Modulation of CXCR4 expression and SDF-1alpha functional activity during differentiation of human monocytes and macrophages

The role of blood CXCL12 level in prognosis of coronary artery disease: A meta-analysis

Objective

The role of C-X-C motif chemokine 12 (CXCL12) in atherosclerotic cardiovascular diseases (ASCVDs) has emerged as one of the research hotspots in recent years. Studies reported that the higher blood CXCL12 level was associated with increased major adverse cardiovascular events (MACEs), but the results were inconsistent. The objective of this study was to clarify the prognostic value of the blood CXCL12 level in patients with coronary artery disease (CAD) through meta-analysis.

Methods

All related studies about the association between the blood CXCL12 level and the prognosis of CAD were comprehensively searched and screened according to inclusion criteria and exclusion criteria. The quality of the included literature was evaluated using the Newcastle-Ottawa Scale (NOS). The heterogeneity test was conducted, and the pooled hazard risk (HR) or the odds ratio (OR) with a 95% confidence interval (CI) was calculated using the fixed-effect or random-effects model accordingly. Publication bias was evaluated using Begg's funnel plot and Egger's test. Sensitivity analysis and subgroup analysis were also conducted.

Results

A total of 12 original studies with 2,959 CAD subjects were included in the final data combination. The pooled data indicated a significant association between higher CXCL12 levels and MACEs both in univariate analysis (HR 5.23, 95% CI 2.48–11.04) and multivariate analysis (HR 2.53, 95% CI 2.03–3.16) in the CXCL12 level as the category variable group. In the CXCL12 level as the continuous variable group, the result also indicated that the higher CXCL12 level significantly predicted future MACEs (multivariate OR 1.55, 95% CI 1.02–2.35). Subgroup analysis of the CXCL12 level as the category variable group found significant associations in all acute coronary syndrome (ACS) (univariate HR 9.72, 95% CI 4.69–20.15; multivariate HR 2.47, 95% CI 1.79–3.40), non-ACS (univariate HR 2.73, 95% CI 1.65–4.54; multivariate HR 3.49, 95% CI 1.66–7.33), Asian (univariate HR 7.43, 95% CI 1.70–32.49; multivariate HR 2.21, 95% CI 1.71–2.85), Caucasian (univariate HR 3.90, 95% CI 2.73–5.57; multivariate HR 3.87, 95% CI 2.48–6.04), short-term (univariate HR 9.36, 95% CI 4.10–21.37; multivariate HR 2.72, 95% CI 1.97–3.76), and long-term (univariate HR 2.86, 95% CI 1.62–5.04; multivariate HR 2.38, 95% CI 1.76–3.22) subgroups. Subgroup analysis of the CXCL12 level as the continuous variable group found significant associations in non-ACS (multivariate OR 1.53, 95% CI 1.23–1.92), Caucasian (multivariate OR 3.83, 95% CI 1.44–10.19), and long-term (multivariate OR 1.62, 95% CI 1.37–1.93) subgroups, but not in ACS (multivariate OR 1.36, 95% CI 0.67–2.75), Asian (multivariate OR 1.40, 95% CI 0.91–2.14), and short-term (multivariate OR 1.16, 95% CI 0.28–4.76) subgroups. No significant publication bias was found in this meta-analysis.

Conclusion

The higher blood CXCL12 level is associated with increased MACEs in patients with CAD, and the blood CXCL12 level may serve as an important prognostic index for CAD. Integrating the blood CXCL12 level into CAD risk assessment tools may provide more comprehensive messages for evaluating and managing patients with CAD.

Role and implications of the CXCL12/CXCR4/CXCR7 axis in atherosclerosis: still a debate

Atherosclerosis is one of the leading causes of mortality and morbidity worldwide. Chemokines and their receptors are implicated in the pathogenesis of atherosclerosis. CXCL12 is a member of the chemokine family exerting a myriad role in atherosclerosis through its classical CXCR4 and atypical ACKR3 (CXCR7) receptors. The modulatory and regulatory functional spectrum of CXCL12/CXCR4/ACKR3 axis in atherosclerosis spans from proatherogenic, prothrombotic and proinflammatory to atheroprotective, plaque stabilizer and dyslipidemia rectifier. This diverse continuum is executed in a wide range of biological units including endothelial cells (ECs), progenitor cells, macrophages, monocytes, platelets, lymphocytes, neutrophils and vascular smooth muscle cells (VSMCs) through complex heterogeneous and homogenous coupling of CXCR4 and ACKR3 receptors, employing different downstream signalling pathways, which often cross-talk among themselves and with other signalling interactomes. Hence, a better understanding of this structural and functional heterogeneity and complex phenomenon involving CXCL12/CXCR4/ACKR3 axis in atherosclerosis would not only help in formulation of novel therapeutics, but also in elucidation of the CXCL12 ligand and its receptors, as possible diagnostic and prognostic biomarkers.Key messagesThe role of CXCL12 per se is proatherogenic in atherosclerosis development and progression.The CXCL12 receptors, CXCR4 and ACKR3 perform both proatherogenic and athero-protective functions in various cell typesDue to functional heterogeneity and cross talk of CXCR4 and ACKR3 at receptor level and downstream pathways, regional boosting with specific temporal and spatial modulators of CXCL12, CXCR4 and ACKR3 need to be explored.

Radionuclide imaging of inflammation in atherosclerotic vascular disease among people living with HIV infection: current practice and future perspective

People living with human immunodeficiency virus (HIV) infection have twice the risk of atherosclerotic vascular disease compared with non-infected individuals. Inflammation plays a critical role in the development and progression of atherosclerotic vascular disease. Therapies targeting inflammation irrespective of serum lipid levels have been shown to be effective in preventing the occurrence of CVD. Radionuclide imaging is a viable method for evaluating arterial inflammation. This evaluation is useful in quantifying CVD risk and for assessing the effectiveness of anti-inflammatory treatment. The most tested radionuclide method for quantifying arterial inflammation among people living with HIV infection has been with F-18 FDG PET/CT. The level of arterial uptake of F-18 FDG correlates with vascular inflammation and with the risk of development and progression of atherosclerotic disease. Several limitations exist to the use of F-18 FDG for PET quantification of arterial inflammation. Many targets expressed on macrophage, a significant player in arterial inflammation, have the potential for use in evaluating arterial inflammation among people living with HIV infection. The review describes the clinical utility of F-18 FDG PET/CT in assessing arterial inflammation as a risk for atherosclerotic disease among people living with HIV infection. It also outlines potential newer probes that may quantify arterial inflammation in the HIV-infected population by targeting different proteins expressed on macrophages.

Imaging of chemokine receptor CXCR4 expression in culprit and nonculprit coronary atherosclerotic plaque using motion-corrected [68Ga]pentixafor PET/CT

Purpose

The chemokine receptor CXCR4 is a promising target for molecular imaging of CXCR4⁺ cell types, e.g. inflammatory cells, in cardiovascular diseases. We speculated that a specific CXCR4 ligand, [⁶⁸Ga]pentixafor, along with novel techniques for motion correction, would facilitate the in vivo characterization of CXCR4 expression in small culprit and nonculprit coronary atherosclerotic lesions after acute myocardial infarction by motion-corrected targeted PET/CT.

Methods

CXCR4 expression was analysed ex vivo in separately obtained arterial wall specimens. [⁶⁸Ga]Pentixafor PET/CT was performed in 37 patients after stent-based reperfusion for a first acute ST-segment elevation myocardial infarction. List-mode PET data were reconstructed to five different datasets using cardiac and/or respiratory gating. Guided by CT for localization, the PET signals of culprit and various groups of nonculprit coronary lesions were analysed and compared.

Results

Ex vivo, CXCR4 was upregulated in atherosclerotic lesions, and mainly colocalized with CD68⁺ inflammatory cells. In vivo, elevated CXCR4 expression was detected in culprit and nonculprit lesions, and the strongest CXCR4 PET signal (median SUV_max 1.96; interquartile range, IQR, 1.55–2.31) was observed in culprit coronary artery lesions. Stented nonculprit lesions (median SUV_max 1.45, IQR 1.23–1.88; P = 0.048) and hot spots in naive remote coronary segments (median SUV_max 1.34, IQR 1.23–1.74; P = 0.0005) showed significantly lower levels of CXCR4 expression. Dual cardiac/respiratory gating provided the strongest CXCR4 PET signal and the highest lesion detectability.

Conclusion

We demonstrated the basic feasibility of motion-corrected targeted PET/CT imaging of CXCR4 expression in coronary artery lesions, which was triggered by vessel wall inflammation but also by stent-induced injury. This novel methodology may serve as a platform for future diagnostic and therapeutic clinical studies targeting the biology of coronary atherosclerotic plaque.

