Ginsenoside Rb1 Promotes Motor Functional Recovery and Axonal Regeneration in Post-stroke Mice through cAMP/PKA/CREB Signaling Pathway

The central nervous system (CNS) has a poor self-repairing capability after injury because of the inhibition of axonal regeneration by many myelin-associated inhibitory factors. Therefore, ischemic stroke usually leads to disability. Previous studies reported that Ginsenoside Rb1 (GRb1) plays a role in neuronal protection in acute phase after ischemic stroke, but its efficacy in post-stroke and the underlying mechanism are not clear. Recent evidences demonstrated GRb1 promotes neurotransmitter release through the cAMP-depend protein kinase A (PKA) pathway, which is related to axonal regeneration. The present study aimed to determine whether GRb1 improves long-term motor functional recovery and promotes cortical axon regeneration in post-stroke. Adult male C57BL/6 mice were subjected to distal middle cerebral artery occlusion (dMCAO). GRb1 solution (5 mg/ml) or equal volume of normal saline was injected intraperitoneally for the first time at 24 h after surgery, and then daily injected until day 14. Day 3, 7, 14 and 28 after dMCAO were used as observation time points. Motor functional recovery was assessed with Rota-rod test and grid walking task. The expression of growth-associated protein 43 (GAP43) and biotinylated dextran amine (BDA) was measured to evaluate axonal regeneration. The levels of cyclic AMP (cAMP) and PKA were measured by Elisa, PKAc and phosphorylated cAMP response element protein (pCREB) were determined by western blot. Our results shown that GRb1 treatment improved motor function and increased the expression of GAP43 and BDA in ipsilesional and contralateral cortex. GRb1 significantly elevated cAMP and PKA, increased the protein expression of PKAc and pCREB. However, the effects of GRb1 were eliminated by H89 intervention (a PKA inhibitor). These results suggested that GRb1 improved functional recovery in post-stroke by stimulating axonal regeneration and brain repair. The underlying mechanism might be up-regulating the expression of cAMP/PKA/CREB pathway.

Dynamic Changes of Microglia/Macrophage M1 and M2 Polarization in Theiler's Murine Encephalomyelitis

Microglia and macrophages play a central role for demyelination in Theiler's murine encephalomyelitis (TME) virus infection, a commonly used infectious model for chronic-progressive multiple sclerosis. In order to determine the dynamic changes of microglia/macrophage polarization in TME, the spinal cord of Swiss Jim Lambert (SJL) mice was investigated by gene expression profiling and immunofluorescence. Virus persistence and demyelinating leukomyelitis were confirmed by immunohistochemistry and histology. Electron microscopy revealed continuous myelin loss together with abortive myelin repair during the late chronic infection phase indicative of incomplete remyelination. A total of 59 genes out of 151 M1- and M2-related genes were differentially expressed in TME virus-infected mice over the study period. The onset of virus-induced demyelination was associated with a dominating M1 polarization, while mounting M2 polarization of macrophages/microglia together with sustained prominent M1-related gene expression was present during the chronic-progressive phase. Molecular results were confirmed by immunofluorescence, showing an increased spinal cord accumulation of CD16/32(+) M1-, arginase-1(+) M2- and Ym1(+) M2-type cells associated with progressive demyelination. The present study provides a comprehensive database of M1-/M2-related gene expression involved in the initiation and progression of demyelination supporting the hypothesis that perpetuating interaction between virus and macrophages/microglia induces a vicious circle with persistent inflammation and impaired myelin repair in TME.

Effect of Lentiviral shRNA of Nogo Receptor on Rat Cortex Neuron Axon Outgrowth

Background and Aims:

Axon growth is crucial for injured neural tissue to recover; however it is difficult to achieve in general. Axon outgrowth is inhibited by the activation of the Nogo receptor (NgR) by one of three different ligands. The present study aimed to suppress the inhibitory effect of the three inhibitory proteins to facilitate axon outgrowth.

Methods:

A lentiviral vector, siNgR199 (that has the capacity to interfere with the gene of NgR expression), was constructed for suppressing the gene transcription of NgR. Rat cortex neurons and oligodendrocytes were prepared to observe the effect of siNgR199 on facilitating axon outgrowth.

Results:

After transfection, the lentiviral siRNA of NgR remained in target neurons for almost two weeks whereas the conventional siRNA of NgR remained in neurons less than five days. Lentivirus-mediated delivery of exogenous small interfering RNA (siNgR199) targeting NgR significantly reduced the expression of this receptor and promoted axon outgrowth. In contrast, provision of naked siRNA targeting NgR (NgRsiRNA) showed less inhibitory effect on NgR protein expression and did not affect axon outgrowth.

