TGF-β Suppresses β-Catenin-Dependent Tolerogenic Activation Program in Dendritic Cells

The mechanisms that underlie the critical dendritic cell (DC) function in maintainance of peripheral immune tolerance are incompletely understood, although the β-catenin signaling pathway is critical for this role. The molecular details by which β-catenin signaling is regulated in DCs are unknown. Mechanical disruption of murine bone marrow-derived DC (BMDC) clusters activates DCs while maintaining their tolerogenic potential and this activation is associated with β-catenin signaling, providing a useful model with which to explore tolerance-associated β-catenin signaling in DCs. In this report, we demonstrate novel molecular features of the signaling events that control DC activation in response to mechanical stimulation. Non-canonical β-catenin signaling is an essential component of this tolerogenic activation and is modulated by adhesion molecules, including integrins. This unique β-catenin-dependent signaling pathway is constitutively active at low levels, suggesting that mechanical stimulation is not necessarily required for induction of this unique activation program. We additionally find that the immunomodulatory cytokine TGF-β antagonizes β-catenin in DCs, thereby selectively suppressing signaling associated with tolerogenic DC activation while having no impact on LPS-induced, β-catenin-independent immunogenic activation. These findings provide new molecular insight into the regulation of a critical signaling pathway for DC function in peripheral immune tolerance

Transcriptional programming of dendritic cells for enhanced MHC class II antigen presentation

6 1 Dendritic cells (DCs) orchestrate adaptive immune responses by efficiently processing and presenting pathogen-derived peptides in complex with major histocompatibility complex (MHC) class I or MHC class II molecules, resulting in the activation of functionally distinct antigen-specific CTL or helper T cells, respectively 1 . Targeted delivery of antigens in vivo to CD11b − or CD11b + DCs and the 'preferential' activation of cytotoxic or helper T cells, respectively, suggests a functional divergence among DC subsets for MHCI versus MHC class II antigen presentation that mirrors the dichotomy of effector T cells 2 . These functional differences seem to reflect cell-intrinsic features of DC subsets and are correlated with differences in expression of genes associated with the MHC class I and MHC class II antigen presentation pathways 2 . The regulatory determinants and molecular basis of functional specialization among DC subsets remain to be established. Investigations of functional heterogeneity among DC subsets in vivo have relied heavily on correlations between the expression of various cell surface markers and a variety of cellular and functional properties-for example, correlation of the expression of CD8α or CD103 on select DC subsets with the specialization of those populations for cross-presentation. As the expression of surface markers used to discriminate DC populations can vary according to their environmental niche or functional state, such analyses can result in misleading conclusions. In contrast, the transcriptional determinants and gene targets that program cellular fate and effector functions are robust to environmental perturbation. Therefore, elucidation of the gene-regulatory networks that underlie development and differentiation of DC subsets is essential to illuminate the unifying principles that govern shared and divergent functions of these populations 3 . The development of mouse models that allow genetic ablation of select DC subsets has enabled substantial advances in this regard. Deficiency of the transcription factor BATF3 results in the selective loss of resident and migratory CD11b − but not CD11b + DCs 4 . BATF3-deficient mice show impaired anti-viral and anti-tumor CTL responses while helper T cell-mediated antibody responses are unaffected 5 . These findings provide crucial genetic evidence for a predominant role of CD11b − DCs in CTL immunity. However, genetic analysis of CD11b + DCs and their proposed role in priming helper T cell immune responses has been lacking 3 . The closely related immune-specific transcription factors IRF4 and IRF8 are attractive candidates as key determinants of the functionally specialized states of DCs. IRF8 is required for the development of resident and migratory CD11b − DCs, whereas IRF4 is critical for the generation of their CD11b + counterparts 4,6-10 . In keeping with their subset-specific developmental functions, IRF4 and IRF8 are expressed reciprocally in CD11b + and CD11b − splenic, lung and gut DC population

Blood transcriptomic signature in type-2 biomarker low severe asthma and asthma control.

BackgroundPatients with Type-2 (T2) cytokine-low severe asthma often have persistent symptoms despite suppression of T2-inflammation with corticosteroids (CS).ObjectivesTo analyze whole blood transcriptome from 738 samples in T2-biomarker high/low severe asthma patients to relate transcriptomic signatures to T2-biomarkers and asthma symptom scores.MethodsBulk RNAseq data were generated for blood samples (baseline, Week24, Week48) from 301 participants recruited to a randomized clinical trial of CS optimization in severe asthma. Unsupervised clustering, differential gene expression analysis, and pathway analysis were performed. Patients were grouped by T2-biomarker status and symptoms. Associations between clinical characteristics and differentially expressed genes (DEGs) associated with biomarker and symptom levels were investigated.ResultsUnsupervised clustering identified two clusters; Cluster 2 patients were blood eosinophil low/symptom high and more likely to be receiving oral CS (OCS). Differential gene expression analysis of these clusters, with and without stratification for OCS, identified 2,960 and 4,162 DEGs respectively. 627/2,960 genes remained after adjusting for OCS by subtracting OCS signature genes. Pathway analysis identified dolichyl-diphosphooligosaccharide biosynthesis and assembly of RNA polymerase I complex as significantly enriched pathways. No stable DEGs were associated with high symptoms in T2-biomarker low patients, but numerous associated with elevated T2-biomarkers, including 15 that were up-regulated at all time-points irrespective of symptom level.ConclusionsOCS have a considerable effect on whole blood transcriptome. DEG analysis demonstrates a clear T2-biomarker transcriptomic signature, but no signature was found in association with T2-biomarker low patients, including those with a high symptom burden