Tetraspanins at a glance

Extracellular Vesicle Marker Changes Associated With Disease Activity in Relapsing-Remitting Multiple Sclerosis

BACKGROUND AND OBJECTIVES

Multiple sclerosis (MS), neuromyelitis optica spectrum disorder (NMOSD), and myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) are autoimmune disorders of the CNS causing severe neurologic impairment. Evidence suggests that extracellular vesicles (EVs) may play a disease-specific role in the orchestration of the immune cell response of MS, NMOSD, and MOGAD. In addition, EVs are considered as a potential source of biomarkers that may allow us to establish molecular signatures for these diseases and perhaps as well to follow treatment effects and disease progression. The aim of this study was to analyze the composition of EVs in patients with relapsing-remitting MS (RRMS) (n = 52), NMOSD (n = 19), and MOGAD (n = 10) and healthy controls ([HCs], n = 15).

METHODS

The concentrations of neurofilament light chain (NfL) and glial fibrillary acidic protein (GFAP) were determined in plasma using single-molecule array (SIMOA). The size and concentration of tetraspanin-presenting EVs were evaluated in plasma samples with a single-particle interferometric resonance imaging sensor (SP-IRIS). Tetraspanin-independent analyses were performed by nanoparticle-tracking analysis (NTA) after EV isolation by size exclusion (SmartSEC) and cryo-electron microscopy observations. EV epitopes were analyzed by extended multiplex analysis using flow cytometry.

RESULTS

The plasma concentration of NfL and GFAP was significantly higher in patients with RRMS than in HCs. For patients with NMOSD, only GFAP increased. The density of EVs assessed by NTA was lower in plasma of patients with RRMS than in HC plasma. In addition, the 3 disease groups presented increased mean EV sizes in comparison with HCs. Tetraspanin-based EV analyses by SP-IRIS allowed us to observe a modest difference in the level of CD81 in RRMS EVs. In patients with RRMS, but not in those with NMOSD and MOGAD, multiplex/flow cytometry analyses revealed changes in the EV levels of CD29, CD31, and CD69 associated with the time elapsed since the last relapse. The negative correlations established between the vesicular levels of CD31, CD40, CD44, CD49c, CD69, and NfL or GFAP z-scores suggest a negative relationship specifically in RRMS.

DISCUSSION

We speculate that the higher release of EVs containing CD29, CD31, CD40, CD44, CD49c, and CD69 in plasma, at low levels of circulating NfL/GFAP, may be associated with reduced immune cell activity in RRMS. These EV markers may characterize patients with RRMS in disease stabilization.

TSPAN31 Activates Fatty Acid Metabolism and PI3K/AKT Pathway to Promote Tumor Progression in Breast Cancer

Breast cancer (BC) is one of the most common human malignancies, but the mechanisms of BC have not been fully elucidated. Recently, tetraspanin 31 (TSPAN31) is reported to be linked to cancer progression. However, the function of TSPAN31 remains unclear in BC. Investigation of the function and potential mechanism of TSPAN31 in BC was the purpose of this study. Immunohistochemistry, western blot, and quantitative real-time polymerase chain reaction were applied to measure TSPAN31 expression. Loss and gain functional experiments were utilized to survey the influences of TSPAN31 on BC biological process, including cell growth, invasion, migration, and fatty acid metabolism. Mechanistically, Kyoto Encyclopedia of Genes and Genomes analysis based on DepMap database and Gene Set Enrichment Analysis based on The Cancer Genome Atlas database were executed to find TSPAN31-related pathway. Western blot was carried out to assess the changes of fatty acid synthase (FASN), sterol regulatory element binding protein 1 (SREBP1), acyl-CoA synthetase long-chain family member 1 (ACSL1), phosphatidylinositol 3-kinase (PI3K), phosphorylated (p)-PI3K, protein kinase B (AKT), and p-AKT. In human non-triple negative breast cancer tissues and cells, TSPAN31 expression was upregulated. TSPAN31 knockdown induced BC cell apoptosis, inhibited cell proliferation, invasion, migration, and fatty acid metabolism, and reduced the protein levels of FASN, SREBP1, ACSL1, p-PI3K/PI3K, and p-AKT/AKT. In contrast, TSPAN31 overexpression led to the opposite results. Additionally, the activator of PI3K (740 Y-P) attenuated the inhibition of TSPAN31 knockdown on fatty acid metabolism, proliferation, and invasion in BC cells. Through activation of fatty acid metabolism and PI3K/AKT pathway, TSPAN31 played a carcinogenic role in BC. For the mechanism of BC tumorigenesis, our study provides an interesting insight.

In-depth amino acid mutational analysis of the key interspecific incompatibility factor Stigmatic Privacy 1

In plants, there is an active prezygotic interspecific-incompatibility mechanism to prevent unfavorable hybrids between two species. We previously reported that an uncharacterized protein with four-transmembrane domains, named as Stigmatic Privacy 1 (SPRI1), is responsible for rejecting heterospecific pollen grains in Arabidopsis thaliana. However, the lack of notable functional domains in SPRI1 has limited our understanding of its biochemical properties. In this study, we conducted a functional analysis of the SPRI1 protein through point-mutational experiments and biochemical analysis. We explored the molecular regulatory mechanisms of SPRI1 and the relationships with its function. Alanine- and glycine-scanning experiments together with the evolutional analysis showed that the structural integrity of the C-terminal regions of the extracellular domain of this protein is important for its function. In addition, we found two cysteines (C67 and C80) within the extracellular domain that may be involved in the formation of intermolecular disulfide bonds. These cysteine residues are required for the stabilization of the SPR1 protein. Furthermore, SPRI1 may form homo-multimers and is present as part of a ∼300 kDa complex. Our present study indicates that SPRI1 forms large protein machinery for the rejection of hetero-specific pollen in stigmatic papilla cells.

CD63, a new therapeutical candidate for cholesterol homeostasis regulation through extracellular vesicles?

CD63 is a tetraspanin initially associated with late endosomes and contributes to numerous functions at the cell level, such as intracellular endosomal and lysosomal trafficking, adhesion, and motility. CD63 also plays a key role in the biogenesis and release of exosomes, i.e., small extracellular vesicles (EVs) of endosomal origin, facilitating the formation of multivesicular bodies (MVBs), the coordination with the endosomal sorting complexes required for transport (ESCRT) machinery, the selection of cargoes carried by future exosomes, and the fusion of MVBs with the plasma membrane for exosome release. In a recent publication in Nature Cell Biology, Guillaume van Niel's team provides arguments in favor of another EV-linked function for CD63, namely the regulation of cholesterol storage and release by small EVs of endogenous origin. Complemented by two other publications from the teams of Keisuke Ito and Xabier Ostreikoetxea, which respectively describe the role of (i) mitochondrial metabolism on CD63 function and (ii) the link between the reduced CD63+ small EVs and dyslipidemia, these arguments highlight the key role of CD63 in the regulation of cholesterol homeostasis through exosomes and more widely small EVs in physiological and pathological conditions. Future research on CD63 may thus redefine our approach to cellular lipid management and therapeutic lipid delivery.

HSV-1 virions and related particles: biogenesis and implications in the infection

Virion formation and egress are sophisticated processes that rely on the spatial and temporal organization of host cell membranes and the manipulation of host machineries involved in protein sorting, membrane bending, fusion, and fission. These processes result in the formation of infectious virions, defective particles, and various vesicle-like structures. In herpes simplex virus 1 (HSV-1) infections, virions and capsid-less particles, known as light (L)-particles, are formed. HSV-1 infection also stimulates the release of particles that resemble extracellular vesicles (EVs). In productively infected cells, most EVs are generated through the CD63 tetraspanin biogenesis pathway and lack viral components. A smaller subset of EVs, generated through the endosomal sorting complexes required for transport (ESCRT) pathway, contains both viral and host factors. Viral mechanisms tightly regulate EV biogenesis, including the inhibition of autophagy-a process critical for increased production of CD63+ EVs during HSV-1 infection. Mutant viruses that fail to suppress autophagy instead promote microvesicle production from the plasma membrane. Additionally, the viral protein ICP0 (Infected Cell Protein 0) enhances EV biogenesis during HSV-1 infection. The different types of particles can be separated by density gradients due to their distinct biophysical properties. L-particles and ESCRT+ EVs display a pro-viral role, supporting viral replication, whereas CD63+ EVs exhibit antiviral effects. Overall, these studies highlight that HSV-1 infection yields numerous and diverse particles, with their type and composition shaped by the ability of the virus to evade host responses. These particles likely shape the infectious microenvironment and determine disease outcomes.

