Regulation of expression of fibronectin and its receptor, alpha 5 beta 1, during development and regeneration of peripheral nerve

Epothilone B loaded in acellular nerve allograft enhanced sciatic nerve regeneration in rats

BACKGROUND

Epothilone B (EpoB) is a microtubule-stabilizing agent with neuroprotective properties.

OBJECTIVES

This study examines the regenerative properties of ANA supplemented with EpoB on a sciatic nerve deficit in male Wistar rats.

METHODS

For this purpose, the 10 mm nerve gap was filled with acellular nerve allografts (ANAs) containing EpoB at 0.1, 1, and 10 nM concentrations. The sensorimotor recovery was evaluated up to 16 weeks after the operation. Real-time PCR, histomorphometry analysis, and electrophysiological evaluation were also used to evaluate the process of nerve regeneration.

RESULTS

ANA/EpoB (0.1 nM) significantly improved sensorimotor recovery in rats compared to ANA, ANA/EpoB (1 nM), and ANA/EpoB (10 nM) groups. This led to reduced muscle atrophy, improved sciatic functional index, and thermal paw withdrawal reflex latency, indicating nerve regeneration and target organ reinnervation. The electrophysiological and histomorphometry findings also confirmed the ANA/EpoB regenerative properties (0.1 nM). EpoB only enhanced ANA regenerative properties at 0.1 nM, with no therapeutic effects at higher concentrations.

CONCLUSION

Totally, we concluded that ANA loaded with 0.1 nM EpoB can effectively reconstruct the transected sciatic nerve in rats, likely by enhancing axonal sprouting and extension.

A neural-related gene risk score for head and neck squamous cell carcinoma

OBJECTIVES

This study aimed to establish a neural-related gene risk score (NRGRS) for the prediction of head and neck squamous cell carcinoma prognosis and explore its predictive value on the benefit of immune checkpoint inhibitor therapy.

METHODS

Based on the transcriptome data of HNSCC patients (n = 546) from The Cancer Genome Atlas database, 37 neural-related hub genes were identified by weighted gene co-expression network analysis. Four genes (ITGA5, PYGM, GNG7 and ATP2A3) were identified to construct NRGRS using Lasso-Cox regression method based on the derivation cohort and validated in the Gene Expression Omnibus cohort (n = 109). The survival analysis was performed to validate the prognostic value of NRGRS and immune characteristics in NRGRS-defined subgroups were analyzed.

RESULTS

NRGRS-high patients had a worse overall survival than NRGRS-low patients. Tumors with high NRGRS were more likely to have high infiltration of naive CD4+ T cells, M0, M2 macrophages and resting mast cells, which illustrated suppressive immunity and less benefit from immunotherapy therapy.

CONCLUSION

NRGRS strongly correlates with survival and is a promising biomarker to predict immunotherapy benefits for head and neck cancer patients. This study provides evidence for the potential correlation between neural-related transcriptome alteration and immune activity.

Brief Electrical Stimulation Promotes Recovery after Surgical Repair of Injured Peripheral Nerves

Injured peripheral nerves regenerate their axons in contrast to those in the central nervous system. Yet, functional recovery after surgical repair is often disappointing. The basis for poor recovery is progressive deterioration with time and distance of the growth capacity of the neurons that lose their contact with targets (chronic axotomy) and the growth support of the chronically denervated Schwann cells (SC) in the distal nerve stumps. Nonetheless, chronically denervated atrophic muscle retains the capacity for reinnervation. Declining electrical activity of motoneurons accompanies the progressive fall in axotomized neuronal and denervated SC expression of regeneration-associated-genes and declining regenerative success. Reduced motoneuronal activity is due to the withdrawal of synaptic contacts from the soma. Exogenous neurotrophic factors that promote nerve regeneration can replace the endogenous factors whose expression declines with time. But the profuse axonal outgrowth they provoke and the difficulties in their delivery hinder their efficacy. Brief (1 h) low-frequency (20 Hz) electrical stimulation (ES) proximal to the injury site promotes the expression of endogenous growth factors and, in turn, dramatically accelerates axon outgrowth and target reinnervation. The latter ES effect has been demonstrated in both rats and humans. A conditioning ES of intact nerve days prior to nerve injury increases axonal outgrowth and regeneration rate. Thereby, this form of ES is amenable for nerve transfer surgeries and end-to-side neurorrhaphies. However, additional surgery for applying the required electrodes may be a hurdle. ES is applicable in all surgeries with excellent outcomes.

Regenerative capacity of neural tissue scales with changes in tissue mechanics post injury

Spinal cord injuries have devastating consequences for humans, as mammalian neurons of the central nervous system (CNS) cannot regenerate. In the peripheral nervous system (PNS), however, neurons may regenerate to restore lost function following injury. While mammalian CNS tissue softens after injury, how PNS tissue mechanics changes in response to mechanical trauma is currently poorly understood. Here we characterised mechanical rat nerve tissue properties before and after in vivo crush and transection injuries using atomic force microscopy-based indentation measurements. Unlike CNS tissue, PNS tissue significantly stiffened after both types of tissue damage. This nerve tissue stiffening strongly correlated with an increase in collagen I levels. Schwann cells, which crucially support PNS regeneration, became more motile and proliferative on stiffer substrates in vitro, suggesting that changes in tissue stiffness may play a key role in facilitating or impeding nervous system regeneration.

Single-cell RNA sequencing defines disease-specific differences between chronic nodular prurigo and atopic dermatitis

BACKGROUND

Chronic nodular prurigo (CNPG) is an inflammatory skin disease that is maintained by a chronic itch-scratch cycle likely rooted in neuroimmunological dysregulation. This condition may be associated with atopy in some patients, and there are now promising therapeutic results from blocking type 2 cytokines such as IL-4, IL-13, and IL-31.

OBJECTIVES

This study aimed to improve the understanding of pathomechanisms underlying CNPG as well as molecular relationships between CNPG and atopic dermatitis (AD).

METHODS

We profiled skin lesions from patients with CNPG in comparison with AD and healthy control individuals using single-cell RNA sequencing combined with T-cell receptor sequencing.

RESULTS

We found type 2 immune skewing in both CNPG and AD, as evidenced by CD4+ helper T cells expressing IL13. However, only AD harbored an additional, oligoclonally expanded CD8A+IL9R+IL13+ cytotoxic T-cell population, and immune activation pathways were highly upregulated in AD, but less so in CNPG. Conversely, CNPG showed signatures of extracellular matrix organization, collagen synthesis, and fibrosis, including a unique population of CXCL14-IL24+ secretory papillary fibroblasts. Besides known itch mediators such as IL31 and oncostatin M, we also detected increased levels of neuromedin B in fibroblasts of CNPG lesions compared with AD and HC, with neuromedin B receptors detectable on some nerve endings.

