Strategies to limit dysmyelination during secondary degeneration following neurotrauma

Following trauma to the central nervous system （CNS）, cells in the lesion site die rapidly. In addition, neurons and glia be- yond the initial lesion are vulnerable. These cells can undergo delayed death due to metabolic events that follow the initial trauma, via mechanisms thought to he triggered by gluta- mate-induced excitotoxicity and Ca2＋ overload, leading to mitochondrial dysfunction, associated with increased oxida- tive stress （Camello-Almaraz et al., 2006; Peng and Jou, 2010）. The resultant death of areas of grey and white matter adjacent to the lesion site is termed secondary degeneration, and is a feature of brain and spinal cord injury （Park et al., 2004; Gi- aume et al., 2007）. Secondary degeneration contributes sub- stantially to functional loss following neurotrauma （Profyris et al., 2004; Farkas and Povlishock, 2007） and rescuing this intact, but vulnerable, tissue is considered critical to mini- mising adverse sequelae and improving long term functional outcomes after CNS trauma （Fehlings et al., 2012）. However, our understanding of many of the metabolic events thought to contribute to secondary degeneration is based largely on in vitro studies （Khodorov, 2004; Tretter et al., 2007; Peng and Jou, 2010） and there is a need to confirm the relevance of these mechanisms in vivo, as well as their structural and func- tional consequences.

Mechanisms and treatment strategies of demyelinating and dysmyelinating Charcot-Marie-Tooth disease

Schwann cells,the myelinating glia of the peripheral nervous system,wrap axons multiple times to build their myelin sheath.Myelin is of paramount importance for axonal integrity and fast axon potential propagation.However,myelin is lacking or dysfunctional in several neuropathies including demyelinating and dysmyelinating Charcot-M arie-To oth disease.Charcot-Marie-To oth disease represents the most prevalent inherited neuropathy in humans and is classified either as axonal,demyelinating or dysmyelinating,or as intermediate.The demyelinating or dysmyelinating forms of Charcot-Marie-Tooth disease constitute the majority of the disease cases and are most frequently due to mutations in the three following myelin genes:peripheral myelin protein 22,myelin protein ze ro and gap junction beta 1(coding for Connexin 32) causing Charcot-M arie-Tooth disease type 1A,Charcot-Marie-Tooth disease type 1B,and X-linked Charcot-M arie-Tooth disease type 1,respectively.The resulting perturbation of myelin structure and function leads to axonal demyelination or dysmyelination and causes severe disabilities in affected patients.No treatment to cure or slow down the disease progression is currently available on the market,howeve r,scientific discoveries led to a better understanding of the pathomechanisms of the disease and to potential treatment strategies.In this review,we describe the features and molecular mechanisms of the three main demyelinating or dysmyelinating forms of Charcot-Marie-Tooth disease,the rodent models used in research,and the emerging therapeutic approaches to cure or counteract the progression of the disease.

Oligodendrocyte pathology in fetal alcohol spectrum disorders

The pathology of fetal alcohol syndrome and the less severe fetal alcohol spectrum disorders includes brain dysmyelination.Recent studies have shed light on the molecular mechanisms underlying these white matter abnormalities.Rodent models of fetal alcohol syndrome and human studies have shown suppressed oligodendrocyte differentiation and apoptosis of oligodendrocyte precursor cells.Ethanol exposure led to reduced expression of myelin basic protein and delayed myelin basic protein expression in rat and mouse models of fetal alcohol syndrome and in human histopathological specimens.Several studies have reported increased expression of many chemokines in dysmyelinating disorders in central nervous system,including multiple sclerosis and fetal alcohol syndrome.Acute ethanol exposure reduced levels of the neuroprotective insulin-like growth factor-1 in fetal and maternal sheep and in human fetal brain tissues,while ethanol increased the expression of tumor necrosis factor α in mouse and human neurons.White matter lesions have been induced in the developing sheep brain by alcohol exposure in early gestation.Rat fetal alcohol syndrome models have shown reduced axon diameters,with thinner myelin sheaths,as well as reduced numbers of oligodendrocytes,which were also morphologically aberrant oligodendrocytes.Expressions of markers for mature myelination,including myelin basic protein,also were reduced.The accumulating knowledge concerning the mechanisms of ethanol-induced dysmyelination could lead to the development of strategies to prevent dysmyelination in children exposed to ethanol during fetal development.Future studies using fetal oligodendrocyte-and oligodendrocyte precursor cell-derived exosomes isolated from the mother's blood may identify biomarkers for fetal alcohol syndrome and even implicate epigenetic changes in early development that affect oligodendrocyte precursor cell and oligodendrocyte function in adulthood.By combining various imaging modalities with molecular studies,it may be possible to determine which fetuses are at risk and to intervene therapeutically early in the pregnancy.