KLF15 Cistromes Reveal a Hepatocyte Pathway Governing Plasma Corticosteroid Transport and Systemic Inflammation

Circulating corticosteroids orchestrate stress adaptation, including inhibition of inflammation. While pathways governing corticosteroid biosynthesis and intracellular signaling are understood, less is known about mechanisms controlling plasma corticosteroid transport. Here, we show hepatocyte KLF15 (Kruppel-like factor 15) controls plasma corticosteroid transport and inflammatory responses through direct transcriptional activation of Serpina6, which encodes corticosteroid binding globulin (CBG). Klf15-deficient mice have profoundly low CBG, reduced plasma corticosteroid binding capacity, and heightened mortality during inflammatory stress. These defects are completely rescued by reconstituting CBG, supporting that KLF15 works primarily through CBG to control plasma corticosterone homeostasis. To understand transcriptional mechanisms, we generated the first KLF15 cistromes using newly engineered Klf153xFLAG mice. Unexpectedly, liver KLF15 is predominantly promoter-enriched, including Serpina6, where it binds a palindromic GC-rich motif, opens chromatin, and transactivates genes with minimal associated gene repression. Overall, we provide new mechanistic insight into KLF15 function and identify a hepatocyte-intrinsic transcriptional module that potently regulates systemic corticosteroid transport and inflammation. ChIP-seq (n=2) was used to define KLF15 binding map while RNA-seq (control vs KLF15-LKO, n=4) was used for gene expression and ATAC-seq (control vs KLF15-LKO, n=2) for open chromatin profiling.循环糖皮质激素（circulating corticosteroids）可协调应激适应过程，包括抑制炎症反应。尽管目前对糖皮质激素的生物合成通路及细胞内信号调控机制已有清晰认知，但关于血浆糖皮质激素转运的调控机制仍有待深入探究。本研究证实，肝细胞Kruppel样因子15（Kruppel-like factor 15, KLF15）可通过直接转录激活编码糖皮质激素结合球蛋白（corticosteroid binding globulin, CBG）的Serpina6基因，调控血浆糖皮质激素转运与炎症应答。Klf15敲除小鼠体内CBG水平显著降低，血浆糖皮质激素结合能力下降，且在炎症应激状态下死亡率显著升高。通过重组表达CBG可完全挽救上述表型缺陷，表明KLF15主要通过CBG介导血浆皮质酮稳态的调控。为解析其转录调控机制，本研究利用新构建的Klf15 3xFLAG标记小鼠，首次获取了KLF15顺反组（cistromes）。出乎意料的是，肝脏KLF15主要富集于基因启动子区域，包括Serpina6基因；KLF15可结合该处的回文GC富集基序，开放染色质结构，并转录激活靶基因，且几乎不伴随基因沉默效应。综上，本研究为KLF15的功能提供了全新的机制性见解，并鉴定出一个肝细胞内源性转录模块，该模块可强效调控全身性糖皮质激素转运与炎症反应。本研究采用染色质免疫共沉淀测序（ChIP-seq，n=2）绘制KLF15结合图谱，利用RNA测序（RNA-seq，对照组 vs KLF15肝脏特异性敲除组，n=4）分析基因表达差异，并通过转座酶可及性测序（ATAC-seq，对照组 vs KLF15肝脏特异性敲除组，n=2）开展开放染色质谱分析。