Concept and molecular basis of axonal regeneration after central nervous system injury

Fascin-1 limits myosin activity in microglia to control mechanical characterization of the injured spinal cord

BACKGROUND

Mechanical softening of the glial scar region regulates axonal regeneration to impede neurological recovery in central nervous system (CNS) injury. Microglia, a crucial cellular component of the glial scar, facilitate neuronal survival and neurological recovery after spinal cord injury (SCI). However, the critical mechanical characterization of injured spinal cord that harmonizes neuroprotective function of microglia remains poorly understood.

METHODS

Spinal cord tissue stiffness was assessed using atomic force microscopy (AFM) in a mouse model of crush injury. Pharmacological depletion of microglia using PLX5622 was used to explore the effect of microglia on mechanical characterization. Conditional knockout of Fascin-1 in microglia (Fascin-1 CKO) alone or in combination with inhibition of myosin activity was performed to delve into relevant mechanisms of microglia regulating mechanical signal. Immunofluorescence staining was performed to evaluate the related protein levels, inflammatory cells, and neuron survival after SCI. The Basso mouse scale score was calculated to assess functional recovery.

RESULTS

Spinal cord tissue significantly softens after SCI. Microglia depletion or Fascin-1 knockout in microglia limits tissue softening and alters mechanical characterization, which leads to increased tissue pathology and impaired functional recovery. Mechanistically, Fascin-1 inhibits myosin activation to promote microglial migration and control mechanical characterization after SCI.

CONCLUSIONS

We reveal that Fascin-1 limits myosin activity to regulate mechanical characterization after SCI, and this mechanical signal should be considered in future approaches for the treatment of CNS diseases.

Nanomaterial-Based Approaches for Neural Regeneration

Mechanical, thermal, chemical, or ischemic injury of the central or peripheral nervous system results in neuron loss, neurite damage, and/or neuronal dysfunction, almost always accompanied by sensorimotor impairment which alters the patient's life quality. The regenerative strategies for the injured nervous system are currently limited and mainly allow partial functional recovery, so it is necessary to develop new and effective approaches for nervous tissue regenerative therapy. Nanomaterials based on inorganic or organic and composite or hybrid compounds with tunable physicochemical properties and functionality proved beneficial for the transport and delivery/release of various neuroregenerative-relevant biomolecules or cells. Within the following paragraphs, we will emphasize that nanomaterial-based strategies (including nanosized and nanostructured biomaterials) represent a promising alternative towards repairing and regenerating the injured nervous system.

Biochemical events related to glial response in spinal cord injury

Introducción. La lesión de la médula espinal (LME) es un evento devastador con implicaciones físicas, psicológicas y socioeconómicas. En el tejido cercano a la lesión se instauran cambios morfofisiológicos que determinan la recuperación funcional del segmento medular y de los órganos efectores dependientes de los tractos axonales lesionados.Objetivo. Describir los eventos bioquímicos secuenciales más relevantes de la respuesta de las células gliales posterior a la LME.Materiales y métodos. Se realizó una búsqueda de publicaciones científicas de los últimos 18 años en las bases de datos PubMed y ScienceDirect, bajo los términos en inglés spinal cord injury (SCI), SCI pathophysiology, SCI inflammation, microglia in SCI, glial scar y chondroitin sulfate proteoglycans (CSPG).Resultados. Los procesos fisiopatológicos que se producen después de la LME determinan la recuperación neurológica de los pacientes. La activación de las células gliales juega un papel importante, ya que promueve la producción de moléculas bioactivas y la formación de barreras físicas que inhiben la regeneración neural.Conclusión. El conocimiento de los cambios neurobiológicos ocurridos tras la LME permite una mayor comprensión de la fisiopatología y favorece la búsqueda de nuevas alternativas terapéuticas que limiten la progresión de la lesión primaria y que minimicen el daño secundario responsable de la disfunción neurológica.

RGMa inhibition with human monoclonal antibodies promotes regeneration, plasticity and repair, and attenuates neuropathic pain after spinal cord injury

Traumatic spinal cord injury (SCI) causes a cascade of degenerative events including cell death, axonal damage, and the upregulation of inhibitory molecules which prevent regeneration and limit recovery. Repulsive guidance molecule A (RGMa) is a potent neurite growth inhibitor in the central nervous system, exerting its repulsive activity by binding the Neogenin receptor. Here, we show for the first time that inhibitory RGMa is markedly upregulated in multiple cell types after clinically relevant impact-compression SCI in rats, and importantly, also in the injured human spinal cord. To neutralize inhibitory RGMa, clinically relevant human monoclonal antibodies were systemically administered after acute SCI, and were detected in serum, cerebrospinal fluid, and in the injured tissue. Rats treated with RGMa blocking antibodies showed significantly improved recovery of motor function and gait. Furthermore, RGMa blocking antibodies promoted neuronal survival, and enhanced the plasticity of descending serotonergic pathways and corticospinal tract axonal regeneration. RGMa antibody also attenuated neuropathic pain responses, which was associated with fewer activated microglia and reduced CGRP expression in the dorsal horn caudal to the lesion. These results show the therapeutic potential of the first human RGMa antibody for SCI and uncovers a new role for the RGMa/Neogenin pathway on neuropathic pain.