CONCLUSIONS

These data show that CNPG does not harbor the strong disease-specific immune activation pathways that are typically found in AD but is rather characterized by upregulated stromal remodeling mechanisms that might have a direct impact on itch fibers.

3D Bioprinting of Hyaline Articular Cartilage: Biopolymers, Hydrogels, and Bioinks

The musculoskeletal system, consisting of bones and cartilage of various types, muscles, ligaments, and tendons, is the basis of the human body. However, many pathological conditions caused by aging, lifestyle, disease, or trauma can damage its elements and lead to severe disfunction and significant worsening in the quality of life. Due to its structure and function, articular (hyaline) cartilage is the most susceptible to damage. Articular cartilage is a non-vascular tissue with constrained self-regeneration capabilities. Additionally, treatment methods, which have proven efficacy in stopping its degradation and promoting regeneration, still do not exist. Conservative treatment and physical therapy only relieve the symptoms associated with cartilage destruction, and traditional surgical interventions to repair defects or endoprosthetics are not without serious drawbacks. Thus, articular cartilage damage remains an urgent and actual problem requiring the development of new treatment approaches. The emergence of biofabrication technologies, including three-dimensional (3D) bioprinting, at the end of the 20th century, allowed reconstructive interventions to get a second wind. Three-dimensional bioprinting creates volume constraints that mimic the structure and function of natural tissue due to the combinations of biomaterials, living cells, and signal molecules to create. In our case-hyaline cartilage. Several approaches to articular cartilage biofabrication have been developed to date, including the promising technology of 3D bioprinting. This review represents the main achievements of such research direction and describes the technological processes and the necessary biomaterials, cell cultures, and signal molecules. Special attention is given to the basic materials for 3D bioprinting-hydrogels and bioinks, as well as the biopolymers underlying the indicated products.

Tissue-resident glial cells associate with tumoral vasculature and promote cancer progression

Cancer cells are embedded within the tissue and interact dynamically with its components during cancer progression. Understanding the contribution of cellular components within the tumor microenvironment is crucial for the success of therapeutic applications. Here, we reveal the presence of perivascular GFAP+/Plp1+ cells within the tumor microenvironment. Using in vivo inducible Cre/loxP mediated systems, we demonstrated that these cells derive from tissue-resident Schwann cells. Genetic ablation of endogenous Schwann cells slowed down tumor growth and angiogenesis. Schwann cell-specific depletion also induced a boost in the immune surveillance by increasing tumor-infiltrating anti-tumor lymphocytes, while reducing immune-suppressor cells. In humans, a retrospective in silico analysis of tumor biopsies revealed that increased expression of Schwann cell-related genes within melanoma was associated with improved survival. Collectively, our study suggests that Schwann cells regulate tumor progression, indicating that manipulation of Schwann cells may provide a valuable tool to improve cancer patients' outcomes.

Thy-1 (CD90), Integrins and Syndecan 4 are Key Regulators of Skin Wound Healing

Acute skin wound healing is a multistage process consisting of a plethora of tightly regulated signaling events in specialized cells. The Thy-1 (CD90) glycoprotein interacts with integrins and the heparan sulfate proteoglycan syndecan 4, generating a trimolecular complex that triggers bi-directional signaling to regulate diverse aspects of the wound healing process. These proteins can act either as ligands or receptors, and they are critical for the successful progression of wound healing. The expression of Thy-1, integrins, and syndecan 4 is controlled during the healing process, and the lack of expression of any of these proteins results in delayed wound healing. Here, we review and discuss the roles and regulatory events along the stages of wound healing that support the relevance of Thy-1, integrins, and syndecan 4 as crucial regulators of skin wound healing.

Reverse Phase Protein Array Reveals Correlation of Retinoic Acid Metabolism With Cardiomyopathy in Friedreich's Ataxia

Identifying biomarkers is important for assessment of disease progression, prediction of symptom development, and determination of treatment effectiveness. While unbiased analyses of differential gene expression using next-generation sequencing methods are now routinely conducted, proteomics studies are more challenging because of traditional methods predominantly being low throughput and offering a limited dynamic range for simultaneous detection of hundreds of proteins that drastically differ in their intracellular abundance. We utilized a sensitive and high-throughput proteomic technique, reverse phase protein array (RPPA), to attain protein expression profiles of primary fibroblasts obtained from patients with Friedreich's ataxia (FRDA) and unaffected controls (CTRLs). The RPPA was designed to detect 217 proteins or phosphorylated proteins by individual antibody, and the specificity of each antibody was validated prior to the experiment. Among 62 fibroblast samples (44 FRDA and 18 CTRLs) analyzed, 30 proteins/phosphoproteins were significantly changed in FRDA fibroblasts compared with CTRL cells (p < 0.05), mostly representing signaling molecules and metabolic enzymes. As expected, frataxin was significantly downregulated in FRDA samples, thus serving as an internal CTRL for assay integrity. Extensive bioinformatics analyses were conducted to correlate differentially expressed proteins with critical disease parameters (e.g., selected symptoms, age of onset, guanine-adenine-adenine sizes, frataxin levels, and Functional Assessment Rating Scale scores). Members of the integrin family of proteins specifically associated with hearing loss in FRDA. Also, RPPA data, combined with results of transcriptome profiling, uncovered defects in the retinoic acid metabolism pathway in FRDA samples. Moreover, expression of aldehyde dehydrogenase family 1 member A3 differed significantly between cardiomyopathy-positive and cardiomyopathy-negative FRDA cohorts, demonstrating that metabolites such as retinol, retinal, or retinoic acid could become potential predictive biomarkers of cardiac presentation in FRDA.

Fibronectin in development and wound healing

Fibronectin structure and composition regulate contextual cell signaling. Recent advances have been made in understanding fibronectin and its role in tissue organization and repair. This review outlines fibronectin splice variants and their functions, evaluates potential therapeutic strategies targeting or utilizing fibronectin, and concludes by discussing potential future directions to modulate fibronectin function in development and wound healing.

αV integrins in Schwann cells promote attachment to axons, but are dispensable in vivo

In the developing peripheral nervous system, Schwann cells (SCs) extend their processes to contact, sort, and myelinate axons. The mechanisms that contribute to the interaction between SCs and axons are just beginning to be elucidated. Using a SC-neuron coculture system, we demonstrate that Arg-Gly-Asp (RGD) peptides that inhibit α_V -containing integrins delay the extension of SCs elongating on axons. α_V integrins in SC localize to sites of contact with axons and are expressed early in development during radial sorting and myelination. Short interfering RNA-mediated knockdown of the α_V integrin subunit also delays SC extension along axons in vitro, suggesting that α_V -containing integrins participate in axo-glial interactions. However, mice lacking the α_V subunit in SCs, alone or in combination with the potentially compensating α₅ subunit, or the α_V partners β₃ or β₈ , myelinate normally during development and remyelinate normally after nerve crush, indicating that overlapping or compensatory mechanisms may hide the in vivo role of RGD-binding integrins.

