Somatic mutations in TBX3 promote hepatic clonal expansion by accelerating VLDL secretion

We’ve previously demonstrated that hepatocytes with Tbx3 deletions have increased cellular fitness and clonally expand during metabolic-dysfunction associated steatotic liver disease (MASLD) development. TBX3 is a transcription factor that is critical for embryonic development, but has never been studied within the context of MASLD. Here, we show that somatic mutations in TBX3 are found in human patients with MASLD. Liver specific deletion of Tbx3 in mice protects against diet induced MASLD through upregulating VLDL-TG particle secretion. TBX3 transcriptionally suppresses the conventional secretory pathway and cholesterol biosynthesis. Hdlbp is a direct target of TBX3 that is responsible for altered VLDL secretion. In contrast to WT TBX3, TBX3 harboring somatic mutations found in humans failed to suppress VLDL secretion in vivo. In conclusion, mutations in TBX3 promote clonal expansion during MASLD development through increased lipid disposal, demonstrating clonal fitness can benefit the liver even at the cost of hyperlipidemia. High throughput sequencing of DNA from the CUT&RUN protocol of stable H2.35 mouse hepatocyte cell line overexpressing a V5 tagged mouse Tbx3 compared to an IgG isotype control (n=3) and ChIP-sequencing of human TBX3 from mouse livers overexpressing Ty1 tagged TBX3 via AAV compared to an IgG isotype control (n=4).

本课题组前期研究证实，在代谢功能障碍相关性脂肪性肝病（MASLD）的发生发展过程中，Tbx3缺失的肝细胞细胞适应性提升并发生克隆扩增。TBX3是一类对胚胎发育至关重要的转录因子，但此前从未在MASLD的研究背景下开展相关研究。本研究发现，MASLD患者体内存在TBX3体细胞突变。小鼠肝脏特异性敲除Tbx3可通过上调极低密度脂蛋白-甘油三酯（VLDL-TG）颗粒的分泌，抵御饮食诱导的MASLD。TBX3可通过转录作用抑制经典分泌通路与胆固醇生物合成过程。Hdlbp是TBX3的直接靶基因，其介导了VLDL分泌的异常改变。与野生型TBX3不同，携带人类体细胞突变的TBX3无法在体内抑制VLDL分泌。综上，TBX3突变通过增强脂质清除能力，促进MASLD发生发展过程中的克隆扩增，这表明即便以高脂血症为代价，克隆适应性仍可对肝脏产生有益影响。本研究附带的高通量测序数据集包含两组：① 过表达V5标签小鼠Tbx3的稳定H2.35小鼠肝细胞系，采用CUT&RUN实验流程提取DNA后进行高通量测序，以IgG同型对照作为对照组（n=3）；② 通过腺相关病毒（AAV）介导在小鼠肝脏中过表达Ty1标签TBX3的样本，进行人源TBX3的染色质免疫沉淀测序（ChIP-seq），同样以IgG同型对照作为对照组（n=4）。