Proliferation of a subpopulation of reactive astrocytes following needle-insertion lesion in rat

It is well known that traumatic injuries of the CNS induce a gliotic reaction, characterized by the presence of reactive astrocytes. Reactive astrocytes exhibit enhanced expression of the astrocyte-specific intermediate filament, glial fibrillary acidic protein (GFAP), hypertrophy, and thickened processes. Recently, we have demonstrated that injuries of the CNS induce a re-expression of an embryonic intermediate filament-associated protein, IFAP-70/280kDa. Based on IFAP-70/280kDa immunolabeling, we have shown that reactive astrocytes, activated by stab-wound injury, can be divided into two major groups: 1. persistent IFAP⁺/GFAP⁺ cells which are close to the wound in the area of glial scar, and 2. transient IFAP ^-/GFAP⁺ cells which are farther from the wound. In this study, we use BrdU incorporation to examine proliferation in these two groups of reactive astrocytes induced by stab injury of the rat cerebrum. Triple/double-label immunofluorescence microscopy was performed using antibodies to IFAP-70/280kDa, GFAP, and BrdU. The results showed that BrdU ⁺ reactive astrocytes (GFAP⁺) were always IFAB-70/280kDa⁺ as well However, not all IFAP⁺ reactive astrocytes are BrdU⁺. BrdU⁺ signal was not observed in any IFAP^- reactive astrocytes. At five days post-lesion, IFAP ⁺ reactive astrocytes were increasing in the area of the wound (0-50 μm from the wound edge), but had reached a peak in the proximal area (50-800 μm away from the wound edge). At eight days post-lesion, IFAP⁺ reactive astrocytes achieved the highest percentage in the wound area. At the same time, BrdU-containing reactive astrocytes occupied an area closer to the wound. By 20 days post-lesion, following the formation of the gliotic scar at the stab-wound, a few IFAP⁺/GFAP⁺ cells still persisted. BrdU-containing reactive astrocytes were only observed in the scar. These results indicate that many IFAP⁺ reactive astrocytes close to the wound, in contrast to the IFAP^- ones farther from the wound, appear to regain their proliferative potential to increase in number and participate in the formation of the gliotic scar.