The chemokine receptor CXCR4 is essential for vascularization of the gastrointestinal tract

MicroRNA-34a suppresses KLF2 to promote pathological angiogenesis through the CXCR4/CXCL12 pathway in age-related macular degeneration

Age-related macular degeneration (AMD), characterized by pathologic choroidal neovascularization (CNV), is a leading cause of vision loss in the elderly. Vascular endothelial growth factor A (VEGFa) antagonists can prevent acute vision loss, but high treatment burden and loss of efficacy with chronic therapy highlight the need to explore alternative mechanisms. Recently, microRNA-34a (miR-34a) has emerged as a key regulator in aging and age-related diseases, but its role in neovascular AMD is unclear. In an injury-induced murine CNV model, we discovered miR-34a promoted pathological angiogenesis, without altering expression of Vegfa or its receptor Kdr, the canonical regulators of CNV. Mechanistically, miR-34a directly targets and inhibits the transcription factor KLF2 thereby upregulating the pro-angiogenic factors CXCR4 and CXCL12. Finally, we show miR-34a exacerbates CNV in aged mice and is expressed in CNV lesions excised from wet AMD patients. These findings establish a causal link between the age-related miR-34a and neovascularization in AMD.

Teaser

Identification of a molecular mechanism involved in the pathogenesis of a prevalent and debilitating age-related ocular disease.

Endothelial-specific CXCL12 regulates neovascularization during tissue repair and tumor progression

C-X-C motif chemokine ligand 12 (CXCL12; Stromal Cell-Derived Factor 1 [SDF-1]), most notably known for its role in embryogenesis and hematopoiesis, has been implicated in tumor pathophysiology and neovascularization. However, its cell-specific role and mechanism of action have not been well characterized. Previous work by our group has demonstrated that hypoxia-inducible factor (HIF)-1 modulates downstream CXCL12 expression following ischemic tissue injury. By utilizing a conditional CXCL12 knockout murine model, we demonstrate that endothelial-specific deletion of CXCL12 (eKO) modulates ischemic tissue survival, altering tissue repair and tumor progression without affecting embryogenesis and morphogenesis. Loss of endothelial-specific CXCL12 disrupts critical endothelial-fibroblast crosstalk necessary for stromal growth and vascularization. Using murine parabiosis with novel transcriptomic technologies, we demonstrate that endothelial-specific CXCL12 signaling results in downstream recruitment of non-inflammatory circulating cells, defined by neovascularization modulating genes. These findings indicate an essential role for endothelial-specific CXCL12 expression during the neovascular response in tissue injury and tumor progression.

A neuro-lymphatic communication guides lymphatic development by CXCL12 and CXCR4 signaling

Lymphatic vessels grow through active sprouting and mature into a vascular complex that includes lymphatic capillaries and collecting vessels that ensure fluid transport. However, the signaling cues that direct lymphatic sprouting and patterning remain unclear. In this study, we demonstrate that chemokine signaling, specifically through CXCL12 and CXCR4, plays crucial roles in regulating lymphatic development. We show that LEC-specific Cxcr4-deficient mouse embryos and CXCL12 mutant embryos exhibit severe defects in lymphatic sprouting, migration and lymphatic valve formation. We also discovered that CXCL12, originating from peripheral nerves, directs the migration of dermal lymphatic vessels to align with nerves in developing skin. Deletion of Cxcr4 or blockage of CXCL12 and CXCR4 activity results in reduced VEGFR3 levels on the LEC surface. This, in turn, impairs VEGFC-mediated VEGFR3 signaling and downstream PI3K and AKT activities. Taken together, these data identify previously unknown chemokine signaling originating from peripheral nerves that guides dermal lymphatic sprouting and patterning. Our work identifies for the first time a neuro-lymphatics communication during mouse development and reveals a previously unreported mechanism by which CXCR4 modulates VEGFC, VEGFR3 and AKT signaling.

Adamts9 is required for the development of primary ovarian follicles and maintenance of female sex in zebrafish†

Previous studies have suggested that adamts9 (a disintegrin and metalloprotease with thrombospondin type-1 motifs, member 9), an extracellular matrix (ECM) metalloprotease, participates in primordial germ cell (PGC) migration and is necessary for female fertility. In this study, we found that adamts9 knockout (KO) led to reduced body size, and female-to-male sex conversion in late juvenile or adult zebrafish; however, primary sex determination was not affected in early juveniles of adamts9 KO. Overfeeding and lowering the rearing density rescued growth defects in female adamts9 KO fish but did not rescue defects in ovarian development in adamts9 KO. Delayed PGC proliferation, significantly reduced number and size of Stage IB follicles (equivalent to primary follicles) in early juveniles of adamts9 KO, and arrested development at Stage IB follicles in mid- or late-juveniles of adamts9 KO are likely causes of female infertility and sex conversion. Via RNAseq, we found significant enrichment of differentially expressed genes involved in ECM organization during sexual maturation in ovaries of wildtype fish; and significant dysregulation of these genes in adamts9 KO ovaries. RNAseq analysis also showed enrichment of inflammatory transcriptomic signatures in adult ovaries of these adamts9 KO. Taken together, our results indicate that adamts9 is critical for development of primary ovarian follicles and maintenance of female sex, and loss of adamts9 leads to defects in ovarian follicle development, female infertility, and sex conversion in late juveniles and mature adults. These results show that the ECM and extracellular metalloproteases play major roles in maintaining ovarian follicle development in zebrafish.

Chemokine receptor CXCR7 antagonism ameliorates cardiac and renal fibrosis induced by mineralocorticoid excess

Cardiorenal fibrosis is a common feature of chronic cardiovascular disease and recent data suggests that cytokines and chemokines may also drive fibrosis. Here we tested the hypothesis that CXCR7, a highly conserved chemokine receptor, contributes to cardiac and renal fibrosis. We generated an anti-mouse CXCR7-specific monoclonal antibody (CXCR7 mAb) and tested its anti-fibrotic actions in cardiorenal fibrosis induced using the deoxycorticosterone acetate/uni-nephrectomy (DOCA-UNX) model. CXCR7 mAb treatment (10 mg/kg, twice weekly for 6 weeks) significantly attenuated the development of cardiac and renal fibrosis, and reduced fibrotic and inflammatory gene expression levels, in the absence of an effect on blood pressure. Immunohistochemical analysis demonstrated an increase in the vascular expression of CXCR7 in DOCA-UNX-treated mice. This study demonstrated that a CXCR7 mediated pathway plays a significant role in cardiac and renal fibrosis induced by DOCA-UNX treatment. Accordingly, antagonism of CXCR7 may provide a therapeutic opportunity to mitigate against fibrosis in the setting of mineralocorticoid excess.

Allosteric modulation of the CXCR4:CXCL12 axis by targeting receptor nanoclustering via the TMV-TMVI domain

CXCR4 is a ubiquitously expressed chemokine receptor that regulates leukocyte trafficking and arrest in both homeostatic and pathological states. It also participates in organogenesis, HIV-1 infection, and tumor development. Despite the potential therapeutic benefit of CXCR4 antagonists, only one, plerixafor (AMD3100), which blocks the ligand-binding site, has reached the clinic. Recent advances in imaging and biophysical techniques have provided a richer understanding of the membrane organization and dynamics of this receptor. Activation of CXCR4 by CXCL12 reduces the number of CXCR4 monomers/dimers at the cell membrane and increases the formation of large nanoclusters, which are largely immobile and are required for correct cell orientation to chemoattractant gradients. Mechanistically, CXCR4 activation involves a structural motif defined by residues in TMV and TMVI. Using this structural motif as a template, we performed in silico molecular modeling followed by in vitro screening of a small compound library to identify negative allosteric modulators of CXCR4 that do not affect CXCL12 binding. We identified AGR1.137, a small molecule that abolishes CXCL12-mediated receptor nanoclustering and dynamics and blocks the ability of cells to sense CXCL12 gradients both in vitro and in vivo while preserving ligand binding and receptor internalization.

Pan-cancer integrative analyses dissect the remodeling of endothelial cells in human cancers

Therapeutics targeting tumor endothelial cells (TECs) have been explored for decades, with only suboptimal efficacy achieved, partly due to an insufficient understanding of the TEC heterogeneity across cancer patients. We integrated single-cell RNA-seq data of 575 cancer patients from 19 solid tumor types, comprehensively charting the TEC phenotypic diversities. Our analyses uncovered underappreciated compositional and functional heterogeneity in TECs from a pan-cancer perspective. Two subsets, CXCR4 + tip cells and SELE + veins, represented the prominent angiogenic and proinflammatory phenotypes of TECs, respectively. They exhibited distinct spatial organization patterns, and compared to adjacent non-tumor tissues, tumor tissue showed an increased prevalence of CXCR4 + tip cells, yet with SELE + veins depleted. Such functional and spatial characteristics underlie their differential associations with the response of anti-angiogenic therapies and immunotherapies. Our integrative resources and findings open new avenues to understand and clinically intervene in the tumor vasculature.