Urokinase receptor regulates nerve regeneration through its interaction with α5β1-integrin

PURPOSE

Urokinase receptor (uPAR) promotes extracellular matrix proteolysis, regulates adhesion and cell migration, transduces intracellular signals through interactions with the lateral partners. The expression of uPAR and urokinase (uPA) is significantly upregulated in peripheral nerves after injury, however, little is known about uPAR function in nerve regeneration or the molecular mechanisms involved. The purpose of this study is to investigate the role of uPAR in nerve regeneration after traumatic injury of n. Peroneus communis in uPA-/-, uPAR-/- or control mice (WT) and in neuritogenesis in an in vitro Neuro 2A cell model.

RESULTS

Electrophysiological analysis indicates that nerve recovery is significantly impaired in uPAR-/- mice, but not in uPA-/- mice. These data correlate with the reduced amount of NF200-positive axons in regenerating nerves from uPAR-/- mice compared to uPA-/- or control mice. There is an increase in uPAR expression and remarkable colocalization of uPAR with α5 and β1 integrin in uPA-/- mice in recovering nerves, pointing to a potential link between uPAR and its lateral partner α5β1-integrin. Using an in vitro model of neuritogenesis and α325 blocking peptide, which abrogates uPAR-α5β1 interaction in Neuro 2A cells but has no effect on their function, we have further confirmed the significance of uPAR-α5β1 interaction.

CONCLUSION

Taken together, we report evidence pointing to an important role of uPAR, rather than uPA, in peripheral nerve recovery and neuritogenesis.

Remodeling of Substance P Sensory Nerves and Transient Receptor Potential Melastatin 8 (TRPM8) Cold Receptors After Corneal Experimental Surgery

Purpose

To investigate changes in corneal nerves positive to substance P (SP) and transient receptor potential melastatin 8 (TRPM8) and gene expression in the trigeminal ganglia (TG) following corneal surgery to unveil peripheral nerve mechanism of induced dry eye-like pain (DELP).

Methods

Surgery was performed on mice by removing the central epithelial and anterior stromal nerves. Mice were euthanized at different times up to 15 weeks. Immunostaining was performed with TRPM8, SP, or protein gene product 9.5 (PGP9.5) antibodies, and epithelial nerve densities were calculated. The origin of TRPM8- and SP-TG neurons were analyzed by retrograde tracing. Gene expression in TG was studied by real-time PCR analysis.

Results

SP-positive epithelial corneal nerves were more abundant than TRPM8 and were expressed in different TG neurons. After injury, epithelial nerve regeneration occurs in two distinct stages. An early regeneration of the remaining epithelial bundles reached the highest density on day 3 and then rapidly degraded. From day 5, the epithelial nerves originated from the underlying stromal nerves were still lower than normal levels by week 15. The SP- and TRPM8-positive nerve fibers followed the same pattern as the total nerves. TRPM8-positive terminals increased slowly and reached only half of normal values by 3 months. Corneal sensitivity gradually increased and reached normal values on day 12. Corneal injury also induced significant changes in TG gene expression, decreasing trpm8 and tac1 genes.

Conclusions

Abnormal SP expression, low amounts of TRPM8 terminals, and hypersensitive nerve response occur long after the injury and changes in gene expression in the TG suggest a contribution to the pathogenesis of corneal surgery-induced DELP.

Blood vessels guide Schwann cell migration in the adult demyelinated CNS through Eph/ephrin signaling

Schwann cells (SC) enter the central nervous system (CNS) in pathophysiological conditions. However, how SC invade the CNS to remyelinate central axons remains undetermined. We studied SC migratory behavior ex vivo and in vivo after exogenous transplantation in the demyelinated spinal cord. The data highlight for the first time that SC migrate preferentially along blood vessels in perivascular extracellular matrix (ECM), avoiding CNS myelin. We demonstrate in vitro and in vivo that this migration route occurs by virtue of a dual mode of action of Eph/ephrin signaling. Indeed, EphrinB3, enriched in myelin, interacts with SC Eph receptors, to drive SC away from CNS myelin, and triggers their preferential adhesion to ECM components, such as fibronectin via integrinβ1 interactions. This complex interplay enhances SC migration along the blood vessel network and together with lesion-induced vascular remodeling facilitates their timely invasion of the lesion site. These novel findings elucidate the mechanism by which SC invade and contribute to spinal cord repair.

Integrins promote axonal regeneration after injury of the nervous system

Integrins are cell surface receptors that form the link between extracellular matrix molecules of the cell environment and internal cell signalling and the cytoskeleton. They are involved in several processes, e.g. adhesion and migration during development and repair. This review focuses on the role of integrins in axonal regeneration. Integrins participate in spontaneous axonal regeneration in the peripheral nervous system through binding to various ligands that either inhibit or enhance their activation and signalling. Integrin biology is more complex in the central nervous system. Integrins receptors are transported into growing axons during development, but selective polarised transport of integrins limits the regenerative response in adult neurons. Manipulation of integrins and related molecules to control their activation state and localisation within axons is a promising route towards stimulating effective regeneration in the central nervous system.

Fibronectin Promotes Survival and Migration of Primary Neural Stem Cells Transplanted into the Traumatically Injured Mouse Brain

Multipotential stem cells are an attractive choice for cell therapy after traumatic brain injury (TBI), as replacement of multiple cell types may be required for functional recovery. In the present study, neural stem cells (NSCs) derived from the germinal zone of E14.5 GFP-expressing mouse brains were cultured as neurospheres in FGF2-enhanced medium. When FGF2 was removed in vitro, NSCs expressed phenotypic markers for neurons, astrocytes, and oligodendrocytes and exhibited migratory behavior in the presence of adsorbed fibronectin (FN). NSCs (105 cells) were transplanted into mouse brains 1 week after a unilateral, controlled, cortical contusion (depth = 1 mm, velocity = 6 m/s, duration = 150 ms) (n = 19). NSCs were injected either directly into the injury cavity with or without an injectable FN-based scaffold [collagen I (CnI)/ FN gel; n = 14] or into the striatum below the injury cavity (n = 5). At all time points examined (1 week to 3 months posttransplant), GFP+ cells were confined to the ipsilateral host brain tissue. At 1 week, cells injected into the injury cavity lined the injury penumbra while cells inserted directly into the striatum remained in or around the needle track. Striatal transplants had a lower number of surviving GFP+ cells relative to cavity injections at the 1 week time point (p < 0.01). At the longer survival times (3 weeks–3 months), 63–76% of transplanted cells migrated into the fimbria hippocampus regardless of injection site, perhaps due to cues from the degenerating hippocampus. Furthermore, cells injected into the cavity within a FN-containing matrix showed increased survival and migration at 3 weeks (p < 0.05 for both) relative to injections of cells alone. These results suggest that FGF2-responsive NSCs present a promising approach for cellular therapy following trauma and that the transplant location and environment may play an important role in graft survival and integration.

