Mice deficient in the chemokine receptor CXCR4 exhibit impaired limb innervation and myogenesis

The development of thoracic and abdominal muscle depends on SDF1 and CXCR4

In vertebrates, the lateral body wall muscle formation is thought to be initiated by direct outgrowth of the dermomyotomes resulting in the elongation of the hypaxial myotomes. This contrasts with the formation of the muscles of the girdle, limbs and intrinsic tongue muscles, which originate from long-range migrating progenitors. Previous work shows that the migration of these progenitors requires CXCR4 which is specifically expressed in the migrating cells, but not in the dermomyotome. Here, we show that cells in the ventrolateral-lip (VLL) of the dermomyotome at the flank level express CXCR4 in a pattern consistent with that of Pax3 and MyoR. In ovo gain-of-function experiments using electroporation of SDF-1 constructs into the VLL resulted in increased expression of c-Met, Pax3 and MyoD. In contrast, a loss-of-function approach by implantation of CXCR4-inhibitor beads into the VLL of the flank region caused a reduction in the expression of these markers. These data show that CXCR4 is expressed in the VLL, and by experimentally manipulating the CXCR4/SDF-1 signaling, we demonstrate the importance of this axis in body wall muscle development.

Wiring the ocular surface: A focus on the comparative anatomy and molecular regulation of sensory innervation of the cornea

The cornea is richly innervated with sensory nerves that function to detect and clear harmful debris from the surface of the eye, promote growth and survival of the corneal epithelium and hasten wound healing following ocular disease or trauma. Given their importance to eye health, the neuroanatomy of the cornea has for many years been a source of intense investigation. Resultantly, complete nerve architecture maps exist for adult human and many animal models and these maps reveal few major differences across species. Interestingly, recent work has revealed considerable variation across species in how sensory nerves are acquired during developmental innervation of the cornea. Highlighting such species-distinct key differences, but also similarities, this review provides a full, comparative anatomy analysis of sensory innervation of the cornea for all species studied to date. Further, this article comprehensively describes the molecules that have been shown to guide and direct nerves toward, into and through developing corneal tissue as the final architectural pattern of the cornea's neuroanatomy is established. Such knowledge is useful for researchers and clinicians seeking to better understand the anatomical and molecular basis of corneal nerve pathologies and to hasten neuro-regeneration following infection, trauma or surgery that damage the ocular surface and its corneal nerves.

Targeting CXCR4 and CD47 Receptors: An Overview of New and Old Molecules for a Biological Personalized Anticancer Therapy

Biological therapy, with its multifaceted applications, has revolutionized the treatment of tumors, mainly due to its ability to exclusively target cancer cells and reduce the adverse effects on normal tissues. This review focuses on the therapies targeting the CXCR4 and CD47 receptors. We surveyed the results of early clinical trials testing compounds classified as nonpeptides, small peptides, CXCR4 antagonists or specific antibodies whose activity reduces or completely blocks the intracellular signaling pathways and cell proliferation. We then examined antibodies and fusion proteins against CD47, the receptor that acts as a “do not eat me” signal to phagocytes escaping immune surveillance. Despite these molecules being tested in early clinical trials, some drawbacks are emerging that impair their use in practice. Finally, we examined the ImmunoGenic Surrender mechanism that involves crosstalk and co-internalization of CXCR4 and CD47 upon engagement of CXCR4 by ligands or other molecules. The favorable effect of such compounds is dual as CD47 surface reduction impact on the immune response adds to the block of CXCR4 proliferative potential. These results suggest that a combination of different therapeutic approaches has more beneficial effects on patients’ survival and may pave the way for new accomplishments in personalized anticancer therapy.

The chemokine receptor CXCR4 regulates satellite cell activation, early expansion, and self-renewal, in response to skeletal muscle injury

Acute skeletal muscle injury is followed by satellite cell activation, proliferation, and differentiation to replace damaged fibers with newly regenerated muscle fibers, processes that involve satellite cell interactions with various niche signals. Here we show that satellite cell specific deletion of the chemokine receptor CXCR4, followed by suppression of recombination escapers, leads to defects in regeneration and satellite cell pool repopulation in both the transplantation and in situ injury contexts. Mechanistically, we show that endothelial cells and FAPs express the gene for the ligand, SDF1α, and that CXCR4 is principally required for proper activation and for transit through the first cell division, and to a lesser extent the later cell divisions. In the absence of CXCR4, gene expression in quiescent satellite cells is not severely disrupted, but in activated satellite cells a subset of genes normally induced by activation fail to upregulate normally. These data demonstrate that CXCR4 signaling is essential to normal early activation, proliferation, and self-renewal of satellite cells.

Distinctive exercise-induced inflammatory response and exerkine induction in skeletal muscle of people with type 2 diabetes

Mechanistic insights into the molecular events by which exercise enhances the skeletal muscle phenotype are lacking, particularly in the context of type 2 diabetes. Here, we unravel a fundamental role for exercise-responsive cytokines (exerkines) on skeletal muscle development and growth in individuals with normal glucose tolerance or type 2 diabetes. Acute exercise triggered an inflammatory response in skeletal muscle, concomitant with an infiltration of immune cells. These exercise effects were potentiated in type 2 diabetes. In response to contraction or hypoxia, cytokines were mainly produced by endothelial cells and macrophages. The chemokine CXCL12 was induced by hypoxia in endothelial cells, as well as by conditioned medium from contracted myotubes in macrophages. We found that CXCL12 was associated with skeletal muscle remodeling after exercise and differentiation of cultured muscle. Collectively, acute aerobic exercise mounts a noncanonical inflammatory response, with an atypical production of exerkines, which is potentiated in type 2 diabetes.

At the Bench: Pre-clinical evidence for multiple functions of CXCR4 in cancer

Signaling through chemokine receptor, C-X-C chemokine receptor type 4 (CXCR4) regulates essential processes in normal physiology, including embryogenesis, tissue repair, angiogenesis, and trafficking of immune cells. Tumors co-opt many of these fundamental processes to directly stimulate proliferation, invasion, and metastasis of cancer cells. CXCR4 signaling contributes to critical functions of stromal cells in cancer, including angiogenesis and multiple cell types in the tumor immune environment. Studies in animal models of several different types of cancers consistently demonstrate essential functions of CXCR4 in tumor initiation, local invasion, and metastasis to lymph nodes and distant organs. Data from animal models support clinical observations showing that integrated effects of CXCR4 on cancer and stromal cells correlate with metastasis and overall poor prognosis in >20 different human malignancies. Small molecules, Abs, and peptidic agents have shown anticancer efficacy in animal models, sparking ongoing efforts at clinical translation for cancer therapy. Investigators also are developing companion CXCR4-targeted imaging agents with potential to stratify patients for CXCR4-targeted therapy and monitor treatment efficacy. Here, pre-clinical studies demonstrating functions of CXCR4 in cancer are reviewed.

