mTORC1 Loss Impairs Epidermal Adhesion via Rho Kinase Activation

In this study, we use the epidermis as a model system to elucidate the cellular effects and signaling feedback sequelae of mTORC1 loss-of-function in epithelial tissue. In mice with conditional epidermal loss of mTORC1 components Rheb or Rptor, we find that mTORC1 loss-of-function unexpectedly results in a profound skin barrier defect with epidermal abrasions, blistering and early postnatal lethality, due to a thinned epidermis with decreased desmosome expression and incomplete biochemical differentiation. Impaired cell-cell adhesion in the context of mTORC1 loss-of-function is caused by constitutive activation of Rho kinase (ROCK) signaling with increased cytoskeletal tension, and inhibition or silencing of ROCK1 is sufficient to rescue keratinocyte adhesion and biochemical differentiation. mTORC1 loss-of-function results in marked feedback up-regulation of upstream TGF-β signaling, triggering ROCK activity and its downstream effects on desmosomal gene expression. These findings elucidate a novel role for mTORC1 in the regulation of epithelial barrier formation, cytoskeletal tension and cell adhesion and underscore the complexity of signaling feedback after mTORC1 inhibition We analysed gene expression changes between wild-type (3 biological replicates) and Rheb cKO (3 biological replicates) epidermal RNA samples, using the Partek Genomics Suite and QIAGEN Ingenuity Pathway Analysis platforms. The 'Rptor KRT14cre' and 'Rheb KRT14cre' mice have the C57BL/6J and C57BL/6J-*Aw-J*/J background, respectively.本研究以表皮作为模型系统，旨在阐明上皮组织中哺乳动物雷帕霉素靶蛋白复合物1（mTORC1）功能缺失所引发的细胞效应与信号反馈后续效应。在条件性表皮敲除mTORC1组分Rheb或Rptor的小鼠中，我们意外发现，mTORC1功能缺失会导致严重的皮肤屏障缺陷，表现为表皮擦伤、水疱形成以及出生早期致死，其原因在于表皮变薄、桥粒（desmosome）表达下调以及生化分化不全。mTORC1功能缺失背景下的细胞间黏附受损，是由Rho激酶（ROCK）信号通路组成型激活伴随细胞骨架张力升高所引发；而抑制或沉默ROCK1，足以挽救角质形成细胞（keratinocyte）的黏附能力与生化分化过程。mTORC1功能缺失会导致上游转化生长因子β（TGF-β）信号通路出现显著的反馈上调，进而触发ROCK活性及其对桥粒相关基因表达的下游效应。本研究结果阐明了mTORC1在上皮屏障形成、细胞骨架张力调控与细胞间黏附过程中的全新功能，并突显了mTORC1抑制后信号反馈网络的复杂性。我们采用Partek基因组分析套件（Partek Genomics Suite）与QIAGEN Ingenuity通路分析（QIAGEN Ingenuity Pathway Analysis）平台，分析了野生型（3个生物学重复）与Rheb条件性敲除（Rheb cKO，3个生物学重复）的表皮RNA样本之间的基因表达差异。Rptor KRT14cre与Rheb KRT14cre小鼠的遗传背景分别为C57BL/6J与C57BL/6J-Aw-J/J。