Merosin promotes neurite growth and Schwann cell migration in vitro and nerve regeneration in vivo: evidence using an antibody to merosin, ARM-1

LAMA2 Neuropathies: Human Findings and Pathomechanisms From Mouse Models

Merosin deficient Congenital Muscular Dystrophy (MDC1A), or LAMA2-related muscular dystrophy (LAMA2-RD), is a recessive disorder resulting from mutations in the LAMA2 gene, encoding for the alpha-2 chain of laminin-211. The disease is predominantly characterized by progressive muscular dystrophy affecting patient motor function and reducing life expectancy. However, LAMA2-RD also comprises a developmentally-associated dysmyelinating neuropathy that contributes to the disease progression, in addition to brain abnormalities; the latter often underappreciated. In this brief review, we present data supporting the impact of peripheral neuropathy in the LAMA2-RD phenotype, including both mouse models and human studies. We discuss the molecular mechanisms underlying nerve abnormalities and involved in the laminin-211 pathway, which affects axon sorting, ensheathing and myelination. We conclude with some final considerations of consequences on nerve regeneration and potential therapeutic strategies.

Review : Axons, Schwann Cells, and Neurotrophic Factors

As most elegantly confirmed by the recent success in deriving mice with null mutations in the genes for specific neurotrophic factors or their respective receptors, it is clear that neurotrophic factors alone or in combination are essential for the development of many classes of neurons. Specific neurotrophic factors have now been characterized that have actions on primary sensory afferents, sympathetic and parasym pathetic neurons, and motor neurons—the major contributors to the axon bundles that comprise the periph eral nervous system. The peripheral tissues or "end organs" that these neurons innervate have traditionally been thought of as the key source of neurotrophic factor support, but it is now evident that this "target- derived neurotrophic factor hypothesis" has restricted validity. Rather, the totality of neurotrophic support required to promote the survival, maturation, and maintenance of a neuron appears to be derived not only from targets, but also from support cells and possibly even neurons themselves. In this article, we review the role played by multiple sources of neurotrophic factors, especially factors derived from non-neuronal cells, not only in development, but also in the maintenance and regenerative responses of the adult PNS. In par ticular, we focus on neurotrophic factors of the neurotrophin family and ciliary neurotrophic factor. The Neuro scientist 1:192-199, 1995

Retinoic acid regulates Schwann cell migration via NEDD9 induction by transcriptional and post-translational mechanisms

Schwann cell migration is essential during the regenerative response to nerve injury, however, the factors that regulate this phenomenon are not yet clear. Here we describe that retinoic acid (RA), whose production and signaling activity are greatly enhanced during nerve regeneration, increases Schwann cell migration. This is accompanied by the up-regulation of NEDD9, a member of the CAS family of scaffold proteins previously implicated in migratory and invasive behavior in gliomas, melanomas and the neural crest cells from which Schwann cells derive. This RA-induced NEDD9 accumulation is due to augmented mRNA levels, as well as an increase of NEDD9 protein stability. Although all NEDD9 phospho-isoforms present in Schwann cells are induced by the retinoid, the hormone also changes its phosphorylation status, thus altering the ratio between the different isoforms. Silencing NEDD9 in Schwann cells had no effect on basal migratory ability, but completely abrogated RA-induced enhanced migration. Collectively, our results indicate that RA could be a major regulator of Schwann cell migration after nerve injury, thus offering a new insight into peripheral nerve repair.

Protocatechuic Acid from Alpinia oxyphylla Induces Schwann Cell Migration via ERK1/2, JNK and p38 Activation

Alpinia oxyphylla MIQ (Alpinate Oxyphyllae Fructus, AOF) is an important traditional Chinese medicinal herb whose fruits is widely used to prepare tonics and is used as an aphrodisiac, anti salivary, anti diuretic and nerve-protective agent. Protocatechuic acid (PCA), a simple phenolic compound was isolated from the kernels of AOF. This study investigated the role of PCA in promoting neural regeneration and the underlying molecular mechanisms. Nerve regeneration is a complex physiological response that takes place after injury. Schwann cells play a crucial role in the endogenous repair of peripheral nerves due to their ability to proliferate and migrate. The role of PCA in Schwann cell migration was determined by assessing the induced migration potential of RSC96 Schwann cells. PCA induced changes in the expression of proteins of three MAPK pathways, as determined using Western blot analysis. In order to determine the roles of MAPK (ERK1/2, JNK, and p38) pathways in PCA-induced matrix-degrading proteolytic enzyme (PAs and MMP2/9) production, the expression of several MAPK-associated proteins was analyzed after siRNA-mediated inhibition assays. Treatment with PCA-induced ERK1/2, JNK, and p38 phosphorylation that activated the downstream expression of PAs and MMPs. PCA-stimulated ERK1/2, JNK and p38 phosphorylation was attenuated by individual pretreatment with siRNAs or MAPK inhibitors (U0126, SP600125, and SB203580), resulting in the inhibition of migration and the uPA-related signal pathway. Taken together, our data suggest that PCA extract regulate the MAPK (ERK1/2, JNK, and p38)/PA (uPA, tPA)/MMP (MMP2, MMP9) mediated regeneration and migration signaling pathways in Schwann cells. Therefore, PCA plays a major role in Schwann cell migration and the regeneration of damaged peripheral nerve.

Alpinia Oxyphylla Miquel Fruit Extract Activates MAPK-mediated Signaling of PAs and MMP2/9 to Induce Schwann Cell Migration and Nerve Regeneration

Objectives

This study investigates the molecular mechanisms by which Alpiniae oxyphyllae fructus (AOF) promotes neuron regeneration.

Methods

A piece of silicone rubber was guided across a 15 mm gap in the sciatic nerve of a rat. This nerve gap was then filled with different concentrations of AOF extract (0-200 mg/ml). We investigated the role of MAPK (ERK1/2, JNK and p38) pathways for AOF-induced matrix-degrading proteolytic enzyme (PAs and MMP2/9) production in RSC96 Schwann cells.

Results

The results showed that AOF increased the expressions of uPA, tPA, MMP-9, and MAPKs in vivo. In vitro, our results show that treatment with AOF extract induces ERK1/2, JNK, and p38 phosphorylation to activate the downstream PAs and MMPs signaling expression. AOF-stimulated ERK1/2, JNK, and p38 phosphorylation attenuated by individual pretreatment with siRNAs or inhibitors (U0126, SP600125 and SB203580), resulting in migration and uPA-related signal pathway inhibition.

Conclusions

Taken together our data suggests the MAPKs (ERK1/2, JNK and p38), PAs (uPA, tPA), MMP (MMP2, MMP9) regenerative and migration signaling pathway of Schwann cells regulated by AOF extract might play a major role in Schwann cell migration and damaged peripheral nerve regeneration.

Inflammation modulates expression of laminin in the central nervous system following ischemic injury

BACKGROUND

Ischemic stroke induces neuronal death in the core of the infarct within a few hours and the secondary damage in the surrounding regions over a long period of time. Reduction of inflammation using pharmacological reagents has become a target of research for the treatment of stroke. Cyclooxygenase 2 (COX-2), a marker of inflammation, is induced during stroke and enhances inflammatory reactions through the release of enzymatic products, such as prostaglandin (PG) E2.

METHODS

Wild-type (WT) and COX-2 knockout (COX-2KO) mice were subjected to middle cerebral artery occlusion (MCAO). Additionally, brain slices derived from these mice or brain microvascular endothelial cells (BMECs) were exposed to oxygen-glucose deprivation (OGD) conditions. The expression levels of extracellular matrix (ECM) proteins were assessed and correlated with the state of inflammation.

RESULTS

We found that components of the ECM, and specifically laminin, are transiently highly upregulated on endothelial cells after MCAO or OGD. This upregulation is not observed in COX-2KO mice or WT mice treated with COX-2 inhibitor, celecoxib, suggesting that COX-2 is associated with changes in the levels of laminins.

CONCLUSIONS

Taken together, we report that transient ECM remodeling takes place early after stroke and suggest that this increase in ECM protein expression may constitute an effort to revascularize and oxygenate the tissue.