Current status of the small molecule anti-HIV drugs in the pipeline or recently approved

Human Immunodeficiency Virus (HIV) is the causative agent of Acquired Immunodeficiency Syndrome (AIDS) with high morbidity and mortality rates. Treatment of AIDS/HIV is being complicated by increasing resistance to currently used antiretroviral (ARV) drugs, mainly in low- and middle-income countries (LMICs) due to drug misuse, poor drug supply and poor treatment monitoring. However, progress has been made in the development of new ARV drugs, targeting different HIV components (Fig. 1). This review aims at presenting and discussing the progress made towards the discovery of new ARVs that are at different stages of clinical trials as of July 2024. For each compound, the mechanism of action, target biomolecule, genes associated with resistance, efficacy and safety, class, and phase of clinical trial are discussed. These compounds include analogues of nucleoside reverse transcriptase inhibitors (NRTIs) - islatravir and censavudine; non-nucleoside reverse transcriptase inhibitors (NNRTIs) - Rilpivirine, elsulfavirine and doravirine; integrase inhibitors namely cabotegravir and dolutegravir and chemokine coreceptors 5 and 2 (CC5/CCR2) antagonists for example cenicriviroc. Also, fostemsavir is being developed as an attachment inhibitor while lenacapavir, VH4004280 and VH4011499 are capsid inhibitors. Others are maturation inhibitors such as GSK-254, GSK3532795, GSK3739937, GSK2838232, and other compounds labelled as miscellaneous (do not belong to the classical groups of anti-HIV drugs or to the newer classes) such as obefazimod and BIT225. There is a considerable progress in the development of new anti-HIV drugs and the effort will continue since HIV infections has no cure or vaccine till now. Efforts are needed to reduce the toxicity of available drugs or discover new drugs with new classes which can delay the development of resistance.

The story of clobenpropit and CXCR4: can be an effective drug in cancer and autoimmune diseases?

Clobenpropit is a histamine H3 receptor antagonist and has developed as a potential therapeutic drug due to its ability to inhibit CXCR4, a chemokine receptor involved in autoimmune diseases and cancer pathogenesis. The CXCL12/CXCR4 axis involves several biological phenomena, including cell proliferation, migration, angiogenesis, inflammation, and metastasis. Accordingly, inhibiting CXCR4 can have promising clinical outcomes in patients with malignancy or autoimmune disorders. Based on available knowledge, Clobenpropit can effectively regulate the release of monocyte-derived inflammatory cytokine in autoimmune diseases such as juvenile idiopathic arthritis (JIA), presenting a potential targeted target with possible advantages over current therapeutic approaches. This review summarizes the intricate interplay between Clobenpropit and CXCR4 and the molecular mechanisms underlying their interactions, comprehensively analyzing their impact on immune regulation. Furthermore, we discuss preclinical and clinical investigations highlighting the probable efficacy of Clobenpropit for managing autoimmune diseases and cancer. Through this study, we aim to clarify the immunomodulatory role of Clobenpropit and its advantages and disadvantages as a novel therapeutic opportunity.

The complex nature of CXCR4 mutations in WHIM syndrome

Heterozygous autosomal dominant mutations in the CXCR4 gene cause WHIM syndrome, a severe combined immunodeficiency disorder. The mutations primarily affect the C-terminal region of the CXCR4 chemokine receptor, specifically several potential phosphorylation sites critical for agonist (CXCL12)-mediated receptor internalization and desensitization. Mutant receptors have a prolonged residence time on the cell surface, leading to hyperactive signaling that is responsible for some of the symptoms of WHIM syndrome. Recent studies have shown that the situation is more complex than originally thought, as mutant WHIM receptors and CXCR4 exhibit different dynamics at the cell membrane, which also influences their respective cellular functions. This review examines the functional mechanisms of CXCR4 and the impact of WHIM mutations in both physiological and pathological conditions.

Efficacy of Cisplatin-CXCR4 Antagonist Combination Therapy in Oral Cancer

Cisplatin is a platinum-based compound that is widely used for treating inoperable oral squamous cell carcinoma (OSCC) in Japan; however, resistance to cisplatin presents a challenge and innovative approaches are required. We aimed to investigate the therapeutic potential of targeting the chemokine receptor CXCR4, which is involved in angiogenesis and tumor progression, using the CXCR4 inhibitor AMD3100, in combination with cisplatin. AMD3100 induced necrosis and bleeding in OSCC xenografts by inhibiting angiogenesis. We investigated the combined ability of AMD3100 plus cisplatin to enhance the antitumor effect in cisplatin-resistant OSCC. An MTS assay identified HSC-2 cells as cisplatin-resistant cells in vitro. Mice treated with the cisplatin-AMD combination exhibited the most significant reduction in tumor volume, accompanied by extensive hemorrhage and necrosis. Histological examination indicated thin and short tumor vessels in the AMD and cisplatin-AMD groups. These results indicated that cisplatin and AMD3100 had synergistic antitumor effects, highlighting their potential for vascular therapy of refractory OSCC. Antitumor vascular therapy using cisplatin combined with a CXCR4 inhibitor provides a novel strategy for addressing cisplatin-resistant OSCC.

Impact of plerixafor use in the mobilization of blood grafts for autologous hematopoietic cell transplantation

Plerixafor (PLER), a reversible antagonist of the CXC chemokine receptor type 4, has been in clinical use for mobilization of blood grafts for autologous hematopoietic cell transplantation (AHCT) for about 15 years. Initially PLER was investigated in placebo-controlled trials with the granulocyte colony-stimulating factor (G-CSF) filgrastim. It has also been used in combination with chemotherapy plus G-CSF in patients who had failed a previous mobilization attempt or appeared to mobilize poorly with current mobilization (preemptive use). This review summarizes what is known regarding addition of PLER to standard mobilization regimens. PLER increases mobilization of CD34+ cells, decreases the number of apheresis sessions needed to achieve collection targets and increases the proportion of patients who can proceed to AHCT. It appears also to increase the amount of various lymphocyte subsets in the grafts collected. In general, hematologic recovery after AHCT has been comparable to patients mobilized without PLER, although slower platelet recovery has been observed in some studies of patients who mobilize poorly. In phase III studies, long-term outcome has been comparable to patients mobilized without PLER. This also appears to be the case in patients receiving plerixafor for poor or suboptimal mobilization of CD34+ cells. In practice, PLER is safe and has not been shown to increase tumor cell mobilization.

Disruption of placental ACKR3 impairs growth and hematopoietic development of offspring

ACKR3 scavenges and degrades the stem cell recruiting chemokine CXCL12, which is essential for proper embryonic and, in particular, haematopoietic development. Here, we demonstrate strong expression of ACKR3 on trophoblasts. Using a maternally administered pharmacological blocker and Cre-mediated genetic approaches, we demonstrate that trophoblast ACKR3 is essential for preventing movement of CXCL12 from the mother to the embryo, with elevated plasma CXCL12 levels being detected in embryos from ACKR3-blocker-treated mothers. Mice born to mothers treated with the blocker are lighter and shorter than those born to vehicle-treated mothers and, in addition, display profound anaemia associated with a markedly reduced bone marrow haematopoietic stem cell population. Importantly, although the haematopoietic abnormalities are corrected as mice age, our studies reveal a postnatal window during which offspring of ACKR3-blocker-treated mice are unable to mount effective inflammatory responses to inflammatory/infectious stimuli. Overall, these data demonstrate that ACKR3 is essential for preventing CXCL12 transfer from mother to embryo and for ensuring properly regulated CXCL12 control over the development of the haematopoietic system.

