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Updated: Jul 5, 2025
Quantitative Analysis of Cellular Composition in Advanced Atherosclerotic Lesions of Smooth Muscle Cell Lineage-Tracing Mice
Published on: February 20, 2019
Conditional deletion of Ccl2 in smooth muscle cells does not reduce early atherosclerosis in mice
Stine Gunnersen1,2, Jeong Tangkjær Shim1,2, Fan Liu3,4
1Atherosclerosis Research Unit, Department of Clinical Medicine, Aarhus University, Palle Juul-Jensens Boulevard 11, 8200 Aarhus N, Denmark.
Background And Aims:
C-C motif chemokine ligand 2 (CCL2) is a pro-inflammatory chemokine important for monocyte recruitment to the arterial wall and atherosclerotic plaques. Global knockout of Ccl2 reduces plaque formation and macrophage content in mice, but the importance of different plaque cell types in mediating this effect has not been resolved. Smooth muscle cells (SMCs) can adopt a potentially pro-inflammatory function with expression of CCL2. The present study aimed to test the hypothesis that SMC-secreted CCL2 is involved in early atherogenesis in mice.
Methods:
SMC-restricted Cre recombinase was activated at 6 weeks of age in mice with homozygous floxed or wildtype Ccl2 alleles. Separate experiments in mice lacking the Cre recombinase transgene were conducted to control for genetic background effects. Hypercholesterolemia and atherosclerosis were induced by a tail vein injection of recombinant adeno-associated virus (rAAV) encoding proprotein convertase subtilisin/kexin type 9 (PCSK9) and a high-fat diet for 12 weeks.
Results:
Unexpectedly, mice with SMC-specific Ccl2 deletion developed higher levels of plasma cholesterol and larger atherosclerotic plaques with more macrophages compared with wild-type littermates. When total cholesterol levels were incorporated into the statistical analysis, none of the effects on plaque development between groups remained significant. Importantly, changes in plasma cholesterol and atherosclerosis remained in mice lacking Cre recombinase indicating that they were not caused by SMC-specific CCL2 deletion but by effects of the floxed allele or passenger genes.
Conclusions:
SMC-specific deficiency of Ccl2 does not significantly affect early plaque development in hypercholesterolemic mice.
Insights
Smooth muscle cell-specific deletion of C-C motif chemokine ligand 2 (CCL2) did not impact early atherosclerosis development in mice. This suggests CCL2 from smooth muscle cells is not a primary driver of early plaque formation in this model.
Area of Science:
- Cardiovascular Biology
- Immunology
- Atherosclerosis Research
Background:
- C-C motif chemokine ligand 2 (CCL2) promotes monocyte recruitment to arterial walls and atherosclerotic plaques.
- Global CCL2 knockout reduces plaque formation, but the role of specific cell types remains unclear.
- Smooth muscle cells (SMCs) can express CCL2, potentially contributing to inflammation.
Purpose of the Study:
- To investigate the hypothesis that CCL2 secreted by SMCs contributes to early atherogenesis in mice.
- To determine the specific role of SMC-derived CCL2 in the development of atherosclerosis.
Main Methods:
- SMC-restricted Cre recombinase was used to delete the Ccl2 gene in mice.
- Hypercholesterolemia and atherosclerosis were induced via PCSK9-encoding rAAV injection and a high-fat diet.
- Control groups included mice lacking Cre recombinase and wild-type littermates.
Main Results:
- Mice with SMC-specific Ccl2 deletion unexpectedly showed higher plasma cholesterol and larger atherosclerotic plaques with more macrophages.
- These effects on plaque development were not significant when total cholesterol levels were accounted for statistically.
- Observed changes in cholesterol and atherosclerosis persisted in Cre-negative control mice, indicating they were not due to SMC-specific Ccl2 deletion.
Conclusions:
- SMC-specific deficiency of Ccl2 does not significantly alter early plaque development in hypercholesterolemic mice.
- The study suggests that CCL2 derived from smooth muscle cells is not a critical mediator of early atherosclerosis in this experimental model.
