The senescent marker p16INK4a enhances macrophage foam cells formation

BACKGROUND: The senescence marker p16INK4a, which constitutes part of the genome 9p21.3 cardiovascular disease (CVD) risk allele, is believed to play a role in foam cells formation. This study aims to unravel the role of p16INK4a in mediating macrophage foam cells formation, cellular senescence, and autophagy lysosomal functions.

METHODS: The mammalian expression plasmid pCMV-p16INK4a was used to induce p16INK4a overexpression in THP-1 macrophages. Next, wild-type and p16INK4a-overexpressed macrophages were incubated with oxidized LDL to induce foam cells formation. Lipids accumulation was evaluated using Oil-red-O staining and cholesterol efflux assay, as well as expression of scavenger receptors CD36 and LOX-1. Cellular senescence in macrophage foam cells were determined through analysis of senescence-associated β-galactosidase activity and other SASP factors expression. Meanwhile, autophagy induction was assessed through detection of autophagosome formation and LC3B/p62 markers expression.

RESULTS: The findings showed that p16INK4a enhanced foam cells formation with increased scavenger receptors CD36 and LOX-1 expression and reduced cholesterol efflux in THP-1 macrophages. Besides, β-galactosidase activity was enhanced, and SASP factors such as IL-1α, TNF-α, and MMP9 were up-regulated. In addition, p16INK4a is also shown to induce autophagy, as well as increasing autophagy markers LC3B and p62 expression.

CONCLUSIONS: This study provides insights on p16INK4a in mediating macrophages foam cells formation, cellular senescence, and foam cells formation.