Is the soluble KDI domain of gamma1 laminin a regeneration factor for the mammalian central nervous system?

Self-assembling multidomain peptide hydrogels accelerate peripheral nerve regeneration after crush injury

Multidomain peptide (MDP) hydrogels are a class of self-assembling materials that have been shown to elicit beneficial responses for soft tissue regeneration. However, their capacity to promote nervous system regeneration remains unknown. The peripheral nervous system (PNS) substantially recovers after injury, partly due to the abundance of extracellular matrix (ECM) components in its basal lamina. However, severe peripheral nerve injuries that significantly damage the ECM continue to be a major clinical challenge as they occur at a high rate and can be extremely detrimental to patients' quality of life. In this study, a panel of eight MDPs were designed to contain various motifs mimicking extracellular matrix components and growth factors and successfully self-assembled into injectable, nanofibrous hydrogels. Using an in vitro screening system, various lysine based MDPs were found to enhance neurite outgrowth. To test their capacity to promote nerve regeneration in vivo, rat sciatic nerve crush injury was performed with MDP hydrogels injected directly into the injury sites. MDP hydrogels were found to enhance macrophage recruitment to the injury site and degrade efficiently over time. Rats that were injected with the MDP hydrogel K2 and laminin motif-containing MDPs K2-IIKDI and K2-IKVAV were found to have significantly accelerated functional recovery and remyelination compared to those injected with HBSS or other MDPs. These results demonstrate that MDPs enhance neurite outgrowth and promote a multicellular pro-regenerative response in peripheral nerve injury. This study provides important insights into the potential of MDPs as biomaterials for nerve regeneration and other clinical applications.

Laminin-γ1 chain and stress inducible protein 1 synergistically mediate PrPC-dependent axonal growth via Ca2+ mobilization in dorsal root ganglia neurons

Prion protein (PrP(C)) is a cell surface glycoprotein that is abundantly expressed in nervous system. The elucidation of the PrP(C) interactome network and its significance on neural physiology is crucial to understanding neurodegenerative events associated with prion and Alzheimer's diseases. PrP(C) co-opts stress inducible protein 1/alpha7 nicotinic acetylcholine receptor (STI1/α7nAChR) or laminin/Type I metabotropic glutamate receptors (mGluR1/5) to modulate hippocampal neuronal survival and differentiation. However, potential cross-talk between these protein complexes and their role in peripheral neurons has never been addressed. To explore this issue, we investigated PrP(C)-mediated axonogenesis in peripheral neurons in response to STI1 and laminin-γ1 chain-derived peptide (Ln-γ1). STI1 and Ln-γ1 promoted robust axonogenesis in wild-type neurons, whereas no effect was observed in neurons from PrP(C) -null mice. PrP(C) binding to Ln-γ1 or STI1 led to an increase in intracellular Ca(2+) levels via distinct mechanisms: STI1 promoted extracellular Ca(2+) influx, and Ln-γ1 released calcium from intracellular stores. Both effects depend on phospholipase C activation, which is modulated by mGluR1/5 for Ln-γ1, but depends on, C-type transient receptor potential (TRPC) channels rather than α7nAChR for STI1. Treatment of neurons with suboptimal concentrations of both ligands led to synergistic actions on PrP(C)-mediated calcium response and axonogenesis. This effect was likely mediated by simultaneous binding of the two ligands to PrP(C). These results suggest a role for PrP(C) as an organizer of diverse multiprotein complexes, triggering specific signaling pathways and promoting axonogenesis in the peripheral nervous system.

Approaches to repairing the damaged spinal cord: overview

Affecting young people during the most productive period of their lives, spinal cord injury (SCI) is a devastating problem for modern society. In the past, treating SCI seemed frustrating and hopeless because of the tremendous morbidity and mortality, life-shattering impact, and limited therapeutic options associated with the condition. Today, however, an understanding of the underlying pathophysiological mechanisms, the development of neuroprotective interventions, and progress toward regenerative interventions are increasing hope for functional restoration. In this chapter, we provide an overview of various repair strategies for the injured spinal cord. Special attention will be paid to strategies that promote spontaneous regeneration, including functional electrical stimulation, cell replacement, neuroprotection, and remyelination. The concept that limited rebuilding can provide a disproportionate improvement in quality of life is emphasized throughout. New surgical procedures, pharmacological treatments, and functional neuromuscular stimulation methods have evolved over the last decades and can improve functional outcomes after spinal cord injury; however, limiting secondary injury remains the primary goal. Tissue replacement strategies, including the use of embryonic stem cells, become an important tool and can restore function in animal models. Controlled clinical trials are now required to confirm these observations. The ultimate goal is to harness the body's own potential to replace lost central nervous system cells by activation of endogenous progenitor cell repair mechanisms.

