Cyclin G2 promotes the formation of smooth muscle cells derived foam cells in atherosclerosis via PP2A/NF-κB/LOX-1 pathway

Background: To investigate the role and underlying mechanism of cyclin G2 (G2-type cyclin) in the formation of vascular smooth muscle cells (VSMCs) derived foam cells.

Methods: The levels of α-SMA (alpha-SM-actin), p-NF-κB (phosphorylation nuclear transcription factors kappa B), and LOX-1 (lectin-like oxidized low-density lipoprotein receptor-1) were measured by immunohistochemistry and western blotting. The mouse aortic root smooth muscle cell line MOVAS was transfected to over-express cyclin G2, which were then stimulated with 80 µg/mL ox-LDL (oxidized low-density lipoprotein) to induce foam cell formation. DT-061 an activator of PP2A (protein Phosphatase 2A) agonist was used to verify the role of PP2A in the process.

Results: Knocking out the Ccng2 gene in apoE^-/- mice alleviated aortic lipid plaque, foam cell formulation, ameliorative body weight, and LDL-cholesterol. We observed that the number of α-SMA positive cells was significantly decreased in apoE^-/-Ccng^2-/- mice compared to apoE^-/- mice. Also, the protein levels of p-NF-κB and LOX-1 were markedly reduced in the aortic root of apoE^-/-Ccng2^-/- mice. Upon stimulation with ox-LDL, upregulated cyclin G2 increased the intracellular lipid accumulation in MOVAS cells. Also, it suppressed the activity of PP2A but up-regulated LOX-1. Additionally, the cell nuclear translocation of p-NF-κB was increased. Interestingly, DT-061 intervention, re-activating the activity of PP2A, reduced the levels of nuclear p-NF-κB and LOX-1. This led to decreased lipid endocytosis reducing the formation of VSMCs- derived foam cells.

Conclusions: Cyclin G2 increases the nuclear translocation of p-NF-κB by reducing the enzymatic activity of PP2A and upregulating LOX-1, thereby promotes the formation of VSMCs -derived foam cells in atherosclerosis.