Functional Crosstalk between PCSK9 Internalization and Pro-Inflammatory Activation in Human Macrophages: Role of Reactive Oxygen Species Release

Abstract

Atherosclerosis is a cardiovascular disease caused mainly by dyslipidemia and is characterized by the formation of an atheroma plaque and chronic inflammation. Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a protease that induces the degradation of the LDL receptor (LDLR), which contributes to increased levels of LDL cholesterol and the progress of atherosclerosis. Given that macrophages are relevant components of the lipidic and inflammatory environment of atherosclerosis, we studied the effects of PCSK9 treatment on human macrophages. Our data show that human macrophages do not express PCSK9 but rapidly incorporate the circulating protein through the LDLR and also activate the pro-inflammatory TLR4 pathway. Both LDLR and TLR4 are internalized after incubation of macrophages with exogenous PCSK9. PCSK9 uptake increases the production of reactive oxygen species and reduces the expression of genes involved in lipid metabolism and cholesterol efflux, while enhancing the production of pro-inflammatory cytokines through a TLR4-dependent mechanism. Under these conditions, the viability of macrophages is compromised, leading to increased cell death. These results provide novel insights into the role of PCSK9 in the crosstalk of lipids and cholesterol metabolism through the LDLR and on the pro-inflammatory activation of macrophages through TLR4 signaling. These pathways are relevant in the outcome of atherosclerosis and highlight the relevance of PCSK9 as a therapeutic target for the treatment of cardiovascular diseases.

G-Protein-Coupled Receptor 91-Dependent Signalling Does Not Influence Vascular Inflammation and Atherosclerosis in Hyperlipidaemic Mice

“…In this context, another potential explanation for no major phenotype in our experiments with Gpr91−/− mice could be related to the stage of the disease, and whether GPR91 may affect the late stages of atherosclerosis warrants future investigation. Notably, PCSK9, which was overexpressed in our mice following an AAV injection, has been linked to both LDLR-dependent and -independent mechanisms that promote pro-inflammatory macrophage responses [63][64][65][66]. Although both groups in our study seemed to not exhibit exacerbated atherogenesis when compared to previous studies using rAAV-mPcsk9 or Ldlr−/− mice [44], whether PCSK9 influences the succinate/GPR91 axis warrants further investigation.…”

PCSK9 Confers Inflammatory Properties to Extracellular Vesicles Released by Vascular Smooth Muscle Cells

“…In line with these findings, the overexpression of gain-of-function mutant of PCSK9 (D377Y) in Ldlr −/− mice induced pro-inflammatory macrophages activation (e.g., IL-1β, TNF-α and MCP-1 were raised) [ 55 ]. Furthermore, the internalization of PCSK9 in macrophages increased the production of reactive oxygen species and that of pro-inflammatory cytokines through a TLR4-dependent mechanism [ 56 ].…”

Cholesterol‐autoxidation metabolites in host defense against infectious diseases

“…ROS increased by 7‐KC mediates the conversion of human monocyte‐derived anti‐inflammatory MUs (M2) to proinflammatory MUs (M1) via activating NF‐κB [47, 48]. The current studies are inconclusive regarding whether these metabolites distort human MU M1 differentiation or they only transiently induce proinflammatory properties [49]. Besides, 7‐KC causes the overproduction of ROS through mitochondrial damage, followed by the activation of MAPK‐NF‐κB signaling pathway and murine MU apoptosis [50].…”