Till Örebro universitet

Background and Aims: LDL-c is cleared from the circulation mainly by hepatic LDL-receptor mediated endocytosis. Defective LDL-c clearance and hence its elevation in circulation is one of the risk factors for myocardial infarction (MI). A soluble LDL-R (sLDL-R) exists in human plasma and exhibits strong correlation with circulating LDL-c and conditions that promote chronic inflammation. However, the mechanistic interplay between sLDL-R, inflammation and MI remains to be investigated.

Methods: In vitro studies using HepG2 cells treated with TNF-α, and a nested case-control study was conducted to investigate the relationship between plasma sLDL-R, TNF-α and risk of future MI.

Results: Stimulation of HepG2 cells with TNF-α induces release of sLDL-R with limited effect on surface expression of LDL-R. TNF-α induces gene expression of peptidases ADAM17 and MMP14 in HepG2 cells, and inhibition of ADAM17 and MMP-14 significantly reduces the TNF-α induced sLDL-R release. Although TNF-α treatment of HepG2 cells has limited effect on LDL-c endocytosis, HepG2 cells incubated with recombinant sLDL-R showed reduced LDL-c uptake in a dose-dependent manner. In a nested case-control study, baseline sLDL-R in plasma was positively correlated with plasma total cholesterol level. Further, a 2-fold increase in plasma sLDL-R was associated with 2.1x higher risk of future MI. Using mediation analyses, we determined that significant proportion of the association is mediated by elevation in plasma cholesterol level.

Conclusions: Our study suggests that sLDL-R is generated by TNF-α via membrane shedding. Further, an increase in sLDL-R could inhibit hepatic clearance of LDL-c increasing its half-life in the circulation and contributing to the pathogenesis of MI.