Interleukin 21 Drives a Hypermetabolic State and CD4+ T-Cell-Associated Pathogenicity in Chronic Intestinal Inflammation

BACKGROUND & AIMS

Incapacitated regulatory T cells (Tregs) contribute to immune-mediated diseases. Inflammatory Tregs are evident during human inflammatory bowel disease; however, mechanisms driving the development of these cells and their function are not well understood. Therefore, we investigated the role of cellular metabolism in Tregs relevant to gut homeostasis.

METHODS

Using human Tregs, we performed mitochondrial ultrastructural studies via electron microscopy and confocal imaging, biochemical and protein analyses using proximity ligation assay, immunoblotting, mass cytometry and fluorescence-activated cell sorting, metabolomics, gene expression analysis, and real-time metabolic profiling utilizing the Seahorse XF analyzer. We used a Crohn's disease single-cell RNA sequencing dataset to infer the therapeutic relevance of targeting metabolic pathways in inflammatory Tregs. We examined the superior functionality of genetically modified Tregs in CD4+ T-cell-induced murine colitis models.

RESULTS

Mitochondria-endoplasmic reticulum appositions, known to mediate pyruvate entry into mitochondria via voltage-dependent anion channel 1 (VDAC1), are abundant in Tregs. VDAC1 inhibition perturbed pyruvate metabolism, eliciting sensitization to other inflammatory signals reversible by membrane-permeable methyl pyruvate supplementation. Notably, interleukin (IL) 21 diminished mitochondria-endoplasmic reticulum appositions, resulting in enhanced enzymatic function of glycogen synthase kinase 3 β, a putative negative regulator of VDAC1, and a hypermetabolic state that amplified Treg inflammatory response. Methyl pyruvate and glycogen synthase kinase 3 β pharmacologic inhibitor (LY2090314) reversed IL21-induced metabolic rewiring and inflammatory state. Moreover, IL21-induced metabolic genes in Tregs in vitro were enriched in human Crohn's disease intestinal Tregs. Adoptively transferred Il21r-/- Tregs efficiently rescued murine colitis in contrast to wild-type Tregs.

CONCLUSIONS

IL21 triggers metabolic dysfunction associated with Treg inflammatory response. Inhibiting IL21-induced metabolism in Tregs may mitigate CD4+ T-cell-driven chronic intestinal inflammation.

G9a Modulates Lipid Metabolism in CD4 T Cells to Regulate Intestinal Inflammation

BACKGROUND & AIMS

Although T-cell intrinsic expression of G9a has been associated with murine intestinal inflammation, mechanistic insight into the role of this methyltransferase in human T-cell differentiation is ill defined, and manipulation of G9a function for therapeutic use against inflammatory disorders is unexplored.

METHODS

Human naive T cells were isolated from peripheral blood and differentiated in vitro in the presence of a G9a inhibitor (UNC0642) before being characterized via the transcriptome (RNA sequencing), chromatin accessibility (assay for transposase-accessible chromatin by sequencing), protein expression (cytometry by time of flight, flow cytometry), metabolism (mitochondrial stress test, ultrahigh performance liquid chromatography-tandem mas spectroscopy) and function (T-cell suppression assay). The in vivo role of G9a was assessed using 3 murine models.

RESULTS

We discovered that pharmacologic inhibition of G9a enzymatic function in human CD4 T cells led to spontaneous generation of FOXP3+ T cells (G9a-inibitors-T regulatory cells [Tregs]) in vitro that faithfully reproduce human Tregs, functionally and phenotypically. Mechanistically, G9a inhibition altered the transcriptional regulation of genes involved in lipid biosynthesis in T cells, resulting in increased intracellular cholesterol. Metabolomic profiling of G9a-inibitors-Tregs confirmed elevated lipid pathways that support Treg development through oxidative phosphorylation and enhanced lipid membrane composition. Pharmacologic G9a inhibition promoted Treg expansion in vivo upon antigen (gliadin) stimulation and ameliorated acute trinitrobenzene sulfonic acid-induced colitis secondary to tissue-specific Treg development. Finally, Tregs lacking G9a expression (G9a-knockout Tregs) remain functional chronically and can rescue T-cell transfer-induced colitis.

CONCLUSION

G9a inhibition promotes cholesterol metabolism in T cells, favoring a metabolic profile that facilitates Treg development in vitro and in vivo. Our data support the potential use of G9a inhibitors in the treatment of immune-mediated conditions including inflammatory bowel disease.