Facile micropatterning of dual hydrogel systems for 3D models of neurite outgrowth

Understanding how microenvironmental factors influence neurite growth is important to inform studies in nerve regeneration, plasticity, development, and neurophysiology. In vitro models attempting to more accurately mimic the physiological environment by provision of a 3D growth matrix may provide useful foundations. Some limitations of thick 3D culture models include hampered solute transport, less-robust neurite growth than on 2D substrates, and difficulty in achieving spatial control of growth. To this end, we describe a 3D dual hydrogel model for embryonic rat day 15 dorsal root ganglion tissue explant growth using a digital micromirror device for dynamic mask projection photolithography. The photolithography method developed allowed simple, reproducible, one-step fabrication of thick hydrogel constructs on a variety of substrates, including permeable cell culture inserts. The relationships between projected mask size, crosslinked hydrogel resolution, and gel thickness were characterized, and resolution was found generally to decrease with increasing gel thickness. Cell viability in thick (481 μm) hydrogel constructs was significantly greater on permeable supports than glass, suggesting transport limitations were somewhat alleviated. The observed neurite growth was abundant and occurred in a spatially controlled manner throughout the 3D environment, a crucial step in the quest for a more effective biomimetic model of neurite outgrowth.

Carboxymethylated chitosan stimulates proliferation of Schwann cells in vitro via the activation of the ERK and Akt signaling pathways

Proliferation of Schwann cell in the injured peripheral nerve supports axonal regeneration and also is critical for the regeneration of injured nerves. In this publication, carboxymethylated chitosan (CMCS) was studied to determine its capacity (i) to induce proliferation and synthesis of proliferating cell nuclear antigen (PCNA) and (ii) to activate mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK/ERK) and phosphatidylinositil-3 kinase (PI3K)/Akt signaling pathways in rat Schwann cells. CMCS was found to induce proliferation and PCNA synthesis in Schwann cells in a dose and time dependent manner. CMCS was shown to phosphorylate ERK1/2 and Akt in Schwann cell proliferation. The phosphorylation of ERK1/2 and Akt in Schwann cells was blocked by the MEK inhibitor PD98059 and the PI3K inhibitor wortmannin. In addition, inhibition of the MEK/ERK or the PI3K/Akt signaling pathways significantly decreased the proliferative effects of CMCS in Schwann cells. Overall, the above results indicate that CMCS stimulates proliferation of Schwann cells by activating the intracellular signaling cascades of ERK1/2 and PI3K/Akt.

Dilong: role in peripheral nerve regeneration

Dilong, also known as earthworm, has been widely used in traditional Chinese medicine (TCM) for thousands of years. Schwann cell migration and proliferation are critical for the regeneration of injured nerves and Schwann cells provide an essentially supportive role for neuron regeneration. However, the molecular mechanisms of migration and proliferation induced by dilongs in Schwann cells remain unclear. Here, we discuss the molecular mechanisms that includes (i) migration signaling, MAPKs (mitogen-activated protein kinases), mediated PAs and MMP2/9 pathway; (ii) survival and proliferative signaling, IGF-I (insulin-like growth factor-I)-mediated PI3K/Akt pathways and (iii) cell cycle regulation. Dilong stimulate RSC96 cell proliferation and migration. It can induce phosphorylation of ERK1/2 and p38, but not JNK, and activate the downstream signaling expression of PAs (plasminogen activators) and MMPs (matrix metalloproteinases) in a time-dependent manner. In addition, Dilong stimulated ERK1/2 and p38 phosphorylation was attenuated by pretreatment with chemical inhibitors (U0126 and SB203580), and small interfering ERK1/2 and p38 RNA, resulting in migration and uPA-related signal pathway inhibition. Dilong also induces the phosphorylation of IGF-I-mediated PI3K/Akt pathway, activates protein expression of PCNA (proliferating cell nuclear antigen) and cell cycle regulatory proteins (cyclin D1, cyclin E and cyclin A) in a time-dependent manner. In addition, it accelerates G₁-phase progression with earlier S-phase entry and significant numbers of cells entered the S-phase. The siRNA-mediated knockdown of PI3K that significantly reduces PI3K protein expression levels, resulting in Bcl₂ survival factor reduction, revealing a marked blockage of G₁ to S transition in proliferating cells. These results reveal the unknown RSC96 cell migration and proliferation mechanism induced by dilong, which find use as a new medicine for nerve regeneration.

Schwann Cell Migration Induced by Earthworm Extract via Activation of PAs and MMP2/9 Mediated through ERK1/2 and p38

The earthworm, which has stasis removal and wound-healing functions, is a widely used Chinese herbal medicine in China. Schwann cell migration is critical for the regeneration of injured nerves. Schwann cells provide an essentially supportive activity for neuron regeneration. However, the molecular migration mechanisms induced by earthworms in Schwann cells remain unclear. Here, we investigate the roles of MAPK (ERK1/2, JNK and p38) pathways for earthworm-induced matrix-degrading proteolytic enzyme (PAs and MMP2/9) production in Schwann cells. Moreover, earthworm induced phosphorylation of ERK1/2 and p38, but not JNK, activate the downstream signaling expression of PAs and MMPs in a time-dependent manner. Earthworm-stimulated ERK1/2 and p38 phosphorylation was attenuated by pretreatment with U0126 and SB203580, resulting in migration and uPA-related signal pathway inhibition. The results were confirmed using small interfering ERK1/2 and p38 RNA. These results demonstrated that earthworms can stimulate Schwann cell migration and up-regulate PAs and MMP2/9 expression mediated through the MAPK pathways, ERK1/2 and p38. Taken together, our data suggests the MAPKs (ERK1/2, p38)-, PAs (uPA, tPA)-, MMP (MMP2, MMP9) signaling pathway of Schwann cells regulated by earthworms might play a major role in Schwann cell migration and nerve regeneration.

Neuroprotective effect of atorvastatin in an experimental model of nerve crush injury

BACKGROUND

Statins have therapeutic benefits for the management of several disorders. A short-term course of a high-dose statin pretreatment has demonstrated neuroprotective effects against neurological diseases. However, the molecular basis underlying the neuroprotective action of statins remains unclear.

OBJECTIVE

We investigated whether a short-term course of high-dose atorvastatin pretreatment has beneficial effects in protecting sciatic nerve from crush injury.

METHODS

Atorvastatin (5 mg/kg) or saline was given orally to Sprague-Dawley rats for 7 days before injury. The rats were subjected to crush injury in the left sciatic nerve with a vessel clamp. Biochemical, functional, electrophysiological, and morphological alterations occurring during injury-induced degeneration/regeneration were examined.

RESULTS

Atorvastatin improved injury-induced neurobehavioral/electrophysiological changes and axonal loss. Damage-associated alterations, including structural disruption, oxidative stress, inflammation, and apoptosis, were attenuated by atorvastatin. After injury, regeneration-associated genes, including growth-associated protein-43, myelin basic protein, ciliary neurotrophic factor, and collagen, were upregulated by atorvastatin. The suppression of extracellular signal-regulated kinase, AKT, signal transducer and activators of transcription-1, and necrosis factor-kappaB and the elevated activation of c-Jun N-terminal kinase, Smad2/3, and activating protein-1 were associated with the neuroprotective action of atorvastatin.

CONCLUSION

These findings suggest that a short-term course of high-dose atorvastatin pretreatment can protect against sciatic nerve crush injury through modifying intracellular or extracellular environments, making it favorable for regeneration.

