Identification of carboxypeptidase N as an enzyme responsible for C-terminal cleavage of stromal cell-derived factor-1alpha in the circulation

Hereditary angioedema with normal C1 inhibitor associated with carboxypeptidase N deficiency

Background

Hereditary angioedema (HAE) is a potentially life-threatening disorder characterized by recurrent episodes of subcutaneous or submucosal swelling. HAE with normal C1 inhibitor (HAE-nC1-INH) is an underdiagnosed condition. Although the association with genetic variants has been identified for some families, the genetic causes in many patients with HAE-nC1-INH remain unknown. The role of genes associated with bradykinin catabolism is not fully understood.

Objective

We sought to investigate the biological parameters and the genes related to kallikrein-kinin system in families with a clinical phenotype of HAE-nC1-INH and presenting with a carboxypeptidase N (CPN) deficiency.

Methods

This study includes 4 families presenting with HAE-nC1-INH and CPN deficiency. Patients' clinical records were examined, biological parameters of kallikrein-kinin system were measured, and genetics was analyzed by next-generation sequencing and Sanger sequencing. Predictive algorithms (Human Splicing Finder, Sorting Intolerant From Tolerant, Polymorphism Phenotyping v2, MutationTaster, and ClinPred) were used to classify variants as affecting splicing, as benign to deleterious, or as disease-causing.

Results

Patients presented with angioedema and urticaria, mainly on face/lips, but also with abdominal pain or laryngeal symptoms. Affected patients displayed low CPN activity-30% to 50% of median value in plasma. We identified 3 variants of the CPN1 gene encoding the catalytic 55-kDa subunit of CPN: c.533G>A, c.582A>G, and c.734C>T. CPN deficiency associated with genetic variants segregated with HAE-nC1-INH symptoms in affected family members.

Conclusions

CPN1 gene variants are associated with CPN deficiency and HAE-nC1-INH symptoms in 4 unrelated families. Genetic CPN deficiency may contribute to bradykinin and anaphylatoxin accumulation, with synergistic effects in angioedema and urticarial symptoms.

An emerging paradigm of CXCL12 involvement in the metastatic cascade

The chemokine CXCL12, also known as stromal cell-derived factor 1 (SDF1), has emerged as a pivotal regulator in the intricate molecular networks driving cancer progression. As an influential factor in the tumor microenvironment, CXCL12 plays a multifaceted role that spans beyond its traditional role as a chemokine inducing invasion and metastasis. Indeed, CXCL12 has been assigned functions related to epithelial-to-mesenchymal transition, cancer cell stemness, angiogenesis, and immunosuppression, all of which are currently viewed as specialized biological programs contributing to the "metastatic cascade" among other cancer hallmarks. Its interaction with its cognate receptor, CXCR4, initiates a cascade of events that not only shapes the metastatic potential of tumor cells but also defines the niches within the secondary organs that support metastatic colonization. Given the profound implications of CXCL12 in the metastatic cascade, understanding its mechanistic underpinnings is of paramount importance for the targeted elimination of rate-limiting steps in the metastatic process. This review aims to provide a comprehensive overview of the current knowledge surrounding the role of CXCL12 in cancer metastasis, especially its molecular interactions rationalizing its potential as a therapeutic target.

Proteolytic inactivation of CXCL12 in the lungs and circulation of COVID-19 patients

The human chemokine stromal cell-derived factor-1 (SDF-1) or CXCL12 is involved in several homeostatic processes and pathologies through interaction with its cognate G protein-coupled receptor CXCR4. Recent research has shown that CXCL12 is present in the lungs and circulation of patients with coronavirus disease 2019 (COVID-19). However, the question whether the detected CXCL12 is bioactive was not addressed. Indeed, the activity of CXCL12 is regulated by NH2- and COOH-terminal post-translational proteolysis, which significantly impairs its biological activity. The aim of the present study was to characterize proteolytic processing of CXCL12 in broncho-alveolar lavage (BAL) fluid and blood plasma samples from critically ill COVID-19 patients. Therefore, we optimized immunosorbent tandem mass spectrometry proteoform analysis (ISTAMPA) for detection of CXCL12 proteoforms. In patient samples, this approach uncovered that CXCL12 is rapidly processed by site-specific NH2- and COOH-terminal proteolysis and ultimately degraded. This proteolytic inactivation occurred more rapidly in COVID-19 plasma than in COVID-19 BAL fluids, whereas BAL fluid samples from stable lung transplantation patients and the non-affected lung of lung cancer patients (control groups) hardly induced any processing of CXCL12. In COVID-19 BAL fluids with high proteolytic activity, processing occurred exclusively NH2-terminally and was predominantly mediated by neutrophil elastase. In low proteolytic activity BAL fluid and plasma samples, NH2- and COOH-terminal proteolysis by CD26 and carboxypeptidases were observed. Finally, protease inhibitors already approved for clinical use such as sitagliptin and sivelestat prevented CXCL12 processing and may therefore be of pharmacological interest to prolong CXCL12 half-life and biological activity in vivo.

Efficacy Evaluation of SDF-1α-Based Polypeptides in an Acute Myocardial Infarction Model Using Structure-Based Drug Design

Stromal cell-derived factor-1 alpha (SDF-1α, CXCL12) mediates the migration of circulating cells to desired sites for tissue development, homeostasis, and regeneration and can be used to promote cardiac regeneration by recruiting stem cells. However, the use of SDF-1α in the injured heart necessitates not only higher binding affinity to its receptor, CXCR4+, but also better robustness against enzymatic degradation than other SDF-1 isoforms. Here, we conduct a screening of SDF-1α analog peptides that were designed by structure-based drug design (SBDD), a type of computer-aided drug design (CADD). We have developed in vitro and in vivo methods that enable us to estimate the effect of peptides on the migration of human mesenchymal stem cells (hMSCs) and cardiac regeneration in acute myocardial infarction (AMI)-induced animals, respectively. We demonstrate that one type of SDF-1α analog peptide, SDP-4, among the four analog peptides preselected by SBDD, is more potent than native SDF-1α for cardiac regeneration in myocardial infarction. It is interesting to note that the migratory effects of SDP-4 determined by a wound healing assay, a Transwell assay, and a 2D migration assay are comparable to those of SDF-1α. These results suggest that in vivo, as well as in vitro, screening of peptides developed by SBDD is a quintessential process to the development of a novel therapeutic compound for cardiac regeneration. Our finding also has an implication that the SDP-4 peptide is an excellent candidate for use in the regeneration of an AMI heart.

Identification of Novel Vascular Genes Downstream of Islet2 and Nr2f1b Transcription Factors

The genetic regulation of vascular development is not elucidated completely. We previously characterized the transcription factors Islet2 (Isl2) and Nr2f1b as being critical for vascular growth. In this study, we further performed combinatorial microarrays to identify genes that are potentially regulated by these factors. We verified the changed expression of several targets in isl2/nr2f1b morphants. Those genes expressed in vessels during embryogenesis suggested their functions in vascular development. We selectively assayed a potential target follistatin a (fsta). Follistatin is known to inhibit BMP, and BMP signaling has been shown to be important for angiogenesis. However, the fsta’s role in vascular development has not been well studied. Here, we showed the vascular defects in ISV growth and CVP patterning while overexpressing fsta in the embryo, which mimics the phenotype of isl2/nr2f1b morphants. The vascular abnormalities are likely caused by defects in migration and proliferation. We further observed the altered expression of vessel markers consistent with the vascular defects in (fli:fsta) embryos. We showed that the knockdown of fsta can rescue the vascular defects in (fli:fsta) fish, suggesting the functional specificity of fsta. Moreover, the decreased expression of fsta rescues abnormal vessel growth in isl2 and nr2f1b morphants, indicating that fsta functions downstream of isl2/nr2f1b. Lastly, we showed that Isl2/Nr2f1b control vascular development, via Fsta–BMP signaling in part. Collectively, our microarray data identify many interesting genes regulated by isl2/nr2f1b, which likely function in the vasculature. Our research provides useful information on the genetic control of vascular development.

