Altres ajuts: We are grateful for the support from a Fundació La Marató de TV3 grant (120530 to M.P.C. and M.V.), an ERC grant (242630-RERE to M.P.C.),European Union Seventh Framework Programme (FP7/2007-2013) under the Marie Curie IntraEuropean Fellowship (274882 to W.A.X). SEV-2012-0208.

Parkinson's disease is a common neurodegenerative disorder, which is due to the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and for which no definitive cure is currently available. Cellular functions in mouse and human tissues can be restored after fusion of bone marrow (BM)-derived cells with a variety of somatic cells. Here, after transplantation of hematopoietic stem and progenitor cells (HSPCs) in the SNpc of two different mouse models of Parkinson's disease, we significantly ameliorated the dopaminergic neuron loss and function. We show fusion of transplanted HSPCs with neurons and with glial cells in the ventral midbrain of Parkinson's disease mice. Interestingly, the hybrids can undergo reprogramming in vivo and survived up to 4 weeks after transplantation, while acquiring features of mature astroglia. These newly generated astroglia produced Wnt1 and were essential for functional rescue of the dopaminergic neurons. Our data suggest that glial-derived hybrids produced upon fusion of transplanted HSPCs in the SNpc can rescue the Parkinson's disease phenotype via a niche-mediated effect, and can be exploited as an efficient cell-therapy approach. A definitive therapy for Parkinson's disease is not available. Here, we transplanted hematopoietic stem and progenitor cells into the substantia nigra of brains of two different mouse models of Parkinson's disease. These transplanted cells fused with neurons and glial cells of the recipient mice. Four weeks after transplantation, the hybrids acquired features of mature astroglia, secreted Wnt1, and functionally ameliorated dopaminergic neuron loss. Current cell therapy approaches are being pursued in the striatum with the aim to increase dopamine levels. Here we show that the loss of dopaminergic neurons can be protected against by direct actions in the substantia nigra.