Dopamine cross-reacts with adrenoreceptors in cortical astrocytes to induce BDNF expression, CREB signaling and morphological transformation.

Expression of brain-derived neurotrophic factor (BDNF) is induced in cultured rat cortical astrocytes by catecholamines norepinephrine and dopamine as well as selective α1 and ß adrenergic agonists. However, it has remained unknown which receptors mediate dopamine-induced BDNF upregulation in astrocytes. Here, we demonstrate that ß adrenoreceptors are the main mediators of this effect in cultured cortical astrocytes, while α1 adrenoreceptors and D1 dopamine receptors contribute to a lesser extent. We show that in cortical astrocytes BDNF exon IV and exon VI containing mRNAs are induced by dopamine and norepinephrine via CREB-dependent signaling and that this regulation is mediated by a mechanism that is distinct from activity-dependent CREB-mediated activation of BDNF transcription in neurons. We also show that regulation of BDNF promoters IV and VI by catecholamines requires a distal regulatory element in the BDNF locus. Finally, we demonstrate that dopamine-induced astrocyte stellation and induction of CREB signaling are mediated by cross-reaction of dopamine with ß adrenoreceptors.

PCSK9 deficiency alters brain lipid composition without affecting brain development and function.

PCSK9 induces lysosomal degradation of the low-density lipoprotein (LDL) receptor (LDLR) in the liver, hereby preventing removal of LDL cholesterol from the circulation. Accordingly, PCSK9 inhibitory antibodies and siRNA potently reduce LDL cholesterol to unprecedented low levels and are approved for treatment of hypercholesterolemia. In addition, PCSK9 inactivation alters the levels of several other circulating lipid classes and species. Brain function is critically influenced by cholesterol and lipid composition. However, it remains unclear how the brain is affected long-term by the reduction in circulating lipids as achieved with potent lipid lowering therapeutics such as PCSK9 inhibitors. Furthermore, it is unknown if locally expressed PCSK9 affects neuronal circuits through regulation of receptor levels. We have studied the effect of lifelong low peripheral cholesterol levels on brain lipid composition and behavior in adult PCSK9 KO mice. In addition, we studied the effect of PCSK9 on neurons in culture and in vivo in the developing cerebral cortex. We found that PCSK9 reduced LDLR and neurite complexity in cultured neurons, but neither PCSK9 KO nor overexpression affected cortical development in vivo. Interestingly, PCSK9 deficiency resulted in changes of several lipid classes in the adult cortex and cerebellum. Despite the observed changes, PCSK9 KO mice had unchanged behavior compared to WT controls. In conclusion, our findings demonstrate that altered PCSK9 levels do not compromise brain development or function in mice, and are in line with clinical trials showing that PCSK9 inhibitors have no adverse effects on cognitive function.