CZ-7, a new derivative of Claulansine F, promotes remyelination induced by cuprizone by enhancing myelin debris clearance

A review focuses on a neglected and controversial component of SCI: myelin debris

Myelin sheath, as the multilayer dense structure enclosing axons in humans and other higher organisms, may rupture due to various injury factors after spinal cord injury, thus producing myelin debris. The myelin debris contains a variety of myelin-associated inhibitors (MAIs) and lipid, all inhibiting the repair after spinal cord injury. Through summary and analysis, the present authors found that the inhibition of myelin debris can be mainly divided into two categories: firstly, the direct inhibition mediated by MAIs; secondly, the indirect inhibition mediated by lipid such as cholesterol. It is worth noting that phagocytes are required in the latter indirect inhibition, such as professional phagocytes (macrophages et al.) and non-professional phagocytes (astrocytes et al.). Moreover, complement and the immune system also participate in the phagocytosis of myelin debris, working together with phagocytes to aggravate spinal cord injury. In conclusion, this paper focuses on the direct and indirect effects of myelin debris on spinal cord injury, aiming to provide new inspiration and reflection for the basic research of spinal cord injury and the conception of related treatment.

The paradoxical role of zinc on microglia

Zinc is an essential trace element for humans, and its homeostasis is essential for the health of the central nervous system. Microglia, the resident immune cells in the central nervous system, play the roles of sustaining, nourishing, and immune surveillance. Microglia are sensitive to microenvironment changes and are easily activated to M1 phenotype to enhance disease progression or the M2 phenotype to improve peripheral nerves injury repair. Zinc is requisite for microglial activation, However, the cytotoxicity outcome of zinc against microglia, the activated microglia phenotype, and activated microglia function are ambiguous. Herein, we have reviewed the neurological function of zinc and microglia, particularly the ambiguous role of zinc on microglia. We also pay attention to the role of zinc homeostasis on microglial function within the central nervous system disease. Finally, we observe the relationship between zinc and microglia, attempting to design new therapeutic measures against major nervous system disorders.

CZK, a novel alkaloid derivative from Clausena lansium, alleviates ischemic stroke injury through Nrf2-mediated antioxidant effects

Anti-oxidant stress is a potential strategy for the treatment of ischemic stroke. Here, we found a novel free radical scavenger termed as CZK, which is derived from alkaloids contained in Clausena lansium. In this study, we first compared cytotoxicity and biological activity between CZK and its parent's compound Claulansine F. It was found that CZK had lower cytotoxicity and improved anti-oxygen-glucose deprivation/reoxygenation (OGD/R) injury than its parent's compound. Free radical scavenging test showed that CZK had a strong inhibitory effect on hydroxyl free radicals with the IC₅₀ of 77.08 nM. Intravenous injection of CZK (50 mg/kg) significantly alleviated ischemia-reperfusion injury, manifested by reduced neuronal damage and decreased oxidative stress. Consistent with the findings, the activities of superoxide dismutase (SOD) and reduced glutathione (GSH) were increased. Molecular docking predicted that CZK might be combined with nuclear factor erythroid 2-related factor 2 (Nrf2) complex. Our results also confirmed that CZK upregulated the contents of Nrf2 and its target gene products Heme Oxygenase-1 (HO-1), and NAD(P)H: Quinone Oxidoreductase 1 (NQO1). In conclusion, CZK had a potential therapeutic effect for ischemic stroke by activating Nrf2-mediated antioxidant system.