Functional self-assembling peptide nanofiber hydrogel for peripheral nerve regeneration

Peripheral nerves are fragile and easily damaged, usually resulting in nervous tissue loss, motor and sensory function loss. Advances in neuroscience and engineering have been significantly contributing to bridge the damage nerve and create permissive environment for axonal regrowth across lesions. We have successfully designed two self-assembling peptides by modifying RADA 16-I with two functional motifs IKVAV and RGD. Nanofiber hydrogel formed when combing the two neutral solutions together, defined as RADA 16-Mix that overcomes the main drawback of RADA16-I associated with low pH. In the present study, we transplanted the RADA 16-Mix hydrogel into the transected rat sciatic nerve gap and effect on axonal regeneration was examined and compared with the traditional RADA16-I hydrogel. The regenerated nerves were found to grow along the walls of the large cavities formed in the graft of RADA16-I hydrogel, while the nerves grew into the RADA 16-Mix hydrogel toward distal position. RADA 16-Mix hydrogel induced more axons regeneration and Schwann cells immigration than RADA16-I hydrogel, resulting in better functional recovery as determined by the gait-stance duration percentage and the formation of new neuromuscular junction structures. Therefore, our results indicated that the functional SAP RADA16-Mix nanofibrous hydrogel provided a better environment for peripheral nerve regeneration than RADA16-I hydrogel and could be potentially used in peripheral nerve injury repair.

Extracellular matrix components as therapeutics for spinal cord injury

There is no treatment for people with spinal cord injury that leads to significant functional improvements. The extracellular matrix is an intricate, 3-dimensional, structural framework that defines the environment for cells in the central nervous system. The components of extracellular matrix have signaling and regulatory roles in the fate and function of neuronal and non-neuronal cells in the central nervous system. This review discusses the therapeutic potential of extracellular matrix components for spinal cord repair.

■ REVIEW : Gene Expression in Nerve Regeneration

Injury of peripheral nerve in mammals leads to a complex but stereotypical pattern of histological events that comprise a highly reproducible sequence of degenerative reactions (Wallerian degeneration) succeeded by regenerative responses. These reactions are based on a corresponding sequence of cellular and mo lecular interactions that, in turn, reflect the differential expression of specific genes with functions in nerve degeneration and repair. We report on more than 60 genes and their products that show a specific pattern of regulation following peripheral nerve lesion. The group of regulated genes encoding, e.g., transcription factors, growth factors and their receptors, cytokines, neuropeptides, myelin proteins and lipid carriers, and cytoskeletal proteins as well as extracellular matrix and cell adhesion molecules. We describe and compare the distinct time-courses and cellular origin of expression and further discuss established or putative mo lecular interrelationships and functions with respect to the contribution of these genes/gene products to the molecular regeneration program of the PNS. NEUROSCIENTIST 3:112-122, 1997

Autocrine fibronectin from differentiating mesenchymal stem cells induces the neurite elongation in vitro and promotes nerve fiber regeneration in transected spinal cord injury

Extracellular matrix (ECM) expression is temporally and spatially regulated during the development of stem cells. We reported previously that fibronectin (FN) secreted by bone marrow mesenchymal stem cells (MSCs) was deposited on the surface of gelatin sponge (GS) soon after culture. In this study, we aimed to assess the function of accumulated FN on neuronal differentiating MSCs as induced by Schwann cells (SCs) in three dimensional transwell co‐culture system. The expression pattern and amount of FN of differentiating MSCs was examined by immunofluorescence, Western blot and immunoelectron microscopy. The results showed that FN accumulated inside GS scaffold, although its mRNA expression in MSCs was progressively decreased during neural induction. MSC‐derived neuron‐like cells showed spindle‐shaped cell body and long extending processes on FN‐decorated scaffold surface. However, after blocking of FN function by application of monoclonal antibodies, neuron‐like cells showed flattened cell body with short and thick neurites, together with decreased expression of integrin β1. In vivo transplantation study revealed that autocrine FN significantly facilitated endogenous nerve fiber regeneration in spinal cord transection model. Taken together, the present results showed that FN secreted by MSCs in the early stage accumulated on the GS scaffold and promoted the neurite elongation of neuronal differentiating MSCs as well as nerve fiber regeneration after spinal cord injury. This suggests that autocrine FN has a dynamic influence on MSCs in a three dimensional culture system and its potential application for treatment of traumatic spinal cord injury. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1902–1911, 2016.

Signaling of extracellular matrices for tissue regeneration and therapeutics

Cells receive important regulatory signals from their extracellular matrix (ECM) and the physical property of the ECM regulates important cellular behaviors like cell proliferation, migration and differentiation. A large part of tissue formation and regeneration depends on cellular interaction with its ECM. A comprehensive understanding of the mechanistic biochemical pathway of the ECM components is necessary for the design of a biomaterial scaffold for tissue engineering. Depending on the type of tissue, the ECM requirement might be different and this would influence its downstream intracellular cell signaling. Here, we reviewed the ECM and its signaling pathway by discussing: 1) classification of the ECM into hard, elastic and soft tissue based on its physical properties, 2) proliferation and differentiation control of the ECM, 3) roles of membrane receptor and its intracellular regulation factor, 4) ECM remodeling via inside-out signaling. By providing a comprehensive overview of the ECM's role in mechanotransduction and the self-regulatory effect of cells back on the ECM, we hope to provide a better insight of the physical and biochemical cues from the ECM. A sound understanding on the in vivo ECM has implication on the choice of materials and surface coating of biomimetic scaffolds used for tissue regeneration and therapeutics in a cell-free scaffold.

The lh3 Glycosyltransferase Directs Target-Selective Peripheral Nerve Regeneration

Functional PNS regeneration requires injured axons to return to their original synaptic targets, yet the mechanisms underlying target-selective regeneration have remained elusive. Using live-cell imaging in zebrafish we find that regenerating motor axons exhibit a strong preference for their original muscle territory and that axons probe both correct and incorrect trajectories extensively before selecting their original path. We show that this process requires the glycosyltransferase lh3 and that post-injury expression of lh3 in Schwann cells is sufficient to restore target-selective regeneration. Moreover, we demonstrate that Schwann cells neighboring the transection site express the lh3 substrate collagen4a5 and that during regeneration collagen4a5 destabilizes axons probing inappropriate trajectories to ensure target-selective regeneration, possibly through the axonal repellant slit1a. Our results demonstrate that selective ECM components match subpopulations of regenerating axons with their original targets and reveal a previously unappreciated mechanism that conveys synaptic target selection to regenerating axons in vivo. VIDEO ABSTRACT.