Crosstalk between skeletal and neural tissues is critical for skeletal health

Emerging evidence in the literature describes a physical and functional association between the neural and skeletal systems that forms a neuro-osteogenic network. This communication between bone cells and neural tissues within the skeleton is important in facilitating bone skeletal growth, homeostasis and repair. The growth and repair of the skeleton is dependent on correct neural innervation for correct skeletal developmental growth and fracture repair, while pathological conditions such as osteoporosis are accelerated by disruptions to sympathetic innervation. To date, different molecular mechanisms have been reported to mediate communication between bone and neural populations. This review highlights the important role of various cell surface receptors, cytokines and associated ligands as potential regulators of skeletal development, homeostasis, and repair, by mediating interactions between the skeletal and nervous systems. Specifically, this review describes how Bone Morphogenetic Proteins (BMPs), Eph/ephrin, Chemokine CXCL12, Calcitonin Gene-related Peptide (CGRP), Netrins, Neurotrophins (NTs), Slit/Robo and the Semaphorins (Semas) contribute to the cross talk between bone cells and peripheral nerves, and the importance of these interactions in maintaining skeletal health.

The CXCR4/SDF-1 Axis in the Development of Facial Expression and Non-somitic Neck Muscles

Trunk and head muscles originate from distinct embryonic regions: while the trunk muscles derive from the paraxial mesoderm that becomes segmented into somites, the majority of head muscles develops from the unsegmented cranial paraxial mesoderm. Differences in the molecular control of trunk versus head and neck muscles have been discovered about 25 years ago; interestingly, differences in satellite cell subpopulations were also described more recently. Specifically, the satellite cells of the facial expression muscles share properties with heart muscle. In adult vertebrates, neck muscles span the transition zone between head and trunk. Mastication and facial expression muscles derive from the mesodermal progenitor cells that are located in the first and second branchial arches, respectively. The cucullaris muscle (non-somitic neck muscle) originates from the posterior-most branchial arches. Like other subclasses within the chemokines and chemokine receptors, CXCR4 and SDF-1 play essential roles in the migration of cells within a number of various tissues during development. CXCR4 as receptor together with its ligand SDF-1 have mainly been described to regulate the migration of the trunk muscle progenitor cells. This review first underlines our recent understanding of the development of the facial expression (second arch-derived) muscles, focusing on new insights into the migration event and how this embryonic process is different from the development of mastication (first arch-derived) muscles. Other muscles associated with the head, such as non-somitic neck muscles derived from muscle progenitor cells located in the posterior branchial arches, are also in the focus of this review. Implications on human muscle dystrophies affecting the muscles of face and neck are also discussed.

The Role of Immune Factors in Shaping Fetal Neurodevelopment

Fetal neurodevelopment in utero is profoundly shaped by both systemic maternal immunity and local processes at the maternal-fetal interface. Immune pathways are a critical participant in the normal physiology of pregnancy and perturbations of maternal immunity due to infections during this period have been increasingly linked to a diverse array of poor neurological outcomes, including diseases that manifest much later in postnatal life. While experimental models of maternal immune activation (MIA) have provided groundbreaking characterizations of the maternal pathways underlying pathogenesis, less commonly examined are the immune factors that serve pathogen-independent developmental functions in the embryo and fetus. In this review, we explore what is known about the in vivo role of immune factors in fetal neurodevelopment during normal pregnancy and provide an overview of how MIA perturbs the proper orchestration of this sequence of events. Finally, we discuss how the dysregulation of immune factors may contribute to the manifestation of a variety of neurological disorders.

Cxcr4 and Sdf-1 are critically involved in the formation of facial and non-somitic neck muscles

The present study shows that the CXCR4/SDF-1 axis regulates the migration of second branchial arch-derived muscles as well as non-somitic neck muscles. Cxcr4 is expressed by skeletal muscle progenitor cells in the second branchial arch (BA2). Muscles derived from the second branchial arch, but not from the first, fail to form in Cxcr4 mutants at embryonic days E13.5 and E14.5. Cxcr4 is also required for the development of non-somitic neck muscles. In Cxcr4 mutants, non-somitic neck muscle development is severely perturbed. In vivo experiments in chicken by means of loss-of-function approach based on the application of beads loaded with the CXCR4 inhibitor AMD3100 into the cranial paraxial mesoderm resulted in decreased expression of Tbx1 in the BA2. Furthermore, disrupting this chemokine signal at a later stage by implanting these beads into the BA2 caused a reduction in MyoR, Myf5 and MyoD expression. In contrast, gain-of-function experiments based on the implantation of SDF-1 beads into BA2 resulted in an attraction of myogenic progenitor cells, which was reflected in an expansion of the expression domain of these myogenic markers towards the SDF-1 source. Thus, Cxcr4 is required for the formation of the BA2 derived muscles and non-somitic neck muscles.

Pigeon foot feathering reveals conserved limb identity networks

The tetrapod limb is a stunning example of evolutionary diversity, with dramatic variation not only among distantly related species, but also between the serially homologous forelimbs (FLs) and hindlimbs (HLs) within species. Despite this variation, highly conserved genetic and developmental programs underlie limb development and identity in all tetrapods, raising the question of how limb diversification is generated from a conserved toolkit. In some breeds of domestic pigeon, shifts in the expression of two conserved limb identity transcription factors, PITX1 and TBX5, are associated with the formation of feathered HLs with partial FL identity. To determine how modulation of PITX1 and TBX5 expression affects downstream gene expression, we compared the transcriptomes of embryonic limb buds from pigeons with scaled and feathered HLs. We identified a set of differentially expressed genes enriched for genes encoding transcription factors, extracellular matrix proteins, and components of developmental signaling pathways with important roles in limb development. A subset of the genes that distinguish scaled and feathered HLs are also differentially expressed between FL and scaled HL buds in pigeons, pinpointing a set of gene expression changes downstream of PITX1 and TBX5 in the partial transformation from HL to FL identity. We extended our analyses by comparing pigeon limb bud transcriptomes to chicken, anole lizard, and mammalian datasets to identify deeply conserved PITX1- and TBX5-responsive components of the limb identity program. Our analyses reveal a suite of predominantly low-level gene expression changes that are conserved across amniotes to regulate the identity of morphologically distinct limbs.

Dux4 controls migration of mesenchymal stem cells through the Cxcr4-Sdf1 axis

We performed transcriptome profiling of human immortalized myoblasts (MB) transiently expressing double homeobox transcription factor 4 (DUX4) and double homeobox transcription factor 4 centromeric (DUX4c) and identified 114 and 70 genes differentially expressed in DUX4- and DUX4c-transfected myoblasts, respectively. A significant number of differentially expressed genes were involved in inflammation, cellular migration and chemotaxis suggesting a role for DUX4 and DUX4c in these processes. DUX4 but not DUX4c overexpression resulted in upregulation of the CXCR4 (C-X-C motif Receptor 4) and CXCL12 (C-X-C motif ligand 12 also known as SDF1) expression in human immortalized myoblasts. In a Transwell cell migration assay, human bone marrow-derived mesenchymal stem cells (BMSCs) were migrating more efficiently towards human immortalized myoblasts overexpressing DUX4 as compared to controls; the migration efficiency of DUX4-transfected BMSCs was also increased. DUX4c overexpression in myoblasts or in BMSCs had no impact on the rate of BMSC migration. Antibodies against SDF1 and CXCR4 blocked the positive effect of DUX4 overexpression on BMSC migration. We propose that DUX4 controls the cellular migration of mesenchymal stem cells through the CXCR4 receptor.

