Signaling from membrane semaphorin 4D in T lymphocytes

Research Advances in the Immunomodulatory Functions of CD100/SEMA4D and Their Roles in Viral Infectious Diseases

CD100/SEMA4D, a member of the Semaphorin family, is a transmembrane glycoprotein that regulates neurogenesis, immune modulation, and angiogenesis, with its immunoregulatory roles having attracted considerable attention. It is dynamically expressed on the surface of diverse immune cells-including T cells, B cells, dendritic cells (DCs), and natural killer (NK) cells-with expression levels modulated by cellular activation states. CD100 exists in two functional forms: membrane-bound CD100 (mCD100) and soluble CD100 (sCD100) generated via proteolytic cleavage. Recent studies have highlighted its critical involvement in viral infectious diseases. This review systematically summarizes the molecular characteristics, expression patterns, and regulatory functions of CD100 on different immune cells, and discusses its role in viral infectious diseases and its clinical application potential.

Downregulation of N6-methyladenosine (m6A) methylation of Sema4D mRNA contributes to Treg dysfunction and allograft rejection

Regulatory T cells (Tregs) have been shown to be involved in the induction of transplantation tolerance in numerous models. Our previous work demonstrated that methyltransferase-like 14 (METTL14) loss impaired Treg function and hindered the establishment of transplantation tolerance. However, the underlying mechanisms remain unclear. In this study, we found that METTL14 knockdown in Tregs significantly impaired their regulatory function, leading to poor allograft function and accelerated transplant rejection. Using methylated RNA immunoprecipitation- and mRNA-sequencing approaches, we discovered that METTL14 deficiency fostered the expression of semaphorin 4D (Sema4D) mRNA, a key semaphorin family member with immunoregulatory activity. Methylation of target adenosines reduced Sema4D mRNA degradation, a process mediated by the METTL14-YTH N6-methyladenosine RNA binding protein 2 axis. Inhibition of Sema4D suppressed its interaction with its receptor, thereby preserving Treg immunoregulation capability and prolonging allograft survival through the p21-activated kinase-signal transducer and activator of transcription 5signaling pathway. Importantly, Sema4D expression in kidney transplant biopsies were negatively correlated with renal allograft survival. In summary, our findings suggest that METTL14 deficiency in Tregs leads to transplant rejection and reveal for the first time that Sema4D may serve as a potential therapeutic target to enhance Treg function in transplantation.

Microglia-astrocyte crosstalk is regulated by Astragalus polysaccharides mediated through suppression of Sema4D-PlexinB2 signaling in experimental autoimmune encephalomyelitis

The crosstalk between microglia inflamed in multiple sclerosis (MIMS) and astrocytes inflamed in MS (AIMS) is a crucial factor in the formation of the central inflammatory microenvironment and neurotoxicity. Astragalus polysaccharides (APS), an important bioactive component extracted from the dried root of Astragalus, was previously found by our team to attenuate the formation of pro-inflammatory microglia and neurological dysfunction in the experimental autoimmune encephalomyelitis (EAE) mice, a classic model of MS. To investigate the effect of APS on the MIMS-AIMS crosstalk and its underlying mechanism, in this study, a mouse model of EAE and a co-culture model of microglia-astrocytes in vitro were established. It was discovered that APS can alleviate the neurological dysfunction of EAE mice and effectively inhibit the formation of MIMS and AIMS both in vivo and in vitro. Furthermore, it was found that APS can suppress the inflammatory factors of MIMS-AIMS crosstalk in EAE mice and the resulting neurotoxicity in vivo and in vitro. The Sema4D-PlexinB2 signaling is essential for MIMS-AIMS crosstalk and promotes CNS inflammation. We demonstrated that APS can inhibit this signaling in vivo and in vitro. Treatment of recombinant Sema4D protein on cultured astrocytes in vitro significantly increases pro-inflammatory and neurotoxic factors, while APS significantly inhibits them. Conversely, after knockdown of Sema4D expression in microglia, APS no longer improves the neurotoxicity from MIMS-AIMS crosstalk. Overall, these results indicate that APS may modulate MIMS-AIMS crosstalk via the Sema4D-PlexinB2 signaling. This study provides a scientific basis for APS as a potential treatment candidate for demyelinating diseases.

Deciphering the CNS-glioma dialogue: Advanced insights into CNS-glioma communication pathways and their therapeutic potential

The field of cancer neuroscience has rapidly evolved, shedding light on the complex interplay between the nervous system and cancer, with a particular focus on the relationship between the central nervous system (CNS) and gliomas. Recent advancements have underscored the critical influence of CNS activity on glioma progression, emphasizing the roles of neurons and neuroglial cells in both the onset and evolution of gliomas. This review meticulously explores the primary communication pathways between the CNS and gliomas, encompassing neuro-glioma synapses, paracrine mechanisms, extracellular vesicles, tunneling nanotubes, and the integrative CNS-immune-glioma axis. It also evaluates current and emerging therapeutic interventions aimed at these pathways and proposes forward-looking perspectives for research in this domain.