Selective PDE4 subtype inhibition provides new opportunities to intervene in neuroinflammatory versus myelin damaging hallmarks of multiple sclerosis

Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system (CNS) characterized by focal inflammatory lesions and prominent demyelination. Even though the currently available therapies are effective in treating the initial stages of disease, they are unable to halt or reverse disease progression into the chronic progressive stage. Thus far, no repair-inducing treatments are available for progressive MS patients. Hence, there is an urgent need for the development of new therapeutic strategies either targeting the destructive immunological demyelination or boosting endogenous repair mechanisms. Using in vitro, ex vivo, and in vivo models, we demonstrate that selective inhibition of phosphodiesterase 4 (PDE4), a family of enzymes that hydrolyzes and inactivates cyclic adenosine monophosphate (cAMP), reduces inflammation and promotes myelin repair. More specifically, we segregated the myelination-promoting and anti-inflammatory effects into a PDE4D- and PDE4B-dependent process respectively. We show that inhibition of PDE4D boosts oligodendrocyte progenitor cells (OPC) differentiation and enhances (re)myelination of both murine OPCs and human iPSC-derived OPCs. In addition, PDE4D inhibition promotes in vivo remyelination in the cuprizone model, which is accompanied by improved spatial memory and reduced visual evoked potential latency times. We further identified that PDE4B-specific inhibition exerts anti-inflammatory effects since it lowers in vitro monocytic nitric oxide (NO) production and improves in vivo neurological scores during the early phase of experimental autoimmune encephalomyelitis (EAE). In contrast to the pan PDE4 inhibitor roflumilast, the therapeutic dose of both the PDE4B-specific inhibitor A33 and the PDE4D-specific inhibitor Gebr32a did not trigger emesis-like side effects in rodents. Finally, we report distinct PDE4D isoform expression patterns in human area postrema neurons and human oligodendroglia lineage cells. Using the CRISPR-Cas9 system, we confirmed that pde4d1/2 and pde4d6 are the key targets to induce OPC differentiation. Collectively, these data demonstrate that gene specific PDE4 inhibitors have potential as novel therapeutic agents for targeting the distinct disease processes of MS.

Therapeutic effect of combination vitamin D3 and siponimod on remyelination and modulate microglia activation in cuprizone mouse model of multiple sclerosis

Stimulation of remyelination is critical for the treatment of multiple sclerosis (MS) to alleviate symptoms and protect the myelin sheath from further damage. The current study aimed to investigate the possible therapeutic effects of combining vitamin D3 (Vit D3) and siponimod (Sipo) on enhancing remyelination and modulating microglia phenotypes in the cuprizone (CPZ) demyelination mouse model. The study was divided into two stages; demyelination (first 5 weeks) and remyelination (last 4 weeks). In the first 5 weeks, 85 mice were randomly divided into two groups, control (n = 20, standard rodent chow) and CPZ (n = 65, 0.3% CPZ mixed with chow for 6 weeks, followed by 3 weeks of standard rodent chow). At week 5, the CPZ group was re-divided into four groups (n = 14) for remyelination stages; untreated CPZ (0.2 ml of CMC orally), CPZ+Vit D3 (800 IU/kg Vit D3 orally), CPZ+Sipo (1.5 mg/kg Sipo orally), and CPZ+Vit D3 (800 IU/kg Vit D3) + Sipo (1.5 mg/kg Sipo orally). Various behavioral tasks were performed to evaluate motor performance. Luxol Fast Blue (LFB) staining, the expression level of myelin basic protein (MBP), and M1/M2 microglia phenotype genes were assessed in the corpus callosum (CC). The results showed that the combination of Vit D3 and Sipo improved behavioral deficits, significantly promoted remyelination, and modulated expression levels of microglia phenotype genes in the CC at early and late remyelination stages. These results demonstrate for the first time that a combination of Vit D3 and Sipo can improve the remyelination process in the cuprizone (CPZ) mouse model by attenuating the M1 microglia phenotype. This may help to improve the treatment of MS patients.

Drug-induced microglial phagocytosis in multiple sclerosis and experimental autoimmune encephalomyelitis and the underlying mechanisms

