Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system. Various pre-clinical models with different specific features of the disease are available to study MS pathogenesis and to develop new therapeutic options. During the last decade, the model of toxic demyelination induced by cuprizone has become more and more popular, and it has contributed substantially to our understanding of distinct yet important aspects of the MS pathology. Here, we aim to provide a practical guide on how to use the cuprizone model and which pitfalls should be avoided.

Cell migration is a fundamental phenomenon that underlies tissue morphogenesis, wound healing, immune response, and cancer metastasis. Great progresses have been made in research methodologies, with cell migration identified as a highly orchestrated process. Brain is considered the most complex organ in the human body, containing many types of neural cells with astrocytes playing crucial roles in monitoring normal functions of the central nervous system. Astrocytes are mostly quiescent under normal physiological conditions in the adult brain but become migratory after injury. Under most known pathological conditions in the brain, spinal cord and retina, astrocytes are activated and become hypertrophic, hyperplastic, and up-regulating GFAP based on the grades of severity. These three observations are the hallmark in glia scar formation-astrogliosis. The reactivation process is initiated with structural changes involving cell process migration and ended with cell migration. Detailed mechanisms in astrocyte migration have not been studied extensively and remain largely unknown. Here, we therefore attempt to review the mechanisms in migration of astrocytes.

Oligodendrocytes are integral to efficient neuronal signaling. Loss of myelinating oligodendrocytes is a central feature of many neurological diseases, including multiple sclerosis (MS). The results of neuropathological studies suggest that oligodendrocytes react with differing sensitivity to toxic insults, with some cells dying early during lesion development and some cells being resistant for weeks. This proposed graded vulnerability has never been demonstrated but provides an attractive window for therapeutic interventions. Furthermore, the biochemical pathways associated with graded oligodendrocyte vulnerability have not been well explored. We used immunohistochemistry and serial block‐face scanning electron microscopy (3D‐SEM) to show that cuprizone‐induced metabolic stress results in an “out of phase” degeneration of oligodendrocytes. Although expression induction of stress response transcription factors in oligodendrocytes occurs within days, subsequent oligodendrocyte apoptosis continues for weeks. In line with the idea of an out of phase degeneration of oligodendrocytes, detailed ultrastructural reconstructions of the axon–myelin unit demonstrate demyelination of single internodes. In parallel, genome wide array analyses revealed an active unfolded protein response early after initiation of the cuprizone intoxication. In addition to the cytoprotective pathways, the pro‐apoptotic transcription factor DNA damage‐inducible transcript 3 (DDIT3) was induced early in oligodendrocytes. In advanced lesions, DDIT3 was as well expressed by activated astrocytes. Toxin‐induced oligodendrocyte apoptosis, demyelination, microgliosis, astrocytosis, and acute axonal damage were less intense in the Ddit3‐null mutants. This study identifies DDIT3 as an important regulator of graded oligodendrocyte vulnerability in a MS animal model. Interference with this stress cascade might offer a promising therapeutic approach for demyelinating disorders.

Microglia are the resident innate immune cells of the central nervous system (CNS) parenchyma. To determine the impact of microglia on disease development and progression in neurodegenerative and neuroinflammatory diseases, it is essential to distinguish microglia from peripheral macrophages/monocytes, which are eventually equally recruited. It has been suggested that transmembrane protein 119 (TMEM119) serves as a reliable microglia marker that discriminates resident microglia from blood‐derived macrophages in the human and murine brain. Here, we investigated the validity of TMEM119 as a microglia marker in four in vivo models (cuprizone intoxication, experimental autoimmune encephalomyelitis (EAE), permanent filament middle cerebral artery occlusion (fMCAo), and intracerebral 6‐hydroxydopamine (6‐OHDA) injections) as well as post mortem multiple sclerosis (MS) brain tissues. In all applied animal models and post mortem MS tissues, we found increased densities of ionized calcium‐binding adapter molecule 1+ (IBA1+) cells, paralleled by a significant decrease in TMEM119 expression. In addition, other cell types in peripheral tissues (i.e., follicular dendritic cells and brown adipose tissue) were also found to express TMEM119. In summary, this study demonstrates that TMEM119 is not exclusively expressed by microglia nor does it label all microglia, especially under cellular stress conditions. Since novel transgenic lines have been developed to label microglia using the TMEM119 promotor, downregulation of TMEM119 expression might interfere with the results and should, thus, be considered when working with these transgenic mouse models.