Endothelial cell protein C receptor‐mediated redistribution and tissue‐level accumulation of factor VIIa

Abstract

BackgroundRecent studies show that activated factor VII (FVIIa) binds to the endothelial cell protein C receptor (EPCR) on the vascular endothelium; however, the importance of this interaction in hemostasis or pathophysiology is unknown.ObjectiveThe aim of the present study was to investigate the role of the FVIIa interaction with EPCR on the endothelium in mediating FVIIa transport from the circulation to extravascular tissues.MethodsWild-type, EPCR-deficient or ECPR-over-expressing mice were injected with human recombinant (r)FVIIa (120 μg kg−1 body weight) via the tail vein. At varying time intervals after rFVIIa administration, blood and various tissues were collected to measure FVIIa antigen and activity levels. Tissue sections were analyzed by immunohistochemistry for FVIIa and EPCR.ResultsThe data reveal that, after intravenous (i.v.) injection, rFVIIa rapidly disappears from the blood and associates with the endothelium in an EPCR-dependent manner. Immunohistochemical analyses revealed that the association of FVIIa with the endothelium was maximal at 30 min and thereafter progressively declined. The FVIIa association with the endothelium was undetectable at time points exceeding 24 h post-FVIIa administration. The levels of rFVIIa accumulated in tissue correlate with expression levels of EPCR in mice and FVIIa associated with tissues remained functionally active for periods of at least 7 days.ConclusionsThe observation that an EPCR-dependent association of FVIIa with the endothelium is most pronounced soon after rFVIIa administration and subsequently declines temporally, combined with the retention of functionally active FVIIa in tissue homogenates for extended periods, indicates that FVIIa binding to EPCR on the endothelium facilitates the transport of FVIIa from circulation to extravascular tissues where TF resides.

Sustained correction of FVII deficiency in dogs using AAV-mediated expression of zymogen FVII

“…27 Notably, the interaction of the endothelial protein C receptor (EPCR) with human FVII in mice may be involved in the FVII biodistribution after bolus infusion. 28 It is unclear if human FVII can interact with endogenous EPCR in animals other than mice, such as dogs or nonhuman primates, or if endogenous EPCR can modulate FVII levels when the latter is expressed continuously via AAV. Nevertheless, and in contrast to previous studies using a human FVII transgene in nonhuman primates, 10 the use of cFVII in the FVII-G96E dogs ensures that the endogenous EPCR, tissue factor, or other interaction with AAV-expressed FVII retains its species specificity.…”

The endothelial protein C receptor enhances hemostasis of FVIIa administration in hemophilic mice in vivo

“…44 Additionally, an EPCR role in the FVII/FVIIa tissue distribution and, possibly, its catabolism has also been suggested. 18 Such EPCR-dependent processes are not expected to be present in the mouse. Whether this is an evolutionary adaptation is unclear, given the lack of data on the FVII/FVIIa-EPCR interaction in other species, and more experiments need to be conducted.…”

“…Notably, in a study of rhFVIIa secondary prophylaxis in hemophilic patients with inhibitors, patients receiving daily rhFVIIa infusions for 3 months, followed by a 3-month postprophylaxis period, showed clinical benefits even in the postprophylaxis period. 46 Previous mouse studies suggested that rhFVIIa is transported via an EPCR-dependent mechanism to the extravascular space, 18 where it can persist for extended periods of time in complex with TF, 47 potentially preventing minor bleeds before they escalate. Such mechanism may explain the prolonged clinical benefits of rhFVIIa prophylaxis.…”

“…Mouse models of EPCR overexpression or deficiency have suggested that EPCR is involved in the biodistribution and tissue persistence of administered rhFVIIa in vivo. 18 Previous studies on the role of EPCR in rhFVIIa-dependent FXa and thrombin generation 17,[19][20][21] have not clarified whether EPCR contributes to the mechanism of action of high-dose rhFVIIa administration in hemophilia. An appropriate model system to address this in vivo would require normal interactions between rhFVIIa and TF, as well as EPCR.…”

Endothelial cell protein C receptor: a multiliganded and multifunctional receptor

“…EPCR-mediated endocytosis and recycling facilitate the transport of its cargo across the endothelial cell barrier and thus influence the catabolism and bioavailability of its ligands. 20,21 EPCR endocytosis and the subsequent intracellular trafficking are regulated by specific Rab GTPases in a temporospatial-dependent manner. 22 …”