A genetic variant of CXCR4 predicts pegylated interferon-alpha treatment response in HBeAg-positive chronic hepatitis B patients

Chemokine receptor 4 (CXCR4) plays a vital role in immunoregulation during hepatitis B virus (HBV) infection. This study aimed to screen single-nucleotide polymorphisms (SNPs) of CXCR4 for predicting pegylated interferon-alpha (PegIFNα) therapy response in chronic hepatitis B (CHB) patients. This retrospective cohort study enrolled a total of 945 CHB patients in two cohorts (Cohort 1, n = 238; Cohort 2, n = 707), and all the patients were hepatitis B e antigen (HBeAg)-positive and treated with PegIFNα for 48 weeks and followed up for 24 weeks. Twenty-two tag SNPs were selected in CXCR4 and its flanking region. A polygenic score (PGS) was utilized to evaluate the cumulative effect of multiple SNPs. The relationships between CXCR4 SNPs and PGS and PegIFNα treatment response were explored in the two cohorts. Among the 22 candidate SNPs of CXCR4, rs28367495 (T > C) was significantly linked to PegIFNα treatment response in both cohorts. In patients with more number of rs28367495 C allele, a higher rate of combined response (CR, defined as HBeAg seroconversion and HBV DNA level < 3.3 log10 IU/mL; P = 1.51 × 10-4), a lower mean hepatitis B surface antigen (HBsAg) level (P = 4.76 × 10-4), and a higher mean HBsAg decline (P = 3.88 × 10-4) at Week 72 were achieved. Moreover, a PGS integrating CXCR4_rs28367495 and five previously reported SNPs was strongly correlated with CR (P = 1.26 × 10-13), HBsAg level (P = 4.90 × 10-4), and HBsAg decline (P = 0.005) in all the patients of the two cohorts. CXCR4_rs28367495 is a promising indicator for predicting the responsiveness to PegIFNα treatment for HBeAg-positive CHB patients. The new PGS may further improve the prediction performance.

Cx4Mab-1: A Novel Anti-Mouse CXCR4 Monoclonal Antibody for Flow Cytometry

The CXC chemokine receptor 4 (CXCR4, CD184) is a member of the G protein-coupled receptor family that is expressed in most leukocytes. Overexpression of CXCR4 is associated with poor prognosis in not only hematopoietic malignancy but also solid tumors. Because CXCR4 is an attractive target for tumor therapy, reliable preclinical murine models using anti-CXCR4 monoclonal antibodies (mAbs) have been warranted. This study established a novel anti-mouse CXCR4 (mCXCR4) mAb using the Cell-Based Immunization and Screening method. Flow cytometric analysis showed that an anti-mCXCR4 mAb, Cx4Mab-1 (rat IgG2a, kappa), recognized mCXCR4-overexpressed Chinese hamster ovary-K1 (CHO/mCXCR4) cells and endogenously mCXCR4-expressing mouse myeloma P3X63Ag8U.1 (P3U1) cells. Furthermore, Cx4Mab-1 did not recognize mCXCR4-knockout P3U1 cells. The dissociation constants of Cx4Mab-1 for CHO/mCXCR4 and P3U1 were determined as 6.4 × 10-9 M and 2.3 × 10-9 M, respectively, indicating that Cx4Mab-1 possesses a high affinity to both endogenous and exogenous mCXCR4-expressing cells. These results indicate that Cx4Mab-1 could be a useful tool for preclinical mouse models.

CXCR4 Is a Potential Target for Anti-HIV Gene Therapy

The human immunodeficiency virus (HIV) epidemic is a global issue. The estimated number of people with HIV is 39,000,000 to date. Antiviral therapy is the primary approach to treat the infection. However, it does not allow for a complete elimination of the pathogen. The advances in modern gene therapy methods open up new possibilities of effective therapy. One of these areas of possibility is the development of technologies to prevent virus penetration into the cell. Currently, a number of technologies aimed at either the prevention of virus binding to the CCR5 coreceptor or its knockout are undergoing various stages of clinical trials. Since HIV can also utilize the CXCR4 coreceptor, technologies to modify this receptor are also required. Standard knockout of CXCR4 is impossible due to its physiological significance. This review presents an analysis of interactions between individual amino acids in CXCR4 and physiological ligands and HIV gp120. It also discusses potential targets for gene therapy approaches aimed at modifying the coreceptor.

Biological and mutational analyses of CXCR4-antagonist interactions and design of new antagonistic analogs

The chemokine receptor CXCR4 has become an attractive therapeutic target for HIV-1 infection, hematopoietic stem cell mobilization, and cancer metastasis. A wide variety of synthetic antagonists of CXCR4 have been developed and studied for a growing list of clinical applications. To compare the biological effects of different antagonists on CXCR4 functions and their common and/or distinctive molecular interactions with the receptor, we conducted head-to-head comparative cell-based biological and mutational analyses of the interactions with CXCR4 of eleven reported antagonists, including HC4319, DV3, DV1, DV1 dimer, V1, vMIP-II, CVX15, LY2510924, IT1t, AMD3100, and AMD11070 that were representative of different structural classes of D-peptides, L-peptide, natural chemokine, cyclic peptides, and small molecules. The results were rationalized by molecular modeling of CXCR4-antagonist interactions from which the common as well as different receptor binding sites of these antagonists were derived, revealing a number of important residues such as W94, D97, H113, D171, D262, and E288, mostly of negative charge. To further examine this finding, we designed and synthesized new antagonistic analogs by adding positively charged residues Arg to a D-peptide template to enhance the postulated charge-charge interactions. The newly designed analogs displayed significantly increased binding to CXCR4, which supports the notion that negatively charged residues of CXCR4 can engage in interactions with moieties of positive charge of the antagonistic ligands. The results from these mutational, modeling and new analog design studies shed new insight into the molecular mechanisms of different types of antagonists in recognizing CXCR4 and guide the development of new therapeutic agents.

Maternal CXCR4 deletion results in placental defects and pregnancy loss mediated by immune dysregulation

CXCR4 is a key regulator of the development of NK cells and DCs, both of which play an important role in early placental development and immune tolerance at the maternal-fetal interface. However, the role of CXCR4 in pregnancy is not well understood. Our study demonstrates that adult-induced global genetic CXCR4 deletion, but not uterine-specific CXCR4 deletion, was associated with increased pregnancy resorptions and decreased litter size. CXCR4-deficient mice had decreased NK cells and increased granulocytes in the decidua, along with increased leukocyte numbers in peripheral blood. We found that CXCR4-deficient mice had abnormal decidual NK cell aggregates and NK cell infiltration into trophoblast areas beyond the giant cell layer. This was associated with low NK cell expression of granzyme B, a NK cell granule effector, indicative of NK cell dysfunction. Pregnancy failure in these mice was associated with abnormalities in placental vascular development and increased placental expression of inflammatory genes. Importantly, adoptive BM transfer of WT CXCR4+ BM cells into CXCR4-deficient mice rescued the reproductive deficits by normalizing NK cell function and mediating normal placental vascular development. Collectively, our study found an important role for maternal CXCR4 expression in immune cell function, placental development, and pregnancy maintenance.

Targeting a cell-specific microRNA repressor of CXCR4 ameliorates atherosclerosis in mice

The CXC chemokine receptor 4 (CXCR4) in endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) is crucial for vascular integrity. The atheroprotective functions of CXCR4 in vascular cells may be counteracted by atherogenic functions in other nonvascular cell types. Thus, strategies for cell-specifically augmenting CXCR4 function in vascular cells are crucial if this receptor is to be useful as a therapeutic target in treating atherosclerosis and other vascular disorders. Here, we identified miR-206-3p as a vascular-specific CXCR4 repressor and exploited a target-site blocker (CXCR4-TSB) that disrupted the interaction of miR-206-3p with CXCR4 in vitro and in vivo. In vitro, CXCR4-TSB enhanced CXCR4 expression in human and murine ECs and VSMCs to modulate cell viability, proliferation, and migration. Systemic administration of CXCR4-TSB in Apoe-deficient mice enhanced Cxcr4 expression in ECs and VSMCs in the walls of blood vessels, reduced vascular permeability and monocyte adhesion to endothelium, and attenuated the development of diet-induced atherosclerosis. CXCR4-TSB also increased CXCR4 expression in B cells, corroborating its atheroprotective role in this cell type. Analyses of human atherosclerotic plaque specimens revealed a decrease in CXCR4 and an increase in miR-206-3p expression in advanced compared with early lesions, supporting a role for the miR-206-3p-CXCR4 interaction in human disease. Disrupting the miR-206-3p-CXCR4 interaction in a cell-specific manner with target-site blockers is a potential therapeutic approach that could be used to treat atherosclerosis and other vascular diseases.

