Knockdown of transglutaminase-2 prevents early age-induced vascular changes in mice

Abstract Purpose: To determine whether the absence of transglutaminase 2 enzyme (TG2) in TG2 knockout mice (TG2-/-) protect them against early age-related functional and histological arterial changes. Methods: Pulse wave velocity (PWV) was measured using non-invasive Doppler and mean arterial pressure (MAP) was measured in awake mice using tail-cuff system. Thoracic aortas were excised for evaluation of endothelial dependent vasodilation (EDV) by wire myography, as well as histological analyses. Results: PWV and MAP were similar in TG2-/-mice to age-matched wild type (WT) control mice. Old WT mice exhibited a markedly attenuated EDV as compared to young WT animals. The TG2-/-young and old mice had enhanced EDV responses (p<0.01) as compared to WT mice. There was a significant increase in TG2 crosslinks by IHC in WT old group compared to Young, with no stain in the TG2-/-animals. Optical microscopy examination of Old WT mice aorta showed thinning and fragmentation of elastic laminae. Young WT mice, old and young TG2-/-mice presented regularly arranged and parallel elastic laminae of the tunica media. Conclusion: The genetic suppression of TG2 delays the age-induced endothelial dysfunction and histological modifications.

Tissue transglutaminase (TG2) activity regulates osteoblast differentiation and mineralization in the SAOS-2 cell line

Tissue transglutaminase (type II, TG2) has long been postulated to directly promote skeletal matrix calcification and play an important role in ossification. However, limited information is available on the expression, function and modulating mechanism of TG2 during osteoblast differentiation and mineralization. To address these issues, we cultured the well-established human osteosarcoma cell line SAOS-2 with osteo-inductive conditioned medium and set up three time points (culture days 4, 7, and 14) to represent different stages of SAOS-2 differentiation. Osteoblast markers, mineralization, as well as TG2 expression and activity, were then assayed in each stage. Furthermore, we inhibited TG activity with cystamine and then checked SAOS-2 differentiation and mineralization in each stage. The results showed that during the progression of osteoblast differentiation SAOS-2 cells presented significantly high levels of osteocalcin (OC) mRNA, bone morphogenetic protein-2 (BMP-2) and collagen I, significantly high alkaline phosphatase (ALP) activity, and the increased formation of calcified matrix. With the same tendency, TG2 expression and activity were up-regulated. Furthermore, inhibition of TG activity resulted in a significant decrease of OC, collagen I, and BMP-2 mRNA and of ALP activity and mineralization. This study demonstrated that TG2 is involved in osteoblast differentiation and may play a role in the initiation and regulation of the mineralization processes. Moreover, the modulating effects of TG2 on osteoblasts may be related to BMP-2.

Transglutaminases, thioredoxins and protein disulphide isomerase: diverse enzymes with a common goal of cross-linking proteins in lower organisms.

Prokaryotes and various eukaryotes have remarkable ability to survive under adverse physiologic conditions and protect themselves from environmental stresses. An important mechanism by which they accomplish this is by synthesizing rigid and biochemically inert structures around them. In general, these structures are highly stable and resistant to mechanical and chemical insults. Biochemically, they are composed of complex carbohydrates, such as chitin and heavily crosslinked scaffold of proteins to form complex structures, such as sheath, cuticle, and epicuticle. Transglutaminases (TGases) are a family of enzymes that share catalytic function with thioredoxin and protein disulphide isomerases (PDI) and catalyze protein crosslink reaction by establishing epsilon-(gamma-glutamyl)lysine isopeptide bonds. The isopeptide bonds thus formed are of great physiologic significance because once formed, they cannot be hydorlysed by any known enzymes of the eukaryote system and exhibit high resistance to reducing agents, detergents, and chaotropic agents. Therefore, it is likely that protective structures viz., sheath, cuticle, epicuticle, and viral core proteins synthesized by microorganisms involve active participation of TGases. In this review, we briefly describe the current knowledge of non-mammalian TGases and their possible role in growth, development, and survival of small organisms. Special reference is made to filarial nematode and bacterial TGases since they are the most well-characterized and studied enzymes among non-mammalian TGases.