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

Cell-specific expression and function of laminin at the neurovascular unit

Laminin, a major component of the basal lamina (BL), is a heterotrimeric protein with many isoforms. In the CNS, laminin is expressed by almost all cell types, yet different cells synthesize distinct laminin isoforms. By binding to its receptors, laminin exerts a wide variety of important functions. However, due to the reciprocal and cell-specific expression of laminin in different cells at the neurovascular unit, its functions in blood-brain barrier (BBB) maintenance and BBB repair after injury are not fully understood. In this review, we focus on the expression and functions of laminin and its receptors in the neurovascular unit under both physiological and pathological conditions. We first briefly introduce the structures of laminin and its receptors. Next, the expression and functions of laminin and its receptors in the CNS are summarized in a cell-specific manner. Finally, we identify the knowledge gap in the field and discuss key questions that need to be answered in the future. Our goal is to provide a comprehensive overview on cell-specific expression of laminin and its receptors in the CNS and their functions on BBB integrity.

Basal lamina changes in neurodegenerative disorders

BACKGROUND

Neurodegenerative disorders are a group of age-associated diseases characterized by progressive degeneration of the structure and function of the CNS. Two key pathological features of these disorders are blood-brain barrier (BBB) breakdown and protein aggregation.

MAIN BODY

The BBB is composed of various cell types and a non-cellular component---the basal lamina (BL). Although how different cells affect the BBB is well studied, the roles of the BL in BBB maintenance and function remain largely unknown. In addition, located in the perivascular space, the BL is also speculated to regulate protein clearance via the meningeal lymphatic/glymphatic system. Recent studies from our laboratory and others have shown that the BL actively regulates BBB integrity and meningeal lymphatic/glymphatic function in both physiological and pathological conditions, suggesting that it may play an important role in the pathogenesis and/or progression of neurodegenerative disorders. In this review, we focus on changes of the BL and its major components during aging and in neurodegenerative disorders, including Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). First, we introduce the vascular and lymphatic systems in the CNS. Next, we discuss the BL and its major components under homeostatic conditions, and summarize their changes during aging and in AD, PD, and ALS in both rodents and humans. The functional significance of these alterations and potential therapeutic targets are also reviewed. Finally, key challenges in the field and future directions are discussed.

CONCLUSIONS

Understanding BL changes and the functional significance of these changes in neurodegenerative disorders will fill the gap of knowledge in the field. Our goal is to provide a clear and concise review of the complex relationship between the BL and neurodegenerative disorders to stimulate new hypotheses and further research in this field.

Laminins and their receptors in the CNS

Laminin, an extracellular matrix protein, is widely expressed in the central nervous system (CNS). By interacting with integrin and non-integrin receptors, laminin exerts a large variety of important functions in the CNS in both physiological and pathological conditions. Due to the existence of many laminin isoforms and their differential expression in various cell types in the CNS, the exact functions of each individual laminin molecule in CNS development and homeostasis remain largely unclear. In this review, we first briefly introduce the structure and biochemistry of laminins and their receptors. Next, the dynamic expression of laminins and their receptors in the CNS during both development and in adulthood is summarized in a cell-type-specific manner, which allows appreciation of their functional redundancy/compensation. Furthermore, we discuss the biological functions of laminins and their receptors in CNS development, blood-brain barrier (BBB) maintenance, neurodegeneration, stroke, and neuroinflammation. Last, key challenges and potential future research directions are summarized and discussed. Our goals are to provide a synthetic review to stimulate future studies and promote the formation of new ideas/hypotheses and new lines of research in this field.

Edaravone protects neurons in the rat substantia nigra against 6-hydroxydopamine-induced oxidative stress damage

To investigate the mechanism of the neuroprotective effect of edaravone in substantia nigra (SN) of the 6-OHDA-induced rat model of Parkinson's disease. Animal model of Parkinson's disease was induced in male Sprague-Dawley rats by injecting 6-OHDA into the left medial forebrain bundle. Subsequently, rats were intraperitoneally injected with 0.3, 1, or 3 mg/kg of edaravone for 14 days or with 3 mg/kg edaravone for 14 days followed by 14 days of no treatment. We evaluated the effect of edaravone on the rotational and normal behavior of the rats, and on the number of tyrosine hydroxylase (TH)-positive cells, the amount of Nissl bodies, and the levels of glutathione (GSH), and malondialdehyde (MDA) in the SN. Edaravone treatment at 3 mg/kg significantly reduced apomorphine-induced rotational behavior (P < 0.01), improved the spontaneous behavior, prevented the decrease in the levels of TH-positive cells, Nissl bodies and GSH, and inhibited the increase in the levels of MDA (P < 0.05) in SN of rats with 6-OHDA-induced PD. Edaravone exerted a long-term neuroprotective effects in 6-OHDA-induced PD animal model by attenuating changes in the levels of GSH and MDA in SN, caused by oxidative stress. Edaravone prevented 6-OHDA-induced behavioral changes and de-pigmentation of SN that results from the loss of dopaminergic neurons.

