SET7 lysine methyltransferase mediates the up-regulation of NADPH oxidase expression, oxidative stress, and NLRP3 inflammasome priming in atherosclerosis.

backgroundDysregulation of histone methylation-based epigenetic mechanisms leads to either transient or long-lasting transcriptomic alterations in vascular and immune cells with important consequences on atherosclerotic plaque development and stability. We hypothesized that the epigenetic enzyme SET7 lysine methyltransferase contributes to the up-regulation of NADPH oxidase (Nox) and NLRP3 inflammasome expression in atherosclerosis.

methodsTo test this hypothesis, we examined human non-atherosclerotic and atherosclerotic tissue samples, apolipoprotein E-deficient (ApoE-/-) mice, and human macrophages (Mac) employing real-time PCR, Western blot, immunofluorescence microscopy, and histological techniques. Male ApoE-/- mice with established atherosclerosis were randomized to receive concomitant with the high-fat diet, 5 mg/kg (R)-PFI-2, a selective SET7 pharmacological inhibitor, or its vehicle, every other day for 4 weeks.

resultsThe results revealed that SET7 mRNA and protein, and H3K4me1 levels were significantly elevated in human carotid atherosclerotic lesions, aorta of atherosclerotic mice, and in cultured pro-inflammatory Mac. In the atherosclerotic mice, pharmacological blockade of SET7 catalytic activity with the specific inhibitor, significantly reduced atherosclerotic plaque development, decreased the aortic up-regulation of mRNA and protein levels of Nox catalytic subunits, mitigated the formation of NT-/4HNE-protein adducts, attenuated NLRP3 gene and protein expression, and reduced pro-caspase-1 and pro-IL18 cleavage. In polarized pro-inflammatory human M1-Mac, SET7-oriented pharmacological intervention reduced the transcriptional up-regulation of Nox catalytic subunits, NLRP3, caspase-1, IL1β, and IL18, and the secretion IL1β and TNFα. Transient overexpression of SET7 in human endothelial cells enhanced mRNA levels of Nox1, Nox2, Nox4, Nox5, and p22phox.

conclusionThe novel results show that SET7 regulates important mechanisms leading to enhanced formation of reactive oxygen species and pro-inflammatory cytokines release in atherosclerosis. The data recommend SET7 as a promising target for pharmacological interventions and as supportive therapeutic strategy in atherosclerotic cardiovascular diseases.