Neuroprotective effects of laminin and its KDI domain

Successful treatment of neurodegenerative diseases and CNS trauma are the most intractable problems in modern medicine. Numerous reports have shown the strong role that laminins have on the survival, regeneration and development of various types of cells, including neural cells. It would be desirable to take advantage of laminin activities for therapeutic purposes. However, there are at least ten laminin variants and the trimeric molecules are of the order of 800,000 molecular weight. Furthermore, human laminins are not available in quantity. Therefore, we and others have taken the approach of determining which domains of the laminin molecules are functional in the CNS, and whether short peptides from these regions exhibit biological activities with the intent of testing their potential for therapeutic use. Understanding the role of laminins and their small biologically active peptide domains, such as the KDI (lysine–aspartic acid–isoleucine) peptide from γ1 laminin, in neuronal development, CNS trauma (spinal cord injury and stroke) and neurodegenerative disorders (amyotrophic lateral sclerosis, Alzheimer’s disease and Parkinson’s disease) may help to develop clinically applicable methods to treat the presently untreatable CNS diseases and trauma even in the near future.

A review of published reports on neuroprotection in spinal cord injury

STUDY DESIGN

Literature review.

OBJECTIVES

To review the main published current neuroprotection research trends and results in spinal cord injury (SCI).

SETTING

This paper is the result of a collaboration between a group of European scientists.

METHODS

Recent studies, especially in genetic, immune, histochemical and bio (nano)-technological fields, have provided new insight into the cellular and molecular mechanisms occurring within the central nervous system (NS), including SCIs. As a consequence, a new spectrum of therapies aiming to antagonize the 'secondary injury' pathways (that is, to provide neuroprotection) and also to repair such classically irreparable structures is emerging. We reviewed the most significant published works related to such novel, but not yet entirely validated, clinical practice therapies.

RESULTS

There have been identified many molecules, primarily expressed by heterogenous glial and neural subpopulations of cells, which are directly or indirectly critical for tissue damaging/sparing/re-growth inhibiting, angiogenesis and neural plasticity, and also various substances/energy vectors with regenerative properties, such as MAG (myelin-associated glycoprotein), Omgp (oligodendrocyte myelin glycoprotein), KDI (synthetic: Lysine-Asparagine-Isoleucine 'gamma-1 of Laminin Kainat Domain'), Nogo (Neurite outgrowth inhibitor), NgR (Nogo protein Receptor), the Rho signaling pathway (superfamily of 'Rho-dopsin gene-including neurotransmitter-receptors'), EphA4 (Ephrine), GFAP (Glial Fibrillary Acidic Protein), different subtypes of serotonergic and glutamatergic receptors, antigens, antibodies, immune modulators, adhesion molecules, scavengers, neurotrophic factors, enzymes, hormones, collagen scar inhibitors, remyelinating agents and neurogenetic/plasticity inducers, all aiming to preserve/re-establish the morphology and functional connections across the lesion site. Accordingly, modern research and experimental SCI therapies focus on several intricate, rather overlapping, therapeutic objectives and means, such as neuroprotective, neurotrophic, neurorestorative, neuroreparative, neuroregenerative, neuro(re)constructive and neurogenetic interventions.

CONCLUSION

The first three of these therapeutical directions are generically assimilated as neuroprotective, and are synthetically presented and commented in this paper in an attempt to conceptually systematize them; thus, the aim of this article is, by emphasizing the state-of-the art in the domain, to optimize theoretical support in selecting the most effective pharmacological and physical interventions for preventing, as much as possible, paralysis, and for maximizing recovery chances after SCI.