Transplantation of bone marrow stromal cells for peripheral nerve repair

Cell transplantation using bone marrow stromal cells (BMSCs) to alleviate neurological deficits has recently become the focus of research in regenerative medicine. Evidence suggests that secretion of various growth-promoting substances likely plays an important role in functional recovery against neurological diseases. In an attempt to identify a possible mechanism underlying the regenerative potential of BMSCs, this study investigated the production and possible contribution of neurotrophic factors by transected sciatic nerve defect in a rat model with a 15 mm gap. Cultured BMSCs became morphologically homogeneous with fibroblast-like shape after ex vivo expansion. We provided several pieces of evidence for the beneficial effects of implanted fibroblast-like BMSCs on sciatic nerve regeneration. When compared to silicone tube control animals, this treatment led to (i) improved walking behavior as measured by footprint analysis, (ii) reduced loss of gastrocnemius muscle weight and EMG magnitude, and (iii) greater number of regenerating axons within the tube. Cultured fibroblast-like BMSCs constitutively expressed trophic factors and supporting substances, including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), ciliary neurotrophic factor (CNTF), collagen, fibronectin, and laminin. The progression of the regenerative process after BMSC implantation was accompanied by elevated expression of neurotrophic factors at both early and later phases. These results taken together, in addition to documented Schwann cell-like differentiation, provide evidence indicating the strong association of neurotrophic factor production and the regenerative potential of implanted BMSCs.

Cdc2-mediated Schwann cell migration during peripheral nerve regeneration

Schwann cell migration facilitates peripheral nerve regeneration after injury. We have recently found increased activation of Cdc2 kinase in regenerating sciatic nerves. Here we show that Cdc2 phosphorylation of caldesmon regulates Schwann cell migration and nerve regeneration. A robust but transient increase in Cdc2 expression was found in cultured Schwann cells prepared from the sciatic nerve in rats that had undergone crush injury for 7 days. These `injury-preconditioned' Schwann cells exhibited enhanced migration compared with non-preconditioned control cells and treatment with the cdk inhibitor roscovitine prevented cell migration. After transduction with recombinant Cdc2 DNA adenoviral vectors, Schwann cells were implanted into sciatic nerves; those expressing wild-type Cdc2 migrated further in the distal direction than those expressing dominant-negative Cdc2. We identified caldesmon as a downstream substrate of Cdc2 in Schwann cells and its phosphorylation by Cdc2 changed its subcellular localization. Overexpression of dominant-negative caldesmon significantly counteracted the migration effect caused by Cdc2. Finally, neurite outgrowth of cultured DRG sensory neurons, facilitated by co-culture with injury-preconditioned Schwann cells, was suppressed by roscovitine treatment. The results indicate that activation of the Cdc2-caldesmon pathway is necessary for Schwann cell migration and suggest a role for this pathway in peripheral axonal growth.

Modulation of extracellular matrix components by metalloproteinases and their tissue inhibitors during degeneration and regeneration of rat sural nerve

The success of peripheral nervous system regeneration has been associated with changes on the microenvironment, particularly on the extracellular matrix (ECM) components. In the present study we analyzed by indirect immunohistochemistry, electron microscopy and Western blotting, the distribution of ECM components, metalloproteinases (MMPs) and their tissue inhibitors (TIMPs), during Wallerian degeneration (WD) and nerve regeneration (2nd, 7th and 21st days after injury) on crushed rat sural nerves. Our results showed that laminin alpha3-chain and alpha2-chain are over expressed during the early stages of degeneration and regeneration respectively, whereas type IV collagen expression increased progressively after crush. On the other hand, the expression of chondroitin sulfate was down regulated during the early stages of degeneration, returning progressively to normal values during nerve regeneration. The expression of MMP-3 was almost normal immediately after lesion, and then reduced progressively achieving the smallest expression at 21 days after crush; on the contrary, the expression of MMP-7 increased significantly immediately after crush (2nd day) returning to normal values afterwards. TIMP-1 and TIMP-2 were over expressed at the beginning of WD, returning progressively to normal values after that. These results indicate that the modifications of ECM components, which are favorable for nerve regeneration, are correlated with changes on the balance between MMPs and TIMPs.

Impeded interaction between Schwann cells and axons in the absence of laminin alpha4

The Schwann cell basal lamina (BL) is required for normal myelination. Loss or mutations of BL constituents, such as laminin-2 (alpha2beta1gamma1), lead to severe neuropathic diseases affecting peripheral nerves. The function of the second known laminin present in Schwann cell BL, laminin-8 (alpha4beta1gamma1), is so far unknown. Here we show that absence of the laminin alpha4 chain, which distinguishes laminin-8 from laminin-2, leads to a disturbance in radial sorting, impaired myelination, and signs of ataxia and proprioceptive disturbances, whereas the axonal regenerative capacity is not influenced. In vitro studies show poor axon growth of spinal motoneurons on laminin-8, whereas it is extensive on laminin-2. Schwann cells, however, extend longer processes on laminin-8 than on laminin-2, and, in contrast to the interaction with laminin-2, solely use the integrin receptor alpha6beta1 in their interaction with laminin-8. Thus, laminin-2 and laminin-8 have different critical functions in peripheral nerves, mediated by different integrin receptors.

Exercise, cognition and Alzheimer's disease: More is not necessarily better

Regional hypoperfusion, associated with a reduction in cerebral metabolism, is a hallmark of Alzheimer's disease (AD) and contributes to cognitive decline. Cerebral perfusion and hence cognition can be enhanced by exercise. The present review describes first how the effects of exercise on cerebral perfusion in AD are mediated by nitric oxide (NO) and tissue-type plasminogen activator, the release of which is regulated by NO. A conclusion of clinical relevance is that exercise may not be beneficial for the cognitive functioning of all people with dementia if cardiovascular risk factors are present. The extent to which cardiovascular risk factors play a role in the selection of older people with dementia in clinical studies will be addressed in the second part of the review in which the effects of exercise on cognition are presented. Only eight relevant studies were found in the literature, emphasizing the paucity of studies in this field. Positive effects of exercise on cognition were reported in seven studies, including two that excluded and two that included patients with cardiovascular risk factors. These findings suggest that cardiovascular risk factors do not necessarily undo the beneficial effects of exercise on cognition in cognitively impaired people. Further research is called for, in view of the limitations of the clinical studies reviewed here.

SPARC-like 1 regulates the terminal phase of radial glia-guided migration in the cerebral cortex

Differential adhesion between migrating neurons and transient radial glial fibers enables the deployment of neurons into appropriate layers in the developing cerebral cortex. The identity of radial glial signals that regulate the termination of migration remains unclear. Here, we identified a radial glial surface antigen, SPARC (secreted protein acidic and rich in cysteine)-like 1, distributed predominantly in radial glial fibers passing through the upper strata of the cortical plate (CP) where neurons end their migration. Neuronal migration and adhesion assays indicate that SPARC-like 1 functions to terminate neuronal migration by reducing the adhesivity of neurons at the top of the CP. Cortical neurons fail to achieve appropriate positions in the absence of SPARC-like 1 function in vivo. Together, these data suggest that antiadhesive signaling via SPARC-like 1 on radial glial cell surfaces may enable neurons to recognize the end of migration in the developing cerebral cortex.

Collagen XVII and BPAG1 expression in the retina: evidence for an anchoring complex in the central nervous system

The ectoderm gives rise not only to the skin but also to the entire CNS. This common embryonic lineage suggests that some molecular isoforms might serve analogous functions in both tissues. Indeed, not only are laminins important components of dermal adhesion mechanisms, but they also regulate some aspects of synaptic development in both the CNS and the PNS. In the skin, laminins are part of a hemidesmosome complex essential for basal keratinocyte adhesion that includes collagen XVII (BP180) and BPAG1 (dystonin/BP230). Here, we show that CNS neurons also express collagen XVII and BPAG1 and that these molecules are expressed in the adult and developing retina. In the retina, isoforms of collagen XVII and BPAG1 are colocalized with laminins at photoreceptor synapses and around photoreceptor outer segments; both molecules are expressed by rods, whereas cones express collagen XVII but not BPAG1. Moreover, biochemical data demonstrate that collagen XVII complexes with retinal laminins. We propose that collagen XVII and BPAG1 isoforms may help to anchor elements of the rod photoreceptor cytomatrix to the extracellular matrix.

