Loss Of Nuclear Receptor Subfamily 4 Group A 1 (NR4A1) Results In Impaired Postthrombotic Vein Wall Remodeling By Promoting A Dysregulated Antifibrinolytic Phenotype In Monocytes

Objectives: Nuclear Receptor Subfamily 4 Group A1 (NR4A1) is a suppressor of monocyte/macrophage (MO/Mϕ) inflammatory output that antagonizes TGFβ-signaling. As NR4A1 inhibits epithelial-to-mesenchymal transition and tissue fibrosis, we sought to determine the role of NR4A1 in MO/Mϕ mediated post-thrombotic vein wall remodeling, which when exaggerated, can result in post-thrombotic syndrome (PTS). Methods: To assess the role of MO/Mϕ NR4A1 in post-thrombotic vein wall remodeling, we employed a knockout-rescue schema which featured whole mouse loss of function ( Nr4a1 -/- ) models and adoptive bone marrow derived MO/Mϕtransfer from Nr4a1 replete mice (WT-BMDMs). Stasis venous thrombosis was induced by the inferior vena cava (IVC) ligation. Characterization of vein wall remodeling/endothelialization was performed using Masson Trichrome staining and CD31 immunostaining, respectively. Quantitation of mRNA and protein levels of factors critical for MO/Mϕ-mediated vein wall remodeling was performed using qRT-PCR and ELISA, and matrix metalloproteinase (MMP) activity was measured using zymography. Results: We observed that Nr4a1 -/- mice exhibited impaired vein wall remodeling after 8- and 14-days post IVC ligation as indicated by thicker vein wall measurements and impaired luminal endothelialization. Adoptive transfer of WT-BMDMs into Nr4a1 -/- mice rescued this phenotype (Fig. 1A-C). Nr4a1 -/- mice did not exhibit any differences in thrombus burden (data not shown). Finally, although we observed induced mRNA levels of Mmp2 and Mmp9 in the vein walls of Nr4a1 -/- mice that underwent adoptive transfer, we noted suppressed MMP2 enzyme activity despite no compensatory changes in MMP9 activity or TGFβ/IL6 levels (Fig. 1D, data not shown). Conclusions: NR4A1 loss results in impaired post-thrombotic vein wall remodeling and agonism of NR4A1 may be a potential therapeutic strategy to combat PTS.