A bloody brake on myelin repair

Insights Into Central Nervous System Glial Cell Formation and Function From Zebrafish

The term glia describes a heterogenous collection of distinct cell types that make up a large proportion of our nervous system. Although once considered the glue of the nervous system, the study of glial cells has evolved significantly in recent years, with a large body of literature now highlighting their complex and diverse roles in development and throughout life. This progress is due, in part, to advances in animal models in which the molecular and cellular mechanisms of glial cell development and function as well as neuron-glial cell interactions can be directly studied in vivo in real time, in intact neural circuits. In this review we highlight the instrumental role that zebrafish have played as a vertebrate model system for the study of glial cells, and discuss how the experimental advantages of the zebrafish lend themselves to investigate glial cell interactions and diversity. We focus in particular on recent studies that have provided insight into the formation and function of the major glial cell types in the central nervous system in zebrafish.

Reelin depletion protects against autoimmune encephalomyelitis by decreasing vascular adhesion of leukocytes

Neuroinflammation as a result of immune cell recruitment into the central nervous system (CNS) is a key pathogenic mechanism of multiple sclerosis (MS). However, current anti-inflammatory interventions depleting immune cells or directly targeting their trafficking into the CNS can have serious side effects, highlighting a need for better immunomodulatory strategies. We detected increased Reelin concentrations in the serum of patients with MS, resulting in increased endothelial permeability to leukocytes through increased nuclear factor κB-mediated expression of vascular adhesion molecules. We thus investigated the prophylactic and therapeutic potential of Reelin immunodepletion in experimental autoimmune encephalomyelitis (EAE) and further validated the results in Reelin knockout mice. Removal of plasma Reelin by either approach protected against neuroinflammation and largely abolished the neurological consequences by reducing endothelial permeability and immune cell accumulation in the CNS. Our findings suggest Reelin depletion as a therapeutic approach with an inherent good safety margin for the treatment of MS and other diseases where leukocyte extravasation is a major driver of pathogenicity.

The Drainage of Interstitial Fluid in the Deep Brain is Controlled by the Integrity of Myelination

In searching for the drainage route of the interstitial fluid (ISF) in the deep brain, we discovered a regionalized ISF drainage system as well as a new function of myelin in regulating the drainage. The traced ISF from the caudate nucleus drained to the ipsilateral cortex along myelin fiber tracts, while in the opposite direction, its movement to the adjacent thalamus was completely impeded by a barrier structure, which was identified as the converged, compact myelin fascicle. The regulating and the barrier effects of myelin were unchanged in AQP4-knockout rats but were impaired as the integrity of boundary structure of drainage system was destroyed in a demyelinated rat model. We thus proposed that the brain homeostasis was maintained within each ISF drainage division locally, rather than across the brain as a whole. A new brain division system and a new pathogenic mechanism of demyelination are therefore proposed.

Cell Signaling in Neuronal Stem Cells

The defining characteristic of neural stem cells (NSCs) is their ability to multiply through symmetric divisions and proliferation, and differentiation by asymmetric divisions, thus giving rise to different types of cells of the central nervous system (CNS). A strict temporal space control of the NSC differentiation is necessary, because its alterations are associated with neurological dysfunctions and, in some cases, death. This work reviews the current state of the molecular mechanisms that regulate the transcription in NSCs, organized according to whether the origin of the stimulus that triggers the molecular cascade in the CNS is internal (intrinsic factors) or whether it is the result of the microenvironment that surrounds the CNS (extrinsic factors).

Networks of blood proteins in the neuroimmunology of schizophrenia

Levels of certain circulating cytokines and related immune system molecules are consistently altered in schizophrenia and related disorders. In addition to absolute analyte levels, we sought analytes in correlation networks that could be prognostic. We analyzed baseline blood plasma samples with a Luminex platform from 72 subjects meeting criteria for a psychosis clinical high-risk syndrome; 32 subjects converted to a diagnosis of psychotic disorder within two years while 40 other subjects did not. Another comparison group included 35 unaffected subjects. Assays of 141 analytes passed early quality control. We then used an unweighted co-expression network analysis to identify highly correlated modules in each group. Overall, there was a striking loss of network complexity going from unaffected subjects to nonconverters and thence to converters (applying standard, graph-theoretic metrics). Graph differences were largely driven by proteins regulating tissue remodeling (e.g. blood-brain barrier). In more detail, certain sets of antithetical proteins were highly correlated in unaffected subjects (e.g. SERPINE1 vs MMP9), as expected in homeostasis. However, for particular protein pairs this trend was reversed in converters (e.g. SERPINE1 vs TIMP1, being synthetical inhibitors of remodeling of extracellular matrix and vasculature). Thus, some correlation signals strongly predict impending conversion to a psychotic disorder and directly suggest pharmaceutical targets.

Fibrinogen in neurological diseases: mechanisms, imaging and therapeutics

The blood coagulation protein fibrinogen is deposited in the brain in a wide range of neurological diseases and traumatic injuries with blood-brain barrier (BBB) disruption. Recent research has uncovered pleiotropic roles for fibrinogen in the activation of CNS inflammation, induction of scar formation in the brain, promotion of cognitive decline and inhibition of repair. Such diverse roles are possible in part because of the unique structure of fibrinogen, which contains multiple binding sites for cellular receptors and proteins expressed in the nervous system. The cellular and molecular mechanisms underlying the actions of fibrinogen are beginning to be elucidated, providing insight into its involvement in neurological diseases, such as multiple sclerosis, Alzheimer disease and traumatic CNS injury. Selective drug targeting to suppress the damaging functions of fibrinogen in the nervous system without affecting its beneficial effects in haemostasis opens a new fibrinogen therapeutics pipeline for neurological disease.