Substratum preferences of motor and sensory neurons in postnatal and adult rats

After peripheral nerve injuries, damaged axons can regenerate but functional recovery is limited by the specific reinnervation of targets. In this study we evaluated if motor and sensory neurites have a substrate preference for laminin and fibronectin in postnatal and adult stages. In postnatal dorsal root ganglia (DRG) explants, sensory neurons extended longer neurites on collagen matrices enriched with laminin (~50%) or fibronectin (~35%), whereas motoneurons extended longer neurites (~100%) in organotypic spinal cord slices embedded in fibronectin-enriched matrix. An increased percentage of parvalbumin-positive neurites (presumptive proprioceptive) vs. neurofilament-positive neurites was also found in DRG in fibronectin-enriched matrix. To test if the different preference of neurons for extracellular matrix components was maintained in vivo, these matrices were used to fill a chitosan guide to repair a 6-mm gap in the sciatic nerve of adult rats. However, the number of regenerating motor and sensory neurons after 1 month was similar between groups. Moreover, none of the retrotraced sensory neurons in DRG was positive for parvalbumin, suggesting that presumptive proprioceptive neurons had poor regenerative capabilities compared with other peripheral neurons. Using real-time PCR we evaluated the expression of α5β1 (receptor for fibronectin) and α7β1 integrin (receptor for laminin) in spinal cord and DRG 2 days after injury. Postnatal animals showed a higher increase of α5β1 integrin, whereas both integrins were similarly expressed in adult neurons. Therefore, we conclude that motor and sensory axons have a different substrate preference at early postnatal stages but this difference is lost in the adult.

Functionalized α-Helical Peptide Hydrogels for Neural Tissue Engineering

Trauma to the central and peripheral nervous systems often lead to serious morbidity. Current surgical methods for repairing or replacing such damage have limitations. Tissue engineering offers a potential alternative. Here we show that functionalized α-helical-peptide hydrogels can be used to induce attachment, migration, proliferation and differentiation of murine embryonic neural stem cells (NSCs). Specifically, compared with undecorated gels, those functionalized with Arg-Gly-Asp-Ser (RGDS) peptides increase the proliferative activity of NSCs; promote their directional migration; induce differentiation, with increased expression of microtubule-associated protein-2, and a low expression of glial fibrillary acidic protein; and lead to the formation of larger neurospheres. Electrophysiological measurements from NSCs grown in RGDS-decorated gels indicate developmental progress toward mature neuron-like behavior. Our data indicate that these functional peptide hydrogels may go some way toward overcoming the limitations of current approaches to nerve-tissue repair.

Transcriptome profiling of granulosa and theca cells during dominant follicle development in the horse

Several aspects of equine ovarian physiology are unique among domestic species. Moreover, follicular growth patterns are very similar between horses and humans. This study aimed to characterize, for the first time, global gene expression profiles associated with growth and preovulatory (PO) maturation of equine dominant follicles. Granulosa cells (GCs) and theca interna cells (TCs) were harvested from follicles (n = 5) at different stages of an ovulatory wave in mares corresponding to early dominance (ED; diameter ≥22 mm), late dominance (LD; ≥33 mm) and PO stage (34 h after administration of crude equine gonadotropins at LD stage), and separately analyzed on a horse gene expression microarray, followed by validation using quantitative PCR and immunoblotting/immunohistochemistry. Numbers of differentially expressed transcripts (DETs; ≥2-fold; P < 0.05) during the ED-LD and LD-PO transitions were 546 and 2419 in GCs and 5 and 582 in TCs. The most prominent change in GCs was the down-regulation of transcripts associated with cell division during both ED-LD and LD-PO. In addition, DET sets during LD-PO in GCs were enriched for genes involved in cell communication/adhesion, antioxidation/detoxification, immunity/inflammation, and cholesterol biosynthesis. In contrast, the largest change in TCs during the LD-PO transition was an up-regulation of genes involved in immune activation, with other DET sets mapping to GPCR/cAMP signaling, lipid/amino acid metabolism, and cell proliferation/survival and differentiation. In conclusion, distinct expression profiles were identified between growing and PO follicles and, particularly, between GCs and TCs within each stage. Several DETs were identified that have not been associated with follicle development in other species.

Neuregulin-1/glial growth factor stimulates Schwann cell migration by inducing α5 β1 integrin-ErbB2-focal adhesion kinase complex formation

After peripheral nerve injury, Schwann cells gain a migratory phenotype and remodel their extracellular matrix to provide a supportive environment for axonal regeneration. The soluble neuregulin-1 isoform, that is, glial growth factor (GGF), is expressed in regenerating axons of injured peripheral nerves and regulates Schwann cell motility by activating the ErbB family of tyrosine kinase receptors, but how GGF/ErbB signaling contributes to Schwann cell motility remains unclear. Here, we show that GGF stimulates Schwann cell migration by inducing the formation of a protein complex containing the fibronectin receptor α5β1 integrin, ErbB2, and focal adhesion kinase (FAK). ErbB2 co-localizes and co-immunoprecipitates with the focal complex members including α5β1 integrin and FAK after GGF treatment. These effects of GGF appear to involve FAK activation, which occurs downstream of ErbB2 stimulation. RNAi-mediated down-regulation of α5 integrin expression in primary cultured Schwann cells resulted in significantly decreased interaction between FAK and ErbB2, as well as decreased GGF-induced migration. An increase in the α5β1 integrin-ErbB2-FAK complex formation was observed in injured nerve Schwann cells, but not uninjured control. Taken together, these data suggest that GGF plays an important modulatory role in Schwann cell migration after nerve crush by inducing α5β1 integrin-ErbB2-FAK complex formation.

Proregenerative properties of ECM molecules

After traumatic injuries to the nervous system, regrowing axons encounter a complex microenvironment where mechanisms that promote regeneration compete with inhibitory processes. Sprouting and axonal regrowth are key components of functional recovery but are often counteracted by inhibitory molecules. This review covers extracellular matrix molecules that support neuron axonal outgrowth.

Specificity of peripheral nerve regeneration: interactions at the axon level

Peripheral nerves injuries result in paralysis, anesthesia and lack of autonomic control of the affected body areas. After injury, axons distal to the lesion are disconnected from the neuronal body and degenerate, leading to denervation of the peripheral organs. Wallerian degeneration creates a microenvironment distal to the injury site that supports axonal regrowth, while the neuron body changes in phenotype to promote axonal regeneration. The significance of axonal regeneration is to replace the degenerated distal nerve segment, and achieve reinnervation of target organs and restitution of their functions. However, axonal regeneration does not always allows for adequate functional recovery, so that after a peripheral nerve injury, patients do not recover normal motor control and fine sensibility. The lack of specificity of nerve regeneration, in terms of motor and sensory axons regrowth, pathfinding and target reinnervation, is one the main shortcomings for recovery. Key factors for successful axonal regeneration include the intrinsic changes that neurons suffer to switch their transmitter state to a pro-regenerative state and the environment that the axons find distal to the lesion site. The molecular mechanisms implicated in axonal regeneration and pathfinding after injury are complex, and take into account the cross-talk between axons and glial cells, neurotrophic factors, extracellular matrix molecules and their receptors. The aim of this review is to look at those interactions, trying to understand if some of these molecular factors are specific for motor and sensory neuron growth, and provide the basic knowledge for potential strategies to enhance and guide axonal regeneration and reinnervation of adequate target organs.

