Center for Molecular Medicine Cologne

Sabine Eming / Maria Leptin - C 7

The role of TOR pathway components in skin function

A decline in skin regenerative capacity, increased skin fragility with disturbed barrier function and impaired wound healing are leading causes of increasing morbidity and mortality in the elderly. Understanding the underlying molecular and cellular mechanisms is important for the development of strategies to intervene in aging- and disease-associated loss of skin function. The aim of this project is to understand the role of the nutrition-sensing pathway, and specifically of TOR signalling, in skin homeostasis, regeneration and aging.

Introduction

Rapamycin inhibits cell growth and is used in the clinic for treating diseases such as cancer. The molecular target of rapamycin, the Ser/Thr kinase TOR, senses and integrates a variety of environmental cues from nutrients and growth factors, acting as a nexus point for cellular signals to control growth and metabolism. TOR forms two distinct multi-protein complexes, TOR complex 1 (TORC1) and 2 (TORC2). Altering the activity of components of the TOR pathway either genetically or by pharmaceutical intervention can extend healthy lifespan in laboratory animals. It is not clear to what extent this is due to organ-specific or systemic effects, and indeed in some organs reduction of TOR signalling can be detrimental, and the specific roles of TOR at the cellular level are just beginning to emerge. The effect on lifespan is conserved in evolution and can be studied in many laboratory model organisms. Here we make use of the advantages of Drosophila and the mouse to explore the function of TOR pathway components in skin homeostasis and regenerative capacity.  

TORC1 signalling regulates epidermal integrity and morphology in Drosophila, mice and humans

We developed and established multiple new tools and methods in mouse and Drosophila to explore the role of TOR in epidermal morphogenesis and homeostasis. We revealed the need for TOR signalling for efficient wound healing and epidermal morphogenesis both in mouse and Drosophila and have begun to dissect the downstream effectors. We found that  TORC1 and TORC2 affect epidermal morphogenesis, epithelial differentiation and homeostasis through distinct mechanisms. In addition to Drosophila and mice, we also investigated human tissue from patients with impaired wound healing. The complementary analyses of the three model systems strengthened our findings through cross-validation between Drosophila , mouse and human. 

Specifically, we found that the insulin and TOR signalling systems affect wound healing both in flies and mice, with distinct functions for the two TOR complexes. In flies, the effect of TORC1 is mediated by S6K. We have also discovered that TOR signalling influences cell polarity and morphology, which may ultimately help to explain the effect of problems in wound healing in diabetic patients and other situations of misregulated insulin signalling. Katharina Emmerich investigated in her doctoral thesis the activation of TOR signalling components in tissue sections from patients with normal healing skin wounds and disturbed wound healing conditions. Her findings revealed disturbed TORC1 activation (reduced S6 phosphorylation) in patients with wounds  that failed to heal normally compared to wounds in control subjects. This also shows a conserved role of TORC1/S6K signalling in wound healing from from non-vertebrat to humans.

We now find in Drosophila that normal levels of TORC1 signaling are also necessary for healthy, intact epithelial cells to maintain their proper shape and architecture. Interfering with the TORC1 signalling cascade (at any level from AMPK to Raptor) in the epidermis under nutrient-rich conditions results in a range of defects: cell-cell junctions disintegrate; cells lose their polarity, change their morphology and form syncytia. In addition, their acto-myosin network appears to become over-activated. Similarly, in the mammalian epidermis, loss of TORC1 compromises the barrier function of the skin barrier due to a decrease of junctional proteins (Ding et al. 2016; Asrani et al. 2017). We have investigated the role of pathways downstream of TORC1 in causing these defects and find that misregulation of autophagy is a major cause. Our findings support the hypothesis that TORC1 and insulin signalling affect cell shape and wound healing both through translational regulation and through an intersection with the autophagy pathway (Ding et al., 2016; Kakanj et al., 2016; K.E. doctoral thesis 2019; and unpublished results).

TORC2 regulates de novo epidermal lipid synthesis and filaggrin processing during cornification

Interestingly, epidermal knockdown of TORC2 had no effects on cell shape, morphology or wound healing in Drosophila  larvae. In contrast, epidermis-specific Rictor deficiency in mice uncovered TORC2 as a critical metabolic signalling relay of epidermal function. First, we identified TORC2 as regulator of de novo epidermal lipid synthesis and filaggrin processing during cornification (Figure 1) (Ding et al., J Allergy Clin Immunol, in press). Our findings provide new insights into the mechanisms of epidermal barrier formation and could open up new therapeutic opportunities to restore defective epidermal barrier conditions in patients. Secondly, we identified TORC2 as an important regulator of epidermal stem cell plasticity in the context of hair follicle function.

Medical relevance of findings

Our findings may help to explain the effect of problems in wound healing in diabetic patients and other situations of misregulated insulin signalling.

Mice with epidermal-specific Rictor deficiency develop an ichthyosis-like phenotype and might serve as a new preclinical disease model for studying epidermal barrier defects at the molecular level.

Our findings suggest that altered TORC2 activity may represent a predisposing factor for skin disorders associated with disrupted epidermal barrier function.

Perspectives

We uncovered novel and important functions of TOR in epidermal morphogenesis and homeostasis. Our studies funded by the CMMC provide tractable means to establish a solid research program to further tackle functional consequences of different TOR pathway components in skin function. Our findings have contributed to the acquisition of new extramural funding (FOR2599, FOR2240, SFB829). In addition, we are in the process of assembling a research program to obtain further funding to build on our discoveries and continue to investigate the specific downstream effector modules of TORC1 and TORC2 in epidermal function, and to find out how these processes can be exploited for the treatment of disease.