C-X-C motif chemokine ligand 12 improves the developmental potential of bovine oocytes by activating SH2 domain-containing tyrosine phosphatase 2 during maturation†

In vitro maturation of mammalian oocytes is an important means in assisted reproductive technology. Most bovine immature oocytes complete nuclear maturation, but less than half develop to the blastocyst stage after fertilization. Thus, inefficient in vitro production is mainly caused by a suboptimal in vitro culture process, in which oocyte quality appears to be the limiting factor. In our study, a potential maternal regulator, C-X-C motif chemokine ligand 12, was identified by analyzing transcriptome data. C-X-C motif chemokine ligand 12 supplementation promoted the developmental potential of oocytes by improving protein synthesis and reorganizing cortical granules and mitochondria during in vitro maturation, which eventually increased blastocyst formation efficiency and cell number after parthenogenesis, fertilization, and cloning. All these promoting effects by C-X-C motif chemokine ligand 12 were achieved by activating SH2 domain-containing tyrosine phosphatase 2, thereby promoting the mitogen-activated protein kinase signaling pathway. These findings provide an in vitro maturation system that closely resembles the maternal environment to provide high-quality oocytes for in vitro production.

CXC chemokine receptor 4 (CXCR4) blockade in cancer treatment

CXC chemokine receptor type 4 (CXCR4) is a member of the G protein-coupled receptors (GPCRs) superfamily and is specific for CXC chemokine ligand 12 (CXCL12, also known as SDF-1), which makes CXCL12/CXCR4 axis. CXCR4 interacts with its ligand, triggering downstream signaling pathways that influence cell proliferation chemotaxis, migration, and gene expression. The interaction also regulates physiological processes, including hematopoiesis, organogenesis, and tissue repair. Multiple evidence revealed that CXCL12/CXCR4 axis is implicated in several pathways involved in carcinogenesis and plays a key role in tumor growth, survival, angiogenesis, metastasis, and therapeutic resistance. Several CXCR4-targeting compounds have been discovered and used for preclinical and clinical cancer therapy, most of which have shown promising anti-tumor activity. In this review, we summarized the physiological signaling of the CXCL12/CXCR4 axis and described the role of this axis in tumor progression, and focused on the potential therapeutic options and strategies to block CXCR4.

Crk/Crkl regulates early angiogenesis in mouse embryos by accelerating endothelial cell maturation

Rationale

Ubiquitously expressed cytoplasmic adaptors CRK and CRKL mediate multiple signaling pathways in mammalian embryogenesis. They are also associated with cardiovascular defects occurring in Miller-Dieker syndrome and 22q11.2 deletion syndrome, respectively. The embryonic mesoderm contributes to the formation of the cardiovascular system, yet the roles that Crk and Crkl play there are not understood on a single cell level.

Objectives

To determine functions of Crk and Crkl in the embryonic mesoderm during early mouse vascular development. Secondly, we will examine the molecular mechanisms responsible for early embryonic endothelial cell (EC) defects by performing single cell RNA-sequencing (scRNA-seq) and in vivo validation experiments.

Methods and Results

Inactivation of both Crk and Crkl together using Mesp1 ^Cre resulted embryonic lethality with severe vascular defects. Although vasculogenesis appeared normal, angiogenesis was disrupted both in the yolk sac and embryo proper, leading to disorganized vascular networks. We performed scRNA-seq of the Mesp1 ^Cre mesodermal lineage and found that there was upregulation of a great number of angiogenesis and cell migration related genes in ECs in the mutants, including NOTCH signaling genes such as Dll4 and Hey1 . Further bioinformatic analysis of EC subpopulations identified a relative increase in the number of more differentiated angiogenic ECs and decrease in EC progenitors. Consistent with this, we identified an expansion of Dll4 expressing cells within abnormal arteries, in vivo . Also, our bioinformatic data indicates that there is dysregulated expression of lineage genes that promote EC differentiation causing accelerated cell fate progression during EC differentiation.

Conclusions

Our results show that Crk and Crkl are crucial for regulating early embryonic angiogenesis. Combined inactivation of Crk/Crkl caused precocious EC maturation with an increase of atypical differentiated angiogenic ECs and failed vascular remodeling. This is in part due to increased NOTCH signaling and altered expression of cell migration genes.

Severe CD8+ T Lymphopenia in WHIM Syndrome Caused by Selective Sequestration in Primary Immune Organs

Warts, hypogammaglobulinemia, infections, and myelokathexis (WHIM) syndrome is an ultra-rare combined primary immunodeficiency disease caused by heterozygous gain-of-function mutations in the chemokine receptor CXCR4. WHIM patients typically present with recurrent acute infections associated with myelokathexis (severe neutropenia due to bone marrow retention of mature neutrophils). Severe lymphopenia is also common, but the only associated chronic opportunistic pathogen is human papillomavirus and mechanisms are not clearly defined. In this study, we show that WHIM mutations cause more severe CD8 than CD4 lymphopenia in WHIM patients and WHIM model mice. Mechanistic studies in mice revealed selective and WHIM allele dose-dependent accumulation of mature CD8 single-positive cells in thymus in a cell-intrinsic manner due to prolonged intrathymic residence, associated with increased CD8 single-positive thymocyte chemotactic responses in vitro toward the CXCR4 ligand CXCL12. In addition, mature WHIM CD8+ T cells preferentially home to and are retained in the bone marrow in mice in a cell-intrinsic manner. Administration of the specific CXCR4 antagonist AMD3100 (plerixafor) in mice rapidly and transiently corrected T cell lymphopenia and the CD4/CD8 ratio. After lymphocytic choriomeningitis virus infection, we found no difference in memory CD8+ T cell differentiation or viral load between wild-type and WHIM model mice. Thus, lymphopenia in WHIM syndrome may involve severe CXCR4-dependent CD8+ T cell deficiency resulting in part from sequestration in the primary lymphoid organs, thymus, and bone marrow.

Novel mechanisms and therapeutic targets in atherosclerosis: inflammation and beyond

This review based on the ESC William Harvey Lecture in Basic Science 2022 highlights recent experimental and translational progress on the therapeutic targeting of the inflammatory components in atherosclerosis, introducing novel strategies to limit side effects and to increase efficacy. Since the validation of the inflammatory paradigm in CANTOS and COLCOT, efforts to control the residual risk conferred by inflammation have centred on the NLRP3 inflammasome-driven IL-1β-IL6 axis. Interference with the co-stimulatory dyad CD40L-CD40 and selective targeting of tumour necrosis factor-receptor associated factors (TRAFs), namely the TRAF6-CD40 interaction in macrophages by small molecule inhibitors, harbour intriguing options to reduce established atherosclerosis and plaque instability without immune side effects. The chemokine system crucial for shaping immune cell recruitment and homoeostasis can be fine-tuned and modulated by its heterodimer interactome. Structure-function analysis enabled the design of cyclic, helical, or linked peptides specifically targeting or mimicking these interactions to limit atherosclerosis or thrombosis by blunting myeloid recruitment, boosting regulatory T cells, inhibiting platelet activity, or specifically blocking the atypical chemokine MIF without notable side effects. Finally, adventitial neuroimmune cardiovascular interfaces in advanced atherosclerosis show robust restructuring of innervation from perivascular ganglia and employ sensory neurons of dorsal root ganglia to enter the central nervous system and to establish an atherosclerosis-brain circuit sensor, while sympathetic and vagal efferents project to the celiac ganglion to create an atherosclerosis-brain circuit effector. Disrupting this circuitry by surgical or chemical sympathectomy limited disease progression and enhanced plaque stability, opening exciting perspectives for selective and tailored intervention beyond anti-inflammatory strategies.

CXCR4 and CXCL12 signaling regulates the development of extrinsic innervation to the colorectum

The gastrointestinal tract is innervated by an intrinsic neuronal network, known as the enteric nervous system (ENS), and by extrinsic axons arising from peripheral ganglia. The nerve of Remak (NoR) is an avian-specific sacral neural crest-derived ganglionated structure that extends from the cloaca to the proximal midgut and, similar to the pelvic plexus, provides extrinsic innervation to the distal intestine. The molecular mechanisms controlling extrinsic nerve fiber growth into the gut is unknown. In vertebrates, CXCR4, a cell-surface receptor for the CXCL12 chemokine, regulates migration of neural crest cells and axon pathfinding. We have employed chimeric tissue recombinations and organ culture assays to study the role of CXCR4 and CXCL12 molecules in the development of colorectal innervation. CXCR4 is specifically expressed in nerve fibers arising from the NoR and pelvic plexus, while CXCL12 is localized to the hindgut mesenchyme and enteric ganglia. Overexpression of CXCL12 results in significantly enhanced axonal projections to the gut from the NoR, while CXCR4 inhibition disrupts nerve fiber extension, supporting a previously unreported role for CXCR4 and CXCL12 signaling in extrinsic innervation of the colorectum.

