Growth factors in the CNS and their effects on oligodendroglia

Nervous System Response to Neurotrauma: A Narrative Review of Cerebrovascular and Cellular Changes After Neurotrauma

Neurotrauma is a significant cause of morbidity and mortality worldwide. For instance, traumatic brain injury (TBI) causes more than 30% of all injury-related deaths in the USA annually. The underlying cause and clinical sequela vary among cases. Patients are liable to both acute and chronic changes in the nervous system after such a type of injury. Cerebrovascular disruption has the most common and serious effect in such cases because cerebrovascular autoregulation, which is one of the main determinants of cerebral perfusion pressure, can be effaced in brain injuries even in the absence of evident vascular injury. Disruption of the blood-brain barrier regulatory function may also ensue whether due to direct injury to its structure or metabolic changes. Furthermore, the autonomic nervous system (ANS) can be affected leading to sympathetic hyperactivity in many patients. On a cellular scale, the neuroinflammatory cascade medicated by the glial cells gets triggered in response to TBI. Nevertheless, cellular and molecular reactions involved in cerebrovascular repair are not fully understood yet. Most studies were done on animals with many drawbacks in interpreting results. Therefore, future studies including human subjects are necessarily needed. This review will be of relevance to clinicians and researchers interested in understanding the underlying mechanisms in neurotrauma cases and the development of proper therapies as well as those with a general interest in the neurotrauma field.

Intrauterine infection/inflammation during pregnancy and offspring brain damages: possible mechanisms involved

Intrauterine infection is considered as one of the major maternal insults during pregnancy. Intrauterine infection during pregnancy could lead to brain damage of the developmental fetus and offspring. Effects on the fetal, newborn, and adult central nervous system (CNS) may include signs of neurological problems, developmental abnormalities and delays, and intellectual deficits. However, the mechanisms or pathophysiology that leads to permanent brain damage during development are complex and not fully understood. This damage may affect morphogenic and behavioral phenotypes of the developed offspring, and that mice brain damage could be mediated through a final common pathway, which includes over-stimulation of excitatory amino acid receptor, over-production of vascularization/angiogenesis, pro-inflammatory cytokines, neurotrophic factors and apoptotic-inducing factors.

In vitro injury model for oligodendrocytes: development, injury, and recovery

In this study we investigated the effects of severe hypothermia (cryoinjury) on oligodendrocyte (OL) cell marker expression and morphological features. We used a chemically defined cell culture medium, glial development medium (GDM), which favored the optimal expression of the OL phenotype in CG4 cells. Experiments using CG4 cells cultured in 2% serum or in GDM were conducted in parallel. After severe hypothermia, cells were reanimated at 37 degrees C and 4.5% CO(2) and cultured in either GDM or in medium supplemented with 2% serum. In either medium, around 70% of the total number of cells detached within 2 to 4 hours following reanimation. Oligodendroglial markers such as A2B5, O4, Tf, ferritin, tubulin, and MBP were examined by double and triple immunofluorescence. All of these markers except MBP re-appeared at different times during the recovery period for up to 48 hours. Glial fibrillary acidic protein (GFAP) and heat shock protein 60 (HSP-60) were used as injury markers. The presence of serum induced HSP-60 expression, while GDM did not. All CG4 cells expressed HSP-60 in response to hypothermia independently of the cell culture medium used. Cryoinjury induced a spectrum of morphological changes in CG4 cells. The expression of OL specific markers was also influenced by hypothermia. Moreover both, serum and cryoinjury induced the expression of HSP-60 that colocalized with OL and myelin markers. The expression of GFAP by injured cells but not by normal cells corroborated the state of injury of CG4 cells.

Effects of lipopolysaccharide on oligodendrocyte progenitor cells are mediated by astrocytes and microglia

Oligodendrocytes are the primary cells injured in periventricular leukomalacia (PVL), a predominant form of brain white matter lesion in preterm infants. To explore the possible linkage between white matter injury and maternal infection, purified rat O-2A progenitor (Oligodendrocyte-type 2 astrocyte progenitor) cell cultures were used as a model in studying the effects of lipopolysaccharide (LPS), an endotoxin, on survival and differentiation of oligodendrocytes and the involvement of other glial cells in the effects of LPS. O-2A progenitor cells were cultured from optic nerves of 7-day-old rat pups in a chemically defined medium (CDM). Astrocyte and microglia cell cultures were prepared from the cortex of 1-day-old rat brains in the CDM. Direct treatment of LPS (1 microg/ml) to O-2A cells had no effect on viability or differentiation of these cells. When O-2A progenitor cells were cultured in the conditioned medium obtained from either astrocyte or microglial cell cultures for 48 hr, survival rate and differentiation of O-2A cells into mature oligodendrocytes were greatly enhanced as measured by the MTT assay and immunocytochemistry. The conditioned medium obtained from astrocytes or microglia treated with LPS for 48 hr, however, failed to show such a promotional effect on viability and differentiation of O-2A cells. When 5 microg/ml LPS was used to stimulate astrocytes or microglia, the conditioned medium from these glial cell cultures caused O-2A cell injury. The overall results indicate that astrocytes and microglia may promote viability and differentiation of O-2A progenitor cells under physiological conditions, but they may also mediate cytotoxic effects of LPS on oligodendrocytes under an infectious disease biochemical environment.

