Dissecting the regional diversity of glial cells by applying -omic technologies

Abstract

With an estimated number of approximately 10,000 different proteins in each single mammalian cell [16], in-depth identification of a cell's entire proteome Dissecting the regional diversity of glial cells by applying -omic technologies Abstract Neuronal as well as glial cells contribute to higher order brain functions. Many observations show that neurons and glial cells are not only physically highly intermingled but are physiologically tightly connected and mutually depend at various levels on each other. Moreover, macroglia classes like astrocytes, NG2 cells and oligodendrocytes are not at all homogenous cell populations but do possess a markedly heterogeneity in various aspects similar to neurons. The diversity of differences in morphology, functionality and, cellular activity has been acknowledged recently and will be integrated into a concept of brain function that pictures a neural rather than a puristical neuronal world. With the recent progress in "omic" technologies, an unbiased and exploratory approach toward an enhanced understanding of glial heterogeneity has become possible. Here, we provide an overview on current technical transcriptomic and proteomic approaches used to dissect glial heterogeneity of the brain. is still a major challenge for modern proteomic technologies. In addition, the total number of different/unique proteins per synapse is estimated to be at approximately 2000-2500 [17], which are often under control of different activity-dependent turnover rates. While today's state-of-theart MS instruments routinely sequence single purified proteins with subfemtomolar sensitivity, the effective identification of low-abundance proteins is orders of magnitude lower in complex mixtures due to limited dynamic range and sequencing speed and due to the common, strong bias toward acquiring MS/MS data on higher abundance molecules. Hence, to tackle activity-dependent proteome alterations entire, functionally heterogeneous brain regions with different subtypes of neurons and macroglial cells are usually being sampled at the loss of cell-type specificity and spatial resolution. The characterization of a proteome is an even more difficult challenge if temporal and spatial aspects of a proteome or a subpopulation of the proteome have to be taken into consideration. Thus, the separation and enrichment of the subproteome in question is key for its successful characterization. To overcome the above mentioned limitations, several cellular and biochemical (subcellular) enrichment strategies combined with proteomics have been developed to increase sensitivity and selectivity for the analysis of neuronal and glial proteomes, and to finally dissolve cellular heterogeneity of neural cells in the brain (. Fig. 2a-b). KeywordsConcerning cellular selectivity, intracellular proteomes and secretomes from cultured primary astrocytes and astroglial cell lines have been characterized in detail by several labs as proteomic approaches as indicated above require a much larger quantity than transcriptomic approaches. Analys...