Vimentin mRNA expression increases after corticospinal axotomy in the adult hamster

Abstract

We examined changes in vimentin gene expression during Wallerian degeneration after corticospinal axotomy in the adult hamster. Vimentin, which is the product of a type III intermediate filament (IF) gene, is expressed in various cells of mesenchymal origin, including microvascular endothelial cells, microglia and developing astrocytes. While increases in vimentin protein have been observed after various types of central nervous system (CNS) injury, it is not known whether this increase is due to increased vimentin mRNA expression. There is also conflicting evidence as to which cells are expressing increased levels of vimentin. In the present study we used in situ hybridization and double-label immunofluorescence techniques to address these issues. A 35S-labeled vimentin cDNA probe was used for in situ hybridizations of brain stem sections obtained 2, 7 and 14 days after unilateral transection of the corticospinal tract in the caudal medulla of adult hamsters. Autoradiography showed that an increase in vimentin mRNA associated with the degenerating corticospinal tract occurred by 2 days after axotomy and that the levels remained elevated for at least 14 days. Immunoblotting and immunocytochemical studies indicated that vimentin protein levels were increased in the degenerating corticospinal tract. Double-label immunofluorescence revealed many vimentin-positive cells and processes that were also labeled with GFAP antibody. In addition, cells and processes that were vimentin-negative but GFAP-positive were also found in the degenerating tract. We suggest that the reactive cells which possessed both vimentin and GFAP were reactive astrocytes of astroblastic origin while those that expressed only GFAP were derived from mature astrocytes. Other vimentin-positive cells/processes did not label with anti-GFAP and thus were either microglial, endothelial or inflammatory cells. These results demonstrate that an increase in vimentin mRNA occurs during Wallerian degeneration after corticospinal axotomy and that this increase is likely to be due to contributions from more than one cell type.

Glial scar and axonal regeneration in the CNS: lessons from GFAP and vimentin transgenic mice

“…A similar regulation of GF AP mRNA is also observed at distance from the lesion site, in the projection areas [40,41,51]. After injury, the 88 reexpression of VIM occurs in astrocytes close to the injury and at distance from the lesion site in a subset of astrocytes associated with Wallerian degeneration [7,29,44].…”

Selective ablation of astrocytes by intracerebral injections of ?-aminoadipate

“…Vim is the intermediate filament (IF) protein which is present in astrocytes early in development (Dahl et al, 1981) and is gradually replaced by GFAP as the main IF protein in astrocytes during maturation (Pixley and De Vellis, 1984;Stichel et al, 1991). Vim is usually undetectable in gray matter astrocytes of adult animals (see Khurgel et al, 1992), but it appears to be re-expressed in these cells following activation of astrocytes due to trauma (Calvo et al, 1991;Mikucki and Oblinger, 1991;Petito et al, 1990;Schiffer et al, 1986;Takamiya et al, 1988) or seizure activity (Khurgel et al, 1992(Khurgel et al, , 1995. Therefore, the presence of Vim+ astrocytes a t the site of vehicle injection (Fig.…”

Role of Astrocytes in Post-traumatic Epilepsy

“…Although GFAP has been a useful biomarker for assessing astrocyte reactivity to date, there remains an unmet need for better markers. Vimentin is another intermediate filament that expressed in astrocytes early in development, but appears to be gradually replaced by GFAP during development (62, 63). Recent transcriptomic studies have revealed some reactive astrocyte genes that might prove to be a better marker for assessing astrocyte reactivity (1).…”