Myelin-associated glycoprotein-mediated signaling in central nervous system pathophysiology

Connexin43 Contributes to Alzheimer's Disease by Promoting the Mitochondria-Associated Membrane-Related Autophagy Inhibition

The perturbed structure and function of mitochondria-associated membranes (MAM), instead of the amyloid cascade, have been gradually proposed to play a basic role in the pathogenesis of Alzheimer's disease (AD). Notably, autophagy inhibition is one of the main mechanisms of MAM dysfunction and plays an important role in neuronal injury. However, the upstream molecular mechanism underlying the MAM dysfunctions remains elusive. Here, we defined an unexpected and critical role of connexin43 (Cx43) in regulating the MAM structure. The expression levels of Cx43 and mitofusin-2 (MFN2, the MAM biomarker) increase significantly in 9-month-old APPswe/PS1dE9 double-transgenic AD model mice, and there is an obvious colocalization relationship. Moreover, both AD mice and cells lacking Cx43 exhibit an evident reduction in the MAM contact sites, which subsequently promotes the conversion from microtubule-associated protein 1 light-chain 3B I (LC3B-I) to LC3B-II via inhibition mTOR-dependent pathway and then initiates the generation of autophagosomes. Autophagosome formation ultimately promotes β-amyloid (Aβ) clearance and attenuates Aβ-associated pathological changes in AD, mainly including astrogliosis and neuronal apoptosis. Our findings not only reveal a previously unrecognized effect of Cx43 on MAM upregulation but also highlight the major player of MAM-induced autophagy inhibition in Cx43-facilitated AD pathogenesis, providing a novel insight into the alternative therapeutic strategies for the early treatment of AD.

New insights into the immunologic role of oligodendrocyte lineage cells in demyelination diseases

Oligodendrocyte lineage cells (OL-lineage cells) are a cell population that are crucial for mammalian central nervous system (CNS) myelination. OL-lineage cells go through developmental stages, initially differentiating into oligodendrocyte precursor cells (OPCs), before becoming immature oligodendrocytes, then mature oligodendrocytes (OLs). While the main function of cell lineage is in myelin formation, and increasing number of studies have turned to explore the immunological characteristics of these cells. Initially, these studies focused on discovering how OPCs and OLs are affected by the immune system, and then, how these immunological changes influence the myelination process. However, recent studies have uncovered another feature of OL-lineage cells in our immune systems. It would appear that OL-lineage cells also express immunological factors such as cytokines and chemokines in response to immune activation, and the expression of these factors changes under various pathologic conditions. Evidence suggests that OL-lineage cells actually modulate immune functions. Indeed, OL-lineage cells appear to play both "victim" and "agent" in the CNS which raises a number of questions. Here, we summarize immunologic changes in OL-lineage cells and their effects, as well as consider OL-lineage cell changes which influence immune cells under pathological conditions. We also describe some of the underlying mechanisms of these changes and their effects. Finally, we describe several studies which use OL-lineage cells as immunotherapeutic targets for demyelination diseases.

New Insights into the Roles of Nogo-A in CNS Biology and Diseases

Nogos have become a hot topic for its well-known number Nogo-A's big role in clinical matters. It has been recognized that the expression of Nogo-A and the receptor NgR1 inhibit the neuron's growth after CNS injuries or the onset of the MS. The piling evidence supports the notion that the Nogo-A is also involved in the synaptic plasticity, which was shown to negatively regulate the strength of synaptic transmission. The occurrence of significant schizophrenia-like behavioral phenotypes in Nogo-A KO rats also added strong proof to this conclusion. This review mainly focuses on the structure of Nogo-A and its corresponding receptor-NgR1, its intra- and extra-cellular signaling, together with its major physiological functions such as regulation of migration and distribution and its related diseases like stroke, AD, ALS and so on.

Spatio-temporal expression of paired immunoglobulin-like receptor-B in the adult mouse brain after focal cerebral ischaemia

PRIMARY OBJECTIVE

Paired immunoglobulin-like receptor-B (PirB) is another receptor, except for the Nogo receptor, that is involved in inhibition of axons regeneration after central nervous system injury. However, the expression of PirB in focal cerebral ischaemic brain remains unclear. Herein, this study investigated spatial-temporal expression of PirB in the mouse brain following transient focal cerebral ischaemia.

METHODS AND PROCEDURE

Adult male C57BL/6 mice underwent a 60-minute transient occlusion of middle cerebral artery. Mice were killed and brain samples were harvested at 30 minutes, 2 hours, 24 hours, 3 days and 7 days after reperfusion. Expression of PirB in the brain was determined by reverse transcriptase-polymerase chain reaction (RT-PCR), western blot analysis and immunohistochemical staining.

MAIN OUTCOMES AND RESULTS

The results showed that PirB was mainly expressed in ischaemic penumbra. PirB mRNA and protein expression began to increase at 2 hours, peaked at 24 hours and lasted for 7 days after reperfusion in the ischaemic penumbra. By using immunofluorescence, PirB signals were co-localized with NeuN-positive neurons.