CXCR4 blockade in macrophage promotes angiogenesis in ischemic hindlimb by modulating autophagy

Chemokine receptor CXCR4 plays a crucial role in leukocyte recruitment and inflammation regulation to influence tissue repair in ischemic diseases. Here we assessed the effect of CXCR4 expression in macrophages on angiogenesis in the ischemic hindlimb of a mouse. Inflammatory cells were increased in the ischemic muscles of hindlimb, and CXCR4 was highly expressed in the infiltrated macrophages but not in neutrophils. Myeloid-specific CXCR4 knockout attenuated macrophage infiltration and subsequent reduced inflammatory response in the ischemic hindlimb, accompanied with better blood reperfusion and higher capillary density as compared with that in LysM Cre^+/- (Cre) mice. Similar outcomes were also observed in CRE mice whose bone marrow cells were replaced with those from CXCR4-deficient mice. Gene ontology cluster analysis reviewed that Decorin, a negative regulator of angiogenesis, was reduced in CXCR4-deficient macrophages. CXCR4-deficient macrophages were less inducible into M1 phase by lipopolysaccharide and more favorable for M2 polarization under oxygen/glucose deprivation condition. Enhanced autophagy was detected in CXCR4-deficient macrophages, which was associated with less expression of both Decorin and the inflammatory cytokines. In summary, myeloid-specific CXCR4 deficiency reduced monocyte infiltration and the secretion of inflammatory cytokines and Decorin from macrophages, thus blunting inflammation response and promoting angiogenesis in the ischemic hindlimb.

CXC chemokine ligand 12 (CXCL12) in atherosclerosis: An underlying therapeutic target

CXC chemokine ligand 12 (CXCL12) is a specific chemokine ligand and plays a significant role in cell chemotaxis. Upon binding to CXC chemokine receptor 4 (CXCR4) or CXCR7, CXCL12 can activate different signaling cascades to regulate cell proliferation, migration, and metabolism. CXCL12 exerts a pro-atherogenic action by aggravating multiple pathogenesis of atherogenesis, including dyslipidemia, inflammation, neointima hyperplasia, angiogenesis, and insulin resistance. Serum CXCL12 levels are also markedly increased in patients with atherosclerosis-associated disease. The present review focuses on recent advances in CXCL12 research in the pathogenesis of atherosclerosis together with its clinical values. This may provide insight into potential novel therapies for atherosclerosis.

Natural nitration of CXCL12 reduces its signaling capacity and chemotactic activity in vitro and abrogates intra-articular lymphocyte recruitment in vivo

The chemokine CXCL12/stromal cell-derived factor-1 is important for leukocyte migration to lymphoid organs and inflamed tissues and stimulates tumor development. In vitro, CXCL12 activity through CXCR4 is abolished by proteolytic processing. However, limited information is available on in vivo effects of posttranslationally modified CXCL12. Natural CXCL12 was purified from the coculture supernatant of stromal cells stimulated with leukocytes and inflammatory agents. In this conditioned medium, CXCL12 with a nitration on Tyr⁷, designated [3-NT⁷]CXCL12, was discovered via Edman degradation. CXCL12 and [3-NT⁷]CXCL12 were chemically synthesized to evaluate the biological effects of this modification. [3-NT⁷]CXCL12 recruited β-arrestin 2 and phosphorylated the Akt kinase similar to CXCL12 in receptor-transfected cells. Also the affinity of CXCL12 and [3-NT⁷]CXCL12 for glycosaminoglycans, the G protein-coupled chemokine receptor CXCR4 and the atypical chemokine receptor ACKR3 were comparable. However, [3-NT⁷]CXCL12 showed a reduced ability to enhance intracellular calcium concentrations, to generate inositol triphosphate, to phosphorylate ERK1/2 and to induce monocyte and lymphocyte chemotaxis in vitro. Moreover, nitrated CXCL12 failed to induce in vivo extravasation of lymphocytes to the joint. In summary, nitration on Tyr⁷ under inflammatory conditions is a novel natural posttranslational regulatory mechanism of CXCL12 which may downregulate the CXCR4-mediated inflammatory and tumor-promoting activities of CXCL12.

The unique structural and functional features of CXCL12

The CXC chemokine CXCL12 is an important factor in physiological and pathological processes, including embryogenesis, hematopoiesis, angiogenesis and inflammation, because it activates and/or induces migration of hematopoietic progenitor and stem cells, endothelial cells and most leukocytes. Therefore, CXCL12 activity is tightly regulated at multiple levels. CXCL12 has the unique property of existing in six splice variants in humans, each having a specific tissue distribution and in vivo activity. Controlled splice variant transcription and mRNA stability determine the CXCL12 expression profile. CXCL12 fulfills its functions in homeostatic and pathological conditions by interacting with its receptors CXC chemokine receptor 4 (CXCR4) and atypical chemokine receptor 3 (ACKR3) and by binding to glycosaminoglycans (GAGs) in tissues and on the endothelium to allow a proper presentation to passing leukocytes. Homodimerizaton and heterodimerization of CXCL12 and its receptors can alter their signaling activity, as exemplified by the synergy between CXCL12 and other chemokines in leukocyte migration assays. Receptor binding may also initiate CXCL12 internalization and its subsequent removal from the environment. Furthermore, CXCL12 activity is regulated by posttranslational modifications. Proteolytic removal of NH₂- or COOH-terminal amino acids, citrullination of arginine residues by peptidyl arginine deiminases or nitration of tyrosine residues reduce CXCL12 activity. This review summarizes the interactions of CXCL12 with the cellular environment and discusses the different levels of CXCL12 activity regulation.

Fine-tune regulation of carboxypeptidase N1 controls vascular patterning during zebrafish development

Vascular development is regulated by complicated signals and molecules in vertebrates. In this study, we characterized a novel function of carboxypeptidase N1 (Cpn1) in the vasculature. We show that cpn1 mRNA is expressed in developing vessels. The knockdown of cpn1 by morpholino injection impairs the growth of intersegmental vessels (ISV) and caudal vein plexus (CVP), suggesting the role of cpn1 in vascular development. We showed that vascular defects are not caused by cell death but are due to the impairment of migration and proliferation. Consistent with vascular growth defects, loss of cpn1 affects the expression of the vascular markers flt4, mrc1, flk, stabilin, and ephrinb2. Furthermore, the overexpression of cpn1 impaired the growth of ISV and CVP, but the remodeling expression of vascular markers was different from the knockdown of cpn1, indicating the differential regulation mechanisms in cpn1-overexpressing embryos. We examine the interaction between cpn1 and multiple signals and observed that cpn1 is regulated by Notch/VEGF signals for ISV growth and likely regulates BMP signals for CVP patterning. In conclusion, we demonstrate that cpn1 has a critical role in the vascular development of zebrafish. We also reveal a fine-tune regulation of cpn1 that controls vascular patterning mediated by multiple signals.

A novel recombinant antibody specific to full-length stromal derived factor-1 for potential application in biomarker studies

Background

Stromal derived factor-1α (SDF-1α/CXCL12) is a chemokine that is up-regulated in diseases characterised by tissue hypoxia, including myocardial infarction, ischaemic cardiomyopathy and remote ischaemic conditioning (RIC), a technique of cyclical, non-injurious ischaemia applied remote from the heart that protects the heat from lethal ischaemia-reperfusion injury. Accordingly, there is considerable interest in SDF-1α as a potential biomarker of such conditions. However, SDF-1α is rapidly degraded and inactivated by dipeptidyl peptidase 4 and other peptidases, and the kinetics of intact SDF-1α remain unknown.

Methods & results

To facilitate investigation of full-length SDF-1α we established an ELISA using a novel recombinant human antibody we developed called HCI.SDF1. HCI.SDF1 is specific to the N-terminal sequence of all isoforms of SDF-1 and has a comparable K_D to commercially available antibodies. Together with a detection antibody specific to the α-isoform, HCI.SDF1 was used to specifically quantify full-length SDF-1α in blood for the first time. Using RIC applied to the hind limb of Sprague-Dawley rats or the arms of healthy human volunteers, we demonstrate an increase in SDF-1α using a commercially available antibody, as previously reported, but an unexpected decrease in full-length SDF-1α after RIC in both species.

Conclusions

We report for the first time the development of a novel recombinant antibody specific to full-length SDF-1. Applied to RIC, we demonstrate a significant decrease in SDF-1α that is at odds with the literature and suggests a need to investigate the kinetics of full-length SDF-1α in conditions characterised by tissue hypoxia.

