Cxcl12/Cxcr4 signaling controls the migration and process orientation of A9-A10 dopaminergic neurons.

CXCL12/CXCR4 signaling has been reported to regulate three essential processes for the establishment of neural networks in different neuronal systems: neuronal migration, cell positioning and axon wiring. However, it is not known whether it regulates the development of A9-A10 tyrosine hydroxylase positive (TH(+)) midbrain dopaminergic (mDA) neurons. We report here that Cxcl12 is expressed in the meninges surrounding the ventral midbrain (VM), whereas CXCR4 is present in NURR1(+) mDA precursors and mDA neurons from E10.5 to E14.5. CXCR4 is activated in NURR1(+) cells as they migrate towards the meninges. Accordingly, VM meninges and CXCL12 promoted migration and neuritogenesis of TH(+) cells in VM explants in a CXCR4-dependent manner. Moreover, in vivo electroporation of Cxcl12 at E12.5 in the basal plate resulted in lateral migration, whereas expression in the midline resulted in retention of TH(+) cells in the IZ close to the midline. Analysis of Cxcr4(-/-) mice revealed the presence of VM TH(+) cells with disoriented processes in the intermediate zone (IZ) at E11.5 and marginal zone (MZ) at E14. Consistently, pharmacological blockade of CXCR4 or genetic deletion of Cxcr4 resulted in an accumulation of TH(+) cells in the lateral aspect of the IZ at E14, indicating that CXCR4 is required for the radial migration of mDA neurons in vivo. Altogether, our findings demonstrate that CXCL12/CXCR4 regulates the migration and orientation of processes in A9-A10 mDA neurons.

The beta-chemokines CCL2 and CCL7 are two novel differentiation factors for midbrain dopaminergic precursors and neurons.

beta-chemokines are secreted factors that regulate diverse functions in the adult brain, such as neuro-immune responses and neurotransmission, but their function in the developing brain is largely unknown. We recently found that the orphan nuclear receptor, Nurr1, up regulates CCL2 and CCL7 in neural stem cells, suggesting a possible function of beta-chemokines in midbrain development. Here we report that two beta-chemokines, CCL2 and CCL7, and two of their receptors, CCR1 and CCR2, are expressed and developmentally regulated in the ventral midbrain (VM). Moreover, we found that the expression of CCL7 was down regulated in the Nurr1 knockout mice, linking CCL7 to dopamine (DA) neuron development. When the function of CCL2 and CCL7 was examined, we found that they selectively enhanced the differentiation of Nurr1+ precursors into DA neurons, but not their survival or progenitor proliferation in primary precursor cultures. Moreover, both CCL2 and CCL7 promoted neuritogenesis in midbrain DA neuron cultures. Thus, our results show for the first time a function of beta-chemokines in the developing brain and identify beta-chemokines as novel class of pro-differentiation factors for midbrain DA neurons. These data also suggest that beta-chemokines may become useful tools to enhance the differentiation of DA cell preparations for cell replacement therapy and drug discovery in Parkinson's disease (PD).

Alpha-chemokines regulate proliferation, neurogenesis, and dopaminergic differentiation of ventral midbrain precursors and neurospheres.

Increasing evidence suggests that alpha-chemokines serve several important functions in the nervous system, including regulation of neuroimmune responses, neurotransmission, neuronal survival, and central nervous system development. In this study, we first examined the function of two alpha-chemokines, chemokine ligand (CXCL) 6 and CXCL8, and their receptors, CXCR1 and CXCR2, in the developing rat ventral midbrain (VM). We found that CXCR2 and CXCL6 are regulated during VM development and that CXCL6 promotes the differentiation of nurr77-related receptor (Nurr1)+ precursors into dopaminergic (DA) neurons in vitro. Intriguingly, CXCL8, a ligand expressed only in Homo sapiens, enhanced progenitor cell division, neurogenesis, and tyrosine hydroxylase-positive (TH+) cell number in rodent precursor and neurosphere cultures. CXCL1, the murine ortholog of CXCL8, was developmentally regulated in the VM and exhibited activities similar but not identical to those of CXCL8. TH+ cells derived from chemokine-treated VM neurospheres coexpressed Nurr1 and VMAT and were functionally active, as shown by calcium (Ca(2+)) fluxes in response to AMPA. In conclusion, our data demonstrate that CXCL1, CXCL6, and CXCL8 increase the number of DA neurons in VM precursor and neurosphere cultures by diverse mechanisms. Thus, alpha-chemokines may find an application in the preparation of cells for drug development or Parkinson's disease cell replacement therapy.