Discovery of Bis-Imidazoline Derivatives as New CXCR4 Ligands

The chemokine receptor CXCR4 and its ligand CXCL12 regulate leukocyte trafficking, homeostasis and functions and are potential therapeutic targets in many diseases such as HIV-1 infection and cancers. Here, we identified new CXCR4 ligands in the CERMN chemical library using a FRET-based high-throughput screening assay. These are bis-imidazoline compounds comprising two imidazole rings linked by an alkyl chain. The molecules displace CXCL12 binding with submicromolar potencies, similarly to AMD3100, the only marketed CXCR4 ligand. They also inhibit anti-CXCR4 mAb 12G5 binding, CXCL12-mediated chemotaxis and HIV-1 infection. Further studies with newly synthesized derivatives pointed out to a role of alkyl chain length on the bis-imidazoline properties, with molecules with an even number of carbons equal to 8, 10 or 12 being the most potent. Interestingly, these differ in the functions of CXCR4 that they influence. Site-directed mutagenesis and molecular docking predict that the alkyl chain folds in such a way that the two imidazole groups become lodged in the transmembrane binding cavity of CXCR4. Results also suggest that the alkyl chain length influences how the imidazole rings positions in the cavity. These results may provide a basis for the design of new CXCR4 antagonists targeting specific functions of the receptor.

Thirty-five years since the discovery of chemotactic cytokines, interleukin-8 and MCAF: A historical overview

Inflammation is a host defense response to various invading stimuli, but an excessive and persistent inflammatory response can cause tissue injury, which can lead to irreversible organ damage and dysfunction. Excessive inflammatory responses are believed to link to most human diseases. A specific type of leukocyte infiltration into invaded tissues is required for inflammation. Historically, the underlying molecular mechanisms of this process during inflammation were an enigma, compromising research in the fields of inflammation, immunology, and pathology. However, the pioneering discovery of chemotactic cytokines (chemokines), monocyte-derived neutrophil chemotactic factor (MDNCF; interleukin [IL]-8, CXCL8) and monocyte chemotactic and activating factor (MCAF; monocyte chemotactic factor 1 [MCP-1], CCL2) in the late 1980s finally enabled us to address this issue. In this review, we provide a historical overview of chemokine research over the last 35 years.

CXCL12/CXCR4: An amazing challenge and opportunity in the fight against fibrosis

Fibrosis is a pathological process caused by abnormal wound healing response, which often leads to excessive deposition of extracellular matrix, distortion of organ architecture, and loss of organ function. Aging is an important risk factor for the development of organ fibrosis. C-X-C receptor 4 (CXCR4) is the predominant chemokine receptor on fibrocytes, C-X-C motif ligand 12 (CXCL12) is the only ligand of CXCR4. Accumulated evidence have confirmed that CXCL12/CXCR4 can be involved in multiple pathological mechanisms in fibrosis, such as inflammation, immunity, epithelial-mesenchymal transition, and angiogenesis. In addition, CXCL12/CXCR4 have also been shown to improve fibrosis levels in many organs including the heart, liver, lung and kidney; thus, they are promising targets for anti-fibrotic therapy. Notably, inhibitors of CXCL12 or CXCR4 also play an important role in various fibrosis-related diseases. In summary, this review systematically summarizes the role of CXCL12/CXCR4 in fibrosis, and this information is of great significance for understanding CXCL12/CXCR4. This will also contribute to the design of further studies related to CXCL12/CXCR4 and fibrosis, and shed light on potential therapies for fibrosis.

Ablation of CXCR4 expression in cardiomyocytes exacerbates isoproterenol‑induced cell death and heart failure

CXCR4 is a seven‑transmembrane‑spanning Gi‑coupled receptor for the SDF‑1 chemokine and plays a critical role in cardiovascular development and post‑injury repair. However, the specific role of CXCR4 in cardiomyocytes is incompletely understood. It was hypothesized that CXCR4 activation in cardiomyocytes antagonizes β‑adrenoceptor/Gs signaling‑induced cardiac dysfunction. Cardiomyocyte‑specific CXCR4 knockout (CXCR4‑^CMKO) mice were generated by crossing CXCR4^fl/fl and MHC‑Cre^+/‑ mice. Their cardiac structure and function in the basal state are equivalent to that of the control MHC‑Cre^+/‑ littermates until at least 4 months old. However, following continuous subcutaneous administration of isoproterenol (Iso) via an osmotic mini‑pump, the ventricular myocardial contractility, dilation, cardiomyocyte apoptosis, and interstitial fibrosis are worse in CXCR4‑^CMKO mice than in MHC‑Cre^+/‑ littermates. In the cultured H9C2 cardiomyocytes, SDF‑1 treatment markedly attenuated Iso‑induced apoptosis and reduction in phospho‑Akt, and this protective effect was lost by knockdown of CXCR4 or by co‑treatment with Gi inhibitors. In conclusion, CXCR4 promotes cardiomyocyte survival and heart function during β‑adrenergic stress.

Aberrant regulation of CXCR4 in cancer via deviant microRNA-targeted interactions

CXCR4 is involved in many facets of cancer, including being a major player in establishing metastasis. This is in part due to the deregulation of CXCR4, which can be attributed to many genetic and epigenetic mechanisms, including aberrant microRNA-CXCR4 interaction. MicroRNAs (miRNAs) are a type of small non-coding RNA that primarily targets the 3' UTR of mRNA transcripts, which in turn suppresses mRNA and subsequent protein expression. In this review, we reported and characterized the many aberrant miRNA-CXCR4 interactions that occur throughout human cancers. In particular, we reported known target sequences located on the 3' UTR of CXCR4 transcripts that tumour suppressor miRNAs bind and therefore regulate expression by. From these aberrant interactions, we also documented affected downstream genes/pathways and whether a particular tumour suppressor miRNA was reported as a prognostic marker in its respected cancer type. In addition, a limited number of cancer-causing miRNAs coined 'oncomirs' were reported and described in relation to CXCR4 regulation. Moreover, the mechanisms underlying both tumour suppressor and oncomir deregulations concerning CXCR4 expression were also explored. Furthermore, the miR-146a-CXCR4 axis was delineated in oncoviral infected endothelial cells in the context of virus-causing cancers. Lastly, miRNA-driven therapies and CXCR4 antagonist drugs were discussed as potential future treatment options in reported cancers pertaining to deregulated miRNA-CXCR4 interactions.

Chemokine signaling synchronizes angioblast proliferation and differentiation during pharyngeal arch artery vasculogenesis

Developmentally, the great vessels of the heart originate from the pharyngeal arch arteries (PAAs). During PAA vasculogenesis, PAA precursors undergo sequential cell fate decisions that are accompanied by proliferative expansion. However, how these two processes are synchronized remains poorly understood. Here, we find that the zebrafish chemokine receptor Cxcr4a is expressed in PAA precursors, and genetic ablation of either cxcr4a or the ligand gene cxcl12b causes PAA stenosis. Cxcr4a is required for the activation of the downstream PI3K/AKT cascade, which promotes not only PAA angioblast proliferation, but also differentiation. AKT has a well-known role in accelerating cell-cycle progression through the activation of cyclin-dependent kinases. Despite this, we demonstrate that AKT phosphorylates Etv2 and Scl, the key regulators of angioblast commitment, on conserved serine residues, thereby protecting them from ubiquitin-mediated proteasomal degradation. Altogether, our study reveals a central role for chemokine signaling in PAA vasculogenesis through orchestrating angioblast proliferation and differentiation.

Biologic Functions of Hydroxychloroquine in Disease: From COVID-19 to Cancer

Chloroquine (CQ) and Hydroxychloroquine (HCQ), initially utilized in the treatment of malaria, have now developed a long list of applications. Despite their clinical relevance, their mechanisms of action are not clearly defined. Major pathways by which these agents are proposed to function include alkalinization of lysosomes and endosomes, downregulation of C-X-C chemokine receptor type 4 (CXCR4) expression, high-mobility group box 1 protein (HMGB1) inhibition, alteration of intracellular calcium, and prevention of thrombus formation. However, there is conflicting data present in the literature. This is likely the result of the complex overlapping pathways between these mechanisms of action that have not previously been highlighted. In fact, prior research has focused on very specific portions of particular pathways without describing these in the context of the extensive CQ/HCQ literature. This review summarizes the detailed data regarding CQ/HCQ's mechanisms of action while also providing insight into the overarching themes. Furthermore, this review provides clinical context to the application of these diverse drugs including their role in malaria, autoimmune disorders, cardiovascular disease, thrombus formation, malignancies, and viral infections.