Electronic supplementary material

The online version of this article (10.1007/s00259-018-4076-2) contains supplementary material, which is available to authorized users.

Localized SDF-1α Delivery Increases Pro-Healing Bone Marrow-Derived Cells in the Supraspinatus Muscle Following Severe Rotator Cuff Injury

To examine how the chemotactic agent stromal cell-derived factor-1alpha (SDF-1α) modulates the unique cellular milieu within rotator cuff muscle following tendon injury, we developed an injectable, heparin-based microparticle platform to locally present SDF-1α within the supraspinatus muscle following severe rotator cuff injury. SDF-1α loaded, degradable, N-desulfated heparin-based microparticles were fabricated, injected into a rat model of severe rotator cuff injury, and were retained for up to 7 days at the site. The resultant inflammatory cell and mesenchymal stem cell populations were analyzed compared to uninjured contralateral controls and, after 7 days, the fold-change in anti-inflammatory, M2-like macrophages (CD11b+CD68+CD163+, 4.3X fold-change) and mesenchymal stem cells (CD29+CD44+CD90+, 3.0X, respectively) was significantly greater in muscles treated with SDF-1α loaded microparticles than unloaded microparticles or injury alone. Our results indicate that SDF-1α loaded microparticles may be a novel approach to shift the cellular composition within the supraspinatus muscle and create a more pro-regenerative milieu, which may provide a platform to improve muscle repair following rotator cuff injury in the future.

The CXCR4 antagonist plerixafor (AMD3100) promotes proliferation of Ewing sarcoma cell lines in vitro and activates receptor tyrosine kinase signaling

BACKGROUND

The CXCR4 receptor antagonist plerixafor (AMD3100) is raising interest as an anti-cancer agent that disrupts the CXCL12-CXCR4 chemokine - receptor interaction between neoplastic cells and their microenvironment in tumor progression and metastasis. Here, we investigated plerixafor for anti-cancer activity in Ewing sarcoma, a rare and aggressive cancer of bone and soft tissues.

METHODS

We used a variety of methods such as cell viability and migration assays, flow cytometry, phospho-tyrosine arrays and western blotting to determine plerixafor effects on five characterized Ewing sarcoma cell lines and a low-passage culture in vitro.

RESULTS

Unexpectedly, plerixafor led to an increase in cell viability and proliferation in standard cell growth conditions, and to chemotactic migration towards plerixafor. Exploring potential molecular mechanisms underlying this effect, we found that Ewing sarcoma cell lines divided into classes of high- and low-level CXCR4 surface expression. Proliferative plerixafor responses were observed in both groups, maintained despite significant CXCR4 down-regulation or inhibition of Gαi-protein signal transduction, and involved activation of multiple receptor tyrosine kinases (DDR2, MERTK, MST1R, NTRK1, RET), the most prominent being platelet-derived growth factor receptor beta (PDGFRB). PDGFRB was activated in response to inhibition of the CXCL12-CXCR4 axis by plerixafor and/or pertussis toxin (Gαi-protein inhibitor). Dasatinib, a multi-kinase inhibitor of both PDGFRB and the CXCR4 downstream kinase SRC, counteracted this activation in some but not all cell lines.

CONCLUSION

These data suggest a feedback interaction between the CXCR4 chemokine receptor and RTK signaling cascades that elicits compensatory cell survival signaling and can shift the net effect of plerixafor towards proliferation. PDGFRB was identified as a candidate driver RTK and potential therapeutic co-target for CXCR4 in Ewing sarcoma. Although as yet limited to in vitro studies, these findings call for further investigation in the cancer - microenvironment interplay in vivo.

Transcriptional and translational-uncoupling in regulation of the CXCL12 and its receptors CXCR4, 7 in THP-1 monocytes and macrophages

INTRODUCTION

The chemokine CXCL12 and its receptors CXCR4 and 7 play crucial roles in the immune system. In the present study, regulation of this pathway was further examined using the in-vitro model of undifferentiated human THP-1 monocytes (u-THP-1) and phorbol 12-myristate 13-acetate (PMA)-differentiated THP-1 macrophages (d-THP-1), to assess the effects of differentiation and the TLR4 ligand lipopolysaccharide (LPS) on the pathway.

METHODS/RESULTS

Differentiation did not affect the CXCR4, 7 mRNA levels. Interestingly, the CXCL12 and CXCR7 proteins but not CXCR4 were found to be up-regulated during differentiation. LPS, through CD14-dependent pathway, induced CXCL12 and CXCR4, 7 mRNA levels to a greater magnitude in d- than u-THP-1. The induction effect on CXCL12 stimulated by LPS was confirmed using ELISA. Increased migration of u-THP-1 was observed using conditioned medium from LPS-treated d-THP-1. Additionally, d-THP-1, although expressed higher CXCR7 protein levels, failed to migrate toward CXCL12. In contrast, LPS did not affect CXCR4, 7 protein levels.

CONCLUSION

Hence, this study indicated that CXCL12, CXCR4, and CXCR7 were differentially expressed and regulated in u-THP-1 and d-THP-1 cells in response to external stimuli. Importantly, we reported here a novel observation that uncoupling exists between transcriptional and translational regulation of CXCR4, 7 expressions by differentiation and TLR stimuli.

[68Ga]Pentixafor-PET/MRI for the detection of Chemokine receptor 4 expression in atherosclerotic plaques

PURPOSE

The expression of chemokine receptor type 4 (CXCR4) was found co-localized with macrophages on the atherosclerotic vessel wall and participated in the initial emigration of leukocytes. Gallium-68 [⁶⁸Ga]Pentixafor has recently been introduced for the imaging of atherosclerosis by targeting CXCR4. We sought to evaluate human atherosclerotic lesions using [⁶⁸Ga]Pentixafor PET/MRI.

METHODS

Thirty-eight oncology patients underwent [⁶⁸Ga]Pentixafor PET/MR imaging at baseline. Maximum standardized uptake values (SUV_max) were derived from hot lesions in seven arterial segments and target-to-blood ratios (TBR) were calculated. ANOVA post-hoc and paired t test were performed for statistical comparison, Spearman's correlation coefficient between uptake ratios and cardiovascular risk factors were assessed. The reproducibility of [⁶⁸Ga]Pentixafor PET/MRI was assessed in seven patients with a follow-up exanimation by Pearson's regression and Bland-Altman plots analysis.

RESULTS

Thirty-four of 38 patients showed 611 focal [⁶⁸Ga]Pentixafor uptake that followed the contours of the large arteries. Both prevalence and mean TBR_max were highest in the descending aorta. There were significantly higher TBR values found in men (1.9 ± 0.3) as compared to women (1.7 ± 0.2; p < 0.05). Patients with mean TBR_max > 1.7 showed a significantly higher incidence of diabetes, hypertension hypercholesterolemia and history of cardiovascular disease than patients with mean TBR_max ≤ 1.7. [⁶⁸Ga]Pentixafor uptake showed a good reproducibility (r = 0.6, p < 0.01), and there was no difference between the mean TBR_max values of plaque lesions (TBR_baseline1.8 ± 0.3 vs TBR_follow-up1.8 ± 0.3) (p = 0.9).

CONCLUSION

Patients with high arterial uptake showed increased incidence of cardiovascular risk factors, suggesting a potential role of [⁶⁸Ga]Pentixafor in characterization of atherosclerosis.

Integrating MRI and Chemokine Receptor CXCR4-Targeted PET for Detection of Leukocyte Infiltration in Complicated Urinary Tract Infections After Kidney Transplantation

Complicated urinary tract infections (UTIs) are frequent in immunosuppressed patients after kidney transplantation and may lead to allograft failure or urosepsis. Noninvasive detection of allograft involvement as well as localization of the primary site of infection are challenging. Therefore, we sought to determine whether molecularly targeted PET, combined with diffusion-weighted MRI, enables detection of leukocytes in renal allografts. Methods: Thirteen kidney transplant recipients with complicated UTIs underwent both PET with a specific CXCR4 ligand, ⁶⁸Ga-pentixafor, and diffusion-weighted MRI. The spatial distribution and intensity of CXCR4 upregulation in renal allografts as determined by SUVs on PET and diffusion restriction as determined by apparent diffusion coefficients (ADCs) on MRI were analyzed and compared with urinalysis, clinical chemistry and bacteriology, and biopsy, if available. Results: Combined PET/MRI detected acute allograft infection in 9 patients and lower UTI/nonurologic infections in the remaining 4 patients. Leukocyte infiltration was identified by areas of CXCR4 upregulation compared with unaffected parenchyma in PET (SUV_mean, 4.6 vs. 3.7; P < 0.01), corresponding to areas with increased cell density in MRI (ADC_min, 0.89 vs. 1.59 × 10^-3 mm²/s, P < 0.01). Allograft CXCR4 signal was paralleled by CXCR4 upregulation in lymphoid organs. Histopathologic evaluation supported a correlation between CXCR4 signal and presence of leukocytes. Conclusion: Combined CXCR4-targeted PET/MRI with ⁶⁸Ga-pentixafor may enable the noninvasive detection of leukocytes in renal allografts. This novel methodology may refine the characterization of infectious and inflammatory kidney diseases and may serve as a platform for future clinical studies targeting allograft infection.