Inhibition of Sema4D attenuates pressure overload-induced pathological myocardial hypertrophy via the MAPK/NF-κB/NLRP3 pathways

Sema4D (CD100) is closely related to pathological and physiological processes, including tumor growth, angiogenesis and cardiac development. Nevertheless, the role and mechanism of Sema4D in cardiac hypertrophy are still unclear to date. To assess the impact of Sema4D on pathological cardiac hypertrophy, TAC surgery was performed on C57BL/6 mice which were transfected with AAV9-mSema4D-shRNA or AAV9-mSema4D adeno-associated virus by tail vein injection. Our results indicated that Sema4D knockdown mitigated cardiac hypertrophy, fibrosis and dysfunction when exposed to pressure overload, and Sema4D downregulation markedly inhibited cardiomyocyte hypertrophy induced by angiotensin II. Meanwhile, Sema4D overexpression had the opposite effect in vitro and in vivo. Furthermore, analysis of signaling pathways showed that Sema4D activated the MAPK pathway during cardiac hypertrophy induced by pressure overload, and the pharmacological mitogen-activated protein kinase kinase 1/2 inhibitor U0126 almost completely reversed Sema4D overexpression-induced deteriorated phenotype, resulting in improved cardiac function. Further research indicated that myocardial hypertrophy induced by Sema4D was closely related to the expression of the pyroptosis-related proteins PP65, NLRP3, caspase-1, ASC, GSDMD, IL-18 and IL-1β. In conclusion, our study demonstrated that Sema4D regulated the process of pathological myocardial hypertrophy through modulating MAPK/NF-κB/NLRP3 pathway, and Sema4D may be the promising interventional target of cardiac hypertrophy and heart failure.

Differential Effects on the Translation of Immune-Related Alternatively Polyadenylated mRNAs in Melanoma and T Cells by eIF4A Inhibition

Targeting the translation initiation complex eIF4F, which binds the 5' cap of mRNAs, is a promising anti-cancer approach. Silvestrol, a small molecule inhibitor of eIF4A, the RNA helicase component of eIF4F, inhibits the translation of the mRNA encoding the signal transducer and activator of transcription 1 (STAT1) transcription factor, which, in turn, reduces the transcription of the gene encoding one of the major immune checkpoint proteins, i.e., programmed death ligand-1 (PD-L1) in melanoma cells. A large proportion of human genes produce multiple mRNAs differing in their 3'-ends through the use of alternative polyadenylation (APA) sites, which, when located in alternative last exons, can generate protein isoforms, as in the STAT1 gene. Here, we provide evidence that the STAT1α, but not STAT1β protein isoform generated by APA, is required for silvestrol-dependent inhibition of PD-L1 expression in interferon-γ-treated melanoma cells. Using polysome profiling in activated T cells we find that, beyond STAT1, eIF4A inhibition downregulates the translation of some important immune-related mRNAs, such as the ones encoding TIM-3, LAG-3, IDO1, CD27 or CD137, but with little effect on the ones for BTLA and ADAR-1 and no effect on the ones encoding CTLA-4, PD-1 and CD40-L. We next apply RT-qPCR and 3'-seq (RNA-seq focused on mRNA 3' ends) on polysomal RNAs to analyze in a high throughput manner the effect of eIF4A inhibition on the translation of APA isoforms. We identify about 150 genes, including TIM-3, LAG-3, AHNAK and SEMA4D, for which silvestrol differentially inhibits the translation of APA isoforms in T cells. It is therefore crucial to consider 3'-end mRNA heterogeneity in the understanding of the anti-tumor activities of eIF4A inhibitors.

The emerging roles of semaphorin4D/CD100 in immunological diseases

In vertebrates, the semaphorin family of proteins is composed of 21 members that are divided into five subfamilies, i.e. classes 3 to 7. Semaphorins play crucial roles in regulating multiple biological processes, such as neural remodeling, tissue regeneration, cancer progression, and, especially, in immunological regulation. Semaphorin 4D (SEMA4D), also known as CD100, is an important member of the semaphorin family and was first characterized as a lymphocyte-specific marker. SEMA4D has diverse effects on immunologic processes, including immune cell proliferation, differentiation, activation, and migration, through binding to its specific membrane receptors CD72, PLXNB1, and PLXNB2. Furthermore, SEMA4D and its underlying signaling have been increasingly linked with several immunological diseases. This review focuses on the significant immunoregulatory role of SEMA4D and the associated underlying mechanisms, as well as the potential application of SEMA4D as a diagnostic marker and therapeutic target for the treatment of immunological diseases.

Adiponectin-expressing Treg facilitate T lymphocyte development in thymic nurse cell complexes

Adiponectin is a well-known insulin sensitizer and anti-inflammatory molecule, possessing therapeutic potentials in cardiovascular, metabolic and cancer diseases. Results of the present study demonstrate that adiponectin is expressed in a population of regulatory T-cells (Treg) resided within the thymic nurse cell (TNC) complexes. Adoptive transfer of adiponectin-expressing Treg precursors effectively attenuated obesity, improved glucose and insulin tolerance, prevented fatty liver injuries in wild-type mice fed a high-fat diet, and significantly inhibited breast cancer development in MMTV-PyVT transgenic mice. Within the TNC complexes, locally produced adiponectin bound to and regulated the expression as well as the distribution of CD100, a transmembrane lymphocyte semaphorin, in turn modulating the lymphoepithelial interactions to facilitate T-cell development and maturation. In summary, adiponectin plays an important role in the selection and development of T lymphocytes within the TNC complexes. Adiponectin-expressing Treg represent a promising candidate for adoptive cell immunotherapy against obesity-related metabolic and cancer diseases.