Extrinsic cellular and molecular mediators of peripheral axonal regeneration

The ability of injured peripheral nerves to regenerate and reinnervate their original targets is a characteristic feature of the peripheral nervous system (PNS). On the other hand, neurons of the central nervous system (CNS), including retinal ganglion cell (RGC) axons, are incapable of spontaneous regeneration. In the adult PNS, axonal regeneration after injury depends on well-orchestrated cellular and molecular processes that comprise a highly reproducible series of degenerative reactions distal to the site of injury. During this fine-tuned process, named Wallerian degeneration, a remodeling of the distal nerve fragment prepares a permissive microenvironment that permits successful axonal regrowth originating from the proximal nerve fragment. Therefore, a multitude of adjusted intrinsic and extrinsic factors are important for surviving neurons, Schwann cells, macrophages and fibroblasts as well as endothelial cells in order to achieve successful regeneration. The aim of this review is to summarize relevant extrinsic cellular and molecular determinants of successful axonal regeneration in rodents that contribute to the regenerative microenvironment of the PNS.

Fibronectin supports neurite outgrowth and axonal regeneration of adult brain neurons in vitro

The molecular basis of axonal regeneration of central nervous system (CNS) neurons remains to be fully elucidated. In part, this is due to the difficulty in maintaining CNS neurons in vitro. Here, we show that dissociated neurons from the cerebral cortex and hippocampus of adult mice may be maintained in culture for up to 9 days in defined medium without added growth factors. Outgrowth of neurites including axons was observed from both CNS sources and was significantly greater on plasma fibronectin than on other substrata such as laminin and merosin. Neurite outgrowth on fibronectin appears to be mediated by α5β1 integrin since a recombinant fibronectin fragment containing binding sites for this receptor was as effective as intact fibronectin in supporting neurite outgrowth. Conversely, function-blocking antibodies to α5 and β1 integrin sub-units inhibited neurite outgrowth on intact fibronectin. These results suggest that the axonal regeneration seen in in vivo studies using fibronectin-based matrices is due to the molecule itself and not a consequence of secondary events such as cellular infiltration. They also indicate the domains of fibronectin that may be responsible for eliciting this response.

Vimentin phosphorylation by Cdc2 in Schwann cell controls axon growth via β1-integrin activation

Although preconditioning injury on the peripheral nerve induces axonal regenerative capacity in neurons, it is not known whether similar lesion effects occur in glial cells. Here we demonstrate that Schwann cells are activated by peripheral nerve preinjury and primed to mediate axon regeneration. Cdc2, which was induced from Schwann cells after sciatic nerve injury, phosphorylated vimentin almost exclusively in the distal nerve area. Phospho-vimentin-positive Schwann cells showed increased migration activity and were in close contact with process outgrowth of co-cultured neurons. Vimentin phosphorylation by Cdc2 was involved in β1-integrin activation leading to FAK phoshorylation and associated with Erk1/2 activation in Schwann cells. Neurite outgrowth of dorsal root ganglion neurons was increased by co-culture with activated Schwann cells, in which phospho-vimentin signaling was transmitted into β1-integrin activation. Then neurite outgrowth was suppressed by genetic depletion of phospho-vimentin and β1 integrin as well as inhibition of vimentin phosphorylation by Cdc2 inhibitor purvalanol A. The sciatic nerve graft harboring activated Schwann cells into the spinal cord induced Schwann cell migration beyond the graft-host barrier and facilitated regeneration of spinal axons, which was inhibited by purvalanol A pretreatment of the graft. This is the first report to our knowledge demonstrating that activation of phospho-vimentin linked to β1-integrin pathway may mediate transcellular signaling to promote axon growth.

Urokinase plasminogen receptor and the fibrinolytic complex play a role in nerve repair after nerve crush in mice, and in human neuropathies

Remodeling of extracellular matrix (ECM) is a critical step in peripheral nerve regeneration. In fact, in human neuropathies, endoneurial ECM enriched in fibrin and vitronectin associates with poor regeneration and worse clinical prognosis. Accordingly in animal models, modification of the fibrinolytic complex activity has profound effects on nerve regeneration: high fibrinolytic activity and low levels of fibrin correlate with better nerve regeneration. The urokinase plasminogen receptor (uPAR) is a major component of the fibrinolytic complex, and binding to urokinase plasminogen activator (uPA) promotes fibrinolysis and cell movement. uPAR is expressed in peripheral nerves, however, little is known on its potential function on nerve development and regeneration. Thus, we investigated uPAR null mice and observed that uPAR is dispensable for nerve development, whereas, loss of uPAR affects nerve regeneration. uPAR null mice showed reduced nerve repair after sciatic nerve crush. This was a consequence of reduced fibrinolytic activity and increased deposition of endoneurial fibrin and vitronectin. Exogenous fibrinolysis in uPAR null mice rescued nerve repair after sciatic nerve crush. Finally, we measured the fibrinolytic activity in sural nerve biopsies from patients with peripheral neuropathies. We showed that neuropathies with defective regeneration had reduced fibrinolytic activity. On the contrary, neuropathies with signs of active regeneration displayed higher fibrinolytic activity. Overall, our results suggest that enforced fibrinolysis may facilitate regeneration and outcome of peripheral neuropathies.

Fibronectin inhibits chronic pain development after spinal cord injury

Chronic pain following spinal cord injury (SCI) is a highly prevalent clinical condition that is difficult to treat. Using both von Frey filaments and radiant infrared heat to assess mechanical allodynia and thermal hyperalgesia, respectively, we have demonstrated that a one-time injection of fibronectin (50 μg/mL) into the spinal dorsal column (1 μL/min each injection for a total of 5 μL) immediately after SCI inhibits the development of mechanical allodynia (but not thermal hyperalgesia) over an 8-month observation period following spinal cord dorsal column crush (DCC). DCC will only induce mechanical Allodynia, but not thermal hyperalgesia or overt motor deficits. By applying various fibronectin fragments as well as competitive inhibitors, these effects were shown to be dependent on the connecting segment-1 (CS-1) motif of fibronectin. Furthermore, we found that acute fibronectin treatment diminished inflammation and blood-spinal cord barrier permeability, which in turn leads to enhanced fiber sparing and sprouting. In particular, the reduction of serotonin (5-HT) in the superficial dorsal horn, an important descending brainstem system in the modulation of pain, was blocked with fibronectin treatment. We conclude that treatment of SCI with fibronectin preserves sensory regulation and prevents the development of chronic allodynia, providing a potential therapeutic intervention to treat chronic pain following SCI.