Surface Components and Biological Interactions of Extracellular Vesicles

Extracellular vesicles (EVs) are critical mediators of intercellular communication, carrying bioactive cargo and displaying diverse surface components that reflect their cellular origins and functions. The EV surface, composed of proteins, lipids, and glycocalyx elements, plays a pivotal role in targeting recipient cells, mediating biological interactions, and enabling selective cargo delivery. This review comprehensively examined the molecular architecture of EV surfaces, linking their biogenesis to functional diversity, and highlights their therapeutic and diagnostic potential in diseases such as cancer and cardiovascular disorders. Additionally, we explore emerging applications of EVs, including machine-learning-assisted analysis, chemical integration, and cross-system combinations. The review also discusses some key challenges in the clinical translation of EV-related technologies.

Tetraspanins 10 and 15 support Venezuelan equine encephalitis virus replication in astrocytoma cells

Tetraspanins (Tspans) are transmembrane proteins that coordinate life cycle steps of viruses from distinct families. Here, we identify the human Tspan10 and Tspan15, both members of the TspanC8 subfamily, as replication factors for alphavirus Venezuelan equine encephalitis virus (VEEV) in astrocytoma cells. Pharmacological inhibition and small interfering RNA (siRNA)-mediated silencing of TspanC8 interactor a disintegrin and metalloproteinase 10 (ADAM10) reduced VEEV infection. Silencing of Tspan10, Tspan15, and ADAM10 did not affect VEEV entry but diminished viral genome replication. We report that Tspan10 is important for VEEV infection of several cell lines, while silencing of Tspan15 diminishes infection with several alphaviruses, but not flaviviruses, in astrocytoma cells. Conversely, we demonstrate that siRNA-mediated silencing of Tspan14, another member of the TspanC8 family, enhances infection with lentiviral pseudoparticles harbouring the envelope proteins of VEEV, identifying it as a restriction factor for VEEV entry. Silencing of ADAM10/Tspan15 substrate neuronal (N)-cadherin reduced VEEV infectivity, suggesting potential roles of ADAM10 substrates in VEEV infection. In sum, our study identifies three TspanC8s and ADAM10 as important modulators of VEEV infectivity.

Tetraspanin CD81 serves as a functional entry factor for porcine circovirus type 2 infection

Porcine circovirus type 2 (PCV2) is the primary causative agent of porcine circovirus-associated disease, clinically resulting in immunosuppression and co-infections with other pathogens in infected pigs. The mechanism of PCV2 infection remains unclear. In this study, we firstly found that the tetraspanin CD81 in PK-15 cells interacts with PCV2 Cap protein by using virus overlay protein-binding assay combined with mass spectrometry. Knockdown of the CD81 significantly reduces the levels of the viral Cap mRNA and protein, and viral internalization in PK-15 cells. The critical interaction regions locate in the large extracellular loop (LEL) domain of CD81 and the CD loop region (82-91aa) of the Cap protein, and a polyclonal antibody against the CD81 LEL domain significantly inhibits PCV2 infection. The transmembrane proteoglycan Syndecan-1 interacts with both CD81 and PCV2 Cap, and co-operates with CD81 to promote PCV2 infection in PK-15 cells. Furthermore, CD81 facilitates RhoA activation and enhances the viral internalization and replication in PK-15 cells. It was concluded that the tetraspanin CD81 is a key host factor for PCV2 invasion into PK-15 cells, thus providing new insights into PCV2 life cycle and identifying a potential target for antiviral drug development.IMPORTANCEPorcine circovirus type 2 (PCV2), a significant economic pathogen in the swine industry, presents persistent challenges in its prevention and treatment. Despite extensive research, the mechanism of PCV2 invading host cells remains unclear. In this study, we found and identified a novel interaction between the tetraspanin CD81 and the viral Cap protein during the PCV2 invading PK-15 cells. The transmembrane proteoglycan Syndecan-1 and RhoA are involved in the infection process through the CD81. Moreover, this is the first time that the role of Syndecan-1 in the PCV2 infection process has been demonstrated. Also, a polyclonal antibody against the CD81 extracellular domain significantly inhibits PCV2 infection in PK-15 cells. It not only enriches our understanding of PCV2 life cycle but also offers new perspectives for the development of antiviral therapeutics against circovirus.

Proteomic Insights Into Gingival Crevicular Extracellular Vesicles in Periodontitis and Gestational Diabetes: An Exploratory Study

AIM

To characterize the gingival crevicular fluid (GCF) and plasma extracellular vesicles (EVs) and explore their proteomic cargo in healthy pregnant women compared to those with gestational diabetes mellitus (GDM) and periodontitis.

METHODS

One-hundred and four pregnant women were recruited at 24-30 gestation weeks. GDM was diagnosed by an oral glucose tolerance test. GCF and plasma samples were obtained to isolate EVs and characterized by nanoparticle tracking, immunoassays, electron microscopy and mass spectrometry.

RESULTS

Of the recruits,17.3% women were healthy, 50% had periodontitis and 32.7% had both GDM and periodontitis. Probing depth, clinical attachment loss and bleeding on probing were more severe in GDM and periodontitis pregnancies (p < 0.0001). Additionally, this group showed an increase concentration of total, small and large GCF-EVs (p = 0.0015, p = 0.0011 and p = 0.0008, respectively), with decreased expression of CD9, CD81 and CD81/CD63 ratio (p = 0.0461, p = 0.0164 and p = 0.0005, respectively). No differences were observed in plasmatic EVs concentration or markers expression. Proteomic analysis of GCF-EVs showed peptides of both host and bacterial origin. Gene ontology analysis revealed that proteins of GCF-EVs participate in immune inflammatory responses, glucose metabolism and insulin response mechanisms.

CONCLUSION

GCF-EVs were increased in both GDM and periodontitis, and their proteomic cargo suggest their involvement in immune inflammatory response, glucose metabolism and insulin pathways during pregnancy.

Role of the transmembrane polar residues on CD151 in cholesterol binding

Tetraspanins superfamily proteins have been shown to play an important role in several physiological processes and diseases such as cancer. Transmembrane polar residues of tetraspanins have an implication in regulating the process of cancer metastasis. Tetraspanin CD82 has been demonstrated to exert an anti-metastatic role while mutating polar residues in its transmembrane domains (TMDs) abrogates its metastasis inhibitory role. However, CD151, being pro-metastatic tetraspanin, the role of polar residues in TMDs of CD151 in cholesterol binding and its stability has not been investigated. In this study, we employed bioinformatics analysis of CD151 sequences to determine polar residue in TMDs, molecular docking, dynamics, and normal mode analysis studies to investigate the contribution of polar residues on cholesterol binding by modelling and comparing wild type with polar residue mutant of CD151. The study finds three polar residues viz Asn24, Glu104 and Gln234, in the TMD1, TMD2, and TMD4, respectively, in CD151 that are conserved in most vertebrates indicating their functional significance. Furthermore, we found that these polar residues are required for CD151 stability and facilitate stable interactions with cholesterol. Further cholesterol binding influenced the differences in the distance between large and small extracellular domains of CD151 indicating its important role in the open and closed conformation of the protein. In summary, CD151 exists in open and closed conformation by regulating its interactions with cholesterol. This interaction may modulate the cell membrane dynamics suggesting its potential implication in cancer metastasis.

In silico study suggests potential drugs that target CD151 to treat breast cancer and glioblastoma

Recently tetraspanin CD151 has been identified as an important biological target involved in metastatic processes which include cell adhesion, tumor progression processes, and so forth in different types of cancers, such as breast cancer and glioblastoma. This in Silico study considered 1603 compounds from the Food and Drug Administration database, after performing an ADMET analysis; we selected 853 ligands, which were used for docking analysis. The most promising ligands were selected from docking studies, based on two criteria: (a) showed lowest affinity to the CD151 protein and (b) they interact with the QRD motif, located in the second extracellular loop. Furthermore, we investigate the stability of the protein-ligand complexes through MD simulations as well as free energy MM-PBSA calculations. From these results, loperamide and glipizide were identified as the best evaluated drugs. We suggest an in vitro analysis is needed to confirm our in silico prediction studies.

