LRP5-dependent transport of polyunsaturated fatty acids serves as an immune checkpoint for natural killer cells

Polyunsaturated fatty acids (PUFAs) play a crucial role in tumor development by influencing not only tumor cells but also immune cells within the tumor microenvironment. Here, we explored the mechanisms by which PUFAs are transported and function within immune cells to regulate tumor growth. We found that PUFA transport through LDL receptor–related protein 5 (LRP5) into natural killer (NK) cells played an essential role in modulating the cells’ antitumor function. LRP5 deficiency or expression of LRP5 lacking the LDLa domain enhanced the cytotoxicity and antitumor activity of NK cells both in vivo and in culture. However, wild-type NK cells cultured in the absence of PUFAs and NK cells from mice fed a PUFA-free diet also exhibited enhanced cytotoxicity, eliminating the functional difference between wild-type and NK cells expressing LDLa domain–deficient LRP5. Mechanistically, LRP5-mediated PUFA transport suppressed mTORC1 signaling and glycolysis in NK cells, a metabolic pathway essential for NK cell cytotoxicity. Thus, our study identified LRP5 as an immune checkpoint that restrains NK cell activity through PUFA transport–dependent suppression of mTORC1 signaling.