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(Circulation Research. 2009;105:713.)
© 2009 American Heart Association, Inc.

Integrative Physiology

Vascular-Directed Tissue Factor Pathway Inhibitor Overexpression Regulates Plasma Cholesterol and Reduces Atherosclerotic Plaque Development

Shuchong Pan, Thomas A. White, Tyra A. Witt, Anca Chiriac, Cheri S. Mueske, Robert D. Simari

From the Division of Cardiovascular Diseases and Internal Medicine, Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, Minn.

Correspondence to Robert D. Simari, MD, Mayo Clinic, 200 First Street SW, Rochester, MN 55905. E-mail simari.robert{at}mayo.edu

Rationale: Tissue factor pathway inhibitor (TFPI) is a potent regulator of the tissue factor pathway and is found in plasma in association with lipoproteins.

Objective: To determine the role of TFPI in the development of atherosclerosis, we bred mice which overexpress TFPI into the apolipoprotein E–deficient (apoE^–/–) background.

Methods and Results: On a high-fat diet, smooth muscle 22 (SM22)-TFPI/apoE^–/– mice were shown to have less aortic plaque burden compared to apoE^–/– mice. Unexpectedly, SM22-TFPI/apoE^–/– had lower plasma cholesterol levels compared to apoE^–/– mice. Furthermore, SM22-TFPI mice fed a high-fat diet had lower cholesterol levels than did wild-type mice. Because TFPI is associated with lipoproteins and its carboxyl terminus (TFPIct) has been shown to be a ligand for the very-low-density lipoprotein (VLDL) receptor, we hypothesized that TFPI overexpression may regulate lipoprotein distribution. We quantified VLDL binding and uptake in vitro in mouse aortic smooth muscle cells from SM22-TFPI and wild-type mice. Mouse aortic smooth muscle cells from SM22-TFPI mice demonstrated higher VLDL binding and internalization compared to those from wild-type mice. Because SM22-TFPI mice have increased circulating levels of TFPI antigen, we examined whether TFPIct may act to alter lipoprotein distribution. In vitro, TFPIct increased VLDL binding, uptake, and degradation in murine embryonic fibroblasts. Furthermore, this effect was blocked by heparinase treatment. In vivo, systemic administration of TFPIct reduced plasma cholesterol levels in apoE^–/– mice.

Conclusions: These studies suggest that overexpression of TFPI lowers plasma cholesterol through the interaction of its carboxyl terminus with lipoproteins and heparan sulfate proteoglycans.

Key Words: atherosclerosis • coagulation • murine models • tissue factor • lipoproteins