Figure 3.

Fatty acid (FA) in the tumor microenvironment. The increase of FA exists in various tumor microenvironments. Tumor fibroblasts release a large of FA into the microenvironment, and some of the FA are absorbed by tumor cells for energy generation. Of course, tumor cells themselves also promote FA synthesis by increasing the activity of ACLY, ACC and FASN. Meanwhile, PCK1 induces FA synthesis through SREBP pathway, which is considered to be a specific way of tumor cells. FA produced by tumor cells can also be transported into the microenvironment and become part of the composition of exogenous FA. These exogenous FA are transported by CD36 receptors on the macrophages to activate FAO and promote M2-type polarization of macrophages. Macrophages themselves also adapt to this environment by down-regulation SIRT4 and RIPK3 and activating PPAR.