Laboratory for Experimental Orthopaedics, Department of Orthopaedics, Justus Liebig University Giessen, 35392 Giessen, Germany.
Mathematical Institute, Justus Liebig University Giessen, 35392 Giessen, Germany.
Int J Mol Sci. 2022 Feb 22;23(5):2409. doi: 10.3390/ijms23052409.
(1) Background: Synovial fluid (SF) from knee joints with osteoarthritis (OA) has increased levels of phospholipids (PL). We have reported earlier that TGF-ß and IGF-1 stimulate fibroblast-like synoviocytes (FLS) to synthesize increased amounts of PLs. The current study examined whether IL-1ß induces the release of PLs in FLS and the underlying mechanism. (2) Methods: Cultured human OA FLS were treated with IL-1ß alone and with pathway inhibitors or with synthetic liver X receptor (LXR) agonists. Cholesterol hydroxylases, ABC transporters, apolipoproteins (APO), LXR, sterol regulatory binding proteins (SREBPs), and 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) were analyzed by RT-PCR, Western blot, and ELISA. The release of radiolabeled PLs from FLS was determined, and statistical analysis was performed using R (N = 5-9). (3) Results: Like synthetic LXR agonists, IL-1ß induced a 1.4-fold greater release of PLs from FLS. Simultaneously, IL-1ß upregulated the level of the PL transporter ABCA1 and of cholesterol hydroxylases CH25H and CYP7B1. IL-1ß and T0901317 stimulated the expression of SREBP1c, whereas only T0901317 enhanced SREBP2, HMGCR, APOE, LXRα, and ABCG1 additionally. (4) Conclusions: IL-1ß partially controls PL levels in OA-SF by affecting the release of PLs from FLS. Our data show that IL-1ß upregulates cholesterol hydroxylases and thus the formation of oxysterols, which, as natural agonists of LXR, increase the level of active ABCA1, in turn enhancing the release of PLs.
(1) 背景：骨关节炎（OA）膝关节滑液（SF）中磷脂（PL）水平升高。我们之前报道过 TGF-β和 IGF-1 刺激成纤维样滑膜细胞（FLS）合成更多的 PL。本研究探讨了 IL-1β是否诱导 FLS 释放 PL 及其潜在机制。
(2) 方法：用 IL-1β单独或用通路抑制剂或合成肝 X 受体（LXR）激动剂处理培养的人 OA FLS。用 RT-PCR、Western blot 和 ELISA 分析胆固醇羟化酶、ABC 转运体、载脂蛋白（APO）、LXR、固醇调节元件结合蛋白（SREBPs）和 3-羟基-3-甲基戊二酰辅酶 A 还原酶（HMGCR）。测定 FLS 释放放射性标记的 PL，并使用 R（N = 5-9）进行统计分析。
(3) 结果：与合成 LXR 激动剂一样，IL-1β诱导 FLS 释放 PL 的能力增加了 1.4 倍。同时，IL-1β上调了 PL 转运体 ABCA1 和胆固醇羟化酶 CH25H 和 CYP7B1 的水平。IL-1β和 T0901317 刺激 SREBP1c 的表达，而只有 T0901317 额外增强 SREBP2、HMGCR、APOE、LXRα和 ABCG1。
(4) 结论：IL-1β通过影响 FLS 释放 PL 来部分控制 OA-SF 中的 PL 水平。我们的数据表明，IL-1β上调胆固醇羟化酶，从而形成氧化固醇，作为 LXR 的天然激动剂，增加活性 ABCA1 的水平，进而增强 PL 的释放。