Spatial and temporal distribution of laminins in permanent focal ischemic brain damage of the adult rat

Laminins are extracellular matrix glycoproteins with multiple functions in the central nervous system, including maintenance of the blood-brain barrier. Because ischemic brain damage results in rapid degradation of extracellular matrix, we used immunocytochemistry on rat central nervous system after permanent focal ischemia to identify laminins involved in pathophysiology of stroke. At 24 hr after stroke, laminin-1 is transiently expressed by neurons inside the ischemic core, but from 2-3 days to 28 days it is expressed only in basement membrane structures. During the first 24 hr, alpha1, alpha5, beta1, and gamma1 laminins are transiently expressed in neurons within the ischemic core as an acute reaction of the brain to ischemia. Rapid induction of gamma1 laminin but no other laminin in reactive astrocytes surrounding the ischemic core is clear at 24 hr, and importantly, expression of gamma1 laminin in astrocytes surrounding the ischemic core intensifies during the first days and persists up to 28 days after stroke. At 2-3 days, gamma1 laminin immunoreactive barrier of reactive astrocytes is already fully formed, isolating the ischemic area from the healthy brain. Similar to gamma1 laminin, its KDI domain localizes in reactive astrocytes isolating the ischemic core. Results indicate that gamma1 laminin and its KDI domain are rapidly induced in glial cells after stroke and their expression persists, forming a molecular barrier between the healthy and the damaged brain. Thus, gamma1 laminin is involved in pathology of stroke and is likely to serve a protective function, considering its potent neuroprotective role after spinal cord injury and in neurodegenerative disorders.

Selective overexpression of gamma1 laminin in astrocytes in amyotrophic lateral sclerosis indicates an involvement in ALS pathology

Our earlier studies indicate that the KDI tripeptide of gamma1 laminin reverts paralysis and protects adult rat CNS from excitotoxicity of glutamate and from oxidative stress. Here we show that gamma1 laminin is selectively overexpressed in reactive astrocytes of the amyotrophic lateral sclerosis (ALS) spinal cord, with both gray and white matter astrocytes overexpressing gamma1 laminin. Intensely gamma1 laminin-positive, aggressive-looking reactive astrocytes of the lateral columns of both cervical and thoracic spinal cord surround the lateral ventral horns and roots and extend into the area of the lateral corticospinal tract. In the cervical ALS spinal cord, large numbers of strongly gamma1 laminin-immunoreactive astrocytes are also present in the dorsal columns of the ascending sensory pathways. No other laminin or any other ALS-associated protein localizes in this manner. This unique distribution of gamma1 laminin-immunoreactive astrocytes in the ALS white matter together with our recent results on the efficacy of the KDI domain as a neuronal protector strongly suggest that gamma1 laminin may be expressed by astrocytes of the ALS spinal cord as a protective measure intended to aid neuronal survival. Further comparative studies on ALS spinal cord tissues and those of the animal models of ALS are needed to clarify the specific role of gamma1 laminin and its KDI domain in ALS and its putative interactions with the additional ALS-associated factors, such as excitotoxicity, oxidative stress, and neurofilament accumulation. Most importantly, further studies are urgently needed to test the potential of the KDI tripeptide as a therapeutic treatment for ALS.

KDI tripeptide of gamma1 laminin protects rat dopaminergic neurons from 6-OHDA induced toxicity

Our previous studies indicate that the KDI (Lys-Asp-Ile) tripeptide of gamma1 laminin protects central neurons from mechanical trauma and excitotoxicity. At least part of the neuroprotective effect of the KDI tripeptide may be mediated by its inhibitory function on ionotropic glutamate receptors. We studied the protective effect of the KDI tripeptide against 6-hydroxy-dopamine (6-OHDA) induced neurotoxicity in a rat experimental model of Parkinson's disease (PD). We found that a single unilateral injection of the KDI tripeptide into the substantia nigra before an injection of 6-OHDA protected the dopaminergic neurons from the neurotoxicity of 6-OHDA. Compared to rats treated with 6-OHDA alone, the KDI + 6-OHDA-treated substantia nigra was relatively intact with large numbers of dopaminergic neurons present at the injection side. In the rats treated with 6-OHDA alone, no dopaminergic neurons were detected, and the substantia nigra-area at the injection side was filled with blood-containing cavities. Quantification of the rescue effect of the KDI tripeptide indicated that, in animals receiving KDI before 6-OHDA, 33% of tyrosine hydroxylase-positive dopaminergic neurons of the substantia nigra were present as compared to the contralateral non-injected side. In animals receiving 6-OHDA alone, only 1.4% of the tyrosine hydroxylase expressing dopaminergic neurons could be verified. If this much protection were achieved in humans, it would be sufficient to diminish or greatly alleviate the clinical symptoms of PD. We propose that the KDI tripeptide or its derivatives might offer a neuroprotective biological alternative for treatment of PD.

