Crosstalk between Foxp3+ Regulatory T Cells and Type 2 Immunity in Maintaining Adipose Tissue Homeostasis
Final Report Abstract
The overall aim of our project was to investigate how adipose tissue (AT)-residing Foxp3+ regulatory T (Treg) cells and eosinophils (Eos) cooperatively control AT metabolism, with a particular emphasis on the relative contribution of individual developmental Foxp3+ Treg cell sublineages (pTreg and tTreg cells) to the maintenance of AT homeostasis, and on the mechanisms that govern the dynamic changes in the population size of AT-residing Treg cells and eosinophils during manifestation of obesity. Since project start in 09/2018, we performed a series of mechanistic kinetics studies in the well-established C57Bl/6 mouse model of high-fat diet (HFD)-induced obesity. For this, cohorts of age-matched C57Bl/6 wild-type (WT) and various genetically manipulated mouse lines on the C57Bl/6 background were fed with normal diet (ND, 10 kcal%fat) and HFD (60 kcal%fat), prior to metabolic and immune phenotyping at different time-periods after initiation of ND-/HFD-feeding (6, 10, 16, and 20 wks). Initial results established that HFD feeding consistently promotes obesity in all mouse lines included in the project proposal, as judged by markedly increased body and visceral AT (VAT) weight. Furthermore, constitutive Eo deficiency in HFD-fed Adbl-GATA mice was found to have a negligible impact on AT Foxp3+ Treg cells (population size, phenotype, activation status, etc.), which appears at odds with our initial hypothesis outlined in Aim 2 of the project proposal. However, complementary studies (Aim 1) in C57Bl/6.Foxp3RFP/GFP mice with differential fluorochrome reporter expression in Foxp3+ Treg cell developmental sublineages (RFP+GFP+: tTreg cells; RFP+GFP-: pTreg cells), established that the time-dependent manifestation of obesity was accompanied by unexpectedly dynamic changes in the pTreg/tTreg cell phenotype and population size, characterized by initial population expansion followed by a subsequent contraction phase, albeit at different kinetics: in fact, the pTreg cell population size peaked as early as at 6 wks after initiation of HFD feeding, was then maintained at constant levels during obesity manifestation (10 and 16 wks), before it dropped to steady-state levels at the end of the observation period (20 wks), despite ongoing HFD-induced type 1 immunity. In contrast, the tTreg cell population size slowly but consistently increased over 16 wks, before it collapsed below steady-state levels at 20 wks, which was accompanied by dysregulated expression of key members of the so-called ‘Treg cell signature’, e.g. substantially decreased expression levels of CD25, while CD127 (IL-7Rα) expression was markedly increased. Lineage-tracing experiments revealed that the observed dramatic loss of tTreg cells in Foxp3RFP/GFP mice with advanced obesity can be attributed to the dedifferentiation of tTreg cells with an initially Foxp3+ CD25hlghIL-7Rlow phenotype into nonfunctional Foxp3-CD25hlowIL-7R+ ‘ex-tTreg’ cells, in all likelihood driven by pro-inflammatory cytokines locally produced in the AT of obese mice. These dynamic changes in the phenotype and population size of AT-residing pTreg and tTreg cells provided first experimental evidence that both developmental Foxp3+ Treg cell sublineages may exert specialized non-redundant effector functions in AT homeostasis and manifestation of HFD-induced obesity. In fact, subsequent studies in mice with selective deficiency in either one of the two Foxp3+ Treg cell developmental sublineages provided evidence that ‘tTreg only’ mice lacking the pTreg cell population are far more sensitive to the manifestation of HFD-induced obesity, as revealed by e.g. accelerated increase in body weight and enhanced polarization of AT-residing macrophages towards an M1 phenotype. Consistently, we found that ‘pTreg only’ mice, in which the absence of tTreg cells is at least partly compensated by increased pTreg cells numbers, are essentially resistant to the manifestation of HFD-induced obesity. Until the end of the funding period, ongoing mechanistic studies (e.g. global gene expression analysis by single cell RNA-Seq) aim to identify the exact molecular mechanisms that govern the differential role of AT-residing pTreg/tTreg cells in AT homeostasis, while functional studies address the possibility that the targeted enhancement of pTreg cell-activity in vivo may increase the threshold for HFD-induced obesity in WT mice.
Publications
- Approaches to discriminate naturally induced Foxp3+ Treg cells of intra- and extrathymic origin: Helios, Neuropilin-1, and Foxp3RFP/GFP. J Clin Cell Immunol. 2018;9(1): 540
Dohnke S, Schreiber M, Schallenberg S, Simonetti M, Fischer L, Garbe AI, Chatzigeorgiou A, and Kretschmer K
(See online at https://doi.org/10.4172/2155-9899.1000540) - Innate immune cells in the adipose tissue. Rev Endocr Metab Disord. 2018 Jun 19
Chung KJ, Nati M, Chavakis T, Chatzigeorgiou A
(See online at https://doi.org/10.1007/s11154-018-9451-6) - Increased Neutrophil Extracellular Traps Related to Smoking Intensity and Subclinical Atherosclerosis in Patients with Type 2 Diabetes. Thromb Haemost. 2020 Aug 9
Chatzigeorgiou A, Mitroulis I, Chrysanthopoulou A, Legaki AI, Ritis K, Tentolouris N, Protogerou AD, Koutsilieris M, Sfikakis PP
(See online at https://doi.org/10.1055/s-0040-1714371) - Metabolic inflammation as an instigator of fibrosis during non-alcoholic fatty liver disease. World J Gastroenterol. 2020 May 7;26(17):1993-2011
Katsarou A, Moustakas II, Pyrina I, Lembessis P, Koutsilieris M, Chatzigeorgiou A
(See online at https://doi.org/10.3748/wjg.v26.i17.1993) - Robo4-mediated pancreatic endothelial integrity decreases inflammation and islet destruction in autoimmune diabetes. FASEB J. 2020 Feb;34(2):3336-3346
Troullinaki M, Chen LS, Witt A, Pyrina I, Phieler J, Kourtzelis I, Chmelar J, Sprott D, Gercken B, Koutsilieris M, Chavakis T, Chatzigeorgiou A
(See online at https://doi.org/10.1096/fj.201900125rr) - The Role of Senescence in the Development of Nonalcoholic Fatty Liver Disease and Progression to Nonalcoholic Steatohepatitis. Hepatology. 2020 Jan;71(1):363-374
Papatheodoridi AM, Chrysavgis L, Koutsilieris M, Chatzigeorgiou A
(See online at https://doi.org/10.1002/hep.30834)
