The fifth epidermal growth factor like region of thrombomodulin alleviates LPS-induced sepsis through interacting with GPR15

Abstract

Thrombomodulin (TM) exerts cytoprotection via the fifth region of epidermal growth factor (EGF)-like domain of TM (TME5) by interacting with G-protein coupled receptor 15 (GPR15) expressed on cell surface of vascular endothelial cells. TM is also implied to mediate anti-inflammatory functions by unknown mechanism. By applying a lipopolysaccharide (LPS)-induced murine sepsis model, we assessed the role of TME5 in septic inflammation and coagulation. We found that TME5 treatment protected mice in association with ameliorating inflammation and coagulopathy in LPS-induced sepsis. Further study confirmed that TME5 bound GPR15 in vitro. Knock out of GPR15 abolished protective role of TME5 in sepsis model. GPR15 mediated anti-inflammatory function of TME5 through suppression of phosphorylation of IκBα, nuclear translocation of NF-κB and release of pro-inflammatory cytokines in macrophages (Macs). Knock out of GPR15 resulted in dysregulated immune response of Macs, characterised by excessive expression of pro-inflammatory genes and failing to limit immune response. This study indicates that TME5 exerts anti-inflammatory function through inhibition of NF-κB in a GPR15-dependent manner. The use of TME5 may be a potential therapeutic option for treatment of sepsis.

Differential phosphorylation signals control endocytosis of GPR15

“…GPR15 was also found to mediate homing of dendritic epidermal T-cells to skin in fetal mice, possibly contributing to the establishment of skin barrier function ( Lahl et al , 2014 ). In addition, a more recent study revealed an anti-inflammatory function of GPR15 in vascular endothelial cells ( Pan et al , 2017 ). Collectively these findings highlight GPR15 as a novel therapeutic target of immune disorders and infectious diseases.…”

Cytoprotective and pro-angiogenic functions of thrombomodulin are preserved in the C loop of the fifth epidermal growth factor-like domain

“… 37 Of note, the use of TME5 significantly alleviated graft- versus -host disease (GvHD) in a murine model. 37 TME5 also rescues mice from LPS-induced sepsis, 26 further confirming the anti-inflammatory function of TME5C.…”

“…Our previous study found that the cytoprotective effects of TM were preserved in TME5. 24 , 26 TME5 consists of three loops: A, B, and C ( Figure 1A ). The C-loop in the C-terminal subdomain is formed by a stretch of amino acids between the fifth and sixth cysteine residues, and its amino acid sequence is longer than those of the other two loops.…”

“… 24 Furthermore, we found that G protein-coupled receptor 15 (GPR15) expressed on vascular ECs is indispensable for the cytoprotective functions of TME5. 25 , 26 …”

Peripheral Tissue Chemokines: Homeostatic Control of Immune Surveillance T Cells

“…GPR15 is also involved in the intestinal immune homeostasis in mice (but not humans) via its regulation of the local Treg cell compartment [65,66]. The two identified ligands, a thrombomodulin-derived protein fragment [67] and C10ORF99-encoded protein GPR15L [68], do not mediate 10 chemotaxis of GPR15 + cells, suggesting that a migration-unrelated mechanism underlies the GPR15 controlled processes in tissue immune homeostasis.…”