Background Alternatively Spliced Tissue Factor (asTF) is a novel isoform of full-length Tissue Factor (fl-TF) that exhibits angiogenic activity. Although asTF has been detected in human plaques, it is unknown whether its expression in atherosclerosis causes increased neovascularization and an advanced plaque phenotype. Methods and Results Carotid (n=10) and coronary specimens (n=8), from patients with stable or unstable angina, were classified as complicated or uncomplicated based on plaque morphology. Analysis of asTF expression and cell type –specific expression revealed a strong expression and co-localization of asTF with macrophages and neovessels within complicated, but not un-complicated, human plaques. Our results showed that the angiogenic activity of asTF is mediated via HIF-1α up-regulation through integrins and activation of phosphatidylinositol-kinase (PI3K)/Akt and mitogen-activated protein kinase (MAPK) pathways. HIF-1α up-regulation by asTF also was associated with increased VEGF expression in primary human endothelial cells, and VEGF-Trap significantly reduced the angiogenic effect of asTF in vivo. Furthermore, asTF gene transfer significantly increased neointima formation and neovascularization following carotid wire injury in ApoE−/− mice. Conclusions The results of this study provide strong evidence that asTF promotes neointima formation and angiogenesis in an experimental model of accelerated atherosclerosis. Herein, we demonstrate that the angiogenic effect of asTF is mediated via the activation of the HIF-1/VEGF signaling. This mechanism may be relevant to neovascularization, progression and associated complications of human atherosclerosis as suggested by the increased expression of asTF in complicated vs. uncomplicated human carotid and coronary plaques.

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Introduction: Alternatively Spliced Tissue Factor (asTF) is novel isoform of tissue factor with angiogenic activity mediated via HIF-1α signaling (Giannarelli, AHA 13). asTF is highly expressed in human complicated atherosclerotic plaques (Giannarelli, ACC 13); however, it is unknown whether asTF has a functional role in atherogenesis. Hypothesis: asTF promotes atherosclerotic plaque progression, inflammation and angiogenesis. Methods: ApoE-/- mice (8-weeks old; n=15) were fed a Western-type diet from 2 weeks before surgery continuing through the experiment. Immediately after transluminal wire injury of the left common carotid artery (LCCA), LCCA was incubated with lentivirus encoding asTF-GFP (asTF+ group; n=10) or GFP (asTF- control group; n=5). Four weeks after, blood and spleen were collected for flow cytometry analysis of neutrophils and monocytes. LCCA was removed and processed for H&E, Oil-Red O staining and immunostaining for macrophages (MOMA-2 and MAC-3), vascular smooth muscle cells (VSMC, α-actin), endothelial cells (CD31) and HIF-1α. Results: Neointimal thickness and plaque lipid accumulation were significantly greater in asTF+ vs asTF- mice (Fig 1, A-C). An increase in plaque macrophages, neovessels and HIF-1α was observed in asTF+ vs asTF- (Fig 1, D-F). Medial thickness and VSMC density were similar between groups. Increased circulating neutrophils and Ly6C high (classical/inflammatory) monocytes were observed in asTF+ vs asTF- mice (Fig 1, G,H). In contrast, circulating Ly6C low (patrolling) monocytes were significantly reduced (Fig 1, I). Similar findings were observed in the spleen (Fig 1, J-L). Conclusions: Our results demonstrate that asTF expressed within atherosclerotic lesions promotes plaque progression towards a more advanced phenotype and is associated with systemic proinflammatory status. These data makes asTF an attractive marker of plaque vulnerability and a potential therapeutic target for plaque stabilization.

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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.