Division of Regulatory Glycobiology, Institute of Molecular Biomembrane and Glycobiology, Tohoku Medical and Pharmaceutical University, Sendai, Miyagi, Japan.
Graduate School of Integrated Sciences for Life, Hiroshima University, Higashi-Hiroshima, Japan.
J Biol Chem. 2024 Aug;300(8):107558. doi: 10.1016/j.jbc.2024.107558. Epub 2024 Jul 11.
α1,6-Fucosyltransferase (Fut8) is the enzyme responsible for catalyzing core fucosylation. Exogenous L-fucose upregulates fucosylation levels through the GDP-fucose salvage pathway. This study investigated the relationship between core fucosylation and immunoglobulin G (IgG) amounts in serum utilizing WT (Fut8), Fut8 heterozygous knockout (Fut8), and Fut8 knockout (Fut8) mice. The IgG levels in serum were lower in Fut8 and Fut8 mice compared with Fut8 mice. Exogenous L-fucose increased IgG levels in Fut8 mice, while the ratios of core fucosylated IgG versus total IgG showed no significant difference among Fut8, Fut8, and Fut8 mice treated with L-fucose. These ratios were determined by Western blot, lectin blot, and mass spectrometry analysis. Real-time PCR results demonstrated that mRNA levels of IgG Fc and neonatal Fc receptor, responsible for protecting IgG turnover, were similar among Fut8, Fut8, and Fut8 mice treated with L-fucose. In contrast, the expression levels of Fc-gamma receptor Ⅳ (FcγRⅣ), mainly expressed on macrophages and neutrophils, were increased in Fut8 mice compared to Fut8 mice. The effect was reversed by administrating L-fucose, suggesting that core fucosylation primarily regulates the IgG levels through the Fc-FcγRⅣ degradation pathway. Consistently, IgG internalization and transcytosis were suppressed in FcγRⅣ-knockout cells while enhanced in Fut8-knockout cells. Furthermore, we assessed the expression levels of specific antibodies against ovalbumin and found they were downregulated in Fut8 mice, with potential recovery observed with L-fucose administration. These findings confirm that core fucosylation plays a vital role in regulating IgG levels in serum, which may provide insights into a novel mechanism in adaptive immune regulation.
α1,6-岩藻糖基转移酶（Fut8）是催化核心岩藻糖基化的酶。外源性 L-岩藻糖通过 GDP-岩藻糖补救途径上调岩藻糖基化水平。本研究利用 WT（Fut8）、Fut8 杂合敲除（Fut8）和 Fut8 敲除（Fut8）小鼠研究了核心岩藻糖基化与血清免疫球蛋白 G（IgG）量之间的关系。与 Fut8 小鼠相比，Fut8 和 Fut8 小鼠血清中的 IgG 水平较低。外源性 L-岩藻糖增加了 Fut8 小鼠的 IgG 水平，而 Fut8、Fut8 和 Fut8 小鼠用 L-岩藻糖处理后核心岩藻糖基化 IgG 与总 IgG 的比值没有显著差异。这些比值通过 Western blot、凝集素印迹和质谱分析确定。实时 PCR 结果表明，L-岩藻糖处理后 Fut8、Fut8 和 Fut8 小鼠的 IgG Fc 和新生儿 Fc 受体（负责保护 IgG 周转率）的 mRNA 水平相似。相比之下，Fut8 小鼠中 Fc-γ 受体Ⅳ（FcγRⅣ）的表达水平升高，FcγRⅣ 主要表达在巨噬细胞和中性粒细胞上。用 L-岩藻糖处理后，这种作用被逆转，表明核心岩藻糖糖基化主要通过 Fc-FcγRⅣ 降解途径调节 IgG 水平。一致地，FcγRⅣ 敲除细胞中的 IgG 内化和转胞作用受到抑制，而 Fut8 敲除细胞中的 IgG 内化和转胞作用增强。此外，我们评估了针对卵清蛋白的特异性抗体的表达水平，发现它们在 Fut8 小鼠中下调，用 L-岩藻糖给药观察到潜在恢复。这些发现证实核心岩藻糖糖基化在调节血清 IgG 水平中起着重要作用，这可能为适应性免疫调节中的新机制提供了启示。