Tetraspanin32 (TSPAN32) is downregulated in rheumatoid arthritis: Evidence from animal models and patients

This study aimed to investigate the role of TSPAN32, a member of the tetraspanin family, in rheumatoid arthritis (RA). The objective was to assess the expression levels of TSPAN32 in experimental RA models and in RA patient immune cells, exploring its potential as a regulatory factor in RA pathogenesis. The study employed adjuvant-induced arthritis in rats and collagen-induced arthritis (CIA) in mice as experimental models. Ex vivo analyses included evaluating TSPAN32 expression in immune cells at different stages of the disease. In silico data analysis involved examining transcriptomic datasets from drug-naïve and treated RA patients to correlate TSPAN32 expression with clinical parameters. TSPAN32 overexpression experiments in splenocytes from CIA mice aimed to demonstrate its functional impact on antigen-specific immune responses. The animal models revealed a significant downregulation of TSPAN32, particularly in synovial-infiltrating T cells. Also, TSPAN32 overexpression inhibited pro-inflammatory cytokine production in splenocytes. In RA patients, TSPAN32 was consistently downregulated in circulating and synovial-infiltrating T cells, as well as in CD8+ T cells, B cells and NK cells. Drug treatment did not significantly alter TSPAN32 levels. Negative correlations were observed between TSPAN32 expression and inflammatory markers (CRP, ESR) and clinical scores (SDAI) in RA patients. This study suggests that reduced TSPAN32 expression characterizes pathogenic T-cell populations in RA, highlighting its potential as biomarker for inflammation and disease activity. TSPAN32 may play a crucial role in shaping adaptive immune responses in RA, opening avenues for novel therapeutic strategies targeting this tetraspanin family member.

The Antigen-Specific Response of NK Cells to SARS-CoV-2 Correlates With KIR2DS4 Expression

Natural killer (NK) cells play a pivotal role in the immune response against viral infections, including SARS-CoV-2. However, our understanding of memory NK cell responses in the context of SARS-CoV-2 remains limited. To address this, we investigated the memory-like response of NK cells to SARS-CoV-2 peptides, presented by autologous cells. Blood samples from 45 donors underwent analysis for SARS-CoV-2 IgG antibodies, categorizing them into four groups based on the antibody kind and level. NK cells from SARS-CoV-2-experienced donors demonstrated enhanced degranulation and activation levels, IFNγ production and proliferative potential in response to SARS-CoV-2 peptides. Investigation of highly proliferating NK cells demonstrated the formation of distinct clusters depending on the SARS-CoV-2 peptide supplementation and the donor group. RNA sequencing revealed differential gene expression patterns, highlighting metabolism, protein transport, and immune response genes. Notably, KIR2DS4 expression correlated with enhanced IFNγ production, degranulation and proliferation levels, suggesting a role in SARS-CoV-2 recognition. Collectively, these findings provide detailed insights into antigen-specific NK cell responses to SARS-CoV-2 peptides, indicating potential mechanisms underlying NK cell activation in antiviral immunity.

New perspectives of the role of skeletal muscle derived extracellular vesicles in the pathogenesis of amyotrophic lateral sclerosis: the 'dying back' hypothesis

Amyotrophic lateral sclerosis (ALS), is a progressive neurodegenerative disease that affects nerve cells in the brain and the spinal cord, and is characterized by muscle weakness, paralysis and ultimately, respiratory failure. The exact causes of ALS are not understood, though it is believed to combine genetic and environmental factors. Until now, it was admitted that motor neurons (MN) in the brain and spinal cord degenerate, leading to muscle weakness and paralysis. However, as ALS symptoms typically begin with muscle weakness or stiffness, a new hypothesis has recently emerged to explain the development of the pathology, that is, the 'dying back hypothesis', suggesting that this degeneration starts at the connections between MN and muscles, resulting in the loss of muscle function. Over time, this damage extends along the length of the MN, ultimately affecting their cell bodies in the spinal cord and brain. While the dying back hypothesis provides a potential framework for understanding the progression of ALS, the exact mechanisms underlying the disease remain complex and not fully understood. In this review, we are positioning the role of extracellular vesicles as new actors in ALS development.

Proteomic landscape of tunneling nanotubes reveals CD9 and CD81 tetraspanins as key regulators

Tunneling nanotubes (TNTs) are open actin- and membrane-based channels, connecting remote cells and allowing direct transfer of cellular material (e.g. vesicles, mRNAs, protein aggregates) from the cytoplasm to the cytoplasm. Although they are important especially, in pathological conditions (e.g. cancers, neurodegenerative diseases), their precise composition and their regulation were still poorly described. Here, using a biochemical approach allowing to separate TNTs from cell bodies and from extracellular vesicles and particles (EVPs), we obtained the full composition of TNTs compared to EVPs. We then focused on two major components of our proteomic data, the CD9 and CD81 tetraspanins, and further investigated their specific roles in TNT formation and function. We show that these two tetraspanins have distinct non-redundant functions: CD9 participates in stabilizing TNTs, whereas CD81 expression is required to allow the functional transfer of vesicles in the newly formed TNTs, possibly by regulating docking to or fusion with the opposing cell.

Prostaglandin F2 Receptor Negative Regulator (PTGFRN) Expression Correlates With a Metastatic-like Phenotype in Epidermoid Carcinoma, Pediatric Medulloblastoma, and Mesothelioma

Prostaglandin F2 receptor negative regulator (PTGFRN) is a transmembrane protein associated with metastatic characteristics of certain cancer types. However, it remains poorly characterized and its direct function in cancer remains unclear. The study presented here aims to further examine whether PTGFRN expression affects a cancer cell's phenotype, as well as metastatic-like characteristics. We used stable shRNA and cDNA transfections to respectively knockdown and overexpress PTGFRN in three different cancer cell lines, two of which are representative of rare and aggressive cancers (Mesothelioma and Pediatric Medulloblastoma). We then examined the characteristics of the resulting clones and showed a decrease in proliferation, migration, colony formation, and spheroid growth capabilities in cells where PTGFRN expression had been inhibited, while cells overexpressing PTGFRN showed the opposite. In addition, we showed that PTGFRN displayed direct binding to two protein partners, Integrin β1 and E. Cadherin, the latter of which is a novel direct binding partner to PTGFRN. Furthermore, silencing PTGFRN expression impacted the cellular process of autophagy, thereby providing another avenue by which PTGFRN potentially contributes to a cancer cell phenotype. Our findings demonstrate the potential role of PTGFRN in cancer metastasis and suggest PTGFRN as a future target for drug development in the treatment of metastatic cancers.

Composition, functions, and applications of exosomal membrane proteins

Exosomes play a crucial role in various biological processes, such as human development, immune responses, and disease occurrence. The membrane proteins on exosomes are pivotal factors for their biological functionality. Currently, numerous membrane proteins have been identified on exosome membranes, participating in intercellular communication, mediating target cell recognition, and regulating immune processes. Furthermore, membrane proteins from exosomes derived from cancer cells can serve as relevant biomarkers for early cancer diagnosis. This article provides a comprehensive review of the composition of exosome membrane proteins and their diverse functions in the organism's biological processes. Through in-depth exploration of exosome membrane proteins, it is expected to offer essential foundations for the future development of novel biomedical diagnostics and therapies.

Tetraspanin proteins in membrane remodeling processes

Membrane remodeling is a fundamental cellular process that is crucial for physiological functions such as signaling, membrane fusion and cell migration. Tetraspanins (TSPANs) are transmembrane proteins of central importance to membrane remodeling events. During these events, TSPANs are known to interact with themselves and other proteins and lipids; however, their mechanism of action in controlling membrane dynamics is not fully understood. Since these proteins span the membrane, membrane properties such as rigidity, curvature and tension can influence their behavior. In this Review, we summarize recent studies that explore the roles of TSPANs in membrane remodeling processes and highlight the unique structural features of TSPANs that mediate their interactions and localization. Further, we emphasize the influence of membrane curvature on TSPAN distribution and membrane domain formation and describe how these behaviors affect cellular functions. This Review provides a comprehensive perspective on the multifaceted function of TSPANs in membrane remodeling processes and can help readers to understand the intricate molecular mechanisms that govern cellular membrane dynamics.

