The metastatic tumor antigen 1-transglutaminase-2 pathway is involved in self-limitation of monosodium urate crystal-induced inflammation by upregulating TGF-β1

Abstract

IntroductionTransglutaminase 2 (TG2), a protein crosslinking enzyme with multiple biochemical functions, has been connected to various inflammatory processes. In this study, the involvement of TG2 in monosodium urate (MSU) crystal-induced inflammation was studied.MethodsImmunohistochemistry, reverse transcription-polymerase chain reaction (RT-PCR) were performed to detect TG2 expression in synovial fluid mononuclear cells (SFMCs) and synovial tissue from patients with gouty arthritis. MSU crystal-exposed RAW264.7 mouse macrophages were analyzed for interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), transforming growth factor β1 (TGF-β1) and TG2 expression by RT-PCR and enzyme-linked immunosorbent assay (ELISA). TG2 small interfering (si)-RNA-mediated silencing and overexpression in RAW264.7 cells were used to evaluate the involvement of TG2 in resolving MSU crystal-induced inflammation. The role of metastatic tumor antigen 1 (MTA1), a master chromatin modifier, was investigated by MTA1 si-RNA-mediated knockdown. In addition, the inflammatory responses were followed in wild type and TG2 null mice after being challenged with MSU crystals in an in vivo peritonitis model.ResultsTG2 expression was up-regulated in the synovium tissue and SFMCs from patients with gouty arthritis. The levels of MTA1, TG2, TGF-β1, IL-1β and TNF-α mRNAs were consistently increased in MSU crystal-stimulated RAW264.7 cells. si-MTA1 impaired the basal, as well as the MSU crystal-induced expression of TG2 and TGF-β1, but increased that of IL-1β and TNF-α. TG2 overexpression dramatically suppressed MSU crystal-induced IL-1β and TNF-α, but significantly enhanced the TGF-β1 production. Neutralizing TGF-β antibodies or inhibition of the crosslinking activity of TG2 attenuated these effects. On the contrary, loss of TG2 resulted in a reduced TGF-β, but in an increased IL-1β and TNF-α production in MSU crystal-stimulated RAW264.7 cells and mouse embryonic fibroblasts (MEFs). MSU crystal-stimulated IL-1β production was Janus kinase 2 (JAK2)-signaling dependent and TG2-induced TGF-β suppressed the activity of it. Finally, TG2-deficient mice exhibited hyper inflammatory responses after being challenged with MSU crystals in an in vivo peritonitis model.ConclusionsThese findings reveal an inherent regulatory role of the MTA1-TG2 pathway in the self-limitation of MSU crystal-induced inflammation via positively regulating the levels of active TGF-β1 in macrophages that opposes the MSU crystal-induced JAK2-dependent pro-inflammatory cytokine formation.Electronic supplementary materialThe online version of this article (doi:10.1186/s13075-015-0592-7) contains supplementary material, which is available to authorized users.

Transglutaminase 2 in human diseases

“…The N-terminus of LTBPs has been shown to be a substrate for TG2 which promotes their covalent incorporation into the extracellular matrix [ 26 ]. In addition, TG2 was found to contribute to the activation of macrophage-derived TGF-β [ 27 ], and to promote TGF-β1 transcription [ 28 ].…”

“…As described above, TG2 facilitates deposition and stabilization of ECM by facilitating TGF-β activation and crosslinking of ECM, respectively [ 25 – 28 ]. Still, there are controversial data available about the role of TG2 in plaque stability.…”

“…These phagocytes activate the NLRP3 inflammasome, resulting in the activation of caspase-1 and processing and secretion of interleukin-1β (IL-1β) which drive the inflammation. In addition to contributing to the clearance of dying neutrophils, it was also shown that the metastatic tumor antigen 1- TG2 pathway regulates the production of TGF-β1 in macrophages which opposes the MSU crystal-induced JAK2-dependent pro-inflammatory cytokine formation of IL-1β [ 149 ]. In line with these findings TG2 expression was found to be up-regulated in the synovium tissue and synovial fluid mononuclear cells from patients with gouty arthritis [ 149 ].…”

“…In addition to contributing to the clearance of dying neutrophils, it was also shown that the metastatic tumor antigen 1- TG2 pathway regulates the production of TGF-β1 in macrophages which opposes the MSU crystal-induced JAK2-dependent pro-inflammatory cytokine formation of IL-1β [ 149 ]. In line with these findings TG2 expression was found to be up-regulated in the synovium tissue and synovial fluid mononuclear cells from patients with gouty arthritis [ 149 ]. In addition, it was also shown that the ribosomal protein S19 (RP S19) polymer cross-linked at Lys122 and Gln137 by transglutaminases released from apoptotic neutrophils acts as a C5aR ligand during the resolution phase of acute inflammation.…”

How Factors Involved in the Resolution of Crystal-Induced Inflammation Target IL-1β

“…In particular, a higher transglutaminase (TG) 2 expression in crystal-exposed macrophages has been linked to TGFβ production (Yen et al, 2015) which, in turn, downregulates IL-1β release through the inhibition of the Janus kinase (JAK) 2 signaling. TG is indeed highly expressed in gout and has been shown to enhance phagocytosis of apoptotic leukocytes by macrophages limiting neutrophil accumulation and promoting resolution (Rose et al, 2006).…”