甲状腺激素(TH)是骨重建的重要调节剂,甲状腺疾病,特别是甲状腺功能亢进,能够损害骨骼质量和抗骨折性。TH对骨骼的作用是由Thra和Thrb编码的甲状腺激素受体(TR)TRα1和TRβ1介导的,分别。缺乏Thra(Thra0/0)和Thrb(Thrb-/-)的小鼠的骨骼表型已得到充分描述,并表明TRα1是骨骼中TH作用的主要介质。考虑到骨细胞可能会受到这些突变小鼠的系统性TH变化的影响,在这里,我们仅在细胞水平研究了TR基因敲除对成骨细胞的影响.从Thra0/0获得的原代成骨细胞,thrb-/-,和各自的野生型(WT)小鼠的分化潜力进行了分析,体外活性和TH反应性。Thra,但Thrb基因敲除不能促进早期分化和活动,与相应的WT细胞相比,成熟和晚期成骨细胞。有趣的是,在WT和Thra缺乏的成骨细胞中,TH增加了成骨细胞标记基因和TH靶基因Klf9的矿化能力和表达,Thrb敲除减轻了成骨细胞对短期(48h)和长期(10d)TH治疗的反应性。Further,我们发现Rankl的比例很低,一种强效的破骨细胞刺激剂,超过骨保护素,破骨细胞抑制剂,在Thrb缺乏的成骨细胞中,从Thrb-/-成骨细胞获得的上清液减少了体外原代破骨细胞的数量。根据仅TH处理的WT成骨细胞中增加的Rankl/Opg比率,这些细胞的上清液,但不是来自TH处理的Thrb-/-成骨细胞增加了Trap和Ctsk在破骨细胞中的表达,提示破骨细胞通过Trβ1间接刺激成骨细胞。总之,我们的研究表明Thra和Thrb对活动的影响不同,成骨细胞在体外的分化和TH反应,强调了TRβ1介导骨TH作用的重要性。
Thyroid hormones (TH) are important modulators of bone remodeling and thus, thyroid diseases, in particular hyperthyroidism, are able to compromise bone quality and fracture resistance. TH actions on bone are mediated by the thyroid hormone receptors (TR) TRα1 and TRβ1, encoded by
Thra and Thrb, respectively. Skeletal phenotypes of mice lacking
Thra (Thra0/0 ) and Thrb (Thrb-/- ) are well-described and suggest that TRα1 is the predominant mediator of TH actions in bone. Considering that bone cells might be affected by systemic TH changes seen in these mutant mice, here we investigated the effects of TR knockout on osteoblasts exclusively at the cellular level. Primary osteoblasts obtained from Thra0/0 , Thrb-/- , and respective wildtype (WT) mice were analyzed regarding their differentiation potential, activity and TH responsiveness in vitro.
Thra, but not Thrb knockout promoted differentiation and activity of early, mature and late osteoblasts as compared to respective WT cells. Interestingly, while mineralization capacity and expression of osteoblast marker genes and TH target gene Klf9 was increased by TH in WT and
Thra-deficient osteoblasts, Thrb knockout mitigated the responsiveness of osteoblasts to short (48 h) and long term (10 d) TH treatment. Further, we found a low ratio of Rankl, a potent osteoclast stimulator, over osteoprotegerin, an osteoclast inhibitor, in Thrb-deficient osteoblasts and in line, supernatants obtained from Thrb-/- osteoblasts reduced numbers of primary osteoclasts in vitro. In accordance to the increased Rankl/Opg ratio in TH-treated WT osteoblasts only, supernatants from these cells, but not from TH-treated Thrb-/- osteoblasts increased the expression of Trap and Ctsk in osteoclasts, suggesting that osteoclasts are indirectly stimulated by TH via TRβ1 in osteoblasts. In conclusion, our study shows that both
Thra and Thrb differentially affect activity, differentiation and TH response of osteoblasts in vitro and emphasizes the importance of TRβ1 to mediate TH actions in bone.