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MTORC1 Loss Impairs Epidermal Adhesion via Rho Kinase Activation

ABSTRACT: 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

ORGANISM(S): Mus musculus

PROVIDER: GSE102026 | GEO | 2020/04/14

REPOSITORIES: GEO

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Project description:The mechanistic target of rapamycin (mTOR) pathway integrates diverse environmental inputs, including immune signals and metabolic cues, to direct T cell fate decisions1. Activation of mTOR, comprised of mTORC1 and mTORC2 complexes, delivers an obligatory signal for proper activation and differentiation of effector CD4+ T cells2,3, whereas in the regulatory T cell (Treg) compartment, the Akt-mTOR axis is widely acknowledged as a crucial negative regulator of Treg de novo differentiation4-8 and population expansion9. However, whether mTOR signaling affects the homeostasis and function of Tregs remains largely unexplored. Here we show that mTORC1 signaling is a pivotal positive determinant of Treg function. Tregs have elevated steady-state mTORC1 activity compared to naïve T cells. Signals via T cell receptor (TCR) and IL-2 provide major inputs for mTORC1 activation, which in turn programs suppressive function of Tregs. Disruption of mTORC1 through Treg-specific deletion of the essential component Raptor leads to a profound loss of Treg suppressive activity in vivo and development of a fatal early-onset inflammatory disorder. Mechanistically, Raptor/mTORC1 signaling in Tregs promotes cholesterol/lipid metabolism, with the mevalonate pathway particularly important for coordinating Treg proliferation and upregulation of suppressive molecules CTLA-4 and ICOS to establish Treg functional competency. In contrast, mTORC1 does not directly impact the expression of Foxp3 or anti- and pro-inflammatory cytokines in Tregs, suggesting a non-conventional mechanism for Treg functional regulation. Lastly, we provide evidence that mTORC1 maintains Treg function partly through inhibiting the mTORC2 pathway. Our results demonstrate that mTORC1 acts as a fundamental ‘rheostat’ in Tregs to link immunological signals from TCR and IL-2 to lipogenic pathways and functional fitness, and highlight a central role of metabolic programming of Treg suppressive activity in immune homeostasis and tolerance. We used microarrays to explore the gene expression profiles differentially expressed in regulatory T-cells from wild-type and CD4(cre) x Raptor(fl/fl) mice

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MTORC1 Loss Impairs Epidermal Adhesion via Rho Kinase Activation

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