Notch receptor-ligand interactions during T cell development, a ligand endocytosis-driven mechanism

Investigation of the Shared Biomarkers in Heterotopic Ossification Between Ossification of the Ligamentum Flavum and Ankylosing Spondylitis

STUDY DESIGN

Bioinformatics analysis of Gene Expression Omnibus (GEO).

OBJECTIVE

Ossification of the ligamentum flavum (OLF) and ankylosing spondylitis (AS) represent intricate conditions marked by the gradual progression of endochondral ossification. This investigation endeavors to unveil common biomarkers associated with heterotopic ossification and explore the potential molecular regulatory mechanisms.

METHODS

Microarray and RNA-sequencing datasets retrieved from the Gene Expression Omnibus (GEO) repository were harnessed to discern differentially expressed genes (DEGs) within the OLF and AS datasets. Subsequently, Weighted Gene Co-expression Network Analysis (WGCNA) was implemented to pinpoint co-expression modules linked to OLF and AS. Common genes were further subjected to an examination of functional pathway enrichment. Moreover, hub intersection genes were identified using the Least Absolute Shrinkage and Selection Operator (LASSO) regression, followed by an evaluation of diagnostic performance in external OLF and AS cohorts. Lastly, an analysis of immune cell infiltration was conducted to scrutinize the correlation of immune cell presence with shared biomarkers in OLF and AS.

RESULTS

A total of 1353 and 91 Differentially Expressed Genes (DEGs) were identified in OLF and AS, respectively. Using the Weighted Gene Co-expression Network Analysis (WGCNA), 2 modules were found to be notably significant for OLF and AS. The integrative bioinformatic analysis revealed 3 hub genes (MAB21L2, MEGF10, ISLR) as shared risk biomarkers, with MAB21L2 being the central focus. Receiver Operating Characteristic (ROC) analysis exhibited a strong diagnostic potential for these hub genes. Gene Ontology (GO) analysis indicated their involvement in the positive regulation of myoblast proliferation. Notably, MAB21L2 was singled out as the optimal common biomarker for OLF and AS. Furthermore, an analysis of immune infiltration demonstrated a correlation between MAB21L2 expression and changes in immune cells. Activated CD8 T cells were identified as shared differential immune infiltrating cells significantly linked to MAB21L2 in both OLF and AS.

CONCLUSION

This study represents the first instance of identifying MAB21L2 as a prospective diagnostic marker for patients contending with OLF associated with AS. The research results indicate that the ECM-receptor interaction and the cell-cell adhesion may play a role in both disease processes. This newfound knowledge not only enhances our understanding of the pathogenesis behind spinal ligament ossification but also uncovers potential targets for therapeutic interventions.

Differential Effects of Four Canonical Notch-Activating Ligands on c-Kit+ Cardiac Progenitor Cells

Notch signaling, an important signaling pathway in cardiac development, has been shown to mediate the reparative functions of c-kit+ progenitor cells (CPCs). However, it is unclear how each of the four canonical Notch-activating ligands affects intracellular processes in c-kit+ cells when used as an external stimulus. Neonatal c-kit+ CPCs were stimulated using four different chimeric Notch-activating ligands tethered to Dynabeads, and the resulting changes were assessed using TaqMan gene expression arrays, with subsequent analysis by principal component analysis (PCA). Additionally, functional outcomes were measured using an endothelial cell tube formation assay and MSC migration assay to assess the paracrine capacity to stimulate new vessel formation and recruit other reparative cell types to the site of injury. Gene expression data showed that stimulation with Jagged-1 is associated with the greatest pro-angiogenic gene response, including the expression of VEGF and basement membrane proteins, while the other canonical ligands, Jagged-2, Dll-1, and Dll-4, are more associated with regulatory and epigenetic changes. The functional assay showed differential responses to the four ligands in terms of angiogenesis, while none of the ligands produced a robust change in migration. These data demonstrate how the four Notch-activating ligands differentially regulate CPC gene expression and function.

DL4-μbeads induce T cell lineage differentiation from stem cells in a stromal cell-free system

T cells are pivotal effectors of the immune system and can be harnessed as therapeutics for regenerative medicine and cancer immunotherapy. An unmet challenge in the field is the development of a clinically relevant system that is readily scalable to generate large numbers of T-lineage cells from hematopoietic stem/progenitor cells (HSPCs). Here, we report a stromal cell-free, microbead-based approach that supports the efficient in vitro development of both human progenitor T (proT) cells and T-lineage cells from CD34⁺cells sourced from cord blood, GCSF-mobilized peripheral blood, and pluripotent stem cells (PSCs). DL4-μbeads, along with lymphopoietic cytokines, induce an ordered sequence of differentiation from CD34⁺ cells to CD34⁺CD7⁺CD5⁺ proT cells to CD3⁺αβ T cells. Single-cell RNA sequencing of human PSC-derived proT cells reveals a transcriptional profile similar to the earliest thymocytes found in the embryonic and fetal thymus. Furthermore, the adoptive transfer of CD34⁺CD7⁺ proT cells into immunodeficient mice demonstrates efficient thymic engraftment and functional maturation of peripheral T cells. DL4-μbeads provide a simple and robust platform to both study human T cell development and facilitate the development of engineered T cell therapies from renewable sources.