Odd skipped-related 1 identifies a population of embryonic fibro-adipogenic progenitors regulating myogenesis during limb development

Fibro-adipogenic progenitors (FAPs) are an interstitial cell population in adult skeletal muscle that support muscle regeneration. During development, interstitial muscle connective tissue (MCT) cells support proper muscle patterning, however the underlying molecular mechanisms are not well understood and it remains unclear whether adult FAPs and embryonic MCT cells share a common lineage. We show here that mouse embryonic limb MCT cells expressing the transcription factor Osr1, differentiate into fibrogenic and adipogenic cells in vivo and in vitro defining an embryonic FAP-like population. Genetic lineage tracing shows that developmental Osr1⁺ cells give rise to a subset of adult FAPs. Loss of Osr1 function leads to a reduction of myogenic progenitor proliferation and survival resulting in limb muscle patterning defects. Transcriptome and functional analyses reveal that Osr1⁺ cells provide a critical pro-myogenic niche via the production of MCT specific extracellular matrix components and secreted signaling factors.

Fibro-adipogenic progenitors (FAPs) form part of interstitial muscle connective tissue (MCT) in adults but the origin of this non-myogenic lineage is unclear. Here, the authors show that Odd skipped related 1 (Osr1) in mice marks embryonic MCT, giving rise to FAPs, and loss of Osr1 in the limb causes muscle defects.

Binding of the chemokine CXCL12α to its natural extracellular matrix ligand heparan sulfate enables myoblast adhesion and facilitates cell motility

The chemokine CXCL12α is a potent chemoattractant that guides the migration of muscle precursor cells (myoblasts) during myogenesis and muscle regeneration. To study how the molecular presentation of chemokines influences myoblast adhesion and motility, we designed multifunctional biomimetic surfaces as a tuneable signalling platform that enabled the response of myoblasts to selected extracellular cues to be studied in a well-defined environment. Using this platform, we demonstrate that CXCL12α, when presented by its natural extracellular matrix ligand heparan sulfate (HS), enables the adhesion and spreading of myoblasts and facilitates their active migration. In contrast, myoblasts also adhered and spread on CXCL12α that was quasi-irreversibly surface-bound in the absence of HS, but were essentially immotile. Moreover, co-presentation of the cyclic RGD peptide as integrin ligand along with HS-bound CXCL12α led to enhanced spreading and motility, in a way that indicates cooperation between CXCR4 (the CXCL12α receptor) and integrins (the RGD receptors). Our findings reveal the critical role of HS in CXCL12α induced myoblast adhesion and migration. The biomimetic surfaces developed here hold promise for mechanistic studies of cellular responses to different presentations of biomolecules. They may be broadly applicable for dissecting the signalling pathways underlying receptor cross-talks, and thus may guide the development of novel biomaterials that promote highly specific cellular responses.

Knockdown of CXCL14 disrupts neurovascular patterning during ocular development

The C-X-C motif ligand 14 (CXCL14) is a recently discovered chemokine that is highly conserved in vertebrates and expressed in various embryonic and adult tissues. CXCL14 signaling has been implicated to function as an antiangiogenic and anticancer agent in adults. However, its function during development is unknown. We previously identified novel expression of CXCL14 mRNA in various ocular tissues during development. Here, we show that CXCL14 protein is expressed in the anterior eye at a critical time during neurovascular development and in the retina during neurogenesis. We report that RCAS-mediated knockdown of CXCL14 causes severe neural defects in the eye including precocious and excessive innervation of the cornea and iris. Absence of CXCL14 results in the malformation of the neural retina and misprojection of the retinal ganglion neurons. The ocular neural defects may be due to loss of CXCL12 modulation since recombinant CXCL14 diminishes CXCL12-induced axon growth in vitro. Furthermore, we show that knockdown of CXCL14 causes neovascularization of the cornea. Altogether, our results show for the first time that CXCL14 plays a critical role in modulating neurogenesis and inhibiting ectopic vascularization of the cornea during ocular development.

COUP-TFII regulates satellite cell function and muscular dystrophy

Duchenne muscular dystrophy (DMD) is a severe and progressive muscle-wasting disease caused by mutations in the dystrophin gene. Although dystrophin deficiency in myofiber triggers the disease's pathological changes, the degree of satellite cell (SC) dysfunction defines disease progression. Here, we have identified chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) hyperactivity as a contributing factor underlying muscular dystrophy in a dystrophin-deficient murine model of DMD. Ectopic expression of COUP-TFII in murine SCs led to Duchenne-like dystrophy in the muscles of control animals and exacerbated degenerative myopathies in dystrophin-deficient mice. COUP-TFII-overexpressing mice exhibited regenerative failure that was attributed to deficient SC proliferation and myoblast fusion. Mechanistically, we determined that COUP-TFII coordinated a regenerative program through combined regulation of multiple promyogenic factors. Furthermore, inhibition of COUP-TFII preserved SC function and counteracted the muscle weakness associated with Duchenne-like dystrophy in the murine model, suggesting that targeting COUP-TFII is a potential treatment for DMD. Together, our findings reveal a regulatory role of COUP-TFII in the development of muscular dystrophy and open up a potential therapeutic opportunity for managing disease progression in patients with DMD.

PTH/SDF-1α cotherapy induces CD90+CD34- stromal cells migration and promotes tissue regeneration in a rat periodontal defect model

Stromal cell-derived factor-1α (SDF-1α) is a key stem cell homing factor that is crucial for recruitment of stem cells to many diseased organs. However, the therapeutic activity of SDF-1α is potentially limited by N-terminal cleavage at position-2 proline by a cell surface protein CD26/dipeptidyl peptidase-IV (DPP-IV). Parathyroid hormone (PTH) is a DPP-IV inhibitor and has been suggested as a promising agent for periodontal tissue repair. The purpose of this study was to explore the effects of a cell-free system comprising SDF-1α and scaffold plus PTH systemic application on periodontal tissue regeneration in vivo. The results showed that PTH/SDF-1α cotherapy improved the quantity of regenerated bone and resulted in better organization of ligament interface. We further investigated the possible mechanisms, and found that PTH/SDF-1α cotherapy enhanced CD90+CD34- stromal cells migration in vivo, increased the number of CXCR4 + cells in periodontal defects, induced early bone osteoclastogenesis and enhanced the expression of runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP) and collagen I (Col I) in newly formed bone tissue. In conclusion, this cell-free tissue engineering system with local administration of SDF-1α and systemic application of PTH could be employed to induce CD90+CD34- stromal cells recruitment and promote periodontal tissue regeneration.

Development of the shoulder girdle musculature

The muscles of the shoulder region are important for movements of the upper limbs and for stabilizing the girdle elements by connecting them to the trunk. They have a triple embryonic origin. First, the branchiomeric shoulder girdle muscles (sternocleidomastoideus and trapezius muscles) develop from the occipital lateral plate mesoderm using Tbx1 over the course of this development. The second population of cells constitutes the superficial shoulder girdle muscles (pectoral and latissimus dorsi muscles), which are derived from the wing premuscle mass. This muscle group undergoes a two-step development, referred to as the "in-out" mechanism. Myogenic precursor cells first migrate anterogradely into the wing bud. Subsequently, they migrate in a retrograde manner from the wing premuscle mass to the trunk. SDF-1/CXCR4 signaling is involved in this outward migration. A third group of shoulder muscles are the rhomboidei and serratus anterior muscles, which are referred to as deep shoulder girdle muscles; they are thought to be derived from the myotomes. It is, however, not clear how myotome cells make contact to the scapula to form these two muscles. In this review, we discuss the development of the shoulder girdle muscle in relation to the different muscle groups.

