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First published online 13 March 2007
doi: 10.1242/jcs.03423

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Synemin is expressed in reactive astrocytes in neurotrauma and interacts differentially with vimentin and GFAP intermediate filament networks

Runfeng Jing^1,*, Ulrika Wilhelmsson^2,*, William Goodwill¹, Lizhen Li², Yihang Pan¹, Milos Pekny^2, and Omar Skalli^1,,

¹ Department of Cellular Biology and Anatomy and Feist-Weiller Cancer Center, Louisiana State University Health Sciences Center, Shreveport, LA 71130, USA
² Center for Brain Repair and Rehabilitation, Department of Clinical Neuroscience and Rehabilitation, Institute of Neuroscience and Physiology, Sahlgrenska Academy, Göteborg University, Medicinaregatan 9A, 41390 Göteborg, Sweden

Author for correspondence (e-mail: oskall{at}lsuhsc.edu)

Accepted 7 February 2007

Immature astrocytes and astrocytoma cells contain synemin and three other intermediate filament (IF) proteins: glial fibrillary acidic protein (GFAP), vimentin and nestin. Here, we show that, after neurotrauma, reactive astrocytes produce synemin and thus propose synemin as a new marker of reactive astrocytes. Comparison of synemin mRNA and protein levels in brain tissues and astrocyte cultures from wild-type, Vim^-/- and Gfap^-/-Vim^-/- mice showed that in the absence of vimentin, synemin protein was undetectable although synemin mRNA was present at wild-type levels. By contrast, in Gfap^-/- astrocytes, synemin protein and mRNA levels, as well as synemin incorporation into vimentin IFs, were unaltered. Biochemical assays with purified proteins suggested that synemin interacts with GFAP IFs like an IF-associated protein rather than like a polymerization partner, whereas the opposite was true for synemin interaction with vimentin. In transfection experiments, synemin did not incorporate into normal, filamentous GFAP networks, but integrated into vimentin and GFAP heteropolymeric networks. Thus, alongside GFAP, vimentin and nestin, reactive astrocytes contain synemin, whose accumulation is suppressed post-transcriptionally in the absence of a polymerization partner. In astrocytes, this partner is vimentin and not GFAP, which implies a functional difference between these two type III IF proteins.

Key words: Astrocytes, Intermediate filament, GFAP, Vimentin

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