Key Laboratory of Tropical & Subtropical Fishery Resource Application & Cultivation, Pearl River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou, 510380, PR China; College of Marine Sciences, South China Agriculture University, Guangzhou, 510640, PR China.
Key Laboratory of Tropical & Subtropical Fishery Resource Application & Cultivation, Pearl River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou, 510380, PR China.
Fish Shellfish Immunol. 2019 May;88:595-605. doi: 10.1016/j.fsi.2019.03.032. Epub 2019 Mar 16.
Lipid droplets (LDs) are increasingly being recognized as important immune modulators in mammals, in additional to their function of lipid ester deposition. However, the role of LDs in fish immunity remains poorly understood. In this study, the function of LDs in the innate immune response of Ctenopharyngodon idella kidney (CIK) cells, which are the equivalent of myeloid cells in vertebrates, was investigated. LD number and TG content significantly increased in the CIK cells following exposure to lipopolysaccharide (LPS), peptidoglycan (PGN), and polyriboinosinic-polyribocytidylic acid (Poly [I: C]) for 24 h, accompanied by increases in the relative expression of several innate immune genes. However, fatty acid compositions of the triglycerides were not changed after treatment with these three pathogenic mimics. LPS, PGN, and Poly (I: C) did not alter the relative expressions of lipogenic (FAS, SCD, and DGAT) and lipid catabolic (PPARα, ATGL, and CPT-1) genes. However, these treatments did increase the mRNA levels of lipid transportation genes (FATP/CD36, ACSL1, and ACSL4), and also decreased the non-esterified fatty acid level in the medium. To further explore the role of LDs in the immune response, CIK cells were incubated with different concentrations (0, 100, 200, 300, 400, 500 μM) of exogenous lipid mix (LM; oleic acid [OA]:linoleic acid [LA]:linolenic acid [LNA] = 2:1:1), and were then transferred to a lipid-free medium and incubated for 24 h. LD size and number increased with the increase in lipid levels, and this was accompanied by increased expression of innate immune genes, including MyD88, IRF3, and IL-1β, which were expressed at their highest levels in 300 μM exogenous lipid mix. Interestingly, after incubating with different fatty acids (LM, OA, LA, LNA, arachidonic acid [ARA], and docosahexaenoic acid [DHA]; 300 μM), ARA and DHA were more potent in inducing LD formation and innate immune gene expression in the CIK cells. Finally, atglistatin, an ATGL inhibitor, effectively attenuated the expression of most genes upregulated by ARA or DHA, suggesting that lipolysis may be involved in the regulation of immune genes at the transcriptional level. Overall, the findings of this study demonstrate that LDs are functional organelles that could act as modulators in the innate immune response of CIK cells. Additionally, long-chain polyunsaturated fatty acid enriched LDs play a unique role in regulating this process.
脂滴（LDs）除了具有沉积脂质酯的功能外，在哺乳动物中也越来越被认为是重要的免疫调节剂。然而，鱼类免疫中 LD 的作用仍知之甚少。在这项研究中，研究了 LD 在硬骨鱼类髓样细胞（CIK）固有免疫反应中的功能，这些细胞相当于脊椎动物中的髓样细胞。脂多糖（LPS）、肽聚糖（PGN）和聚肌苷酸-聚胞苷酸（Poly [I：C]）处理 24 小时后，CIK 细胞中的 LD 数量和 TG 含量显著增加，同时几种固有免疫基因的相对表达也增加。然而，在用这三种致病模拟物处理后，三酰基甘油的脂肪酸组成没有改变。LPS、PGN 和 Poly（I：C）均未改变脂肪生成（FAS、SCD 和 DGAT）和脂质分解代谢（PPARα、ATGL 和 CPT-1）基因的相对表达。然而，这些处理确实增加了脂质转运基因（FATP/CD36、ACSL1 和 ACSL4）的 mRNA 水平，并降低了培养基中非酯化脂肪酸的水平。为了进一步探讨 LD 在免疫反应中的作用，将 CIK 细胞与不同浓度（0、100、200、300、400、500 μM）的外源性脂质混合物（LM；油酸[OA]：亚油酸[LA]：亚麻酸[LNA]=2:1:1）孵育，然后转移到无脂培养基中孵育 24 小时。随着脂质水平的升高，LD 大小和数量增加，同时固有免疫基因的表达也增加，包括 MyD88、IRF3 和 IL-1β，在 300 μM 外源性脂质混合物中表达水平最高。有趣的是，在用不同脂肪酸（LM、OA、LA、LNA、花生四烯酸[ARA]和二十二碳六烯酸[DHA]；300 μM）孵育后，ARA 和 DHA 更能诱导 CIK 细胞中 LD 的形成和固有免疫基因的表达。最后，ATGL 抑制剂 atglistatin 有效减弱了 ARA 或 DHA 上调的大多数基因的表达，表明脂肪分解可能参与了免疫基因在转录水平的调节。总的来说，这项研究的结果表明，LDs 是具有功能的细胞器，可以作为 CIK 细胞固有免疫反应的调节剂。此外，富含长链多不饱和脂肪酸的 LD 在调节这一过程中起着独特的作用。
