Origin, lineage and function of cerebellar glia

The glial cells of the cerebellum, and particularly astrocytes and oligodendrocytes, are characterized by a remarkable phenotypic variety, in which highly peculiar morphological features are associated with specific functional features, unique among the glial cells of the entire CNS. Here, we provide a critical report about the present knowledge of the development of cerebellar glia, including lineage relationships between cerebellar neurons, astrocytes and oligodendrocytes, the origins and the genesis of the repertoire of glial types, and the processes underlying their acquisition of mature morphological and functional traits. In parallel, we describe and discuss some fundamental roles played by specific categories of glial cells during cerebellar development. In particular, we propose that Bergmann glia exerts a crucial scaffolding activity that, together with the organizing function of Purkinje cells, is necessary to achieve the normal pattern of foliation and layering of the cerebellar cortex. Moreover, we discuss some of the functional tasks of cerebellar astrocytes and oligodendrocytes that are distinctive of cerebellar glia throughout the CNS. Notably, we report about the regulation of synaptic signalling in the molecular and granular layer mediated by Bergmann glia and parenchymal astrocytes, and the functional interaction between oligodendrocyte precursor cells and neurons. On the whole, this review provides an extensive overview of the available literature and some novel insights about the origin and differentiation of the variety of cerebellar glial cells and their function in the developing and mature cerebellum.

Expression of LPP3 in Bergmann glia is required for proper cerebellar sphingosine-1-phosphate metabolism/signaling and development

Bioactive lipids serve as intracellular and extracellular mediators in cell signaling in normal and pathological conditions. Here we describe that an important regulator of some of these lipids, the lipid phosphate phosphatase-3 (LPP3), is abundantly expressed in specific plasma membrane domains of Bergmann glia (BG), a specialized type of astrocyte with key roles in cerebellum development and physiology. Mice selectively lacking expression of LPP3/Ppap2b in the nervous system are viable and fertile but exhibit defects in postnatal cerebellum development and modifications in the cytoarchitecture and arrangement of BG with a mild non-progressive motor coordination defect. Lipid and gene profiling studies in combination with pharmacological treatments suggest that most of these effects are associated with alterations in sphingosine-1-phosphate (S1P) metabolism and signaling. Altogether our data indicate that LPP3 participates in several aspects of neuron-glia communication required for proper cerebellum development.

Interrelationships between astrocyte function, oxidative stress and antioxidant status within the central nervous system

Astrocytes have, until recently, been thought of as the passive supporting elements of the central nervous system. However, recent developments suggest that these cells actually play a crucial and vital role in the overall physiology of the brain. Astrocytes selectively express a host of cell membrane and nuclear receptors that are responsive to various neuroactive compounds. In addition, the cell membrane has a number of important transporters for these compounds. Direct evidence for the selective co-expression of neurotransmitters, transporters on both neurons and astrocytes, provides additional evidence for metabolic compartmentation within the central nervous system. Oxidative stress as defined by the excessive production of free radicals can alter dramatically the function of the cell. The free radical nitric oxide has attracted a considerable amount of attention recently, due to its role as a physiological second messenger but also because of its neurotoxic potential when produced in excess. We provide, therefore, an in-depth discussion on how this free radical and its metabolites affect the intra and intercellular physiology of the astrocyte(s) and surrounding neurons. Finally, we look at the ways in which astrocytes can counteract the production of free radicals in general by using their antioxidant pathways. The glutathione antioxidant system will be the focus of attention, since astrocytes have an enormous capacity for, and efficiency built into this particular system.