Alternatively Spliced Tissue Factor Promotes Atherosclerosis by Increasing Foam Cell Formation via LOX-1 and SR-A1 up-regulation

Abstract

Introduction: Alternatively Spliced Tissue Factor (asTF) is an isoform of tissue factor that is expressed in human atherosclerotic plaques and promotes plaque progression in experimental atherosclerosis (Giannarelli C, Circulation 2014). Hypothesis: asTF is the isoform of tissue factor that most strongly promotes atherosclerosis by increasing foam cell formation. Methods: ApoE-/- mice (8 weeks old) were fed a Western-type diet starting 2 weeks before surgery. Immediately after transluminal wire injury of the left common carotid artery (LCCA), LCCA was incubated with lentivirus encoding asTF-GFP (asTF+;n=10), fl-TF-GFP (fl-TF+, n=10) or GFP (controls; n=5). Four weeks after, LCCA was removed and processed for the quantification of plaque size (H&E) and lipid accumulation (Oil-Red O). The effect of asTF on foam cell formation was tested in vitro by treating THP-1 derived macrophages with oxLDL (75μg/ml), with asTF (10nM) or vehicle. Total cholesterol (TC) and cholesterol esters (CE) were measured in lipid cell extracts. The mRNA levels of the oxLDL scavenger receptors LOX-1, SR-A1 and CD36 in macrophages and foam cells were assessed using qRT-PCR. Results: Plaque size and lipid accumulation were significantly greater in asTF+ vs. fl-TF+ and control mice (Fig.1, A-D). In vitro results showed that asTF promotes TC and CE accumulation in foam cells (Fig.1, E,F). Gene expression studies showed that asTF significantly increased the mRNA expression of scavenger receptors LOX-1, SR-A1 in both macrophages and foam cells (Fig.1, G-I). An increase in mRNA levels of CD36 (1.4-fold) was only detected in asTF-treated foam cells. Conclusions: In vivo results suggest that asTF promote plaque progression and lipid accumulation. In vitro studies imply that asTF promotes foam cell formation by increasing the expression of oxLDL scavenger receptors implicated in lipoprotein uptake by macrophages. These studies suggest a functional role for asTF in atherosclerotic plaque progression.