Two-photon excited fluorescence (TPEF) may be useful to identify macrophage subsets based on their metabolic activity
Coraline Borowczyk1, Jeanny Laroche-Traineau1, Julien Brevier2
1CRMSB CNRS UMR5536, INSB, Bordeaux, France.
Background And Aims:
Atherosclerosis is characterized by the formation of lipid plaques within the arterial wall. In such plaques, the massive and continuous recruitment of circulating monocyte-derived macrophages induces inflammation, leading to plaque destabilization and rupture. Plaque vulnerability is linked to the presence of (i) a large lipid core that contains necrotic, "foamy" macrophages (FMs), (ii) a thin fibrous cap that cannot limit the prothrombotic lipid core, and potentially (iii) an imbalance between inflammatory and immunoregulatory macrophages. These opposite macrophage functions rely on the use of different energy pathways (glycolysis and oxidative phosphorylation, respectively) that may lead to different levels of the auto-fluorescent cofactors nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD). We hypothesized that high-resolution two-photon excited autofluorescence (TPEF) imaging of these cofactors may be used to monitor the metabolic activity and cellular responses of macrophages in atherosclerotic plaques.
Methods:
Different models of human FMs were generated by exposure to acetylated or oxidized low-density lipoproteins (LDL), with/without human carotid extract (CE). Their phenotype and optical properties were compared with those of extremely polarized macrophages, inflammatory M1 (MLPS+IFNγ) and immunoregulatory M2 (MIL4+IL13).
Results:
These FM models displayed an intermediate phenotype with low levels of M1 and M2 "specific" markers. Moreover, the NADH and FAD autofluorescence profiles of FMoxLDL ± CE cells were significantly distinct from those of M1 and M2 macrophages.
Conclusions:
TPEF imaging may be useful to follow the metabolic activity and cellular responses of the different macrophage subtypes present in atherosclerotic plaques in order to detect vulnerable areas.
Insights
Two-photon excited autofluorescence (TPEF) imaging of NADH and FAD cofactors can distinguish macrophage subtypes in atherosclerosis. This technique may help identify vulnerable plaque areas by monitoring macrophage metabolic activity.
Area of Science:
- Cardiovascular Biology
- Cellular Metabolism
- Medical Imaging
Background:
- Atherosclerosis involves lipid plaque formation and macrophage recruitment, leading to inflammation and plaque instability.
- Plaque vulnerability is associated with lipid cores, thin fibrous caps, and imbalanced macrophage populations (inflammatory vs. immunoregulatory).
- Macrophage metabolic pathways (glycolysis, oxidative phosphorylation) influence their function and levels of autofluorescent cofactors (NADH, FAD).
Purpose of the Study:
- To investigate the potential of two-photon excited autofluorescence (TPEF) imaging for monitoring macrophage metabolic activity and cellular responses in atherosclerotic plaques.
- To determine if TPEF imaging of NADH and FAD autofluorescence can differentiate macrophage subtypes within atherosclerotic lesions.
Main Methods:
- Generated human foamy macrophage (FM) models using acetylated or oxidized low-density lipoproteins (LDL) with or without human carotid extract (CE).
- Compared the phenotype and optical properties of these FM models with highly polarized M1 (inflammatory) and M2 (immunoregulatory) macrophages.
- Utilized high-resolution TPEF imaging to analyze the autofluorescence profiles of NADH and FAD in different macrophage models.
Main Results:
- FM models exhibited an intermediate phenotype, with low levels of M1 and M2 specific markers.
- Significant differences were observed in the NADH and FAD autofluorescence profiles between FM models and M1/M2 macrophages.
- TPEF imaging revealed distinct optical properties related to cofactor autofluorescence in different macrophage subtypes.
Conclusions:
- TPEF imaging of NADH and FAD autofluorescence can differentiate macrophage subtypes based on their metabolic state.
- This imaging technique holds promise for assessing macrophage metabolic activity and cellular responses within atherosclerotic plaques.
- TPEF imaging may serve as a valuable tool for detecting vulnerable areas in atherosclerotic lesions by characterizing macrophage populations.
