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

Abstract

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.

Tissue transglutaminase is involved in mechanical load–induced osteogenic differentiation of human ligamentum flavum cells

“…Furthermore, inhibition of TGM2 activity in the cultures by CYS significantly attenuated mechanical load-induced ALP activity ( Figure 5). The results are proportionally consistent with a previous study that TGM2 is involved in the initiation and regulation of the mineralization processes in osteosarcoma cell line SAOS-2 (40). Based on the above findings, it could be reasonably inferred that centrifugal force induces osteogenic differentiation of human ligamentum flavum cells possibly via TGM2-dependent mechanism.…”

“…Yin et al demonstrated that TGM2 gene expression and enzyme activity were upregulated during SAOS-2 osteoblast differentiation and mineralization. Inhibition of TGM activity significantly decreased osteocalcin (OC) and collagen-I gene expression, and ALP activity (40). In the present study, mechanical load significantly induced TGM2 gene expression and enzyme activity in human ligamentum flavum cells.…”

“…BMP-2 belongs to the TGF-β superfamily and is a potent bone cell-differentiating factor as well as bone-formation stimulator. The modulating effects of TGM2 on osteoblasts are related to BMP-2 (40). In addition to that, our previous study demonstrated that mechanical load increased the production of PGE2 and NO as well as pro-inflammatory cytokines, IL-1α, IL-1β and IL-6, gene expression in human ligamentum flavum cells (4).…”

Transglutaminase factor XIII promotes arthritis through mechanisms linked to inflammation and bone erosion

“…51 Osteoblasts and osteoblastic cell lines have been reported to express both fXIIIA and tissue transglutaminase 2 (TG2). 52,53 Despite the local expression differences in crucial osteologic effectors observed in fXIIIA 2/2 mice, no overt skeletal abnormalities have been reported for fXIIIA 2/2 mice. Additionally, studies have reported that baseline skeletal properties of TG2-deficient mice are unaltered.…”

Tendinopathy in diabetes mellitus patients—Epidemiology, pathogenesis, and management

“…The increase in matrix stiffness as a result of AGE formation and transglutaminase 2 activation may modify the niche and hence promote nontenocyte differentiation of stem cells in tendons. 64,65 In this regard, transglutaminase 2 was reported to regulate osteoblast differentiation in vitro 101 and to mediate the activation of the β-catenin signaling pathway which is central in vascular calcification. 102 Proteoglycans are key regulators of tendon function and are responsible for cell migration, differentiation, collagen fibril assembly, and fiber sliding.…”