Novel interactions of transglutaminase-2 with heparan sulphate proteoglycans: reflection on physiological implications

This mini-review brings together information from publications and recent conference proceedings that have shed light on the biological interaction between transglutaminase-2 and heparan sulphate proteoglycans. We subsequently draw hypothesis of possible implications in the wound healing process. There is a substantial overlap in the action of transglutaminase-2 and the heparan sulphate proteoglycan syndecan-4 in normal and abnormal wound repair. Our latest findings have identified syndecan-4 as a possible binding and signalling partner of fibronectinbound TG2 and support the idea that transglutaminase-2 and syndecan-4 acts in synergy

Knockdown of vimentin reduces mesenchymal phenotype of cholangiocytes in the Mdr2−/− mouse model of primary sclerosing cholangitis (PSC)

Background: Cholangiocytes are the target cells of cholangiopathies including primary sclerosing cholangitis (PSC). Vimentin is an intermediate filament protein that has been found in various types of mesenchymal cells. The aim of this study is to evaluate the role of vimentin in the progression of biliary damage/liver fibrosis and whether there is a mesenchymal phenotype of cholangiocytes in the Mdr2(-/-) model of PSC.Methods: In vivo studies were performed in 12 wk. Mdr2(-/-) male mice with or without vimentin Vivo-Morpholino treatment and their corresponding control groups. Liver specimens from human PSC patients, human intrahepatic biliary epithelial cells (HIBEpiC) and human hepatic stellate cell lines (HHSteCs) were used to measure changes in epithelial-to-mesenchymal transition (EMT).Findings: There was increased mesenchymal phenotype of cholangiocytes inMdr2(-/-) mice, which was reduced by treatment of vimentin Vivo-Morpholino. Concomitant with reduced vimentin expression, there was decreased liver damage, ductular reaction, biliary senescence, liver fibrosis and TGF-beta 1 secretion in Mdr2(-/-) mice treated with vimentin Vivo-Morpholino. Human PSC patients and derived cell lines had increased expression of vimentin and other mesenchymal markers compared to healthy controls and HIBEpiC, respectively. In vitro silencing of vimentin in HIBEpiC suppressed TGF-beta 1-induced EMT and fibrotic reaction. HHSteCs had decreased fibrotic reaction and increased cellular senescence after stimulation with cholangiocyte supernatant with reduced vimentin levels.Interpretation: Our study demonstrated that knockdown of vimentin reduces mesenchymal phenotype of cholangiocytes, which leads to decreased biliary senescence and liver fibrosis. Inhibition of vimentin may be a key therapeutic target in the treatment of cholangiopathies including PSC. Published by Elsevier B.V

Tissue transglutaminase inhibits the TRPV5-dependent calcium transport in an N-glycosylation-dependent manner.

Contains fulltext : 109998.pdf (publisher's version ) (Closed access)Tissue transglutaminase (tTG) is a multifunctional Ca(2+)-dependent enzyme, catalyzing protein crosslinking. The transient receptor potential vanilloid (TRPV) family of cation channels was recently shown to contribute to the regulation of TG activities in keratinocytes and hence skin barrier formation. In kidney, where active transcellular Ca(2+) transport via TRPV5 predominates, the potential effect of tTG remains unknown. A multitude of factors regulate TRPV5, many secreted into the pro-urine and acting from the extracellular side. We detected tTG in mouse urine and in the apical medium of polarized cultures of rabbit connecting tubule and cortical collecting duct (CNT/CCD) cells. Extracellular application of tTG significantly reduced TRPV5 activity in human embryonic kidney cells transiently expressing the channel. Similarly, a strong inhibition of transepithelial Ca(2+) transport was observed after apical application of purified tTG to polarized rabbit CNT/CCD cells. Furthermore, tTG promoted the aggregation of the plasma membrane-associated fraction of TRPV5. Using patch clamp analysis, we observed a reduction in the pore diameter after tTG treatment, suggesting distinct structural changes in TRPV5 upon crosslinking by tTG. As N-linked glycosylation of TRPV5 is a key step in regulating channel function, we determined the effect of tTG in the N-glycosylation-deficient TRPV5 mutant. In the absence of N-linked glycosylation, TRPV5 was insensitive to tTG. Taken together, these observations imply that tTG is a novel extracellular enzyme inhibiting the activity of TRPV5. The inhibition of TRPV5 occurs in an N-glycosylation-dependent manner, signifying a common final pathway by which distinct extracellular factors regulate channel activity.01 maart 201