Novel Noninvasive Nuclear Medicine Imaging Techniques for Cardiac Inflammation

PURPOSE OF REVIEW

Inflammation is a key player in a wide range of cardiovascular and myocardial diseases. Given the numerous implications of inflammatory processes in disease initiation and progression, functional imaging modalities including positron emission tomography (PET) represent valuable diagnostic, prognostic, and monitoring tools in patient management. Since increased glucose metabolism is a hallmark of inflammation, PET using the radiolabeled glucose analog [18F]-2-deoxy-2-fluoro-d-glucose (FDG) is the mainstay diagnostic test for nuclear imaging of (cardiac) inflammation. Recently, new approaches using more specific tracers to overcome the limited specificity of FDG have emerged.

RECENT FINDINGS

PET imaging has proven its value in a number of inflammatory conditions of the heart including myocarditis, endocarditis, sarcoidosis, or reactive changes after myocardial infarction. In infection-related endocarditis, FDG-PET and white blood cell scintigraphy have been implemented in current guidelines. FDG-PET is considered as nuclear medical gold standard in myocarditis, pericarditis, or sarcoidosis. Novel strategies, including targeting of somatostatin receptors or C-X-C motif chemokine receptor CXCR4, have shown promising results in first studies.

SUMMARY

Nuclear medicine techniques offer valuable information in the assessment of myocardial inflammation. Given the possibility to directly visualize inflammatory activity, they represent useful tools for diagnosis, risk stratification, and therapy monitoring.

The CCL2/CCR2 Axis Affects Transmigration and Proliferation but Not Resistance to Chemotherapy of Acute Myeloid Leukemia Cells

Acute myeloid leukemia (AML) has a high mortality rate despite chemotherapy and transplantation. Both CXCR4/SDF-1 and VLA-4/VCAM1 axes are involved in leukemia protection but little is known about the role of CCL2/CCR2 in AML biology and protection against chemotherapy. We measured CCR2 expression in AML cell lines and primary AML cells by flow cytometry (FCM), real time PCR (RT-PCR) and western blot (WB). CCL2 production was quantified by solid phase ELISA in peripheral blood (PB) and bone marrow (BM) serum. We measured chemotaxis in a transwell system with different concentrations of CCL2/CCR2 blockers; cell cycle with BrDU and propidium iodide and proliferation with yellow tetrazolium MTT. We determined synergy in in vitro cell apoptosis combining chemotherapy and CCL2/CCR2 blockade. Finally, we performed chemoprotection studies in an in vivo mouse model. Of 35 patients, 23 (65%) expressed CCR2 by FCM in PB. Two cell lines expressed high levels of CCR2 (THP-1 and murine AML). RT-PCR and WB confirmed CCR2 production. CCL2 solid phase ELISA showed significantly lower levels of CCL2 in PB and BM compared to normal controls. Chemotaxis experiments confirmed a dose-dependent migration in AML primary cells expressing CCR2 and THP-1 cells. A significant inhibition of transmigration was seen after CCL2/CCR2 blockade. Proliferation of CCR2+ AML cell lines was slightly increased (1.4-fold) after axis stimulation. We observed a non-significant increase in phase S THP-1 cells exposed to CCL2 and a concomitant decrease of cells in G1. The chemotherapy studies did not show a protective effect of CCL2 on cytarabine-induced apoptosis or synergy with chemotherapy after CCL2/CCR2 blockade both in vitro and in vivo. In conclusion, CCL2/CCR2 axis is expressed in the majority of monocytoid AML blasts. The axis is involved in cell trafficking and proliferation but no in vitro and in vivo chemotherapy protective effect was seen.

(68)Ga-Pentixafor-PET/CT for Imaging of Chemokine Receptor 4 Expression in Glioblastoma

Chemokine receptor-4 (CXCR4) has been reported to be overexpressed in glioblastoma (GBM) and to be associated with poor survival. This study investigated the feasibility of non-invasive CXCR4-directed imaging with positron emission tomography/computed tomography (PET/CT) using the radiolabelled chemokine receptor ligand ⁶⁸Ga-Pentixafor.

15 patients with clinical suspicion on primary or recurrent glioblastoma (13 primary, 2 recurrent tumors) underwent ⁶⁸Ga-Pentixafor-PET/CT for assessment of CXCR4 expression prior to surgery. O-(2-¹⁸F-fluoroethyl)-L-tyrosine (¹⁸F-FET) PET/CT images were available in 11/15 cases and were compared visually and semi-quantitatively (SUV_max, SUV_mean). Tumor-to-background ratios (TBR) were calculated for both PET probes. ⁶⁸Ga-Pentixafor-PET/CT results were also compared to histological CXCR4 expression on neuronavigated surgical samples.

⁶⁸Ga-Pentixafor-PET/CT was visually positive in 13/15 cases with SUV_mean and SUV_max of 3.0±1.5 and 3.9±2.0 respectively. Respective values for ¹⁸F-FET were 4.4±2.0 (SUV_mean) and 5.3±2.3 (SUV_max). TBR for SUV_mean and SUV_max were higher for ⁶⁸Ga-Pentixafor than for ¹⁸F-FET (SUV_mean 154.0±90.7 vs. 4.1±1.3; SUV_max 70.3±44.0 and 3.8±1.2, p<0.01), respectively. Histological analysis confirmed CXCR4 expression in tumor areas with high ⁶⁸Ga-Pentixafor uptake; regions of the same tumor without apparent ⁶⁸Ga-Pentixafor uptake showed no or low receptor expression.

In this pilot study, ⁶⁸Ga-Pentixafor retention has been observed in the vast majority of glioblastoma lesions and served as readout for non-invasive determination of CXCR4 expression. Given the paramount importance of the CXCR4/SDF-1 axis in tumor biology, ⁶⁸Ga-Pentixafor-PET/CT might prove a useful tool for sensitive, non-invasive in-vivo quantification of CXCR4 as well as selection of patients who might benefit from CXCR4-directed therapy.

MIF and CXCL12 in Cardiovascular Diseases: Functional Differences and Similarities

Coronary artery disease (CAD) as part of the cardiovascular diseases is a pathology caused by atherosclerosis, a chronic inflammatory disease of the vessel wall characterized by a massive invasion of lipids and inflammatory cells into the inner vessel layer (intima) leading to the formation of atherosclerotic lesions; their constant growth may cause complications such as flow-limiting stenosis and plaque rupture, the latter triggering vessel occlusion through thrombus formation. Pathophysiology of CAD is complex and over the last years many players have entered the picture. One of the latter being chemokines (small 8-12 kDa cytokines) and their receptors, known to orchestrate cell chemotaxis and arrest. Here, we will focus on the chemokine CXCL12, also known as stromal cell-derived factor 1 (SDF-1) and the chemokine-like function chemokine, macrophage migration-inhibitory factor (MIF). Both are ubiquitously expressed and highly conserved proteins and play an important role in cell homeostasis, recruitment, and arrest through binding to their corresponding chemokine receptors CXCR4 (CXCL12 and MIF), ACKR3 (CXCL12), and CXCR2 (MIF). In addition, MIF also binds to the receptor CD44 and the co-receptor CD74. CXCL12 has mostly been studied for its crucial role in the homing of (hematopoietic) progenitor cells in the bone marrow and their mobilization into the periphery. In contrast to CXCL12, MIF is secreted in response to diverse inflammatory stimuli, and has been associated with a clear pro-inflammatory and pro-atherogenic role in multiple studies of patients and animal models. Ongoing research on CXCL12 points at a protective function of this chemokine in atherosclerotic lesion development. This review will focus on the role of CXCL12 and MIF and their differences and similarities in CAD of high risk patients.

