TNFα-stimulated gene-6 (TSG6) activates macrophage phenotype transition to prevent inflammatory lung injury

Abstract

TNFα-stimulated gene-6 (TSG6), a 30-kDa protein generated by activated macrophages, modulates inflammation; however, its mechanism of action and role in the activation of macrophages are not fully understood. Here we observed markedly augmented LPS-induced inflammatory lung injury and mortality in TSG6 −/− mice compared with WT (TSG6 +/+ ) mice. Treatment of mice with intratracheal instillation of TSG6 prevented LPS-induced lung injury and neutrophil sequestration, and increased survival in mice. We found that TSG6 inhibited the association of TLR4 with MyD88, thereby suppressing NF-κB activation. TSG6 also prevented the expression of proinflammatory proteins (iNOS, IL-6, TNFα, IL-1β, and CXCL1) while increasing the expression of antiinflammatory proteins (CD206, Chi3l3, IL-4, and IL-10) in macrophages. This shift was associated with suppressed activation of proinflammatory transcription factors STAT1 and STAT3. In addition, we observed that LPS itself up-regulated the expression of TSG6 in TSG6 +/+ mice, suggesting an autocrine role for TSG6 in transitioning macrophages. Thus, TSG6 functions by converting macrophages from a proinflammatory to an anti-inflammatory phenotype secondary to suppression of TLR4/NF-κB signaling and STAT1 and STAT3 activation. However, there appears to be little constitutive expression of TSG6 (3). TSG6 is synthesized in response to proinflammatory mediators, including lipopolysaccharide (LPS), TNFα, and IL-1β (3-5). TSG6 is composed of an HA-binding LINK domain and a CUB (complement protein subcomponents C1r/C1s, urchin embryonic growth factor, and bone morphogenetic protein) domain (3, 4) To date, only the HA-binding protein CD44 has been shown to function as a TSG6 receptor (6).TSG6 has a potent but poorly understood function in suppressing inflammation through inhibition of neutrophil migration and production of proinflammatory cytokines (7,8). This effect of TSG6 has been demonstrated in several models. TSG6 was shown to prevent inflammation and tissue injury in rodent models of arthritis (9), myocardial infarction (10), corneal injury (11), and peritonitis (12). Both IL-1β and TNFα induced the synthesis of TSG6 in MSCs, monocytes/macrophages, and fibroblasts (2, 4, 5). Administration of human MSCs in mice prevented endotoxin (LPS)-induced acute lung injury (ALI), and, importantly, this effect was abrogated using cells pretreated with TSG6-siRNA to suppress TSG6 expression (13). TSG6 also delayed the onset of autoimmune diabetes by suppressing the activation of T cells and antigen-presenting cells (14), further supporting its role in dampening the adaptive immune response.In the present study, we addressed the role of TSG6 in ALI, an acute inflammatory disease that injures the lung's vascular barrier, resulting in severe protein-rich pulmonary edema and hypoxemia, associated with ∼50% mortality (15). There is a profound release of proinflammatory cytotoxic mediators from activated alveolar macrophages and other inflammatory cells sequestered in lungs (15). Macrophages in ALI are a...

Reactive microglia and astrocytes in neonatal intraventricular hemorrhage model are blocked by mesenchymal stem cells

“…MSC‐derived microvesicles show strong and acute immune modulatory activity, reducing MAPK and STAT activity within hours (Jaimes, Naaldijk, Wenk, Leovsky, & Emmrich, ). In other studies, TNFα‐stimulated gene‐6 (TSG6), identified as an active component of the MSC secretome, shows an anti‐inflammatory effect in LPS‐stimulated microglia and reduces phosphorylation of STAT1 (Liu et al, ; Mittal et al, ). Similarly, it is possible that the effect of MSCs we observed in this study can be mediated by microvesicles.…”

TAK1 Regulates Endothelial Integrity Through Stabilization of Junctions via GSK3β and FoxO1

“…At 72 h after transfection, cells were used for following experiments. Bone marrow-derived macrophages (BMDMs) from mice were generated by culture of bone marrow cells as described (61 Immunostaining: ECs grown on glass coverslips were washed with HBSS and fixed with 3% paraformaldehyde for 20 minutes. Cells were permeabilized with 0.1% Triton-X-100 for 15 min at 4°C.…”

Cutaneous Wounds in Mice Lacking Tumor Necrosis Factor-stimulated Gene-6 Exhibit Delayed Closure and an Abnormal Inflammatory Response

“…Additionally, TSG-6 protein is able to inhibit neutrophil migration via the TSG-6 Link domain (Cao et al 2004;Getting et al 2002) which interacts with neutrophil chemokines such as human CXCL8, and with glycosaminoglycans (GAGs) on endothelial cell surfaces (Dyer et al 2016;Dyer et al 2014). Furthermore, TSG-6, as well as HC-HA complexes, have been shown to promote the polarization of macrophages to an alternatively activated/ anti-inflammatory M2 phenotype instead of the classically activated/ proinflammatory M1 phenotype (Ferrer et al 2017;He et al 2013;Mittal et al 2016). Given the ability of TSG-6 to regulate the behavior of neutrophils and macrophages, we postulated that TSG-6 may be important in cutaneous wound healing.…”

“…One of these enzymes is Tumor necrosis factor (TNF)-stimulated gene-6 (TSG-6) protein, also known as TNF-induced protein 6 (Tnfip6 or Tnfaip6). TSG-6, first identified by Lee et al (Lee et al 1990) in human foreskin fibroblasts stimulated with the pro-inflammatory cytokine TNFa, encodes a secretory glycoprotein with a molecular weight of ~30-35 kDa (Milner and Day 2003;Mittal et al 2016;Wisniewski et al 1993).…”