Atypical Chemokine Receptor 3 Generates Guidance Cues for CXCL12-Mediated Endothelial Cell Migration

JPT2 Affects Trophoblast Functions and Macrophage Polarization and Metabolism, and Acts as a Potential Therapeutic Target for Recurrent Spontaneous Abortion

Recurrent spontaneous abortion (RSA) is a pregnancy-related condition with complex etiology. Trophoblast dysfunction and abnormal macrophage polarization and metabolism are associated with RSA; however, the underlying mechanisms remain unknown. Jupiter microtubule-associated homolog 2 (JPT2) is essential for calcium mobilization; however, its role in RSA remains unclear. In this study, it is found that the expression levels of JPT2, a nicotinic acid adenine dinucleotide phosphate-binding protein, are decreased in the villous tissues of patients with RSA and placental tissues of miscarried mice. Mechanistically, it is unexpectedly found that abnormal JPT2 expression regulates trophoblast function and thus involvement in RSA via c-Jun N-terminal kinase (JNK) signaling, but not via calcium mobilization. Specifically, on the one hand, JPT2 deficiency inhibits trophoblast adhesion, migration, and invasion by inhibiting the JNK/atypical chemokine receptor 3 axis. On the other hand, trophoblast JPT2 deficiency contributes to M1 macrophage polarization by promoting the accumulation of citrate and reactive oxygen species via inhibition of the JNK/interleukin-6 axis. Self-complementary adeno-associated virus 9-JPT2 treatment alleviates embryonic resorption in abortion-prone mice. In summary, this study reveals that JPT2 mediates the remodeling of the immune microenvironment at the maternal-fetal interface, suggesting its potential as a therapeutic target for RSA.

exFINDER: identify external communication signals using single-cell transcriptomics data

Cells make decisions through their communication with other cells and receiving signals from their environment. Using single-cell transcriptomics, computational tools have been developed to infer cell-cell communication through ligands and receptors. However, the existing methods only deal with signals sent by the measured cells in the data, the received signals from the external system are missing in the inference. Here, we present exFINDER, a method that identifies such external signals received by the cells in the single-cell transcriptomics datasets by utilizing the prior knowledge of signaling pathways. In particular, exFINDER can uncover external signals that activate the given target genes, infer the external signal-target signaling network (exSigNet), and perform quantitative analysis on exSigNets. The applications of exFINDER to scRNA-seq datasets from different species demonstrate the accuracy and robustness of identifying external signals, revealing critical transition-related signaling activities, inferring critical external signals and targets, clustering signal-target paths, and evaluating relevant biological events. Overall, exFINDER can be applied to scRNA-seq data to reveal the external signal-associated activities and maybe novel cells that send such signals.

Novel Populations of Lung Capillary Endothelial Cells and Their Functional Significance

The role of the lung's microcirculation and capillary endothelial cells in normal physiology and the pathobiology of pulmonary diseases is unequivocally vital. The recent discovery of molecularly distinct aerocytes and general capillary (gCaps) endothelial cells by single-cell transcriptomics (scRNAseq) advanced the field in understanding microcirculatory milieu and cellular communications. However, increasing evidence from different groups indicated the possibility of more heterogenic structures of lung capillaries. Therefore, we investigated enriched lung endothelial cells by scRNAseq and identified five novel populations of gCaps with distinct molecular signatures and roles. Our analysis suggests that two populations of gCaps that express Scn7a(Na+) and Clic4(Cl-) ion transporters form the arterial-to-vein zonation and establish the capillary barrier. We also discovered and named mitotically-active "root" cells (Flot1+) on the interface between arterial, Scn7a+, and Clic4 + endothelium, responsible for the regeneration and repair of the adjacent endothelial populations. Furthermore, the transition of gCaps to a vein requires a venous-capillary endothelium expressing Lingo2. Finally, gCaps detached from the zonation represent a high level of Fabp4, other metabolically active genes, and tip-cell markers showing angiogenesis-regulating capacity. The discovery of these populations will translate into a better understanding of the involvement of capillary phenotypes and their communications in lung disease pathogenesis.

exFINDER: identify external communication signals using single-cell transcriptomics data

Cells make decisions through their communication with other cells and receiving signals from their environment. Using single-cell transcriptomics, computational tools have been developed to infer cell-cell communication through ligands and receptors. However, the existing methods only deal with signals sent by the measured cells in the data, the received signals from the external system are missing in the inference. Here, we present exFINDER, a method that identifies such external signals received by the cells in the single-cell transcriptomics datasets by utilizing the prior knowledge of signaling pathways. In particular, exFINDER can uncover external signals that activate the given target genes, infer the external signal-target signaling network (exSigNet), and perform quantitative analysis on exSigNets. The applications of exFINDER to scRNA-seq datasets from different species demonstrate the accuracy and robustness of identifying external signals, revealing critical transition-related signaling activities, inferring critical external signals and targets, clustering signal-target paths, and evaluating relevant biological events. Overall, exFINDER can be applied to scRNA-seq data to reveal the external signal-associated activities and maybe novel cells that send such signals.

