背景：

滤泡辅助性T（Follicular T-helper，Tfh）细胞是促进生发中心（Germinal center，GC）反应和驱动体液免疫应答的关键免疫细胞亚群。Tfh细胞的异常扩增与功能失调促进系统性红斑狼疮（Systemic lupus erythematosus，SLE）等自身免疫性疾病的发生发展。甲羟戊酸（Mevalonate，MVA）途径是生物体内合成异戊二烯类代谢物如香叶基香叶基焦磷酸（Geranylgeranyl pyrophosphate，GGPP）的核心通路。GGPP在香叶基香叶基转移酶（Geranylgeranyl transferase，GGTase）的催化下共价结合于小G蛋白（如RAB家族）碳端的半胱氨酸位点，调控小G蛋的功能与定位。然而，MVA途径来源的关键代谢物GGPP在Tfh细胞形成及SLE病理进展中的作用及机制尚不明确。

目的：

探究MVA途径来源的GGPP在Tfh细胞形成及SLE病理进展中的作用及机制，并评估抑制GGPP功能轴治疗SLE的可行性。

方法： 

1. 通过代谢组学、化学抑制剂、基因沉默技术、流式细胞术及RT-qPCR等方法，在体内外免疫模型中考察GGPP功能轴关键限速酶3-羟基-3-甲基戊二酰辅酶A还原酶（3-hydroxy-3-methylglutaryl-coenzyme A reductase，HMGCR）、香叶基香叶基二磷酸合酶1（Geranylgeranyl pyrophosphate synthase 1，GGPS1）、香叶基香叶基转移酶 Ⅱ（Geranylgeranyl transferase Ⅱ，GGTase Ⅱ）对Tfh细胞形成的调控作用。

2. 通过RNA测序、膜蛋白组学测序、流式细胞术、RT-qPCR及ELISA等方法探究GGPP功能轴调控Tfh细胞形成的机制；使用RAB家族的siRNA文库筛选调控CXCR5膜表达的RAB蛋白；对RAB蛋白的香叶基香叶基化修饰位点进行点突变，通过免疫荧光、流式细胞术、共聚焦显微成像、免疫电镜的技术考察香叶基香叶基化在RAB蛋白调控CXCR5膜表达中的作用并解析其分子机制；

3. 通过RT-qPCR及流式细胞术等方法检测SLE患者外周血CD4⁺ T及循环Tfh细胞中GGPP功能轴相关基因的表达水平，并使用Western blot及RT-qPCR等技术探究其上游调控机制；

4. 在自发性MRL/lpr红斑狼疮小鼠和BM12诱导性红斑狼疮小鼠模型中，评估抑制GGPP功能轴对SLE的治疗效果。

结果：

在体内外免疫模型中，抑制GGPP功能轴可显著阻碍Tfh细胞形成过程；

GGPP功能轴通过促进Tfh细胞相关膜分子的表达调控Tfh细胞形成，其中，CXCR5对该轴的调控作用最为敏感；GGPP功能轴通过介导RAB35香叶基香叶基化修饰促进内吞循环过程调控CXCR5的膜表达；

3. 在SLE患者外周血CD4⁺ T及Tfh细胞中，GGPP功能轴相关基因表达水平显著上调，且与疾病活动度呈正相关。T细胞受体（T cell receptor，TCR）信号通过胆固醇调节元件结合蛋白2（Sterol regulatory element-binding protein 2，SREBP2）、早期生长反应因子1（Early growth response 1，EGR1）和E2F转录因子1（E2F transcription factor 1，E2F1）介导的转录程序是该轴激活的上游调控机制；

4. 在自发性MRL/lpr红斑狼疮小鼠和BM12诱导性红斑狼疮小鼠模型中，GGPP功能轴抑制剂显著降低细胞膜CXCR5的表达，减少脾脏Tfh及GC B细胞数量，改善SLE病情。

