Xavier Michelet

Regulatory iNKT cells lack expression of the transcription factor PLZF and control the homeostasis of Treg cells and macrophages in adipose tissue

iNKT cells are CD1d-restricted lipid-sensing innate T cells that express the transcription factor PLZF. iNKT cells accumulate in adipose tissue, where they are anti-inflammatory, but the factors that contribute to their anti-inflammatory nature, and their targets in adipose tissue are unknown. Here we report that adipose tissue iNKT cells have a unique transcriptional program and produce interleukin 2 (IL-2) and IL-10. Unlike other iNKT cells, they lack PLZF, but express the transcription factor E4BP4, which controls their IL-10 production. Adipose iNKT cells are a tissue resident population that induces an anti-inflammatory phenotype in macrophages and, through production of IL-2, controls the number, proliferation and suppressor function of adipose regulatory T (Treg) cells. Thus, adipose tissue iNKT cells are unique regulators of immune homeostasis in this tissue.Invariant natural killer T cells (iNKT cells) are lipid-sensing innate T cells that are restricted by the antigen-presenting molecule CD1d and express the transcription factor PLZF. iNKT cells accumulate in adipose tissue, where they are anti-inflammatory, but the factors that contribute to their anti-inflammatory nature, as well as their targets in adipose tissue, are unknown. Here we found that iNKT cells in adipose tissue had a unique transcriptional program and produced interleukin 2 (IL-2) and IL-10. Unlike other iNKT cells, they lacked PLZF but expressed the transcription factor E4BP4, which controlled their IL-10 production. The adipose iNKT cells were a tissue-resident population that induced an anti-inflammatory phenotype in macrophages and, through the production of IL-2, controlled the number, proliferation and suppressor function of regulatory T cells (Treg cells) in adipose tissue. Thus, iNKT cells in adipose tissue are unique regulators of immunological homeostasis in this tissue.

The autophagosomal protein LGG-2 acts synergistically with LGG-1 in dauer formation and longevity in C. elegans

Autophagy has an important function in degrading cytoplasmic components to maintain cellular homeostasis, but is also required during development. The formation of the autophagic vesicles requires the recruitment of the Atg8 ubiquitin-like proteins to the membrane of the nascent autophagosomes. Atg8 is a highly conserved gene which has been duplicated during metazoan evolution. In this report we have investigated, in the nematode C. elegans, the functions and localizations of the two Atg8p homologues LGG-2 and LGG-1. Phylogenetic analyses suggest that LGG-2 is more closely related to the human protein LC3 than LGG-1. LGG-1 but not LGG-2 is able to functionally complement the atg8 mutant yeast. The C-terminal glycine residue of LGG-2 is essential for post-translational modification and localization to the autophagosomes. During C. elegans development the two proteins share a similar expression pattern and localization but LGG-2 is more abundant in the neurons. Using genetic tools to either reduce or increase the autophagic flux we show that both LGG-2 and LGG-1 are addressed to the autophagosomal/lysosomal degradative system. We also demonstrate that the localization of both proteins is modified in several physiological processes when autophagy is induced, namely during diapause “dauer” larval formation, starvation and aging. Finally, we demonstrate that both LGG-2 and LGG-1 act synergistically and are involved in dauer formation and longevity of the worm.

Induction of autophagy in ESCRT mutants is an adaptive response for cell survival in C. elegans.

Endosomes and autophagosomes are two vesicular compartments involved in the degradation and recycling of cellular material. They both undergo a maturation process and finally fuse with the lysosome. In mammals, the convergence between endosomes and autophagosomes is a multistep process that can generate intermediate vesicles named amphisomes. Using knockdowns and mutants of the ESCRT machinery (ESCRT-0–ESCRT-III, ATPase VPS-4) and the autophagic pathway (LGG-1, LGG-2, ATG-7, TOR), we analyzed in vivo the functional links between endosomal maturation and autophagy in Caenorhabditis elegans. We report here that, despite a strong heterogeneity of their developmental phenotypes, all ESCRT mutants present an accumulation of abnormal endosomes and autophagosomes. We show that this accumulation of autophagosomes is secondary to the formation of enlarged endosomes and is due to the induction of the autophagic flux and not a blockage of fusion with lysosomes. We demonstrate that the induction of autophagy is not responsible for the lethality of ESCRT mutants but has a protective role on cellular degradation. We also show that increasing the basal level of autophagy reduces the formation of enlarged endosomes in ESCRT mutants. Together, our data indicate that the induction of autophagy is a protective response against the formation of an abnormal vesicular compartment.