Role of Toll-like receptors in exosome biogenesis and angiogenesis capacity

Adaptive inflammation consists of multiple cellular changes and molecular reactions to protect host cells against several pathological conditions. Along with the activation of varied immune cells, the production and secretion of cytokines arrays can regulate the progression of inflammatory response in a paracrine manner. Among different molecular cascades, Toll-like receptors (TLRs) are activated in response to several pathological conditions and damage signals. It has been indicated that extracellular vesicles, especially exosomes (Exos) are key bioshuttles with specific cargoes and are involved in cell-to-cell communication. The role of Exos in the initiation, progression, and cession of inflammation has been previously addressed in terms of cytokine transmission. Whether and how the activation of TLRs can alter the Exo biogenesis and angiogenesis potential in immune cells and endothelial cells (ECs) remains to be elucidated. Here, the cross-talk between the TLRs, Exo biogenesis, and angiogenesis has been highlighted.

New insights into the role of tetraspanin 6, 7, and 8 in physiology and pathology

BACKGROUND

The tetraspanin (TSPAN) family comprises 33 membrane receptors involved in various physiological processes in humans. Tetrasapanins are surface proteins expressed in cells of various organisms. They are localised to the cell membrane by four transmembrane domains (TM4SF). These domains bind several cell surface receptors and signalling proteins to tetraspanin-enriched lipid microdomains (TERM or TEM). Tetraspanins play a critical role in anchoring many proteins. They also act as a scaffold for cell signalling proteins.

AIM

To summarise how tetraspanins 6, 7 and 8 contribute to the carcinogenesis process in different types of cancer.

METHODS

To provide a comprehensive review of the role of tetraspanins 6, 7 and 8 in cancer biology, we conducted a thorough search in PubMed, Embase and performed manual search of reference list to collect and extract data.

DISCUSSION

The assembly of tetraspanins covers an area of approximately 100-400 nm. Tetraspanins are involved in various biological processes such as membrane fusion, aggregation, proliferation, adhesion, cell migration and differentiation. They can also regulate integrins, cell surface receptors and signalling molecules. Tetraspanins form direct bonds with proteins and other members of the tetraspanin family, forming a hierarchical network of interactions and are thought to be involved in cell and membrane compartmentalisation. Tetraspanins have been implicated in cancer progression and have been shown to have multiple binding partners and to promote cancer progression and metastasis. Clinical studies have documented a correlation between the level of tetraspanin expression and the prediction of cancer progression, including breast and lung cancer.

CONCLUSIONS

Tetraspanins are understudied in almost all cell types and their functions are not clearly defined. Fortunately, it has been possible to identify the basic mechanisms underlying the biological role of these proteins. Therefore, the purpose of this review is to describe the roles of tetraspanins 6, 7 and 8.

Cotton plants overexpressing the Bacillus thuringiensis Cry23Aa and Cry37Aa binary-like toxins exhibit high resistance to the cotton boll weevil (Anthonomus grandis)

The cotton boll weevil (CBW, Anthonomus grandis) stands as one of the most significant threats to cotton crops (Gossypium hirsutum). Despite substantial efforts, the development of a commercially viable transgenic cotton event for effective open-field control of CBW has remained elusive. This study describes a detailed characterization of the insecticidal toxins Cry23Aa and Cry37Aa against CBW. Our findings reveal that CBW larvae fed on artificial diets supplemented exclusively with Cry23Aa decreased larval survival by roughly by 69%, while supplementation with Cry37Aa alone displayed no statistical difference compared to the control. However, the combined provision of both toxins in the artificial diet led to mortality rates approaching 100% among CBW larvae (LC50 equal to 0.26 PPM). Additionally, we engineered transgenic cotton plants by introducing cry23Aa and cry37Aa genes under control of the flower bud-specific pGhFS4 and pGhFS1 promoters, respectively. Seven transgenic cotton events expressing high levels of Cry23Aa and Cry37Aa toxins in flower buds were selected for greenhouse bioassays, and the mortality rate of CBW larvae feeding on their T0 and T1 generations ranged from 75% to 100%. Our in silico analyses unveiled that Cry23Aa displays all the hallmark characteristics of β-pore-forming toxins (β-PFTs) that bind to sugar moieties in glycoproteins. Intriguingly, we also discovered a distinctive zinc-binding site within Cry23Aa, which appears to be involved in protein-protein interactions. Finally, we discuss the major structural features of Cry23Aa that likely play a role in the toxin's mechanism of action. In view of the low LC50 for CBW larvae and the significant accumulation of these toxins in the flower buds of both T0 and T1 plants, we anticipate that through successive generations of these transgenic lines, cotton plants engineered to overexpress cry23Aa and cry37Aa hold promise for effectively managing CBW infestations in cotton crops.

CD151 Maintains Endolysosomal Protein Quality to Inhibit Vascular Inflammation

BACKGROUND

Tetraspanin CD151 is highly expressed in endothelia and reinforces cell adhesion, but its role in vascular inflammation remains largely unknown.

METHODS

In vitro molecular and cellular biological analyses on genetically modified endothelial cells, in vivo vascular biological analyses on genetically engineered mouse models, and in silico systems biology and bioinformatics analyses on CD151-related events.

RESULTS

Endothelial ablation of Cd151 leads to pulmonary and cardiac inflammation, severe sepsis, and perilous COVID-19, and endothelial CD151 becomes downregulated in inflammation. Mechanistically, CD151 restrains endothelial release of proinflammatory molecules for less leukocyte infiltration. At the subcellular level, CD151 determines the integrity of multivesicular bodies/lysosomes and confines the production of exosomes that carry cytokines such as ANGPT2 (angiopoietin-2) and proteases such as cathepsin-D. At the molecular level, CD151 docks VCP (valosin-containing protein)/p97, which controls protein quality via mediating deubiquitination for proteolytic degradation, onto endolysosomes to facilitate VCP/p97 function. At the endolysosome membrane, CD151 links VCP/p97 to (1) IFITM3 (interferon-induced transmembrane protein 3), which regulates multivesicular body functions, to restrain IFITM3-mediated exosomal sorting, and (2) V-ATPase, which dictates endolysosome pH, to support functional assembly of V-ATPase.

CONCLUSIONS

Distinct from its canonical function in strengthening cell adhesion at cell surface, CD151 maintains endolysosome function by sustaining VCP/p97-mediated protein unfolding and turnover. By supporting protein quality control and protein degradation, CD151 prevents proteins from (1) buildup in endolysosomes and (2) discharge through exosomes, to limit vascular inflammation. Also, our study conceptualizes that balance between degradation and discharge of proteins in endothelial cells determines vascular information. Thus, the IFITM3/V-ATPase-tetraspanin-VCP/p97 complexes on endolysosome, as a protein quality control and inflammation-inhibitory machinery, could be beneficial for therapeutic intervention against vascular inflammation.

A guide to the expanding field of extracellular vesicles and their release in regulated cell death programs

Homeostasis disruption is visible at the molecular and cellular levels and may often lead to cell death. This vital process allows us to maintain the more extensive system's integrity by keeping the different features (genetic, metabolic, physiologic, and individual) intact. Interestingly, while cells can die in different manners, dying cells still communicate with their environment. This communication was, for a long time, perceived as only driven by the release of soluble factors. However, it has now been reconsidered with the increasing interest in extracellular vesicles (EVs), which are discovered to be released during different regulated cell death programs, with the observation of specific effects. EVs are game changers in the paradigm of cell-cell communication with tremendous implications in fundamental research with regard to noncell autonomous functions, as well as in biomarkers research, all of which are geared toward diagnostic and therapeutic purposes. This review is composed of two main parts. The first is a comprehensive presentation of the state of the art of the EV field at large. In the second part, we focus on EVs discovered to be released during different regulated cell death programs, also known as cell death EVs (cdEVs), and EV-associated specific effects on recipient cells in the context of cell death and inflammation/inflammatory responses.