Ubiquitin is a versatile scaffold protein for the generation of molecules with de novo binding and advantageous drug-like properties

In the search for effective therapeutic strategies, protein-based biologicals are under intense development. While monoclonal antibodies represent the majority of these drugs, other innovative approaches are exploring the use of scaffold proteins for the creation of binding molecules with tailor-made properties. Ubiquitin is especially suited for this strategy due to several key characteristics. Ubiquitin is a natural serum protein, 100% conserved across the mammalian class and possesses high thermal, structural and proteolytic stability. Because of its small size and lack of posttranslational modifications, it can be easily produced in Escherichia coli. In this work we provide evidence that ubiquitin is safe as tested experimentally in vivo. In contrast to previously published results, we show that, in our hands, ubiquitin does not act as a functional ligand of the chemokine receptor CXCR4. Cellular assays based on different signaling pathways of the receptor were conducted with the natural agonist SDF-1 as a benchmark. In none of the assays could a response to ubiquitin treatment be elicited. Furthermore, intravenous application to mice at high concentrations did not induce any detectable effect on cytokine levels or hematological parameters.

The CXCL12/CXCR4 chemokine ligand/receptor axis in cardiovascular disease

The chemokine receptor CXCR4 and its ligand CXCL12 play an important homeostatic function by mediating the homing of progenitor cells in the bone marrow and regulating their mobilization into peripheral tissues upon injury or stress. Although the CXCL12/CXCR4 interaction has long been regarded as a monogamous relation, the identification of the pro-inflammatory chemokine macrophage migration inhibitory factor (MIF) as an important second ligand for CXCR4, and of CXCR7 as an alternative receptor for CXCL12, has undermined this interpretation and has considerably complicated the understanding of CXCL12/CXCR4 signaling and associated biological functions. This review aims to provide insight into the current concept of the CXCL12/CXCR4 axis in myocardial infarction (MI) and its underlying pathologies such as atherosclerosis and injury-induced vascular restenosis. It will discuss main findings from in vitro studies, animal experiments and large-scale genome-wide association studies. The importance of the CXCL12/CXCR4 axis in progenitor cell homing and mobilization will be addressed, as will be the function of CXCR4 in different cell types involved in atherosclerosis. Finally, a potential translation of current knowledge on CXCR4 into future therapeutical application will be discussed.

Intracellular trafficking and endocytosis of CXCR4 in fetal mesenchymal stem/stromal cells

Background

Fetal mesenchymal stem/stromal cells (MSC) represent a developmentally-advantageous cell type with translational potential.

To enhance adult MSC migration, studies have focussed on the role of the chemokine receptor CXCR4 and its ligand SDF-1 (CXCL12), but more recent work implicates an intricate system of CXCR4 receptor dimerization, intracellular localization, multiple ligands, splice variants and nuclear accumulation. We investigated the intracellular localization of CXCR4 in fetal bone marrow-derived MSC and role of intracellular trafficking in CXCR4 surface expression and function.

Results

We found that up to 4% of human fetal MSC have detectable surface-localized CXCR4. In the majority of cells, CXCR4 is located not at the cell surface, as would be required for ‘sensing’ migratory cues, but intracellularly. CXCR4 was identified in early endosomes, recycling endosomes, and lysosomes, indicating only a small percentage of CXCR4 travelling to the plasma membrane. Notably CXCR4 was also found in and around the nucleus, as detected with an anti-CXCR4 antibody directed specifically against CXCR4 isoform 2 differing only in N-terminal sequence. After demonstrating that endocytosis of CXCR4 is largely independent of endogenously-produced SDF-1, we next applied the cytoskeletal inhibitors blebbistatin and dynasore to inhibit endocytotic recycling. These increased the number of cells expressing surface CXCR4 by 10 and 5 fold respectively, and enhanced the number of cells migrating to SDF1 in vitro (up to 2.6 fold). These molecules had a transient effect on cell morphology and adhesion, which abated after the removal of the inhibitors, and did not alter functional stem cell properties.

Conclusions

We conclude that constitutive endocytosis is implicated in the regulation of CXCR4 membrane expression, and suggest a novel pharmacological strategy to enhance migration of systemically-transplanted cells.

CXCR4: a virus's best friend?

Viruses are dependent on their hosts for replication and dispersal in the environment; thus, the most successful viruses are those that co-evolve with their hosts. CXCR4 is a cellular chemokine receptor that plays central roles in development, hematopoiesis, and immune surveillance through signaling induced by its ligand, CXCL12. The CXCR4-CXCL12 axis has been besieged by many pathogens that employ a range of strategies to modify or exploit CXCR4 activity. While CXCR4 was identified as a critical co-factor for entry of HIV into CD4+ T cells early on, other viruses may utilize CXCR4 to gain cell entry as well. Moreover, several viruses have been found to modulate CXCR4 expression or alter its functional activity, with direct effects on cell trafficking, immune responses, cell proliferation, and cell survival. Because CXCR4 is targeted by a diverse group of viral pathogens, modification of host CXCR4 signaling activity is emerging as a common theme in virus persistence and is likely to be important for subversion of the host immune system. This review highlights major viral pathogens that use and abuse CXCR4 and explores the possible reasons why this chemokine receptor has become "a virus's best friend".

Heparin-binding epidermal growth factor-like growth factor/diphtheria toxin receptor in normal and neoplastic hematopoiesis

Heparin-binding EGF-like growth factor (HB-EGF) belongs to the EGF family of growth factors. It is biologically active either as a molecule anchored to the membrane or as a soluble form released by proteolytic cleavage of the extracellular domain. HB-EGF is involved in relevant physiological and pathological processes spanning from proliferation and apoptosis to morphogenesis. We outline here the main activities of HB-EGF in connection with normal or neoplastic differentiative or proliferative events taking place primitively in the hematopoietic microenvironment.

Bone marrow-specific deficiency of nuclear receptor Nur77 enhances atherosclerosis

RATIONALE

Nuclear receptor Nur77, also known as NR4A1, TR3, or NGFI-B, is expressed in human atherosclerotic lesions in macrophages, endothelial cells, T cells and smooth muscle cells. Macrophages play a critical role in atherosclerosis and the function of Nur77 in lesion macrophages has not yet been investigated.

OBJECTIVE

This study aims to delineate the function of Nur77 in macrophages and to assess the effect of bone marrow-specific deficiency of Nur77 on atherosclerosis.

METHODS AND RESULTS

We investigated Nur77 in macrophage polarization using bone marrow-derived macrophages (BMM) from wild-type and Nur77-knockout (Nur77(-/-)) mice. Nur77(-/-) BMM exhibit changed expression of M2-specific markers and an inflammatory M1-phenotype with enhanced expression of interleukin-12, IFNγ, and SDF-1α and increased NO synthesis in (non)-stimulated Nur77(-/-) BMM cells. SDF-1α expression in nonstimulated Nur77(-/-) BMM is repressed by Nur77 and the chemoattractive activity of Nur77(-/-) BMM is abolished by SDF-1α inhibiting antibodies. Furthermore, Nur77(-/-) mice show enhanced thioglycollate-elicited migration of macrophages and B cells. The effect of bone marrow-specific deficiency of Nur77 on atherosclerosis was studied in low density lipoprotein receptor-deficient (Ldlr(-/-)) mice. Ldlr(-/-) mice with a Nur77(-/-)-deficient bone marrow transplant developed 2.1-fold larger atherosclerotic lesions than wild-type bone marrow-transplanted mice. These lesions contain more macrophages, T cells, smooth muscle cells and larger necrotic cores. SDF-1α expression is higher in lesions of Nur77(-/-)-transplanted mice, which may explain the observed aggravation of lesion formation.

CONCLUSIONS

In conclusion, in bone marrow-derived cells the nuclear receptor Nur77 has an anti-inflammatory function, represses SDF-1α expression and inhibits atherosclerosis.

The chemokine CXCL12 regulates monocyte-macrophage differentiation and RUNX3 expression

Monocytes are versatile cells that can express different functional programs in response to microenvironmental signals. We show that primary blood monocytes secrete the CXCL12 chemokine, and express the CXCR4 and CXCR7 receptors, leading to an autocrine/paracrine loop that contribute to shape monocyte differentiation to a distinct type of macrophages, with an enhanced expression of CD4, CD14, and CD163, or dendritic cells, with a reduced functional ability to stimulate antigen-specific T-lymphocyte responses. The in vivo relevance of CXCL12 production by mononuclear phagocytes was studied in metastatic melanoma tissues by a thoroughly immunofluorescence phenotyping of CXCL12(high) expressing cells, which were CD45(+), coexpressed the macrophage antigens CD68, CD163, and CD209 and constituted the 60%-90% of tumor-associated macrophages. Microarray analysis of primary monocytes revealed that the vascular endothelial growth factor and the angiogenic chemokine CCL1 mRNA levels were up-regulated in response to CXCL12, leading to enhanced expression of both proteins. In addition, we found that CXCL12 autocrine/paracrine signaling down-regulates the expression of the transcription factor RUNX3 and contributes to maintain the long-term CD4 and CD14 expression in monocytes/macrophages. Together, these results suggest that autocrine CXCL12 production modulates differentiation of monocytes toward a distinct program with proangiogenic and immunosuppressive functions.

