Chromogranin A regulates gut permeability via the antagonistic actions of its proteolytic peptides

AIM: A 'leaky' gut barrier has been implicated in the initiation and progression of a multitude of diseases, e.g., inflammatory bowel disease (IBD), irritable bowel syndrome, and celiac disease. Here we show how pro-hormone Chromogranin A (CgA), produced by the enteroendocrine cells, and Catestatin (CST: hCgA352-372 ), the most abundant CgA-derived proteolytic peptide, affect the gut barrier. METHODS: Colon tissues from region-specific CST-knockout (CST-KO) mice, CgA-knockout (CgA-KO) and WT mice were analyzed by immunohistochemistry, Western blot, ultrastructural and flowcytometry studies. FITC-dextran assays were used to measure intestinal barrier function. Mice were supplemented with CST or CgA fragment pancreastatin (PST: CgA250-301 ). The microbial composition of cecum was determined. CgA and CST levels were measured in blood of IBD patients. RESULTS: Plasma levels of CST were elevated in IBD patients. CST-KO mice displayed (i) elongated tight, adherens junctions and desmosomes similar to IBD patients, (ii) elevated expression of Claudin 2, and (iii) gut inflammation. Plasma FITC-dextran measurements showed increased intestinal paracellular permeability in the CST-knockout mice. This correlated with a higher ratio of Firmicutes to Bacteroidetes, a dysbiotic pattern commonly encountered in various diseases. Supplementation of CST-knockout mice with recombinant CST restored paracellular permeability and reversed inflammation, whereas CgA-knockout mice supplementation with CST and/or PST in CgA-KO mice showed that intestinal paracellular permeability is regulated by the antagonistic roles of these two peptides: CST reduces and PST increases permeability. CONCLUSION: The pro-hormone CgA regulates the intestinal paracellular permeability. CST is both necessary and sufficient to reduce permeability and primarily acts by antagonizing PST

Human regulatory T cells locally differentiate and are functionally heterogeneous within the inflamed arthritic joint

Objective: Tregs are crucial for immune regulation, and environment-driven adaptation of effector (e)Tregs is essential for local functioning. However, the extent of human Treg heterogeneity in inflammatory settings is unclear. Methods: We combined single-cell RNA- and TCR-sequencing on Tregs derived from three to six patients with juvenile idiopathic arthritis (JIA) to investigate the functional heterogeneity of human synovial fluid (SF)-derived Tregs from inflamed joints. Confirmation and suppressive function of the identified Treg clusters was assessed by flow cytometry. Results: Four Treg clusters were identified; incoming, activated eTregs with either a dominant suppressive or cytotoxic profile, and GPR56 +CD161 +CXCL13 + Tregs. Pseudotime analysis showed differentiation towards either classical eTreg profiles or GPR56 +CD161 +CXCL13 + Tregs supported by TCR data. Despite its most differentiated phenotype, GPR56 +CD161 +CXCL13 + Tregs were shown to be suppressive. Furthermore, BATF was identified as an overarching eTreg regulator, with the novel Treg-associated regulon BHLHE40 driving differentiation towards GPR56 +CD161 +CXCL13 + Tregs, and JAZF1 towards classical eTregs. Conclusion: Our study reveals a heterogeneous population of Tregs at the site of inflammation in JIA. SF Treg differentiate to a classical eTreg profile with a more dominant suppressive or cytotoxic profile that share a similar TCR repertoire, or towards GPR56 +CD161 +CXCL13 + Tregs with a more distinct TCR repertoire. Genes characterising GPR56 +CD161 +CXCL13 + Tregs were also mirrored in other T-cell subsets in both the tumor and the autoimmune setting. Finally, the identified key regulators driving SF Treg adaptation may be interesting targets for autoimmunity or tumor interventions

Homeostatic function and inflammatory activation of ileal CD8+ tissue-resident T cells is dependent on mucosal location

Background & Aims: Tissue-resident memory T (Trm) cells, both of the CD4 and CD8 lineage, have been implicated in disease flares in inflammatory bowel disease. However, data are conflicting regarding the profile of human CD8 + Trm cells, with studies suggesting both proinflammatory and regulatory functions. It is crucial to understand the functional profile of these cells in the context of (new) therapeutic strategies targeting (trafficking of) gut Trm cells. Methods: Here, we performed imaging mass cytometry, flow cytometry, and RNA-sequencing to compare lamina propria and intraepithelial CD103 +/–CD69 +CD8 + Trm cells in healthy control subjects and patients with active ileal Crohn's disease. Results: Our data revealed that lamina propria CD103 +CD69 +CD8 + T cells have a classical Trm cell profile with active pathways for regulating cell survival/death and cytokine signaling, whereas intraepithelial CD103 +CD69 +CD8 + T cells display tightly regulated innate-like cytotoxic profile. Furthermore, within lamina propria CD8 +CD103 – Trm cells, an Itgb2 +GzmK +KLRG1 + population distinct from CD103 + CD8 + Trm cells is found. During chronic inflammation, especially intraepithelial CD103 +CD69 +CD8 + T cells displayed an innate proinflammatory profile with concurrent loss of homeostatic functions. Conclusions: Altogether, these compartmental and inflammation-induced differences indicate that therapeutic strategies could have a different impact on the same immune cells depending on the local compartment and presence of an inflammatory milieu, and should be taken into account when investigating short- and long-term effects of new gut T cell–targeting drugs

