Evolutionary conservation of the tissue factor disulfide bonds and identification of a possible oxidoreductase binding motif

Plasma tissue factor coagulation activity in post-acute myocardial infarction patients

INTRODUCTION

Coagulation is involved in fibroproliferative responses following acute myocardial infarction (AMI). Left ventricular (LV) remodeling following AMI is closely associated with progression to heart failure. This study aims to assess the association between plasma tissue factor activity and LV remodeling in post-AMI patients.

METHODS

We studied 228 patients with AMI and 57 healthy subjects. Patients with AMI were categorized into two age- and sex-matched groups: patients with adverse LV remodeling or reverse LV remodeling, defined by an increase or decrease, respectively, in LV end systolic volume by ≥15% over 6 months. TF activity was measured in plasma collected at baseline (within 72 hours of revascularization), 1 month and 6 months post-AMI. Multiple level longitudinal data analysis with structural equation (ML-SEM) model was used to assess the impact of various clinical variables on TF activity in post-AMI.

RESULTS

Plasma TF activity in post-AMI patients at baseline (29.05 ± 10.75 pM) was similar to that in healthy subjects but fell at 1 month (21.78 ± 8.23, p<0.001) with partial recovery by 6 months (25.84 ± 8.80, p<0.001) after AMI. Plasma TF activity at 6 month post-AMI was better restored in patients with reverse LV remodeling than those with adverse LV remodeling (27.35 ± 7.14 vs 24.34 ± 9.99; p=0.009) independent of gender, age and relevant cardiovascular risk factors.

CONCLUSIONS

Plasma TF activity decreased after AMI but was better restored at 6 months in patients with reverse LV remodeling. The clinical significance of changes in post-AMI plasma TF activity needs further investigation.

Murine tissue factor disulfide mutation causes a bleeding phenotype with sex specific organ pathology and lethality

Tissue factor is highly expressed in sub-endothelial tissue. The extracellular allosteric disulfide bond Cys186-Cys209 of human tissue factor shows high evolutionary conservation and in vitro evidence suggests that it significantly contributes to tissue factor procoagulant activity. To investigate the role of this allosteric disulfide bond in vivo, we generated a C213G mutant tissue factor mouse by replacing Cys213 of the corresponding disulfide Cys190-Cys213 in murine tissue factor. A bleeding phenotype was prominent in homozygous C213G tissue factor mice. Pre-natal lethality of 1/3rd of homozygous offspring was observed between E9.5 and E14.5 associated with placental hemorrhages. After birth, homozygous mice suffered from bleedings in different organs and reduced survival. Homozygous C213G tissue factor male mice showed higher incidence of lung bleedings and lower survival rates than females. In both sexes, C213G mutation evoked a reduced protein expression (about 10-fold) and severely reduced pro-coagulant activity (about 1000-fold). Protein glycosylation was impaired and cell membrane exposure decreased in macrophages in vivo. Single housing of homozygous C213G tissue factor males reduced the occurrence of severe bleeding and significantly improved survival, suggesting that inter-male aggressiveness might significantly account for the sex differences. These experiments show that the tissue factor allosteric disulfide bond is of crucial importance for normal in vivo expression, post-translational processing and activity of murine tissue factor. Although C213G tissue factor mice do not display the severe embryonic lethality of tissue factor knock-out mice, their postnatal bleeding phenotype emphasizes the importance of fully functional tissue factor for hemostasis.

Murine tissue factor coagulant activity is critically dependent on the presence of an intact allosteric disulfide

Tissue factor activation (decryption) has been proposed to be dependent on the cysteine 186-cysteine 209 allosteric disulfide in the tissue factor extracellular domain. Tissue factor procoagulant activity is under the control of protein disulfide isomerase-dependent modulation and nitrosylation of this disulfide. Human tissue factor disulfide mutants have been proposed as a model for encrypted tissue factor, but poor expression of these mutants hampers research into tissue factor decryption. We, therefore, investigated whether mouse tissue factor cysteine 186-cysteine 209 disulfide bond mutants form a better suited model for tissue factor decryption. Stable mouse wild-type tissue factor, tissue factor(C190A), tissue factor(C213A) and tissue factor(C190/213A) disulfide mutant-expressing baby hamster kidney cells with equal levels of surface tissue factor were established. Tissue factor coagulant activity on these cells was determined using an active factor Xa-dependent chromogenic assay. The effect of nitrosylation on tissue factor function was also assessed. A tissue factor(C190/213A) mutant exerted marginal procoagulant activity, also after addition of supraphysiological concentration of factor VIIa. Tissue factor(C190A) and tissue factor(C213A) mutants showed reduced activity and the presence of tissue factor dimers. Nitrosylation of wild-type tissue factor cells decreased procoagulant function, an effect which was reversed by incubation with bacitracin, an inhibitor of protein disulfide isomerase, suggesting that this isomerase promotes de-nitrosylation of tissue factor. Mouse tissue factor procoagulant function is dependent on the Cys190-Cys213 disulfide bond and is modulated by nitrosylation. The murine model of disulfide-mutated tissue factor is more suitable for studying tissue factor decryption than are human tissue factor mutants.