Schwann cells and endoneurial extracellular matrix molecules as potential cues for sorting of regenerated axons: a review

Besides very well elaborated microsurgical management of severed peripheral nerves, the clinical results of functional recovery following surgical repair of mixed nerves are disappointing. An improvement of functional recovery after peripheral nerve lesion requires the accurate regeneration of axons to their original target tissues and structures. Therefore, better clinical results could be obtained by a greater understanding of the cellular and molecular biology of selective nerve regeneration. The studies concerning Schwann cells and their endoneurial extracellular matrix as potent cues for selective promotion and influence of regenerating motor and sensory axons are reviewed. Knowledge of the sorting mechanisms of regenerated motor and sensory axons is needed not only for improvement of functional recovery, but also for the development of biocompatible nerve prostheses.

Stimulation of neurite outgrowth in a human nerve scaffold designed for peripheral nerve reconstruction

The clinical outcome of microsurgical reconstruction of large peripheral nerve lesions depends on the availability of suitable graft material. Allogenic nerve grafts are rejected by the immune system. Extracellular-matrix proteins, in contrast to the resident cells, are of low immunogenicity in allografts. Here, human tibial nerve segments were extracted with lysophosphatidyl choline. The obtained cell-free and myelin-free scaffold consisted of empty endoneural tubes with maintained extracellular matrix architecture. The nerve scaffold had mechanical properties comparable to intact nerve, making it suitable for microsurgical reconstruction. Sections of the nerve scaffold were tested as a substrate for the adhesion and neuronal differentiation of human neuroblastoma-derived LAN-5 cells. Nerve extraction removed laminin-2, an isoform of laminin important for peripheral nerve regeneration. Laminin-2 reloading of the nerve scaffold did not improve cell adhesion and axon growth. Chemical crosslinking of heparan sulfate, on the other hand, increased the percentage of adherent cells with outgrowing neurites from 48 to 85%. Combined laminin-2 reloading and heparan sulfate crosslinking reduced the percentage of neurite-forming cells to 22% of the number of adherent cells. Implantation of the nerve scaffold into the peritoneal cavity of mice was not cytotoxic, and neovascularization of the graft material was observed within weeks. In conclusion, extraction of human nerve with detergents revealed a biocompatible nerve scaffold supporting neuronal cell adhesion. Heparan sulfate crosslinking to the scaffold surface improved neurite outgrowth, presumably mediated by midkine, a member of the neurokine family of growth factors, which is secreted by neuroblastoma-derived cells and binds to heparan sulfate.

Constitutive Release of α4 Type V Collagen N-terminal Domain by Schwann Cells and Binding to Cell Surface and Extracellular Matrix Heparan Sulfate Proteoglycans

During peripheral nerve development, Schwann cells synthesize collagen type V molecules that contain alpha4(V) chains. This collagen subunit possesses an N-terminal domain (NTD) that contains a unique high affinity heparin binding site. The alpha4(V)-NTD is adhesive for Schwann cells and sensory neurons and is an excellent substrate for Schwann cell and axonal migration. Here we show that the alpha4(V)-NTD is released constitutively by Schwann cells both in culture and in vivo. In cultures of neonatal rat Schwann cells, alpha4(V)-NTD release is increased significantly by ascorbate treatment, which facilitates collagen post-translational modification and collagen trimer assembly. In peripheral nerve tissue, the alpha4(V)-NTD is localized to the region of the outer Schwann cell membrane and associated extracellular matrix. The released alpha4(V)-NTD binds to the cell surface and extracellular matrix heparan sulfate proteoglycans of Schwann cells. Pull-down assays and immunofluorescent staining showed that the major alpha4(V)-NTD-binding proteins are glypican-1 and perlecan. alpha4(V)-NTD binding occurs via a mechanism that requires the high affinity heparin binding site and that is blocked by soluble heparin, demonstrating that binding to proteoglycans is mediated by their heparan sulfate chains.

Schwann cells synthesize alpha7beta1 integrin which is dispensable for peripheral nerve development and myelination

Defects in laminins or laminin receptors are responsible for various neuromuscular disorders, including peripheral neuropathies. Interactions between Schwann cells and their basal lamina are fundamental to peripheral nerve development and successful myelination. Selected laminins are expressed in the endoneurium, and their receptors are developmentally regulated during peripheral nerve formation. Loss-of-function mutations have confirmed the importance and the role of some of these molecules. Here we show for the first time that another laminin receptor, alpha7beta1 integrin, previously described only in neurons, is also expressed in Schwann cells. The expression of alpha7 appears postnatally, such that alpha7beta1 is the last laminin receptor expressed by differentiating Schwann cells. Genetic inactivation of the alpha7 subunit in mice does not affect peripheral nerve formation or the expression of other laminin receptors. Of note, alpha7beta1 is not necessary for basal lamina formation and myelination. Nonetheless, these data taken together with the previous demonstration of impaired axonal regrowth in alpha7-null mice suggest a possible Schwann cell-autonomous role for alpha7 in nerve regeneration.

Involvement of alpha7beta1 integrin in the conditioning-lesion effect on sensory axon regeneration

Conditioning lesions of peripheral nerves improve axonal regeneration after injury and involve changes in expression of proteins required for axonal growth. Integrin alpha7beta1 expression in motor and sensory neurons increases following nerve lesions and motor axon regeneration is impaired in alpha7 integrin KO mice (J. Neurosci. 20, 1822-1830). To investigate the role of alpha7beta1 integrin in sensory axon regeneration, dorsal root ganglia of adult mice were cultured in gels of laminin-rich extracellular matrix (Matrigel) or collagen. Normal dorsal root ganglia in Matrigel or collagen supplemented with laminin showed spontaneous axonal outgrowth, which was greatly increased in conditioned preparations, but only in the presence of laminin. Conditioned dorsal root ganglia from normal mice cultured with a blocking antibody to beta1 integrin and from alpha7 integrin KO mice showed reduced axonal growth in both Matrigel- and laminin-supplemented collagen gels. Enhanced axonal regeneration after conditioning lesions therefore involves increased responsiveness to laminin and integrin alpha7beta1 expression.

The 4C5 antigen is associated with Schwann cell migration during development and regeneration of the rat peripheral nervous system

The monoclonal antibody 4C5 recognizes a cell surface antigen of the developing central nervous system (CNS) and peripheral nervous system (PNS). In vitro antibody perturbation experiments have shown that the 4C5 antigen is involved in horizontal and vertical migration processes of granule cells during development of the rodent cerebellum. Moreover, results concerning the cellular localization and temporal expression of the 4C5 antigen during development and after injury of the rat sciatic nerve suggested that it may participate in Schwann cell migrations that occur during the above processes. To test this possibility, we examined the effects of our function-blocking antibody on Schwann cell migration in three in vitro bioassays: in tissue cultures from developing sciatic nerve, in dorsal root ganglion cultures on cryostat sections of normal or denervated adult sciatic nerve, and in pure Schwann cell cultures. The results showed that the presence of monoclonal antibody 4C5 in all the above culture systems strongly inhibited Schwann cell migration, indicating that the 4C5 antigen participates in migration processes that take place during development and regeneration of the peripheral nervous system. Moreover, staining of migrating Schwann cells in the presence of monoclonal antibody 4C5 with rhodamine-phalloidin showed that 4C5 antigen activity is associated with actin cytoskeletal organization of these cells, and more specifically with lamellipodia formation.