Lymphangiogenesis Guidance Mechanisms and Therapeutic Implications in Pathological States of the Cornea

Corneal lymphangiogenesis is one component of the neovascularization observed in several inflammatory pathologies of the cornea including dry eye disease and corneal graft rejection. Following injury, corneal (lymph)angiogenic privilege is impaired, allowing ingrowth of blood and lymphatic vessels into the previously avascular cornea. While the mechanisms underlying pathological corneal hemangiogenesis have been well described, knowledge of the lymphangiogenesis guidance mechanisms in the cornea is relatively scarce. Various signaling pathways are involved in lymphangiogenesis guidance in general, each influencing one or multiple stages of lymphatic vessel development. Most endogenous factors that guide corneal lymphatic vessel growth or regression act via the vascular endothelial growth factor C signaling pathway, a central regulator of lymphangiogenesis. Several exogenous factors have recently been repurposed and shown to regulate corneal lymphangiogenesis, uncovering unique signaling pathways not previously known to influence lymphatic vessel guidance. A strong understanding of the relevant lymphangiogenesis guidance mechanisms can facilitate the development of targeted anti-lymphangiogenic therapeutics for corneal pathologies. In this review, we examine the current knowledge of lymphatic guidance cues, their regulation of inflammatory states in the cornea, and recently discovered anti-lymphangiogenic therapeutic modalities.

Atypical Roles of the Chemokine Receptor ACKR3/CXCR7 in Platelet Pathophysiology

The manifold actions of the pro-inflammatory and regenerative chemokine CXCL12/SDF-1α are executed through the canonical GProteinCoupledReceptor CXCR4, and the non-canonical ACKR3/CXCR7. Platelets express CXCR4, ACKR3/CXCR7, and are a vital source of CXCL12/SDF-1α themselves. In recent years, a regulatory impact of the CXCL12-CXCR4-CXCR7 axis on platelet biogenesis, i.e., megakaryopoiesis, thrombotic and thrombo-inflammatory actions have been revealed through experimental and clinical studies. Platelet surface expression of ACKR3/CXCR7 is significantly enhanced following myocardial infarction (MI) in acute coronary syndrome (ACS) patients, and is also associated with improved functional recovery and prognosis. The therapeutic implications of ACKR3/CXCR7 in myocardial regeneration and improved recovery following an ischemic episode, are well documented. Cardiomyocytes, cardiac-fibroblasts, endothelial lining of the blood vessels perfusing the heart, besides infiltrating platelets and monocytes, all express ACKR3/CXCR7. This review recapitulates ligand induced differential trafficking of platelet CXCR4-ACKR3/CXCR7 affecting their surface availability, and in regulating thrombo-inflammatory platelet functions and survival through CXCR4 or ACKR3/CXCR7. It emphasizes the pro-thrombotic influence of CXCL12/SDF-1α exerted through CXCR4, as opposed to the anti-thrombotic impact of ACKR3/CXCR7. Offering an innovative translational perspective, this review also discusses the advantages and challenges of utilizing ACKR3/CXCR7 as a potential anti-thrombotic strategy in platelet-associated cardiovascular disorders, particularly in coronary artery disease (CAD) patients post-MI.

CXCR7 Antagonism Reduces Acute Lung Injury Pathogenesis

Loss of control in the trafficking of immune cells to the inflamed lung tissue contributes to the pathogenesis of life-threatening acute lung injury (ALI) and its more severe form, acute respiratory distress syndrome (ARDS). Targeting CXCR7 has been proposed as a potential therapeutic approach to reduce pulmonary inflammation; however, its role and its crosstalk with the two chemokine receptors CXCR3 and CXCR4 via their shared ligands CXCL11 and CXCL12 is not yet completely understood. The present paper aimed to characterize the pathological role of the CXCR3/CXCR4/CXCR7 axis in a murine model of ALI. Lipopolysaccharide (LPS) inhalation in mice resulted in the development of key pathologic features of ALI/ARDS, including breathing dysfunctions, alteration in the alveolar capillary barrier, and lung inflammation. LPS inhalation induced immune cell infiltration into the bronchoalveolar space, including CXCR3⁺ and CXCR4⁺ cells, and enhanced the expression of the ligands of these two chemokine receptors. The first-in-class CXCR7 antagonist, ACT-1004-1239, increased levels of CXCL11 and CXCL12 in the plasma without affecting their levels in inflamed lung tissue, and consequently reduced CXCR3⁺ and CXCR4⁺ immune cell infiltrates into the bronchoalveolar space. In the early phase of lung inflammation, characterized by a massive influx of neutrophils, treatment with ACT-1004-1239 significantly reduced the LPS-induced breathing pattern alteration. Both preventive and therapeutic treatment with ACT-1004-1239 reduced lung vascular permeability and decreased inflammatory cell infiltrates. In conclusion, these results demonstrate a key pathological role of CXCR7 in ALI/ARDS and highlight the clinical potential of ACT-1004-1239 in ALI/ARDS pathogenesis.