CXCL12/CXCR4/CXCR7 Chemokine Axis in the Central Nervous System: Therapeutic Targets for Remyelination in Demyelinating Diseases

The chemokine CXCL12 plays a vital role in regulating the development of the central nervous system (CNS) by binding to its receptors CXCR4 and CXCR7. Recent studies reported that the CXCL12/CXCR4/CXCR7 axis regulates both embryonic and adult oligodendrocyte precursor cells (OPCs) in their proliferation, migration, and differentiation. The changes in the expression and distribution of CXCL12 and its receptors are tightly associated with the pathological process of demyelination in multiple sclerosis (MS), suggesting that modulating the CXCL12/CXCR4/CXCR7 axis may benefit myelin repair by enhancing OPC recruitment and differentiation. This review aims to integrate the current findings of the CXCL12/CXCR4/CXCR7 signaling pathway in the CNS and to highlight its role in oligodendrocyte development and demyelinating diseases. Furthermore, this review provides potential therapeutic strategies for myelin repair by analyzing the relevance between the pathological changes and the regulatory roles of CXCL12/CXCR4/CXCR7 during MS.

Multi-omics Analysis of Serum Samples Demonstrates Reprogramming of Organ Functions Via Systemic Calcium Mobilization and Platelet Activation in Metastatic Melanoma

Pathophysiologies of cancer-associated syndromes such as cachexia are poorly understood and no routine biomarkers have been established, yet. Using shotgun proteomics, known marker molecules including PMEL, CRP, SAA, and CSPG4 were found deregulated in patients with metastatic melanoma. Targeted analysis of 58 selected proteins with multiple reaction monitoring was applied for independent data verification. In three patients, two of which suffered from cachexia, a tissue damage signature was determined, consisting of nine proteins, PLTP, CD14, TIMP1, S10A8, S10A9, GP1BA, PTPRJ, CD44, and C4A, as well as increased levels of glycine and asparagine, and decreased levels of polyunsaturated phosphatidylcholine concentrations, as determined by targeted metabolomics. Remarkably, these molecules are known to be involved in key processes of cancer cachexia. Based on these results, we propose a model how metastatic melanoma may lead to reprogramming of organ functions via formation of platelet activating factors from long-chain polyunsaturated phosphatidylcholines under oxidative conditions and via systemic induction of intracellular calcium mobilization. Calcium mobilization in platelets was demonstrated to alter levels of several of these marker molecules. Additionally, platelets from melanoma patients proved to be in a rather exhausted state, and platelet-derived eicosanoids implicated in tumor growth were found massively increased in blood from three melanoma patients. Platelets were thus identified as important source of serum protein and lipid alterations in late stage melanoma patients. As a result, the proposed model describes the crosstalk between lipolysis of fat tissue and muscle wasting mediated by oxidative stress, resulting in the metabolic deregulations characteristic for cachexia.

Regulation of Chemokine Activity - A Focus on the Role of Dipeptidyl Peptidase IV/CD26

Chemokines are small, chemotactic proteins that play a crucial role in leukocyte migration and are, therefore, essential for proper functioning of the immune system. Chemokines exert their chemotactic effect by activation of chemokine receptors, which are G protein-coupled receptors (GPCRs), and interaction with glycosaminoglycans (GAGs). Furthermore, the exact chemokine function is modulated at the level of posttranslational modifications. Among the different types of posttranslational modifications that were found to occur in vitro and in vivo, i.e., proteolysis, citrullination, glycosylation, and nitration, NH₂-terminal proteolysis of chemokines has been described most intensively. Since the NH₂-terminal chemokine domain mediates receptor interaction, NH₂-terminal modification by limited proteolysis or amino acid side chain modification can drastically affect their biological activity. An enzyme that has been shown to provoke NH₂-terminal proteolysis of various chemokines is dipeptidyl peptidase IV or CD26. This multifunctional protein is a serine protease that preferably cleaves dipeptides from the NH₂-terminal region of peptides and proteins with a proline or alanine residue in the penultimate position. Various chemokines possess such a proline or alanine residue, and CD26-truncated forms of these chemokines have been identified in cell culture supernatant as well as in body fluids. The effects of CD26-mediated proteolysis in the context of chemokines turned out to be highly complex. Depending on the chemokine ligand, loss of these two NH₂-terminal amino acids can result in either an increased or a decreased biological activity, enhanced receptor specificity, inactivation of the chemokine ligand, or generation of receptor antagonists. Since chemokines direct leukocyte migration in homeostatic as well as pathophysiologic conditions, CD26-mediated proteolytic processing of these chemotactic proteins may have significant consequences for appropriate functioning of the immune system. After introducing the chemokine family together with the GPCRs and GAGs, as main interaction partners of chemokines, and discussing the different forms of posttranslational modifications, this review will focus on the intriguing relationship of chemokines with the serine protease CD26.

Extracellular molecules in hematopoietic stem cell mobilisation

Hematopoietic stem cells are a remarkable resource currently used for the life saving treatment, hematopoietic stem cell transplantation. Today, hematopoietic stem cells are primarily obtained from mobilized peripheral blood following treatment of the donor with the cytokine G-CSF, and in some settings, chemotherapy and/or the CXCR4 antagonist plerixafor. The collection of hematopoietic stem cells is contingent on adequate and timely mobilization of these cells into the peripheral blood. The use of healthy donors, particularly when unrelated to the patient, requires mobilization strategies be safe for the donor. While current mobilization strategies are largely successful, adequate mobilization fails to occur in a significant portion of donors. Understanding the mechanisms involved in the egress of stem cells from the bone marrow provides opportunities to further improve the process of collecting hematopoietic stem cells. Here, the role extracellular components of the blood and bone marrow in the mobilization process are discussed.

Paracrine SDF-1α signaling mediates the effects of PSCs on GEM chemoresistance through an IL-6 autocrine loop in pancreatic cancer cells

Pancreatic cancer exhibits the poorest prognosis among all tumors and is characterized by high resistance to the currently available chemotherapeutic agents. Our previous studies have suggested that stromal components could promote the chemoresistance of pancreatic cancer cells (PCCs). Here, we explored the roles of pancreatic stellate cells (PSCs) and the SDF-1α/CXCR4 axis in pancreatic cancer chemoresitance. Our results showed that primary PSCs typically expressed SDF-1α, whereas its receptor CXCR4 was highly expressed in PCCs. PSC-conditioned medium (PSC-CM) inhibited Gemcitabine (GEM)-induced cytotoxicity and apoptosis in the human PCC line Panc-1, which was antagonized by an SDF-1α neutralizing Ab. Recombinant human SDF-1α (rhSDF-1α) increased IL-6 expression and secretion in Panc-1 cells in a time and dose-dependent manner, and this effect was suppressed by the CXCR4 antagonist AMD3100. rhSDF-1α protected Panc-1 cells from GEM-induced apoptosis, and the protective effect was significantly reduced by blocking IL-6 using a neutralizing antibody. Moreover, rhSDF-1α increased FAK, ERK1/2, AKT and P38 phosphorylation in Panc-1 cells, and either FAK or ERK1/2 inhibition suppressed SDF-1α-upregulated IL-6 expression. SDF-1α-induced AKT activation was almost completely blocked by FAK inhibition. In conclusion, we demonstrate for the first time that PSCs promote the chemoresistance of PCCs to GEM, and this effect is mediated by paracrine SDF-1α/CXCR4 signaling-induced activation of the intracellular FAK-AKT and ERK1/2 signaling pathways and a subsequent IL-6 autocrine loop in PCCs. Our findings indicate that blocking the PSC-PCC interaction by inhibiting SDF-1α/CXCR4 signaling may be a promising therapeutic strategy for overcoming chemoresistance in pancreatic cancer.