Multifaceted role of chemokines in solid tumors: From biology to therapy

Chemokines are small secretory chemotactic cytokines that control the directed migration of immune cells. Chemokines are involved in both anti-and pro-tumorigenic immune responses. Accumulating evidence suggests that the balance between these responses is influenced by several factors such as the stage of tumorigenesis, immune cell activation, recruitment of immune activating or immunosuppressive cells in the tumor microenvironment (TME), and chemokine receptor expression on effector and regulatory target cells. Cancer cells engage in a complex network with their TME components via several factors including growth factors, cytokines and chemokines that are critical for the growth of primary tumor and metastasis. However, chemokines show a multifaceted role in tumor progression including maintenance of stem-like properties, tumor cell proliferation/survival/senescence, angiogenesis, and metastasis. The heterogeneity of solid tumors in primary and metastatic cancers presents a challenge to the development of successful cancer therapy. Despite extensive research on how solid tumors escape immune cell-mediated anti-tumor response, finding an effective therapy for metastatic cancer still remains a challenge. This review discusses the multifarious roles of chemokines in solid tumors including various chemokine signaling pathways such as CXCL8-CXCR1/2, CXCL9, 10, 11-CXCR3, CXCR4-CXCL12, CCL(X)-CCR(X) in primary and metastatic cancers. We further discuss the novel therapeutic approaches that have been developed by major breakthroughs in chemokine research to treat cancer patients by the strategic blockade/activation of these signaling axes alone or in combination with immunotherapies.

CXCL12 defines lung endothelial heterogeneity and promotes distal vascular growth

There is a growing amount of data uncovering the cellular diversity of the pulmonary circulation and mechanisms governing vascular repair after injury. However, the molecular and cellular mechanisms contributing to the morphogenesis and growth of the pulmonary vasculature during embryonic development are less clear. Importantly, deficits in vascular development lead to significant pediatric lung diseases, indicating a need to uncover fetal programs promoting vascular growth. To address this, we used a transgenic mouse reporter for expression of Cxcl12, an arterial endothelial hallmark gene, and performed single-cell RNA sequencing on isolated Cxcl12-DsRed+ endothelium to assess cellular heterogeneity within pulmonary endothelium. Combining cell annotation with gene ontology and histological analysis allowed us to segregate the developing artery endothelium into functionally and spatially distinct subpopulations. Expression of Cxcl12 is highest in the distal arterial endothelial subpopulation, a compartment enriched in genes for vascular development. Accordingly, disruption of CXCL12 signaling led to, not only abnormal branching, but also distal vascular hypoplasia. These data provide evidence for arterial endothelial functional heterogeneity and reveal conserved signaling mechanisms essential for pulmonary vascular development.

Inflammation down regulates stromal cell-derived factor 1α in the early phase of pulpitis

The key to prevent pulp necrosis in the early stage of pulpitis is to promote tissue repair, which begins with cell migration. Stromal cell-derived factor 1α (SDF-1α) has been proven to promote cell migration. Related research has so far concentrated on the biological effects of SDF-1α while its expression in pulpitis is still unclear. We investigated the effect of inflammation on SDF-1α in dental pulp and the underlying regulatory mechanisms. First, rat pulpitis models were established by exposing pulp. SDF-1α was decreased on the 3rd day but increased on the 7th day. Next, lipopolysaccharide from Porphyromonas gingivalis (Pg.LPS) was applied to dental pulp cells (DPCs). Within 24 h, SDF-1α decreased, but after 48 h, it steadily increased. Similarly, SDF-1α expression in human chronic pulpitis tissues was also increased. To investigate the effect of altered SDF-1α on DPC migration, cell supernatants collected following Pg.LPS treatment were utilized to stimulate DPCs, and the number of migrated cells was correlated with changes in SDF-1α secretion. Finally, we explored the regulatory mechanisms of SDF-1α down-regulation in the early phase of pulpitis. Within 24 h, JNK/c-Jun pathway was activated in DPC inflammation. When JNK pathway was suppressed, SDF-1α rose. Furthermore, tumor necrosis factor receptor 2 (TNFR2) and apoptosis signal-regulated kinase-interacting protein 1 (AIP1) were up-regulated. Knockdown of them abolished Pg.LPS-induced activation of JNK and c-Jun(Ser63) and significantly enhanced SDF-1α. Our findings indicated that in the early phase of pulpitis, inflammation suppressed SDF-1α by up-regulating TNFR2 and AIP1, which activated JNK/c-Jun(Ser63) pathway.

CXCR4+ Treg cells control serum IgM levels and natural IgM autoantibody production by B-1 cells in the bone marrow

Regulatory T (Treg) cells represent a specialized lineage of suppressive CD4⁺ T cells whose functionality is critically dependent on their ability to migrate to and dwell in the proximity of cells they control. Here we show that continuous expression of the chemokine receptor CXCR4 in Treg cells is required for their ability to accumulate in the bone marrow (BM). Induced CXCR4 ablation in Treg cells led to their rapid depletion and consequent increase in mature B cells, foremost the B-1 subset, observed exclusively in the BM without detectable changes in plasma cells or hematopoietic stem cells or any signs of systemic or local immune activation elsewhere. Dysregulation of BM B-1 B cells was associated with a highly specific increase in IgM autoantibodies and total serum IgM levels. Thus, Treg cells control autoreactive B-1 B cells in a CXCR4-dependent manner. These findings have significant implications for understanding the regulation of B cell autoreactivity and malignancies.

Endothelial Cell Insulin Signaling Regulates CXCR4 (C-X-C Motif Chemokine Receptor 4) and Limits Leukocyte Adhesion to Endothelium

BACKGROUND

An activated, proinflammatory endothelium is a key feature in the development of complications of obesity and type 2 diabetes and can be caused by insulin resistance in endothelial cells.

METHODS

We analyzed primary human endothelial cells by RNA sequencing to discover novel insulin-regulated genes and used endothelial cell culture and animal models to characterize signaling through CXCR4 (C-X-C motif chemokine receptor 4) in endothelial cells.

RESULTS

CXCR4 was one of the genes most potently regulated by insulin, and this was mediated by PI3K (phosphatidylinositol 3-kinase), likely through FoxO1, which bound to the CXCR4 promoter. CXCR4 mRNA in CD31+ cells was 77% higher in mice with diet-induced obesity compared with lean controls and 37% higher in db/db mice than db/+ controls, consistent with upregulation of CXCR4 in endothelial cell insulin resistance. SDF-1 (stromal cell-derived factor-1)-the ligand for CXCR4-increased leukocyte adhesion to cultured endothelial cells. This effect was lost after deletion of CXCR4 by gene editing while 80% of the increase was prevented by treatment of endothelial cells with insulin. In vivo microscopy of mesenteric venules showed an increase in leukocyte rolling after intravenous injection of SDF-1, but most of this response was prevented in transgenic mice with endothelial overexpression of IRS-1 (insulin receptor substrate-1).

CONCLUSIONS

Endothelial cell insulin signaling limits leukocyte/endothelial cell interaction induced by SDF-1 through downregulation of CXCR4. Improving insulin signaling in endothelial cells or inhibiting endothelial CXCR4 may reduce immune cell recruitment to the vascular wall or tissue parenchyma in insulin resistance and thereby help prevent several vascular complications.

