The TAK1/ROS pathway: a mediator of adhesive signaling?

组织结构由下层结缔组织维持。在皮肤中，结缔组织的结构和组织为表面上皮细胞提供支持，并产生皮肤的弹性和屏障功能。结缔组织主要由细胞外基质（ECM，其包括胶原）组成。 在结缔组织内，成纤维细胞负责产生和重塑ECM，因此负责结缔组织功能。 响应于损伤，分化的成纤维细胞的一种形式，肌成纤维细胞（所谓肌成纤维细胞是因为其表达高度收缩性蛋白α-平滑肌肌动蛋白）负责产生和重塑新的ECM;肌成纤维细胞在正常修复期间消失，但在瘢痕（纤维化）组织中异常消失。理解成纤维细胞如何促进真皮稳态和修复不仅对于理解成纤维细胞功能和皮肤稳态是必不可少的，而且对于如何正确地工程化替代皮肤组织也是必不可少的，所述替代皮肤组织应该在没有收缩的情况下整合在正常组织内（即，无疤痕）。细胞因子转化生长因子（TGF）β通过经典途径和非经典途径有效诱导成纤维细胞产生和重塑ECM，后者涉及通过整合素β 1和粘着斑激酶（FAK）操作的粘附信号传导。成纤维细胞缺失整合素β 1导致肌成纤维细胞形成受损和组织修复动力学延迟。此外，磷酸酶PTEN（磷酸酶和张力蛋白同源物）的表达（其通过使FAK去磷酸化来灭活粘附信号传导）在活化的真皮成纤维细胞中降低;真皮成纤维细胞的PTEN表达的丧失显著增加了体内真皮厚度，并提高了体内和体外成纤维细胞的ECM产生和收缩反应。TGF β激活激酶（TAK）1通路在FAK下游起作用，促进ECM对TGF β的重塑。成纤维细胞的TAK 1表达是维持正常皮肤厚度和诱导肌成纤维细胞响应组织损伤所必需的。这种非经典的TGF β途径似乎特异性地控制对TGF β的收缩反应。然而，粘附/TAK 1介导成纤维细胞产生和重塑ECM的能力的基本信号传导机制尚不清楚。我们还表明，成纤维细胞积极进行ECM生产/重塑整合素β 1介导的活性氧的产生所需的基因表达与ECM的生产和重塑。总的来说，这些数据表明了一个有趣的想法，即成纤维细胞通过粘附信号传导/TAK/ROS依赖性机制主动参与ECM重塑以响应TGF β等因子的能力。然而，这一假设尚未得到评估，这是本提案的主题。

Tissue architecture is maintained by the underlying connective tissue. In skin, the structure and organization of connective tissue provides support for surface epithelia and generates the skin’s elasticity and barrier functions. Connective tissue is comprised largely of extracellular matrix (ECM, which includes collagen). Within connective tissue, fibroblasts, which are responsible for producing and remodeling the ECM and hence for connective tissue function. In response to injury, a form of differentiated fibroblast, the myofibroblast (so called as it expresses the highly contractile protein alpha-smooth muscle actin), is responsible for producing and remodeling new ECM; myofibroblasts disappear during normal repair but, in scarred (fibrotic) tissue abnormally. Understanding how fibroblasts contribute to dermal homeostasis and repair is essential not only for understanding fibroblast function and skin homeostasis but also how to properly engineer replacement skin tissue which should integrate within the normal tissue without contractions (i.e., without scarring). The cytokine transforming growth factor (TGF) beta potently induces fibroblasts to produce and remodel ECM via both canonical pathway and non-canonical pathways, the latter of which involves adhesive signaling operating through integrin beta1 and focal adhesion kinase (FAK). Loss of integrin beta1 by fibroblasts results in impaired myofibroblast formation and delayed tissue repair kinetics. Moreover, expression of the phosphatase PTEN (Phosphatase and tensin homolog), which inactivates adhesive signaling by dephosphorylating FAK, is decreased in activated dermal fibroblasts; loss of PTEN expression by dermal fibroblasts significantly increased dermal thickness in vivo and elevated ECM production and contractile responses by fibroblasts both in vivo and in vitro. TGFbeta activated kinase (TAK)1 pathway operates downstream of FAK to promote ECM remodeling in response to TGFbeta. TAK1 expression by fibroblasts is required for maintaining normal skin thickness and for the induction of myofibroblasts in response to tissue injury. This non-canonical TGF beta pathway appears to specifically control contractile responses to TGF beta. However, the fundamental signaling mechanisms through which adhesion/TAK1 mediates the ability of fibroblasts to produce and remodel ECM are unclear. We also showed that fibroblasts actively undergoing ECM production/remodeling have integrin beta 1-mediated ROS generation was required for the expression of genes involved with ECM production and remodeling. Collectively, these data suggest the intriguing idea that the ability of fibroblasts to actively engage in ECM remodeling in response to factors such as TGF beta occurs via an adhesive signaling/TAK/ROS-dependent mechanism. However, this hypothesis has not been evaluated, and is the subject of this proposal.