Meningeal cells influence midbrain development and the engraftment of dopamine progenitors in Parkinsonian mice

Dopaminergic neuroblasts, isolated from ventral midbrain fetal tissue, have been shown to structurally and functionally integrate, and alleviate Parkinsonian symptoms following transplantation. The use of donor tissue isolated at an age younger than conventionally employed can result in larger grafts - a consequence of improved cell survival and neuroblast proliferation at the time of implantation. However studies have paid little attention to removal of the meninges from younger tissue, due to its age-dependent tight attachment to the underlying brain. Beyond the protection of the central nervous system, the meninges act as a signaling center, secreting a variety of trophins to influence neural development and additionally impact on neural repair. However it remains to be elucidated what influence these cells have on ventral midbrain development and grafted dopaminergic neuroblasts. Here we examined the temporal role of meningeal cells in graft integration in Parkinsonian mice and, using in vitro approaches, identified the mechanisms underlying the roles of meningeal cells in midbrain development. We demonstrate that young (embryonic day 10), but not older (E12), meningeal cells promote dopaminergic differentiation as well as neurite growth and guidance within grafts and during development. Furthermore we identify stromal derived factor 1 (SDF1), secreted by the meninges and acting on the CXCR4 receptor present on dopaminergic progenitors, as a contributory mediator in these effects. These findings identify new and important roles for the meningeal cells, and SDF1/CXCR4 signaling, in ventral midbrain development as well as neural repair following cell transplantation into the Parkinsonian brain.

Proregenerative properties of ECM molecules

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

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.

Metabotropic glutamate receptors transduce signals for neurite outgrowth after binding of the prion protein to laminin γ1 chain

The prion protein (PrP(C)) is highly expressed in the nervous system, and its abnormal conformer is associated with prion diseases. PrP(C) is anchored to cell membranes by glycosylphosphatidylinositol, and transmembrane proteins are likely required for PrP(C)-mediated intracellular signaling. Binding of laminin (Ln) to PrP(C) modulates neuronal plasticity and memory. We addressed signaling pathways triggered by PrP(C)-Ln interaction in order to identify transmembrane proteins involved in the transduction of PrP(C)-Ln signals. The Ln γ1-chain peptide, which contains the Ln binding site for PrP(C), induced neuritogenesis through activation of phospholipase C (PLC), Ca(2+) mobilization from intracellular stores, and protein kinase C and extracellular signal-regulated kinase (ERK1/2) activation in primary cultures of neurons from wild-type, but not PrP(C)-null mice. Phage display, coimmunoprecipitation, and colocalization experiments showed that group I metabotropic glutamate receptors (mGluR1/5) associate with PrP(C). Expression of either mGluR1 or mGluR5 in HEK293 cells reconstituted the signaling pathways mediated by PrP(C)-Ln γ1 peptide interaction. Specific inhibitors of these receptors impaired PrP(C)-Ln γ1 peptide-induced signaling and neuritogenesis. These data show that group I mGluRs are involved in the transduction of cellular signals triggered by PrP(C)-Ln, and they support the notion that PrP(C) participates in the assembly of multiprotein complexes with physiological functions on neurons.

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.

Triptolide protects against 1-methyl-4-phenyl pyridinium-induced dopaminergic neurotoxicity in rats: implication for immunosuppressive therapy in Parkinson's disease

OBJECTIVE

Neuroinflammation with microglial activation has been implicated to have a strong association with the progressive dopaminergic neuronal loss in Parkinson's disease (PD). The present study was undertaken to evaluate the activation profile of microglia in 1-methyl-4-phenyl pyridinium (MPP+)-induced hemiparkinsonian rats. Triptolide, a potent immunosuppressant and microglia inhibitor, was then examined for its efficacy in protecting dopaminergic neurons from injury and ameliorating behavioral disabilities induced by MPP+.

METHODS

The rat model of PD was established by intranigral microinjection of MPP+. At baseline and on day 1, 3, 7, 14, 21 following MPP+ injection, the degree of microglial activation was examined by detecting the immunodensity of OX-42 (microglia marker) in the substantia nigra (SN). The number of viable dopaminergic neurons was determined by measuring tyrosine hydroxylase (TH) positive neurons in the SN. Behavioral performances were evaluated by counting the number of rotations induced by apomorphine, calculating scores of forelimb akinesia and vibrissae-elicited forelimb placing asymmetry.

RESULTS

Intranigral injection of MPP+ resulted in robust activation of microglia, progressive depletion of dopaminergic neurons, and ongoing aggravation of behavioral disabilities in rats. Triptolide significantly inhibited microglial activation, partially prevented dopaminergic cells from death and improved behavioral performances.

CONCLUSION

These data demonstrated for the first time a neuroprotective effect of triptolide on dopaminergic neurons in MPP+-induced hemiparkinsonian rats. The protective effect of triptolide may, at least partially, be related to the inhibition of MPP+-induced microglial activation. Our results lend strong support to the use of immunosuppressive agents in the management of PD.

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.