Glial cells play active roles in neuronal survival, as well as neuroprotection against toxic insult. Recent studies suggest that the brain
protein glia maturation factor (
GMF) is involved in intracellular signaling in glia. This study investigated whether or not
GMF plays a role in the survival-promoting and neuroprotective functions of glia. C6
glioma cells were transfected in vitro with
GMF utilizing an adenovirus vector. The transfected cells overexpressed
GMF intracellularly, but did not secrete the
protein. The
conditioned medium (CM) was obtained from the
GMF-transfected cells (CM-
GMF) and tested on primary neuronal cultures, consisting of cerebellar granule cells (CGC). The CGC cultures were utilized because these cultures have a background level of cell death, and the survival-promoting, i.e. neurotrophic effect, of the CM could be tested. In addition, since CGC cultures are
ethanol-sensitive (
ethanol enhances neuronal death), the
neuroprotective effect of the CM against
ethanol-induced cell death was tested also. We demonstrated that the CM-
GMF had an enhanced neurotrophic effect as well as an increased
neuroprotective effect against
ethanol-induced cell death compared to control CM obtained from untransfected C6 cells (CM-Mock) or CM obtained from cells transfected with an unrelated gene (CM-LacZ). Because
neurotrophins have trophic and protective effects, we investigated whether
GMF-transfection upregulated the expression of
neurotrophins in C6 cells. RT-PCR verified that
GMF-transfected C6 cells had increased
mRNA levels for
BDNF and
NGF. Immunoblotting corroborated the RT-PCR results and indicated that CM-
GMF contained greater concentrations of
BDNF and
NGF protein compared to CM-Mock and CM-LacZ. A soluble TrkB-
IgG fusion
protein, which selectively binds
BDNF and prevents its binding to the neuronal
TrkB receptor, eliminated the neurotrophic effect of CM-
GMF; whereas anti-
NGF antibody was ineffective in preventing this effect, suggesting that the neurotrophic effect was due to
BDNF. On the other hand, both the TrkB-
IgG fusion
protein and anti-
NGF reduced neuroprotection, suggesting that
BDNF and
NGF both contribute to the
neuroprotective effect of CM-
GMF. In conclusion,
GMF upregulates the expression of
BDNF and
NGF in C6 cells, and these factors exert neurotrophic and neuroprotective functions on primary neurons.