| dc.description.abstracteng | Norepinephrine (NE), a catecholamine produced by dopamine β-hydroxylase, is released either as a hormone from the adrenal medulla into the blood, or as a neurotransmitter in the brain. Norepinephrine signaling serves as a global regulator of the brain, but there is still some functional selectivity in release and in the expression patterns of the various adrenergic receptor subtypes in different brain regions, to permit more specific sculpting of responses in the brain (O'Donnell et al., 2012).Extensive physiological and behavioral studies have demonstrated that NE/β2-adrenergic signaling could facilitate the induction of spike-timing-dependent plasticity (STDP) at excitatory synapses (Lin et al., 2003; Seol et al., 2007; Zhou et al., 2013) and enhances memory (Ji et al., 2003; Lemon et al., 2009; Miranda et al., 2011; Tronel et al., 2004), potentially through inhibiting dendritic potassium conductance and therefore increase the propagation of dendritic action potentials (Hoffman and Johnston, 1999; Watanabe et al., 2002). However, it remains unknown which potassium channels are involved in the modulation of dendritic excitability by NE/ β2-adrenergic signaling, and how these potassium channels are mobilized in response to β2-adrenergic receptor activation.
Our preliminary data showed that NE (norepinephrine) blocked the delayed onset of action potentials and induced the inactivation of D-type currents. This effect was mediated by signaling scaffolding SAP97, which belongs to the DLG-MAGUK family and has been indicated to regulate membrane expression and stabilization of PDZ-ligand-containing receptors and ion channels (Kim et al., 1995; Tiffany et al., 2000). A plausible mechanism would be the NE-induced reduction in surface expression of Kv1.1.
In this study, we showed that in primary hippocampus neurons, NE signaling, through β2 adrenergic receptor activity, induced internalization of endogenous Kv1.1. Additionally, the NE-induced internalization of Kv1.1 was impaired in SAP97 knockout neurons, suggesting that NE/β2-adrenergic receptor signaling can regulate surface Kv1.1 trafficking in a SAP97 dependent manner. Furthermore, we designed a PDZ/ligand class switch model by using compensatory mutants of SAP97 and Kv1.1, and characterized that the binding activity of SAP97 PDZ12 tandem was required for its interaction with the C-terminal PDZ domain binding motif of Kv1.1 and NE-mediated Kv1.1 internalization. Moreover, we found the PKA-mediated phosphorylation of Kv1.1 was also responsible for the mobility of potassium channels in response to adrenergic signaling.
Overall, this study reveals a role of SAP97 in linking adrenergic signaling to the modulation of potassium channels surface expression, and provide a mechanistic understanding how G protein-coupled receptors regulate dendritic excitability. | de |