Syndecan-4 Knockout Leads to Reduced Extracellular Transglutaminase-2 and Protects against Tubulointerstitial Fibrosis

Abstract

Transglutaminase type 2 (TG2) is an extracellular matrix crosslinking enzyme with a pivotal role in kidney fibrosis. The interaction of TG2 with the heparan sulfate proteoglycan syndecan-4 (Sdc4) regulates the cell surface trafficking, localization, and activity of TG2 in vitro but remains unstudied in vivo. We tested the hypothesis that Sdc4 is required for cell surface targeting of TG2 and the development of kidney fibrosis in CKD. Wild-type and Sdc4-null mice were subjected to unilateral ureteric obstruction and aristolochic acid nephropathy (AAN) as experimental models of kidney fibrosis. Analysis of renal scarring by Masson trichrome staining, kidney hydroxyproline levels, and collagen immunofluorescence demonstrated progressive fibrosis associated with increases in extracellular TG2 and TG activity in the tubulointerstitium in both models. Knockout of Sdc-4 reduced these effects and prevented AAN-induced increases in total and active TGF-b1. In wild-type mice subjected to AAN, extracellular TG2 colocalized with Sdc4 in the tubular interstitium and basement membrane, where TG2 also colocalized with heparan sulfate chains. Heparitinase I, which selectively cleaves heparan sulfate, completely abolished extracellular TG2 in normal and diseased kidney sections. In conclusion, the lack of Sdc4 heparan sulfate chains in the kidneys of Sdc4-null mice abrogates injury-induced externalization of TG2, thereby preventing profibrotic crosslinking of extracellular matrix and recruitment of large latent TGF-b1. This finding suggests that targeting the TG2-Sdc4 interaction may provide a specific interventional strategy for the treatment of CKD.

Beyond Tissue Injury—Damage-Associated Molecular Patterns, Toll-Like Receptors, and Inflammasomes Also Drive Regeneration and Fibrosis

“…For example, the HS-proteoglycan, syndecan interacts via its HS chains with transglutaminase type 2, an enzyme that promotes ECM crosslinking in fibrosis. 135 Consistently, the lack of syndecan protects from renal fibrosis. 135 In addition, fibronectin can induce fibroblast differentiation via interaction with a 4 b 7 integrin.…”

“…135 Consistently, the lack of syndecan protects from renal fibrosis. 135 In addition, fibronectin can induce fibroblast differentiation via interaction with a 4 b 7 integrin. 136 As another avenue of DAMPs regulating fibrogenesis, decorin sequesters TGF-b in the ECM 137 or compete with TGF-b for receptor binding.…”

Proteomic Profiling Reveals the Transglutaminase-2 Externalization Pathway in Kidneys after Unilateral Ureteric Obstruction

“…in TG2 secretion rather than expression. 12 Protein class annotation terms were associated with ECM components, cytoskeletal organization, and cell adhesion, forming significant clusters of the UUO proteome (P#0.05) ( Figure 5A, Supplemental Table 4A). Among the proteins most significantly associated with TG2 in the UUO kidney (P#0.001 in Table 1), which were also intensified in the UUO proteome ( Figure 5C, right panel), there were periostin (a marker of progressive kidney injury in animal models of CKD), 23 myosin-1D, PROF1, CAZA-2, heat shock protein b1, FN, laminin, collagen (COCA1), and actin nucleation complex ARC1B.…”

“…4 Furthermore, TG2 enhances TGF-b activation, [6][7][8] the prototypical profibrotic cytokine in CKD. 9 Inhibition of extracellular TG2 activity 10,11 or knockout (KO) of the heparan sulfate (HS) proteoglycan syndecan-4 (SDC4), 12 which is responsible for TG2 extracellular trafficking through an undiscovered mechanism, 13 ameliorates kidney fibrosis in experimental models of CKD.…”

“…17 Furthermore, we know that the association of TG2 with the HS proteoglycan SDC4 favors the enzyme secretion in mouse dermal fibroblasts 13 and in vivo. 12 With the aim of unraveling the mechanism of TG2 secretion in CKD, in this study, we report a comprehensive and unbiased analysis of the membrane interactome of TG2 in kidneys subjected to unilateral ureteric obstruction (UUO). An enrichment of extracellular vesicle (EV) proteins was identified in TG2 membrane complexes.…”