Chemokine C-X-C receptor 4 mediates recruitment of bone marrow-derived nonhematopoietic and immune cells to the pregnant uterus†

Bone marrow-derived progenitor cells (BMDPCs) are mobilized to the circulation in pregnancy and get recruited to the pregnant decidua where they contribute functionally to decidualization and successful implantation. However, the molecular mechanisms underlying BMDPCs recruitment to the decidua are unknown. CXCL12 ligand and its CXCR4 receptor play crucial roles in the mobilization and homing of stem/progenitor cells to various tissues. To investigate the role of CXCL12-CXCR4 axis in BMDPCs recruitment to decidua, we created transgenic GFP mice harboring CXCR4 gene susceptible to tamoxifen-inducible Cre-mediated ablation. These mice served as BM donors into wild-type C57BL/6 J female recipients using a 5-fluorouracil-based nongonadotoxic submyeloablation to achieve BM-specific CXCR4 knockout (CXCR4KO). Successful CXCR4 ablation was confirmed by RT-PCR and in vitro cell migration assays. Flow cytometry and immunohistochemistry showed a significant increase in GFP+ BM-derived cells (BMDCs) in the implantation site as compared to the nonpregnant uterus of control (2.7-fold) and CXCR4KO (1.8-fold) mice. This increase was uterus-specific and was not observed in other organs. This pregnancy-induced increase occurred in both hematopoietic (CD45+) and nonhematopoietic (CD45-) uterine BMDCs in control mice. In contrast, in CXCR4KO mice there was no increase in nonhematopoietic BMDCs in the pregnant uterus. Moreover, decidual recruitment of myeloid cells but not NK cells was diminished by BM CXCR4 deletion. Immunofluorescence showed the presence of nonhematopoietic GFP+ cells that were negative for CD45 (panleukocyte) and DBA (NK) markers in control but not CXCR4KO decidua. In conclusion, we report that CXCR4 expression in nonhematopoietic BMDPCs is essential for their recruitment to the pregnant decidua.

CXCR4/CXCL12 Activities in the Tumor Microenvironment and Implications for Tumor Immunotherapy

Simple Summary

Chemokines are small soluble proteins that control and regulate cell trafficking within and between tissues by binding to their receptors. Among them, CXCL12 and its receptor CXCR4 appeared with ancestral vertebrates, are expressed almost ubiquitously, and play essential roles in embryogenesis and organogenesis. In addition, CXCL12 and CXCR4 are involved in antigen recognition by T and B cells and in shaping the tumor microenvironment (TME), mainly towards dampening immune responses. New data indicate that CXCR4 interacts with the surface protein CD47 in a novel form of immunosurveillance, called ImmunoGenic Surrender (IGS). Following the co-internalization of CXCR4 and CD47 in tumor cells, macrophages phagocytose them and cross-present their antigens to the adaptive immune system, leading to tumor rejection in a fraction of mice. All of these specific activities of CXCL12 and CXCR4 in antigen presentation might be complementary to current immunotherapies.

Abstract

CXCR4 is a G-Protein coupled receptor that is expressed nearly ubiquitously and is known to control cell migration via its interaction with CXCL12, the most ancient chemokine. The functions of CXCR4/CXCL12 extend beyond cell migration and involve the recognition and disposal of unhealthy or tumor cells. The CXCR4/CXCL12 axis plays a relevant role in shaping the tumor microenvironment (TME), mainly towards dampening immune responses. Notably, CXCR4/CXCL12 cross-signal via the T and B cell receptors (TCR and BCR) and co-internalize with CD47, promoting tumor cell phagocytosis by macrophages in an anti-tumor immune process called ImmunoGenic Surrender (IGS). These specific activities in shaping the immune response might be exploited to improve current immunotherapies.

Synthesis and Evaluation of Novel Tetrahydronaphthyridine CXCR4 Antagonists with Improved Drug-like Profiles

Our first-generation CXCR4 antagonist TIQ15 was rationally modified to improve drug-like properties. Introducing a nitrogen atom into the aromatic portion of the tetrahydroisoquinoline ring led to several heterocyclic variants including the 5,6,7,8-tetrahydro-1,6-naphthyridine series, greatly reducing the inhibition of the CYP 2D6 enzyme. Compound 12a demonstrated the best overall properties after profiling a series of isomeric tetrahydronaphthyridine analogues in a battery of biochemical assays including CXCR4 antagonism, CYP 2D6 inhibition, metabolic stability, and permeability. The butyl amine side chain of 12a was substituted with various lipophilic groups to improve the permeability. These efforts culminated in the discovery of compound 30 as a potent CXCR4 antagonist (IC50 = 24 nM) with diminished CYP 2D6 activity, improved PAMPA permeability (309 nm/s), potent inhibition of human immunodeficiency virus entry (IC50 = 7 nM), a cleaner off-target in vitro safety profile, lower human ether a-go-go-related gene channel activity, and higher oral bioavailability in mice (% FPO = 27) compared to AMD11070 and TIQ15.

Neutrophils-From Bone Marrow to First-Line Defense of the Innate Immune System

Neutrophils (polymorphonuclear cells; PMNs) form a first line of defense against pathogens and are therefore an important component of the innate immune response. As a result of poorly controlled activation, however, PMNs can also mediate tissue damage in numerous diseases, often by increasing tissue inflammation and injury. According to current knowledge, PMNs are not only part of the pathogenesis of infectious and autoimmune diseases but also of conditions with disturbed tissue homeostasis such as trauma and shock. Scientific advances in the past two decades have changed the role of neutrophils from that of solely immune defense cells to cells that are responsible for the general integrity of the body, even in the absence of pathogens. To better understand PMN function in the human organism, our review outlines the role of PMNs within the innate immune system. This review provides an overview of the migration of PMNs from the vascular compartment to the target tissue as well as their chemotactic processes and illuminates crucial neutrophil immune properties at the site of the lesion. The review is focused on the formation of chemotactic gradients in interaction with the extracellular matrix (ECM) and the influence of the ECM on PMN function. In addition, our review summarizes current knowledge about the phenomenon of bidirectional and reverse PMN migration, neutrophil microtubules, and the microtubule organizing center in PMN migration. As a conclusive feature, we review and discuss new findings about neutrophil behavior in cancer environment and tumor tissue.

The significance of the SDF-1/CXCR4 signaling pathway in the normal development

Chemokines are chemoattractants that can regulate cell movement and adhesion. SDF-1 [stromal cell-derived factor-1 (SDF-1)] is a homeostatic CXC chemokine. SDF-1 and its receptors [CXC chemokine receptor 4 (CXCR4)] form a signaling pathway that plays critical roles in different pathological and physiological mechanisms, including embryogenesis, wound healing, angiogenesis, tumor growth, and proliferation. Therefore, the current review aimed to summarize the related studies that addressed the molecular signature of the SDF-1/CXCR4 pathway and to explain how this axis is involved in normal events.

CCRL2 Modulates Physiological and Pathological Angiogenesis During Retinal Development

Chemerin is a multifunctional protein involved in the regulation of inflammation, metabolism, and tumorigenesis. It binds to three receptors, CMKLR1, GPR1 and CCRL2. CMKLR1 is a fully functional receptor mediating most of the known activities of chemerin. CCRL2 does not seem to couple to any intracellular signaling pathway and is presently considered as an atypical receptor able to present the protein to cells expressing CMKLR1. CCRL2 is expressed by many cell types including leukocyte subsets and endothelial cells, and its expression is strongly upregulated by inflammatory stimuli. We recently reported that chemerin can negatively regulate the angiogenesis process, including during the development of the vascular network in mouse retina. The role of CCRL2 in angiogenesis was unexplored so far. In the present work, we demonstrate that mice lacking CCRL2 exhibit a lower density of vessels in the developing retina and this phenotype persists in adulthood, in a CMKLR1-dependent manner. Vascular sprouting was not affected, while vessel pruning, and endothelial cell apoptosis were increased. Pathological angiogenesis was also reduced in CCRL2^-/- mice in a model of oxygen-induced retinopathy. The phenotype closely mimics that of mice overexpressing chemerin, and the concentration of chemerin was found elevated in the blood of newborn mice, when the retinal vasculature develops. CCRL2 appears therefore to regulate the distribution and concentration of chemerin in organs, regulating thereby its bioactivity.

FGD5 regulates endothelial cell PI3 kinase-β to promote neo-angiogenesis

Angiogenesis is required in embryonic development and tissue repair in the adult. Vascular endothelial growth factor (VEGF) initiates angiogenesis, and VEGF or its receptor is targeted therapeutically to block pathological angiogenesis. Additional pro-angiogenic cues, such as CXCL12 acting via the CXCR4 receptor, co-operate with VEGF/VEGFR2 to cue vascular patterning. We studied the role of FGD5, an endothelial Rho GTP/GDP exchange factor (RhoGEF), to regulate CXCR4-dependent signals in the endothelial cell (EC). Patient-derived renal cell carcinomas produce a complex milieu of growth factors that stimulated sprouting angiogenesis and endothelial tip cell differentiation ex vivo that was blocked by EC FGD5 loss. In a simplified model, CXCL12 augmented sprouting and tip gene expression under conditions where VEGF was limiting. CXCL12-stimulated tip cell differentiation was dependent on PI3 kinase (PI3K)-β activity. Knockdown of EC FGD5 abolished CXCR4 signaling to PI3K-β and Akt. Further, inhibition of Rac1, a Rho GTPase required for PI3K-β activity, recapitulated the signaling defects of FGD5 deficiency, suggesting that FGD5 may regulate PI3K-β activity through Rac1. Overexpression of a RhoGEF deficient, Dbl domain-deleted FGD5 mutant reduced CXCL12-stimulated Akt phosphorylation and failed to rescue PI3K signaling in native FGD5-deficient EC, indicating that FGD5 RhoGEF activity is required for FDG5 function. Endothelial expression of mutant PI3K-β with an inactivated Rho binding domain confirmed that CXCL12-stimulated PI3K activity in EC requires Rac1-GTP co-regulation. Together, this data identify the role of FGD5 to generate Rac1-GTP to regulate pro-angiogenic CXCR4-dependent PI3K-β signaling in EC. Inhibition of FGD5 activity may complement current angiogenesis inhibitor drugs.