Total body irradiation is permissive for mesenchymal stem cell-mediated new bone formation following local transplantation

Skeletal injury is a major clinical challenge accentuated by the decrease of bone marrow-derived mesenchymal stem/stromal cells (BMSCs) with age or disease. Numerous experimental and clinical studies have revealed that BMSCs hold great promise for regenerative therapies due to their direct osteogenic potential and indirect trophic/paracrine actions. Increasing evidence suggests that stromal cell-derived factor-1 (SDF-1) is involved in modulating the host response to the injury. Common problems with BMSC therapy include poor cell engraftment, which can be addressed by total body irradiation (TBI) prior to transplantation. In this study, we tested the hypothesis that direct tibial transplantation of BMSCs drives endogenous bone formation in a dose-dependent manner, which is enhanced by TBI, and investigated the potential role of SDF-1 in facilitating these events. We found that TBI is permissive for transplanted BMSCs to engraft and contribute to new bone formation. Bone marrow (BM) interstitial fluid analysis revealed no differences of SDF-1 splice variants in irradiated animals compared to controls, despite the increased mRNA and protein levels expressed in whole BM cells. This correlated with increased dipeptidyl peptidase IV activity and the failure to induce chemotaxis of BMSCs in vitro. We found increased mRNA expression levels of the major SDF-1-cleaving proteases in whole BM cells from irradiated animals suggesting distinct spatial differences within the BM in which SDF-1 may play different autocrine and paracrine signaling roles beyond the immediate cell surface microenvironment.

Direct effects of DPP-4 inhibition on the vasculature. Reconciling basic evidence with lack of clinical evidence

Diabetes is burdened by macrovascular and microvascular complications that collectively reduce life expectancy. As the ultimate goal of diabetes treatment is to prevent excess morbidity and mortality associated with its complications, the interest on cardiovascular effects of glucose lowering medications is high. Dipeptidyl peptidase-4 inhibitors (DPP-4i) lower blood glucose by protecting the incretin hormone glucagon-like peptide-1 (GLP-1) from enzymatic degradation, thereby restoring meal-stimulated insulin release. DPP-4 has several non-incretin substrates, including cytokines, chemokines, and neurohormones, which can exert favourable, but also unpredictable, vascular effects, once they are stabilized by DPP-4i. Choi et al. now provide additional evidence that DPP-4i counteracts vascular smooth muscle cell proliferation and migration, resulting in an attenuation of neointimal hyperplasia. Though several other in vitro, preclinical, and preliminary clinical studies on surrogate end-points suggest that DPP-4i can exert similar direct vasculoprotective actions, results of placebo-controlled phase IV trials have so far shown no reduction cardiovascular endpoints by DPP-4i. In this commentary, we put DPP-4 pleiotropy and complexity into context, trying to reconcile why results from basic science have not yet translated into clinical evidence of cardiovascular protection.

Mesenchymal stem cell expression of SDF-1β synergizes with BMP-2 to augment cell-mediated healing of critical-sized mouse calvarial defects

Bone has the potential for spontaneous healing. This process, however, often fails in patients with comorbidities. Tissue engineering combining functional cells, biomaterials and osteoinductive cues may provide alternative treatment strategies. We have recently demonstrated that stromal cell-derived factor-1β (SDF-1β) works in concert with bone morphogenetic protein-2 (BMP-2) to potentiate osteogenic differentiation of bone marrow-derived mesenchymal stem/stromal cells (BMSCs). Here, we test the hypothesis that SDF-1β overexpressed in Tet-Off-SDF-1β BMSCs, delivered on acellular dermal matrix (ADM), synergistically augments BMP-2-induced healing of critical-sized mouse calvarial defects. BMSC therapies alone showed limited bone healing, which was increased with co-delivery of BMP-2. This was further enhanced in Tet-Off-SDF-1β BMSCs + BMP-2. Only limited BMSC retention on ADM constructs was observed after 4 weeks in vivo, which was increased with BMP-2 co-delivery. In vitro cell proliferation studies showed that supplementing BMP-2 to Tet-Off BMSCs significantly increased the cell number during the first 24 h. Consequently, the increased cell numbers decreased the detectable BMP-2 levels in the medium, but increased cell-associated BMP-2. The data suggest that SDF-1β provides synergistic effects supporting BMP-2-induced, BMSC-mediated bone formation and appears suitable for optimization of bone augmentation in combination therapy protocols. Copyright © 2015 John Wiley & Sons, Ltd.

Exome analysis reveals differentially mutated gene signatures of stage, grade and subtype in breast cancers

Breast cancers exhibit highly heterogeneous molecular profiles. Although gene expression profiles have been used to predict the risks and prognostic outcomes of breast cancers, the high variability of gene expression limits its clinical application. In contrast, genetic mutation profiles would be more advantageous than gene expression profiles because genetic mutations can be stably detected and the mutational heterogeneity widely exists in breast cancer genomes. We analyzed 98 breast cancer whole exome samples that were sorted into three subtypes, two grades and two stages. The sum deleterious effect of all mutations in each gene was scored to identify differentially mutated genes (DMGs) for this case-control study. DMGs were corroborated using extensive published knowledge. Functional consequences of deleterious SNVs on protein structure and function were also investigated. Genes such as ERBB2, ESP8, PPP2R4, KIAA0922, SP4, CENPJ, PRCP and SELP that have been experimentally or clinically verified to be tightly associated with breast cancer prognosis are among the DMGs identified in this study. We also identified some genes such as ARL6IP5, RAET1E, and ANO7 that could be crucial for breast cancer development and prognosis. Further, SNVs such as rs1058808, rs2480452, rs61751507, rs79167802, rs11540666, and rs2229437 that potentially influence protein functions are observed at significantly different frequencies in different comparison groups. Protein structure modeling revealed that many non-synonymous SNVs have a deleterious effect on protein stability, structure and function. Mutational profiling at gene- and SNV-level revealed differential patterns within each breast cancer comparison group, and the gene signatures correlate with expected prognostic characteristics of breast cancer classes. Some of the genes and SNVs identified in this study show high promise and are worthy of further investigation by experimental studies.

Mesenchymal stem cell expression of stromal cell-derived factor-1β augments bone formation in a model of local regenerative therapy

Bone has the potential for spontaneous healing. However, this process often fails in patients with co-morbidities requiring clinical intervention. Numerous studies have revealed that bone marrow-derived mesenchymal stem/stromal cells (BMSCs) hold great potential for regenerative therapies. Common problems include poor cell engraftment, which can be addressed by irradiation prior to transplantation. Increasing evidence suggests that stromal cell-derived factor-1 (SDF-1) is involved in bone formation. However, osteogenic contributions of the beta splice variant of SDF-1 (SDF-1β), which is highly expressed in bone, remain unclear. Using the tetracycline (Tet)-regulatory system we have shown that SDF-1β enhances BMSC osteogenic differentiation in vitro. Here we test the hypothesis that SDF-1β augments bone formation in vivo in a model of local BMSC transplantation following irradiation. We found that SDF-1β, expressed at high levels in Tet-Off-SDF-1β BMSCs, augments the cell-mediated therapeutic effects resulting in enhanced bone formation, as evidenced by ex vivo μCT and bone histomorphometry. The data demonstrate the specific contribution of SDF-1β to BMSC-mediated bone formation, and validate the feasibility of the Tet-Off technology to regulate SDF-1β expression in vivo. In conclusion, SDF-1β provides potent synergistic effects supporting BMSC-mediated bone formation and appears a suitable candidate for optimization of bone augmentation in translational protocols.

Inkjet-based biopatterning of SDF-1β augments BMP-2-induced repair of critical size calvarial bone defects in mice

BACKGROUND

A major problem in craniofacial surgery is non-healing bone defects. Autologous reconstruction remains the standard of care for these cases. Bone morphogenetic protein-2 (BMP-2) therapy has proven its clinical utility, although non-targeted adverse events occur due to the high milligram-level doses used. Ongoing efforts explore the use of different growth factors, cytokines, or chemokines, as well as co-therapy to augment healing.

METHODS

Here we utilize inkjet-based biopatterning to load acellular DermaMatrix delivery matrices with nanogram-level doses of BMP-2, stromal cell-derived factor-1β (SDF-1β), transforming growth factor-β1 (TGF-β1), or co-therapies thereof. We tested the hypothesis that bioprinted SDF-1β co-delivery enhances BMP-2 and TGF-β1-driven osteogenesis both in-vitro and in-vivo using a mouse calvarial critical size defect (CSD) model.

RESULTS

Our data showed that BMP-2 bioprinted in low-doses induced significant new bone formation by four weeks post-operation. TGF-β1 was less effective compared to BMP-2, and SDF-1β therapy did not enhance osteogenesis above control levels. However, co-delivery of BMP-2+SDF-1β was shown to augment BMP-2-induced bone formation compared to BMP-2 alone. In contrast, co-delivery of TGF-β1+SDF-1β decreased bone healing compared to TGF-β1 alone. This was further confirmed in vitro by osteogenic differentiation studies using MC3T3-E1 pre-osteoblasts.

