Mono-2-ethylhexyl phthalic acid (MEHP) is the most toxic metabolite of the plasticizer di-2-ethylhexyl phthalic acid (DEHP), and studies have shown that MEHP causes serious reproductive effects. However, its exact mechanisms of action remain elusive. In this study, we aimed to investigate the reproductive effects of MEHP and preliminarily explore its underlying molecular mechanisms. We found that TM3 cells gradually secreted less testosterone and intracellular free cholesterol with increasing MEHP exposure. MEHP exposure inhibited lipophagy and the Sirt1/Foxo1/Rab7 signaling pathway in TM3 cells, causing aberrant accumulation of intracellular lipid droplets. Addition of the Sirt1 agonist SRT1720 and Rab7 agonist ML-098 alleviated the inhibition of lipophagy and increased free cholesterol and testosterone contents in TM3 cells. SRT1720 alleviated the inhibitory effect of MEHP on the Sirt1/Foxo1/Rab7 signaling pathway, whereas ML-098 only alleviated the inhibition of Rab7 protein expression by MEHP and had no effect on Sirt1 and Foxo1 protein expression. This suggests that MEHP inhibits lipophagy in TM3 cells by suppressing the Sirt1/Foxo1/Rab7 signaling pathway, ultimately leading to a further decrease in cellular testosterone secretion. This study improves our current understanding of the toxicity and molecular mechanisms of action of MEHP and provides new insights into the reproductive effects of phthalic acid esters.

中文翻译：

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MEHP 通过 Sirt1/Foxo1/Rab7 信号通路抑制 TM3 细胞自噬对睾酮合成的影响

邻苯二甲酸单-2-乙基己基酯（MEHP）是增塑剂邻苯二甲酸二-2-乙基己基酯（DEHP）毒性最强的代谢物，研究表明MEHP会造成严重的生殖影响。然而，其确切的作用机制仍然难以捉摸。本研究旨在探讨MEHP的生殖效应并初步探讨其潜在的分子机制。我们发现，随着 MEHP 暴露的增加，TM3 细胞逐渐分泌较少的睾酮和细胞内游离胆固醇。 MEHP 暴露抑制 TM3 细胞中的脂肪吞噬和 Sirt1/Foxo1/Rab7 信号通路，导致细胞内脂滴异常积累。添加 Sirt1 激动剂 SRT1720 和 Rab7 激动剂 ML-098 可减轻 TM3 细胞中脂肪吞噬的抑制并增加游离胆固醇和睾酮含量。 SRT1720减轻了MEHP对Sirt1/Foxo1/Rab7信号通路的抑制作用，而ML-098仅减轻了MEHP对Rab7蛋白表达的抑制，对Sirt1和Foxo1蛋白表达没有影响。这表明MEHP通过抑制Sirt1/Foxo1/Rab7信号通路来抑制TM3细胞的脂噬，最终导致细胞睾酮分泌进一步减少。这项研究提高了我们目前对 MEHP 的毒性和分子作用机制的理解，并为邻苯二甲酸酯的生殖影响提供了新的见解。