Properties of human astrocytes and NG2 glia

Since animal models are inevitable for medical research, information on species differences in glial cell properties is critical for successful translational research. Here, we review current knowledge about morphological and functional properties of human astrocytes and NG2 glial cells and compare these data with those obtained for the comparable cells in rodents. Morphological analyses of astrocytes in the neocortex of rodents versus humans have demonstrated clear differences. In contrast, the functional properties of astrocytes or NG2 glial cells in these species are surprisingly similar. However, these findings should be interpreted with caution, as so far functional analyses of human cells are only available from neocortex and hippocampus, and it is known from rodent studies that the properties of astrocytes in different brain regions may vary considerably. Moreover, technical challenges render astrocyte electrophysiological measurements in situ unreliable, and human cell properties may be affected by medications. Nevertheless, based on the limited data currently available, there is substantial similarity between human and rodent astrocytes with regard to those functional properties studied to date. The unique morphological characteristics of astrocytes in human neocortex call for further physiological analysis. The basic properties for NG2 glia are even less completely evaluated with regard to the question of species differences but no glaring differences have been reported so far. In conclusion, it remains justifiable to employ mouse or rat models to investigate the etiology of human CNS diseases that might involve astrocytes or NG2 glia. Previous studies have suggested that human and rodent astrocytes differ greatly in their properties. However, careful analysis reveals many similarities in the functional characteristics of astrocytes and NG2 glia across species.