Langerhans cell homeostasis in mice is dependent on mTORC1 but not mTORC2 function

Abstract

Key Points• mTORC1 activity in DCs by conditional deletion of Raptor leads to a progressive loss of LCs in the skin of mice.• mTORC1 but not mTORC2 is required for epidermal LC homeostasis.The PI3K/Akt/mTOR pathway has emerged as a critical regulator of dendritic cell (DC) development and function. The kinase mTOR is found in 2 distinct complexes, mTORC1 and mTORC2. In this study, we show that mTORC1 but not mTORC2 is required for epidermal Langerhans cell (LC) homeostasis. Although the initial seeding of the epidermis with LCs is not affected, the lack of mTORC1 activity in DCs by conditional deletion of Raptor leads to a progressive loss of LCs in the skin of mice. Ablation of mTORC2 function by deletion of Rictor results in a modest reduction of LCs in skin draining lymph nodes. In young mice Raptor-deficient LCs show an increased tendency to leave the skin, leading to a higher frequency of migratory DCs in skin draining lymph nodes, indicating that the loss of LCs results from enhanced migration. LCs lacking Raptor are smaller and display reduced expression of Langerin, E-cadherin, ␤-catenin, and CCR7 but unchanged levels of MHC-II, ruling out enhanced spontaneous maturation. Ki-67 and annexin V stainings revealed a faster turnover rate and increased apoptosis of Raptor-deficient LCs, which might additionally affect the preservation of the LC network. Taken IntroductionDendritic cells (DCs) are specialized antigen-presenting cells essential for the initiation of adaptive immune responses and the maintenance of tolerance to self-antigens. 1 The outcome of antigen recognition by a T cell is dependent on the expression of distinct costimulatory and coinhibitory molecules as well as pro and anti-inflammatory cytokines expressed by the DC. 2 DCs develop from hematopoietic stem cells through specialized progenitor cells. Under steady-state conditions 3 major types of DCs differing in their location, phenotype, and function exist, the plasmacytoid DCs (pDCs), lymphoid organ resident DCs (rDCs), and peripheral tissue migratory DCs (mDCs). 3 In skin draining lymph nodes (sLNs) the mDC subset includes epidermal Langerhans cells (LCs) and Langerin ϩ and Langerin Ϫ dermal DCs (dDCs). LCs and Langerin ϩ dDCs can be distinguished by the absence and presence of the integrin ␣ E subunit CD103, respectively. 4 In recent years it has become increasingly evident that the PI3K/Akt/mTOR pathway plays an important role in DC development and function. 5 The mammalian target of rapamycin mTOR is a conserved serine/threonine kinase found in 2 distinct multiprotein complexes termed mTORC1 and mTORC2. 6 Raptor and Rictor are components essential for the assembly and the specific functions of mTORC1 and mTORC2, respectively. The macrolide drug rapamycin specifically blocks the function of mTORC1. Although originally described as rapamycin insensitive, 7,8 increasing evidence indicates that prolonged rapamycin treatment also inhibits mTORC2. 9,10 MTORC1 is regulated by extracellular signals, which trigger the phosphatidylinositol 3Ј-ki...

The late endosomal adaptor molecule p14 (LAMTOR2) represents a novel regulator of Langerhans cell homeostasis

“…Interestingly, a recent report showed that raptor-mediated disruption of mTORC1 signaling critically affects LC homeostasis. 39 ERK as well as mTOR signaling are known to mediate/regulate fundamental cellular processes like growth factor signaling, 12 cell growth and proliferation, 12,40 as well as the nutritional status of the cell. 9,10 This may connect cell ontogeny and mTOR/ERK signaling in that less mTORC1/ERK signaling (as shown for LCs) results in less proliferation and less inhibition (ie, promotion) of catabolic 40 processes such as apoptosis, as we have established.…”

PI3-Kinase-γ Has a Distinct and Essential Role in Lung-Specific Dendritic Cell Development

“…Akt1 À/À and Akt2 À/À mice were provided by O. Tschopp (University of Zü rich). ItgaxRictor-Raptor fl/fl mice were provided by T. Broker (Kellersch and Brocker, 2013). All animals were housed in individually ventilated cages under specific-pathogen-free conditions at the ETH Phenomics Facility and used for experiments at between 6 and 14 weeks of age unless otherwise stated.…”

“…Conversely, FLT3L-mediated expansion of pre-DCs in the spleen and to a lesser degree in the blood and lung was decreased with Rapamycin ( Figure S5A). In order to more comprehensively address the role of the mTOR pathway in DC development, we analyzed mice deficient in both RAPTOR and RICTOR specifically in DCs (Kellersch and Brocker, 2013). These two proteins are key components of mTORC1 and mTORC2, respectively (Weber and Gutmann, 2012).…”

Dendritic cell metabolism

“…These effects can be inhibited by rapamycin 17 . Moreover, the Cd11c –Cre-mediated deletion of Raptor , which encodes a key component of mTORC1, alters steady-state DC populations, increasing the numbers of splenic cDCs 20 but reducing the numbers of epidermal Langerhans cells 21 . Generally consistent with these findings, the tamoxifen-induced oestrogen receptor–Cre-mediated deletion of floxed Tsc1 (which encodes tuberous sclerosis 1, another negative regulator of mTORC1), results in enhanced outgrowth of DCs from GM-CSF-stimulated bone marrow cultures 22 .…”