Microglia are resident macrophages of the central nervous system (CNS). It plays a significant role in immune surveillance under physiological conditions. On stimulation by pathogens, microglia change their phenotypes, phagocytize toxic molecules, secrete pro-inflammatory/anti-inflammatory factors, promotes tissue repair, and maintain the homeostasis in CNS. Accumulation of myelin debris in multiple sclerosis (MS)/experimental autoimmune encephalomyelitis (EAE) inhibits remyelination by decreasing the phagocytosis by microglia and prevent the recovery of MS/EAE. Drug induced microglia phagocytosis could be a novel therapeutic intervention for the treatment of MS/EAE. But the abnormal phagocytosis of neurons and synapses by activated microglia will lead to neuronal damage and degeneration. It indicates that the phagocytosis of microglia has many beneficial and harmful effects in central neurodegenerative diseases. Therefore, simply promoting or inhibiting the phagocytic activity of microglia may not achieve ideal therapeutic results. However, limited reports are available to elucidate the microglia mediated phagocytosis and its underlying molecular mechanisms. On this basis, the present review describes microglia-mediated phagocytosis, drug-induced microglia phagocytosis, molecular mechanism, and novel approach for MS/EAE treatment.

Rg1 exerts protective effect in CPZ-induced demyelination mouse model via inhibiting CXCL10-mediated glial response

Myelin damage and abnormal remyelination processes lead to central nervous system dysfunction. Glial activation-induced microenvironment changes are characteristic features of the diseases with myelin abnormalities. We previously showed that ginsenoside Rg1, a main component of ginseng, ameliorated MPTP-mediated myelin damage in mice, but the underlying mechanisms are unclear. In this study we investigated the effects of Rg1 and mechanisms in cuprizone (CPZ)-induced demyelination mouse model. Mice were treated with CPZ solution (300 mg· kg^-1· d^-1, ig) for 5 weeks; from week 2, the mice received Rg1 (5, 10, and 20 mg· kg^-1· d^-1, ig) for 4 weeks. We showed that Rg1 administration dose-dependently alleviated bradykinesia and improved CPZ-disrupted motor coordination ability in CPZ-treated mice. Furthermore, Rg1 administration significantly decreased demyelination and axonal injury in pathological assays. We further revealed that the neuroprotective effects of Rg1 were associated with inhibiting CXCL10-mediated modulation of glial response, which was mediated by NF-κB nuclear translocation and CXCL10 promoter activation. In microglial cell line BV-2, we demonstrated that the effects of Rg1 on pro-inflammatory and migratory phenotypes of microglia were related to CXCL10, while Rg1-induced phagocytosis of microglia was not directly related to CXCL10. In CPZ-induced demyelination mouse model, injection of AAV-CXCL10 shRNA into mouse lateral ventricles 3 weeks prior CPZ treatment occluded the beneficial effects of Rg1 administration in behavioral and pathological assays. In conclusion, CXCL10 mediates the protective role of Rg1 in CPZ-induced demyelination mouse model. This study provides new insight into potential disease-modifying therapies for myelin abnormalities.

The roles of microglia and astrocytes in phagocytosis and myelination: Insights from the cuprizone model of multiple sclerosis

In human demyelinating diseases such as multiple sclerosis (MS), an imbalance between demyelination and remyelination can trigger progressive degenerative processes. The clearance of myelin debris (phagocytosis) from the site of demyelination by microglia is critically important to achieve adequate remyelination and to slow the progression of the disease. However, how microglia phagocytose the myelin debris, and why clearance is impaired in MS, is not fully known; likewise, the role of the microglia in remyelination remains unclear. Recent studies using cuprizone (CPZ) as an animal model of central nervous system demyelination revealed that the up‐regulation of signaling proteins in microglia facilitates effective phagocytosis of myelin debris. Moreover, during demyelination, protective mediators are released from activated microglia, resulting in the acceleration of remyelination in the CPZ model. In contrast, inadequate microglial activation or recruitment to the site of demyelination, and the production of toxic mediators, impairs remyelination resulting in progressive demyelination. In addition to the microglia‐mediated phagocytosis, astrocytes play an important role in the phagocytic process by recruiting microglia to the site of demyelination and producing regenerative mediators. The current review is an update of these emerging findings from the CPZ animal model, discussing the roles of microglia and astrocytes in phagocytosis and myelination.