Conclusions:

Lentiviral siRNA of NgR effectively suppresses the expression of NgR in cultured neurons that facilitates the axon outgrowth. The data implicate that lentiviral siRNA of NgR has therapeutic potential in facilitating the recovery of injured neural tissue.

Synaptic rearrangement following axonal injury: Old and new players

Following axotomy, the contact between motoneurons and muscle fibers is disrupted, triggering a retrograde reaction at the neuron cell body within the spinal cord. Together with chromatolysis, a hallmark of such response to injury is the elimination of presynaptic terminals apposing to the soma and proximal dendrites of the injured neuron. Excitatory inputs are preferentially eliminated, leaving the cells under an inhibitory influence during the repair process. This is particularly important to avoid glutamate excitotoxicity. Such shift from transmission to a regeneration state is also reflected by deep metabolic changes, seen by the regulation of several genes related to cell survival and axonal growth. It is unclear, however, how exactly synaptic stripping occurs, but there is substantial evidence that glial cells play an active role in this process. In one hand, immune molecules, such as the major histocompatibility complex (MHC) class I, members of the complement family and Toll-like receptors are actively involved in the elimination/reapposition of presynaptic boutons. On the other hand, plastic changes that involve sprouting might be negatively regulated by extracellular matrix proteins such as Nogo-A, MAG and scar-related chondroitin sulfate proteoglycans. Also, neurotrophins, stem cells, physical exercise and several drugs seem to improve synaptic stability, leading to functional recovery after lesion. This article is part of a Special Issue entitled 'Neuroimmunology and Synaptic Function'.

[Novel aspects of diagnostics and therapy of spinal cord diseases]

BACKGROUND

Both non-traumatic and traumatic spinal cord injuries have in common that a relatively minor structural lesion can cause profound sensorimotor and autonomous dysfunction. Besides treating the cause of the spinal cord injury the main goal is to restore lost function as far as possible.

AIM

This article provides an overview of current innovative diagnostic (imaging) and therapeutic approaches (neurorehabilitation and neuroregeneration) aiming for recovery of function after non-traumatic and traumatic spinal cord injuries.

MATERIAL AND METHODS

An analysis of the current scientific literature regarding imaging, rehabilitation and rehabilitation strategies in spinal cord disease was carried out.

RESULTS

Novel magnetic resonance imaging (MRI) based techniques (e.g. diffusion-weighted MRI and functional MRI) allow visualization of structural reorganization and specific neural activity in the spinal cord. Robotics-driven rehabilitative measures provide training of sensorimotor function in a targeted fashion, which can even be continued in the homecare setting. From a preclinical point of view, defined stem cell transplantation approaches allow for the first time robust structural repair of the injured spinal cord.

CONCLUSION

Besides well-established neurological and functional scores, MRI techniques offer the unique opportunity to provide robust and reliable "biomarkers" for restorative therapeutic interventions. Function-oriented robotics-based rehabilitative interventions alone or in combination with stem cell based therapies represent promising approaches to achieve substantial functional recovery, which go beyond current rehabilitative treatment efforts.

Spontaneous age-related neurite branching in Caenorhabditis elegans

The analysis of morphological changes that occur in the nervous system during normal aging could provide insight into cognitive decline and neurodegenerative disease. Previous studies have suggested that the nervous system of Caenorhabditis elegans maintains its structural integrity with age despite the deterioration of surrounding tissues. Unexpectedly, we observed that neurons in aging animals frequently displayed ectopic branches and that the prevalence of these branches increased with time. Within age-matched populations, the branching of mechanosensory neurons correlated with decreased response to light touch and decreased mobility. The incidence of branching was influenced by two pathways that can affect the rate of aging, the Jun kinase pathway and the insulin/IGF-1 pathway. Loss of Jun kinase signaling, which slightly shortens lifespan, dramatically increased and accelerated the frequency of neurite branching. Conversely, inhibition of the daf-2 insulin/IGF-1-like signaling pathway, which extends lifespan, delayed and suppressed branching, and this delay required DAF-16/FOXO activity. Both JNK-1 and DAF-16 appeared to act within neurons in a cell-autonomous manner to influence branching, and, through their tissue-specific expression, it was possible to disconnect the rate at which branching occurred from the overall rate of aging of the animal. Old age has generally been associated with the decline and deterioration of different tissues, except in the case of tumor cell growth. To our knowledge, this is the first indication that aging can potentiate another form of growth, the growth of neurite branches, in normal animals.