Identification of STAM1 as a novel effector of ventral projection of spinal motor neurons

During spinal cord development, motor neuron (MN) axons exit the spinal cord ventrally, although the molecular basis for this process remains poorly understood. STAM1 and Hrs form a complex involved with endosomal targeting of cargo proteins, including the chemokine receptor CXCR4. Interestingly, the absence of CXCR4 signaling in spinal MNs is known to enforce improper extension of the axons into the dorsal side of the spinal cord. Here we report that the MN-specific Isl1-Lhx3 complex directly transactivates the Stam1 gene and STAM1 functions in determining the ventral spinal MN axonal projections. STAM1 is co-expressed with Hrs in embryonic spinal MNs, and knock-down of STAM1 in the developing chick spinal cord results in down-regulation of the expression of CXCR4, accompanied by dorsally projecting motor axons. Interestingly, overexpression of STAM1 or CXCR4 also results in dorsal projection of motor axons, suggesting that proper CXCR4 protein level is critical for the ventral motor axon trajectory. Our results reveal a critical regulatory axis for the ventral axonal trajectory of developing spinal MNs, consisting of the Isl1-Lhx3 complex, STAM1 and CXCR4.

Alternations in genes expression of pathway signaling in esophageal tissue with atresia: results of expression microarray profiling

Esophageal atresia (EA) is a congenital defect of the esophagus involving the interruption of the esophagus with or without connection to the trachea (tracheoesophageal fistula [TEF]). EA/TEF may occur as an isolated anomaly, may be part of a complex of congenital defects (syndromic), or may develop within the context of a known syndrome or association. The molecular mechanisms underlying the development of EA are poorly understood. It is supposed that a combination of multigenic factors and epigenetic modification of genes play a role in its etiology. The aim of our work was to assess the human gene expression microarray study in esophageal tissue samples. Total RNA was extracted from 26 lower pouches of esophageal tissue collected during thoracoscopic EA repair in neonates with the isolated (IEA) and the syndromic form (SEA). We identified 787 downregulated and 841 upregulated transcripts between SEA and controls, and about 817 downregulated and 765 upregulated probes between IEA and controls. Fifty percent of these genes showed differential expression specific for either IEA or SEA. Functional pathway analysis revealed substantial enrichment for Wnt and Sonic hedgehog, as well as cytokine and chemokine signaling pathways. Moreover, we performed reverse transcription polymerase chain reaction study in a group of SHH and Wnt pathways genes with differential expression in microarray profiling to confirm the microarray expression results. We verified the altered expression in SFRP2 gene from the Wnt pathway as well as SHH, GLI1, GLI2, and GLI3 from the Sonic hedgehog pathway. The results suggest an important role of these pathways and genes for EA/TEF etiology.

Stromal-derived factor-1α/CXCL12-CXCR4 chemotactic pathway promotes perineural invasion in pancreatic cancer

Perineural invasion (PNI) is considered as an alternative route for the metastatic spread of pancreatic cancer cells; however, the molecular changes leading to PNI are still poorly understood. In this study, we show that the CXCL12/CXCR4 axis plays a pivotal role in the neurotropism of pancreatic cancer cells to local peripheral nerves. Immunohistochemical staining results revealed that CXCR4 elevation correlated with PNI in 78 pancreatic cancer samples. Both in vitro and in vivo PNI models were applied to investigate the function of the CXCL12/CXCR4 signaling in PNI progression and pathogenesis. The results showed that the activation of the CXCL12/CXCR4 axis significantly increased pancreatic cancer cells invasion and promoted the outgrowth of the dorsal root ganglia. CXCL12 derived from the peripheral nerves stimulated the invasion and chemotactic migration of CXCR4-positive cancer cells in a paracrine manner, eventually leading to PNI. In vivo analyses revealed that the abrogation of the activated signaling inhibited tumor growth and invasion of the sciatic nerve toward the spinal cord. These data indicate that the CXCL12/CXCR4 axis may be a novel therapeutic target to prevent the perineural dissemination of pancreatic cancer.

Hypaxial muscle: controversial classification and controversial data?

Hypaxial muscle is the anatomical term commonly used when referring to all the ventrally located musculature in the body of vertebrates, including muscles of the body wall and the limbs. Yet these muscles had very humble beginnings when vertebrates evolved from their chordate ancestors, and complex anatomical changes and changes in underlying gene regulatory networks occurred. This review summarises the current knowledge and controversies regarding the development and evolution of hypaxial muscles.

Recruitment of skeletal muscle progenitors to secondary sites: a role for CXCR4/SDF-1 signalling in skeletal muscle development

During embryonic development, myogenesis occurs in different functional muscle groups at different time points depending on the availability of their final destinations. Primary trunk muscle consists of the intrinsic dorsal (M. erector spinae) and ventral (cervical, thoracic, abdominal) muscles. In contrast, secondary trunk muscles are established from progenitor cells that have migrated initially from the somites into the limb buds and thereafter returned to the trunk. Furthermore, craniofacial muscle constitutes a group that originates from four different sources and employs a different set of regulatory molecules. Development of muscle groups at a distance from their origins involves the maintenance of a pool of progenitor cells capable of proliferation and directed cell migration. We review here the data concerning somite-derived progenitor cell migration to the limbs and subsequent retrograde migration in the establishment of secondary trunk muscle in chicken and mouse. We review the function of SDF-1 and CXCR4 in the control of this process referring to our previous work in shoulder muscle and cloacal/perineal muscle development. Some human anatomical variations and malformations of secondary trunk muscles are discussed.

SDF-1 enhances wound healing of critical-sized calvarial defects beyond self-repair capacity

Host blood circulating stem cells are an important cell source that participates in the repair of damaged tissues. The clinical challenge is how to improve the recruitment of circulating stem cells into the local wound area and enhance tissue regeneration. Stromal-derived factor-1 (SDF-1) has been shown to be a potent chemoattractant of blood circulating stem cells into the local wound microenvironment. In order to investigate effects of SDF-1 on bone development and the repair of a large bone defect beyond host self-repair capacity, the BMP-induced subcutaneous ectopic bone formation and calvarial critical-sized defect murine models were used in this preclinical study. A dose escalation of SDF-1 were loaded into collagen scaffolds containing BMP, VEGF, or PDGF, and implanted into subcutaneous sites at mouse dorsa or calvarial critical-sized bone defects for 2 and 4 weeks. The harvested biopsies were examined by microCT and histology. The results demonstrated that while SDF-1 had no effect in the ectopic bone model in promoting de novo osteogenesis, however, in the orthotopic bone model of the critical-sized defects, SDF-1 enhanced calvarial critical-sized bone defect healing similar to VEGF, and PDGF. These results suggest that SDF-1 plays a role in the repair of large critical-sized defect where more cells are needed while not impacting de novo bone formation, which may be associated with the functions of SDF-1 on circulating stem cell recruitment and angiogenesis.

CXCR4 and CXCR7 form a functional receptor unit for SDF-1/CXCL12 in primary rodent microglia

AIMS

Microglial cells have been originally identified as a target for the CXC chemokine, SDF-1, by their expression of CXCR4. More recently, it has been recognized that SDF-1 additionally binds to CXCR7, which depending on the cell type acts as either a nonclassical, a classical or a scavenger chemokine receptor. Here, we asked whether primary microglial cells additionally express CXCR7 and if so how this chemokine receptor functions in this cell type.

