Abstract 17503: Role of Blood Coagulation Factor V Expressed by Vascular Smooth Muscle Cells in vascular Remodeling
Introduction - Blood coagulation factor V (fV) is synthesized in liver and present in blood, where it plays a central role in blood coagulation. FV is also expressed by cultured vascular smooth muscle cells (VSMC), and fV antigen has been detected in atherosclerotic plaque, suggesting that extrahepatic expression of fV plays an important role in vascular wall function and disease. However, very little is known about the functional impact of fV expression by VSMC, and it is unknown if fV is expressed locally within the arterial wall in vivo.
Methods - We generated transgenic (Tg) mice with liver-specific fV transgene expression and crossed them to mice carrying a null fV mutation (fV+/- mice) to generate Tg rescue mice lacking native expression of fV (Tg+ fV-/-). We isolated, cultured, and characterized aortic VSMC from Tg+ fV-/- mice and compared results to control Tg+ fV+/+ or wild-type (C57BL/6J) mouse VSMC. We studied the effect of fV expression on VSMC proliferation in vitro, and used reverse transcriptase (RT) PCR to assess fV expression in murine aorta.
Results VSMC from Tg+ fV+/+ mice proliferated faster than Tg+ fV-/- VSMC, at time points ranging from 24-96 hrs (Absorbance values, as noted with MTT assay, at all time points were statistically significant; at 48 hrs, Tg+ fV+/+ vs Tg+ fV-/-, n = 4; P <0.001). Cell cycle analysis with flowcytometry suggested that there were fewer cells in active division phases at different time points in the Tg+ fV-/- VSMC. The difference in VSMC proliferation rates between groups persisted in the presence of hirudin, a potent and highly specific thrombin inhibitor (P < 0.05). RT-PCR demonstrated that fV was expressed in both WT mouse cultured VSMC and aortic tissue in vivo.
Conclusions - Expression of fV by VSMC promotes cell proliferation. This effect appears to be partly mediated not only by downstream thrombin, which activates VSMC, but also by a thrombin independent mechanism. fV is expressed in vivo in vascular tissue. These results offer important insights into the biological effects of fV and suggest that it has vascular functions distinct from its role in blood coagulation.
- © 2011 by American Heart Association, Inc.