T cells derived from stem cells can be harnessed for regenerative medicine and cancer immunotherapy, but current technologies limit production and translation. Here, the authors present a serum-free, stromal-cell free DLL4-coated microbead method for the scalable production of T-lineage cells from multiple sources of stem cells.

IL-18 acts in synergy with IL-7 to promote ex vivo expansion of T lymphoid progenitor cells

Although IL-18 has not previously been shown to promote T lymphopoiesis, results obtained via a novel data mining algorithm (global microarray meta-analysis) led us to explore a predicted role for this cytokine in T cell development. IL-18 is a member of the IL-1 cytokine family that has been extensively characterized as a mediator of inflammatory immune responses. To assess a potential role for IL-18 in T cell development, we sort-purified mouse bone marrow-derived common lymphoid progenitor cells, early thymic progenitors (ETPs), and double-negative 2 thymocytes and cultured these populations on OP9-Delta-like 4 stromal layers in the presence or absence of IL-18 and/or IL-7. After 1 wk of culture, IL-18 promoted proliferation and accelerated differentiation of ETPs to the double-negative 3 stage, similar in efficiency to IL-7. IL-18 showed synergy with IL-7 and enhanced proliferation of both the thymus-derived progenitor cells and the bone marrow-derived common lymphoid progenitor cells. The synergistic effect on the ETP population was further characterized and found to correlate with increased surface expression of c-Kit and IL-7 receptors on the IL-18-treated cells. In summary, we successfully validated the global microarray meta-analysis prediction that IL-18 affects T lymphopoiesis and demonstrated that IL-18 can positively impact bone marrow lymphopoiesis and T cell development, presumably via interaction with the c-Kit and IL-7 signaling axis.

Notch1 is an important mediator for enhancing of B-cell activation and antibody secretion by Notch ligand

The roles of Notch1 and Notch2 in T-cell function have been well studied, but the functional roles of Notch in B cells have not been extensively investigated, except for Notch2 involvement in peripheral marginal zone B-cell differentiation. This study examined the roles of Notch1 in murine primary B cells. During B-cell activation by B-cell receptor ligation, Notch1 was up-regulated while Notch2 was not. In addition, Notch1 up-regulation itself did not contribute to the further activation of B cells, but the Notch ligand was important for Notch1-mediated further B-cell activation. Moreover, Notch1 deficiency significantly decreased B-cell activation and antibody secretion under the presence of Notch ligand. These data suggest that Notch1 is an important mediator for enhancing B-cell activation and antibody secretion by Notch ligand.

An overview of the intrathymic intricacies of T cell development

The generation of a functional and diverse repertoire of T cells occurs in the thymus from precursors arriving from the bone marrow. In this article, we introduce the various stages of mouse thymocyte development and highlight recent work using various in vivo, and, where appropriate, in vitro models of T cell development that led to discoveries in the regulation afforded by transcription factors and receptor-ligand signaling pathways in specifying, maintaining, and promoting the T cell lineage and the production of T cells. This review also discusses the role of the thymic microenvironment in providing a niche for the successful development of T cells. In particular, we focus on advances in Notch signaling and developments in Notch ligand interactions in this process.

Intrinsic selectivity of Notch 1 for Delta-like 4 over Delta-like 1

Notch signaling makes critical contributions to cell fate determination in all metazoan organisms, yet remarkably little is known about the binding affinity of the four mammalian Notch receptors for their three Delta-like and two Jagged family ligands. Here, we utilized signaling assays and biochemical studies of purified recombinant ligand and receptor molecules to investigate the differences in signaling behavior and intrinsic affinity between Notch1-Dll1 and Notch1-Dll4 complexes. Systematic deletion mutagenesis of the human Notch1 ectodomain revealed that epidermal growth factor (EGF) repeats 6-15 are sufficient to maintain signaling in a reporter assay at levels comparable with the full-length receptor, and identified important contributions from EGF repeats 8-10 in conveying an activating signal in response to either Dll1 or Dll4. Truncation studies of the Dll1 and Dll4 ectodomains showed that the MNNL-EGF3 region was both necessary and sufficient for full activation. Plate-based and cell binding assays revealed a specific, calcium-dependent interaction between cell-surface and recombinant Notch receptors and ligand molecules. Finally, direct measurement of the binding affinity of Notch1 EGF repeats 6-15 for Dll1 and Dll4 revealed that Dll4 binds with at least an order of magnitude higher affinity than Dll1. Together, these studies give new insights into the features of ligand recognition by Notch1, and highlight how intrinsic differences in the biochemical behavior of receptor-ligand complexes can influence receptor-mediated responses of developmental signaling pathways.