic zone, cell-rich zone, and in the pulpal connective tissue. Furthermore, in health, strong MT1 and MT2 expression was distributed similarly in all 3 pulpal zones. In contrast, during disease, expression of MT2 was reduced in inflamed pulpal tissues (P-value< 0.001), but not MT1 (P-value = 0.559). Co-culturing of melatonin with LPS resulted in the reduction of COX-2 and IL-1 β expression in primary pulpal fibroblasts, indicating that melatonin may play an antagonistic role to LPS infection in pulpal fibroblasts. Human dental pulp abundantly expressed melatonin and its receptors MT1 and MT2 in the odontoblastic layers and pulpal connective tissue layers. Melatonin exerted antagonistic activity against LPS-mediated COX-2 and IL-1 β induction in pulpal fibroblasts, suggesting its therapeutic potential for pulpal inflammation and a possible role of pulpal melatonin in an immunomodulation via functional melatonin receptors expressed in dental pulp.

中文翻译：

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褪黑素拮抗脂多糖诱导的牙髓成纤维细胞反应。

已知牙髓炎症是由多种信号通路介导的。但是，褪黑激素是否在牙髓炎症中起调节作用尚不清楚。这项研究旨在阐明褪黑激素及其受体在人类牙髓组织中的原位表达，以及褪黑激素对脂多糖（LPS）感染的牙髓成纤维细胞拮抗作用的作用。通过免疫组织化学染色研究了从健康牙齿收获的牙髓组织中褪黑激素的表达。它的受体，褪黑激素受体1（MT1）和褪黑激素受体2（MT2），也在从健康牙齿和被诊断患有不可逆性牙髓炎的发炎牙齿中分离出的牙髓组织中进行了免疫染色。随后进行形态分析。LPS感染培养的牙髓成纤维细胞后，使用逆转录聚合酶链反应（RT-PCR）检查了环氧化酶（COX）和白介素1β（IL-1β）的转录本。进行mRNA表达的分析以研究褪黑素通过COX和IL-1β诱导对LPS刺激的拮抗作用。使用Mann-Whitney U检验和单向ANOVA进行统计分析以确定显着性水平。褪黑激素在牙质母细胞区，细胞富集区以及牙髓结缔组织内的健康牙髓组织中表达。此外，在健康方面，强烈的MT1和MT2表达相似地分布在所有3个牙髓区。相反，在疾病期间，发炎的牙髓组织中MT2的表达降低（P值<0.001），而MT1则未降低（P值= 0.559）。褪黑素与LPS的共培养导致初级牙髓成纤维细胞中COX-2和IL-1β表达的降低，表明褪黑素可能对牙髓成纤维细胞中的LPS感染起拮抗作用。人牙髓在牙质母细胞层和牙髓结缔组织层中大量表达褪黑激素及其受体MT1和MT2。褪黑素对牙髓成纤维细胞中的LPS介导的COX-2和IL-1β诱导具有拮抗活性，表明其对牙髓炎症的治疗潜力以及牙髓褪黑素在通过牙髓中表达的功能性褪黑激素受体进行免疫调节中的可能作用。人牙髓在牙质母细胞层和牙髓结缔组织层中大量表达褪黑激素及其受体MT1和MT2。褪黑素对牙髓成纤维细胞中的LPS介导的COX-2和IL-1β诱导具有拮抗活性，表明其对牙髓炎症的治疗潜力以及牙髓褪黑素在通过牙髓中表达的功能性褪黑激素受体进行免疫调节中的可能作用。人牙髓在牙质母细胞层和牙髓结缔组织层中大量表达褪黑激素及其受体MT1和MT2。褪黑素对牙髓成纤维细胞中的LPS介导的COX-2和IL-1β诱导具有拮抗活性，表明其对牙髓炎症的治疗潜力以及牙髓褪黑素在通过牙髓中表达的功能性褪黑激素受体进行免疫调节中的可能作用。