Extracellular Vesicles in Malaria: Shedding Light on Pathogenic Depths

Malaria, a life-threatening infectious disease caused by Plasmodium falciparum, remains a significant global health challenge, particularly in tropical and subtropical regions. The epidemiological data for 2021 revealed a staggering toll, with 247 million reported cases and 619,000 fatalities attributed to the disease. This formidable global health challenge continues to perplex researchers seeking a comprehensive understanding of its pathogenesis. Recent investigations have unveiled the pivotal role of extracellular vesicles (EVs) in this intricate landscape. These tiny, membrane-bound vesicles, secreted by diverse cells, emerge as pivotal communicators in malaria's pathogenic orchestra. This Review delves into the multifaceted roles of EVs in malaria pathogenesis, elucidating their impact on disease progression and immune modulation. Insights into EV involvement offer potential therapeutic and diagnostic strategies. Integrating this information identifies targets to mitigate malaria's global impact. Moreover, this Review explores the potential of EVs as diagnostic biomarkers and therapeutic targets in malaria. By deciphering the intricate dialogue facilitated by these vesicles, new avenues for intervention and novel strategies for disease management may emerge.

CD81 suppresses NF-κB signaling and is downregulated in hepatitis C virus expressing cells

The tetraspanin CD81 is one of the main entry receptors for Hepatitis C virus, which is a major causative agent to develop liver cirrhosis and hepatocellular carcinoma (HCC). Here, we identify CD81 as one of few surface proteins that are downregulated in HCV expressing hepatoma cells, discovering a functional role of CD81 beyond mediating HCV entry. CD81 was downregulated at the mRNA level in hepatoma cells that replicate HCV. Kinetics of HCV expression were increased in CD81-knockout cells and accompanied by enhanced cellular growth. Furthermore, loss of CD81 compensated for inhibition of pro-survival TBK1-signaling in HCV expressing cells. Analysis of functional phenotypes that could be associated with pro-survival signaling revealed that CD81 is a negative regulator of NF-κB. Interaction of the NF-κB subunits p50 and p65 was increased in cells lacking CD81. Similarly, we witnessed an overall increase in the total levels of phosphorylated and cellular p65 upon CD81-knockout in hepatoma cells. Finally, translocation of p65 in CD81-negative hepatoma cells was markedly induced upon stimulation with TNFα or PMA. Altogether, CD81 emerges as a regulator of pro-survival NF-κB signaling. Considering the important and established role of NF-κB for HCV replication and tumorigenesis, the downregulation of CD81 by HCV and the associated increase in NF-κB signaling might be relevant for viral persistence and chronic infection.

Microscopic clusters feature the composition of biochemical tetraspanin-assemblies and constitute building-blocks of tetraspanin enriched domains

Biochemical approaches revealed that tetraspanins are multi-regulatory proteins forming a web, where they act in tetraspanin-enriched-microdomains (TEMs). A microscopic criterion differentiating between web and TEMs is lacking. Using super-resolution microcopy, we identify co-assemblies between the tetraspanins CD9 and CD81 and CD151 and CD81. CD9 assemblies contain as well the CD9/CD81-interaction partner EWI-2. Moreover, CD9 clusters are proximal to clusters of the CD81-interaction partner CD44 and CD81-/EWI-2-interacting ezrin-radixin-moesin proteins. Assemblies scatter unorganized across the cell membrane; yet, upon EWI-2 elevation, they agglomerate into densely packed arranged-crowds in a process independent from actin dynamics. In conclusion, microscopic clusters are equivalent to biochemical tetraspanin-assemblies, defining in their entirety the tetraspanin web. Cluster-agglomeration enriches tetraspanins, which makes agglomerations to a microscopic complement of TEMs. The microscopic classification of tetraspanin assemblies advances our understanding of this enigmatic protein family, whose members play roles in a plethora of cellular functions, diseases, and pathogen infections.

Exosomes in Cancer: Diagnostic and Therapeutic Applications

Small extracellular vesicles called exosomes are produced by cells and contain a range of biomolecules, including proteins, lipids, and nucleic acids. Exosomes have been implicated in the development and spread of cancer, and recent studies have shown that their contents may be exploited as biomarkers for early detection and ongoing surveillance of the disease. In this review article, we summarize the current knowledge on exosomes as biomarkers of cancer. We discuss the various methods used for exosome isolation and characterization, as well as the different types of biomolecules found within exosomes that are relevant for cancer diagnosis and prognosis. We also highlight recent studies that have demonstrated the utility of exosomal biomarkers in different types of cancer, such as lung cancer, breast cancer, and pancreatic cancer. Overall, exosomes show great promise as noninvasive biomarkers for cancer detection and monitoring. Exosomes have the ability to transform cancer diagnostic and therapeutic paradigms, providing promise for more efficient and individualized. This review seeks to serve as an inspiration for new ideas and research in the never-ending fight against cancer. Moreover, further studies are needed to validate their clinical utility and establish standardized protocols for their isolation and analysis. With continued research and development, exosomal biomarkers have the potential to revolutionize cancer diagnosis and treatment.

A precise balance of TETRASPANIN1/TORNADO2 activity is required for vascular proliferation and ground tissue patterning in Arabidopsis

The molecular mechanisms guiding oriented cell divisions in the root vascular tissues of Arabidopsis thaliana are still poorly characterised. By overlapping bulk and single-cell transcriptomic datasets, we unveiled TETRASPANIN1 (TET1) as a putative regulator in this process. TET1 is expressed in root vascular cells, and loss-of-function mutants contain fewer vascular cell files. We further generated and characterised a CRISPR deletion mutant and showed, unlike previously described mutants, that the full knock out is additionally missing endodermal cells in a stochastic way. Finally, we show that HA-tagged versions of TET1 are functional in contrast to fluorescent TET1 translational fusions. Immunostaining using HA-TET1 lines complementing the mutant phenotype suggested a dual plasma membrane and intracellular localisation in the root vasculature and a polar membrane localisation in the young cortex, endodermal and initial cells. Taken together, we show that TET1 is involved in both vascular proliferation and ground tissue patterning. Our initial results pave the way for future work to decipher its precise mode of action.

Exosome Mediated Cell-Cell Crosstalk in Tissue Injury and Repair

The landscape of exosome research has undergone a significant paradigm shift, with a departure from early conceptions of exosomes as vehicles for cellular waste disposal towards their recognition as integral components of cellular communication with therapeutic potential. This chapter presents an exhaustive elucidation of exosome biology, detailing the processes of exosome biogenesis, release, and uptake, and their pivotal roles in signal transduction, tissue repair, regeneration, and intercellular communication. Additionally, the chapter highlights recent innovations and anticipates future directions in exosome research, emphasizing their applicability in clinical settings. Exosomes have the unique ability to navigate through tissue spaces to enter the circulatory system, positioning them as key players in tissue repair. Their contributory role in various processes of tissue repair, although in the nascent stages of investigation, stands out as a promising area of research. These vesicles function as a complex signaling network for intracellular and organ-level communication, critical in both pathological and physiological contexts. The chapter further explores the tissue-specific functionality of exosomes and underscores the advancements in methodologies for their isolation and purification, which have been instrumental in expanding the scope of exosome research. The differential cargo profiles of exosomes, dependent on their cellular origin, position them as prospective diagnostic biomarkers for tissue damage and regenerative processes. Looking ahead, the trajectory of exosome research is anticipated to bring transformative changes to biomedical fields. This includes advancing diagnostic and prognostic techniques that utilize exosomes as non-invasive biomarkers for a plethora of diseases, such as cancer, neurodegenerative, and cardiovascular conditions. Additionally, engineering exosomes through alterations of their native content or surface properties presents a novel frontier, including the synthesis of artificial or hybrid variants with enhanced functional properties. Concurrently, the ethical and regulatory frameworks surrounding exosome research, particularly in clinical translation, will require thorough deliberation. In conclusion, the diverse aspects of exosome research are coalescing to redefine the frontiers of diagnostic and therapeutic methodologies, cementing its importance as a discipline of considerable consequence in the biomedical sciences.

