Cytokine-induced conversion of mesencephalic-derived progenitor cells intodopamine neurons

We have previously shown that a combination of the cytokines interleukin (I L)-1, IL-11, leukemia inhibitory factor (LIF), and glial cell line-derived neurotrophic factor (GDNF) can convert rat fetal (E14.5) mesencephalic prog enitor cells into tyrosine hydroxylase (TH)-immunoreactive (ir) neurons in vitro. The experiments described here characterize the mesencephalic progen itor cells and their cytokine-induced conversion into dopamine (DA) neurons . For all experiments, we used bromodeoxyuridine (BrdU)ir cultures of (E14. 5) mesencephalic progenitor cells that had been expanded at least 21 days. We first demonstrated that IL-1 induced DA neuron conversion in mesencephal ic progenitors, but not in striatal progenitors (P<0.001). Thus, these cell s should be classified as lineage-restricted progenitors, and not omnipoten t stem cells. To further characterize cell populations in these cultures, w e used monoclonal antibodies against Hu tan early marker for neurons), grow th-associated protein (GAP)-43 (a marker far neuronal process extension), T H (a marker for DA neurons), and glial fibrillary acidic protein (GFAP, a m arker for astrocytes). We assessed (E14.5) mesencephalic progenitor cell cu ltures (plated at 125,000 cells/cm(2)) incubated in the cytokine mixture (d escribed above) or in complete media (CM, negative control). Following 7 da ys incubation, GFAP-positive cells formed a nearly confluent carpet in both types of cultures. However, numbers of Hu-ir and GAP-43-ir cells in the cy tokine-incubated cultures far exceeded those in CM-incubated controls (P=0. 0003, P=0.0001, respectively), while numbers of TH-ir cells were 58-fold gr eater in the cytokine-incubated cultures versus CM-incubated controls. The TH phenotype persisted for 7 days following withdrawal of the differentiati on media. Numerous double-labeled cells that were BrdU-ir and also TH-ir, o r Hu-ir and also TH-ir, were observed in the cytokine-incubated cultures. T hese data suggest that cytokines "drive" the conversion of progenitor cells into DA neurons.