Laminin chains in rat and human peripheral nerve: distribution and regulation during development and after axonal injury

During nerve growth, axons are dependent upon contact with matrix components, such as laminins, for elongation, guidance, and trophic support. Semiquantitative in situ hybridization histochemistry and immunohistochemistry (IHC) were used to identify laminin chains in normal peripheral nerves, during postnatal development, after sciatic nerve transection (SNT), and after sciatic nerve crush (SNC). Laminin alpha2, alpha4, beta1, beta2, and gamma1 chain mRNAs were all expressed at high levels in newborn rat sciatic nerves with declining levels during later developmental stages. At the adult stage, no laminin chain mRNA was detectable. Of interest, the mRNA levels for alpha4 chain declined faster than those for alpha2. After SNT, laminin alpha2, alpha4, beta1, and gamma1 mRNA levels were up-regulated at the site of the injury, with the most profound reaction in the proximal nerve stump. Laminin alpha2 and alpha4 chains differed in that the mRNA levels of alpha4 were up-regulated earlier and declined quicker, whereas alpha2 had a later onset, with high levels remaining even after 6 weeks. After SNC, there was an initial up-regulation of the same laminin chain mRNAs as after SNT in the nerve, however, less intense, and at 6 weeks after SNC, all laminin mRNA levels studied had returned to normal. IHC of adult human normal and transected peripheral nerves stained positive for laminin alpha2, alpha4, beta1, and gamma1 chains in close relation to neurofilament labeled axons. Laminin alpha3, alpha4, alpha5, beta1, beta2, and gamma1 chains were found in blood vessel-like structures and alpha3, alpha4, alpha5, beta2, and gamma1 in the perineurium. These results and a previously published description of integrin regulation in spinal motoneurons suggest that both laminin-2 (alpha2beta1gamma1) and laminin-8 (alpha4beta1gamma1) are important for the postnatal nerve development and axonal regeneration after injury and that laminin-8 may have important functions especially early postnatally and early after adult nerve lesion.

The oestrogenized rat myometrium inhibits organotypic sympathetic reinnervation

Chronic administration of oestrogen to rats during the infantile/prepubertal period provokes, at 28 days of age, complete loss of noradrenaline-labelled intrauterine sympathetic nerves. It is not known whether oestrogen inhibits the growth or causes the degeneration of developing uterine sympathetic nerves, or whether the uterus recovers its innervation following cessation of infantile/prepubertal oestrogen treatment. In the present study, we analysed the time-course of the effects of oestrogen on the development of uterine sympathetic nerves in the rat, using histochemical methods. In addition, the pattern of sympathetic reinnervation of the uterus of intact and ovariectomised females was assessed 3 and 6 months after cessation of chronic oestrogen treatment. The ability of sympathetic nerves to reinnervate the oestrogenized uterine tissue was assessed in intraocular transplants of uterine myometrium into ovariectomised host rats. Early exposure to oestrogen did not inhibit the approach of sympathetic nerves to the uterus, but prevented the normal growth and maturation of intrauterine sympathetic fibres and abolished the innervation that reached the organ before initiation of treatment. Three or six months following cessation of oestrogen treatment, most of the sympathetic nerves were restricted to the mesometrium and mesometrial entrance, whereas intrauterine innervation remained persistently depressed as a consequence of a sustained oestrous-like state provoked by ovarian dysfunction (polycystic ovary). An organotypic regrowth of uterine sympathetic nerves was observed in ovariectomised infantile/prepubertal oestrogen-treated animals. After 5 weeks in oculo, the innervation of oestrogenized myometrial transplants was reduced by 50%, and substantial changes in the pattern of reinnervation were observed. In control transplants, 86% of the nerves were terminal varicose myometrial and perivascular nerve fibres, whereas 14% were preterminal nerve bundles. In oestrogenized myometrial transplants, 83% of the noradrenaline-labelled intercepting nerves were enlarged preterminal bundles and only 17% were terminal fibres. These results indicate that the oestrogenized myometrium is unattractive for sympathetic nerves and inhibits organotypic sympathetic reinnervation.

Local administration of vasoactive intestinal peptide after nerve transection accelerates early myelination and growth of regenerating axons

Our goal was to determine whether local injections of vasoactive intestinal peptide (VIP) promote early stages of regeneration after nerve transection. Sciatic nerves were transected bilaterally in 2 groups of 10 adult mice. In the first group, 15 microg (20 microL) of VIP were injected twice daily into the gap between transected ends of the right sciatic nerve for 7 days (4 mice) or 14 days (6 mice). The same number of mice in the second group received placebo injections (20 microL of 0.9% sterile saline) in the same site, twice daily, for the same periods. After 7 days, axon sizes, relationships with Schwann cells and degree of myelination were compared in electron micrographs of transversely sectioned distal ends of proximal stumps. Fourteen days after transection, light and electron microscopy were used to compare and measure axons and myelin sheaths in the transection gap, 2-mm distal to the ends of proximal stumps. Distal ends of VIP-treated proximal stumps contained larger axons 7 days after transection. More axons were in 1:1 relationships with Schwann cells and some of them were surrounded by thin myelin sheaths. In placebo-treated proximal stumps, axons were smaller, few were in 1:1 relationships with Schwann cells and no myelin sheaths were observed. In VIP-treated transection gaps, measurements 14 days after transection showed that larger axons were more numerous and their myelin sheaths were thicker. Our results suggest that in this nerve transection model, local administration of VIP promotes and accelerates early myelination and growth of regenerating axons.

Hypermyelinating neuropathy, mental retardation and epilepsy in a case of merosin deficiency

Children with a deficiency of laminin alpha 2 chain generally show an involvement of skeletal muscles, cerebral white matter and peripheral nerves. Among these patients, however, there is increasing evidence of molecular and phenotype heterogeneity. We report a 19-year-old girl with distal weakness, mental retardation and refractory epilepsy in whom elevated serum CK suggested a myopathy. Electrophysiological and neuroimaging examinations as well as studies of nerve and muscle biopsies were performed. Nerve conduction velocities were definitely reduced and brain MRI demonstrated a diffuse white matter involvement. The muscle biopsy showed both myopathic and neurogenic features. By immunohistochemistry laminin alpha 2 chain was mildly reduced in muscle and virtually absent in peripheral nerve. Teasing of sural nerve fibers showed a 'globular' hypermyelination characteristically located at the paranodal regions. A mild loss of myelinated fibers without any demyelination-remyelination changes was found. Haplotype analysis suggested linkage to the LAMA2 locus. Our case is peculiar as the putative mutation probably affects the expression of laminin alpha 2 chain is affected in a tissue specific manner: the protein is virtually absent in peripheral nerves but only mildly reduced in skeletal muscle. As to the disorder of nerve myelination, an absence or abnormal functioning of laminin alpha 2 chain can alter the feed-back control during myelinogenesis, leading to an over-ensheathment of axon. Alternatively, a compensatory up-regulation of other laminins can induce the hyperproduction of myelin sheaths. This case provides new evidence of the phenotypical heterogeneity of the LAMA2 gene and sheds light in understanding the role of laminin alpha 2 chain in myelination of peripheral nerve.

Fibrin inhibits peripheral nerve remyelination by regulating Schwann cell differentiation

Remyelination is a critical step for functional nerve regeneration. Here we show that fibrin deposition in the peripheral nervous system after injury is a key regulator of remyelination. After sciatic nerve crush, fibrin is deposited and its clearance correlates with remyelination. Fibrin induces phosphorylation of ERK1/2 and production of p75 NGF low-affinity receptor in Schwann cells and maintains them in a nonmyelinating state, suppresses fibronectin production, and prevents synthesis of myelin proteins. In mice depleted of fibrin(ogen), remyelination of myelinated axons is accelerated due to the faster transition of the Schwann cells to a myelinating state. Regulation of fibrin clearance and/or deposition could be a key regulatory mechanism for Schwann differentiation after nerve damage.

Nonmuscular involvement in merosin-negative congenital muscular dystrophy

The spectrum of nonmuscular involvement in six children with merosin-negative congenital muscular dystrophy is described. In all children, biochemical, neuroradiologic, cardiac, and neurophysiologic studies were performed. Cerebral structures that were myelinated at gestation, including internal capsule, corpus callosum, brainstem, and cerebellar white matter, demonstrated no abnormalities, whereas the periventricular and subcortical white matter, which were myelinated in the first postnatal year, demonstrated signs of leukoencephalopathy. Cerebrospinal fluid analysis revealed an elevated albumin cerebrospinal fluid to serum ratio in the younger children. Electroencephalogram results were abnormal in the two elder children. One child suffered from congestive cardiomyopathy. The increase in nerve conduction velocity in these children over the years lagged behind those of healthy patients, pointing to a demyelinating neuropathy. We conclude that in merosin-negative congenital muscular dystrophy patients, nonmuscular involvement includes the central and peripheral nervous system and the heart. The pattern of myelination of the brain and nerve conduction slowing suggests a myelination arrest. Merosin deficiency can give rise to a congestive cardiomyopathy, which is of no clinical relevance in the majority of children.