Characterization of metabolic phenotypes and distinctive genes in mice with low-weight gain

Being overweight exacerbates various metabolic diseases, necessitating the identification of target molecules for obesity control. In the current study, we investigated common physiological features related to metabolism in mice with low weight gain: (1) G protein-coupled receptor, family C, group 5, member B-knockout; (2) gastric inhibitory polypeptide receptor-knockout; and (3) Iroquois-related homeobox 3-knockout. Moreover, we explored genes involved in metabolism by analyzing differentially expressed genes (DEGs) between low-weight gain mice and the respective wild-type control mice. The common characteristics of the low-weight gain mice were low inguinal white adipose tissue (iWAT) and liver weight despite similar food intake along with lower blood leptin levels and high energy expenditure. The DEGs of iWAT, epididymal (gonadal) WAT, brown adipose tissue, muscle, liver, hypothalamus, and hippocampus common to these low-weight gain mice were designated as candidate genes associated with metabolism. One such gene tetraspanin 7 (Tspan7) from the iWAT was validated using knockout and overexpressing mouse models. Mice with low Tspan7 expression gained more weight, while those with high Tspan7 expression gained less weight, confirming the involvement of the Tspan7 gene in weight regulation. Collectively, these findings suggest that the candidate gene list generated in this study contains potential target molecules for obesity regulation. Further validation and additional data from low-weight gain mice will aid in understanding the molecular mechanisms associated with obesity.

HTLV-1 biofilm polarization maintained by tetraspanin CD82 is required for efficient viral transmission

IMPORTANCE

In the early stages of infection, human T-lymphotropic virus type 1 (HTLV-1) dissemination within its host is believed to rely mostly on cell-to-cell contacts. Past studies unveiled a novel mechanism of HTLV-1 intercellular transmission based on the remodeling of the host-cell extracellular matrix and the generation of cell-surface viral assemblies whose structure, composition, and function resemble bacterial biofilms. These polarized aggregates of infectious virions, identified as viral biofilms, allow the bulk delivery of viruses to target cells and may help to protect virions from immune attacks. However, viral biofilms' molecular and functional description is still in its infancy, although it is crucial to fully decipher retrovirus pathogenesis. Here, we explore the function of cellular tetraspanins (CD9, CD81, CD82) that we detect inside HTLV-1 particles within biofilms. Our results demonstrate specific roles for CD82 in the cell-surface distribution and intercellular transmission of HTLV-1 biofilms, which we document as two essential parameters for efficient viral transmission. At last, our findings indicate that N-glycosylation of cell-surface molecules, including CD82, is required for the polarization of HTLV-1 biofilms and for the efficient transmission of HTLV-1 between T-lymphocytes.

Early-life stress triggers long-lasting organismal resilience and longevity via tetraspanin

Early-life stress experiences can produce lasting impacts on organismal adaptation and fitness. How transient stress elicits memory-like physiological effects is largely unknown. Here we show that early-life thermal stress strongly up-regulates tsp-1, a gene encoding the conserved transmembrane tetraspanin in C. elegans. TSP-1 forms prominent multimers and stable web-like structures critical for membrane barrier functions in adults and during aging. The up-regulation of TSP-1 persists even after transient early-life stress. Such regulation requires CBP-1, a histone acetyl-transferase that facilitates initial tsp-1 transcription. Tetraspanin webs form regular membrane structures and mediate resilience-promoting effects of early-life thermal stress. Gain-of-function TSP-1 confers marked C. elegans longevity extension and thermal resilience in human cells. Together, our results reveal a cellular mechanism by which early-life thermal stress produces long-lasting memory-like impact on organismal resilience and longevity.

A novel tetraspanin-related gene signature for predicting prognosis and immune invasion status of lung adenocarcinoma

BACKGROUND

Lung adenocarcinoma (LUAD), the most common subtype of lung cancer, is the primary contributor to cancer-linked fatalities. Dysregulation in the proliferation of cells and death is primarily involved in its development. Recently, tetraspanins, a group of transmembrane proteins, have gained increasing attention for their potential role in the progression of LUAD. Hence, our endeavor involved the development of a novel tetraspanin-based model for the prognostication of lung cancer.

METHODS

A comprehensive set of bioinformatics tools was utilized to evaluate the expression of tetraspanin-related genes and assess their significance regarding prognosis. Hence, a robust risk signature was established through machine learning. The prognosis-predictive value of the signature was evaluated in terms of clinical application, functional enrichment, and the immune landscape.

RESULTS

The research first identified differential expression of tetraspanin genes in patients with LUAD via publicly available databases. The resulting data were indicative of the value that nine of them held regarding prognosis. Five distinct elements were utilized in the establishment of a tetraspanin-related model (TSPAN7, TSPAN11, TSPAN14, UPK1B, and UPK1A). Furthermore, as per the median risk scores, the participants were classified into high- and low-risk groups. The model was validated using inner and outer validation sets. Notably, consensus clustering and prognostic score grouping analysis revealed that tetraspanin-related features affect tumor prognosis by modulating tumor immunity. A nomogram based on the tetraspanin gene was constructed with the aim of enhancing the poor prognosis of high-risk groups and facilitating clinical application.

CONCLUSION

Through machine learning algorithms and in vitro experiments, a novel tetraspanin-associated signature was developed and validated for survival prediction in patients with LUAD that reflects tumor immune infiltration. This could potentially provide new and improved measures for diagnosis and therapeutic interventions for LUAD.

Genome-wide CRISPR-Cas9 Knockout Screening Reveals a TSPAN3-mediated Endo-lysosome Pathway Regulating the Degradation of α-Synuclein Oligomers

Misfolding and aggregation of α-Synuclein (α-Syn), which are hallmark pathological features of neurodegenerative diseases such as Parkinson's disease (PD) and dementia with Lewy Bodies, continue to be significant areas of research. Among the diverse forms of α-Syn - monomer, oligomer, and fibril, the oligomer is considered the most toxic. However, the mechanisms governing α-Syn oligomerization are not yet fully understood. In this study, we utilized genome-wide CRISPR/Cas9 loss-of-function screening in human HEK293 cells to identify negative regulators of α-Syn oligomerization. We found that tetraspanin 3 (TSPAN3), a presumptive four-pass transmembrane protein, but not its homolog TSPAN7, significantly modulates α-Syn oligomer levels. TSPAN3 was observed to interact with α-Syn oligomers, regulate the amount of α-Syn oligomers on the cell membrane, and promote their degradation via the clathrin-AP2 mediated endo-lysosome pathway. Our findings highlight TSPAN3 as a potential regulator of α-Syn oligomers, presenting a promising target for future PD prevention and treatment strategies.

Effects on exocytosis by two HSV-1 mutants unable to block autophagy

IMPORTANCE

Pathogens often hijack extracellular vesicle (EV) biogenesis pathways for assembly, egress, and cell-to-cell spread. Herpes simplex virus 1 (HSV-1) infection stimulated EV biogenesis through a CD63 tetraspanin biogenesis pathway and these EVs activated antiviral responses in recipient cells restricting the infection. HSV-1 inhibits autophagy to evade the host, and increased CD63 exocytosis could be a coping mechanism, as CD63 is involved in both cargo delivery to lysosomes during autophagy and exocytosis. We analyzed exocytosis after infection with two HSV-1 mutants, a ΔICP34.5 and a ΔICP0, that could not inhibit autophagy. Unlike HSV-1(F), neither of these viruses stimulated increased EV biogenesis through the CD63 pathway. ΔICP34.5 stimulated production of microvesicles and apoptotic bodies that were CD63-negative, while ΔICP0 displayed an overall reduced production of EVs. These EVs activated innate immunity gene expression in recipient cells. Given the potential use of these mutants for therapeutic purposes, the immunomodulatory properties of EVs associated with them may be beneficial.