CONCLUSION

PirB expression is up-regulated in ischaemic penumbra following transient focal cerebral ischaemia. PirB expression in neurons may play important pathological roles in the inhibition of axonal regeneration after stroke, suggesting that the inhibition of PirB expression may enhance axonal regeneration and functional recovery after stroke.

Myelin-specific proteins: a structurally diverse group of membrane-interacting molecules

The myelin sheath is a multilayered membrane in the nervous system, which has unique biochemical properties. Myelin carries a set of specific high-abundance proteins, the structure and function of which are still poorly understood. The proteins of the myelin sheath are involved in a number of neurological diseases, including autoimmune diseases and inherited neuropathies. In this review, we briefly discuss the structural properties and functions of selected myelin-specific proteins (P0, myelin oligodendrocyte glycoprotein, myelin-associated glycoprotein, myelin basic protein, myelin-associated oligodendrocytic basic protein, P2, proteolipid protein, peripheral myelin protein of 22 kDa, 2',3'-cyclic nucleotide 3'-phosphodiesterase, and periaxin); such properties include, for example, interactions with lipid bilayers and the presence of large intrinsically disordered regions in some myelin proteins. A detailed understanding of myelin protein structure and function at the molecular level will be required to fully grasp their physiological roles in the myelin sheath.

Regulation of axonal regeneration following the central nervous system injury in adult mammalian

It has been well established that the recovery ability of central nervous system (CNS) is very poor in adult mammals. As a result, CNS trauma generally leads to severe and persistent functional deficits. Thus, the investigation in this field becomes a "hot spot". Up to date, accumulating evidence supports the hypothesis that the failure of CNS neurons to regenerate is not due to their intrinsic inability to grow new axons, but due to their growth state and due to lack of a permissive growth environment. Therefore, any successful approaches to facilitate the regeneration of injured CNS axons will likely include multiple steps: keeping neurons alive in a certain growth-state, preventing the formation of a glial scar, overcoming inhibitory molecules present in the myelin debris, and giving direction to the growing axons. This brief review focused on the recent progress in the neuron regeneration of CNS in adult mammals.

Nogo-A and myelin-associated glycoprotein differently regulate oligodendrocyte maturation and myelin formation

Nogo-A is one of the most potent oligodendrocyte-derived inhibitors for axonal regrowth in the injured adult CNS. However, the physiological function of Nogo-A in development and in healthy oligodendrocytes is still unknown. In the present study, we investigated the role of Nogo-A for myelin formation in the developing optic nerve. By quantitative real-time PCR, we found that the expression of Nogo-A increased faster in differentiating oligodendrocytes than that of the major myelin proteins MBP (myelin basic protein), PLP (proteolipid protein)/DM20, and CNP (2',3'-cyclic nucleotide 3'-phosphodiesterase). The analysis of optic nerves and cerebella of mice deficient for Nogo-A (Nogo-A(-/-)) revealed a marked delay of oligodendrocyte differentiation, myelin sheath formation, and axonal caliber growth within the first postnatal month. The combined deletion of Nogo-A and MAG caused a more severe transient hypomyelination. In contrast to MAG(-/-) mice, Nogo-A(-/-) mutants did not present abnormalities in the structure of myelin sheaths and Ranvier nodes. The common binding protein for Nogo-A and MAG, NgR1, was exclusively upregulated in MAG(-/-) animals, whereas the level of Lingo-1, a coreceptor, remained unchanged. Together, our results demonstrate that Nogo-A and MAG are differently involved in oligodendrocyte maturation in vivo, and suggest that Nogo-A may influence also remyelination in pathological conditions such as multiple sclerosis.

Glial precursor cell transplantation therapy for neurotrauma and multiple sclerosis

Traumatic injury to the brain or spinal cord and multiple sclerosis (MS) share a common pathophysiology with regard to axonal demyelination. Despite advances in central nervous system (CNS) repair in experimental animal models, adequate functional recovery has yet to be achieved in patients in response to any of the current strategies. Functional recovery is dependent, in large part, upon remyelination of spared or regenerating axons. The mammalian CNS maintains an endogenous reservoir of glial precursor cells (GPCs), capable of generating new oligodendrocytes and astrocytes. These GPCs are upregulated following traumatic or demyelinating lesions, followed by their differentiation into oligodendrocytes. However, this innate response does not adequately promote remyelination. As a result, researchers have been focusing their efforts on harvesting, culturing, characterizing, and transplanting GPCs into injured regions of the adult mammalian CNS in a variety of animal models of CNS trauma or demyelinating disease. The technical and logistic considerations for transplanting GPCs are extensive and crucial for optimizing and maintaining cell survival before and after transplantation, promoting myelination, and tracking the fate of transplanted cells. This is especially true in trials of GPC transplantation in combination with other strategies such as neutralization of inhibitors to axonal regeneration or remyelination. Overall, such studies improve our understanding and approach to developing clinically relevant therapies for axonal remyelination following traumatic brain injury (TBI) or spinal cord injury (SCI) and demyelinating diseases such as MS.