Cellular Niches for Hematopoietic Stem Cells and Lympho-Hematopoiesis in Bone Marrow During Homeostasis and Blood Cancers

Most types of blood cells, including immune cells are generated from hematopoietic stem cells (HSCs) within bone marrow in the adult. Most HSCs are in contact with and require the special microenvironment known as a niche for their maintenance. It has been thought that HSC niches comprise various types of support cells that provide critical signals, including cytokines and extracellular matrix for HSC regulation. However, among these cells, several lines of evidence have demonstrated that the population of bone marrow-specific mesenchymal stem cells, termed CXC chemokine ligand 12 (CXCL12)-abundant reticular (CAR) cells, which overlap strongly with leptin receptor-expressing (LepR⁺) cells, is the major cellular component of HSC niches. CAR/LepR⁺ cells give rise to most adipocytes and osteoblasts in adult bone marrow and express much higher levels of HSC niche factors, including cytokines CXCL12 and stem cell factor (SCF), which are essential for HSC maintenance, and transcription factors Foxc1 and Ebf3, which are essential for the formation and maintenance of HSC niches than other types of cells. CAR/LepR⁺ cells are present in human bone marrow, undergo fibrotic expansion, and have reduced expression of HSC niche factors in hematopoietic malignancies.

SDF-1 expression after preoperative chemoradiotherapy is associated with prognosis in patients with advanced lower rectal cancer

Stromal cell-derived factor-1 (SDF-1) expression is associated with cancer progression, as a biomarker of prognosis. We clarified the significance of SDF-1 expression on chemoradiotherapy (CRT) resistance and prognosis in advanced lower rectal cancer patients. We evaluated 98 patients with advanced lower rectal cancer who underwent preoperative CRT. All patients received 40 Gy of radiation therapy, with concurrent chemotherapy containing fluorinated pyrimidines, followed by surgical resection. SDF-1 expression in surgical specimens was examined by immunohistochemistry. We divided the patients into SDF-1-positive- (n = 52) and SDF-1-negative groups (n = 46) and compared the clinicopathological factors and survival rates. The SDF-1-positive group was more resistant to CRT than the SDF-1-negative group (non-responder rate, 63.5% vs. 47.8%, respectively ; p = 0.12). Overall survival (OS) in the SDF-1 positive group was significantly poorer vs. the SDF-1-negative group (5-year OS, 73.4% vs. 88.0%, respectively ; p = 0.02), and disease-free survival (DFS) was worse (5-year DFS, 61.0% vs. 74.1%, respectively ; p = 0.07). Multivariate analysis confirmed that SDF-1 expression was a significant independent prognostic predictor of OS (p = 0.04). SDF-1 expression after preoperative CRT is significantly associated with a poor prognosis in advanced lower rectal cancer patients and is a promising biomarker. J. Med. Invest. 68 : 309-314, August, 2021.

Identification of microenvironmental niches for hematopoietic stem cells and lymphoid progenitors-bone marrow fibroblastic reticular cells with salient features

Most lineages of blood cells, including immune cells are generated from hematopoietic stem cells (HSCs) in bone marrow throughout adult life. Since HSCs cannot expand on their own, they require and contact the special microenvironments, termed niches for their maintenance. HSC niches comprise supportive cells that provide adjacent HSCs with critical signals, including cytokines. Although bone marrow microenvironments have been thought to be complex, recent studies have demonstrated that the bone marrow-specific population of fibroblastic reticular cells with long processes, termed CXC chemokine ligand 12 (CXCL12)-abundant reticular (CAR) cells, which overlap strongly with leptin receptor (LepR)-expressing (LepR +) cells, is the major cellular component of niches for HSCs and lymphoid progenitors. CAR cells have salient features, expressing much higher levels of critical HSC niche factors than any other cell populations and function as self-renewing mesenchymal stem cells. Human counterpart of CAR cells is present and affected in diseases, including leukemia. Foxl1 + telocytes recently identified as the niche for intestinal stem cells share some features with CAR cells, suggesting that CAR cells are prototypical fibroblastic reticular cells creating niche for long-lived cells, including tissue stem cells and memory lymphocytes. These findings provided the basis for future mechanistic studies on the crosstalk between hematopoietic cells and microenvironments in both health and disease.

Beyond PROX1: transcriptional, epigenetic, and noncoding RNA regulation of lymphatic identity and function

The lymphatic vascular system acts as the major transportation highway of tissue fluids, and its activation or impairment is associated with a wide range of diseases. There has been increasing interest in understanding the mechanisms that control lymphatic vessel formation (lymphangiogenesis) and function in development and disease. Here, we discuss recent insights into new players whose identification has contributed to deciphering the lymphatic regulatory code. We reveal how lymphatic endothelial cells, the building blocks of lymphatic vessels, utilize their transcriptional, post-transcriptional, and epigenetic portfolio to commit to and maintain their vascular lineage identity and function, with a particular focus on development.

The Role of Post-Translational Modifications of Chemokines by CD26 in Cancer

Chemokines are a large family of small chemotactic cytokines that fulfill a central function in cancer. Both tumor-promoting and -impeding roles have been ascribed to chemokines, which they exert in a direct or indirect manner. An important post-translational modification that regulates chemokine activity is the NH₂-terminal truncation by peptidases. CD26 is a dipeptidyl peptidase (DPPIV), which typically clips a NH₂-terminal dipeptide from the chemokine. With a certain degree of selectivity in terms of chemokine substrate, CD26 only recognizes chemokines with a penultimate proline or alanine. Chemokines can be protected against CD26 recognition by specific amino acid residues within the chemokine structure, by oligomerization or by binding to cellular glycosaminoglycans (GAGs). Upon truncation, the binding affinity for receptors and GAGs is altered, which influences chemokine function. The consequences of CD26-mediated clipping vary, as unchanged, enhanced, and reduced activities are reported. In tumors, CD26 most likely has the most profound effect on CXCL12 and the interferon (IFN)-inducible CXCR3 ligands, which are converted into receptor antagonists upon truncation. Depending on the tumor type, expression of CD26 is upregulated or downregulated and often results in the preferential generation of the chemokine isoform most favorable for tumor progression. Considering the tight relationship between chemokine sequence and chemokine binding specificity, molecules with the appropriate characteristics can be chemically engineered to provide innovative therapeutic strategies in a cancer setting.

The dimeric form of CXCL12 binds to atypical chemokine receptor 1

The pleiotropic chemokine CXCL12 is involved in diverse physiological and pathophysiological processes, including embryogenesis, hematopoiesis, leukocyte migration, and tumor metastasis. It is known to engage the classical receptor CXCR4 and the atypical receptor ACKR3. Differential receptor engagement can transduce distinct cellular signals and effects as well as alter the amount of free, extracellular chemokine. CXCR4 binds both monomeric and the more commonly found dimeric forms of CXCL12, whereas ACKR3 binds monomeric forms. Here, we found that CXCL12 also bound to the atypical receptor ACKR1 (previously known as Duffy antigen/receptor for chemokines or DARC). In vitro nuclear magnetic resonance spectroscopy and isothermal titration calorimetry revealed that dimeric CXCL12 bound to the extracellular N terminus of ACKR1 with low nanomolar affinity, whereas the binding affinity of monomeric CXCL12 was orders of magnitude lower. In transfected MDCK cells and primary human Duffy-positive erythrocytes, a dimeric, but not a monomeric, construct of CXCL12 efficiently bound to and internalized with ACKR1. This interaction between CXCL12 and ACKR1 provides another layer of regulation of the multiple biological functions of CXCL12. The findings also raise the possibility that ACKR1 can bind other dimeric chemokines, thus potentially further expanding the role of ACKR1 in chemokine retention and presentation.