Arf-like GTPase Arl8b regulates lytic granule polarization and natural killer cell-mediated cytotoxicity

By exploiting NK cell LROs (known as lytic granules) as a model, a new role is defined for Arl8b in regulating motility and exocytosis of lytic granules of NK cells. Not only lytic granules but also the MTOC is unable to polarize toward the immune synapse formed between the NK cell and its target in Arl8b-depleted NK cells.

Adipose Type One Innate Lymphoid Cells Regulate Macrophage Homeostasis through Targeted Cytotoxicity

SUMMARY Adipose tissue has a dynamic immune system that adapts to changes in diet and maintains homeostatic tissue remodeling. Adipose type 1 innate lymphoid cells (AT1‐ILCs) promote pro‐inflammatory macrophages in obesity, but little is known about their functions at steady state. Here we found that human and murine adipose tissue harbor heterogeneous populations of AT1‐ILCs. Experiments using parabiotic mice fed a high‐fat diet (HFD) showed differential trafficking of AT1‐ILCs, particularly in response to short‐ and long‐term HFD and diet restriction. At steady state, AT1‐ILCs displayed cytotoxic activity toward adipose tissue macrophages (ATMs). Depletion of AT1‐ILCs and perforin deficiency resulted in alterations in the ratio of inflammatory to anti‐inflammatory ATMs, and adoptive transfer of AT1‐ILCs exacerbated metabolic disorder. Diet‐induced obesity impaired AT1‐ILC killing ability. Our findings reveal a role for AT1‐ILCs in regulating ATM homeostasis through cytotoxicity and suggest that this function is relevant in both homeostasis and metabolic disease. Graphical Abstract Figure. No Caption available. HighlightsAT1‐ILCs are enriched in mouse and human adipose tissue and are predominantly tissue residentAT1‐ILCs kill adipose tissue macrophages (ATMs) and maintain ATM homeostasisSubsets of AT1‐ILCs infiltrate adipose tissue during the onset of obesityIn obesity, AT1‐ILCs are reduced and lose their ability to kill &NA; Boulenouar et al. define different subsets of type 1 innate lymphoid cells (AT1‐ILCs) in human and murine adipose tissues and show that at steady state, AT1‐ILCs kill adipose tissue macrophages (ATMs). In obesity, cytotoxicity is impaired. Interference with AT1‐ILC cytotoxicity impacted ATM homeostasis and systemic metabolism, pointing to its importance in homeostasis and disease.

A Rab3a-dependent complex essential for lysosome positioning and plasma membrane repair.

Encarnação et al. show that Rab3a, together with its newly identified effector NMHC IIA, mediates the positioning of peripheral lysosomes in nonsecretory cells, thereby promoting lysosome exocytosis and plasma membrane repair.

MHC Class II Presentation Is Controlled by the Lysosomal Small GTPase, Arl8b

Dendritic cells (DCs) are specialized APCs with the ability to prime naive T cells. DCs first sample Ags from the environment and then orchestrate their processing and loading onto MHC class II (MHC II) Ag-presenting molecules in lysosomes. Once MHC II molecules have bound a peptide, the MHC II–peptide complex is delivered to the cell surface for presentation to CD4+ T cells. Regulation of Ag uptake via macropinocytosis and phagocytosis has been extensively studied, as well as trafficking in early endocytic vesicles notably regulated by the small GTPase Rab5 and its effectors. However, little is known about the regulators of Ag delivery from early endosomes to lysosomal compartments where the proper pH, proteases, MHC II, invariant chain, and HLA-DM reside, awaiting exogenous Ags for loading. In this article, we report the crucial role of the small GTPase ADP-ribosylation factor-like 8b (Arl8b) in MHC II presentation in DCs. We show for the first time, to our knowledge, that Arl8b localizes to MHC II compartments in DCs and regulates formation of MHC II–peptide complexes. Arl8b-silenced DCs display a defect in MHC II–Ag complex formation and its delivery to the cell surface during infection resulting in a defect in T cell recognition. Our results highlight the role of Arl8b as a trafficking regulator of the late stage of complex formation and MHC II presentation in DCs.

