Protein tyrosine phosphatase receptor kappa regulates glycolysis, de novo lipogenesis and promotes hepatocyte metabolic reprogramming in obesity. Protein tyrosine phosphatase receptor kappa regulates glycolysis, de novo lipogenesis and promotes hepatocyte metabolic reprogramming in obesity

Metabolic dysfunction within the liver is a major cause of human disease worldwide. Fat accumulation, de novo lipogenesis, and glycolysis are key drivers of hepatocyte reprogramming and the consequent metabolic dysfunction-associated steatotic liver disease (MASLD). The underpinning molecular mechanisms affected by steatosis and inflammation in the obese states remain unknown. Here we report that obesity leads to dysregulated expression of protein-tyrosine phosphatases (PTPs) in the liver. Protein Tyrosine Phosphatase Receptor Kappa (PTPRK) expression was increased in hepatocytes during steatosis and inflammation in humans and mice, and positively correlates with PPARγ-induced lipogenic signalling. Supporting this, PTPRK knockout mice displayed reduced fat accumulation in adipose tissue and liver after exposure to an obesogenic diet. Phosphoproteomic analysis in primary hepatocytes and hepatic metabolomics identified specific phosphotyrosine residues in fructose-1,6 bisphosphatase-1 and glycolysis regulation as targets of PTPRK. The changes in glycolysis and de novo lipogenesis revealed PTPRK was a driving force for metabolic reprogramming in hepatocytes. Moreover, hepatoma cell lines showed reduced colony-forming ability after PTPRK silencing in vitro, and PTPRK knockout mice developed smaller tumours after diethylnitrosamine-induced hepatocarcinogenesis in vivo. Through computational modelling, we identified selective PTPRK inhibitors. These compounds decreased glycolytic rates in hepatoma cell lines, PPARγ expression in primary hepatocytes and steatosis in obese mice. In conclusion, our study defines a novel mechanism for the development of MASLD, revealing a key role of PTPRK on hepatic glycolysis regulation with implications in lipid metabolism, and liver tumour development. We propose PTPRK as a potential target for metabolic liver dysfunction, and the identified inhibitors may represent promising candidates for therapy in obesity-associated liver diseases. Overall design: Bulk RNA-Seq of mouse livers with low and high fat for wild type and PTPRK knockout mice.

肝脏代谢功能异常是全球范围内人类疾病的主要诱因之一。脂肪蓄积、从头脂肪生成（de novo lipogenesis）与糖酵解是肝细胞重编程以及后续代谢功能异常相关性脂肪性肝病（metabolic dysfunction-associated steatotic liver disease, MASLD）发生发展的关键驱动因素。肥胖状态下脂肪变性与炎症所影响的核心分子机制仍不明晰。
本研究发现，肥胖会导致肝脏内蛋白酪氨酸磷酸酶（protein-tyrosine phosphatases, PTPs）的表达失调。蛋白酪氨酸磷酸酶受体κ（Protein Tyrosine Phosphatase Receptor Kappa, PTPRK）的表达在人类与小鼠的脂肪变性及炎症阶段的肝细胞中均出现上调，且与过氧化物酶体增殖物激活受体γ（PPARγ）诱导的成脂信号通路呈正相关。与此相符，PTPRK敲除小鼠在致肥胖饮食造模后，其脂肪组织与肝脏内的脂肪蓄积量均有所降低。
对原代肝细胞进行的磷酸化蛋白质组学分析以及肝脏代谢组学分析，鉴定出果糖-1,6-二磷酸酶1（fructose-1,6 bisphosphatase-1）以及糖酵解调控通路中的特定磷酸酪氨酸残基为PTPRK的作用靶点。糖酵解与从头脂肪生成的相关变化表明，PTPRK是肝细胞代谢重编程的核心驱动因素。此外，体外实验中沉默PTPRK后，肝癌细胞系的集落形成能力显著下降；体内实验中，PTPRK敲除小鼠在二乙基亚硝胺（diethylnitrosamine）诱导肝癌发生后，肿瘤体积更小。
通过计算建模，本研究筛选出了选择性PTPRK抑制剂。这类化合物可降低肝癌细胞系的糖酵解速率、原代肝细胞中PPARγ的表达水平，并改善肥胖小鼠的肝脏脂肪变性。
综上，本研究阐明了MASLD发生发展的全新分子机制，揭示了PTPRK在肝脏糖酵解调控中的关键作用，其与脂质代谢及肝脏肿瘤发生均密切相关。本研究提出PTPRK可作为代谢性肝脏功能异常的潜在治疗靶点，且本次筛选得到的抑制剂有望成为肥胖相关性肝脏疾病的潜在治疗候选药物。
实验整体设计：对野生型与PTPRK敲除小鼠的低脂、高脂饮食喂养的肝脏样本进行批量RNA测序（Bulk RNA-Seq）。