METHODS

CXCR4 and CXCR7 expression was analysed in cultured rat microglia and in the brain of animals with permanent occlusion of the middle cerebral artery (MCAO) by either Western blotting, RT-PCR, flow cytometry and/or immunocytochemistry. The function of CXCR4 and CXCR7 was assessed in the presence of selective antagonists.

RESULTS

Cultured primary rat microglia expressed CXCR4 and CXCR7 to similar levels. Treatment with SDF-1 resulted in the activation of Erk1/2 and Akt signalling. Erk1/2 and Akt signalling were required for subsequent SDF-1-dependent promotion of microglial proliferation. In contrast, Erk1/2 signalling was sufficient for SDF-1-induced migration of microglial cells. Both SDF-1-dependent signalling and the resulting effects on microglial proliferation and migration were abrogated following pharmacological inactivation of either CXCR4 or CXCR7. Moreover, treatment of cultured microglia with lipopolysaccharide resulted in the co-ordinated up-regulation of CXCR4 and CXCR7 expression. Likewise, reactive microglia accumulating in the area adjacent to the lesion core in MCAO rats expressed both CXCR4 and CXCR7.

CONCLUSIONS

CXCR4 and CXCR7 form a functional receptor unit in microglial cells, which is up-regulated during activation of microglia both in vitro and in vivo.

The CXCR4/SDF1 axis improves muscle regeneration through MMP-10 activity

The CXCR4/SDF1 axis participates in various cellular processes, including cell migration, which is essential for skeletal muscle repair. Although increasing evidence has confirmed the role of CXCR4/SDF1 in embryonic muscle development, the function of this pathway during adult myogenesis remains to be fully elucidated. In addition, a role for CXCR4 signaling in muscle maintenance and repair has only recently emerged. Here, we have demonstrated that CXCR4 and stromal cell-derived factor-1 (SDF1) are up-regulated in injured muscle, suggesting their involvement in the repair process. In addition, we found that notexin-damaged muscles showed delayed muscle regeneration on treatment with CXCR4 agonist (AMD3100). Accordingly, small-interfering RNA-mediated silencing of SDF1 or CXCR4 in injured muscles impaired muscle regeneration, whereas the addition of SDF1 ligand accelerated repair. Furthermore, we identified that CXCR4/SDF1-regulated muscle repair was dependent on matrix metalloproteinase-10 (MMP-10) activity. Thus, our findings support a model in which MMP-10 activity modulates CXCR4/SDF1 signaling, which is essential for efficient skeletal muscle regeneration.

The effect of delivering the chemokine SDF-1α in a matrix-bound manner on myogenesis

Several chemokines are important in muscle myogenesis and in the recruitment of muscle precursors during muscle regeneration. Among these, the SDF-1α chemokine (CXCL12) is a potent chemoattractant known to be involved in muscle repair. SDF-1α was loaded in polyelectrolyte multilayer films made of poly(L-lysine) and hyaluronan to be delivered locally to myoblast cells in a matrix-bound manner. The adsorbed amounts of SDF-1α were tuned over a large range from 100 ng/cm(2) to 5 μg/cm(2), depending on the initial concentration of SDF-1α in solution, its pH, and on the film crosslinking extent. Matrix-bound SDF-1α induced a striking increase in myoblast spreading, which was revealed when it was delivered from weakly crosslinked films. It also significantly enhanced cell migration in a dose-dependent manner, which again depended on its presentation by the biopolymeric film. The low-crosslinked film was the most efficient in boosting cell migration. Furthermore, matrix-bound SDF-1α also increased the expression of myogenic markers but the fusion index decreased in a dose-dependent manner with the adsorbed amount of SDF-1α. At high adsorbed amounts of SDF-1α, a large number of Troponin T-positive cells had only one nucleus. Overall, this work reveals the importance of the presentation mode of SDF-1α to emphasize its effect on myogenic processes. These films may be further used to provide insight into the role of SDF-1α presented by a biomaterial in physiological or pathological processes.

Cxcl12/Cxcr4 signaling controls the migration and process orientation of A9-A10 dopaminergic neurons

CXCL12/CXCR4 signaling has been reported to regulate three essential processes for the establishment of neural networks in different neuronal systems: neuronal migration, cell positioning and axon wiring. However, it is not known whether it regulates the development of A9-A10 tyrosine hydroxylase positive (TH(+)) midbrain dopaminergic (mDA) neurons. We report here that Cxcl12 is expressed in the meninges surrounding the ventral midbrain (VM), whereas CXCR4 is present in NURR1(+) mDA precursors and mDA neurons from E10.5 to E14.5. CXCR4 is activated in NURR1(+) cells as they migrate towards the meninges. Accordingly, VM meninges and CXCL12 promoted migration and neuritogenesis of TH(+) cells in VM explants in a CXCR4-dependent manner. Moreover, in vivo electroporation of Cxcl12 at E12.5 in the basal plate resulted in lateral migration, whereas expression in the midline resulted in retention of TH(+) cells in the IZ close to the midline. Analysis of Cxcr4(-/-) mice revealed the presence of VM TH(+) cells with disoriented processes in the intermediate zone (IZ) at E11.5 and marginal zone (MZ) at E14. Consistently, pharmacological blockade of CXCR4 or genetic deletion of Cxcr4 resulted in an accumulation of TH(+) cells in the lateral aspect of the IZ at E14, indicating that CXCR4 is required for the radial migration of mDA neurons in vivo. Altogether, our findings demonstrate that CXCL12/CXCR4 regulates the migration and orientation of processes in A9-A10 mDA neurons.

Chemokine CXCL12 in neurodegenerative diseases: an SOS signal for stem cell-based repair

The dynamic relation between stem cells and their niche governs self-renewal and progenitor cell deployment. The chemokine CXCL12 (C-X-C motif ligand 12) and its signaling receptor CXCR4 (C-X-C motif receptor 4) represent an important pathway that regulates homing and maintenance of stem cells in neural niches. Neural stem cells (NSCs) reside in specific niches where communication with blood vessels is regulated by CXCL12. In neurodegenerative diseases and brain tumors, reactive vasculature forms in response to diseased tissues to create new niches that secrete CXCL12, enhancing the recruitment of neural progenitor cells (NPCs) to lesion sites via long-range migration. These observations suggest that the CXCL12-CXCR4 axis maintains NSCs and serves as an emergent salvage signal for initiating endogenous stem cell-based tissue repair.

Inhibition of CD26/DPP-IV enhances donor muscle cell engraftment and stimulates sustained donor cell proliferation

BACKGROUND

Transplantation of myogenic stem cells possesses great potential for long-term repair of dystrophic muscle. In murine-to-murine transplantation experiments, CXCR4 expression marks a population of adult murine satellite cells with robust engraftment potential in mdx mice, and CXCR4-positive murine muscle-derived SP cells home more effectively to dystrophic muscle after intra-arterial delivery in mdx5cv mice. Together, these data suggest that CXCR4 plays an important role in donor cell engraftment. Therefore, we sought to translate these results to a clinically relevant canine-to-canine allogeneic transplant model for Duchenne muscular dystrophy (DMD) and determine if CXCR4 is important for donor cell engraftment.

METHODS

In this study, we used a canine-to-murine xenotransplantation model to quantitatively compare canine muscle cell engraftment, and test the most effective cell population and modulating factor in a canine model of DMD using allogeneic transplantation experiments.