Am80 inhibits stromal cell-derived factor-1-induced chemotaxis in T-cell acute lymphoblastic leukemia cells

C-X-C motif chemokine receptor 4 (CXCR4) and stromal cell-derived factor-1 (SDF-1) play a potent role in metastasis and infiltration of many types of tumors, including T-cell acute lymphoblastic leukemia (T-ALL), into the central nervous system or lymph nodes. Although higher levels of CXCR4 expression have been shown to correlate with shorter survival of patients, effective drugs affecting cell surface CXCR4 expression are still unknown. In the present study, we examined the effects of a synthetic retinoid Am80 on CXCR4 expression of cultured T-ALL cells, such as Jurkat. Am80 inhibited surface CXCR4 expression and SDF-1-induced chemotaxis by the acceleration of CXCR4 internalization via activation of conventional PKC. Am80 may be an effective drug to inhibit the extramedullary infiltration of T-ALL cells.

Distinctive properties of CXC chemokine receptor 4-expressing Cajal-Retzius cells versus GABAergic interneurons of the postnatal hippocampus

The CXC chemokine receptor 4 (CXCR4) for the chemokine (C-X-C motif) ligand 12/stromal cell-derived factor-1 alpha (CXCL12/SDF-1 alpha) is highly expressed in the postnatal CA1 stratum lacunosum-moleculare. However, both the network events triggered by SDF-1 alpha in this microcircuit and the cellular targets of this chemokine remain virtually unexplored. Here, we have studied SDF-1 alpha-mediated neuromodulation of the stratum lacunosum-moleculare by directly comparing the properties of CXCR4-expressing Cajal-Retzius cells vs. CXCR4-non-expressing interneurons, and by recording the electrophysiological effects caused by application of SDF-1 alpha on either cell type. We demonstrate that SDF-1 alpha dramatically reduces spontaneous firing in Cajal-Retzius cells via hyerpolarization, and that cessation of firing is prevented by the CXCR4-specific antagonist AMD3100. In contrast, no effects on the excitability of interneurons of the same layer were observed following exposure to the chemokine. We also provide evidence that, despite the expression of functional glutamate receptors, Cajal-Retzius cells are integrated in the synaptic network of the stratum lacunosum-moleculare via excitatory GABAergic input. Furthermore, we show that the axons of Cajal-Retzius cells target specifically the stratum lacunosum-moleculare and the dentate gyrus, but lack postsynaptic specializations opposite to their axonal varicosities. These results, taken together with our observation that SDF-1 alpha reduces evoked field responses at the entorhinal cortex-CA1 synapse, suggest that Cajal-Retzius cells produce a diffuse output that may impact information processing of stratum lacunosum-moleculare. We propose that pathological alterations of local levels of SDF-1 alpha or CXCR4 expression may affect the functions of an important hippocampal microcircuit.

CXCR3 activation by lentivirus infection suppresses neuronal autophagy: neuroprotective effects of antiretroviral therapy

Previous studies have implicated CXCL12 in the neuropathogenesis of HIV infection. Proteolysis of CXCL12 generates a neurotoxic molecule, CXCL12(5-67), which engages and activates CXCR3, in addition to exhibiting increased expression in the brains of patients with HIV-associated dementia (HAD). Herein, we investigated CXCR3-mediated neuronal injury, particularly, its contribution to autophagy suppression and the concomitant effects of antiretroviral therapy using human brain samples and models of HIV neuropathogenesis. Neurons in the brains of HAD patients and feline immunodeficiency virus (FIV)-infected animals, as well as cultured human neurons, expressed CXCR3, which was modulated in a ligand-specific manner. Exposure of human neurons to CXCL12(5-67) caused a reduction in the autophagy-associated molecule LC3 (P<0.05) and neuronal survival (P<0.05), which recapitulated findings in FIV- and HIV-infected brains (P<0.05). Oral didanosine (ddI) treatment of FIV-infected animals reduced neurobehavioral abnormalities in conjunction with diminished plasma viral load (P<0.05). F4/80 transcript abundance and CXCL12(5-67) immunoreactivity were reduced with restored neuronal LC3 expression in the brains of FIV-infected animals after ddI treatment (P<0.05). ddI treatment also prevented microglial activation and depletion of synaptic proteins in the cortex of FIV-infected animals (P<0.05). These findings indicate that the beneficial effects of ddI might be a consequence of a reduced systemic viral burden and concurrent leukocyte activation, leading to diminished neuroinflammation with preservation of neuronal autophagy by regulating CXCR3 activation.

The HIV-1 Tat protein selectively enhances CXCR4 and inhibits CCR5 expression in megakaryocytic K562 cells

The hematopoietic compartments act as long-term reservoirs for human immunodeficiency virus type-1 (HIV-1). Although hematopoietic progenitor cells (HPCs) are rarely infectable, HPCs committed to the megakaryocytic lineage can be infected and support a productive infection by both the X4 and R5 strains of HIV-1. Indeed, in contrast to the CD34+ progenitors, the lineage-committed HPCs express high levels of the HIV-1 co-receptors, CXCR4 and CCR5. The HIV-1 transactivator (Tat) protein has been shown to alter co-receptor expression in T lymphocytes and macrophages. We hypothesized that Tat may regulate co-receptor expression in lineage-specific HPCs as well. We have monitored the effects of Tat protein on co-receptor expression and on lineage-specific differentiation, using the HPC cell line, K562. Butyric acid (BA)-induced erythroid differentiation in K562 cells was suppressed by 1-100 ng/ml of Tat, as evident from a 70-80% decrease in hemoglobin (Hb) production and a 10-30-fold decrease in glycophorin-A expression. However, Tat treatment enhanced phorbol myristate acetate (PMA)-induced megakaryocytic differentiation, as evident from a 180-210% increase in 3H-serotonin uptake and a 5-12-fold increase in CD61 expression. Tat did not significantly alter co-receptor expression in erythroid cells. However, Tat co-treatment profoundly effected both CXCR4 and CCR5 gene expression and protein levels in megakaryocytic cells. In PMA-stimulated cells, Tat increased CXCR4 and decreased in CCR5 expression, this was potentiated in cells chronically exposed to Tat. In conclusion, Tat protein suppresses erythroid and facilitates megakaryocytic differentiation of K562 cells. In megakaryocytic cells, Tat differentially effected CXCR4 and CCR5 expression. Because megakaryocytes may play a crucial role in HIV-1 infectivity in viral reservoirs, our findings implicate a role for Tat protein in dictating co-receptor usage in lineage-committed HPCs.

Rapamycin Attenuates Atherosclerotic Plaque Progression in Apolipoprotein E Knockout Mice

Rapamycin has been shown to reduce neointimal thickening in the setting of balloon angioplasty and chronic graft vessel disease. This study was designed to test the effect of oral rapamycin on atherosclerotic plaque progression and the possible mechanism involved. Apolipoprotein E (apoE) knockout mice were fed either a diet supplemented with cholesterol or with cholesterol and rapamycin. At 4 and 8 weeks, quantitative analyses of plaque area and macrophage numbers were determined. Plasma cholesterol, triglyceride, and whole-blood rapamycin levels were measured. Rapamycin could be detected in the blood of mice (117+/-7 pg/mL). In mice fed with rapamycin, atherosclerotic lesions covered 22% of the aortic arch as compared with 41% in cholesterol-fed mice. The macrophage count was significantly lower in the rapamycin-fed mice as compared with cholesterol-fed mice. Rapamycin, in a dose-dependent manner, inhibited monocyte chemotaxis elicited by stromal cell-derived factor-1. Lesions in the cholesterol-fed mice had complex atherosclerotic plaque with acellular core, cholesterol clefts, and an abundant collection of monocytes/macrophages. Lesions in the rapamycin-fed mice were mainly composed of monocytes/macrophages. Oral rapamycin is effective in slowing the progression of atherosclerosis. Along with its multitude actions, attenuation of monocyte chemotaxis may be one more way by which rapamycin attenuates plaque progression.

