Deficiency of Plasminogen Receptor, Plg-RKT, Causes Defects in Plasminogen Binding and Inflammatory Macrophage Recruitment in vivo

Miles LA, Baik N, Lighvani S, Khaldoyanidi S, Varki NM, Bai H, Mueller BM, Parmer RJ. J Thromb Haemost. 2016 Oct 7. doi: 10.1111/jth.13532. [Epub ahead of print] PMID: 27714956

Abstract
Essentials Plg-RKT is a novel integral membrane plasminogen receptor. The functions of Plg-RKT in vivo are unknown. Plg-RKT is a key player in macrophage recruitment in the inflammatory response in vivo. Plg-RKT deficiency is not compatible with survival of the species.

SUMMARY:
Background Plg-RKT is a novel integral membrane plasminogen receptor that binds plasminogen via a C-terminal lysine exposed on the cell surface and promotes plasminogen activation on the cell surface by both tissue plasminogen activator and urokinase plasminogen activator. Objectives To evaluate the role of Plg-RKT in vivo we generated Plg-RKT-/- mice using a homologous recombination technique. Methods We characterized the effect of Plg-RKT deletion on reproduction, viability, health and spontaneous thrombosis and inflammation. Results Plg-RKT-/- mice were viable and fertile. Survival of Plg-RKT-/- mice and Plg-RKT+/+ littermates was not significantly different. However, quite strikingly, all pups of Plg-RKT-/- females died within 2 days of birth, consistent with a lactation defect in Plg-RKT-/- mothers. Additionally, there was a significant effect of Plg-RKT deficiency on the growth rates of female, but not male, mice. In experimental peritonitis studies, Plg-RKT-/- mice exhibited a marked defect in macrophage recruitment. As a contributing mechanism, the capacity of Plg-RKT-/- macrophages for plasminogen binding was markedly decreased. Conclusions These studies demonstrate that Plg-RKT is required for plasminogen binding and macrophage migration in vivo. In addition, Plg-RKT deficiency is not compatible with survival of the species, due to the death of all offspring of Plg-RKT-/- females. This new mouse model will be important for future studies aimed at delineating the role of cell surface plasminogen activation in challenge and disease models in vivo.