Schwann cell type V collagen inhibits axonal outgrowth and promotes Schwann cell migration via distinct adhesive activities of the collagen and noncollagen domains

Previously, we reported the cloning of alpha4 type V collagen, a novel member of the collagen type V gene family that is expressed by Schwann cells in developing peripheral nerves (Chernousov et al., 2000). The present study was performed to investigate the effects of this collagen on the adhesion and migration of premyelinating Schwann cells and neurite outgrowth from embryonic dorsal root ganglion neurons. Purified alpha4(V)-containing collagen isolated from Schwann cell conditioned medium (collagen type V(SC)) promoted migration of Schwann cells but inhibited outgrowth of axons from rat embryo dorsal root ganglia. Collagen type V(SC) blocked axonal outgrowth in the presence of otherwise active substrates such as collagen type IV, indicative of active inhibition. The noncollagen N-terminal domain of alpha4(V) promoted Schwann cell adhesion, spreading, and migration. These processes were inhibited by soluble heparin but not by function-blocking antibodies against alpha1- and alpha2-integrins. The collagen domain of pepsin-digested collagen type V was poorly adhesive for Schwann cells. The type V collagen domain but not the alpha4(V) N-terminal domain blocked neurite outgrowth from dorsal root ganglion neurons. In cocultures of dorsal root ganglion neurons and Schwann cells, collagen type V(SC) promoted axon fasciculation and association of axons with Schwann cells. These results suggest that in embryonic peripheral nerves, collagen type V(SC) plays a dual role in regulating cell migration. This represents a heretofore unrecognized function of peripheral nerve collagen fibrils in regulating patterns of peripheral nerve growth during development.

Migration of cells into and out of peripheral nerve isografts in the peripheral and central nervous systems of the adult mouse

Peripheral nerve (PN) isografts provide a favourable environment for axon regeneration after peripheral and central nervous system (CNS) injury, but definitive information on the extent of cellular intermixing between donor and host tissues is lacking. We wished to compare migration patterns in fresh and predegenerate PN grafts, and also compare the extent of cell migration after transplantation to peripheral nervous system (PNS) versus CNS. To discern how host and donor cells interact after PN transplantation, sciatic nerve segments were transplanted from inbred adult mice into PN defects (PN-PN grafts) or into lesioned cerebral cortex of opposite gender siblings. Migrating male cells were identified using a Y-chromosome-specific probe and in situ hybridization methods, and characterized immunohistochemically. The extent of donor and host cellular intermixing was similar in fresh and predegenerate PN-PN isografts. There was substantial intermixing of donor and host cells by 8 days. Many host cells migrating into epineurial regions of grafts were immunopositive for F4/80 (macrophages). The endoneurium of grafted PN was also colonized by host cells; some were F4/80+ but many were immunostained with S-100 (Schwann cell marker). Donor S-100+ Schwann cells rapidly migrated out into proximal and distal host PN and by 12 weeks were found at least 2 mm from the grafts. Endoneurial microvessels in grafts were mostly donor-derived. By comparison, in male PN grafts to female CNS, even after 6 weeks few donor cells had migrated out into surrounding host cortex, despite the observation that almost all grafts contained regenerating axons and were thus attached to host CNS tissue.

The AN2 protein is a novel marker for the Schwann cell lineage expressed by immature and nonmyelinating Schwann cells

The expression of the 330 kDa AN2 glycoprotein was studied in the rodent peripheral nervous system. AN2 is expressed by immature Schwann cells in vitro and in vivo and downregulated as the cells upregulate myelin genes. A subpopulation of nonmyelinating Schwann cells in the adult sciatic nerve retains expression of AN2. In rat sciatic nerve crushes, where Schwann cell numbers increase after initial axonal loss and markers of immature Schwann cells show an upregulation, no increased expression of AN2 was observed. In contrast, AN2 expression was upregulated in nerves from peripheral myelin protein-22-transgenic rats, where immature Schwann cells expand without axonal loss. Furthermore, coculture with neurons upregulated AN2 expression on Schwann cells in vitro. Polyclonal antibodies against AN2 inhibited the migration of an immortalized Schwann cell clone in an in vitro migration assay, and the purified AN2 protein was shown to be neither inhibitory nor permissive for outgrowing dorsal root ganglion neurites. AN2 is thus a novel marker for the Schwann cell lineage. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis of purified AN2 from early postnatal mouse brain demonstrated that AN2 is the murine homolog of the rat NG2 proteoglycan.

Laminins and human disease

The laminin protein family has diverse tissue expression patterns and is involved in the pathology of a number of organs, including skin, muscle, and nerve. In the skin, laminins 5 and 6 contribute to dermal-epidermal cohesion, and mutations in the constituent chains result in the blistering phenotype observed in patients with junctional epidermolysis bullosa (JEB). Allelic heterogeneity is observed in patients with JEB: mutations that results in premature stop codons produce a more severe phenotype than do missense mutations. Gene therapy approaches are currently being studied in the treatment of this disease. A blistering phenotype is also observed in patients with acquired cicatricial pemphigoid (CP). Autoantibodies targeted against laminins 5 and 6 destabilize epithelial adhesion and are pathogenic. In muscle cells, laminin alpha 2 is a component of the bridge that links the actin cytoskeleton to the extracellular matrix. In patients with laminin alpha 2 mutations, the bridge is disrupted and mature muscle cells apoptose. Congenital muscular dystrophy (CMD) results. The role of laminin in diseases of the nervous system is less well defined, but the extracellular protein has been shown to serve an important role in peripheral nerve regeneration. The adhesive molecule influences neurite outgrowth, neural differentiation, and synapse formation. The broad spatial distribution of laminin gene products suggests that laminin may be involved in a number of diseases for which pathogenic mechanisms are still being unraveled.

Influence of laminin-2 on Schwann cell-axon interactions

The dy/dy mouse suffers from a form of muscular dystrophy caused by a substantial reduction in laminin alpha2-chain protein, a major component of both muscle and Schwann cell basal laminae. This article examines the effect of laminin alpha2 deficiency on Schwann cell-axon interactions both in vivo at varying intervals after nerve crush, and in vitro, in cocultures of neurons and Schwann cells. The morphological spectrum of aberrant Schwann cell-axon associations seen in uncrushed dy/dy sciatic nerves was recapitulated during regeneration: myelination of regenerating axons was delayed compared with the process in unaffected mice and the relatively few myelin sheaths which were formed in dy/dy distal nerve stumps were often uncompacted. In vitro, Schwann cells dissociated from adult dy/dy sciatic nerves predictably failed to express detectable laminin alpha2-chain and displayed an unusual multipolar morphology. Branching of neurites, in terms both of numbers of terminal branches and of complexity of branching, from dorsal root ganglia neurons grown on dy/dy Schwann cells, was significantly less extensive than that seen when neurons were cocultured with Schwann cells from unaffected littermates, but this effect was reversed by exogenous laminin-2. Our results lend strong support to the view that laminin-2 is essential for establishing and/or maintaining Schwann cell-axon interactions, in normal and in regenerating nerves.

Laminin expression in adult and developing retinae: evidence of two novel CNS laminins

Components of the extracellular matrix exert myriad effects on tissues throughout the body. In particular, the laminins, a family of heterotrimeric extracellular glycoproteins, have been shown to affect tissue development and integrity in such diverse organs as the kidney, lung, skin, and nervous system. Of these, we have focused on the roles that laminins play in the differentiation and maintenance of the nervous system. Here, we examine the expression of all known laminin chains within one component of the CNS, the retina. We find seven laminin chains-alpha3, alpha4, alpha5, beta2, beta3, gamma2, and gamma3-outside the retinal basement membranes. Anatomically, these chains are coexpressed in one or both of two locations: the matrix surrounding photoreceptors and the first synaptic layer where photoreceptors synapse with retinal interneurons. Biochemically, four of these chains are coisolated from retinal extracts in two independent complexes, confirming that two novel heterotrimers-alpha4beta2gamma3 and alpha5beta2gamma3-are present in the retinal matrix. During development, all four of these chains, along with components of laminin 5 (the alpha3, beta3, and gamma2 chains) are also expressed at sites at which they could exert important effects on photoreceptor development. Together, these data suggest the existence of two novel laminin heterotrimers in the CNS, which we term here laminin 14 (composed of the alpha4, beta2, and gamma3 chains) and laminin 15 (composed of the alpha5, beta2, and gamma3 chains), and lead us to hypothesize that these laminins, along with laminin 5, may play roles in photoreceptor production, stability, and synaptic organization.

