Hepatic stellate cell stearoyl co-A desaturase activates leukotrien B4 receptor 2-ß-catanin cascade to promote liver tumorigenesis.
Hepatocellular carcinoma (HCC) is the 3rd most deadly malignancy. Activated hepatic stellate cells (aHSC) give rise to cancer-associated fibroblasts in HCC and are considered a potential therapeutic target. Here we report that selective ablation of stearoyl CoA desaturase-2 (Scd2) in aHSC globally suppresses nuclear CTNNB1 and YAP1 in tumors and tumor microenvironment and prevents liver tumorigenesis in male mice. Tumor suppression is associated with reduced leukotriene B4 receptor 2 (LTB4R2) and its high affinity oxylipin ligand, 12-hydroxyheptadecatrienoic acid (12-HHTrE).  Genetic or pharmacological inhibition of LTB4R2, recapitulates CTNNB1 and YAP1 inactivation and tumor suppression in culture and in vivo. Single cell RNA sequencing identifies a subset of tumor-associated aHSC expressing Cyp1b1 but no other 12-HHTrE biosynthetic genes.  aHSC release 12-HHTrE in a manner dependent on SCD and CYP1B1 and their conditioned medium reproduces the LTB4R2-mediated tumor-promoting effects of 12-HHTrE in HCC cells.  CYP1B1-expressing aHSC are detected in proximity of LTB4R2-positive HCC cells and the growth of patient HCC organoids is blunted by LTB4R2 antagonism or knockdown.  Collectively, our findings suggest aHSC-initiated 12-HHTrE-LTB4R2-CTNNB1-YAP1 pathway as a potential HCC therapeutic target. Overall design: To examine cell types expressing Cyp1b1 in tumor microenvironment (TME), screening of cell type clusters was done  by scRNA-seq and we found that Cyp1b1 was dominantly expression by Fbln2+ cells. To further characterize these Fbln2+ cells, we enriched Col1a1 expressing cells by isolating GFP+ cells by FACS from DEN+WAD-subjected Rosa26mTmG; Col1a1-Cre (mTmG;CC) mice.This allowed separation of VitA+GFP- quiescent HSC, VitA+GFP+ aHSC and VitA-GFP+ VitA-depleted aHSC and activated PF.