Lack of Protein S in mice causes embryonic lethal coagulopathy and vascular dysgenesis

Abstract

Protein S (ProS) is a blood anticoagulant encoded by the Pros1 gene, and ProS deficiencies are associated with venous thrombosis, stroke, and autoimmunity. These associations notwithstanding, the relative risk that reduced ProS expression confers in different disease settings has been difficult to assess without an animal model. We have now described a mouse model of ProS deficiency and shown that all Pros1 -/-mice die in utero, from a fulminant coagulopathy and associated hemorrhages. Although ProS is known to act as a cofactor for activated Protein C (aPC), plasma from Pros1 +/-heterozygous mice exhibited accelerated thrombin generation independent of aPC, and Pros1 mutants displayed defects in vessel development and function not seen in mice lacking protein C. Similar vascular defects appeared in mice in which Pros1 was conditionally deleted in vascular smooth muscle cells. Mutants in which Pros1 was deleted specifically in hepatocytes, which are thought to be the major source of ProS in the blood, were viable as adults and displayed less-severe coagulopathy without vascular dysgenesis. Finally, analysis of mutants in which Pros1 was deleted in endothelial cells indicated that these cells make a substantial contribution to circulating ProS. These results demonstrate that ProS is a pleiotropic anticoagulant with aPC-independent activities and highlight new roles for ProS in vascular development and homeostasis.

The vitamin K–dependent anticoagulant factor, protein S, inhibits multiple VEGF-A–induced angiogenesis events in a Mer- and SHP2-dependent manner

“…3 The importance of the anticoagulant activity of ProS is revealed by the lethal thrombotic complications suffered by homozygous PROS1-deficient mice. 4 Less severe ProS deficiencies, resulting from heterozygous mutations or polymorphisms, are associated with risks for venous and arterial thrombosis, vascular calcification, and other thrombotic complications. 5 Analysis of either mouse embryos from PROS1 gene mutants or from mice in which PROS1 gene was conditionally deleted in vascular smooth muscle cells revealed defects in vessel development and function not seen in mice lacking protein C (PC), implying thereby the existence of PC-independent major regulatory functions of ProS in vascular development and homeostasis.…”

“…5 Analysis of either mouse embryos from PROS1 gene mutants or from mice in which PROS1 gene was conditionally deleted in vascular smooth muscle cells revealed defects in vessel development and function not seen in mice lacking protein C (PC), implying thereby the existence of PC-independent major regulatory functions of ProS in vascular development and homeostasis. 4 ProS circulates in human plasma at a concentration of ϳ 25 g/mL in free form (40%) and in complex (60%) with C4b-binding protein (C4BP). 1 In humans, most of plasma ProS is thought to be synthesized in the liver by hepatocytes.…”

“…20 Recently, using tissue-specific conditional PROS1 knockout mice, it was demonstrated that extrahepatic ProS represents ϳ 45% of normal circulating ProS and that much of this residual ProS is produced by ECs. 4 ECs play key roles in many processes, among which angiogenesis is a major one. 21,22 Sprouting angiogenesis follows the remodeling and maturation of the primitive vascular plexus during development and plays a major role in adult life as part of both physiologic and pathologic processes.…”

“…23 On this basis, VEGF-A signaling inhibitors or VEGF-A neutralizing antibodies are used for treating pathologic angiogenesis. [21][22][23] Although the endothelium expresses TAM receptors and is a major source of ProS, 4 the pathophysiologic relevance of ProS interactions with ECs and in particularly its possible effects on angiogenesis were not as yet investigated. In the present report, we combined in vivo and in vitro approaches to investigate the role of human ProS in angiogenesis.…”

GAS6 is a key homeostatic immunological regulator of host–commensal interactions in the oral mucosa

“…Despite the high structural homology between GAS6 and PROS1, both ligands have distinct affinities to the TAM receptors and are also differentially expressed in various cell types (9). Furthermore, whereas the functions of GAS6 seem to be limited to those caused by activation of the TAM receptors, PROS1 has TAM receptor-dependent and independent activities (8,(10)(11)(12). In line with their discrete properties, GAS6 and PROS1 were shown to control distinct immune mechanisms in vitro and in vivo (7).…”