The branched-chain amino acid transporter CD98 heavy chain facilitates the development of colonic macrophages associated with apoptosis in macrophage progenitors

CX3CR1+ mononuclear phagocytes extend processes into the intestinal lumen to monitor the intestinal microbiota as well as the chymus. Whether the constituents of the chymus are required for macrophages is not known. Moreover, the molecular mechanisms that control the intestinal ability to distinguish between "innocuous" and "dangerous" antigens remain poorly understood although macrophages play a key role in this process. A comprehensive macrophage development is critical for gut macrophages performing crucial tasks in the intestinal immune system. However, the underlying mechanisms of this development remain elusive. The amino acid transporter CD98, which was first identified as a lymphocyte activation marker, is a multifunctional protein and is associated with a variety of activities, such as those of amino acid transporters, integrin regulators, and fusion regulators. CD98hc interacts with certain integrin β-subunits to mediate signaling events and consequently controls cell migration, survival, and proliferation. To assess the role of branched-chain amino acids on the development of gut macrophages, we generated an inducible knock-out mouse model for the branched-chain amino acid transporter CD98hc specifically in CX3CR1+ intestinal macrophages. We showed that CD98 deficient macrophages attenuate the severity of dextran sodium sulfate-induced colitis clinically, endoscopically, and histologically. Single-cell RNA sequencing of colonic lamina propria macrophages obtained from unmanipulated and healthy mice revealed that silencing CD98 blocks the ‘monocyte waterfall’-development to mature macrophages. Further, we observed that the arrest in macrophage development is associated with increased expression of apoptotic genes. Moreover, patients with Crohn’s disease and ulcerative colitis are characterized by high CD98 expression. Our results demonstrate that CD98 plays a pivotal role in intestinal homeostasis by influencing the development of gut macrophages

IL-20 subfamily cytokines impair the oesophageal epithelial barrier by diminishing filaggrin in eosinophilic oesophagitis.

OBJECTIVE Disruption of the epithelial barrier plays an essential role in developing eosinophilic oesophagitis (EoE), a disease defined by type 2 helper T cell (Th2)-mediated food-associated and aeroallergen-associated chronic inflammation. Although an increased expression of interleukin (IL)-20 subfamily members, IL-19, IL-20 and IL-24, in Th2-mediated diseases has been reported, their function in EoE remains unknown. DESIGN Combining transcriptomic, proteomic and functional analyses, we studied the importance of the IL-20 subfamily for EoE using patient-derived oesophageal three-dimensional models and an EoE mouse model. RESULTS Patients with active EoE have increased expression of IL-20 subfamily cytokines in the oesophagus and serum. In patient-derived oesophageal organoids stimulated with IL-20 cytokines, RNA sequencing and mass spectrometry revealed a downregulation of genes and proteins forming the cornified envelope, including filaggrins. On the contrary, abrogation of IL-20 subfamily signalling in Il20R2 -/- animals resulted in attenuated experimental EoE reflected by reduced eosinophil infiltration, lower Th2 cytokine expression and preserved expression of filaggrins in the oesophagus. Mechanistically, these observations were mediated by the mitogen-activated protein kinase (MAPK); extracellular-signal regulated kinases (ERK)1/2) pathway. Its blockade prevented epithelial barrier impairment in patient-derived air-liquid interface cultures stimulated with IL-20 cytokines and attenuated experimental EoE in mice. CONCLUSION Our findings reveal a previously unknown regulatory role of the IL-20 subfamily for oesophageal barrier function in the context of EoE. We propose that aberrant IL-20 subfamily signalling disturbs the oesophageal epithelial barrier integrity and promotes EoE development. Our study suggests that specific targeting of the IL-20 subfamily signalling pathway may present a novel strategy for the treatment of EoE

Loss of the branched-chain amino acid transporter CD98hc alters the development of colonic macrophages in mice

Comprehensive development is critical for gut macrophages being essential for the intestinal immune system. However, the underlying mechanisms of macrophage development in the colon remain elusive. To investigate the function of branched-chain amino acids in the development of gut macrophages, an inducible knock-out mouse model for the branched-chain amino acid transporter CD98hc in CX3CR1+ macrophages was generated. The relatively selective deletion of CD98hc in macrophage populations leads to attenuated severity of chemically-induced colitis that we assessed by clinical, endoscopic, and histological scoring. Single-cell RNA sequencing of colonic lamina propria macrophages revealed that conditional deletion of CD98hc alters the "monocyte waterfall"-development to MHC II+ macrophages. The change in the macrophage development after deletion of CD98hc is associated with increased apoptotic gene expression. Our results show that CD98hc deletion changes the development of colonic macrophages

Epithelial GPR35 protects from Citrobacter rodentium infection by preserving goblet cells and mucosal barrier integrity.

Goblet cells secrete mucin to create a protective mucus layer against invasive bacterial infection and are therefore essential for maintaining intestinal health. However, the molecular pathways that regulate goblet cell function remain largely unknown. Although GPR35 is highly expressed in colonic epithelial cells, its importance in promoting the epithelial barrier is unclear. In this study, we show that epithelial Gpr35 plays a critical role in goblet cell function. In mice, cell-type-specific deletion of Gpr35 in epithelial cells but not in macrophages results in goblet cell depletion and dysbiosis, rendering these animals more susceptible to Citrobacter rodentium infection. Mechanistically, scRNA-seq analysis indicates that signaling of epithelial Gpr35 is essential to maintain normal pyroptosis levels in goblet cells. Our work shows that the epithelial presence of Gpr35 is a critical element for the function of goblet cell-mediated symbiosis between host and microbiota

Loss of the branched-chain amino acid transporter CD98hc alters the development of colonic macrophages in mice.

Comprehensive development is critical for gut macrophages being essential for the intestinal immune system. However, the underlying mechanisms of macrophage development in the colon remain elusive. To investigate the function of branched-chain amino acids in the development of gut macrophages, an inducible knock-out mouse model for the branched-chain amino acid transporter CD98hc in CX3CR1 macrophages was generated. The relatively selective deletion of CD98hc in macrophage populations leads to attenuated severity of chemically-induced colitis that we assessed by clinical, endoscopic, and histological scoring. Single-cell RNA sequencing of colonic lamina propria macrophages revealed that conditional deletion of CD98hc alters the "monocyte waterfall"-development to MHC II macrophages. The change in the macrophage development after deletion of CD98hc is associated with increased apoptotic gene expression. Our results show that CD98hc deletion changes the development of colonic macrophages

Epithelial GPR35 protects from Citrobacter rodentium infection by preserving goblet cells and mucosal barrier integrity

Goblet cells secrete mucin to create a protective mucus layer against invasive bacterial infection and are therefore essential for maintaining intestinal health. However, the molecular pathways that regulate goblet cell function remain largely unknown. Although GPR35 is highly expressed in colonic epithelial cells, its importance in promoting the epithelial barrier is unclear. In this study, we show that epithelial Gpr35 plays a critical role in goblet cell function. In mice, cell-type-specific deletion of Gpr35 in epithelial cells but not in macrophages results in goblet cell depletion and dysbiosis, rendering these animals more susceptible to Citrobacter rodentium infection. Mechanistically, scRNA-seq analysis indicates that signaling of epithelial Gpr35 is essential to maintain normal pyroptosis levels in goblet cells. Our work shows that the epithelial presence of Gpr35 is a critical element for the function of goblet cell-mediated symbiosis between host and microbiota