CXCL12-CXCR4 interactions modulate prostate cancer cell migration, metalloproteinase expression and invasion

The mechanisms responsible for prostate cancer metastasis are incompletely understood at both the cellular and molecular levels. In this regard, chemokines are a family of small, cytokine-like proteins that induce motility of neoplastic cells, leukocytes and cancer cells. The current study evaluates the molecular mechanisms of CXCL12 and CXCR4 in prostate cancer cell migration and invasion. We report that functional CXCR4 is significantly expressed by prostate cancer cell lines, LNCaP and PC3, when compared with normal prostatic epithelial cells (PrEC). As measured using motility and invasion chamber assays, prostate cancer cells migrated and invaded through extracellular matrix components in response to CXCL12, at rates that corresponded to CXCR4 expression. Anti-CXCR4 antibodies (Abs) significantly impaired the migration and invasive potential of PC3 and LNCaP cells. CXCL12 induction also enhanced collagenase-1 (metalloproteinase-1 (MMP-1)) expression by LNCaP and PC3 cells. Collagenase-3 (MMP-13) was expressed by prostate cancer cells, but it was not expressed by PrEC cells or modulated by CXCL12. CXCL12 increased MMP-2 expression by LNCaP and PC3; however, MMP-9 expression was elevated only in PC3 cells after CXCL12-CXCR4 ligation. PC3 cells also expressed high levels of stromelysin-1 (MMP-3) after CXCL12 stimulation. CXCL12 also significantly increased stromelysin-2 (MMP-10) expression by LNCaP cells. Stromelysin-3 (MMP-11) was expressed by LNCaP cells, but not by PC3 or PrEC cells and CXCL12 induced PC3 MMP-11 expression. Membrane type-1 MMP (MMP-14) was not expressed by PrEC or LNCaP cells, but CXCL12 significantly enhanced MMP-14 expression by PC3 cells. These studies reveal important cellular and molecular mechanisms of CXCR4/CXCL12-mediated prostate cancer cell migration and invasion.

Stromal Cell–Derived Factor-1 and CXCR4 Interaction Is Critical for Development of Transplant Arteriosclerosis

Background— Posttransplant chronic allograft deterioration associated with development of transplant arteriosclerosis (TA) remains an unresolved problem. Recent studies suggest that the smooth muscle cells (SMCs) constituting the neointima are derived from recipient hematopoietic stem cells (HSCs). However, the underlying mechanisms of the process are not yet fully elucidated.

Methods and Results— We examined the genes expressed in allografts at different stages of TA development using a mice aortic transplantation model. Genes were analyzed by a differential mRNA display technique. We show that stromal cell–derived factor-1α (SDF-1α) is a critical molecular target for the treatment of TA. During the course of TA, intragraft SDF-1α expression was upregulated with time, and the circulating HSCs expressing its counterreceptor CXCR4 increased in the recipients receiving allografts. CXCR4-positive HSCs, derived from transplant recipients, migrated into allografts via microvessels in the adventitia and then toward the luminal side. The HSCs differentiated into SMC-like cells, contributing to the in situ formation of the neointima. In support of a functional role for these molecules, in vivo neutralization of SDF-1α inhibited HSC mobilization and significantly attenuated neointimal formation.

Conclusions— Interaction between SDF-1α and CXCR4 plays a key role in TA development. Blockade of SDF-1α may become a new therapeutic modality for TA.

Differential immune cell chemotaxis responses to acute psychological stress in Alzheimer caregivers compared to non-caregiver controls

OBJECTIVE

Caregiving for a spouse with Alzheimer's disease is associated with alterations in various immune cell responses. Chemotaxis of immune cells to chemokines is an important factor involved in lymphocyte migration, which plays an essential role in inflammatory responses to infection and may also be involved in atherogenesis. However, the effects of chronic stress on chemotaxis have not been investigated. The objective of this study was to examine lymphocyte chemotaxis to chemokines, stromal cell-derived factor-1 (SDF-1), N-formyl-methionyl-leucyl-phenylalanine (FMLP), and a beta-adrenergic agonist, isoproteronol (ISO), in response to an acute stressor in Alzheimer's caregivers. Correlations between immune cell chemotaxis and epinephrine and norepinephrine levels were also examined.

METHODS

Caregivers (n = 18) and noncaregiver controls (n = 9) completed a public speaking task. Blood was drawn before and immediately after the task for changes in chemotaxis to FMLP, SDF-1, and ISO, and for epinephrine and norepinephrine levels.

RESULTS

Caregivers had reduced chemotaxis to FMLP, SDF-1, and ISO in response to the speech task, compared with non-caregivers. Also, the direction of the correlations between chemotaxis to FMLP, SDF-1, and ISO and epinephrine levels differed between groups.

CONCLUSIONS

These findings suggest that immune cells released into circulation in response to acute stress are altered in caregivers. Group differences in immune responses may be due to sympathetically mediated alterations, which may have implications for caregivers' ability to successfully mount viable immune responses, as well as, atherogenesis.

Lysophosphatidylcholine up-regulates CXCR4 chemokine receptor expression in human CD4 T cells

Oxidized low-density lipoprotein (OxLDL) is an inflammatory modulator in the atherosclerotic plaque. We examined the effect of lysophosphatidylcholine (lysoPC), a main phospholipid component of OxLDL, on inflammatory responses in human CD4 T cells. We found that lysoPC dose- and time-dependently increased expression of CXCR4, the chemokine receptor on CD4 T cells. This increase was inhibited by caffeic acid phenethyl ester or SN50, nuclear factor-kappaB inhibitors, and also by suppression of G2A expression, the specific receptor for lysoPC, using antisense oligonucleotide. lysoPC enhanced CD4 T cell chemotaxis in response to stromal cell-derived factor-1 (SDF-1), the exclusive ligand for CXCR4. lysoPC also enhanced SDF-1-stimulated production of inflammatory cytokines interleukin-2 and interferon-gamma by CD4 T cells activated by anti-CD3 immunoglobulin G. In conclusion, this study demonstrates that lysoPC directly modulates inflammatory responses in human CD4 T cells. The data suggest that the presence of lysoPC and SDF-1 in atherosclerotic lesions may trigger inflammatory responses mediated by CD4 T cells, which may play an important role in progression of atherosclerosis.

Gene transfer of stromal cell-derived factor-1alpha enhances ischemic vasculogenesis and angiogenesis via vascular endothelial growth factor/endothelial nitric oxide synthase-related pathway: next-generation chemokine therapy for therapeutic neovascularization

BACKGROUND

Stromal cell-derived factor-1alpha (SDF-1alpha) is implicated as a chemokine for endothelial progenitor cells (EPCs). We therefore hypothesized that SDF-1alpha gene transfer would induce therapeutic neovascularization in vivo by functioning as a chemokine of EPC.

METHODS AND RESULTS

To examine SDF-1alpha-induced mobilization of EPC, we used bone marrow-transplanted mice whose blood cells ubiquitously express beta-galactosidase (LacZ). We produced unilateral hindlimb ischemia in the mice and transfected them with plasmid DNA encoding SDF-1alpha or empty plasmids into the ischemic muscles. SDF-1alpha gene transfer mobilized EPCs into the peripheral blood, augmented recovery of blood perfusion to the ischemic limb, and increased capillary density associated with partial incorporation of LacZ-positive cells into the capillaries of the ischemic limb, suggesting that SDF-1alpha induced vasculogenesis and angiogenesis. SDF-1alpha gene transfer did not affect ischemia-induced expression of vascular endothelial growth factor (VEGF) but did enhance Akt and endothelial nitric oxide synthase (eNOS) activity. Blockade of VEGF or NOS prevented all such SDF-1alpha-induced effects.

CONCLUSIONS

SDF-1alpha gene transfer enhanced ischemia-induced vasculogenesis and angiogenesis in vivo through a VEGF/eNOS-related pathway. This strategy might become a novel chemokine therapy for next generation therapeutic neovascularization.

Selective expression of stromal-derived factor-1 in the capillary vascular endothelium plays a role in Kaposi sarcoma pathogenesis

Kaposi sarcoma (KS), the most common neoplasm in patients with AIDS, typically presents with multiple skin lesions characterized by "spindle cells," the vast majority of which are infected with KSHV (Kaposi sarcoma herpes virus, also named HHV-8). In patients with AIDS, the presence of cell-associated KSHV DNA in blood is predictive of subsequent KS development, but the mechanisms by which circulating KSHV-infected cells contribute to AIDS-KS pathogenesis are unclear. Here, we show that the chemokine stromal-derived factor-1 (SDF-1), which is constitutively expressed by skin capillary endothelium and displayed on the endothelial cell surface in association with heparan sulfate, can trigger specific arrest of KSHV-infected cells under physiologic shear flow conditions. Moreover, in the presence of soluble SDF-1 gradients, SDF-1 expressed on the endothelial barrier can promote transendothelial migration of KSHV-infected cells. By triggering specific adhesion of circulating KSHV-infected cells and favoring their entry into the extravascular cutaneous space, endothelial cell-associated SDF-1 in cutaneous capillaries may dictate the preferential occurrence of KS in the skin.

