CD300a and CD300f molecules regulate the function of leukocytes

CD300ld promotes neutrophil bacterial phagocytosis in sepsis

Sepsis is a life-threatening condition caused by a dysregulated immune response to infection. Neutrophils act as first line of defense against infection, but their function can become impaired in sepsis. CD300 antigen-like family member d (CD300ld), predominantly expressed on neutrophils, associates with Fc receptor common gamma-chain (FcRγ chain), a component vital for phagocytosis. In this study, we investigated the role of CD300ld in neutrophil phagocytosis. Our results demonstrate a marked decrease in CD300ld expression on neutrophils isolated from both septic mice and patients. CD300ld was positively correlated with bacterial phagocytosis in neutrophils. The transcriptomic analysis of CD300ld knock-out neutrophils revealed a downregulation of genes related to defense response to bacteria, suggesting that CD300ld is a key modulator of bacterial clearance. Stimulation of CD300ld with an agonist antibody in neutrophils led to the activation of Rac2, a key regulator of actin polymerization, facilitating the enhanced phagocytosis. Furthermore, CD300ld activation significantly enhanced the in vitro phagocytosis of Escherichia coli and Staphylococcus aureus by neutrophils. Septic mice adoptively transferred with CD300ld-activated neutrophils exhibited markedly reduced bacterial loads in the blood and peritoneum, decreased inflammatory cytokine levels, and alleviated organ injury. These findings highlight the critical role of CD300ld signaling in neutrophil-mediated bacterial clearance in sepsis and provide a solid foundation for future research aimed at developing novel immunotherapies against this deadly disease condition.

Inhibitory immunoreceptors CD300a and CD300lf cooperate to regulate mast cell activation

Mast cells (MCs) play a central role in allergic immune responses. MC activation is regulated by several inhibitory immunoreceptors. The CD300 family members CD300a and CD300lf recognize phospholipid ligands and inhibit the FcεRI-mediated activating signal in MCs. While CD300a binds to phosphatidylserine (PS) to inhibit MCs activation, CD300lf function is less clear due to its ability to bind with ceramide and PS. Moreover, it also remains blurring whether CD300a and CD300lf function independently, cooperatively, or by interfering with each other in regulating MC activation. Using imaging and flow cytometric analyses of bone marrow-derived cultured MCs (BMMCs) from wild-type (WT), Cd300a-/-, Cd300lf-/-, and Cd300a-/-Cd300lf-/- mice, we show that CD300lf and CD300a colocalized with PS externalized to the outer leaflet of the plasma membrane with a polar formation upon activation, and CD300lf cooperates with CD300a to inhibit BMMCs activation. CD300lf also colocalized with extracellular ceramide in addition to the internal PS on the cell surface, which results in stronger inhibition of MC activation than CD300lf binding to PS alone. Similarly, although both Cd300a-/- and Cd300lf-/- mice showed decreased rectal temperatures compared with WT mice in the model of passive systemic anaphylaxis, Cd300a-/-Cd300lf-/- mice showed lower rectal temperature than either Cd300a-/- or Cd300lf-/- mice. Our results demonstrate the cooperativity of multiple inhibitory receptors expressed on MCs and their regulatory functions upon binding to respective ligands.

Quercetin Attenuates MRGPRX2-Mediated Mast Cell Degranulation via the MyD88/IKK/NF-κB and PI3K/AKT/ Rac1/Cdc42 Pathway

Background

CMRF35-like molecule-1 (CLM-1) is a receptor of the CD300 family that inhibits MRGPRX2-mediated mast cell degranulation. Understanding the role and mechanism of CLM-1 agonist has significant implications for the treatment of allergic disease. Quercetin is a natural small molecule compound derived from plants and vegetables that has been shown to prevent histamine release by immune cells.

Objective

This study aims to examine the inhibitory effects of quercetin on MRGPRX2-mediated mast cell degranulation via CLM-1.

Results

We found that C48/80 stimulation resulted in significantly increased release of β-hexosaminidase, histamine and Ca2+ in CLM-1-knockdown LAD2 cells than in NC-LAD2 cells. Surface plasmon resonance (SPR) and molecular docking analyses revealed high-affinity binding between quercetin and CLM-1 (K D = 2.962×10-5 mol/L) mediated by the formation of hydrogen bonds. In addition, quercetin can selectively bind to CLM-1 on mast cells, leading to SHP-1 phosphorylation and subsequent inhibition of downstream MyD88/IKK/NF-κB signaling. Furthermore, activation of CLM-1 modulated the surface expression of MRGPRX2 by inhibiting F-actin, leading to internalization of the MRGPRX2 receptor via the PI3K/AKT/ Rac1/Cdc42 pathway.

