PlGF modulates vascular smooth muscle cells phenotype to enhance atherosclerotic plaque stability

Phenotypic switching of vascular smooth muscle cells (VSMCs) is critical for determining atherosclerotic plaque stability; however, the mechanisms that drive a stability-promoting VSMCs phenotype remain unclear. While clinical evidence associates high placental growth factor (PlGF) expression with stable advanced plaques, the underlying pathways are undefined. This study investigates the mechanism by which PlGF regulates VSMCs phenotypic switching to enhance plaque stability.

PlGF expression was quantified in human carotid plaques by immunohistochemistry. Atherosclerosis was induced in ApoE^-/- mice fed a high-fat diet, followed by PlGF administration for 7 days. Plaque size, composition, and the expression of PlGF, Flt-1, CD209/CD163, TGF-β1, α-SMA and CD68 were assessed at 14 and 28 days by immunohistochemistry/immunofluorescence. In vitro, flow cytometry, Western blot, ELISA and conditioned co-culture systems evaluated macrophage polarization, TGF-β1 secretion, and effects on human carotid VSMCs phenotype.

PlGF was elevated in stable human plaques, co-localized with α-SMA in fibrous cap and shoulder regions. In PlGF-treated mice, PlGF, α-SMA and TGF-β1 increased in the fibrous cap and shoulder regions of plaques, while aortic root plaque area decreased. Co-localization of Flt-1/CD209 and TGF-β1/CD209 was enhanced, with TGF-β1/CD209 exceeding TGF-β1/α-SMA. Mechanistically, PlGF polarized macrophages toward an anti-inflammatory phenotype, increasing TGF-β1 secretion, which upregulated α-SMA in VSMCs.

This study identifies a PlGF/anti-inflammatory macrophage/TGF-β1/contractile VSMCs signaling axis that reinforces fibrous cap integrity and promotes plaque stability in advanced atherosclerosis.