Journal of Neuroscience, Vol 14, 4206-4216, Copyright © 1994 by Society for Neuroscience
Transforming growth factor alpha (TGF alpha) expression in degenerating motoneurons of the murine mutant wobbler: a neuronal signal for astrogliosis?
MP Junier, M Coulpier, N Le Forestier, J Cadusseau, F Suzuki, M Peschanski and PA Dreyfus
CJF INSERM 91-02, Fac Medecine, Creteil, France.
The enhanced expression of the trophic factor transforming growth factor
alpha (TGF alpha) in reactive astrocytes following CNS injury suggests that
TGF alpha has a role in the development of astrogliosis. We explored this
hypothesis in the murine mutant wobbler, which presents a progressive
motoneuronal degeneration associated with an astrogliosis. Evolution of
astrogliosis, and expression of TGF alpha precursor (pro-TGF alpha) and of
its receptor were examined over the course of the disease, using
genetically diagnosed animals and immunocytochemical techniques. We report
here that degenerating motoneurons of the cervical spinal cord and a subset
of astrocytes express pro-TGF alpha, prior to the onset of astrogliosis,
when the first clinical manifestations of the disease are observed at 4
weeks of age. TGF alpha expression appeared strongly correlated with
motoneuronal degeneration. All pro-TGF alpha-immunoreactive neurons
exhibited a degenerative morphology, and the number of pro-TGF alpha-
immunoreactive neurons increased with the progression of the disease. At
the glial level, we observed that astrogliosis was a transitory phenomenon
in the wobbler mice, developing in coordination with the motoneuronal
expression of pro-TGF alpha. Astrogliosis became evident in 6-week-old
wobbler mice, when the number of pro-TGF alpha- immunoreactive motoneurons
was maximal, and regressed in older mutant mice in correlation with the
disappearance of pro-TGF alpha- immunoreactive motoneurons. Furthermore,
TGF alpha/EGF receptor immunoreactivity was exclusively localized in a
subset of reactive astrocytes, its expression following closely the course
of the astrogliosis. These data show that TGF alpha synthesis by the
affected motoneurons is an early event in the course of the wobbler
disease, and suggest a role for TGF alpha as a neuronal inducer of
astrocytic reactivity.