Lou Jun-Yang, Laezza Fernanda, Gerber Benjamin R, Xiao Maolei, Yamada Kathryn A, Hartmann Hali, Craig Ann Marie, Nerbonne Jeanne M, Ornitz David M
Department of Molecular Biology and Pharmacology, Washington University School of Medicine, Saint Louis, MO 63110, USA.
J Physiol. 2005 Nov 15;569(Pt 1):179-93. doi: 10.1113/jphysiol.2005.097220. Epub 2005 Sep 15.
Genetic ablation of the fibroblast growth factor (Fgf) 14 gene in mice or a missense mutation in Fgf14 in humans causes ataxia and cognitive deficits. These phenotypes suggest that the neuronally expressed Fgf14 gene is essential for regulating normal neuronal activity. Here, we demonstrate that FGF14 interacts directly with multiple voltage-gated Na(+) (Nav) channel alpha subunits heterologously expressed in non-neuronal cells or natively expressed in a murine neuroblastoma cell line. Functional studies reveal that these interactions result in the potent inhibition of Nav channel currents (I(Na)) and in changes in the voltage dependence of channel activation and inactivation. Deletion of the unique amino terminus of the splice variant of Fgf14, Fgf14-1b, or expression of the splice variant Fgf14-1a modifies the modulatory effects on I(Na), suggesting an important role for the amino terminus domain of FGF14 in the regulation of Na(v) channels. To investigate the function of FGF14 in neurones, we directly expressed Fgf14 in freshly isolated primary rat hippocampal neurones. In these cells, the addition of FGF14-1a-GFP or FGF14-1b-GFP increased I(Na) density and shifted the voltage dependence of channel activation and inactivation. In fully differentiated neurones, FGF14-1a-GFP or FGF14-1b-GFP preferentially colocalized with endogenous Nav channels at the axonal initial segment, a critical region for action potential generation. Together, these findings implicate FGF14 as a unique modulator of Nav channel activity in the CNS and provide a possible mechanism to explain the neurological phenotypes observed in mice and humans with mutations in Fgf14.
小鼠成纤维细胞生长因子（Fgf）14基因的基因消融或人类Fgf14中的错义突变会导致共济失调和认知缺陷。这些表型表明，神经元表达的Fgf14基因对于调节正常神经元活动至关重要。在这里，我们证明FGF14与在非神经元细胞中异源表达或在鼠神经母细胞瘤细胞系中天然表达的多个电压门控Na⁺（Nav）通道α亚基直接相互作用。功能研究表明，这些相互作用导致Nav通道电流（I(Na)）受到有效抑制，并使通道激活和失活的电压依赖性发生变化。删除Fgf14剪接变体Fgf14-1b的独特氨基末端，或表达剪接变体Fgf14-1a，会改变对I(Na)的调节作用，这表明FGF14的氨基末端结构域在调节Na(v)通道中起重要作用。为了研究FGF14在神经元中的功能，我们在新鲜分离的原代大鼠海马神经元中直接表达Fgf14。在这些细胞中，添加FGF14-1a-GFP或FGF14-1b-GFP会增加I(Na)密度，并改变通道激活和失活的电压依赖性。在完全分化的神经元中，FGF14-1a-GFP或FGF14-1b-GFP优先与轴突起始段的内源性Nav通道共定位，轴突起始段是动作电位产生的关键区域。总之，这些发现表明FGF14是中枢神经系统中Nav通道活性的独特调节剂，并提供了一种可能的机制来解释在Fgf14发生突变的小鼠和人类中观察到的神经学表型。
