CCL2 Induces the Production of β2 Adrenergic Receptors and Modifies Astrocytic Responses to Noradrenaline

The decline in brain noradrenaline levels is associated with the progression of certain neurodegenerative diseases. This seems to be due, at least in part, to the ability of noradrenaline to limit glial activation and to reduce the damage associated with it. Our previous studies of the mechanisms involved in this process indicate that noradrenaline induces the production of the chemokine CCL2 in astrocytes. While CCL2 can protect neurons against certain injuries, its overproduction has also proven to be harmful and to prevent noradrenaline neuroprotective effects. Therefore, in this study, we analyze if the modifications caused to astrocytes by an excessive production of CCL2 may alter their response to noradrenaline. Using primary cultures of rat cortical astrocytes, we observed that CCL2 enhances the production of beta 2 adrenergic receptors in these cells. While this potentiates noradrenaline signaling through cAMP, the activation of the transcription factor CREB is inhibited by CCL2. Furthermore, although CCL2 potentiates noradrenaline induction of glycogenolysis, this does not translate into an augmented release of lactate, one of the processes through which astrocytes help support neurons. Additionally, other neuroprotective actions of noradrenaline, such as the production of brain derived neurotrophic factor and the inhibition of the inducible nitric oxide synthase in astrocytes were modified by CCL2. These data suggest that some of the central nervous system alterations related to CCL2 could be due to its effects on adrenergic receptors and its interference with noradrenaline signaling.