Glial cells as targets and producers of neurotrophins

Glial cells fulfill important tasks within the neural network of the central and peripheral nervous systems. The synthesis and secretion of various polypeptidic factors (cytokines) and a number of receptors, with which glial cells are equipped, allow them to communicate with their environment. Evidence has accumulated during recent years that neurotrophins play an important role not only for neurons but also for glial cells. This brief update of some morphological, immunocytochemical, and biochemical characteristics of glial cell lineages conveys our present knowledge about glial cells as targets and producers of neurotrophins under normal and pathological conditions. The chapter discusses the presence of neurotrophin receptors on glial cells, glial cells as producers of neurotrophins, signaling pathways downstream Trk and p75NTR, and the significance of neurotrophins and their receptors for glial cells during development, in cell death and survival, and in neurological disorders.

Radiation myelopathy: new perspective on an old problem

This article discusses recent advances in basic research that alter the view of the pathogenesis of radiation myelopathy and summarizes the available data from developmental neurobiology and preclinical studies on demyelinating diseases. These studies have produced interesting insights into oligodendrocyte development, intercellular signaling pathways, and myelination processes. Current findings suggest that administration of cytokines as platelet-derived growth factor and basic fibroblast growth factor could increase proliferation of oligodendrocyte progenitors, enhance their differentiation, up-regulate synthesis of myelin constituents, and promote myelin regeneration in the adult central nervous system (CNS). Other compounds might also be able to modulate the progression of pathogenic processes that lead to myelopathy. In addition, several possible biological prevention or treatment strategies, for example stimulation of endogenous cellular regeneration and glial cell transplantation, are discussed. Rationally designed animal experiments pursuing such strategies could further elucidate the pathogenesis of radiation-induced CNS damage.

Brain damage in preterm newborns: might enhancement of developmentally regulated endogenous protection open a door for prevention?

We present a two-component model of brain white matter damage in preterm neonates. The insult component comprises infection and hypoxia-ischemia, which are both associated with inflammation-related abnormalities in the white matter. The developmental component comprises at least three factors, ie, immaturity of the ependymal/endothelial, oligodendroglial, and endogenous protection systems. All three factors are likely contributors to an increased vulnerability of the preterm newborn's white matter. In this article, we focus on recent developments in oligodendrocyte biology that support the view of certain cytokines and growth factors as oligotrophins based on their capability to enhance oligodendrocyte development or survival. We suggest that research into networks of developmentally regulated endogenous protectors (such as oligotrophins) is necessary to broaden our perspectives in brain injury prevention in preterm newborns.

Nerve growth factor signal transduction in mature pig oligodendrocytes

It has previously been shown that nerve growth factor (NGF) is of functional significance for mature pig oligodendrocytes (OLs) in culture. The present data give evidence for the expression of TrkA, the so-called high-affinity NGF receptor, and of p75NTR, the so-called low-affinity NGF receptor. TrkA is upregulated during culturing, in contrast to the p75 receptor. Exposure of OLs to NGF induces an autophosphorylation of TrkA via its intrinsic tyrosine kinase. K-252a inhibits the TrkA autophosphorylation, which reduces the OL process formation to control levels. To the tyrosine-phosphorylated sites of TrkA several proteins, such as phospholipase C-gamma1, the adaptor protein SHC, the phosphotyrosine phosphatase SH-PTP2 (SYP) associate via their SH2 phosphotase SH-PTP2 domain. The association of SHC to TrkA is shown by co-immunoprecipitation. Indirect evidence for a possible activation of PLC-gamma1 is given by an NGF-induced increase of oligodendroglial [Ca2+]i. Downstream from TrkA, a mitogen-activated protein kinase cascade, which includes Erk1 and Erk2, is operating. An in-gel myelin basic protein kinase assay revealed that NGF activates predominantly Erk1. Finally, it is shown that NGF stimulates expression of c-fos.

Central nervous system remyelination clinical application of basic neuroscience principles

Studies in both humans and experimental animals have demonstrated that myelin repair in the CNS is a normal physiological response to myelin damage, similar to tissue injury elsewhere in the body. The unanswered question is why myelin repair is incomplete in multiple sclerosis patients. In this paper we review the morphological characteristics of remyelination, discuss the available animal models of CNS demyelination and their usefulness to identify the molecular, cellular, and morphological events involved in CNS myelin repair, examine the use of immunosuppression, immunoglobulins, protein growth factors, and glial cell transplantation at the primary experimental therapies designed to promote CNS remyelination, and address the potential electrophysiological and clinical benefits of myelin repair in the CNS.