Role of epigenetic m6 A RNA methylation in vascular development: mettl3 regulates vascular development through PHLPP2/mTOR-AKT signaling

N⁶ -methyladenosine (m6A) methylation is the most prevalent RNA modification, and it emerges as an important regulatory mechanism of gene expression involved in many cellular and biological processes. However, the role of m⁶ A methylation in vascular development is not clear. The m⁶ A RNA methylation is regulated by dynamic interplay among methyltransferases, binding proteins, and demethylases. Mettl3 is a member of the mettl3-mettl14 methyltransferase complex, referred to as writers that catalyze m6A RNA methylation. Here, we used CRISPR-Cas9 genome editing to develop two lines of knockout (KO) zebrafish for mettl3. Heterozygous mettl3^+/- KO embryos show defective vascular development, which is directly visible in fli-EGFP and flk-EGFP zebrafish. Alkaline phosphatase staining and whole mount in situ hybridization with cdh5, and flk markers demonstrated defective development of intersegmental vessels (ISVs), subintestinal vessels (SIVs), interconnecting vessels (ICVs) and dorsal longitudinal anastomotic vessels (DLAV) in both heterozygous mettl3^+/- and homozygous mettl3^-/- KO zebrafish embryos. Similar phenotypes were observed in zebrafish embryos with morpholino knockdown (KD) of mettl3; however, the vascular defects were rescued fully by overexpression of constitutively active AKT1. KD of METTL3 in human endothelial cells inhibited cell proliferation, migration, and capillary tube formation. Mechanistically, mettl3 KO and KD significantly reduced the levels of m⁶ A RNA methylation, and AKT phosphorylation (S473) by an increase in the expression of phosphatase enzyme PHLPP2 and reduction in the phosphorylation of mTOR (S2481), a member of the phosphatidylinositol 3-kinase-related kinase family of protein kinases. These data suggest that m⁶ A RNA methylation regulates vascular development via PHLPP2/mTOR-AKT signaling.

Involvement of Cxcl12a/Cxcr4b Chemokine System in Mediating the Stimulatory Effect of Embryonic Ethanol Exposure on Neuronal Density in Zebrafish Hypothalamus

BACKGROUND

Embryonic exposure to ethanol (EtOH) produces marked disturbances in neuronal development and alcohol-related behaviors, with low-moderate EtOH doses stimulating neurogenesis without producing apoptosis and high doses having major cytotoxic effects while causing gross morphological abnormalities. With the pro-inflammatory chemokine system, Cxcl12, and its main receptor Cxcr4, known to promote processes of neurogenesis, we examined here this neuroimmune system in the embryonic hypothalamus to test directly if it mediates the stimulatory effects low-moderate EtOH doses have on neuronal development.

METHODS

We used the zebrafish (Danio rerio) model, which develops externally and allows one to investigate the developing brain in vivo with precise control of dose and timing of EtOH delivery in the absence of maternal influence. Zebrafish were exposed to low-moderate EtOH doses (0.1, 0.25, 0.5% v/v), specifically during a period of peak hypothalamic development from 22 to 24 hours postfertilization, and in some tests were pretreated from 2 to 22 hpf with the Cxcr4 receptor antagonist, AMD3100. Measurements in the hypothalamus at 26 hpf were taken of cxcl12a and cxcr4b transcription, signaling, and neuronal density using qRT-PCR, RNAscope, and live imaging of transgenic zebrafish.

RESULTS

Embryonic EtOH exposure, particularly at the 0.5% dose, significantly increased levels of cxcl12a and cxcr4b mRNA in whole embryos, number of cxcl12a and cxcr4b transcripts in developing hypothalamus, and internalization of Cxcr4b receptors in hypothalamic cells. Embryonic EtOH also caused an increase in the number of hypothalamic neurons and coexpression of cxcl12a and cxcr4b transcripts within these neurons. Each of these stimulatory effects of EtOH in the embryo was blocked by pretreatment with the Cxcr4 antagonist AMD3100.

CONCLUSIONS

These results provide clear evidence that EtOH's stimulatory effects at low-moderate doses on the number of hypothalamic neurons early in development are mediated, in part, by increased transcription and intracellular activation of this chemokine system, likely due to autocrine signaling of Cxcl12a at its Cxcr4b receptor within the neurons.