IBD Journal Editorial Fellowship: A Practical Guide for Future Fellows

Inflammatory Bowel Diseases offers an editorial fellowship for GI and IBD fellows with a background in clinical, translational, and basic research and who are interested to experience the editorial process. Herein, the inaugural fellows compile their experience as a guide for future applicants on the fellowship’s responsibilities and highlights.

Child-Turcotte-Pugh versus MELD-XI identify distinct high-risk populations for heart transplantation following ventricular assist device placement

BACKGROUND

Patients with end-stage heart failure frequently have significant congestive hepatopathy requiring hepatology assessment prior to heart transplantation listing. An elevated Model for End-stage Liver Disease score with modification to exclude INR (MELD-XI) has been associated with increased mortality following heart transplantation (HT). This study's primary aim was to examine whether Child-Turcotte-Pugh (CTP) classification is associated with post-transplant mortality in patients bridged to transplant with left ventricular assist devices.

METHODS AND RESULTS

We conducted a retrospective analysis of 134 patients from our center. Age, CTP class, and MELD-XI at HT were included in the multivariate model for the primary outcome, which demonstrated a significant association between 1-year mortality and CTP class (CTP-A HR: .08, CI .01-.46, P < .01; CTP-B HR: .25, CI .05-1.2, P = .08; reference group CTP-C), and MELD-XI (HR: 1.15; CI: 1.03-1.28; P = .01), but no significant difference for age (HR: .97; CI: .93-1.01; P = .15). Only 13/33 patients with CTP improvement after assist device also had improvement in MELD-XI.

CONCLUSIONS

Patients with relatively low MELD-XI scores with discordantly high CTP classification may be a distinct subset for whom MELD-XI underestimates the risk of mortality after heart transplantation compared to CTP.

Evaluation of Charcot Triad, Reynolds Pentad, and Tokyo Guidelines for Diagnosis of Cholangitis Secondary to Choledocholithiasis Across Patient Age Groups

Objective

To determine the prevalence of Charcot triad, Reynolds pentad, and Tokyo Guidelines criteria and clinical outcomes among patients with cholangitis across different age groups.

Patients and Methods

We conducted a retrospective analysis of 257 consecutive hospitalized adult patients with acute cholangitis due to endoscopic retrograde cholangiopancreatography–confirmed choledocholithiasis between January 1, 2015, and December 31, 2019. Patients were divided into 3 age groups: less than 65 years, 65 to 79 years, and 80 years or older. Symptoms, vital signs, and laboratory data on admission were collected. Outcomes included length of hospitalization, intensive care unit stay, and 3-month mortality. Nominal variables were tested with the Pearson χ² test, and continuous variables were tested with the Wilcoxon rank sum test.

Results

Charcot triad decreased with older ages. In the group that was age 80 years or older, malaise was the most common symptom; 33.6% (37 of 110) presented with altered sensorium, 9.1% (10 of 110) had no pain, fever, or jaundice, and positive blood culture results were more frequent. Tokyo cholestasis criterion was present in 96.0% (247 of 257), while inflammation (considered essential for diagnosis) was present in 75.9% (195 of 257). Patients 80 years or older had significantly higher mean length of hospital stay (P<.001) and mean length of intensive care unit stay (P=.021).

Conclusion

Compared with patients in younger age groups, patients with cholangitis who are 80 years or older are less likely to have Charcot triad, are more likely to have features of Reynolds pentad, or present with unexplained malaise. Within the Tokyo Guidelines, cholestasis should replace inflammation as an essential diagnostic criterion.

Antibody-Dependent Cellular Phagocytosis by Macrophages is a Novel Mechanism of Action of Elotuzumab

Elotuzumab, a recently approved antibody for the treatment of multiple myeloma, has been shown to stimulate Fcγ receptor (FcγR)-mediated antibody-dependent cellular cytotoxicity by natural killer (NK) cells toward myeloma cells. The modulatory effects of elotuzumab on other effector cells in the tumor microenvironment, however, has not been fully explored. Antibody-dependent cellular phagocytosis (ADCP) is a mechanism by which macrophages contribute to antitumor potency of monoclonal antibodies. Herein, we studied the NK cell independent effect of elotuzumab on tumor-associated macrophages using a xenograft tumor model deficient in NK and adaptive immune cells. We demonstrate significant antitumor efficacy of single-agent elotuzumab in immunocompromised xenograft models of multiple myeloma, which is in part mediated by Fc-FcγR interaction of elotuzumab with macrophages. Elotuzumab is shown in this study to induce phenotypic activation of macrophages in vivo and mediates ADCP of myeloma cells though a FcγR-dependent manner in vitro Together, these findings propose a novel immune-mediated mechanism by which elotuzumab exerts anti-myeloma activity and helps to provide rationale for combination therapies that can enhance macrophage activity. Mol Cancer Ther; 17(7); 1454-63. ©2018 AACR.

