A combined deficiency of tissue factor and PAR-4 is associated with fatal pulmonary hemorrhage in mice.

INTRODUCTION: Mice with a complete absence of tissue factor (TF) die during embryonic development whereas mice with low levels of TF (Low-TF mice) survive to adulthood. Low-TF mice exhibit spontaneous hemorrhage in various organs, including the lung. In contrast, mice can survive without protease-activated receptor (PAR)-4, which is the major thrombin receptor on mouse platelets. We determined the effect of combining a deficiency PAR-4 (primary hemostasis) with a deficiency in TF (secondary hemostasis) on embryonic development and survival of adult mice.

MATERIALS AND METHODS: Low-TF mice (mTF(-/-), hTF(+/+)) were crossed with PAR-4(-/-) mice to generate heterozygous mice (mTF(+/-), hTF(+/-), PAR-4(+/-)). These mice were intercrossed to generate Low-TF mice lacking PAR-4. Mice surviving to wean were genotyped and survival was monitored for 6months.

RESULTS: We observed the expected number of Low-TF,PAR-4(-/-) mice at wean indicating survival in utero and after birth. However, an absence of PAR-4 was associated with premature death of all Low-TF,PAR-4(-/-) mice in the 6month observational period. This compares with 40% death of the Low-TF,PAR-4(+/+) mice (p=0.003). Low-TF,PAR-4(+/-) mice had an intermediate phenotype with 55% of the mice dying within 6months. The primary cause of mortality of Low-TF,PAR-4(-/-) mice was pulmonary hemorrhage.

CONCLUSIONS: Low-TF,PAR-4(-/-) mice survive into adulthood, but combining a deficiency of primary hemostasis (PAR-4 deficiency) with secondary hemostasis (low levels of TF) leads to premature death primarily due to pulmonary hemorrhage.