Extracellular matrix abnormalities in schizophrenia

Emerging evidence points to the involvement of the brain extracellular matrix (ECM) in the pathophysiology of schizophrenia (SZ). Abnormalities affecting several ECM components, including Reelin and chondroitin sulfate proteoglycans (CSPGs), have been described in subjects with this disease. Solid evidence supports the involvement of Reelin, an ECM glycoprotein involved in corticogenesis, synaptic functions and glutamate NMDA receptor regulation, expressed prevalently in distinct populations of GABAergic neurons, which secrete it into the ECM. Marked changes of Reelin expression in SZ have typically been reported in association with GABA-related abnormalities in subjects with SZ and bipolar disorder. Recent findings from our group point to substantial abnormalities affecting CSPGs, a main ECM component, in the amygdala and entorhinal cortex of subjects with schizophrenia, but not bipolar disorder. Striking increases of glial cells expressing CSPGs were accompanied by reductions of perineuronal nets, CSPG- and Reelin-enriched ECM aggregates enveloping distinct neuronal populations. CSPGs developmental and adult functions, including neuronal migration, axon guidance, synaptic and neurotransmission regulation are highly relevant to the pathophysiology of SZ. Together with reports of anomalies affecting several other ECM components, these findings point to the ECM as a key component of the pathology of SZ. We propose that ECM abnormalities may contribute to several aspects of the pathophysiology of this disease, including disrupted connectivity and neuronal migration, synaptic anomalies and altered GABAergic, glutamatergic and dopaminergic neurotransmission.

Biochemical insights into the role of matrix metalloproteinases in regeneration: challenges and recent developments

Matrix metalloproteinases (MMPs) are a group of proteases that belong to the metazincin family. These proteins consist of similar structures featuring a signaling peptide, a propeptide domain, a catalytic domain where the notable zinc ion binding site is found and a hinge region that binds to the C-terminal hemoplexin domain. MMPs can be produced by numerous cell types through secretion or localization to the cell membrane. While certain chemical compounds have been known to generally inhibit MMPs, naturally occurring proteins known as tissue inhibitors of metalloproteinases (TIMPs) effectively interact with MMPs to modify their biological roles. MMPs are very important enzymes that actively participate in remodeling the extracellular matrix by degrading certain constituents, along with promoting cell proliferation, migration, differentiation, apoptosis and angiogenesis. In normal adult tissue, they are almost undetectable; however, when perturbed through injury, disease or pregnancy, they have elevated expression. The goal of this review is to identify new experimental findings that have provided further insight into the role of MMPs in skeletal muscle, nerve and dermal tissue, as well as in the liver, heart and kidneys. Increased expression of MMPs can improve the regeneration potential of wounds; however, an imbalance between MMP and TIMP expression can prove to be destructive for afflicted tissues.

Lugaro's forgotten legacy: the hypothesis of negative neurotropism

Among the most fascinating riddles in neuroscience is the one concerning the poor regeneration capacity of the adult mammalian CNS. A central aetiological hypothesis for the lack of axonal regeneration in the CNS concerns the inhibitory role of myelin components of the white matter. The main exponent of this hypothesis in the 1980s and 1990s has been Martin Schwab, although before him Martin Berry and others had suggested an inhibitory role for CNS myelin. However, a hypothesis for a negative neurotropic action exerted by CNS white matter was formulated by Lugaro already in 1906. This article is a belated tribute to Lugaro's original contribution in the field of neuroregeneration.

Identification and validation of a Lewis x glycomimetic peptide

Glycans play important roles in regulating cell recognition and interactions to fine tune development, and synaptic plasticity and regeneration in the adult nervous system. The spatial and temporal expression pattern of Lewis(x) (a terminal trisaccharide epitope characterized by alpha1,3-fucosyl-N-acetyl-lactosamine) in the nervous system indicates an important role of this epitope in neurogenesis and brain development. Localization of Lewis(x) in the proliferative subventricular zone of the developing nervous system and also its expression on stem cells of the adult nervous system suggests a role in neurogenesis and hence regeneration. To provide an alternative tool to elucidate the functional roles of Lewis(x), we screened a random peptide phage library against a Lewis(x)-specific antibody to identify a Lewis(x) glycomimetic peptide. We identified a peptide that specifically bound to the Lewis(x)-specific antibody and this binding could be competed by the Lewis(x) glycan. Different aspects of the Lewis(x) glycomimetic peptide were investigated by introducing it in in vitro assays measuring neurite outgrowth and in in vivo assays to determine its efficacy in regeneration of peripheral nerve and spinal cord after injury in adult mice. In vitro, neurite outgrowth triggered by the Lewis(x-)carrying adhesion molecule CD24 was abolished alike by the Lewis(x) glycan and the glycomimetic peptide, while no influence of the glycomimetic peptide was seen in regeneration. Our results validate the use of Lewis(x) glycomimetic peptide as a functionally equivalent structure to the Lewis(x) glycan.