Role of the extracellular matrix during neural crest cell migration

Once specified to become neural crest (NC), cells occupying the dorsal portion of the neural tube disrupt their cadherin-mediated cell-cell contacts, acquire motile properties, and embark upon an extensive migration through the embryo to reach their ultimate phenotype-specific sites. The understanding of how this movement is regulated is still rather fragmentary due to the complexity of the cellular and molecular interactions involved. An additional intricate aspect of the regulation of NC cell movement is that the timings, modes and patterns of NC cell migration are intimately associated with the concomitant phenotypic diversification that cells undergo during their migratory phase and the fact that these changes modulate the way that moving cells interact with their microenvironment. To date, two interplaying mechanisms appear central for the guidance of the migrating NC cells through the embryo: one involves secreted signalling molecules acting through their cognate protein kinase/phosphatase-type receptors and the other is contributed by the multivalent interactions of the cells with their surrounding extracellular matrix (ECM). The latter ones seem fundamental in light of the central morphogenetic role played by the intracellular signals transduced through the cytoskeleton upon integrin ligation, and the convergence of these signalling cascades with those triggered by cadherins, survival/growth factor receptors, gap junctional communications, and stretch-activated calcium channels. The elucidation of the importance of the ECM during NC cell movement is presently favoured by the augmenting knowledge about the macromolecular structure of the specific ECM assembled during NC development and the functional assaying of its individual constituents via molecular and genetic manipulations. Collectively, these data propose that NC cell migration may be governed by time- and space-dependent alterations in the expression of inhibitory ECM components; the relative ratio of permissive versus non-permissive ECM components; and the supramolecular assembly of permissive ECM components. Six multidomain ECM constituents encoded by a corresponding number of genes appear to date the master ECM molecules in the control of NC cell movement. These are fibronectin, laminin isoforms 1 and 8, aggrecan, and PG-M/version isoforms V0 and V1. This review revisits a number of original observations in amphibian and avian embryos and discusses them in light of more recent experimental data to explain how the interaction of moving NC cells with these ECM components may be coordinated to guide cells toward their final sites during the process of organogenesis.

Merosin and congenital muscular dystrophy

Merosin (also called as Laminin-2) is an isoform of laminin comprised of the alpha2, beta1 and gamma1 chains. In European populations, half of the patients with classical congenital muscular dystrophy have mutations of the LAMA2 gene (6q22-23) and present reduced or absence of laminin alpha2 chain. This form is generally referred to as merosin-deficient CMD. Merosin-deficient CMD is characterized by involvement of not only skeletal muscle but also central and peripheral nervous systems: Extensive brain white matter abnormalities are found by magnetic resonance imaging (MRI). However, most patients show no mental retardation. Recent case studies reported that some patients have several structural abnormalities such as abnormal cerebral cortical gyration, hypoplasia of cerebellum and pons, and dilation of ventricles. At present, functions of merosin related to muscle degeneration have not been fully elucidated. In addition, the mechanisms responsible for pathogenesis of diffuse brain white matter abnormalities remain to be determined. As mouse models for merosin-deficient CMD, three spontaneous mutants(dy, dy(2J), dy(PAS1)) and two mutants named dy(W) and dy(3K) by targeted gene disruption have been reported. These mice will help to elucidate the pathogenesis of merosin-deficient CMD and serve to develop therapy.

The extracellular matrix modulates olfactory neurite outgrowth on ensheathing cells

Primary olfactory axons grow along a stereotypical pathway from the nasal cavity to the olfactory bulb through an extracellular matrix rich in laminin and heparan sulfate proteoglycans (HSPGs) and bounded by the expression of chondroitin sulfate proteoglycans (CSPGs). This pathway is pioneered by olfactory ensheathing cells, which provide a substrate conducive for axon growth during early development. In the present study, we examined the effect of several extracellular matrix constituents on the spreading and migration, as well as the neurite outgrowth-promoting properties, of olfactory ensheathing cells. Laminin and Matrigel enhanced the spreading and migration of olfactory ensheathing cells and increased their neurite outgrowth-promoting activity. In contrast, HSPG and CSPG had little effect on the spreading and migration of olfactory ensheathing cells and hence did not promote olfactory neurite outgrowth. In vitro olfactory axons grew preferentially on the surface of olfactory ensheathing cells rather than the underlying extracellular matrix. We propose that olfactory ensheathing cells secrete laminin and HSPGs, which together with other cofactors, stimulate these cells to migrate and adopt a neurite outgrowth-promoting phenotype. Expression of CSPGs in the surrounding mesenchyme confines the growth of ensheathing cells, as well as the axons, which grow on the surface of these cells, to a specific pathway. Thus, the ECM indirectly modulates the growth and guidance of olfactory axons during development.

A 21-kDa surface protein of Mycobacterium leprae binds peripheral nerve laminin-2 and mediates Schwann cell invasion

Nerve damage is the hallmark of Mycobacterium leprae infection, which results from M. leprae invasion of the Schwann cell of the peripheral nervous system. We have recently shown that the laminin-2 isoform, specially the G domain of laminin alpha2 chain, on the Schwann cell-axon unit serves as an initial neural target for M. leprae. However, M. leprae surface molecules that mediate bacterial invasion of peripheral nerves are entirely unknown. By using human alpha2 laminins as a probe, a major 28-kDa protein in the M. leprae cell wall fraction that binds alpha2 laminins was identified. After N-terminal amino acid sequence analysis, PCR-based strategy was used to clone the gene that encodes this protein. Deduced amino acid sequence of this M. leprae laminin-binding protein predicts a 21-kDa molecule (ML-LBP21), which is smaller than the observed molecular size in SDS/PAGE. Immunofluorescence and immunoelectron microscopy on intact M. leprae with mAbs against recombinant (r) ML-LBP21 revealed that the protein is surface exposed. rML-LBP21 avidly bound to alpha2 laminins, the rG domain of the laminin-alpha2 chain, and the native peripheral nerve laminin-2. The role of ML-LBP21 in Schwann cell adhesion and invasion was investigated by using fluorescent polystyrene beads coated with rML-LBP21. Although beads coated with rML-LBP21 alone specifically adhered to and were ingested by primary Schwann cells, these functions were significantly enhanced when beads were preincubated with exogenous alpha2 laminins. Taken together, the present data suggest that ML-LBP21 may function as a critical surface adhesin that facilitates the entry of M. leprae into Schwann cells.

Identification of extracellular matrix ligands for the heparan sulfate proteoglycan agrin

Agrin is a major brain heparan sulfate proteoglycan which is expressed in nearly all basal laminae and in early axonal pathways of the developing central nervous system. To further understand agrin's function during nervous system development, we have examined agrin's ability to interact with several heparin-binding extracellular matrix proteins. Our data show that agrin binds FGF-2 and thrombospondin by a heparan sulfate-dependent mechanism, merosin and laminin by both heparan sulfate-dependent and -independent mechanisms, and tenascin solely via agrin's protein core. Furthermore, agrin's heparan sulfate side chains encode a specificity in interactions with heparin-binding molecules since fibronectin and the cell adhesion molecule L1 do not bind agrin. Surface plasmon resonance studies (BIAcore) reveal a high affinity for agrin's interaction with FGF-2 and merosin (2.5 and 1.8 nM, respectively). Demonstrating a biological significance for these interactions, FGF-2, laminin, and tenascin copurify with immunopurified agrin and immunohistochemistry reveals a partial codistribution of agrin and its ECM ligands in the chick developing visual system. These studies and our previous studies, showing that merosin and NCAM also colocalize with agrin, provide evidence that agrin plays a crucial role in the function of the extracellular matrix and suggest a role for agrin in axon pathway development.