CONCLUSIONS

Our data indicates that sustained release delivery of a low-dose growth factor therapy using biopatterning technology can aid in healing CSD injuries. SDF-1β augments the ability for BMP-2 to drive healing, a result confirmed in vivo and in vitro; however, because SDF-1β is detrimental to TGF-β1-driven osteogenesis, its effect on osteogenesis is not universal.

Identification and characterization of circulating variants of CXCL12 from human plasma: effects on chemotaxis and mobilization of hematopoietic stem and progenitor cells

Mobilization of hematopoietic stem and progenitor cells (HPCs) is induced by treatment with granulocyte-colony stimulating factor, chemotherapy, or irradiation. We observed that these treatments are accompanied by a release of chemotactic activity into the blood. This plasma activity is derived from the bone marrow, liver, and spleen and acts on HPCs via the chemokine receptor CXCR4. A human blood peptide library was used to characterize CXCR4-activating compounds. We identified CXCL12[22-88] and N-terminally truncated variants CXCL12[24-88], CXCL12[25-88], CXCL12[27-88], and CXCL12[29-88]. Only CXCL12[22-88] could effectively bind to CXCR4 and induce intracellular calcium flux and chemotactic migration of HPCs. CXCL12[25-88] and CXCL12[27-88] revealed neither agonistic nor antagonistic activities in vitro, whereas CXCL12[29-88] inhibited CXCL12[22-88]-induced chemotactic migration. Since binding to glycosaminoglycans (GAG) modulates the function of CXCL12, binding to heparin was analyzed. Surface plasmon resonance kinetic analysis showed that N-terminal truncation of Arg22-Pro23 increased the dissociation constant KD by one log10 stage ([22-88]: KD: 5.4 ± 2.6 μM; [24-88]: KD: 54 ± 22.4 μM). Further truncation of the N-terminus decreased the KD ([25-88] KD: 30 ± 4.8 μM; [27-88] KD: 23 ± 1.6 μM; [29-88] KD: 19 ± 5.4 μM), indicating increasing competition for heparin binding. Systemic in vivo application of CXCL12[22-88] as well as CXCL12[27-88] or CXCL12[29-88] induced a significant mobilization of HPCs in mice. Our findings indicate that plasma-derived CXCL12 variants may contribute to the regulation of HPC mobilization by modulating the binding of CXCL12[22-88] to GAGs rather than blocking the CXCR4 receptor and, therefore, may have a contributing role in HPC mobilization.

Expression of SDF-1 and CXCR4 transcript variants and CXCR7 in epithelial ovarian cancer

Chemokine stromal cell-derived factor-1 (SDF-1) and its receptors, CXCR4 and CXCR7, have been implicated in epithelial ovarian cancer progression and metastasis. However, limited data are available on the expression levels of SDF-1 and CXCR4 variants and CXCR7 in human epithelial ovarian cancer. The present study aimed to characterize the expression pattern and levels of SDF-1, CXCR4 and CXCR7 in normal human ovaries and epithelial ovarian cancer. The expression of SDF-1 and CXCR4 transcript variants and CXCR7 was determined by quantitative polymerase chain reaction (qPCR). Plasma SDF-1α levels were determined by commercially available EIA kits and cancer antigen 125 (CA 125) levels were quantified by automated microparticle enzyme immunosorbent assay. High expression levels of SDF-1 transcript variant 1 were identified in ovarian cancer and control ovaries. By contrast, in both groups the expression levels of SDF-1 transcript variants 3 and 4 were extremely low. Furthermore, SDF-1 variant 1 levels were notably higher in epithelial ovarian cancer than in control ovaries, while data for the remaining transcripts were similar in both groups. CXCR4 transcript variant 2 and CXCR7 expression levels in normal and neoplastic ovaries were similar. In both groups, CXCR4 transcript variant 2 was not detected. Plasma SDF-1α levels were notably higher in females with epithelial ovarian cancer than in the control ovaries. Elevated levels of blood SDF-1α were found prior to surgery, 6 days after surgery and following completion of the first chemotherapy course. These increases were independent of the type of epithelial ovarian cancer. Our results suggest that the expression of SDF-1 and the genes controlling alternative splicing are elevated in epithelial ovarian cancer, leading to an increased formation of SDF-1 variant 1. Elevated plasma SDF-1α levels in epithelial ovarian cancer patients are not associated with the presence of tumors and/or metastases, however reflect a general response to the disease.

Matrix metalloproteinase 9 (MMP-9) mediated release of MMP-9 resistant stromal cell-derived factor 1α (SDF-1α) from surface modified polymer films

Preparation of smart materials by coatings of established surfaces with biomolecules will lead to the next generation of functionalized biomaterials. Rejection of implants is still a major problem in medical applications but masking the implant material with protein coatings is a promising approach. These layers not only disguise the material but also equip it with a certain biological function. The anti-inflammatory chemokine stromal cell-derived factor 1α (SDF-1α) is well suited to take over this function, because it efficiently attracts stem cells and promotes their differentiation and proliferation. At least the initial stem cell homing requires the formation of a concentration gradient. Thus, a reliable and robust release mechanism of SDF-1α from the material is essential. Several proteases, most notably matrix metalloproteinases, are upregulated during inflammation, which, in principle, can be exploited for a tightly controlled release of SDF-1α. Herein, we present the covalent immobilization of M-[S4V]-SDF-1α on novel biodegradable polymer films, which consist of heterobifunctional poly(ethylene glycol) and oligolactide-based functionalized macromers. A peptidic linker with a trimeric matrix metalloproteinase 9 (MMP-9) cleavage site (MCS) was used as connection and the linkage between the three components was achieved by combination of expressed protein ligation and Cu(I) catalyzed azide/alkyne cycloaddition. The MCS was used for MMP-9 mediated release of M-[S4V]-SDF-1α from the biomaterial and the released SDF-1α derivative was biologically active and induced strong cell migration, which demonstrates the great potential of this system.

Low-dose bone morphogenetic protein-2/stromal cell-derived factor-1β cotherapy induces bone regeneration in critical-size rat calvarial defects

Increasing evidence suggests that stromal cell-derived factor-1 (SDF-1/CXCL12) is involved in bone formation, though underlying molecular mechanisms remain to be fully elucidated. Also, contributions of SDF-1β, the second most abundant splice variant, as an osteogenic mediator remain obscure. We have shown that SDF-1β enhances osteogenesis by regulating bone morphogenetic protein-2 (BMP-2) signaling in vitro. Here we investigate the dose-dependent contribution of SDF-1β to suboptimal BMP-2-induced local bone formation; that is, a dose that alone would be too low to significantly induce bone formation. We utilized a critical-size rat calvarial defect model and tested the hypotheses that SDF-1β potentiates BMP-2 osteoinduction and that blocking SDF-1 signaling reduces the osteogenic potential of BMP-2 in vivo. In preliminary studies, radiographic analysis at 4 weeks postsurgery revealed a dose-dependent relationship in BMP-2-induced new bone formation. We then found that codelivery of SDF-1β potentiates suboptimal BMP-2 (0.5 μg) osteoinduction in a dose-dependent order, reaching comparable levels to the optimal BMP-2 dose (5.0 μg) without apparent adverse effects. Blocking the CXC chemokine receptor 4 (CXCR4)/SDF-1 signaling axis using AMD3100 attenuated the osteoinductive potential of the optimal BMP-2 dose, confirmed by qualitative histologic analysis. In conclusion, SDF-1β provides potent synergistic effects that support BMP-induced local bone formation and thus appears a suitable candidate for optimization of bone augmentation using significantly lower amounts of BMP-2 in spine, orthopedic, and craniofacial settings.

Sustained release of engineered stromal cell-derived factor 1-α from injectable hydrogels effectively recruits endothelial progenitor cells and preserves ventricular function after myocardial infarction

BACKGROUND

Exogenously delivered chemokines have enabled neovasculogenic myocardial repair in models of ischemic cardiomyopathy; however, these molecules have short half-lives in vivo. In this study, we hypothesized that the sustained delivery of a synthetic analog of stromal cell-derived factor 1-α (engineered stromal cell-derived factor analog [ESA]) induces continuous homing of endothelial progenitor cells and improves left ventricular function in a rat model of myocardial infarction.