Integrins as receptor targets for neurological disorders

This review focuses on the neurobiology of integrins, pathophysiological roles of integrins in neuroplasticity and nervous system disorders, and therapeutic implications of integrins as potential drug targets and possible delivery pathways. Neuroplasticity is a central phenomenon in many neurological conditions such as seizures, trauma, and traumatic brain injury. During the course of many brain diseases, in addition to intracellular compartment changes, alterations in non-cell compartments such as extracellular matrix (ECM) are recognized as an essential process in forming and reorganizing neural connections. Integrins are heterodimeric transmembrane receptors that mediate cell-ECM and cell-cell adhesion events. Although the mechanisms of neuroplasticity remain unclear, it has been suggested that integrins undergo plasticity including clustering through interactions with ECM proteins, modulating ion channels, intracellular Ca(2+) and protein kinase signaling, and reorganization of cytoskeletal filaments. As cell surface receptors, integrins are central to the pathophysiology of many brain diseases, such as epilepsy, and are potential targets for the development of new drugs for neurological disorders.

Matrix metalloproteinase-8 is involved in dermal nerve growth: implications for possible application to pruritus from in vitro models

Cutaneous nerve density is related to abnormal itch perception in dermatoses, such as atopic dermatitis and xerosis. However, the mechanisms underlying the elongation of dermal nerve fibers within the interstitial collagen (CoL) matrix are poorly understood. In this study, a culture system of rat dorsal root ganglion neurons consisting of type I CoL and a Boyden chamber containing a nerve growth factor (NGF) concentration gradient was used. Nerve fibers penetrating into type I CoL gel were observed in the presence of the NGF concentration gradient. Levels of matrix metalloproteinase-8 (MMP-8) mRNA and protein were increased in the cultured neurons and the conditioned medium, respectively. The nerve fiber penetration was dose dependently inhibited by MMP-8 blockers. Moreover, MMP-8 immunoreactivity was partially localized at growth cones in NGF-responsive nerve fibers. Semaphorin 3A stimulation also showed the opposite effects on these NGF-dependent events. Intriguingly, MMP-8 expression was upregulated by type I and III CoLs, which are substrates for this enzyme. These results suggested that MMP-8 is involved in sensory nerve growth within the interstitial CoL matrix through modulation by the axonal guidance molecules and/or extracellular matrix components. These findings provide insight into the development of pruritus involving skin nerve density.

Wallerian degeneration and peripheral nerve conditions for both axonal regeneration and neuropathic pain induction

Wallerian degeneration is a cascade of stereotypical events in reaction to injury of nerve fibres. These events consist of cellular and molecular alterations, including macrophage invasion, activation of Schwann cells, as well as neurotrophin and cytokine upregulation. This review focuses on cellular and molecular changes distal to various types of peripheral nerve injury which simultaneously contribute to axonal regeneration and neuropathic pain induction. In addition to the stereotypical events of Wallerian degeneration, various types of nerve damage provide different conditions for both axonal regeneration and neuropathic pain induction. Wallerian degeneration of injured peripheral nerve is associated with an inflammatory response including rapid upregulation of the immune signal molecules like cytokines, chemokines and transcription factors with both beneficial and detrimental effects on nerve regeneration or neuropathic pain induction. A better understanding of the molecular interactions between the immune system and peripheral nerve injury would open the possibility for targeting these inflammatory mediators in therapeutic interventions. Understanding the pleiotropic effects of cytokines/chemokines, however, requires investigating their highly specific pathways and precise points of action.

Conditional knockout of fibronectin abrogates mouse mammary gland lobuloalveolar differentiation

Fibronectin (Fn) plays an important part in the branching morphogenesis of salivary gland, lung, and kidney. Here, we examine the effect of the conditional knockout of Fn in the mammary epithelium [Fn(MEp-/-)] on postnatal mammary gland development, using Cre-loxP-mediated gene knockout technology. Our data show that Fn deletion causes a moderate retardation in outgrowth and branching of the ductal tree in 5-week-old mice. These defects are partially compensated in virgin 16-week-old mice. However, mammary glands consisting of Fn-deficient epithelial cells fail to undergo normal lobuloalveolar differentiation during pregnancy. The severity of lobuloalveolar impairment ranged from lobular hypoplasia to aplasia in some cases and was associated with the amount of Fn protein recovered from these glands. Decreased rates of mammary epithelial cell proliferation accounted for delayed ductal outgrowth in virgin and lack of alveologenesis in pregnant Fn(MEp-/-) mice. Concomitant decreased expression of integrin beta(1) (Itgb1) and lack of autophosphorylation of focal adhesion kinase (Fak) suggest that this pathology might, at least in part, be mediated by disruption of the Fn/Itgb1/Fak signaling pathway.

Erythropoietin promotes Schwann cell migration and assembly of the provisional extracellular matrix by recruiting beta1 integrin to the cell surface

In peripheral nerve injury, Schwann cells undergo profound phenotypic modulation, adopting a migratory phenotype and remodeling the extracellular matrix so that it is permissive for axonal regrowth. Erythropoietin (Epo) and its receptor (EpoR) are expressed by Schwann cells after nerve injury, regulating inflammatory cytokine expression and minimizing the duration of neuropathic pain. The mechanism of Epo activity in the injured peripheral nerve remains incompletely understood. Herein, we demonstrate that Epo promotes Schwann cell migration in vitro on fibronectin (FN)-coated surfaces. Epo also rapidly recruits beta1 integrin subunit to the Schwann cell surface by a JAK-2-dependent pathway. Although beta1 integrin subunit-containing integrins were not principally responsible for Schwann cell adhesion or migration on FN under basal conditions, beta1 gene-silencing blocked the ability of Epo to promote cell migration. Epo also induced Schwann cell FN expression in vitro and in vivo. The FN was organized into insoluble fibrils by Epo-treated Schwann cells in vitro and into an extensive matrix surrounding Schwann cells in vivo. Our results support a model in which Epo promotes Schwann cell migration and assembly of the provisional extracellular matrix in the injured peripheral nerve by its effects on integrin recruitment to the cell surface and local FN production.

