Abstract
Postmitotic neurons need to keep their cell cycle under control to survive and maintain a differentiated state. This study aims to test the hypothesis that the chemokine CXCL12 regulates neuronal survival and differentiation by promoting Rb function, as suggested by previous studies showing that CXCL12 protects neurons from apoptosis induced by Rb loss. To this end, the effect of CXCL12 on Rb expression and transcriptional activity and the role of Rb in CXCL12-induced neuronal survival were studied. CXCL12 increases Rb protein and RNA levels in rat cortical neurons. The chemokine also stimulates an exogenous Rb promoter expressed in these neurons and counteracts the inhibition of the Rb promoter induced by E2F1 overexpression. Furthermore CXCL12 stimulates Rb activity as a transcription repressor. The effects of CXCL12 are mediated by its specific receptor CXCR4, and do not require the presence of glia. Finally, shRNA studies show that Rb expression is crucial to the neuroprotective activity of CXCL12 as indicated by NMDA-neurotoxicity assays. These findings suggest that proper CXCR4 stimulation in the mature CNS can prevent impairment of the Rb-E2F pathway and support neuronal survival. This is important to maintain CNS integrity in physiological conditions and prevent neuronal injury and loss typical of many neurodegenerative and neuroinflammatory conditions.