Transglutaminase 2 interacts with syndecan-4 and CD44 at the surface of human macrophages to promote removal of apoptotic cells

Abstract

Tissue transglutaminase (TG2) is a multifunctional protein cross-linking enzyme that has been implicated in apoptotic cell clearance but is also important in many other cell functions including cell adhesion, migration and monocyte to macrophage differentiation. Cell surface-associated TG2 regulates cell adhesion and migration, via its association with receptors such as syndecan-4 and β1 and β3 integrins. Whilst defective apoptotic cell clearance has been described in TG2-deficient mice, the precise role of TG2 in apoptotic cell clearance remains ill-defined. Our work addresses the role of macrophage extracellular TG2 in apoptotic cell corpse clearance. Here we reveal TG2 expression and activity (cytosolic and cell surface) in human macrophages and demonstrate that inhibitors of protein crosslinking activity reduce macrophage clearance of dying cells. We show also that cell-impermeable TG2 inhibitors significantly inhibit the ability of macrophages to migrate and clear apoptotic cells through reduced macrophage recruitment to, and binding of, apoptotic cells. Association studies reveal TG2-syndecan-4 interaction through heparan sulphate side chains, and knockdown of syndecan-4 reduces cell surface TG2 activity and apoptotic cell clearance. Furthermore, inhibition of TG2 activity reduces crosslinking of CD44, reported to augment AC clearance. Thus our data define a role for TG2 activity at the surface of human macrophages in multiple stages of AC clearance and we propose that TG2, in association with heparan sulphates, may exert its effect on AC clearance via a mechanism involving the crosslinking of CD44.

Porphyromonas gingivalis gingipains cause defective macrophage migration towards apoptotic cells and inhibit phagocytosis of primary apoptotic neutrophils

“…22, 23 Our previous studies have demonstrated that the human monocyte cell line THP-1, when differentiated, provides an effective model for studying the role of macrophages (MØ) in AC clearance and to assess the role of cytokines and other inflammatory mediators released during this process. 5, 24, 25 To understand the impact of gingipains on the expression of important phagocyte receptors, we examined a panel of innate immune receptors on phagocytes before and after treatment with gingipains.…”

Transglutaminases: Expression in Kidney and Relation to Kidney Fibrosis

“…HS chains have also high affinity binding for TG2 Lortat-Jacob et al 2012) which is associated with the HS chains of syndecan-4 in a variety of cell types Lortat-Jacob et al 2012;Nadella et al 2015;Wang et al 2011Teesalu et al 2012). HS proteoglycans have a physiopathological role in the kidney and have also been suggested to modulate TG2 trafficking in the kidney ).…”

Insights into Transglutaminase 2 Function Gained from Genetically Modified Animal Models

“…Recent work indicates the removal of apoptotic cells may also be facilitated by TG2 interaction with syndecan-4 on the surface of human macrophages, whereby the transamidase activity of cell-surface TG2 crosslinks CD44, a phagocytic receptor on human macrophages, to promote apoptotic cell clearance (Nadella et al 2015).…”