Conclusion

Quercetin is a promising treatment for allergic diseases by acting as a CLM-1 agonist that inhibits MRGPRX2-mediated mast cell degranulation.

Untargeted blood serum proteomics identifies novel proteins related to neurological recovery after human spinal cord injury

BACKGROUND

The discovery of new prognostic biomarkers following spinal cord injury (SCI) is a rapidly growing field that could help uncover the underlying pathological mechanisms of SCI and aid in the development of new therapies. To date, this search has largely focused on the initial days after the lesion. However, during the subacute stage of SCI (weeks to months after the injury), there remains potential for sensorimotor recovery, and numerous secondary events develop in various organs. Additionally, the confounding effects of early interventions after the injury are less likely to interfere with the results.

METHODS

In this study, we conducted an untargeted proteomics analysis to identify biomarkers of recovery in blood serum samples during the subacute phase of SCI patients, comparing those with strong recovery to those with no recovery between 30 and 120 days. We analyzed the fraction of serum that is depleted of the most abundant proteins to unmask proteins that would otherwise go undetected. Linear models were used to identify peptides and proteins related to neurological recovery and we validated changes in some of these proteins using Enzyme-linked Immunosorbent Assay (ELISA).

RESULTS

Our findings reveal that differences in subacute recovery after SCI (from 30 to 120 days) are associated with an enrichment in proteins involved in inflammation, coagulation, and lipid metabolism. Technical validation using commercial ELISAs further confirms that high levels of SERPINE1 and ARHGAP35 are associated with strong neurological recovery, while high levels of CD300a and DEFA1 are associated with a lack of recovery.

CONCLUSIONS

Our study identifies new candidates for biomarkers of neurological recovery and for novel therapeutic targets after SCI.

CD300LF+ microglia impede the neuroinflammation following traumatic brain injury by inhibiting STING pathway

INTRODUCTION

The diversity in microglial phenotypes and functions following traumatic brain injury (TBI) is poorly characterized. The aim of this study was to explore precise targets for improving the prognosis of TBI patients from a microglial perspective.

OBJECTIVES

To assess whether the prognosis of TBI can be improved by modulating microglia function.

RESULTS

In CD300LF-deficient mice, we observed an increase in glial cell proliferation, more extensive neuronal loss, and worsened neurological function post-TBI. Transcriptomic comparisons between CD300LF-positive and CD300LF-negative microglia illuminated that the neuroprotective role of CD300LF is principally mediated by the inhibition of the STING signaling pathway. In addition, this protective effect can be augmented using the STING pathway inhibitor C-176.

CONCLUSIONS

Our research indicates that CD300LF reduces neuroinflammation and promotes neurological recovery after TBI, and that microglia are integral to the protective effects of CD300LF in this context. In summary, our findings highlight CD300LF as a critical molecular regulator modulating the adverse actions of microglia following acute brain injury and propose a novel therapeutic approach to enhance outcomes for patients with TBI.

CD300e: Emerging role and mechanism as an immune-activating receptor

As a transmembrane protein, CD300e is primarily expressed in myeloid cells. It belongs to the CD300 glycoprotein family, functioning as an immune-activating receptor. Dysfunction of CD300e has been suggested in many diseases, such as infections, immune disorders, obesity, and diabetes, signifying its potential as a key biomarker for disease diagnosis and treatment. This review is aimed to explore the roles and potential mechanisms of CD300e in regulating oxidative stress, immune cell activation, tissue damage and repair, and lipid metabolism, shedding light on its role as a diagnostic marker or a therapeutic target, particularly for infections and autoimmune disorders.

HLA-DRB5 Overexpression Promotes Platelet Reduction in Immune Thrombocytopenia Mice Model by Facilitating MHC-II-Mediated Antigen Presentation

INTRODUCTION

Major histocompatibility complex II (MHC-II)-mediated antigen presentation contributes to the pathogenesis of immune thrombocytopenia (ITP). Human leukocyte antigen (HLA)-DRB5 is an MHC-II molecule and this study aims to investigate its role and mechanisms in ITP development.

METHODS

Guinea pig anti-mouse platelet (PLT) serum-induced ITP mice received tail vein injection of HLA-DRB5 overexpressing adenoviral vector/immune receptor expressed on myeloid cells-1 (IREM-1) monoclonal antibody (mAb). PLT count changes in mice blood were assessed by a hematology analyzer. MHC-II/CD80/CD86 expression in mice blood was measured by quantitative real-time-PCR and immunofluorescence assay. CD8+ T-cell proportion in mice blood was detected by flow cytometry.