Autophagy in endosomal mutants: Desperately seeking to survive

The endosomal and autophagic pathways are essential for the degradation and renewal of cellular components. After a complex maturation process, both pathways converge to their final destination, the lysosome. A close link between these two pathways was described along the last decade, notably through the analysis of ESCRT mutants. Although in mammals ESCRT mutants are unable to complete autophagic maturation due to the lack of fusion with the endolysosomal system, the role of ESCRT in the autophagic process still remains an open issue. Using C. elegans, we recently showed that blockage of the endosomal maturation triggers the induction of autophagic activity in ESCRT mutant.1 This increase of autophagic flux is an attempt to correct cellular defects and promote the survival of mutant animals.

Stromal cell cadherin-11 regulates adipose tissue inflammation and diabetes

M2 macrophages, innate lymphoid type 2 cells (ILC2s), eosinophils, Tregs, and invariant NK T cells (iNKT cells) all help to control adipose tissue inflammation, while M1 macrophages, TNF, and other inflammatory cytokines drive inflammation and insulin resistance in obesity. Stromal cells regulate leukocyte responses in lymph nodes, but the role of stromal cells in adipose tissue inflammation is unknown. PDGFRα+ stromal cells are major producers of IL-33 in adipose tissue. Here, we show that mesenchymal cadherin-11 modulates stromal fibroblast function. Cadherin-11-deficient mice displayed increased stromal production of IL-33, with concomitant enhancements in ILC2s and M2 macrophages that helped control adipose tissue inflammation. Higher expression levels of IL-33 in cadherin-11-deficient mice mediated ILC2 activation, resulting in higher IL-13 expression levels and M2 macrophage expansion in adipose tissue. Consistent with reduced adipose tissue inflammation, cadherin-11-deficient mice were protected from obesity-induced glucose intolerance and adipose tissue fibrosis. Importantly, anti-cadherin-11 mAb blockade similarly improved inflammation and glycemic control in obese WT mice. These results suggest that stromal fibroblasts expressing cadherin-11 regulate adipose tissue inflammation and thus highlight cadherin-11 as a potential therapeutic target for the management of obesity.

The ESCRT-II proteins are involved in shaping the sarcoplasmic reticulum in C. elegans.

ABSTRACT The sarcoplasmic reticulum is a network of tubules and cisternae localized in close association with the contractile apparatus, and regulates Ca2+ dynamics within striated muscle cell. The sarcoplasmic reticulum maintains its shape and organization despite repeated muscle cell contractions, through mechanisms which are still under investigation. The ESCRT complexes are essential to organize membrane subdomains and modify membrane topology in multiple cellular processes. Here, we report for the first time that ESCRT-II proteins play a role in the maintenance of sarcoplasmic reticulum integrity in C. elegans. ESCRT-II proteins colocalize with the sarcoplasmic reticulum marker ryanodine receptor UNC-68. The localization at the sarcoplasmic reticulum of ESCRT-II and UNC-68 are mutually dependent. Furthermore, the characterization of ESCRT-II mutants revealed a fragmentation of the sarcoplasmic reticulum network, associated with an alteration of Ca2+ dynamics. Our data provide evidence that ESCRT-II proteins are involved in sarcoplasmic reticulum shaping. Summary: We report that endosomal sorting complex required for transport ESCRT-II proteins are required for the maintenance of the sarcoplasmic reticulum integrity in C. elegans body wall muscle cells.