Acute psychological stress: effects on chemotaxis and cellular adhesion molecule expression

OBJECTIVE

Activation of a psychological stress response increases autonomic activity and enhances immune function by inducing a significant increase in numbers of leukocytes at sites of inflammation. Chemotaxis and cellular adhesion are thought to mediate leukocyte trafficking. In this study, we examine the effects of an acute psychological stress on chemotactic responses of PBMCs and on CAM expression in relation to measures of sympathetic activation.

METHODS

Subjects underwent either a public speaking task (N = 24) or a control condition (N = 13). Blood was drawn before the task, immediately after, and 20 minutes after, the task for changes in percentage of cells expressing cellular adhesion molecules, chemotaxis to chemokines, HR, blood pressure, and E and NE levels.

RESULTS

In response to the laboratory stressor, increases of PBMC chemotaxis to FMLP and SDF-1 were found, which were coupled with increases in the percentages of lymphocytes expressing the integrin Mac-1. Autonomic activity, including blood pressure and circulating levels of catecholamines, increased after administration of the stressor, and correlated with increases of Mac-1.

CONCLUSIONS

These data show that acute stress induces increase of chemotaxis and expression of CAM expression, which may contribute to increased migration and recruitment of immune cells to sites of infection and/or inflammation.

Crosstalk between BCR/ABL oncoprotein and CXCR4 signaling through a Src family kinase in human leukemia cells

Stromal-derived factor (SDF)-1 and its G protein-coupled receptor, CXCR4, regulate stem/progenitor cell migration and retention in the marrow and are required for hematopoiesis. We show here an interaction between CXCR4 and the Src-related kinase, Lyn, in normal progenitors. We demonstrate that CXCR4-dependent stimulation of Lyn is associated with the activation of phosphatidylinositol 3-kinase (PI3-kinase). This chemokine signaling, which involves a Src-related kinase and PI3-kinase, appears to be a target for BCR/ABL, a fusion oncoprotein expressed only in leukemia cells. We show that the binding of phosphorylated BCR/ABL to Lyn results in the constitutive activation of Lyn and PI3-kinase, along with a total loss of responsiveness of these kinases to SDF-1 stimulation. Inhibition of BCR/ABL tyrosine kinase with STI571 restores Lyn responsiveness to SDF-1 signaling. Thus, BCR/ABL perturbs Lyn function through a tyrosine kinase-dependent mechanism. Accordingly, the blockade of Lyn tyrosine kinase inhibits both BCR/ABL-dependent and CXCR4-dependent cell movements. Our results demonstrate, for the first time, that Lyn-mediated pathological crosstalk exists between BCR/ABL and the CXCR4 pathway in leukemia cells, which disrupts chemokine signaling and chemotaxis, and increases the ability of immature cells to escape from the marrow. These results define a Src tyrosine kinases-dependent mechanism whereby BCR/ABL (and potentially other oncoproteins) dysregulates G protein-coupled receptor signaling and function of mammalian precursors.

Enhancement of intracellular signaling associated with hematopoietic progenitor cell survival in response to SDF-1/CXCL12 in synergy with other cytokines

Stromal cell-derived factor 1 (SDF-1/CXCL12) is a multifunctional cytokine. We previously reported that myelopoiesis was enhanced in SDF-1 alpha transgenic mice, probably due in part to SDF-1 alpha enhancement of myeloid progenitor cell (MPC) survival. To understand signaling pathways involved in this activity, we studied the effects on factor-dependent cell line MO7e cells incubated with SDF-1 alpha alone or in combination with other cytokines. SDF-1 alpha induced transient activation of extracellular stress-regulated kinase (ERK1/2), ribosomal S6 kinase (p90RSK) and Akt, molecules implicated in cell survival. Moreover, ERK1/2, p90RSK, and Akt were synergistically activated by SDF-1 alpha in combination with granulocyte-macrophage colony-stimulating factor (GM-CSF), Steel factor (SLF), or thrombopoietin (TPO). Similar effects were seen after pretreatment of MO7e cells with SDF-1 alpha followed by stimulation with the other cytokines, suggesting a priming effect of SDF-1 alpha. Nuclear factor-kappa B (NF-kappa B) did not appear to be involved in SDF-1 alpha actions, alone or in combination with other cytokines. These intracellular effects were consistent with enhanced myeloid progenitor cell survival by SDF-1 alpha after delayed addition of growth factors. SDF-1 alpha alone supported survival of highly purified human cord blood CD34(+++) cells, less purified human cord blood, and MO7e cells; this effect was synergistically enhanced when SDF-1 alpha was combined with low amounts of other survival-promoting cytokines (GM-CSF, SLF, TPO, and FL). SDF-1 may contribute to maintenance of MPCs in bone marrow by enhancing cell survival alone and in combination with other cytokines.

CXCR4 expression on monocytes is up-regulated by dexamethasone and is modulated by autologous CD3+ T cells

Chemokines and their receptors regulate cell migration to sites of inflammation. The glucocorticoid dexamethasone has potent anti-inflammatory effects, yet paradoxically up-regulates expression of some cytokine receptors. We have examined the effects of dexamethasone on chemokine receptor expression. Using an RNase protection assay, we show that dexamethasone up-regulates human peripheral blood mononuclear cell (PBMC) expression of CXCR4 mRNA. Flow cytometric analysis demonstrated that increased expression of CXCR4, but not CXCR1 and CXCR2, occurred on both monocytes and CD3+ T cells in PBMC mixed cultures. A stromal-derived factor (SDF)-1alpha-mediated calcium influx was detected on monocytes. Basal levels of CXCR4 expression on purified monocytes were lower when compared with monocytes in mixed PBMC cultures. Co-culture of monocytes with purified CD3+ T cells led to enhanced basal expression of CXCR4 on monocytes. The use of transwells to partition CD3+ T cells resulted in increased CXCR4 expression on monocytes, suggesting that CD3+ T-cell derived soluble factors regulate CXCR4 expression.

CD30 triggering by agonistic antibodies regulates CXCR4 expression and CXCL12 chemotactic activity in the cell line L540

The tumor necrosis factor receptor family molecule CD30 is expressed by activated and memory T cells, depending on IL-4 stimulation preferentially in association with Th0- and Th2-type responses. It mediates pleiotropic effects primarily of the inhibitory type. Arguing that CD30(+) cells have a peculiar redistribution in disease, it is demonstrated here, in the Hodgkin-derived L540 cell line (an established model for studying CD30 signaling), that CD30 regulates the prototypic lymphoid chemokine receptor CXCR4 (CD184), which plays an important role in many organ systems and is a coreceptor for human immunodeficiency virus-1 entry. CD30 stimulation with agonistic antibodies in L540 cells led to the accumulation of CXCR4 mRNA, which reached a plateau after 4 hours and did not require protein synthesis. It has been reported recently that CD30 up-regulates the transcription of CCR7 mRNA in YT lymphoma cells. After mRNA transcription, membrane expression of CXCR4 in L540 cells increased as early as 12 hours, reached a plateau after 24 hours (MFI +/- SD, 839 +/- 122 vs basal 168 +/- 28; P <.01) and was still increased after 5 days, permitting enhanced sensitivity to the chemotactic activity of CXCR4-ligand CXCL12 (CI +/- SD, 10 +/- 1 vs basal 5 +/- 2; P <.01). CD30 cross-linking also induced the release of CCL5 and CCL3 and the up-regulation of membrane binding capacity for CCL3 and CCL4 and decreased proliferative activity. This new regulatory role of CD30 may be relevant for T-cell maturation and effector responses and for promoting cancer biology.