Compartment-driven imprinting of intestinal CD4 T cells in inflammatory bowel disease and homeostasis

The mucosal immune system is implicated in the etiology and progression of inflammatory bowel diseases. The lamina propria and epithelium of the gut mucosa constitute two separate compartments, containing distinct T-cell populations. Human CD4 T-cell programming and regulation of lamina propria and epithelium CD4 T cells, especially during inflammation, remain incompletely understood. We performed flow cytometry, bulk, and single-cell RNA-sequencing to profile ileal lamina propria and intraepithelial CD4 T cells (CD4CD8αα, regulatory T cells (Tregs), CD69- and CD69high Trm T cells) in controls and Crohn's disease (CD) patients (paired non-inflamed and inflamed). Inflammation results in alterations of the CD4 T-cell population with a pronounced increase in Tregs and migrating/infiltrating cells. On a transcriptional level, inflammation within the epithelium induced T-cell activation, increased IFNγ responses, and an effector Treg profile. Conversely, few transcriptional changes within the lamina propria were observed. Key regulators including the chromatin remodelers ARID4B and SATB1 were found to drive compartment-specific transcriptional programming of CD4 T(reg) cells. In summary, inflammation in CD patients primarily induces changes within the epithelium and not the lamina propria. Additionally, there is compartment-specific CD4 T-cell imprinting, driven by shared regulators, between the lamina propria and the epithelium. The main consequence of intraepithelial adaptation, irrespective of inflammation, seems to be an overall dampening of broad (pro-inflammatory) responses and tight regulation of lifespan. These data suggest differential regulation of the lamina propria and epithelium, with a specific regulatory role in the inflamed epithelium

Antigen-driven PD-1+ TOX+ BHLHE40+ and PD-1+ TOX+ EOMES+ T lymphocytes regulate juvenile idiopathic arthritis in situ

T lymphocytes accumulate in inflamed tissues of patients with chronic inflammatory diseases (CIDs) and express pro-inflammatory cytokines upon re-stimulation in vitro. Further, a significant genetic linkage to MHC genes suggests that T lymphocytes play an important role in the pathogenesis of CIDs including juvenile idiopathic arthritis (JIA). However, the functions of T lymphocytes in established disease remain elusive. Here we dissect the transcriptional and the clonal heterogeneity of synovial T lymphocytes in JIA patients by single-cell RNA sequencing combined with T cell receptor profiling on the same cells. We identify clonally expanded subpopulations of T lymphocytes expressing genes reflecting recent activation by antigen in situ. A PD-1+ TOX+ EOMES+ population of CD4+ T lymphocytes expressed immune regulatory genes and chemoattractant genes for myeloid cells. A PD-1+ TOX+ BHLHE40+ population of CD4+ , and a mirror population of CD8+ T lymphocytes expressed genes driving inflammation, and genes supporting B lymphocyte activation in situ. This analysis points out that multiple types of T lymphocytes have to be targeted for therapeutic regeneration of tolerance in arthritis

Let's be adaptable: Tissue T cell adaptation in homeostasis and inflammation

Chronic inflammatory disorders such as juvenile idiopathic arthritis and Crohn’s disease are characterized by a relapsing-remitting pattern of inflammation. Many therapeutic options are aimed at suppressing the immune system. We do not know, however, how (regulatory) T cells are programmed and adapt during inflammation, and therefore what we can best target therapeutically. In this thesis we have investigated how regulatory T cells, which suppress the immune system, adapt to the environment of residence. We show that these cells acquire an overarching activated and highly suppressive profile irrespective of the type of inflammation, e.g. auto-inflammation in juvenile idiopathic arthritis or inflammation in cancer. The local environment further refines the profile with environment-specific markers for optimal local functioning. Moreover, we have studied how T cells adapt to the epithelium and lamina propria of the intestine. The profile of these cells completely differs even though these environments are separated by a basement membrane of only 7 µm. T cells in the epithelium have the ability to quickly react but also express many regulatory markers translating to an ‘activated-yet-resting’ profile. T cells in the lamina propria have an activated profile with cytokine and granzyme production to quickly react to stimuli. During inflammation in Crohn’s disease the cells in the epithelial layer acquire a profile similar to cells in the lamina propria, which could potentially prolong inflammation. Concluding, the location of a T cell is the main determinant of its profile. This thesis broadens our understanding of local programming and adaptation of the immune system

