AIM: To describe the way stations of high-density lipoprotein(HDL) uptake and its lipid exchange in endothelial cells in vitro and in vivo. METHODS: A combination of fluorescence microscopy using novel fluorescent cho...AIM: To describe the way stations of high-density lipoprotein(HDL) uptake and its lipid exchange in endothelial cells in vitro and in vivo. METHODS: A combination of fluorescence microscopy using novel fluorescent cholesterol surrogates and electron microscopy was used to analyze HDL endocytosis in great detail in primary human endothelial cells. Further, HDL uptake was quantified using radio-labeled HDL particles. To validate the in vitro findings mice were injected with fluorescently labeled HDL and particle uptake in the liver was analyzed using fluorescencemicroscopy. RESULTS: HDL uptake occurred via clathrin-coated pits, tubular endosomes and multivesicular bodies in human umbilical vein endothelial cells. During uptake and resecretion, HDL-derived cholesterol was exchanged at a faster rate than cholesteryl oleate, resembling the HDL particle pathway seen in hepatic cells. In addition, lysosomes were not involved in this process and thus HDL degradation was not detectable. In vivo, we found HDL mainly localized in mouse hepatic endothelial cells. HDL was not detected in parenchymal liver cells, indicating that lipid transfer from HDL to hepatocytes occurs primarily via scavenger receptor, class B, type Ⅰ mediated selective uptake without concomitant HDL endocytosis. CONCLUSION: HDL endocytosis occurs via clathrincoated pits, tubular endosomes and multivesicular bodies in human endothelial cells. Mouse endothelial cells showed a similar HDL uptake pattern in vivo indicating that the endothelium is one major site of HDL endocytosis and transcytosis.展开更多
Phosphoglycerate dehydrogenase(PHGDH)has emerged as a crucial factor in macromolecule synthesis,neutralizing oxidative stress,and regulating methylation reactions in cancer cells,lymphocytes,and endothelial cells.Howe...Phosphoglycerate dehydrogenase(PHGDH)has emerged as a crucial factor in macromolecule synthesis,neutralizing oxidative stress,and regulating methylation reactions in cancer cells,lymphocytes,and endothelial cells.However,the role of PHGDH in tumor-associated macrophages(TAMs)is poorly understood.Here,we found that the T helper 2(Th2)cytokine interleukin-4 and tumor-conditioned media upregulate the expression of PHGDH in macrophages and promote immunosuppressive M2 macrophage activation and proliferation.Loss of PHGDH disrupts cellular metabolism and mitochondrial respiration,which are essential for immunosuppressive macrophages.Mechanistically,PHGDH-mediated serine biosynthesis promotesα-ketoglutarate production,which activates mTORC1 signaling and contributes to the maintenance of an M2-like macrophage phenotype in the tumor microenvironment.Genetic ablation of PHGDH in macrophages from tumor-bearing mice results in attenuated tumor growth,reduced TAM infiltration,a phenotypic shift of M2-like TAMs toward an M1-like phenotype,downregulated PD-L1 expression and enhanced antitumor T-cell immunity.Our study provides a strong basis for further exploration of PHGDH as a potential target to counteract TAM-mediated immunosuppression and hinder tumor progression.展开更多
基金Supported by the Austrian Science Fund,No.P20116-B13 and No.P22838-B13
文摘AIM: To describe the way stations of high-density lipoprotein(HDL) uptake and its lipid exchange in endothelial cells in vitro and in vivo. METHODS: A combination of fluorescence microscopy using novel fluorescent cholesterol surrogates and electron microscopy was used to analyze HDL endocytosis in great detail in primary human endothelial cells. Further, HDL uptake was quantified using radio-labeled HDL particles. To validate the in vitro findings mice were injected with fluorescently labeled HDL and particle uptake in the liver was analyzed using fluorescencemicroscopy. RESULTS: HDL uptake occurred via clathrin-coated pits, tubular endosomes and multivesicular bodies in human umbilical vein endothelial cells. During uptake and resecretion, HDL-derived cholesterol was exchanged at a faster rate than cholesteryl oleate, resembling the HDL particle pathway seen in hepatic cells. In addition, lysosomes were not involved in this process and thus HDL degradation was not detectable. In vivo, we found HDL mainly localized in mouse hepatic endothelial cells. HDL was not detected in parenchymal liver cells, indicating that lipid transfer from HDL to hepatocytes occurs primarily via scavenger receptor, class B, type Ⅰ mediated selective uptake without concomitant HDL endocytosis. CONCLUSION: HDL endocytosis occurs via clathrincoated pits, tubular endosomes and multivesicular bodies in human endothelial cells. Mouse endothelial cells showed a similar HDL uptake pattern in vivo indicating that the endothelium is one major site of HDL endocytosis and transcytosis.
文摘Phosphoglycerate dehydrogenase(PHGDH)has emerged as a crucial factor in macromolecule synthesis,neutralizing oxidative stress,and regulating methylation reactions in cancer cells,lymphocytes,and endothelial cells.However,the role of PHGDH in tumor-associated macrophages(TAMs)is poorly understood.Here,we found that the T helper 2(Th2)cytokine interleukin-4 and tumor-conditioned media upregulate the expression of PHGDH in macrophages and promote immunosuppressive M2 macrophage activation and proliferation.Loss of PHGDH disrupts cellular metabolism and mitochondrial respiration,which are essential for immunosuppressive macrophages.Mechanistically,PHGDH-mediated serine biosynthesis promotesα-ketoglutarate production,which activates mTORC1 signaling and contributes to the maintenance of an M2-like macrophage phenotype in the tumor microenvironment.Genetic ablation of PHGDH in macrophages from tumor-bearing mice results in attenuated tumor growth,reduced TAM infiltration,a phenotypic shift of M2-like TAMs toward an M1-like phenotype,downregulated PD-L1 expression and enhanced antitumor T-cell immunity.Our study provides a strong basis for further exploration of PHGDH as a potential target to counteract TAM-mediated immunosuppression and hinder tumor progression.