RESULTS

We show that CXCR4 expressing cells are important for donor muscle cell engraftment, yet FACS sorted CXCR4-positive cells display decreased engraftment efficiency. However, diprotin A, a positive modulator of CXCR4-SDF-1 binding, significantly enhanced engraftment and stimulated sustained proliferation of donor cells in vivo. Furthermore, the canine-to-murine xenotransplantation model accurately predicted results in canine-to-canine muscle cell transplantation.

CONCLUSIONS

Therefore, these results establish the efficacy of diprotin A in stimulating muscle cell engraftment, and highlight the pre-clinical utility of a xenotransplantation model in assessing the relative efficacy of muscle stem cell populations.

CXCL12 signaling in the development of the nervous system

Chemokines are small, secreted proteins that have been shown to be important regulators of leukocyte trafficking and inflammation. All the known effects of chemokines are transduced by action at a family of G protein coupled receptors. Two of these receptors, CCR5 and CXCR4, are also known to be the major cellular receptors for HIV-1. Consideration of the evolution of the chemokine family has demonstrated that the chemokine Stromal cell Derived Factor-1 or SDF1 (CXCL12) and its receptor CXCR4 are the most ancient members of the family and existed in animals prior to the development of a sophisticated immune system. Thus, it appears that the original function of chemokine signaling was in the regulation of stem cell trafficking and development. CXCR4 signaling is important in the development of many tissues including the nervous system. Here we discuss the manner in which CXCR4 signaling can regulate the development of different structures in the central and peripheral nervous systems and the different strategies employed to achieve these effects.

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 presumed atypical chemokine receptor CXCR7 signals through G(i/o) proteins in primary rodent astrocytes and human glioma cells

SDF-1/CXCL12 binds to the chemokine receptors, CXCR4 and CXCR7, and controls cell proliferation and migration during development, tumorigenesis, and inflammatory processes. It is currently assumed that CXCR7 would represent an atypical or scavenger chemokine receptor which modulates the function of CXCR4. Contrasting this view, we demonstrated recently that CXCR7 actively mediates SDF-1 signaling in primary astrocytes. Here, we provide evidence that CXCR7 affects astrocytic cell signaling and function through pertussis toxin-sensitive G(i/o) proteins. SDF-1-dependent activation of G(i/o) proteins and subsequent increases in intracellular Ca(2+) concentration persisted in primary rodent astrocytes with depleted expression of CXCR4, but were abolished in astrocytes with depleted expression of CXCR7. Moreover, CXCR7-mediated effects of SDF-1 on Erk and Akt signaling as well as on astrocytic proliferation and migration were all sensitive to pertussis toxin. Likewise, pertussis toxin abolished SDF-1-induced activation of Erk and Akt in CXCR7-only expressing human glioma cell lines. Finally, consistent with a ligand-biased function of CXCR7 in astrocytes, the alternate CXCR7 ligand, I-TAC/CXCL11, activated Erk and Akt through β-arrestin. The demonstration that SDF-1-bound CXCR7 activates G(i/o) proteins in astrocytes could help to explain some discrepancies previously observed for the function of CXCR4 and CXCR7 in other cell types.

Histological and transcriptome-wide level characteristics of fetal myofiber hyperplasia during the second half of gestation in Texel and Ujumqin sheep

BACKGROUND

Whether myofibers increase with a pulsed-wave mode at particular developmental stages or whether they augment evenly across developmental stages in large mammals is unclear. Additionally, the molecular mechanisms of myostatin in myofiber hyperplasia at the fetal stage in sheep remain unknown. Using the first specialized transcriptome-wide sheep oligo DNA microarray and histological methods, we investigated the gene expression profile and histological characteristics of developing fetal ovine longissimus muscle in Texel sheep (high muscle and low fat), as a myostatin model of natural mutation, and Ujumqin sheep (low muscle and high fat). Fetal skeletal muscles were sampled at 70, 85, 100, 120, and 135 d of gestation.

RESULTS

Myofiber number increased sharply with a pulsed-wave mode at certain developmental stages but was not augmented evenly across developmental stages in fetal sheep. The surges in myofiber hyperplasia occurred at 85 and 120 d in Texel sheep, whereas a unique proliferative surge appeared at 100 d in Ujumqin sheep. Analysis of the microarray demonstrated that immune and hematological systems' development and function, lipid metabolism, and cell communication were the biological functions that were most differentially expressed between Texel and Ujumqin sheep during muscle development. Pathways associated with myogenesis and the proliferation of myoblasts, such as calcium signaling, chemokine (C-X-C motif) receptor 4 signaling, and vascular endothelial growth factor signaling, were affected significantly at specific fetal stages, which underpinned fetal myofiber hyperplasia and postnatal muscle hypertrophy. Moreover, we identified some differentially expressed genes between the two breeds that could be potential myostatin targets for further investigation.

CONCLUSIONS

Proliferation of myofibers proceeded in a pulsed-wave mode at particular fetal stages in the sheep. The myostatin mutation changed the gene expression pattern in skeletal muscle at a transcriptome-wide level, resulting in variation in myofiber phenotype between Texel and Ujumqin sheep during the second half of gestation. Our findings provide a novel and dynamic description of the effect of myostatin on skeletal muscle development, which contributes to understanding the biology of muscle development in large mammals.

Molecular and cellular mechanisms of mammalian cell fusion

The fusion of one cell with another occurs in development, injury and disease. Despite the diversity of fusion events, five steps in sequence appear common. These steps include programming fusion-competent status, chemotaxis, membrane adhesion, membrane fusion, and post-fusion resetting. Recent advances in the field start to reveal the molecules involved in each step. This review focuses on some key molecules and cellular events of cell fusion in mammals. Increasing evidence demonstrates that membrane lipid rafts, adhesion proteins and actin rearrangement are critical in the final step of membrane fusion. Here we propose a new model for the formation and expansion of membrane fusion pores based on recent observations on myotube formation. In this model, membrane lipid rafts first recruit adhesion molecules and align with opposing membranes, with the help of a cortical actin "wall" as a rigid supportive platform. Second, the membrane adhesion proteins interact with each other and trigger actin rearrangement, which leads to rapid dispersion of lipid rafts and flow of a highly fluidic phospholipid bilayer into the site. Finally, the opposing phospholipid bilayers are then pushed into direct contact leading to the formation of fusion pores by the force generated through actin polymerization. The actin polymerization generated force also drives the expansion of the fusion pores. However, several key questions about the process of cell fusion still remain to be explored. The understanding of the mechanisms of cell fusion may provide new opportunities in correcting development disorders or regenerating damaged tissues by inhibiting or promoting molecular events associated with fusion.

Nuocytes: expanding the innate cell repertoire in type-2 immunity

Activation and differentiation of the Th1 cell population lead to their production of the classical type-1 cytokines IFN-γ, IL-2, and TNF-β, thus promoting type-1 immunity. This is thought to occur via the ligation of TLRs by bacterial and viral products, which in turn, drive production of the essential Th1 cell differentiation factor, IL-12, by dendritic cells (DCs). Concurrent studies have been able to identify the effector cytokines produced by Th2 cells (IL-4, IL-5, IL-9, and IL-13) as being essential for parasitic immunity and also as essential factors in allergic asthma. However, the factors that are critical for initiation of the type-2 response remained obscure. Recently however, two critical observations have led to a more detailed understanding of the innate type-2 response. First, two novel, type-2-inducing cytokines-IL-25 and IL-33-were identified as being necessary for the up-regulation of the type-2 effector cytokines, mirroring the role of IL-12 in the type-1 response. Second, studies focused on target cell populations of IL-25 and IL-33 have identified novel, innate cell populations, which potentially bridge the gap between presentation of the type-2-inducing cytokine and the later adaptive Th2 cell response. In this review, we will discuss these new type-2 innate cell populations, in particular, the recently discovered nuocyte population, which are required for type-2 responses against helminthic parasites.