结论：

本研究发现TCR信号通过SREBP2、EGR1和E2F1转录调控GGPP功能轴相关基因表达，促进Tfh细胞相关分子的膜表达和Tfh细胞的形成，抑制GGPP功能轴减少Tfh细胞形成并改善SLE病情。

Background：

Follicular helper T (Tfh) cells are a key subset of immune cells that promote germinal center (GC) responses and drive humoral immunity. Abnormal expansion and dysfunction of Tfh cells contribute to the pathogenesis of autoimmune diseases such as systemic lupus erythematosus (SLE). The mevalonate (MVA) pathway is the central metabolic route responsible for the biosynthesis of isoprenoids, including geranylgeranyl pyrophosphate (GGPP). GGPP covalently binds to the C-terminal cysteine residues of small GTPases (e.g., the RAB family) under the catalysis of geranylgeranyl transferase (GGTase), thereby regulating their localization and function. However, the role and underlying mechanisms of the MVA pathway-derived metabolite GGPP in Tfh cell generation and the pathogenesis of SLE remain unclear.

Objective:

To investigate the role and mechanism of MVA pathway-derived GGPP in Tfh cell biology and SLE progression, and to evaluate the therapeutic potential of targeting the GGPP axis in SLE.

Methods:

1.Using metabolomics, chemical inhibitors, gene silencing, flow cytometry, and RT-qPCR, this study investigates the regulatory roles of the GGPP functional axis—including key rate-limiting enzymes such as 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR), geranylgeranyl pyrophosphate synthase 1 (GGPS1), and geranylgeranyl transferase II (GGTase II)—on Tfh cell generation in both in vitro and in vivo immune models.

2.To explore the mechanisms by which the GGPP axis regulates Tfh cell generation, we employed RNA sequencing, membrane proteomics, flow cytometry, RT-qPCR, and ELISA. A siRNA library targeting the RAB family was used to screen for regulators of CXCR5 surface expression. Site-directed mutagenesis of the geranylgeranylation sites on RAB proteins, together with immunofluorescence, flow cytometry, confocal imaging, and immuno-electron microscopy, were used to elucidate the molecular mechanism of GGPP-mediated regulation of RAB function in CXCR5 trafficking.

3.RT-qPCR and flow cytometry were used to assess the expression of GGPP axis-related genes in CD4⁺ T cells and Tfh cells from the peripheral blood of SLE patients. Western blotting and RT-qPCR were further applied to investigate the upstream transcriptional regulation of this axis.

4.The therapeutic efficacy of targeting the GGPP signaling axis is evaluated in both spontaneous MRL/lpr lupus-prone mice and BM12 inducible model of SLE.

Results:

1.In both in vivo and in vitro immune models, inhibition of the GGPP functional axis significantly suppresses Tfh generation.

2.The GGPP functional axis drives Tfh cell generation by promoting the surface expression of Tfh-related molecules, with CXCR5 exhibiting the highest sensitivity to GGPP axis. Mechanistically, GGPP-mediated geranylgeranylation of RAB35 enhances the internalization and recycling process, thereby sustaining the surface expression of CXCR5. membrane

3.In peripheral blood CD4⁺ T and Tfh cells from patients with SLE, the expression levels of GGPP axis-related genes are significantly upregulated and positively correlate with disease activity. The activation of this axis is transcriptionally regulated by T cell receptor (TCR) signaling through sterol regulatory element-binding protein 2 (SREBP2), early growth response 1 (EGR1), and E2F transcription factor 1 (E2F1).

4.In both spontaneous MRL/lpr lupus-prone mice and BM12 inducible model of SLE, pharmacological inhibition of GGPP functional axis significantly reduces CXCR5 surface expression, decreases splenic Tfh and GC B cell numbers, and alleviates disease severity.

Conclusion:

This study demonstrates that TCR signaling enhances the expression of GGPP axis-related genes via a transcriptional cascade involving SREBP2, EGR1, and E2F1, thereby promoting surface expression of Tfh-related molecules and Tfh cell generation. pharmacological inhibition of GGPP functional axis suppresses Tfh cell generation and ameliorates SLE pathology.