Lysosomal release of amino acids at ER three-way junctions regulates transmembrane and secretory protein mRNA translation

One-third of the mammalian proteome is comprised of transmembrane and secretory proteins that are synthesized on endoplasmic reticulum (ER). Here, we investigate the spatial distribution and regulation of mRNAs encoding these membrane and secretory proteins (termed "secretome" mRNAs) through live cell, single molecule tracking to directly monitor the position and translation states of secretome mRNAs on ER and their relationship to other organelles. Notably, translation of secretome mRNAs occurred preferentially near lysosomes on ER marked by the ER junction-associated protein, Lunapark. Knockdown of Lunapark reduced the extent of secretome mRNA translation without affecting translation of other mRNAs. Less secretome mRNA translation also occurred when lysosome function was perturbed by raising lysosomal pH or inhibiting lysosomal proteases. Secretome mRNA translation near lysosomes was enhanced during amino acid deprivation. Addition of the integrated stress response inhibitor, ISRIB, reversed the translation inhibition seen in Lunapark knockdown cells, implying an eIF2 dependency. Altogether, these findings uncover a novel coordination between ER and lysosomes, in which local release of amino acids and other factors from ER-associated lysosomes patterns and regulates translation of mRNAs encoding secretory and membrane proteins.

Differential proteomics argues against a general role for CD9, CD81 or CD63 in the sorting of proteins into extracellular vesicles

The tetraspanins CD9, CD81 and CD63 are major components of extracellular vesicles (EVs). Yet, their impact on EV composition remains under-investigated. In the MCF7 breast cancer cell line CD63 was as expected predominantly intracellular. In contrast CD9 and CD81 strongly colocalized at the plasma membrane, albeit with different ratios at different sites, which may explain a higher enrichment of CD81 in EVs. Absence of these tetraspanins had little impact on the EV protein composition as analysed by quantitative mass spectrometry. We also analysed the effect of concomitant knock-out of CD9 and CD81 because these two tetraspanins play similar roles in several cellular processes and associate directly with two Ig domain proteins, CD9P-1/EWI-F/PTGFRN and EWI-2/IGSF8. These were the sole proteins significantly decreased in the EVs of double CD9- and CD81-deficient cells. In the case of EWI-2, this is primarily a consequence of a decreased cell expression level. In conclusion, this study shows that CD9, CD81 and CD63, commonly used as EV protein markers, play a marginal role in determining the protein composition of EVs released by MCF7 cells and highlights a regulation of the expression level and/or trafficking of CD9P-1 and EWI-2 by CD9 and CD81.

Differential effects of sugar and fat on adipose tissue inflammation

Obese individuals experience low grade inflammation initiated within their adipose tissue. However, the early events that lead to the release of these inflammatory factors from adipose tissue are poorly characterized. To separate glucose effects from lipid effects on adipose tissue, we used an adipose-specific TXNIP knockout model where excess basal glucose influx into adipocytes led to modest increase in adiposity without using high fat diet. We found an uncoupling of two events that are generally presumed to be coregulated: (1) an increase of adipose tissue macrophage (ATM) number; and (2) pro-inflammatory activation of ATMs. These two events are associated with different triggering signals: elevated free fatty acids output and extracellular matrix remodeling with increased ATM number, whereas decreased adiponectin level with activated ATM. This separation reflects non-overlapping pathways regulated by glucose and lipids in adipocytes, and neither group alone is sufficient to elicit the full inflammatory response in adipose tissue.

Tetraspanin Tspan8 restrains interferon signaling to stabilize intestinal epithelium by directing endocytosis of interferon receptor

Inflammation can impair intestinal barrier, while increased epithelial permeability can lead to inflammation. In this study, we found that the expression of Tspan8, a tetraspanin expressed specifically in epithelial cells, is downregulated in mouse model of ulcerative disease (UC) but correlated with those of cell-cell junction components, such as claudins and E-cadherin, suggesting that Tspan8 supports intestinal epithelial barrier. Tspan8 removal increases intestinal epithelial permeability and upregulates IFN-γ-Stat1 signaling. We also demonstrated that Tspan8 coalesces with lipid rafts and facilitates IFNγ-R1 localization at or near lipid rafts. As IFN-γ induces its receptor undergoing clathrin- or lipid raft-dependent endocytosis and IFN-γR endocytosis plays an important role in Jak-Stat1 signaling, our analysis on IFN-γR endocytosis revealed that Tspan8 silencing impairs lipid raft-mediated but promotes clathrin-mediated endocytosis of IFN-γR1, leading to increased Stat1 signaling. These changes in IFN-γR1 endocytosis upon Tspan8 silencing correlates with fewer lipid raft component GM1 at the cell surface and more clathrin heavy chain in the cells. Our findings indicate that Tspan8 determines the IFN-γR1 endocytosis route, to restrain Stat1 signaling, stabilize intestine epithelium, and subsequently prevent intestine from inflammation. Our finding also implies that Tspan8 is needed for proper endocytosis through lipid rafts.

Multiple Mechanisms Explain Genetic Effects at the CPED1-WNT16 Bone Mineral Density Locus

PURPOSE OF REVIEW

Chromosome region 7q31.31, also known as the CPED1-WNT16 locus, is robustly associated with BMD and fracture risk. The aim of the review is to highlight experimental studies examining the function of genes at the CPED1-WNT16 locus.

RECENT FINDINGS

Genes that reside at the CPED1-WNT16 locus include WNT16, FAM3C, ING3, CPED1, and TSPAN12. Experimental studies in mice strongly support the notion that Wnt16 is necessary for bone mass and strength. In addition, roles for Fam3c and Ing3 in regulating bone morphology in vivo and/or osteoblast differentiation in vitro have been identified. Finally, a role for wnt16 in dually influencing bone and muscle morphogenesis in zebrafish has recently been discovered, which has brought forth new questions related to whether the influence of WNT16 in muscle may conspire with its influence in bone to alter BMD and fracture risk.

Multiple plasma membrane reporters discern LHFPL5 region that blocks trafficking to the plasma membrane

The mechano-electrical transduction (MET) channel of the inner ear receptor cells, termed hair cells, is a protein complex that enables our senses of hearing and balance. Hair cell MET requires an elaborate interplay of multiple proteins that form the MET channel. One of the MET complex components is the transmembrane protein LHFPL5, which is required for hair cell MET and hearing. LHFPL5 is thought to form a multi-protein complex with other MET channel proteins, such as PCDH15, TMIE, and TMC1. Despite localizing to the plasma membrane of stereocilia, the mechanosensing organelles of hair cells, LHFPL5 requires its binding partner within the MET complex, PCDH15, to localize to the stereocilia tips in hair cells and to the plasma membrane in heterologous cells. Using the Aquaporin 3-tGFP reporter (AGR) for plasma membrane localization, we found that a region within extracellular loop 1, which interacts with PCDH15, precludes the trafficking of AGR reporter to the plasma membrane in heterologous cell lines. Our results suggest that the presence of protein partners may mask endoplasmic reticulum retention regions or enable the proper folding and trafficking of the MET complex components, to facilitate expression of the MET complex at the stereocilia membrane.

The tetraspanin TSPAN5 regulates AMPAR exocytosis by interacting with the AP4 complex

Intracellular trafficking of AMPA receptors is a tightly regulated process which involves several adaptor proteins, and is crucial for the activity of excitatory synapses both in basal conditions and during synaptic plasticity. We found that, in rat hippocampal neurons, an intracellular pool of the tetraspanin TSPAN5 promotes exocytosis of AMPA receptors without affecting their internalisation. TSPAN5 mediates this function by interacting with the adaptor protein complex AP4 and Stargazin and possibly using recycling endosomes as a delivery route. This work highlights TSPAN5 as a new adaptor regulating AMPA receptor trafficking.

Tumor-Derived Exosomes and Their Role in Breast Cancer Metastasis

Breast cancer has been the most common cancer in women worldwide, and metastasis is the leading cause of death from breast cancer. Even though the study of breast cancer metastasis has been extensively carried out, the molecular mechanism is still not fully understood, and diagnosis and prognosis need to be improved. Breast cancer metastasis is a complicated process involving multiple physiological changes, and lung, brain, bone and liver are the main metastatic targets. Exosomes are membrane-bound extracellular vesicles that contain secreted cellular constitutes. The biogenesis and functions of exosomes in cancer have been intensively studied, and mounting studies have indicated that exosomes play a crucial role in cancer metastasis. In this review, we summarize recent findings on the role of breast cancer-derived exosomes in metastasis organotropism and discuss the potential promising clinical applications of targeting exosomes as novel strategies for breast cancer diagnosis and therapy.