Let's be adaptable: Tissue T cell adaptation in homeostasis and inflammation

Chronic inflammatory disorders such as juvenile idiopathic arthritis and Crohn’s disease are characterized by a relapsing-remitting pattern of inflammation. Many therapeutic options are aimed at suppressing the immune system. We do not know, however, how (regulatory) T cells are programmed and adapt during inflammation, and therefore what we can best target therapeutically. In this thesis we have investigated how regulatory T cells, which suppress the immune system, adapt to the environment of residence. We show that these cells acquire an overarching activated and highly suppressive profile irrespective of the type of inflammation, e.g. auto-inflammation in juvenile idiopathic arthritis or inflammation in cancer. The local environment further refines the profile with environment-specific markers for optimal local functioning. Moreover, we have studied how T cells adapt to the epithelium and lamina propria of the intestine. The profile of these cells completely differs even though these environments are separated by a basement membrane of only 7 µm. T cells in the epithelium have the ability to quickly react but also express many regulatory markers translating to an ‘activated-yet-resting’ profile. T cells in the lamina propria have an activated profile with cytokine and granzyme production to quickly react to stimuli. During inflammation in Crohn’s disease the cells in the epithelial layer acquire a profile similar to cells in the lamina propria, which could potentially prolong inflammation. Concluding, the location of a T cell is the main determinant of its profile. This thesis broadens our understanding of local programming and adaptation of the immune system

The elusive case of human intraepithelial T cells in gut homeostasis and inflammation

The epithelial barrier of the gastrointestinal tract is home to numerous intraepithelial T cells (IETs). IETs are functionally adapted to the mucosal environment and are among the first adaptive immune cells to encounter microbial and dietary antigens. They possess hallmark features of tissue-resident T cells: they are long-lived nonmigratory cells capable of rapidly responding to antigen challenges independent of T cell recruitment from the periphery. Gut-resident T cells have been implicated in the relapsing and remitting course and persisting low-grade inflammation of chronic gastrointestinal diseases, including IBD and coeliac disease. So far, most data IETs have been derived from experimental animal models; however, IETs and the environmental makeup differ between mice and humans. With advances in techniques, the number of human studies has grown exponentially in the past 5 years. Here, we review the literature on the involvement of human IETs in gut homeostasis and inflammation, and how these cells are influenced by the microbiota and dietary antigens. Finally, targeting of IETs in therapeutic interventions is discussed. Broad insight into the function and role of human IETs in gut homeostasis and inflammation is essential to identify future diagnostic, prognostic and therapeutic strategies

Resetting the T Cell Compartment in Autoimmune Diseases With Autologous Hematopoietic Stem Cell Transplantation: An Update

Autologous hematopoietic stem cell transplantation (aHSCT) for autoimmune diseases has been applied for two decades as a treatment for refractory patients with progressive disease. The rationale behind aHSCT is that high-dose immunosuppression eliminates autoreactive T and B cells, thereby resetting the immune system. Post-aHSCT the cytotoxic CD8+ T cells normalize via clonal expansion due to homeostatic proliferation within a few months. CD4+ T cells recover primarily via thymopoiesis resulting in complete renewal of the T cell receptor (TCR) repertoire which requires years or never normalize completely. The increase in naïve T cells inducing immune tolerance, renewal of especially the regulatory TCR repertoire, and a less pro-inflammatory functional profile of the CD4+ T cells seem essential for successful immune reconstitution inducing long-term remission. There is currently a knowledge gap regarding the immune response in tissue sites post-aHSCT, as well as disease-specific factors that may determine remission or relapse. Future studies on lymphocyte dynamics and function may pave the way for optimized conditioning regimens with a more individualized approach

Resetting the T cell compartment in autoimmune diseases with autologous hematopoietic stem cell transplantation : An update

Autologous hematopoietic stem cell transplantation (aHSCT) for autoimmune diseases has been applied for two decades as a treatment for refractory patients with progressive disease. The rationale behind aHSCT is that high-dose immunosuppression eliminates autoreactive T and B cells, thereby resetting the immune system. Post-aHSCT the cytotoxic CD8+ T cells normalize via clonal expansion due to homeostatic proliferation within a few months. CD4+ T cells recover primarily via thymopoiesis resulting in complete renewal of the T cell receptor (TCR) repertoire which requires years or never normalize completely. The increase in naïve T cells inducing immune tolerance, renewal of especially the regulatory TCR repertoire, and a less pro-inflammatory functional profile of the CD4+ T cells seem essential for successful immune reconstitution inducing long-term remission. There is currently a knowledge gap regarding the immune response in tissue sites post-aHSCT, as well as disease-specific factors that may determine remission or relapse. Future studies on lymphocyte dynamics and function may pave the way for optimized conditioning regimens with a more individualized approach