In oculo transplants of myometrium from postpartum guinea pigs fail to support sympathetic reinnervation

Sympathetic nerves to the enlarged fetus-containing region of the uterus undergo degenerative changes during late pregnancy and show slow regrowth after parturition. It is not known whether this unusual response of sympathetic nerves to smooth muscle hypertrophy is due to the sensitivity of short adrenergic neurons to hormonal changes, or whether the nerves respond to changes in the neurotrophic capacity of the target. We have investigated this question using in oculo transplantation. Small pieces of myometrium from the uterine horn of virgin guinea pigs, or from the region previously occupied by the placenta and fetus in postpartum guinea pigs, were transplanted into the anterior eye chamber. After 3 wk in oculo, the pattern of reinnervation of the transplants was assessed on whole mount stretch preparations stained for tyrosine hydroxylase. The histology of the transplants was examined in toluidine blue-stained semithin sections. Myometrial transplants from virgin donors and uterine artery transplants from both virgin and postpartum donors became organotypically reinnervated by sympathetic fibres from the host iris. In contrast, sympathetic nerves did not reinnervate myometrial transplants from postpartum donors, although they approached the transplants and became distributed in the surrounding connective tissue. All transplanted tissues showed a normal histological appearance. Both the myometrium and uterine artery from postpartum donors retained a hypertrophic appearance after 3 wk in oculo. We interpret these results to indicate that the degeneration of sympathetic nerves in late pregnancy, as well as their slow regrowth to the uterus after delivery, may be due to changes in uterine smooth muscle rather than a particular sensitivity of short adrenergic neurons to hormonal changes.

Laminin-like proteins are differentially regulated during cerebellar development and stimulate granule cell neurite outgrowth in vitro

The basement membrane glycoprotein laminin-1 is a potent stimulator of neurite outgrowth. Although a variety of laminin isoforms have been described in recent years, the role of alternative laminin isoforms in neural development remains largely uncharacterized. We found that a polyclonal antibody raised against the alpha1, beta1, and gamma1 chains of laminin-1 and a monoclonal antibody raised against the alpha2 chain of laminin-2 detect immunoreactive material in neuronal cell bodies in the developing mouse cerebellum. In addition, laminin-1-like immunoreactivity was found in cell types throughout the cerebellum, but laminin-alpha2-like immunoreactivity was restricted to the Purkinje cells. Purified laminin-1 and laminin-2 stimulated neurite outgrowth in primary cultures of mouse cerebellar granule neurons to a similar extent, whereas the synthetic peptides tested appeared to be active only for cell adhesion and not for stimulation of neurite outgrowth. The E8 proteolytic fragment of laminin-1 contained full neurite outgrowth activity. The identity of laminins expressed in granule neurons was also examined by Western blotting; laminin-like complexes were associated with the cell and appeared to have novel compositions. These results suggest that laminin-like complexes play important roles in cerebellar development.

Control of Schwann cell survival and proliferation: autocrine factors and neuregulins

Postnatal rat Schwann cells secrete factors that prevent the programmed cell death (PCD) of low-density Schwann cells in serum-free culture. These autocrine survival signal(s) do not promote Schwann cell proliferation. Moreover, while NRG and bFGF, which promote proliferation, both rescue a subpopulation of neonatal Schwann cells from PCD, they do not rescue freshly isolated Schwann cells from older animals; other known protein factors tested also do not mimic the autocrine signal. These results suggest that Schwann cells switch their survival dependency around the time of birth from axonal signals such as NRG to autocrine signals. Such an arrangement would be advantageous for the regeneration of peripheral axons following injury. We also compared NRG-induced Schwann cell proliferation using autocrine signals or serum to promote survival. The autocrine signals increase the rate of NRG-stimulated proliferation of low-density Schwann cells in serum-free medium, whereas serum inhibits proliferation by inhibiting both the production of survival signals and the expression of erbB2 and erbB3 receptors; these inhibitions are all reversed by forskolin. In contrast, forskolin has no effect on proliferation when the cells are exposed to high levels of autocrine factors.

Congenital muscular dystrophy, white-matter abnormalities, and neuronal migration disorders: the expanding concept

The congenital muscular dystrophies are a heterogeneous, recessively inherited group of disorders that have been subclassified on the basis of clinical central nervous system involvement. We report two children with "pure" congenital muscular dystrophy, one merosin negative and one merosin positive with extensive white matter and occipital cortical neuromigration abnormalities on magnetic resonance imaging (MRI). The first patient (merosin-negative congenital muscular dystrophy) presented with hypotonia and weakness in the neonatal period and subsequently was found to have a leukoencephalopathy and occipital cortical dysplasia on magnetic resonance imaging. The second patient presented with developmental delay without definite weakness. Initial investigations revealed a leukoencephalopathy and cortical dysplasia, but the patient subsequently was shown to have merosin-positive congenital muscular dystrophy. These patients illustrate that white-matter changes are not specific for merosin-negative congenital muscular dystrophy alone and that extensive cortical abnormality can be found in both groups of patients. In addition, our second patient illustrates a nonmuscular mode of congenital muscular dystrophy presentation that should be considered in patients with a "nonprogressive leukodystrophy."

Neuronal matrix metalloproteinase-2 degrades and inactivates a neurite-inhibiting chondroitin sulfate proteoglycan

Chondroitin sulfate proteoglycans (CSPGs) are implicated in the regulation of axonal growth. We previously reported that the neurite-promoting activity of laminin is inhibited by association with a Schwann cell-derived CSPG and that endoneurial laminin may be inhibited by this CSPG as well [Zuo J, Hernandez YJ, Muir D (1998) Chondroitin sulfate proteoglycan with neurite-inhibiting activity is upregulated after peripheral nerve injury. J Neurobiol 34:41-54]. Mechanisms regulating axonal growth were studied by using an in vitro bioassay in which regenerating embryonic dorsal root ganglionic neurons (DRGn) were grown on sections of normal adult nerve. DRGn achieved slow neuritic growth on sections of normal nerve, which was reduced significantly by treatment with metalloproteinase inhibitors. Similar results were obtained on a synthetic substratum composed of laminin and inhibitory CSPG. DRGn expressed the matrix metalloproteinase, MMP-2, which was transported to the growth cone. Recombinant MMP-2 inactivated the neurite-inhibiting CSPG without hindering the neurite-promoting potential of laminin. Similarly, neuritic growth by DRGn cultured on normal nerve sections was increased markedly by first treating the nerve sections with MMP-2. The proteolytic deinhibition by MMP-2 was equivalent to and nonadditive with that achieved by chondroitinase, suggesting that both enzymes inactivated inhibitory CSPG. Additionally, the increases in neuritic growth resulting from treating nerve sections with MMP-2 or chondroitinase were blocked by anti-laminin antibodies. From these results we conclude that MMP-2 provides a mechanism for the deinhibition of laminin in the endoneurial basal lamina and may play an important role in the regeneration of peripheral nerve.

Synaptic laminin prevents glial entry into the synaptic cleft

Presynaptic and postsynaptic membranes directly oppose each other at chemical synapses, minimizing the delay in transmitting information across the synaptic cleft. Extrasynaptic neuronal surfaces, in contrast, are almost entirely covered by processes from glial cells. The exclusion of glial cells from the synaptic cleft, and the long-term stability of synapses, presumably result in large part from the tight adhesion between presynaptic and postsynaptic elements. Here we show that there is another requirement for synaptic maintenance: glial cells of the skeletal neuromuscular synapse, Schwann cells, are actively inhibited from entering the synaptic cleft between the motor nerve terminal and the muscle fibre. One inhibitory component is laminin 11, a heterotrimeric glycoprotein that is concentrated in the synaptic cleft. Regulation of an inhibitory interaction between glial cells and synaptic cleft components may contribute to synaptic rearrangements, and loss of this inhibition may underlie the loss of synapses that results from injury to the postsynaptic cell.