Maintenance and Regulation of Tendon and Ligament Maturation by TGFbeta Signaling

 描述（由申请人提供）：我们之前已经证明TGFβ信号传导是肌腱细胞命运的关键调节因子：TGFβ信号传导是肌腱标志物的有效诱导剂，肢芽间充质中TGFβ信号传导的破坏导致肌腱发育失败。这一建议是基于对TGFβ信号在肌腱发育后期的作用的观察。我们发现，使用ScxCre肌腱删除器破坏肌腱细胞中的2型TGFβ受体（TβR2）导致出生后早期肌腱退变。有趣的是，肌腱的胚胎发育不受影响，肌腱形成了一个坚固和有组织的胶原基质，但在出生后发育的早期阶段，TβR2;ScxCre幼仔的运动受到干扰，它们的肌腱显示出肌腱标记物逐渐丢失，随后发生退行性过程。此外，我们发现腱细胞去分化不是由于TGFβ信号的内在丢失，因为在孤立的腱细胞斑块中TβR2的丢失没有类似的作用。因此，我们假设TGFβ信号转导的缺失导致肌腱中细胞-细胞或细胞-基质相互作用的破坏，导致腱细胞去分化和肌腱变性。拟议的项目在三个主要方向上遵循这些观察结果，第一个目的是确定是否存在TGFβ信号传导中断将导致肌腱退变的发育时间窗，并开发更有限的表型模型，从而能够跟踪退变过程的全部范围，并将其开发为肌腱病分析系统。在第二个目标中，我们将研究突变肌腱中的细胞和分子变化，以确定维持肌腱细胞命运所必需的关键特征。最后，在第三个目标中，我们基于初步结果分析了激活素信号传导在这一过程中的作用，这些结果显示了TGFβ和激活素信号传导之间的协同相互作用。

 DESCRIPTION (provided by applicant): We have previously shown that TGFβ signaling is a key regulator of the tendon cell fate: TGFβ signaling is a potent inducer of tendon markers and disruption of TGFβ signaling in limb bud mesenchyme resulted in failure of tendon development. This proposal is based on observations regarding the role of TGFβ signaling in later stages of tendon development. We find that disrupting the type 2 TGFβ receptor (TβR2) in tenocytes using the ScxCre tendon deletor resulted in tendon degeneration in early postnatal stages. Interestingly, embryonic development of the tendons was not affected and the tendons developed a robust and organized collagen matrix, but in early stages of postnatal development the movement of TβR2;ScxCre pups was perturbed and their tendons showed gradual loss of tendon markers followed by degenerative processes. Moreover, we find that tenocyte dedifferentiation was not due to an intrinsic loss of TGFβ signaling, since loss of the TβR2 in isolated patches of tenocytes did not have a similar effect. We therefore hypothesize that loss of TGFβ signaling results in disruptions to cell-cell or cell-matrix interactions in tendons leading o tenocyte dedifferentiation and tendon degeneration. The proposed project follows these observations in three major directions, the first aim is to determine if there is a developmental time window in which disruption of TGFβ signaling will lead to tendon degeneration and to develop more limited model of the phenotype that will enable following the full scope of the degenerative process and developing it as a system for analysis of tendinopathy. In the second aim we will investigate the cellular and molecular changes in the mutant tendons to identify the key features essential for maintenance of the tendon cell fate. Finally, in the third aim we analyze the role of activin signaling in this process based on preliminary results that show synergistic interactions between TGFβ and activin signaling.