Lacey Taylor A, Murray Karl D, Trimmer James S, Sack Jon T, Ferns Michael J
Department of Anesthesiology and Pain Medicine, University of California Davis, Davis, California, USA.
Department of Physiology and Membrane Biology, University of California Davis, Davis, California, USA.
Eur J Neurosci. 2025 Sep;62(5):e70243. doi: 10.1111/ejn.70243.
Voltage-gated K channels of the Kv2 family coassemble with electrically silent KvS subunits in specific subpopulations of brain neurons, forming heteromeric Kv2/KvS channels with distinct functional properties. Little is known about the composition and function of Kv2 channels in spinal cord neurons, however. Here, we show that while Kv2.1 is broadly expressed in multiple classes of spinal cord neurons, the Kv6.4 "electrically silent" subunit is specifically expressed in motoneurons. In motoneurons, we find that Kv6.4 protein is coclustered with Kv2.1 and Kv2.2 subunits at endoplasmic reticulum-plasma membrane (ER-PM) junctions beneath C-bouton synapses. In Kv2.1 S590A mutant mice, in which Kv2.1 is unable to bind ER VAP proteins, Kv2.1 and Kv6.4 clustering at ER-PM junctions is severely reduced suggesting Kv2 channels are localized at ER-PM junctions by the same molecular mechanism in motoneurons and brain neurons. Moreover, clustering of Kv6.4, as well as the AMIGO-1 auxiliary subunit, are severely reduced in Kv2.1 knockout mice and moderately reduced in Kv2.2 knockout mice. Thus, expression and localization of Kv6.4 subunits is dependent on Kv2 subunits, likely through their coassembly into heteromeric channels. Finally, we find that presynaptic C-boutons and postsynaptic clusters of the ER-resident sigma-1 receptor are preserved in motoneurons of Kv2 knockout mice. Together, these findings identify a specific Kv2/KvS channel subtype expressed in motoneurons that localizes to C-bouton junctions where it could regulate neuronal excitability and/or signaling at ER-PM junctions.
Kv2家族的电压门控钾通道在脑神经元的特定亚群中与电沉默的KvS亚基共同组装，形成具有独特功能特性的异源Kv2/KvS通道。然而，关于脊髓神经元中Kv2通道的组成和功能知之甚少。在这里，我们表明，虽然Kv2.1在多类脊髓神经元中广泛表达，但Kv6.4“电沉默”亚基在运动神经元中特异性表达。在运动神经元中，我们发现Kv6.4蛋白与Kv2.1和Kv2.2亚基在内质网-质膜（ER-PM）交界处的C型终扣突触下方共聚集。在Kv2.1 S590A突变小鼠中，Kv2.1无法结合内质网VAP蛋白，Kv2.1和Kv6.4在ER-PM交界处的聚集严重减少，这表明Kv2通道通过相同的分子机制定位于运动神经元和脑神经元的ER-PM交界处。此外，在Kv2.1基因敲除小鼠中，Kv6.4以及AMIGO-1辅助亚基的聚集严重减少，在Kv2.2基因敲除小鼠中中度减少。因此，Kv6.4亚基的表达和定位依赖于Kv2亚基，可能是通过它们共同组装成异源通道。最后，我们发现内质网驻留的σ-1受体的突触前C型终扣和突触后簇在Kv2基因敲除小鼠的运动神经元中得以保留。总之，这些发现确定了一种在运动神经元中表达的特定Kv2/KvS通道亚型，该亚型定位于C型终扣连接处，在那里它可以调节神经元兴奋性和/或ER-PM连接处的信号传导。