Identification of Differentially Expressed Genes and Prediction of Expression Regulation Networks in Dysfunctional Endothelium

The detection of early coronary atherosclerosis (ECA) is still a challenge and the mechanism of endothelial dysfunction remains unclear. In the present study, we aimed to identify differentially expressed genes (DEGs) and the regulatory network of miRNAs as well as TFs in dysfunctional endothelium to elucidate the possible pathogenesis of ECA and find new potential markers. The GSE132651 data set of the GEO database was used for the bioinformatic analysis. Principal component analysis (PCA), the identification of DEGs, correlation analysis between significant DEGs, the prediction of regulatory networks of miRNA and transcription factors (TFs), the validation of the selected significant DEGs, and the receiver operating characteristic (ROC) curve analysis as well as area under the curve (AUC) values were performed. We identified ten genes with significantly upregulated signatures and thirteen genes with significantly downregulated signals. Following this, we found twenty-two miRNAs regulating two or more DEGs based on the miRNA–target gene regulatory network. TFs with targets ≥ 10 were E2F1, RBPJ, SSX3, MMS19, POU3F3, HOXB5, and KLF4. Finally, three significant DEGs (TOX, RasGRP3, TSPAN13) were selected to perform validation experiments. Our study identified TOX, RasGRP3, and TSPAN13 in dysfunctional endothelium and provided potential biomarkers as well as new insights into the possible molecular mechanisms of ECA.

Tetraspanin 8 Subfamily Members Regulate Substrate-Specificity of a Disintegrin and Metalloprotease 17

Ectodomain shedding is an irreversible process to regulate inter- and intracellular signaling. Members of the a disintegrin and metalloprotease (ADAM) family are major mediators of ectodomain shedding. ADAM17 is involved in the processing of multiple substrates including tumor necrosis factor (TNF) α and EGF receptor ligands. Substrates of ADAM17 are selectively processed depending on stimulus and cellular context. However, it still remains largely elusive how substrate selectivity of ADAM17 is regulated. Tetraspanins (Tspan) are multi-membrane-passing proteins that are involved in the organization of plasma membrane micro-domains and diverse biological processes. Closely related members of the Tspan8 subfamily, including CD9, CD81 and Tspan8, are associated with cancer and metastasis. Here, we show that Tspan8 subfamily members use different strategies to regulate ADAM17 substrate selectivity. We demonstrate that in particular Tspan8 associates with both ADAM17 and TNF α and promotes ADAM17-mediated TNF α release through recruitment of ADAM17 into Tspan-enriched micro-domains. Yet, processing of other ADAM17 substrates is not altered by Tspan8. We, therefore, propose that Tspan8 contributes to tumorigenesis through enhanced ADAM17-mediated TNF α release and a resulting increase in tissue inflammation.

Unrecognized role of claudin-10b in basolateral membrane infoldings of the thick ascending limb

Claudin-10b is an important component of the tight junction in the thick ascending limb (TAL) of Henle's loop and allows paracellular sodium transport. In immunofluorescence stainings, claudin-10b-positive cells exhibited extensive extra staining of basolateral, column-like structures. The precise localization and function have so far remained elusive. In isolated cortical TAL segments from C57BL/6J mice, kidney-specific claudin-10 knockout mice (cKO), and respective litter mates (WT), we investigated the localization and protein expression and function by fluorescence microscopy and electrophysiological measurements. Ultrastructural analysis of TAL in kidney sections was performed by electron microscopy. Claudin-10b colocalized with the basolateral Na⁺ -K⁺ ATPase and the Cl^- channel subunit barttin, but the lack of claudin-10b did not influence the localization or abundance of these proteins. However, the accessibility of the basolateral infolded extracellular space to ouabain or fluorescein was increased by basolateral Ca²⁺ removal and in the absence of claudin-10b. Ultrastructural analysis by electron microscopy revealed a widening of basolateral membrane infoldings in cKO in comparison to WT. We hypothesize that claudin-10b shapes neighboring membrane invaginations by trans interaction to stabilize and facilitate high-flux salt transport in a water-tight epithelium.

The CD63 homologs, Tsp42Ee and Tsp42Eg, restrict endocytosis and promote neurotransmission through differential regulation of synaptic vesicle pools

The Tetraspanin (Tsp), CD63, is a transmembrane component of late endosomes and facilitates vesicular trafficking through endosomal pathways. Despite being widely expressed in the human brain and localized to late endosomes, CD63's role in regulating endo- and exocytic cycling at the synapse has not been investigated. Synaptic vesicle pools are highly dynamic and disruptions in the mobilization and replenishment of these vesicle pools have adverse neuronal effects. We find that the CD63 homologs, Tsp42Ee and Tsp42Eg, are expressed at the Drosophila neuromuscular junction to regulate synaptic vesicle pools through both shared and unique mechanisms. Tsp42Ee and Tsp42Eg negatively regulate endocytosis and positively regulate neurotransmitter release. Both tsp mutants show impaired locomotion, reduced miniature endplate junctional current frequencies, and increased endocytosis. Expression of human CD63 in Drosophila neurons leads to impaired endocytosis suggesting the role of Tsps in endocytosis is conserved. We further show that Tsps influence the synaptic cytoskeleton and membrane composition by regulating Futsch loop formation and synaptic levels of SCAR and PI(4,5)P2. Finally, Tsp42Ee and Tsp42Eg influence the synaptic localization of several vesicle-associated proteins including Synapsin, Synaptotagmin, and Cysteine String Protein. Together, our results present a novel function for Tsps in the regulation of vesicle pools and provide insight into the molecular mechanisms of Tsp-related synaptic dysfunction.

Multimodal Study of PRPH2 Gene-Related Retinal Phenotypes

PRPH2 gene mutations are frequently found in inherited retinal dystrophies (IRD) and are associated with a wide spectrum of clinical phenotypes. We studied 28 subjects affected by IRD carrying pathogenic PRPH2 mutations, belonging to 11 unrelated families. Functional tests (best-corrected visual acuity measurement, chromatic test, visual field, full-field, 30 Hz flicker, and multifocal electroretinogram), morphological retino-choroidal imaging (optical coherence tomography, optical coherence tomography angiography, and fundus autofluorescence), and clinical data were collected and analyzed. Common primary complaints, with onset in their 40s, were visual acuity reduction and abnormal dark adaptation. Visual acuity ranged from light perception to 20/20 Snellen. Visual field peripheral constriction and central scotoma were found. Chromatic sense was reduced in one third of patients. Electrophysiological tests were abnormal in most of the patients. Choroidal neovascular lesions were detected in five patients. Three novel PRPH2 variants were found in four different families. Based on the present multimodal study, we identified seven distinct PRPH2 phenotypes in 11 unrelated families carrying either different mutations or the same mutation, both within the same family or among them. Fundus autofluorescence modality turned out to be the most adequate imaging method for early recognition of this dystrophy, and the optical coherence tomography angiography was highly informative to promptly detect choroidal neovascularization, even in the presence of the extensive chorioretinal atrophy phenotype.

Neuropilin 1 and its inhibitory ligand mini-tryptophanyl-tRNA synthetase inversely regulate VE-cadherin turnover and vascular permeability

The formation of a functional blood vessel network relies on the ability of endothelial cells (ECs) to dynamically rearrange their adhesive contacts in response to blood flow and guidance cues, such as vascular endothelial growth factor-A (VEGF-A) and class 3 semaphorins (SEMA3s). Neuropilin 1 (NRP1) is essential for blood vessel development, independently of its ligands VEGF-A and SEMA3, through poorly understood mechanisms. Grounding on unbiased proteomic analysis, we report here that NRP1 acts as an endocytic chaperone primarily for adhesion receptors on the surface of unstimulated ECs. NRP1 localizes at adherens junctions (AJs) where, interacting with VE-cadherin, promotes its basal internalization-dependent turnover and favors vascular permeability initiated by histamine in both cultured ECs and mice. We identify a splice variant of tryptophanyl-tRNA synthetase (mini-WARS) as an unconventionally secreted extracellular inhibitory ligand of NRP1 that, by stabilizing it at the AJs, slows down both VE-cadherin turnover and histamine-elicited endothelial leakage. Thus, our work shows a role for NRP1 as a major regulator of AJs plasticity and reveals how mini-WARS acts as a physiological NRP1 inhibitory ligand in the control of VE-cadherin endocytic turnover and vascular permeability.