TGF-beta superfamily members promote survival of midbrain dopaminergic neurons and protect them against MPP+ toxicity.

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Abstract
The superfamily of transforming growth factors‐beta (TGF‐beta) comprises an expanding list of multifunctional proteins serving as regulators of cell proliferation and differentiation. Prominent members of this family include the TGF‐beta s 1‐5, activins, bone morphogenetic proteins and a recently discovered glial cell line‐derived neurotrophic factor (GDNF). In the present study we demonstrate and compare the survival promoting and neuroprotective effects of TGF‐beta 1, ‐2 and ‐3, activin A and GDNF for midbrain dopaminergic neurons in vitro. All proteins increase the survival of tyrosine hydroxylase‐immunoreactive dopaminergic neurons isolated from the embryonic day (E) 14 rat mesencephalon floor to varying extents (TGF‐beta s 2.5‐fold, activin A and GDNF 1.6‐fold). TGF‐beta s, activin A and GDNF did not augment numbers of very rarely observed astroglial cells visualized by using antibodies to glial fibrillary acidic protein and had no effect on cell proliferation monitored by incorporation of BrdU. TGF‐beta 1 and activin A protected dopaminergic neurons against N‐methyl‐4‐phenylpiridinium ion toxicity. Reverse transcription‐polymerase chain reaction (RT‐PCR) analysis indicated that TGF‐beta 2 mRNA, but not GDNF mRNA, is expressed in the E14 rat midbrain floor and in mesencephalic cultures. We conclude that TGF‐beta s 1‐3, activin A and GDNF share a neurotrophic capacity for developing dopaminergic neurons, which is not mediated by astroglial cells and not accompanied by an increase in cell proliferation.