Role of microtubule dynamics in Wallerian degeneration and nerve regeneration after peripheral nerve injury

Wallerian degeneration, the progressive disintegration of distal axons and myelin that occurs after peripheral nerve injury, is essential for creating a permissive microenvironment for nerve regeneration, and involves cytoskeletal reconstruction. However, it is unclear whether microtubule dynamics play a role in this process. To address this, we treated cultured sciatic nerve explants, an in vitro model of Wallerian degeneration, with the microtubule-targeting agents paclitaxel and nocodazole. We found that paclitaxel-induced microtubule stabilization promoted axon and myelin degeneration and Schwann cell dedifferentiation, whereas nocodazole-induced microtubule destabilization inhibited these processes. Evaluation of an in vivo model of peripheral nerve injury showed that treatment with paclitaxel or nocodazole accelerated or attenuated axonal regeneration, as well as functional recovery of nerve conduction and target muscle and motor behavior, respectively. These results suggest that microtubule dynamics participate in peripheral nerve regeneration after injury by affecting Wallerian degeneration. This study was approved by the Animal Care and Use Committee of Southern Medical University, China (approval No. SMU-L2015081) on October 15, 2015.

Physical exercise modulates the astrocytes polarization, promotes myelin debris clearance and remyelination in chronic cerebral hypoperfusion rats

AIMS

White matter damage is the main pathological feature of chronic cerebral hypoperfusion (CCH) and glial activation is crucial in this process. Physical exercise has protective effects on CCH, but the mechanism is unclear. Therefore, this study focuses on investigating the influence of physical exercise on activated astrocytes polarization and its role in CCH.

MAIN METHODS

Rats were given wheel running 48 h after 2VO (2 vessel occlusion) surgery. The cognitive function was evaluated by Morris water maze and novel object recognition test. Inflammatory cytokines expressions were detected by ELISA. Astrocytes polarization was analyzed by immunofluorescence. Myelin debris clearance and remyelination were detected by immunofluorescence and transmission electron microscopy.

KEY FINDINGS

Astrocytes were activated and mainly switched to A1 phenotype in rats 2 and 3 months after 2VO. Myelin debris deposition and limited remyelination can be observed at the corresponding time. Whereas physical exercise can improve the cognitive function of 2VO rats, downregulate the expression of inflammatory factors IL-1α, C1q and TNF, upregulate the release of TGFβ, and promote activated astrocytes transformation from A1 to A2 phenotype. In addition, it can also enhance myelin debris removal and remyelination.

SIGNIFICANCE

These findings suggest that the benefits of physical exercise on white matter repair and cognition improvement may be related to its regulation of astrocytes polarization, which contributes to myelin debris clearance and effective remyelination in CCH.

Fasudil enhances the phagocytosis of myelin debris and the expression of neurotrophic factors in cuprizone-induced demyelinating mice

Multiple sclerosis (MS) is mainly associated with the neuroinflammation and demyelination in the central nervous system (CNS), in which the failure of remyelination results in persistent neurological dysfunction. Fasudil, a typical Rho kinase inhibitor, has been exhibited beneficial effects on several models of neurodegenerative disorders. In this study, we showed that Fasudil promoted the uptake of myelin debris by microglia via cell experiments and through a cuprizone (CPZ)-induced demyelinating model. In vitro, microglia with phagocytic debris exhibited enhanced expression of brain-derived neurotrophic factor (BDNF) and glial cell-derived neurotrophic factor (GDNF), and the conditioned medium promoted the maturation of oligodendrocyte precursor cells (OPCs). Meanwhile, Fasudil upregulated TREM2/DAP12 pathway, which positively regulated the phagocytosis of myelin debris by microglia. Similarly, in vivo, Fasudil intervention enhanced the clearance of myelin debris, upregulated the expression of BDNF and GDNF on microglia, and promoted the formation of Oligo2+/PDGFRα+ OPCs and the maturation of MBP + oligodendrocytes in the brain. Our results showed that Fasudil targeted the phagocytic function of microglia, effectively clearing myelin debris produced during pathological process possibly by upregulating TREM2/DAP12 pathway, accompanied by increased expression of BDNF and GDNF. However, the precise mechanism underlying the effects of Fasudil in promoting phagocytic effects and neurotrophic factors remains to be elucidated.