A role for the Rho-p160 Rho coiled-coil kinase axis in the chemokine stromal cell-derived factor-1alpha-induced lymphocyte actomyosin and microtubular organization and chemotaxis

The possible involvement of the Rho-p160ROCK (Rho coiled-coil kinase) pathway in the signaling induced by the chemokine Stromal cell-derived factor (SDF)-1alpha has been studied in human PBL. SDF-1alpha induced activation of RhoA, but not that of Rac. RhoA activation was followed by p160ROCK activation mediated by RhoA, which led to myosin light chain (MLC) phosphorylation, which was dependent on RhoA and p160ROCK activities. The kinetics of MLC activation was similar to that of RhoA and p160ROCK. The role of this cascade in overall cell morphology and functional responses to the chemokine was examined employing different chemical inhibitors. Inhibition of either RhoA or p160ROCK did not block SDF-1alpha-induced short-term actin polymerization, but induced the formation of long spikes arising from the cell body, which were found to be microtubule based. This morphological change was associated with an increase in microtubule instability, which argues for an active microtubule polymerization in the formation of these spikes. Inhibition of the Rho-p160ROCK-MLC kinase signaling cascade at different steps blocked lymphocyte migration and the chemotaxis induced by SDF-1alpha. Our results indicate that the Rho-p160ROCK axis plays a pivotal role in the control of the cell shape as a step before lymphocyte migration toward a chemotactic gradient.

Cloning and relative expression analysis of rat stromal cell derived factor-1 (SDF-1)1: SDF-1 alpha mRNA is selectively induced in rat model of myocardial infarction

Stromal cell derived factor-1 (SDF-1) is a member of the non-ELR subfamily of CXC chemokines. SDF-1 and its receptor, CXCR4, are essential for cardiogenesis, hematopoiesis, and vasculogenesis during embryonic development, in addition to involvement in chemotaxis of leukocyte subsets and endothelial cells. In order to study SDF-1 expression in a rat model of myocardial infarction, we cloned and functionally expressed the rat SDF-1alpha orthologue. Rat SDF-1alpha is highly conserved, with >95% identity to its known human, feline, and murine counterparts. Constitutive expression of SDF-1 mRNA was observed in heart, brain, liver, and kidney. Significantly, apart from the SDF-1alpha and beta splice variants, expression of the recently identified SDF-1gamma was uniquely abundant in the heart. SDF-1alpha mRNA was selectively induced in permanent coronary artery occlusion model of myocardial infarction in rat, while SDF-1gamma remained unchanged. Such modulation of SDF-1alpha mRNA expression may be indicative of its role in the inflammatory events in cardiovascular disease.

Loss of chemokine SDF-1alpha-mediated CXCR4 signalling and receptor internalization in human hepatoma cell line HepG2

Expression of the chemokine stromal cell-derived factor-1alpha (SDF-1alpha) is absent from many carcinomas, including hepatomas. We note an early signalling defect in the hepatocellular carcinoma (HCC) cell line HepG2 that expresses the CXCR4 receptor and binds biotin-labelled SDF, but fails to stimulate downstream signalling events after engagement with SDF. In HepG2, the SDF/CXCR4 interaction did not result in calcium influx, phosphorylation and internalization of CXCR4, nor in a rapid phosphorylation of p44/42 MAP kinase. There were no CXCR4 mutations in the second chemokine binding loop or C terminal phosphorylation and internalization domains. The downstream signalling machinery in HepG2 appears to be intact since transfection of wild-type CXCR4 restored functional responsiveness. We conclude that HepG2 is unresponsive to SDF stimulation because of a defect located after receptor binding but before the activation of the signalling cascade. A hypothetical blocking molecule could hinder receptor internalization or CXCR4 signalling.

Pharmacological evidence for complex and multiple site interaction of CXCR4 with SDF-1alpha: implications for development of selective CXCR4 antagonists

The C-X-C chemokine SDF-1 and its receptor CXCR4, mediate a pivotal role in the pathophysiology of HIV-1 infection and vascular inflammatory diseases. In this study, we investigated the pharmacological properties of SDF-1alpha interaction with CXCR4 in human leukemia cell lines. Our data, based on [125I]-SDF-1alpha radioligand binding, SDF-1alpha-induced [35S]-GTPgammaS binding and use of specific CXCR4 antagonist AMD3100 reveals the complex nature of SDF-1alpha-CXCR4 interaction. Firstly, homologous competition with cold SDF-1alpha revealed a bimodal ligand displacement curve and secondly, although AMD3100 inhibited both SDF-1alpha-mediated chemotaxis (IC(50)=4.7 nM) and [35S]-GTPgammaS binding (IC(50)=7.4 nM) with high affinity, it was intriguingly up to 3000-fold less potent (IC(50)=15.2 microM) in the radioligand binding assay. These results provide pharmacological evidence for the recently described two-site model for SDF-1alpha-CXCR4 interaction. Accordingly, inhibition of SDF-1alpha binding to one of the receptor sites is sufficient to antagonize function, without causing its complete displacement from the receptor. Furthermore, these findings have important implications in the development and evaluation of CXCR4-selective small molecule antagonists for therapeutic use.

CXCR4 receptor expression on human retinal pigment epithelial cells from the blood-retina barrier leads to chemokine secretion and migration in response to stromal cell-derived factor 1 alpha

Retinal pigment epithelial (RPE) cells form part of the blood-retina barrier and have recently been shown to produce various chemokines in response to proinflammatory cytokines. As the scope of chemokine action has been shown to extend beyond the regulation of leukocyte migration, we have investigated the expression of chemokine receptors on RPE cells to determine whether they could be a target for chemokine signaling. RT-PCR analysis indicated that the predominant receptor expressed on RPE cells was CXCR4. The level of CXCR4 mRNA expression, but not cell surface expression, increased on stimulation with IL-1beta or TNF-alpha. CXCR4 protein could be detected on the surface of 16% of the RPE cells using flow cytometry. Calcium mobilization in response to the CXCR4 ligand stromal cell-derived factor 1alpha (SDF-1alpha) indicated that the CXCR4 receptors were functional. Incubation with SDF-1alpha resulted in secretion of monocyte chemoattractant protein-1, IL-8, and growth-related oncogene alpha. RPE cells also migrated in response to SDF-1alpha. As SDF-1alpha expression by RPE cells was detected constitutively, we postulate that SDF-1-CXCR4 interactions may modulate the affects of chronic inflammation and subretinal neovascularization at the RPE site of the blood-retina barrier.

SDF-1 activity on microvascular endothelial cells: consequences on angiogenesis in in vitro and in vivo models

The chemokine stromal cell-derived factor-1 (SDF-1) has been shown to be involved in cell migration. As the receptor CXCR-4 is expressed on endothelial cells and upregulated by angiogenic factors, we were prompted to study the effect of SDF-1 on angiogenesis in endothelial cells from microvasculature. This study demonstrates that SDF-1 induces an angiogenic effect in vitro, primarily in a tridimensional fibrin gel. The increase in capillary tube formation was evident after a 10-day incubation with SDF-1. This was associated with a mild increase in VEGF production by microvascular endothelial cells (ELISA and rt-PCR) and a potent chemotactic effect. SDF-1 also induced an in vivo angiogenic activity as shown in the model of the rabbit corneal pocket. However, the angiogenesis was located in an area rich in inflammatory cells. The results of our study suggest that these data underline the potential role of SDF-1 in angiogenesis as the microvascular endothelial cells were greatly involved in this process.

Biological effects of stroma-derived factor-1 alpha on normal and CML CD34+ haemopoietic cells

We compared the biological effects of the CXC chemokine SDF-1alpha on immunomagnetically purified CD34+ cells isolated from human normal bone marrow (NBM), leukapheresis products (LP) and patients with chronic myeloid leukaemia (CML). LP CD34+ cells showed a significantly stronger migration response to SDF-1alpha (100 ng/ml) than CD34+ cells isolated from the peripheral blood (PB) of CML patients (P < 0.05). The chemotactic response to SDF-1alpha was also reduced in CML BM CD34+ cells in comparison to NBM CD34+ cells but the observed differences were not statistically significant. In analogy to normal CD34+ cells circulating CML PB CD34+ cells were less responsive to SDF-1alpha than their BM counterparts (P < 0.05). Furthermore, SDF-1alpha elicited similar concentration-dependent growth suppressive effects on normal and CML CD34+ cells (P > 0.05) in colony-forming cell assays. We then demonstrated that SDF-1alpha triggers intracellular calcium increases in CD34+ cells and there were no differences in the time course and dose response characteristics of normal and CML CD34+ cells. The reduced migration response to SDF-1alpha in CML CD34+ cells was not due to a down-regulation of the SDF-1alpha receptor CXCR-4 as flow cytometric analysis revealed similar CXCR-4 expression levels on NBM, LP, CML PB and CML BM CD34+ cells (P > 0.05). Finally, no differences in the modulation of CXCR-4 levels in response to SDF-1alpha and serum were observed in CML and normal CD34+ cells. Our data suggest that the impaired chemotactic response of CML CD34+ cells to SDF-1alpha is not caused by a lack or complete uncoupling of CXCR-4, but may be due to an intracellular signalling defect downstream of the receptor.