ABSTRACT

Obesity is associated with the infiltration of monocytes/macrophages into adipose tissue in which MCP-1 plays a crucial role. But the regulatory mechanism of MCP-1 expression in adipocytes is not well defined. Our results demonstrated that TNF-α induced abundant MCP-1 production in adipocytes, including 3T3-L1 pre- (≈ 9 to 18-fold), mature adipocytes (≈ 4 to 6-fold), and primary adipocytes(< 2-fold), among which 3T3-L1 pre-adipocytes showed the best reactiveness. Thus, 3T3-L1 pre-adipocytes were used for the most of following experiments. At the transcriptional level, TNF-α (20 ng/mL) also promoted the mRNA expression of MCP-1. It is well recognized that the engagement of TNF-α with its receptor can trigger both NF-κB and AP-1 signalling, which was also confirmed in our study (5-fold and 2-fold). Unexpectedly and counterintuitively, multiple NF-κB inhibitors with different mechanisms failed to suppress TNF-α-induced MCP-1 production, but rather the inhibitors for any one of MAPKs (JNK, ERK and p38) could do. This study, for the first time, reveals that MAPKs/AP-1 but not NF-κB signalling is responsible for MCP-1 production in TNF-α-activated adipocytes. These findings provide important insight into the role of AP-1 signalling in adipose tissue, and may lead to the development of therapeutical repositioning strategies in metaflammation.

Abbreviations: AP-1, activator protein-1; CHX, cycloheximide; IR, insulin resistance; MAPK, mitogen-activated protein kinase; NF-κB, nuclear factor κB; RT-qPCR, quantitative real-time PCR; T2DM, type 2 diabetes mellitus; TRE, triphorbol acetate-response element.

摘要

肥胖与单核细胞/巨噬细胞浸润到脂肪组织中有关，其中 MCP-1 起关键作用。但脂肪细胞中 MCP-1 表达的调控机制尚不明确。我们的研究结果表明，TNF-α 在脂肪细胞中诱导大量 MCP-1 产生，包括 3T3-L1 pre-（≈ 9 至 18 倍）、成熟脂肪细胞（≈ 4 至 6 倍）和原代脂肪细胞（< 2 倍），其中3T3-L1前脂肪细胞表现出最好的反应性。因此，3T3-L1 前脂肪细胞用于大多数以下实验。在转录水平，TNF-α (20 ng/mL) 也促进了 MCP-1 的 mRNA 表达。众所周知，TNF-α 与其受体的结合可以触发 NF-κB 和 AP-1 信号传导，这在我们的研究中也得到了证实（5 倍和 2 倍）。出乎意料和违反直觉，多种具有不同机制的 NF-κB 抑制剂未能抑制 TNF-α 诱导的 MCP-1 产生，但任何一种 MAPK（JNK、ERK 和 p38）的抑制剂都可以。这项研究首次揭示了 MAPKs/AP-1 而不是 NF-κB 信号传导负责 TNF-α 激活的脂肪细胞中 MCP-1 的产生。这些发现为了解 AP-1 信号在脂肪组织中的作用提供了重要的见解，并可能导致在元炎症中治疗性重新定位策略的发展。

缩写： AP-1，激活蛋白-1；CHX，放线菌酮；IR，胰岛素抵抗；MAPK，丝裂原活化蛋白激酶；NF-κB，核因子 κB；RT-qPCR，定量实时PCR；T2DM，2型糖尿病；TRE，醋酸三佛醇反应元件。