Tumor Microenvironment Acidity Triggers Lipid Accumulation in Liver Cancer via SCD1 Activation

Acidification is recognized as the predominant characteristic of the tumor microenvironment (TME) and contributes to tumor progression. However, the mechanism of extracellular acidic TME directly influences intercellular pathologic responses remains unclear. Meanwhile, acidic TME is mainly ascribed to aberrant metabolism of lipids and glucose, but whether and how acidity affects metabolic reprogramming, especially for lipid metabolism, is still unknown. We found that lipid was significantly accumulated in liver cancer cells when exposed to acidic TME. Moreover, proteomic analysis showed that differentially expressed proteins were mainly clustered into fatty acid pathways. Subsequently, we found that acidification increased the expression of SCD1 by activating PI3K/AKT signaling pathway. Interestingly, we found that SCD1 directly bound to PPARα in the acidic TME, which vanished after 2-day reverse incubation in pH 7.4 medium, implying extracellular acidosis might influence intercellular function by mediating the binding affinity between SCD1 and PPARα under different pH gradients. In summary, our data revealed that acidosis could significantly trigger fatty acid synthesis to promote liver tumorigenesis by upregulating SCD1 in a PI3K/AKT activation dependent manner and simultaneously promote SCD1 binding to PPARα. Our study not only provides direct mechanistic evidence to support the vital role of acidosis in lipid metabolic reprogramming, but also provides novel insights for determining the binding affinity of functional proteins as a molecular mechanism to better understand the role of the acidic TME in tumor development. Implications: The acidic TME contributes to lipid accumulation in liver cancer by activating the PI3K/AKT signaling pathway and promoting SCD1–PPARα binding.