The repair of brain lesion by implantation of hyaluronic acid hydrogels modified with laminin

The hyaluronic acid (HA) hydrogels modified with laminin were used for implantation in rat brain in present study, in order to investigate its effects in reparation of injury in the CNS. Cross-linked HA hydrogels were synthesized and their characteristics were analyzed. Laminin, an extracellular matrix protein, which participates in neuronal development and survival, was immobilized on the backbone of the hydrogels. Hydrogels unmodified and modified with laminin were implanted into cortical defects mechanically created in rats and their ability to improve tissue reconstruction was then evaluated. After 6 and 12 weeks of implantation, sections of brains were processed with Nissl and Glees staining for revealing neural cell bodies and fibers, with DAB histochemistry for detecting the blood vessels, as well as with immunocytochemistry for recognizing GFAP. The sections were also taken to SEM and TEM for ultrastructral examination. The results showed that the HA hydrogels synthesized had mechanical properties and rheological behavior similar to the brain tissue. After being implanted into the lesion of the cortex, the porous hydrogels created a scaffold, which could support cell infiltration and angiogenesis, and simultaneously inhibit the formation of glial scar. In addition, HA hydrogels modified with laminin could promote neurite extension. It seems possible that the tissue engineering technique may pave the way to repair injury in the CNS as suggested by the results in present study.

Reversible age impairments in neurite outgrowth by manipulations of astrocytic GFAP

Aging is associated with neuron atrophy and impaired sprouting after lesions. In contrast during normal aging without neurodegenerative diseases, astrocytes display increasing activation, with progressive increases of glial fibrillary acidic protein (GFAP) beginning before midlife. Because many neuronal functions depend on astrocytic support, we developed a heterochronic co-culture system to study influences of aging astrocytes on neurons. Neurite outgrowth by embryonic neurons (E18) was markedly less when co-cultured with confluent astrocytes derived from old (24 mo) versus young (3 mo) cortex. These impairments were reversible. Diminishing the GFAP levels of old astrocytes by RNAi restored neurite outgrowth, whereas overexpression of GFAP in young astrocytes modeled these effects of aging by reducing neurite outgrowth. Quantitative relationships were found such that neurites were co-localized with high intensity laminin, which both varied inversely with GFAP. These results implicate increased astrocytic GFAP expression as a proximal cause of neuron atrophy during normal aging.

Integrin messenger RNAs in the red nucleus after axotomy and neurotrophic administration

Integrins are cell surface receptors known to be important for regeneration in the peripheral nervous system. We have investigated the expression of integrin messenger RNAs in red nucleus neurons of adult rats after axotomy and administration of neurotrophic factors. Using radioactive in situ hybridization, messenger RNA for integrin subunits beta1, alpha3, alpha7 and alphaV could be detected. No change of any alpha subunit could be detected after axotomy. In contrast, a small upregulation of beta1 was detected after lesion. Administration of neurotrophin-3 induced a robust further increase in beta1 messenger RNA levels, whereas brain-derived neurotrophic factor did not. By analogy to the peripheral nervous system, we propose that integrins may be important for a regenerative response in central nervous system neurons.