RESULTS

HLA-DRB5 overexpression exacerbated PLT reduction since the 5th day of the establishment of ITP mice model and enhanced MHC-II/CD80/CD86 expression upregulation as well as CD8+ T-cell ratio elevation in the blood of ITP mice, while its effects were reversed by IREM-1 mAb.

CONCLUSION

HLA-DRB5 overexpression upregulates MHC-II-mediated antigen presentation to CD8+ T cells, thus lowering PLT count in the ITP mice model.

A Pilot Urinary Proteome Study Reveals Widespread Influences of Circadian Rhythm Disruption by Sleep Deprivation

It is widely accepted that circadian rhythm disruption caused short- or long-term adverse effects on health. Although many previous studies have focused on exploration of the molecular mechanisms, there is no rapid, convenient, and non-invasive method to reveal the influence on health after circadian rhythm disruption. Here, we performed a high-resolution mass spectrometry-based data-independent acquisition (DIA) quantitative urinary proteomic approach in order to explore whether urine could reveal stress changes to those brought about by circadian rhythm disruption after sleep deprivation. After sleep deprivation, the subjects showed a significant increase in both systolic and diastolic blood pressure compared with routine sleep. More than 2000 proteins were quantified and they contained specific proteins for various organs throughout the body. And a total of 177 significantly up-regulated proteins and 68 significantly down-regulated proteins were obtained after sleep deprivation. These differentially expressed proteins (DEPs) were associated with multiple organs and pathways, which reflected widespread influences of sleep deprivation. Besides, machine learning identified a panel of five DEPs (CD300A, SCAMP3, TXN2, EFEMP1, and MYH11) that can effectively discriminate circadian rhythm disruption. Taken together, our results validate the value of urinary proteome in predicting and diagnosing the changes by circadian rhythm disruption.

Regulation of immune response against third-stage Gnathostoma spinigerum larvae by human genes

Background

Gnathostomiasis is an important zoonosis in tropical areas that is mainly caused by third-stage Gnathostoma spinigerum larvae (G. spinigerum L3).

Objectives

This study aimed to prove whether G. spinigerum L3 produces extracellular vesicles (EVs) and investigate human gene profiles related to the immune response against the larvae.

Methods

We created an immune cell model using normal human peripheral blood mononuclear cells (PBMCs) co-cultured with the larvae for 1 and 3 days, respectively. The PBMCs were harvested for transcriptome sequencing analysis. The EV ultrastructure was examined in the larvae and the cultured medium.

Results

Extracellular vesicle-like particles were observed under the larval teguments and in the pellets in the medium. RNA-seq analysis revealed that 2,847 and 3,118 genes were significantly expressed on days 1 and 3 after culture, respectively. The downregulated genes on day 1 after culture were involved in pro-inflammatory cytokines, the complement system and apoptosis, whereas those on day 3 were involved in T cell-dependent B cell activation and wound healing. Significantly upregulated genes related to cell proliferation, activation and development, as well as cytotoxicity, were observed on day 1, and genes regulating T cell maturation, granulocyte function, nuclear factor-κB and toll-like receptor pathways were predominantly observed on day 3 after culture.

Conclusion

G. spinigerum L3 produces EV-like particles and releases them into the excretory-secretory products. Overall, genotypic findings during our 3-day observation revealed that most significant gene expressions were related to T and B cell signalling, driving T helper 2 cells related to chronic infection, immune evasion of the larvae, and the pathogenesis of gnathostomiasis. Further in-depth studies are necessary to clarify gene functions in the pathogenesis and immune evasion mechanisms of the infective larvae.

Prognostic analysis of uveal melanoma based on the characteristic genes of M2-type macrophages in the tumor microenvironment

Uveal melanoma arises from stromal melanocytes and is the most prevalent primary intraocular tumor in adults. It poses a significant diagnostic and therapeutic challenge due to its high malignancy and early onset of metastases. In recent years, there has been a growing interest in the role of diverse immune cells in tumor cell development and metastasis. Using The Cancer Genome Atlas and the gene expression omnibus databases, and the CIBERSORT method, we investigated the topography of intra-tumor immune infiltration in uveal melanoma in this research. We evaluated the prognosis of uveal melanoma patients using the M2 macrophage immune cell infiltration score in conjunction with clinical tumor patient data. We built a prognostic model based on the distinctive genes of M2 macrophages and combined it with patients' clinical data in the database; we ran a survival prognostic analysis to authenticate the model's accuracy. The functional study revealed the importance of macrophage-associated genes in the development of uveal melanoma. Moreover, the reliability of our prediction model was verified by combining tumor mutational load, immune checkpoint, and drug sensitivity, respectively. Our study provides a reference for the follow-up study of uveal melanoma.

