TIEG1-null tenocytes display age-dependent differences in their gene expression, adhesion, spreading and proliferation properties

The remodeling of extracellular matrix is a crucial mechanism in tendon development and the proliferation of fibroblasts is a key factor in this process. The purpose of this study was to further elucidate the role of TIEG1 in mediating important tenocyte properties throughout the aging process. Wildtype and TIEG1 knockout tenocytes adhesion, spreading and proliferation were characterized on different substrates (fibronectin, collagen type I, gelatin and laminin) and the expression levels of various genes known to be involved with tendon development were analyzed by RT-PCR. The experiments revealed age-dependent and substrate-dependent properties for both wildtype and TIEG1 knockout tenocytes. Taken together, our results indicate an important role for TIEG1 in regulating tenocytes adhesion, spreading, and proliferation throughout the aging process. Understanding the basic mechanisms of TIEG1 in tenocytes may provide valuable information for treating multiple tendon disorders.     

TIEG1 is upregulated in Lrp5/6-mediated valve osteogenesis

We have previously demonstrated that Lrp5/6/β-catenin plays an important role in valve calcification with a specific osteogenic phenotype defined by increased bone mineral content and overall valve thickening. Recent studies indicate that TIEG1 may be involved in mediating the Wnt signaling pathway in bone, which is known to play critical roles in osteoblast differentiation and bone mineralization. Therefore, we sought to test the role of TIEG1 in mediating Wnt signaling, in an established model of hypercholesterolemic valve disease. Our previous model treated null mice with cholesterol diets: Lrp5 ^−/−/ApoE ^−/− mice versus wild-type control (n = 180). Group I (n = 60) normal diet, Group II (n = 60) 0.25% chol diet (w/w), and Group III (n = 60) 0.25% (w/w) chol diet + atorv was tested for gene expression for TIEG1, Lrp6, and Runx2. Real-time polymerase chain reaction confirmed that there is upregulation of the gene expression for TIEG1 and Runx2 in the hypercholesterolemic double knockout and single knockout valves as compared with controls with a mild increase in Lrp6. To confirm the mechanism, coexpression of β-catenin, TIEG1, and LEF1 in valve cells in vitro, led to the coactivation of the TOPFLASH reporter, which was further confirmed by the observation that TIEG1 and β-catenin colocalize with one another in the nucleus of valvular interstitial cells (VICs) following stimulation with transforming growth factor-β treatment, an established activator of TIEG1. Taken together, these data implicate an important role for TIEG1 in mediating valve osteogenesis.     

TIEG及其在TGF-β-Smads通路中的作用

TGF-β诱导早期基因(TGF-β-inducible early gene,TIEG)产物为Sp1样转录因子家族成员,其中TIEG1和TIEG2组成TIEG亚家族。TIEG1的稳定性与泛素-蛋白酶体路径有关。TIEG1C端保守的3锌指结构及N端的转录抑制区对于该蛋白功能的正常发挥十分重要。TIEG作为TGF-β诱导的立即早期转录基因,引起细胞形态发生改变,抑制细胞增殖并诱导凋亡。TIEG1在TGF-β-Smads信号通路中通过Smads成员发挥调节作用,其中与Smad7形成的负反馈环对该信号转导路径尤为重要。     

TIEG与肿瘤的发生发展

β-转化生长因子(transforming growth factor-β,TGF-β)诱导的早期反应基因(TGF-β inducible early gene,TIEG)产物是Sp1样转录因子家族的新成员。TIEG亚家族共有3个成员:TIEG1、TIEG2和TIEG3。TIEG作为一个转录因子,能够调节多个与细胞生长分化有关的基因的表达。近年来研究发现,TIEG异常表达与多种肿瘤的发生发展有关,如乳腺癌、肺癌、胰腺癌、卵巢癌和胃癌;并且最新的研究发现,在某些抗癌药物作用过程中TIEG的表达也明显上调。这些研究结果表明,TIEG可能是一个重要的肿瘤抑制因子,因此有必要对其进行深入研究,有助于加深对肿瘤发生机制的了解。     

Sclerostin antibody treatment rescues the osteopenic bone phenotype of TGFβ inducible early gene-1 knockout female mice

Deletion of TGFβ inducible early gene-1 (TIEG) in mice results in an osteopenic phenotype that exists only in female animals. Molecular analyses on female TIEG knockout (KO) mouse bones identified increased expression of sclerostin, an effect that was confirmed at the protein level in serum. Sclerostin antibody (Scl-Ab) therapy has been shown to elicit bone beneficial effects in multiple animal model systems and human clinical trials. For these reasons, we hypothesized that Scl-Ab therapy would reverse the low bone mass phenotype of female TIEG KO mice. In this study, wildtype (WT) and TIEG KO female mice were randomized to either vehicle control (Veh, n = 12/group) or Scl-Ab therapy (10 mg/kg, 1×/wk, s.c.; n = 12/group) and treated for 6 weeks. Following treatment, bone imaging analyses revealed that Scl-Ab therapy significantly increased cancellous and cortical bone in the femur of both WT and TIEG KO mice. Similar effects also occurred in the vertebra of both WT and TIEG KO animals. Additionally, histomorphometric analyses revealed that Scl-Ab therapy resulted in increased osteoblast perimeter/bone perimeter in both WT and TIEG KO animals, with a concomitant increase in P1NP, a serum marker of bone formation. In contrast, osteoclast perimeter/bone perimeter and CTX-1 serum levels were unaffected by Scl-Ab therapy, irrespective of mouse genotype. Overall, our findings demonstrate that Scl-Ab therapy elicits potent bone-forming effects in both WT and TIEG KO mice and effectively increases bone mass in female TIEG KO mice.