METHODS AND RESULTS

Our previously designed ESA peptide was synthesized by the addition of a fluorophore tag for tracking. Hyaluronic acid was chemically modified with hydroxyethyl methacrylate to form hydrolytically degradable hydrogels through free-radical-initiated crosslinking. ESA was encapsulated in hyaluronic acid hydrogels during gel formation, and then ESA release, along with gel degradation, was monitored for more than 4 weeks in vitro. Chemotactic properties of the eluted ESA were assessed at multiple time points using rat endothelial progenitor cells in a transwell migration assay. Finally, adult male Wistar rats (n=33) underwent permanent ligation of the left anterior descending (LAD) coronary artery, and 100 µL of saline, hydrogel alone, or hydrogel+25 µg ESA was injected into the borderzone. ESA fluorescence was monitored in animals for more than 4 weeks, after which vasculogenic, geometric, and functional parameters were assessed to determine the therapeutic benefit of each treatment group. ESA release was sustained for 4 weeks in vitro, remained active, and enhanced endothelial progenitor cell chemotaxis. In addition, ESA was detected in the rat heart >3 weeks when delivered within the hydrogels and significantly improved vascularity, ventricular geometry, ejection fraction, cardiac output, and contractility compared with controls.

CONCLUSIONS

We have developed a hydrogel delivery system that sustains the release of a bioactive endothelial progenitor cell chemokine during a 4-week period that preserves ventricular function in a rat model of myocardial infarction.

Expression of stromal cell-derived factor-1 receptors CXCR4 and CXCR7 on circulating platelets of patients with acute coronary syndrome and association with left ventricular functional recovery

BACKGROUND

Surface expression of stromal cell-derived factor-1 (SDF-1) on platelets is enhanced during ischaemic events and might play an important role in peripheral homing and myocardial repair. As SDF-1 effects are mediated through CXCR4/CXCR7, we investigated platelet expression of SDF-1/CXCR4/CXCR7 in patients with coronary artery disease (CAD).

METHODS AND RESULTS

Expression of SDF-1, CXCR4, and CXCR7 in platelets was investigated by western blot analysis, immunofluorescence confocal microscopy, and flow cytometry among healthy subjects and patients with acute coronary syndrome (ACS) and stable CAD. In a cohort study, platelet surface expression of CXCR4, CXCR7, and SDF-1 was measured in 215 patients with symptomatic CAD (stable CAD = 112, ACS = 103) at the time of percutaneous coronary intervention. Course of left ventricular ejection fraction (LVEF) was followed up during intrahospital stay and at 3 months. Both CXCR4 and CXCR7 are surface expressed on human platelets and to a higher degree in CAD patients when compared with healthy controls. Platelet surface expression of CXCR7 but not CXCR4 was enhanced in patients with ACS when compared with patients with stable CAD (mean fluorescence intensity 17.8 vs. 15.3, P = 0.004 and 29.0 vs. 26.3, P = 0.122, respectively). CXCR4 and CXCR7 significantly correlated with their ligand SDF-1 on platelets (ρ = 0.273, P < 0.001 and ρ = 0.454, P < 0.001, respectively). Additionally, high CXCR7 expression above the median correlated with the absolute improvement of LVEF% after 5 days and 3 months (46.2, 49.8, 53.7; P = 0.003).

CONCLUSION

These findings indicate that platelet surface expression of CXCR4 and CXCR7 might differentially contribute to SDF-1-mediated effects on regenerative mechanisms following ACS. Studies are warranted to further evaluate the regulatory mechanisms of CXCR4/-7 expression and its prognostic impact on CAD.

SDF-1α in glycan nanoparticles exhibits full activity and reduces pulmonary hypertension in rats

To establish a homing signal in the lung to recruit circulating stem cells for tissue repair, we formulated a nanoparticle, SDF-1α NP, by complexing SDF-1α with dextran sulfate and chitosan. The data show that SDF-1α was barely released from the nanoparticles over an extended period of time in vitro (3% in 7 days at 37 °C); however, incorporated SDF-1α exhibited full chemotactic activity and receptor activation compared to its free form. The nanoparticles were not endocytosed after incubation with Jurkat cells. When aerosolized into the lungs of rats, SDF-1α NP displayed a greater retention time compared to free SDF-1α (64 vs 2% remaining at 16 h). In a rat model of monocrotaline-induced lung injury, SDF-1α NP, but not free form SDF-1α, was found to reduce pulmonary hypertension. These data suggest that the nanoparticle formulation protected SDF-1α from rapid clearance in the lung and sustained its biological function in vivo.

In vivo regulation of chemokine activity by post-translational modification

Cytokines and chemokines represent two important groups of proteins that control the immune system. Dysregulation of the network in which these immunomodulators function can result in uncontrolled inflammation leading to various diseases, including rheumatoid arthritis, characterized by chronic inflammation and bone erosion. Chemokine activity is regulated at multiple levels, such as post-translational modification (PTM) of chemokines and their receptors by specific enzymes including proteases and peptidylarginine deiminases. Many in vitro experiments underscore the importance of post-translational processing of human chemokines. PTMs may enhance or reduce chemokine activity or may alter the receptor specificity of chemokine ligands. However, identification of chemokine isoforms in physiological in vivo settings forms the ultimate proof that PTM of chemokines is relevant in regulating the biological activity of these molecules. This review summarizes current knowledge on the in vivo role for PTMs in the regulation of chemokine activity.

Stromal cell-derived factor-1β mediates cell survival through enhancing autophagy in bone marrow-derived mesenchymal stem cells

Bone marrow-derived mesenchymal stem/stromal cells (BMSCs) hold great potential for cell-based therapy, yet the therapeutic efficacy remains uncertain. Transplanted BMSCs often fail to engraft within the bone marrow (BM), in part due to the poor survival of donor cells in response to inflammatory reactions, hypoxia, oxidative stress, or nutrient starvation. Two basic cell processes, apoptosis and autophagy, could potentially be responsible for the impaired survival of transplanted BMSCs. However, the functional relationship between apoptosis and autophagy in BMSC homeostasis is complex and not well understood. The stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor 4 (CXCR4) signaling axis appears to be critical in maintaining proliferation and survival of BM stem cell populations through improving cell proliferation and survival in response to stress; however, the exact mechanisms remain unclear. We recently described novel genetically engineered Tet-Off-SDF-1β BMSCs, which over-express SDF-1β under tight doxycycline-control, thus providing an ideal model system to investigate the isolated effects of SDF-1β. In this study we tested the hypothesis that SDF-1β can mediate cell survival of BMSCs in vitro through increasing autophagy. We found that SDF-1β had no effect on BMSC proliferation; however, SDF-1β significantly protected genetically engineered BMSCs from H2O2-induced cell death through increasing autophagy and decreasing caspase-3-dependent apoptosis. Taken together, we provide novel evidence that the SDF-1/CXCR4 axis, specifically activated by the SDF-1β isoform, plays a critical role in regulating BMSC survival under oxidative stress through increasing autophagy.

The potential of carboxypeptidase M as a therapeutic target in cancer

INTRODUCTION

In the recent literature, carboxypeptidase M (CPM) emerged as a potential cancer biomarker. CPM modulates receptor signaling of kinins, anaphylatoxins, and chemokines. These CPM substrates affect proliferation, angiogenesis, and apoptosis of cancer cells. What is the evidence that CPM is a drug target for cancer therapy?

AREAS COVERED

The literature was searched using PubMed with the search terms "carboxypeptidase M" and/or "chromosome 12q13-15" eventually combined with general terms related to cancer. Information was retrieved from the GEO database and material of gene expression and proteomic studies.

EXPERT OPINION

CPM is a part of the molecular signature of many cancers. There is good evidence that it is useful for the discrimination and stratification of cancer types, possibly in combination with other markers such as EGFR and MDM2. Whether it is also a drug target remains to be determined. Lung, kidney, brain, and the reproductive system contain relatively high levels of CPM, but its functions in those tissues are largely unknown. CPM is expressed on tumor-associated macrophages. To facilitate the investigation of CPM in tumor-associated inflammation and in the other aspects of tumor biology, it is necessary to develop potent and selective CPM inhibitors.

