Human APOE adenoviral particles

Macrophages play an important role in the pathogenesis of atherosclerosis, but their dynamics within plaques remain unclear. In stable in vivo preparations, large asymmetric foamy macrophages in the intima of carotid plaques are stationary, but smaller round cells near the plaque edge, likely newly recruited monocytes, move laterally along the plaque edge. Here, to test the dynamics of macrophages in plaques over longer periods of time during disease progression and regression, researchers quantified the displacement of nondegradable phagocytic particles within macrophages for up to 6 weeks. By measuring the distance of the particles from the base of the plaque, researchers found that the distance of the particles from the base remained constant regardless of plaque progression or regression. The significantly deeper penetration of labeled cells in progressive disease can be attributed to monocyte recruitment, which creates a new macrophage surface layer over the labeled phagocytic cells. Although individual exceptions may exist, as a group, newly differentiated macrophages are unable to penetrate deeper than the limited depth to which they initially enter, regardless of plaque progression or regression. These limiting dynamics may prevent macrophages from escaping areas of adverse conditions (e.g., hypoxia) and pose a challenge for newly recruited macrophages to clear debris via endocytosis deep within the plaque.

Previous studies have shown that macrophage loss from plaques can be triggered by virally induced ApoE expression in plaque-bearing ApoE−/− mice. Viral transduction with adeno-associated virus 8-ApoE was effective in rapidly and stably reversing plasma cholesterol levels in male mice. In this model, macrophage-borne particles are not removed from plaques during macrophage loss. Therefore, migratory efflux of macrophages is not necessary for their removal, and such migration did not occur in this model. However, subsequent closer examination of plaque sections from these experiments revealed a striking pattern, whereby particles appeared distant from the lumen during disease progression (empty adenoviral vector; Figure 1Aa), whereas particles appeared close to the lumen in resolving treatments (ApoE-encoding adenoviral vector (ad-hApoE3); Figure 1Bb). Importantly, beads were observed to be abundantly present in the cytoplasm of macrophages within plaques in both treatment conditions (Figure 1C). Indeed, quantification of the particle-to-lumen distance confirmed a deeper localization of particles in the empty adenoviral vector group compared to the ad-hApoE3 group (Figure 1D). It was further confirmed that there was no statistical difference in total bead counts among the groups (Figure 1E).

Figure 1. Positional tracking using phagocytic cargo labeling suggests little displacement of central plaque macrophages over several weeks during plaque progression or regression. (Williams J W, et al., 2018)