Crucial Involvement of IL-6 in Thrombus Resolution in Mice via Macrophage Recruitment and the Induction of Proteolytic Enzymes

Abstract

After the ligation of the inferior vena cava (IVC) of wild-type (WT) mice, venous thrombi formed and grew progressively until 5 days and resolved thereafter. Concomitantly, intrathrombotic gene expression of Il6 was enhanced later than 5 days after IVC ligation. IL-6 protein expression was detected mainly in F4/80-positive macrophages in thrombus. When Il6-deficient (Il6 −/−) mice were treated in the same manner, thrombus mass was significantly larger than in WT mice. Moreover, the recovery of thrombosed IVC blood flow was markedly delayed in Il6 −/− compared with WT mice. F4/80-positive macrophages in thrombus expressed proteolytic enzymes such as matrix metalloproteinase (Mmp) 2, Mmp9, and urokinase-type plasminogen activator (Plau); and their mRNA expression was significantly reduced in Il6 −/− mice. Consistently, the administration of anti-IL-6 antibody delayed the thrombus resolution in WT mice, whereas IL-6 administration accelerated thrombus resolution in WT and Il6 −/− mice. Moreover, IL-6 in vitro enhanced Mmp2, Mmp9, and Plau mRNA expression in WT-derived peritoneal macrophages in a dose-dependent manner; and the enhancement was abrogated by a specific Stat3 inhibitor, Stattic. Thus, IL-6/Stat3 signaling pathway can promote thrombus resolution by enhancing Mmp2, Mmp9, and Plau expression in macrophages.

Tocilizumab and Thromboembolism in COVID-19: A Retrospective Hospital-based Cohort Analysis

“…On the contrary, Nosaka et al has recently published a research article in Feb 2020, highlighting the role of IL-6 in thrombus resolution, in which suppression of IL-6 may in fact result in the growth of the thrombus as demonstrated in the rat model [17]. Moreover, IL-6 antagonist has been associated with a reduced level of Factor XIII, chimerin and plasminogen activator inhibitor [18].…”

“…They were 18 males and 6 females. As for ethnicity;17 were Hispanic (74%), 2 African American (9%), and 4 had other ethnicities (17%). Of the 24 patients, 15 patients (65%) survived and 9 patients (35%) expired.…”

COVID-19: the role of excessive cytokine release and potential ACE2 down-regulation in promoting hypercoagulable state associated with severe illness

“…Despite plenty of evidence showing the contribution of IL-6 to increased blood coagulability and thrombus formation, IL-6 could also be necessary for venous thrombus resolution by recruiting macrophages and enhancing expressions of Mmp2, Mmp9, and urokinase-type plasminogen activator (Plau) through IL-6/STAT3 signaling in macrophages [56]. However, the exact role IL-6 plays in thrombus resolution can be controversial because of the in vitro evidence showing up-regulated PAI-1 expression in adipose tissue by IL-6 [57].…”

Resolution of Deep Venous Thrombosis: Proposed Immune Paradigms

“…When collagenolysis is impaired, so is all of DVT resolution, resulting in fewer experimental mice reaching stage 3 when most collagen deposition occurs. In contrast, thrombus resolution is promoted by IL6 signaling, which augments MMP2, MMP9, and uPA in Mo/MΦ cells [125].…”

“…This may explain the lack of a significant difference in thrombus size at 2 days between control and IL-6 -/mice, [21] as both policing and reparative Mo/MΦ function is somewhat impaired. IL-6 -/mice showed impaired resolution at later time points as measured by weaker blood flow and increased 5-day thrombus size [125]. Mice treated with anti-IL6 antibodies have impaired monocyte influx and improved DVT resolution, an effect that was tied to reduced chemokine expression, particularly of MCP-1 [126].…”