Structural perspectives on antimicrobial chemokines

Chemokines are best known as signaling proteins in the immune system. Recently however, a large number of human chemokines have been shown to exert direct antimicrobial activity. This moonlighting activity appears to be related to the net high positive charge of these immune signaling proteins. Chemokines can be divided into distinct structural elements and some of these have been studied as isolated peptide fragments that can have their own antimicrobial activity. Such peptides often encompass the α-helical region found at the C-terminal end of the parent chemokines, which, similar to other antimicrobial peptides, adopt a well-defined membrane-bound amphipathic structure. Because of their relatively small size, intact chemokines can be studied effectively by NMR spectroscopy to examine their structures in solution. In addition, NMR relaxation experiments of intact chemokines can provide detailed information about the intrinsic dynamic behavior; such analyses have helped for example to understand the activity of TC-1, an antimicrobial variant of CXCL7/NAP-2. With chemokine dimerization and oligomerization influencing their functional properties, the use of NMR diffusion experiments can provide information about monomer-dimer equilibria in solution. Furthermore, NMR chemical shift perturbation experiments can be used to map out the interface between self-associating subunits. Moreover, the unusual case of XCL1/lymphotactin presents a chemokine that can interconvert between two distinct folds in solution, both of which have been elucidated. Finally, recent advances have allowed for the determination of the structures of chemokines in complex with glycosaminoglycans, a process that could interfere with their antimicrobial activity. Taken together, these studies highlight several different structural facets that contribute to the way in which chemokines exert their direct microbicidal actions.

Carboxypeptidase M in apoptosis, adipogenesis and cancer

This review covers carboxypeptidase M (CPM) research that appeared in the literature since 2009. The focus is on aspects that are new or interesting from a clinical perspective. Available research tools are discussed as well as their pitfalls and limitations. Evidence is provided to suggest the potential involvement of CPM in apoptosis, adipogenesis and cancer. This evidence derives from the expression pattern of CPM and its putative substrates in cells and tissues. In recent years CPM emerged as a potential cancer biomarker, in well differentiated liposarcoma where the CPM gene is co-amplified with the oncogene MDM2; and in lung adenocarcinoma where coexpression with EGFR correlates with poor prognosis. The available data call for extended investigation of the function of CPM in tumor cells, tumor-associated macrophages, stromal cells and tumor neovascularisation. Such experiments could be instrumental to validate CPM as a therapeutic target.

Overview of the mechanisms regulating chemokine activity and availability

Physiological leukocyte homing and extravasation of leukocytes during inflammatory processes is directed by a number of proteins including adhesion molecules, proteases, cytokines and chemokines. Tight regulation of leukocyte migration is essential to ensure appropriate migration. A number of mechanisms exist that regulate leukocyte migration including up- or down-regulation of chemokine or chemokine receptor gene expression. However, chemokine availability in vivo also depends on the interaction of chemokines with specific glycosaminoglycans such as heparan sulfate on the surface of endothelial layers. Modification of the interaction of chemokines with these glycosaminoglycans alters the presentation of chemokines to chemokine receptors on circulating leukocytes. On top, binding of chemokines to atypical chemokine receptors that do not signal through G proteins affects chemokine availability on the endothelial layers. In addition to mechanisms that modulate chemokine availability, this review summarizes mechanisms that fine-tune chemokine function. These include synergy or antagonism between chemokines and alternative splicing of chemokine genes. Moreover, chemokines may be posttranslationally modified leading to molecules with enhanced or reduced potency to bind to G protein-coupled receptors or GAGs or generating chemokines with altered receptor specificity. Cross-talk between these different mechanisms generates a complex regulatory network that allows the organism to modulate leukocyte migration in a highly specific manner.

Molecular mechanisms underlying adhesion and migration of hematopoietic stem cells

Hematopoietic stem cell transplantation is the most powerful treatment modality for a large number of hematopoietic malignancies, including leukemia. Successful hematopoietic recovery after transplantation depends on homing of hematopoietic stem cells to the bone marrow and subsequent lodging of those cells in specific niches in the bone marrow. Migration of hematopoietic stem cells to the bone marrow is a highly regulated process that requires correct regulation of the expression and activity of various molecules including chemoattractants, selectins and integrins. This review will discuss recent studies that have extended our understanding of the molecular mechanisms underlying adhesion, migration and bone marrow homing of hematopoietic stem cells.

Stromal cell-derived factor-1β potentiates bone morphogenetic protein-2-stimulated osteoinduction of genetically engineered bone marrow-derived mesenchymal stem cells in vitro

Skeletal injuries are among the most prevalent clinical problems and bone marrow-derived mesenchymal stem/stromal cells (BMSCs) have successfully been used for the treatment thereof. Stromal cell-derived factor-1 (SDF-1; CXCL12) is a member of the CXC chemokine family with multiple splice variants. The two most abundant variants, SDF-1α and SDF-1β, share identical amino acid sequences, except for four additional amino acids at the C-terminus of SDF-1β, which may mediate surface stabilization via glycosaminoglycans and protect SDF-1β from proteolytic cleavage, rendering it twice as potent as SDF-1α. Increasing evidence suggests that SDF-1 is involved in bone formation through regulation of recruitment, engraftment, proliferation, and differentiation of stem/progenitor cells. The underlying molecular mechanisms, however, have not yet been fully elucidated. In this study, we tested the hypothesis that SDF-1β can potentiate bone morphogenetic protein-2 (BMP-2)-stimulated osteogenic differentiation and chemotaxis of BMSCs in vitro. Utilizing retrovirus-mediated gene transfer to generate novel Tet-Off-SDF-1β BMSCs, we found that conditional SDF-1β expression is tightly regulated by doxycycline in a dose-dependent and temporal fashion, leading to significantly increased SDF-1β mRNA and protein levels. In addition, SDF-1β was found to enhance BMP-2-stimulated mineralization, mRNA and protein expression of key osteogenic markers, and regulate BMP-2 signal transduction via extracellular signal-regulated kinases 1/2 (Erk1/2) phosphorylation in genetically engineered BMSCs in vitro. We also showed that SDF-1β promotes the migratory response of CXC chemokine receptor 4 (CXCR4)-expressing BMSCs in vitro. Taken together, these data support that SDF-1β can play an important role in BMP-2-stimulated osteogenic differentiation of BMSCs and may exert its biological activity in both an autocrine and paracrine fashion.

Re-engineered stromal cell-derived factor-1α and the future of translatable angiogenic polypeptide design

Smaller engineered analogs of angiogenic cytokines may provide translational advantages, including enhanced stability and function, ease of synthesis, lower cost, and, most important, the potential for modulated delivery via engineered biomaterials. In order to create such a peptide, computational molecular modeling and design was employed to engineer a minimized, highly efficient polypeptide analog of the stromal cell-derived factor-1α (SDF) molecule. After removal of the large, central β-sheet region, a designed diproline linker connected the native N-terminus (responsible for receptor activation and binding) and C-terminus (responsible for extracellular stabilization). This yielded energetic and conformational advantages resulting in a small, low-molecular-weight engineered SDF polypeptide analog (ESA) that was shown to have angiogenic activity comparable to or better than that of recombinant human SDF both in vitro and in a murine model of ischemic heart failure.

A locked, dimeric CXCL12 variant effectively inhibits pulmonary metastasis of CXCR4-expressing melanoma cells due to enhanced serum stability

The CXC chemokine receptor-4 (CXCR4) plays a critical role in cancer by positively regulating cancer cell metastasis and survival. We previously showed that high concentrations of the CXCR4 ligand, wild-type CXCL12 (wtCXCL12), could inhibit colorectal cancer metastasis in vivo, and we have hypothesized that wtCXCL12 dimerizes at high concentration to become a potent antagonist of CXCR4. To address this hypothesis, we engineered a covalently locked, dimeric variant of CXCL12 (CXCL122). Herein, we show that CXCL122 can not only inhibit implantation of lung metastasis of CXCR4-B16-F10 melanoma cells more effectively than AMD3100, but that CXCL122 also blocks the growth of established pulmonary tumors. To identify a basis for the in vivo efficacy of CXCL122, we conducted Western blot analysis and ELISA analyses, which revealed that CXCL122 was stable for at least 12 hours in serum, whereas wtCXCL12 was quickly degraded. CXCL122 also maintained its antagonist properties in in vitro chemotaxis assays for up to 24 hours in serum, whereas wtCXCL12 was ineffective after 6 hours. Heat-inactivation of serum prolonged the stability and function of wtCXCL12 by more than 6 hours, suggesting enzymatic degradation as a possible mechanism for wtCXCL12 inactivation. In vitro analysis of amino-terminal cleavage by enzymes dipeptidylpeptidase IV (DPPIV/CD26) and matrix metalloproteinase-2 (MMP-2) resulted in 25-fold and 2-fold slower degradation rates, respectively, of CXCL122 compared with wtCXCL12. In summary, our results suggest CXCL122 possesses greater potential as an antimetastatic drug as compared with AMD3100 or wtCXCL12, potentially due to enhanced serum stability in the presence of N-terminal degrading enzymes.