The interaction of CD300lf and ceramide reduces the development of periodontitis by inhibiting osteoclast differentiation

AIM

The regulation of osteoclasts (OCs) by inhibitory immunoreceptors maintains bone homeostasis and is considered an important determinant of the extent of periodontal pathology. The aim of this study was to investigate the role of the inhibitory immunoreceptor CD300lf and its ligand ceramide in osteoclastogenesis in periodontitis.

MATERIALS AND METHODS

The expression of CD300lf was measured in vitro and in a ligature-induced periodontitis model. The effect of CD300lf ablation on osteoclastogenesis was examined in ligature-retained and ligature removal periodontitis models. The effect of ceramide, the ligand of CD300lf, was examined in osteoclastogenesis in vitro and in vivo by smearing 20 μg of ceramide dissolved in carboxymethylcellulose on teeth and gingiva every other day in an experimental periodontitis model and ligature removal model.

RESULTS

CD300lf expression was downregulated during osteoclastogenesis. Ablation of CD300lf in the ligature-induced periodontitis model increased the number of OCs and exacerbated bone damage. Bone resorption caused by CD300lf ablation was reversible following ligature removal. CD300lf-ceramide binding suppressed osteoclastogenesis in vitro and inhibited alveolar bone loss in a mouse periodontitis model.

CONCLUSIONS

Our findings reveal that CD300lf-ceramide binding plays a critical negative role in alveolar bone loss in periodontitis by inhibiting OCs differentiation.

Drug delivery targets and strategies to address mast cell diseases

INTRODUCTION

Current and developing mast cell therapeutics are reliant on small molecule drugs and biologics, but few are truly selective for mast cells. Most have cellular and disease-specific limitations that require innovation to overcome longstanding challenges to selectively targeting and modulating mast cell behavior. This review is designed to serve as a frame of reference for new approaches that utilize nanotechnology or combine different drugs to increase mast cell selectivity and therapeutic efficacy.

AREAS COVERED

Mast cell diseases include allergy and related conditions as well as malignancies. Here, we discuss the targets of existing and developing therapies used to treat these disease pathologies, classifying them into cell surface, intracellular, and extracellular categories. For each target discussed, we discuss drugs that are either the current standard of care, under development, or have indications for potential use. Finally, we discuss how novel technologies and tools can be used to take existing therapeutics to a new level of selectivity and potency against mast cells.

EXPERT OPINION

There are many broadly and very few selectively targeted therapeutics for mast cells in allergy and malignant disease. Combining existing targeting strategies with technology like nanoparticles will provide novel platforms to treat mast cell disease more selectively.

Understanding inhibitory receptor function in neutrophils through the lens of CLEC12A

Neutrophils are the first leukocytes recruited from the circulation in response to invading pathogens or injured cells. To eradicate pathogens and contribute to tissue repair, recruited neutrophils generate and release a host of toxic chemicals that can also damage normal cells. To avoid collateral damage leading to tissue injury and organ dysfunction, molecular mechanisms evolved that tightly control neutrophil response threshold to activating signals, the strength and location of the response, and the timing of response termination. One mechanism of response control is interruption of activating intracellular signaling pathways by the 20 inhibitory receptors expressed by neutrophils. The two inhibitory C-type lectin receptors expressed by neutrophils, CLEC12A and DCIR, exhibit both common and distinct molecular and functional mechanisms, and they are associated with different diseases. In this review, we use studies on CLEC12A as a model of inhibitory receptor regulation of neutrophil function and participation in disease. Understanding the molecular mechanisms leading to inhibitory receptor specificity offers the possibility of using physiologic control of neutrophil functions as a pharmacologic tool to control inflammatory diseases.

Glis1 and oxaloacetate in nucleus pulposus stromal cell somatic reprogramming and survival

Regenerative medicine aims to repair degenerate tissue through cell refurbishment with minimally invasive procedures. Adipose tissue (FAT)-derived stem or stromal cells are a convenient autologous choice for many regenerative cell therapy approaches. The intervertebral disc (IVD) is a suitable target. Comprised of an inner nucleus pulposus (NP) and an outer annulus fibrosus (AF), the degeneration of the IVD through trauma or aging presents a substantial socio-economic burden worldwide. The avascular nature of the mature NP forces cells to reside in a unique environment with increased lactate levels, conditions that pose a challenge to cell-based therapies. We assessed adipose and IVD tissue-derived stromal cells through in vitro transcriptome analysis in 2D and 3D culture and suggested that the transcription factor Glis1 and metabolite oxaloacetic acid (OAA) could provide NP cells with survival tools for the harsh niche conditions in the IVD.