Ding X, Willenborg S, Bloch W, Wickström SA, Wagle P, Brodesser S, Roers A, Jais A, Brüning JC, Hall MN, Rüegg MA, Eming SA. (2019) Epidermal mTORC2 controls lipid synthesis and filaggrin processing in epidermal barrier formation. J Allergy Clin Immunol, (in press)

Eming, SA, Wynn, TM, and Martin, P (2017). Inflammation and metabolism in tissue regeneration and repair. Science 356, 1026-1030. 

Kakanj P, Moussian B, Grönke S, Bustos V, Eming SA, Partridge L, Leptin M. (2016) Insulin and TOR signal in parallel through FOXO and S6K to promote epithelial wound healing. Nat Commun 7 , 12972. 

Ding X, Bloch W, Iden S, Rüegg MA, Hall MN, Leptin M, Partridge L, Eming SA. (2016) mTORC1 and mTORC2 regulate skin morphogenesis and epidermal barrier formation. Nat Commun 27;7:13226.

Katharina Emmerich. (2018) Die Rolle von mTOR in der epidermalen Wundheilung (Doctoral Thesis)

 

 

Ding, X., Willenborg, S., Bloch, W., Wickstrom, S.A., Wagle, P., Brodesser, S., Roers, A., Jais, A., Bruning, J.C., Hall, M.N., Ruegg, M.A., and Eming, S.A. (2019). Epidermal mTORC2 controls lipid synthesis and filaggrin processing in epidermal barrier formation. J Allergy Clin Immunol10.1016/j.jaci.2019.07.033.

Kiesewetter, A., Cursiefen, C., Eming, S.A., and Hos, D. (2019). Phase-specific functions of macrophages determine injury-mediated corneal hem- and lymphangiogenesis. Sci Rep 9, 308.

Knipper, J.A., Ding, X., and Eming, S.A. (2019). Diabetes Impedes the Epigenetic Switch of Macrophages into Repair Mode. Immunity 51, 199-201.

Beati H, Peek I, Hordowska P, Honemann-Capito M, Glashauser J, Renschler FA, Kakanj P, Ramrath A, Leptin M, Luschnig S, Wiesner S, and Wodarz A (2018). The adherens junction-associated LIM domain protein Smallish regulates epithelial morphogenesis. J Cell Biol 217, 1079-1095.

Do NN, Willenborg S, Eckes B, Jungst C, Sengle G, Zaucke F, and Eming SA (2018). Myeloid Cell-Restricted STAT3 Signaling Controls a Cell-Autonomous Antifibrotic Repair Program. J Immunol 201, 663-674.

Wollrab V, Belmonte JM, Baldauf L, Leptin M, Nedelec F, and Koenderink GH (2018). Polarity sorting drives remodeling of actin-myosin networks. J Cell Sci 132.

Batinica M, Stephan A, Steiger J, Tantcheva-Poor I, Eming SA, and Fabri M (2017). Stimulus-dependent NETosis by neutrophils from a Papillon-Lefevre Syndrome patient. J Eur Acad Dermatol Venereol 31, e239-e41.

Bukowiecki A, Hos D, Cursiefen C, and Eming SA (2017). Wound-Healing Studies in Cornea and Skin: Parallels, Differences and Opportunities. Int J Mol Sci 18.

Eckes B, and Eming SA (2017). Tissue fibrosis: a pathomechanistically unresolved challenge and scary clinical problem. Exp Dermatol 26, 135-6.

Eming SA, and Tomic-Canic M (2017). Updates in wound healing: Mechanisms and translation. Exp Dermatol 26, 97-8.

Eming SA, Wynn TA, and Martin P (2017). Inflammation and metabolism in tissue repair and regeneration. Science 356, 1026-30.

Hos D, Bukowiecki A, Horstmann J, Bock F, Bucher F, Heindl LM, Siebelmann S, Steven P, Dana R, Eming SA, and Cursiefen C (2017). Transient Ingrowth of Lymphatic Vessels into the Physiologically Avascular Cornea Regulates Corneal Edema and Transparency. Sci Rep 7, 7227.

Lucas T, Schafer F, Muller P, Eming SA, Heckel A, and Dimmeler S (2017). Light-inducible antimiR-92a as a therapeutic strategy to promote skin repair in healing-impaired diabetic mice. Nat Commun 8, 15162.

Prof. Dr. Sabine Eming CMMC Cologne
Prof. Dr. Sabine Eming

Dept. of Dermatology

Principal Investigator C 7

Executive Board Member

Publications - Sabine Eming

Link to PubMed

Prof. Dr. Maria Leptin CMMC Cologne
Prof. Dr. Maria Leptin

Institute for Genetics

Co-Principal Investigator C 7

+49 221 470 3401

+49 221 478 97295

Institute for Genetics

Zülpicher Str. 47

50674 Cologne

http://www.genetik.uni-koeln.de/groups/Leptin/lep_lab.htm

CMMC Profile Page

Curriculum Vitae (CV)

Publications - Maria Leptin

Link to PubMed

Group Members

Xiaolei Ding (PostDoc)
Parisa Kakanj (PostDoc)

Figure 1

Epidermal mTORC2 controls epidermal barrier formation

A) Macroscopic appearance of indicated littermates at P7 representing ichthyosis-like phenotype in RicEKO mice. B) HE-stained back skin sections at P4 demonstrating altered epidermal architecture in RicEKO mice. C) Vulcano plot of differentially regulated transcripts between control and RicEKO epidermis at E19.5.