Regeneration of adult rat spinal cord is promoted by the soluble KDI domain of gamma1 laminin

Regeneration in the central nervous system (CNS) of adult mammals is hampered by formation of a glial scar and by proteins released from the myelin sheaths of injured neuronal pathways. Our recent data indicate that the KDI (Lys-Asp-Ile) domain of gamma1 laminin neutralizes both glial- and myelin-derived inhibitory signals and promotes survival and neurite outgrowth of cultured human spinal cord neurons. We show that after complete transection of the adult rat spinal cord, animals receiving onsite infusion of the KDI domain via osmotic mini-pumps recover and are able to sustain their body weights and walk with their hindlimbs. Animals treated with placebo suffer from irreversible hindlimb paralysis. Microscopic and molecular analyses of the spinal cords indicate that the KDI domain reduces tissue damage at the lesion site and enables neurite outgrowth through the injured area to effect functional recovery of the initially paralyzed animals. That the KDI domain enhances regeneration of acute spinal cord injuries in the adult rat suggests that it may be used to promote regeneration of spinal cord injuries in humans.

The neuroprotective KDI domain of γ1-laminin is a universal and potent inhibitor of ionotropic glutamate receptors

Previous work from this laboratory indicates that the KDI (Lys-Asp-Ile) domain of gamma 1-laminin promotes functional regeneration of adult rat spinal cord injuries and protects adult rat hippocampal neurons against massive neuronal death induced by intracerebral injection of the glutamate analogue kainic acid. In the present study, we used patch clamp recordings on cultured human embryonic neocortical neurons and HEK 293 cells expressing recombinant glutamate receptor subunits to study a putative interaction of the KDI with the glutamate system. We show that the KDI domain of gamma 1-laminin is a universal and potent inhibitor of AMPA, kainate, and NMDA subclasses of glutamate receptors, with a noncompetitive action on the AMPA receptor channel activity. Glutamate neurotoxicity plays a key role in both CNS trauma and neurodegenerative disorders, so this unexpected, novel function of the gamma 1-laminin-derived tripeptide may prove clinically valuable in treatment of CNS trauma and/or disease.

Soluble KDI domain of γ1 laminin protects adult hippocampus from excitotoxicity of kainic acid

Recent data indicate that the soluble KDI domain of gamma1 laminin promotes survival and neurite outgrowth of human central neurons in vitro (Liebkind et al.[2003] J Neurosci Res 73:637-643), and seems to neutralize both glia- and myelin-derived signals that hamper regeneration in the central nervous system (CNS) of adult mammals. We show that damage of adult rat neocortical and hippocampal areas by a stereotaxic injection of kainic acid (KA) is prevented by a preceding injection of the soluble KDI domain. In the presence of the KDI domain, both neocortical and hippocampal areas show extensive gliosis but have viable neurons and glial cells, which are absent and the areas fully destroyed after injection of KA alone. This result indicates that the KDI domain of the gamma1 laminin protects the CNS against excitotoxic insults and promotes survival of both neurons and glial cells. The KDI domain may thus be a potential drug to prevent CNS damage induced by neurodegenerative disorders, mechanical injury, or ischemia.

Neuron-binding human monoclonal antibodies support central nervous system neurite extension

Two human IgMs (sHIgM12 and sHIgM42) were identified that supported in vitro central nervous system (CNS) neurite extension equal to the potent neurite stimulatory molecule laminin. Both IgMs bound to multiple cell types in unfixed CNS tissue and to the surface of neurons in culture. Both monoclonal antibodies (mAbs) overrode the inhibitory effect of CNS mouse myelin on granule cell neurite extension. Neither mAb bound to the surface of mature oligodendrocytes or strictly colocalized with myelin proteins. Sialidase treatment eliminated the neuronal surface binding of both mAbs, whereas blocking sphingolipid synthesis with Fumonisin B1 or removing GPI-linked proteins with PIPLC did not. When used as substrates for mixed neuron/glia aggregates, sHIgM12 and sHIgM42 supported robust neurite extension while astrocytes remained in the aggregates. In contrast, laminin supported astrocyte migration and spreading. Human mAbs that support neurite extension are novel factors that may be of use in encouraging axon repair following injury while minimizing glial cell infiltration. Both human mAbs were isolated from individuals with monoclonal gammopathy. Each individual has carried high mAb titers in circulation for years without detriment. sHIgM12 and sHIgM42 are therefore unlikely to be systemically pathogenic.