Intrafibrillar silicification of collagen scaffolds for sustained release of stem cell homing chemokine in hard tissue regeneration

Traditional bone regeneration strategies relied on supplementation of biomaterials constructs with stem or progenitor cells or growth factors. By contrast, cell homing strategies employ chemokines to mobilize stem or progenitor cells from host bone marrow and tissue niches to injured sites. Although silica-based biomaterials exhibit osteogenic and angiogenic potentials, they lack cell homing capability. Stromal cell-derived factor-1 (SDF-1) plays a pivotal role in mobilization and homing of stem cells to injured tissues. In this work, we demonstrated that 3-dimensional collagen scaffolds infiltrated with intrafibrillar silica are biodegradable and highly biocompatible. They exhibit improved compressive stress-strain responses and toughness over nonsilicified collagen scaffolds. They are osteoconductive and up-regulate expressions of osteogenesis- and angiogenesis-related genes more significantly than nonsilicified collagen scaffolds. In addition, these scaffolds reversibly bind SDF-1α for sustained release of this chemokine, which exhibits in vitro cell homing characteristics. When implanted subcutaneously in an in vivo mouse model, SDF-1α-loaded silicified collagen scaffolds stimulate the formation of ectopic bone and blood capillaries within the scaffold and abrogate the need for cell seeding or supplementation of osteogenic and angiogenic growth factors. Intrafibrillar-silicified collagen scaffolds with sustained SDF-1α release represent a less costly and complex alternative to contemporary cell seeding approaches and provide new therapeutic options for in situ hard tissue regeneration.

C-terminal clipping of chemokine CCL1/I-309 enhances CCR8-mediated intracellular calcium release and anti-apoptotic activity

Carboxypeptidase M (CPM) targets the basic amino acids arginine and lysine present at the C-terminus of peptides or proteins. CPM is thought to be involved in inflammatory processes. This is corroborated by CPM-mediated trimming and modulation of inflammatory factors, and expression of the protease in inflammatory environments. Since the function of CPM in and beyond inflammation remains mainly undefined, the identification of natural substrates can aid in discovering the (patho)physiological role of CPM. CCL1/I-309, with its three C-terminal basic amino acids, forms a potential natural substrate for CPM. CCL1 plays a role not only in inflammation but also in apoptosis, angiogenesis and tumor biology. Enzymatic processing differently impacts the biological activity of chemokines thereby contributing to the complex regulation of the chemokine system. The aim of the present study was to investigate whether (i) CCL1/I-309 is prone to trimming by CPM, and (ii) the biological activity of CCL1 is altered after C-terminal proteolytic processing. CCL1 was identified as a novel substrate for CPM in vitro using mass spectrometry. C-terminal clipping of CCL1 augmented intracellular calcium release mediated by CCR8 but reduced the binding of CCL1 to CCR8. In line with the higher intracellular calcium release, a pronounced increase of the anti-apoptotic activity of CCL1 was observed in the BW5147 cellular model. CCR8 signaling, CCR8 binding and anti-apoptotic activity were unaffected when CPM was exposed to the carboxypeptidase inhibitor DL-2-mercaptomethyl-3-guanidino-ethylthiopropanoic acid. The results of this study suggest that CPM is a likely candidate for the regulation of biological processes relying on the CCL1-CCR8 system.

SDF-1/CXCL12: its role in spinal cord injury

The chemokine stromal cell-derived factor 1 (SDF-1/CXCL12), is not only the most ancient, but also one of the most potent chemotactic factors. Orchestrating the migration of cells as well as promoting axon outgrowth in the presence of myelin inhibitors, SDF-1 is fundamental to central nervous system development, homeostasis and traumatic injury. SDF-1 attracts endogenous stem/precursor cells and immune cells to the injury site and, upon local infusion, enhances axonal sprouting following spinal cord injury. Together these features make SDF-1 a very exciting molecule for spinal cord repair.

The ins and outs of hematopoietic stem cells: studies to improve transplantation outcomes

Deciphering the mechanisms of hematopoietic stem/progenitor cell (HSPC) mobilization and homing is important for the development of strategies to enhance the efficacy of HSPC transplantation and achieve the full potential of HSPC-based cellular therapy. Investigation of these mechanisms has revealed interdependence among the various molecules, pathways and cellular components involved, and underscored the complex nature of these two processes. This review summarizes recent progress in identifying the specific factors implicated in HSPC mobilization and homing, with emphasis on our own work. Particularly, we will discuss our studies on stromal cell-derived factor-1 and its interaction with its receptor CXCR4, proteases (matrix metalloproteinases and carboxypeptidase M), complement proteins (C1q, C3a, C5a, membrane attack complex), sphingosine-1-phosphate, and pharmacologic agents such as the histone deacetylase inhibitor valproic acid and hyaluronic acid.

Computational protein design to reengineer stromal cell-derived factor-1α generates an effective and translatable angiogenic polypeptide analog

BACKGROUND

Experimentally, exogenous administration of recombinant stromal cell-derived factor-1α (SDF) enhances neovasculogenesis and cardiac function after myocardial infarction. Smaller analogs of SDF may provide translational advantages including enhanced stability and function, ease of synthesis, lower cost, and potential modulated delivery via engineered biomaterials. In this study, computational protein design was used to create a more efficient evolution of the native SDF protein.

METHODS AND RESULTS

Protein structure modeling was used to engineer an SDF polypeptide analog (engineered SDF analog [ESA]) that splices the N-terminus (activation and binding) and C-terminus (extracellular stabilization) with a diproline segment designed to limit the conformational flexibility of the peptide backbone and retain the relative orientation of these segments observed in the native structure of SDF. Endothelial progenitor cells (EPCs) in ESA gradient, assayed by Boyden chamber, showed significantly increased migration compared with both SDF and control gradients. EPC receptor activation was evaluated by quantification of phosphorylated AKT, and cells treated with ESA yielded significantly greater phosphorylated AKT levels than SDF and control cells. Angiogenic growth factor assays revealed a distinct increase in angiopoietin-1 expression in the ESA- and SDF-treated hearts. In addition, CD-1 mice (n=30) underwent ligation of the left anterior descending coronary artery and peri-infarct intramyocardial injection of ESA, SDF-1α, or saline. At 2 weeks, echocardiography demonstrated a significant gain in ejection fraction, cardiac output, stroke volume, and fractional area change in mice treated with ESA compared with controls.

CONCLUSIONS

Compared with native SDF, a novel engineered SDF polypeptide analog (ESA) more efficiently induces EPC migration and improves post-myocardial infarction cardiac function and thus offers a more clinically translatable neovasculogenic therapy.

Combined use of a solid-phase hexapeptide ligand library with liquid chromatography and two-dimensional difference gel electrophoresis for intact plasma proteomics

The intact plasma proteome is of great interest in biomarker studies because intact proteins reflect posttranslational protein processing such as phosphorylation that may correspond to disease status. We examined the utility of a solid-phase hexapeptide ligand library in combination with conventional plasma proteomics modalities for comprehensive profiling of intact plasma proteins. Plasma proteins were sequentially fractionated using depletion columns for albumin and immunoglobulin, and separated using an anion-exchange column. Proteins in each fraction were treated with a solid-phase hexapeptide ligand library and compared to those without treatment. Two-dimensional difference gel electrophoresis demonstrated an increased number of protein spots in the treated samples. Mass spectrometric studies of these protein spots with unique intensity in the treated samples resulted in the identification of high- and medium-abundance proteins. Our results demonstrated the possible utility of a solid-phase hexapeptide ligand library to reveal greater number of intact plasma proteins. The characteristics of proteins with unique affinity to the library remain to be clarified by more extensive mass spectrometric protein identification, and optimized protocols should be established for large-scale plasma biomarker studies.