Neutrophil elastase, proteinase 3, and cathepsin G as therapeutic targets in human diseases

Polymorphonuclear neutrophils are the first cells recruited to inflammatory sites and form the earliest line of defense against invading microorganisms. Neutrophil elastase, proteinase 3, and cathepsin G are three hematopoietic serine proteases stored in large quantities in neutrophil cytoplasmic azurophilic granules. They act in combination with reactive oxygen species to help degrade engulfed microorganisms inside phagolysosomes. These proteases are also externalized in an active form during neutrophil activation at inflammatory sites, thus contributing to the regulation of inflammatory and immune responses. As multifunctional proteases, they also play a regulatory role in noninfectious inflammatory diseases. Mutations in the ELA2/ELANE gene, encoding neutrophil elastase, are the cause of human congenital neutropenia. Neutrophil membrane-bound proteinase 3 serves as an autoantigen in Wegener granulomatosis, a systemic autoimmune vasculitis. All three proteases are affected by mutations of the gene (CTSC) encoding dipeptidyl peptidase I, a protease required for activation of their proform before storage in cytoplasmic granules. Mutations of CTSC cause Papillon-Lefèvre syndrome. Because of their roles in host defense and disease, elastase, proteinase 3, and cathepsin G are of interest as potential therapeutic targets. In this review, we describe the physicochemical functions of these proteases, toward a goal of better delineating their role in human diseases and identifying new therapeutic strategies based on the modulation of their bioavailability and activity. We also describe how nonhuman primate experimental models could assist with testing the efficacy of proposed therapeutic strategies.

Targeting chemokine receptors in allergic disease

The directed migration of cells in response to chemical cues is known as chemoattraction, and plays a key role in the temporal and spatial positioning of cells in lower- and higher-order life forms. Key molecules in this process are the chemotactic cytokines, or chemokines, which, in humans, constitute a family of approx. 40 molecules. Chemokines exert their effects by binding to specific GPCRs (G-protein-coupled receptors) which are present on a wide variety of mature cells and their progenitors, notably leucocytes. The inappropriate or excessive generation of chemokines is a key component of the inflammatory response observed in several clinically important diseases, notably allergic diseases such as asthma. Consequently, much time and effort has been directed towards understanding which chemokine receptors and ligands are important in the allergic response with a view to therapeutic intervention. Such strategies can take several forms, although, as the superfamily of GPCRs has historically proved amenable to blockade by small molecules, the development of specific antagonists has been has been a major focus of several groups. In the present review, I detail the roles of chemokines and their receptors in allergic disease and also highlight current progress in the development of relevant chemokine receptor antagonists.

Skeletal muscle fibrosis: the effect of stromal-derived factor-1α-loaded collagen scaffolds

AIM

To develop a model for muscle fibrosis based on full-thickness muscle defects, and to evaluate the effects of implanted stromal-derived factor (SDF)-1α-loaded collagen scaffolds.

METHODS

Full-thickness defects 2 mm in diameter were made in the musculus soleus of 48 rats and either left alone or filled with SDF-1α-loaded collagen scaffolds. At 3, 10, 28 and 56 days postsurgery, muscles were analyzed for collagen deposition, satellite cells, myofibroblasts and macrophages.

RESULTS

A significant amount of collagen-rich fibrotic tissue was formed, which persisted over time. Increased numbers of satellite cells were present around, but not within, the wounds. Satellite cells were further upregulated in regenerating tissue when SDF-1α-loaded collagen scaffolds were implanted. The scaffolds also attracted macrophages, but collagen deposition and myofibroblast numbers were not affected.

CONCLUSION

Persistent muscle fibrosis is induced by full-thickness defects 2 mm in diameter. SDF-1α-loaded collagen scaffolds accelerated muscle regeneration around the wounds, but did not reduce muscle fibrosis.

Dysregulated expression of CXCR4/CXCL12 in subsets of patients with systemic lupus erythematosus

OBJECTIVE

CXCR4 is a chemokine with multiple effects on the immune system. In murine lupus models, we demonstrated that monocytes, neutrophils, and B cells overexpressed CXCR4 and that its ligand, CXCL12, was up-regulated in diseased kidneys. We undertook this study to determine whether CXCR4 expression was increased in peripheral blood leukocytes from patients with systemic lupus erythematosus (SLE) and whether CXCL12 expression was increased in kidneys from patients with SLE.

METHODS

Peripheral blood leukocytes from 31 SLE patients, 8 normal controls, and 9 patients with rheumatoid arthritis were prospectively analyzed by flow cytometry for CXCR4 expression. Biopsy samples (n = 14) from patients with lupus nephritis (LN) were immunostained with anti-CXCL12 antibody.

RESULTS

CD19+ B cells and CD4+ T cells from SLE patients displayed a >2-fold increase (P = 0.0001) and >3-fold increase (P < 0.0001), respectively, in median CXCR4 expression compared with that in controls (n = 7-8). Moreover, CXCR4 expression on B cells was 1.61-fold higher in patients with SLE Disease Activity Index (SLEDAI) scores >10 (n = 8) than in patients with SLEDAI scores ≤10 (n = 16) (P = 0.0008), 1.71-fold higher in patients with class IV LN (n = 5) than in patients with other classes of LN (n = 7) (P = 0.02), and 1.40-fold higher in patients with active neuropsychiatric SLE (NPSLE) (n = 6) than in patients with inactive NPSLE (n = 18) (P = 0.01). CXCL12 was significantly up-regulated in the tubules and glomeruli of kidneys in patients with LN (n = 14), with the percentage of positive cells correlating positively with the severity of LN.

CONCLUSION

CXCR4 appears to be up-regulated in multiple leukocyte subsets in SLE patients. The heightened expression of CXCR4 on B cells in active NPSLE and of CXCL12 in nephritic kidneys suggests that the CXCR4/CXCL12 axis might be a potential therapeutic target for SLE patients with kidney and/or central nervous system involvement.

Chemokine expression and control of muscle cell migration during myogenesis

Adult regenerative myogenesis is vital for restoring normal tissue structure after muscle injury. Muscle regeneration is dependent on progenitor satellite cells, which proliferate in response to injury, and their progeny differentiate and undergo cell-cell fusion to form regenerating myofibers. Myogenic progenitor cells must be precisely regulated and positioned for proper cell fusion to occur. Chemokines are secreted proteins that share both leukocyte chemoattractant and cytokine-like behavior and affect the physiology of a number of cell types. We investigated the steady-state mRNA levels of 84 chemokines, chemokine receptors and signaling molecules, to obtain a comprehensive view of chemokine expression by muscle cells during myogenesis in vitro. A large number of chemokines and chemokine receptors were expressed by primary mouse muscle cells, especially during times of extensive cell-cell fusion. Furthermore, muscle cells exhibited different migratory behavior throughout myogenesis in vitro. One receptor-ligand pair, CXCR4-SDF-1alpha (CXCL12), regulated migration of both proliferating and terminally differentiated muscle cells, and was necessary for proper fusion of muscle cells. Given the large number of chemokines and chemokine receptors directly expressed by muscle cells, these proteins might have a greater role in myogenesis than previously appreciated.

