CCR2 is predominantly expressed on the surface of monocytes and macrophages. When CCL2 binds to CCR2, it triggers a signaling cascade within the responding immune cells, directing them toward the source of the chemokine. Once recruited, macrophages can phagocytose pathogens, secrete inflammatory mediators, present antigens to other immune cells, and participate in tissue repair processes. The interaction between CCL2 and macrophages is crucial for the coordination of immune responses to infection, inflammation, and tissue damage. Dysregulation of this interaction can contribute to various inflammatory diseases and conditions, including atherosclerosis, rheumatoid arthritis, and certain types of cancer.
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Atherosclerosis may cause chronic inflammation. Macrophages are able to remove dead cells, but if there is a problem with the macrophage, it can lead to chronic inflammation and ongoing tissue damage. This study validated the maintenance mechanism of vascular macrophages.
Mural cells sustain a vascular MΦ niche. | |
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![]() Fig.1 Mural cells sustain a vascular MΦ niche.1 |
The functional activation status of macrophages in vivo is detected by mouse Cx3cr1Cre-ERT2 and PC-G5-tdT (Cx3cr1-MFCa-rep). The results showed that macrophages reach the necrotic zone within seconds after aseptic microinjury. Close connections between vascular wall cells and macrophages can be seen in the microvascular bed of multiple organs and the atherosclerotic macrovascular system. Vascular wall cells expressed Ccl2 and Mif in high concentration. |
The role of MC-derived CCL2 in maintaining the MΦ phenotype. | |
![]() Fig.2 MC-derived CCL2 sustains a homeostatic MΦ phenotype across the vascular tree.1 |
In vitro experiments showed that CCL2 could enhance the survival of macrophages. In this study, Ng2cre, Ccl2fl/fl, and ApoE-/- mouse models with CCL2 knockout were constructed. Fig.2 G-J showed that CCL2 knockout results in a decrease in macrophage coverage in the blood vessels of the mouse kidney, but there is no change in macrophage proliferation and the number of blood monocytes. |
Different chemotaxis linkages between SMCs and MΦ chemoattractants. | |
![]() Fig.3 Different chemotaxis linkages between SMCs and MΦ chemoattractants.1 |
Single-cell analysis showed that a population of arterial smooth muscle cells (SMCs) was highly expressed in CCL2. Atherosclerotic mouse SMC had higher expression of CCL2 and MIF. |
SMCs exert chemotactic cues on plaque MΦs. | |
![]() Fig.4 SMCs exert chemotactic cues on plaque MΦs.1 |
Some macrophages migrate between mural cell interactions, and some, although sessile, interact with mural cells by extending protrusions towards mural cells (Fig.4 A-F). Colocalization of macrophages with vascular wall cells has also been observed in human atherosclerotic tissues, and macrophages, although not correlated with the fragility of a-SMA and lesions, are associated with smaller necrotic core regions (Fig.4 K-L). |
Relationship between SMC and MΦ function in the fiber cap. | |
![]() Fig.5 SMCs within the fibrous cap preserve a strategic positioning of plaque MΦs and secure homeostatic MΦ functions.1 |
In vitro experiments to study the migration tendency of macrophages showed that macrophages migrated towards necrotic Jurkat cells or SMC (Fig.5 D). If CCL2 is blocked, macrophage migration to Jurkat cells is reduced (Fig.5 E). By knocking out CCL2 from the blood vessel wall cells, macrophages migrate from the surface of the plaque in the atherosclerotic area to the center of the plaque area (Fig.5 F, G). In the absence of CCL2 expressed in vascular wall cells, the supernatant co-culture of macrophages with necrotic cells reduces macrophage survival and leads to downregulation of macrophage marker genes and upregulation of apoptotic pathway genes (Fig.5 H-I). Direct stimulation of macrophages with CCL2 in vitro can increase macrophage homeostatic function and survival (Fig.5 J-L). However, it does not affect the local proliferation of macrophages and SMCs or the apoptosis of SMCs (Fig.5 M-R). |
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Reference
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