White Matter Injury after Intracerebral Hemorrhage: Pathophysiology and Therapeutic Strategies

Intracerebral hemorrhage (ICH) accounts for 10%–30% of all types of stroke. Bleeding within the brain parenchyma causes gray matter (GM) destruction as well as proximal or distal white matter (WM) injury (WMI) due to complex pathophysiological mechanisms. Because WM has a distinct cellular architecture, blood supply pattern and corresponding function, and its response to stroke may vary from that of GM, a better understanding of the characteristics of WMI following ICH is essential and may shed new light on treatment options. Current evidence using histological, radiological and chemical biomarkers clearly confirms the spatio-temporal distribution of WMI post- ICH. Although certain types of pathological damage such as inflammatory, oxidative and neuro-excitotoxic injury to WM have been identified, the exact molecular mechanisms remain unclear. In this review article, we briefly describe the constitution and physiological function of brain WM, summarize evidence regarding WMI, and focus on the underlying pathophysiological mechanisms and therapeutic strategies.

The effects of Chinese medicines on cAMP/PKA signaling in central nervous system dysfunction

Neuropathological injury in the mammalian adult central nervous system (CNS) may cause axon disruption, neuronal death and lasting neurological deficits. Failure of axon regeneration is one of the major challenges for CNS functional recovery. Recently, the cAMP/PKA signaling pathway has been proven to be a critical regulator for neuronal regeneration, neuroplasticity, learning and memory. Also, previous studies have shown the effects of Chinese medicines on the prevention and treatment of CNS dysfunction mediated in part by cAMP/PKA signaling. In this review, the authors discuss current knowledge of the role of cAMP/PKA signaling pathway in neuronal regeneration and provide an overview of the Chinese medicines that may enable CNS functional recovery via this signaling pathway.

Epigenetic Regulation of BDNF Gene during Development and Diseases

Brain-derived neurotrophic factor (BDNF) is required for the development of the nervous system, proper cognitive function and memory formation. While aberrant expression of BDNF has been implicated in neurological disorders, the transcriptional regulation of BDNF remains to be elucidated. In response to different stimuli, BDNF expression can be initiated from different promoters. Several studies have suggested that the expression of BDNF is regulated by promoter methylation. An emerging theme points to the possibility that histone modifications at the BDNF promoters may link to the neurological pathology. Thus, understanding the epigenetic regulation at the BDNF promoters will shed light on future therapies for neurological disorders. The present review summarizes the current knowledge of histone modifications of the BDNF gene in neuronal diseases, as well as the developmental regulation of the BDNF gene based on data from the Encyclopedia of DNA Elements (ENCODE).

Polyphenols from green tea prevent antineuritogenic action of Nogo-A via 67-kDa laminin receptor and hydrogen peroxide

Axonal regeneration after injury to the CNS is hampered by myelin-derived inhibitors, such as Nogo-A. Natural products, such as green tea, which are neuroprotective and safe for long-term therapy, would complement ongoing various pharmacological approaches. In this study, using nerve growth factor-differentiated neuronal-like Neuroscreen-1 cells, we show that extremely low concentrations of unfractionated green tea polyphenol mixture (GTPP) and its active ingredient, epigallocatechin-3-gallate (EGCG), prevent both the neurite outgrowth-inhibiting activity and growth cone-collapsing activity of Nogo-66 (C-terminal domain of Nogo-A). Furthermore, a synergistic interaction was observed among GTPP constituents. This preventive effect was dependent on 67-kDa laminin receptor (67LR) to which EGCG binds with high affinity. The antioxidants N-acetylcysteine and cell-permeable catalase abolished this preventive effect of GTPP and EGCG, suggesting the involvement of sublethal levels of H2 O2 in this process. Accordingly, exogenous sublethal concentrations of H2 O2 , added as a bolus dose (5 μM) or more effectively through a steady-state generation (1-2 μM), mimicked GTPP in counteracting the action of Nogo-66. Exogenous H2 O2 mediated this action by bypassing the requirement of 67LR. Taken together, these results show for the first time that GTPP and EGCG, acting through 67LR and elevating intracellular sublethal levels of H2 O2 , inhibit the antineuritogenic action of Nogo-A. Currently, several agents are being evaluated for overcoming axonal growth inhibitors to promote functional recovery after stroke and spinal cord injury. Epigallocatechin-3-gallate (EGCG), present in green tea polyphenol mixture (GTPP), prevents antineuritogenic activity of Nogo-A, a myelin-derived axonal growth inhibitor. The preventive action of EGCG involves the cell-surface-associated 67-kDa laminin receptor and H2 O2 . GTPP may complement ongoing efforts to treat neuronal injuries.>