Synergistic effects of osteonectin and brain-derived neurotrophic factor on axotomized retinal ganglion cells neurite outgrowth via the mitogen-activated protein kinase-extracellular signal-regulated kinase 1/2 pathways

Our previous study identified osteonectin (ON) in a screen of factors made by Schwann cells (SCs) which promoted peripheral and central neurons survival and neuritogenesis, however, the mechanisms of ON promoting effects are largely unknown. In the present study, we investigated the effects of ON-deficient SC-conditioned medium (SCCM) and molecular mechanisms of ON, in regulating retinal ganglion cells (RGCs) survival and neurite outgrowth. Neonatal rat RGCs and SCs were purified by immunopanning technique. RGC survival and neuritogenesis reduced significantly when treated with either ON-null mice SCCM or ON-immunodepleted (IP) SCCM (P<0.05). In contrast to wild type SCCM, in the presence of a tyrosine kinase receptor (Trk) inhibitor (K252a), ON-null mice SCCM-induced neuritogenesis were further reduced by 24%. The Trk-mediated signaling pathways became more sensitive to K252a inhibition in the absence of ON. We also showed the synergistic effects of ON and brain-derived neurotrophic factor (BDNF) in promoting RGCs growth and the involvement of ON in two major neurotrophin-mediated signaling pathways, PI-3K-Akt and MAPK-Erk1/2. ON alone activated Akt phosphorylation and increased survival. Blockage of TrkB signalling pathway by TrkB-Fc chimera (BDNF scavenger) or K252a in ON-treated cultures reduced Akt-P level significantly. This suggests that ON induces BDNF synthesis and secretion from RGCs. The enhancement of neuritogenesis and Erk1/2 phosphorylation by ON in BDNF-treated cultures further demonstrate the signaling pathways responsible for the synergistic effect of ON on BDNF-induced neurite outgrowth. To the best of our knowledge, this is the first report showing the synergistic effects of ON on classical neurotrophins which participate in the same signalling pathways in regulating RGC neurite outgrowth.

Expression of alpha5 integrin rescues fibronectin responsiveness in NT2N CNS neuronal cells

The extracellular matrix protein fibronectin is implicated in neuronal regeneration in the peripheral nervous system. In the central nervous system (CNS), fibronectin is up-regulated at sites of penetrating injuries and stroke; however, CNS neurons down-regulate the fibronectin receptor alpha5beta1 integrin during differentiation and generally respond poorly to fibronectin. NT2N CNS neuron-like cells (derived from NT2 precursor cells) have been used in preclinical and clinical studies for treatment of stroke and a variety of CNS injury and disease models. Here we show that, like primary CNS neurons, NT2N cells down-regulate alpha5beta1 integrin during differentiation and respond poorly to fibronectin. The poor neurite outgrowth by NT2N cells on fibronectin can be rescued by transducing NT2 precursors with a retroviral vector expressing alpha5 integrin under the control of the murine stem cell virus 5' long terminal repeat. Sustained alpha5 integrin expression is compatible with the CNS-like neuronal differentiation of NT2N cells and does not prevent robust neurite outgrowth on other integrin ligands. Thus, alpha5 integrin expression in CNS neuronal precursor cells may provide a strategy for enhancing the outgrowth and survival of implanted cells in cell-replacement therapies for CNS injury and disease.

Alterations in integrin expression modulates invasion of pancreatic cancer cells

BACKGROUND

Factors mediating the invasion of pancreatic cancer cells through the extracellular matrix (ECM) are not fully understood.

METHODS

In this study, sub-populations of the human pancreatic cancer cell line, MiaPaCa-2 were established which displayed differences in invasion, adhesion, anoikis, anchorage-independent growth and integrin expression.

RESULTS

Clone #3 displayed higher invasion with less adhesion, while Clone #8 was less invasive with increased adhesion to ECM proteins compared to MiaPaCa-2. Clone #8 was more sensitive to anoikis than Clone #3 and MiaPaCa-2, and displayed low colony-forming efficiency in an anchorage-independent growth assay. Integrins beta 1, alpha 5 and alpha 6 were over-expressed in Clone #8. Using small interfering RNA (siRNA), integrin beta1 knockdown in Clone #8 cells increased invasion through matrigel and fibronectin, increased motility, decreased adhesion and anoikis. Integrin alpha 5 and alpha 6 knockdown also resulted in increased motility, invasion through matrigel and decreased adhesion.

CONCLUSION

Our results suggest that altered expression of integrins interacting with different extracellular matrixes may play a significant role in suppressing the aggressive invasive phenotype. Analysis of these clonal populations of MiaPaCa-2 provides a model for investigations into the invasive properties of pancreatic carcinoma.

Integrin beta 4 in neural cells

Integrin beta 4, one of the heterodimeric receptors, is expressed predominantly on epithelial cells. It is concentrated at the basement membrane zone, where it localizes to specialized adhesion structures called hemidesmosomes. In addition to its adhesive functions, novel insights have emerged regarding the specific roles of integrin beta 4 in their attachment to extracellular matrix and in their signal transduction pathways within the central nervous system (CNS) and peripheral nervous system in the past few years. It has been reported that integrin beta 4 is expressed in several kinds of neural cells including astrocyte, Schwann cells, neurons, and neural stem cells. In the mean while, it is expressed by some Schwann cells in the peripheral nervous system and mediated the Mycobacterium leprae invade the peripheral nervous system to reach the Schwann cells. This review highlights recent progress in the function and regulation of integrin beta 4 in neural cells.

Peripheral regeneration

Whereas the central nervous system (CNS) usually cannot regenerate, peripheral nerves regenerate spontaneously after injury because of a permissive environment and activation of the intrinsic growth capacity of neurons. Functional regeneration requires axon regrowth and remyelination of the regenerated axons by Schwann cells. Multiple factors including neurotrophic factors, extracellular matrix (ECM) proteins, and hormones participate in Schwann cell dedifferentiation, proliferation, and remyelination. We describe the current understanding of peripheral axon regeneration and focus on the molecules and potential mechanisms involved in remyelination.

Neurite outgrowth on a fibronectin isoform expressed during peripheral nerve regeneration is mediated by the interaction of paxillin with alpha4beta1 integrins

BACKGROUND

The regeneration of peripheral nerve is associated with a change in the alternative splicing of the fibronectin primary gene transcript to re-express embryonic isoforms containing a binding site for alpha4beta1 integrins that promote neurite outgrowth. Here we use PC12 cells to examine the role of the interaction between paxillin and the alpha4 integrin cytoplasmic domain in neurite outgrowth.

RESULTS

Expression of alpha4 with mutations in the paxillin-binding domain reduced neurite outgrowth on recombinant embryonic fibronectin fragments relative to wild type alpha4. Over-expression of paxillin promoted neurite outgrowth while a mutant isoform lacking the LD4 domain implicated in the regulation of ARF and Rac GTPases was less effective. Optimal alpha4-mediated migration in leucocytes requires spatial regulation of alpha4 phosphorylation at Ser988, a post-translational modification that blocks paxillin binding to the integrin cytoplasmic domain. In keeping with this alpha4(S988D), which mimics phosphorylated alpha4, did not promote neurite outgrowth. However, alpha4 was not phosphorylated in the PC12 cells, and a non-phosphorylatable alpha4(S988A) mutant promoted neurite outgrowth indistinguishably from the wild type integrin.

CONCLUSION

We establish the importance of the alpha4 integrin-paxillin interaction in a model of axonal regeneration and highlight differing dependence on phosphorylation of alpha4 for extension of neuronal growth cones and migration of non-neural cells.