Deletion of Class II ADP-Ribosylation Factors in Mice Causes Tremor by the Nav1.6 Loss in Cerebellar Purkinje Cell Axon Initial Segments.

ADP-ribosylation factors (ARFs) are a family of small monomeric GTPases comprising six members categorized into three classes: class I (ARF1,2, and 3), class II (ARF4 and 5), and class III (ARF6). In contrast to class I and III ARFs, which are the key regulators in vesicular membrane trafficking, the cellular function of class II ARFs remains unclear. In the present study, we generated class II ARF-deficient mice and found that ARF4 +/-/ARF5-/- mice exhibited essential tremor (ET)-like behaviors. In vivo electrophysiological recordings revealed that ARF4 1 /ARF5 /mice ofboth sexes exhibited abnormal brain activity when moving, raising the possibility of abnormal cerebellar excitability. Slice patch-damp experiments demonstrated the reduced excitability of the cerebellar Purkinje cells (PCs) in ARF4+/-/ARF5-/- mice. Immunohistochemical and electrophysiological analyses revealed a severe and selective decrease of poreforming voltage-dependent NaH channel subunit Navi.6, important for maintaining repetitive action potential firing, in the axon initial segment (AIS) of PCs. Importantly, this decrease in Navi.6 protein localized in the AIS and the consequent tremors in ARF4+/- ARF5 mice could be alleviated by the PC-specific expression of ARF5 using adeno-associated virus vectors. Together, our data demonstrate that the decreased expression of the class IIARF proteins in ARF4+/-/ARF5 mice, leading to a haploinsufficiency of ARF4 in the absence of ARF5, impairs the localization of Navl.6 to the AIS and hence reduces the membrane excitability in PCs, resulting in the ET-like movement disorder. We suggest that class II ARFs function in localizing specific proteins, such as Navl.6, to the AIS. [ABSTRACT FROM AUTHOR]