PPARα Inhibition Overcomes Tumor-Derived Exosomal Lipid-Induced Dendritic Cell Dysfunction

Abstract

SUMMARY Dendritic cells (DCs) orchestrate the initiation, programming, and regulation of anti-tumor immune responses. Emerging evidence indicates that the tumor microenvironment (TME) induces immune dysfunctional tumor-infiltrating DCs (TIDCs), characterized with both increased intracellular lipid content and mitochondrial respiration. The underlying mechanism, however, remains largely unclear. Here, we report that fatty acid-carrying tumor-derived exosomes (TDEs) induce immune dysfunctional DCs to promote immune evasion. Mechanistically, peroxisome proliferator activated receptor (PPAR) α responds to the fatty acids delivered by TDEs, resulting in excess lipid droplet biogenesis and enhanced fatty acid oxidation (FAO), culminating in a metabolic shift toward mitochondrial oxidative phosphorylation, which drives DC immune dysfunction. Genetic depletion or pharmacologic inhibition of PPARα effectively attenuates TDE-induced DC-based immune dysfunction and enhances the efficacy of immunotherapy. This work uncovers a role for TDE-mediated immune modulation in DCs and reveals that PPARα lies at the center of metabolic-immune regulation of DCs, suggesting a potential immunotherapeutic target.

In vitro and ex vivo evaluation of tumor-derived exosome-induced dendritic cell dysfunction in mouse

“…However, it is strongly recommended to use some intracellular organelle markers to exclude contaminations of Golgi bodies (GM130), mitochondria (Cytochrome C) or nucleus (Histone H3). In our study, GM130, Cytochrome C, and Histone H3 was excluded to make sure the purity of exosomes( Yin et al., 2020 ).

Figure 1 Isolation of exosomes from tumor culture medium (A) Illustrative overview of exosome separation.

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“…Morphologies of the purified exosomes were characterized by transmission electron microscopy (TEM; Figure 5 A), showing a mean diameter of ~40 nm, consistent with the size of previous reports ( Kalluri, 2016 ; Kalluri and LeBleu, 2020 ). Western blot analysis revealed the presence of exosome-enriched proteins (e.g., ALIX, HSP70, TSG101, CD9, and CD81)( Hessvik and Llorente, 2017 ; Huang-Doran et al., 2017 )(Data as shown in ( Yin et al., 2020 )). In our experience, we also calculated the amount of exosomes by EXOCET Exosome Quantitation Kit and found that the number of exosomes were highly correlated with the protein content by BCA ( Figure 5 B).…”

“…The dysfunctional DCs was the result of the uptake of TDE-derived FAs. For full details, we refer to ( Yin et al., 2020 ).…”

“…This approach is useful for the interrogating TDE-DC interactions and identification of novel immune regulators. For complete details on the use and execution of this protocol, please refer to Yin et al. (2020) .…”

Metabolism of Dendritic Cells in Tumor Microenvironment: For Immunotherapy

“…Tumor cells can secrete fat-containing exosomes as a fatty acid carrier and activate PPARα of DCs to induce the synthesis of lipid droplets in DCs and enhance FAO, inducing the transformation of DC metabolism from glycolysis to OXPHOS, leading to the dysfunction of DC. As a key molecule of metabolic regulation, PPARα can be used as a target of immunotherapy and has a great potential in anti-tumor therapy ( 80 ).…”