Human regulatory T cells undergo self-inflicted damage via granzyme pathways upon activation

Tregs hold great promise as a cellular therapy for multiple immunologically mediated diseases, given their ability to control immune responses. The success of such strategies depends on the expansion of healthy, suppressive Tregs ex vivo and in vivo following the transfer. In clinical studies, levels of transferred Tregs decline sharply in the blood within a few days of the transfer. Tregs have a high rate of apoptosis. Here, we describe a new mechanism of Treg self-inflicted damage. We show that granzymes A and -B (GrA and GrB), which are highly upregulated in human Tregs upon stimulation, leak out of cytotoxic granules to induce cleavage of cytoplasmic and nuclear substrates, precipitating apoptosis in target cells. GrA and GrB substrates were protected from cleavage by inhibiting granzyme activity in vitro. Additionally, we show - by using cytometry by time of flight (CYTOF) - an increase in GrB-expressing Tregs in the peripheral blood and renal allografts of transplant recipients undergoing rejection. These GrB-expressing Tregs showed an activated phenotype but were significantly more apoptotic than non-GrB expressing Tregs. This potentially novel finding improves our understanding of Treg survival and suggests that manipulating Gr expression or activity might be useful for designing more effective Treg therapies.

Tiam1/Rac1 complex controls Il17a transcription and autoimmunity

RORγt is a master transcription factor of Th17 cells and considered as a promising drug target for the treatment of autoimmune diseases. Here, we show the guanine nucleotide exchange factor, Tiam1, and its cognate Rho-family G protein, Rac1, regulate interleukin (IL)17A transcription and autoimmunity. Whereas Tiam1 genetic deficiency weakens IL-17A expression partially and inhibits the development of experimental autoimmune encephalomyelitis (EAE), deletion of Rac1 in T cells exhibits more robust effects on Th17 cells and EAE. We demonstrate Tiam1 and Rac1 form a complex with RORγt in the nuclear compartment of Th17 cells, and together bind and activate the Il17 promoter. The clinical relevance of these findings is emphasized by pharmacological targeting of Rac1 that suppresses both murine and human Th17 cells as well as EAE. Thus, our findings highlight a regulatory pathway of Tiam1/Rac1 in Th17 cells and suggest that it may be a therapeutic target in multiple sclerosis.

Tiam1 is a guanine nucleotide exchange factor for the Rho-family GTPase Rac1. Here, the authors show that nuclear Tiam1 and Rac1 bind to RORγt on the IL-17 promoter, activating its transcription, and that inhibiting Tiam1/Rac1 is beneficial in a mouse model of autoimmunity.

BCL6 controls Th9 cell development by repressing Il9 transcription

The transcriptional repressor B cell lymphoma 6 (BCL6) is required for the development of Th follicular cells, and it has been shown to suppress Th2 cell differentiation. We demonstrate that BCL6 is a key regulator of Th9 cell development. BCL6 expression is transiently downregulated in polarized Th9 cells, and forced expression of BCL6 in Th9 cells impairs Th9 cell differentiation. In contrast, BCL6 knockdown upregulated IL-9 production in Th9 cells. The function of BCL6 in Th9 cells is under the control of IL-2/JAK3/STAT5 signaling pathway. Using chromatin immunoprecipitation, we show that, in Th9 cells, BCL6 and STAT5 bind to adjacent motifs in the Il9 promoter. Furthermore, we found that STAT5 binding was associated with the abundance of a permissive histone mark at the Il9 promoter, whereas under conditions in which BCL6 binding was predominant, a repressive histone mark was prevalent. The effects of STAT5 and BCL6 on IL-9 transcription were further demonstrated using an IL-9 luciferase reporter assay in which BCL6 repressed STAT5-mediated Il9 transactivation. In experimental autoimmune encephalomyelitis, forced expression of BCL6 in myelin oligodendrocyte glycoprotein35-55-specific Th9 cells resulted in decreased IL-9 production and induction of IFN-γ, causing an exacerbation of the clinical disease. Our findings demonstrate a novel role of BCL6 in the regulation of Th9 cell development and their encephalitogenicity.