Role of cardiac myocyte CXCR4 expression in development and left ventricular remodeling after acute myocardial infarction

RATIONALE

Stromal cell-derived factor (SDF)-1/CXCR4 axis has an instrumental role during cardiac development and has been shown to be a potential therapeutic target for optimizing ventricular remodeling after acute myocardial infarction (AMI) and in ischemic cardiomyopathy. Although a therapeutic target, the specific role of cardiac myocyte CXCR4 (CM-CXCR4) expression following cardiogenesis and survival of cardiac myocyte and left ventricular remodeling after AMI is unknown.

OBJECTIVE

We hypothesized that cardiac myocyte derived CXCR4 is critical for cardiac development, but it may have no role in adulthood secondary to the short transient expression of SDF-1 and the delayed expression of CM-CXCR4 following AMI. To address this issue, we developed congenital and conditional CM-CXCR4(-/-) mouse models.

METHODS AND RESULTS

Two strains of CM-CXCR4(flox/flox) mice were generated by crossing CXCR4(flox/flox) mice with MCM-Cre(+/-) mouse and MLC2v-Cre(+/-) mouse on the C57BL/6J background, yielding CXCR4(flox/flox) MCM-Cre(+/-) and CXCR4(flox/flox)MLC2v-Cre(+/-) mice. Studies demonstrated recombination in both models congenitally in the MLC2v-Cre(+/-) mice and following tamoxifen administration in the MCM-Cre(+/-) mice. Surprisingly the CXCR4(flox/flox)MLC2v-Cre(+/-) are viable, had normal cardiac function, and had no evidence of ventricular septal defect. CXCR4(flox/flox)MCM(+/-) treated with tamoxifen 2 weeks before AMI demonstrated 90% decrease in cardiac CXCR4 expression 48 hours after AMI. Twenty-one days post AMI, echocardiography revealed no statistically significant difference in the wall thickness, left ventricular dimensions or ejection fraction (40.9+/-7.5 versus 34.4+/-2.6%) in CXCR4(flox/flox) mice versus CM-CXCR4(-/-) mice regardless of strategy of Cre expression. No differences in vascular density (2369+/-131 versus 2471+/-126 vessels/mm(2); CXCR4(flox/flox) versus CM-CXCR4(-/-) mouse), infarct size, collagen content, or noninfarct zone cardiac myocyte size were observed 21 days after AMI.

CONCLUSIONS

We conclude that cardiac myocyte-derived CXCR4 is not essential for cardiac development and, potentially because of the mismatch in timings of peaks of SDF-1 and CXCR4, has no major role in ventricular remodeling after AMI.

CXCR7 is an active component of SDF-1 signalling in astrocytes and Schwann cells

The alternative SDF-1 (stromal cell derived factor-1) receptor, CXCR7, has been suggested to act as either a scavenger of extracellular SDF-1 or a modulator of the primary SDF-1 receptor, CXCR4. CXCR7, however, also directly affects the function of various tumor-cell types. Here, we demonstrate that CXCR7 is an active component of SDF-1 signalling in astrocytes and Schwann cells. Cultured cortical astrocytes and peripheral nerve Schwann cells exhibit comparable total and cell-surface levels of expression of both SDF-1 receptors. Stimulation of astrocytes with SDF-1 resulted in the temporary activation of Erk1/2, Akt and PKCzeta/lambda, but not p38 and PKCalpha/beta. Schwann cells showed SDF-1-induced activation of Erk1/2, Akt and p38, but not PKCalpha/beta and PKCzeta/lambda. The respective signalling pattern remained fully inducible in astrocytes from CXCR4-deficient mice, but was abrogated following depletion of astrocytic CXCR7 by RNAi. In Schwann cells, RNAi-mediated depletion of either CXCR4 or CXCR7 silenced SDF-1 signalling. The findings of the astrocytic receptor-depletion experiments were reproduced by CXCR7 antagonist CCX754, but not by CXCR4 antagonist AMD3100, both of which abolished astrocytic SDF-1 signalling. Further underlining the functional importance of CXCR7 signalling in glial cells, we show that the mitogenic effects of SDF-1 on both glial cell types are impaired upon depleting CXCR7.

Spatio-temporal changes of SDF1 and its CXCR4 receptor in the dorsal root ganglia following unilateral sciatic nerve injury as a model of neuropathic pain

There is a growing evidence that chemokines and their receptors play a role in inducing and maintaining neuropathic pain. In the present study, unilateral chronic constriction injury (CCI) of rat sciatic nerve under aseptic conditions was used to investigate changes for stromal derived factor-1 (SDF1) and its CXCR4 receptor in lumbal (L4-L5) and cervical (C7-C8) dorsal root ganglia (DRG) from both sides of naïve, CCI-operated and sham-operated rats. All CCI-operated rats displayed mechanical allodynia and thermal hyperalgesia in hind paws ipsilateral to CCI, but forepaws exhibited only temporal changes of sensitivity not correlated with alterations in SDF1 and CXCR4 proteins. Naïve DRG displayed immunofluorescence for SDF1 (SDF1-IF) in the satellite glial cells (SGC) and CXCR4-IF in the neuronal bodies with highest intensity in small- and medium-sized neurons. Immunofluorescence staining and Western blot analysis confirmed that unilateral CCI induced bilateral alterations of SDF1 and CXCR4 proteins in both L4-L5 and C7-C8 DRG. Only lumbal DRG were invaded by ED-1+ macrophages exhibiting SDF1-IF while elevation of CXCR4-IF was found in DRG neurons and SGC but not in ED-1+ macrophages. No attenuation of mechanical allodynia, but reversed thermal hyperalgesia, in ipsi- and contralateral hind paws was found in CCI-operated rats after i.p. administration of CXCR4 antagonist (AMD3100). These results indicate that SDF1/CXCR4 changes are not limited to DRG associated with injured nerve but that they also spread to DRG non-associated with such nerve. Functional involvement of these alterations in DRG non-associated with injured nerve in neuropathic pain remains to be elucidated.

Targeting the CXCR4/CXCL12 axis in systemic lupus erythematosus

BACKGROUND

CXCR4 antagonists have garnered much interest as promising treatments for cancer metastases and HIV. Given its ability to attract multiple leukocyte subsets and stimulate B cell production and myelopoeisis, recent attention has been directed to these inhibitors in the treatment of autoimmune diseases, such as systemic lupus erythematosus (SLE).

OBJECTIVE

To assess the potential of CXCR4 antagonists in SLE.

METHODS

We reviewed literature on the expression of CXCR4 and its ligand CXCL12, and the effects of CXCR4 antagonists in murine and human SLE.

RESULTS/CONCLUSIONS

CXCR4 and CXCL12 have been found at abundant levels in peripheral blood leukocyte subsets as well as immune and non-immune organs in lupus-prone murine models. While SLE patients have displayed upregulated, downregulated, or unchanged levels of CXCR4 in circulating blood lymphocytes, CXCR4 and CXCL12 were found prominently in the skin and kidney, suggesting that the ultimate destinations of CXCR4(+) cells include these areas. CXCR4 antagonists have been explored in murine lupus models, in which disease severity and nephritis significantly improved. While clinical trials of CXCR4 antagonists in SLE have yet to be initiated, these inhibitors appear to have the potential to improve disease prognosis in severe lupus patients, particularly those with lupus nephritis.