Central nervous system specific high molecular weight ALS2/alsin homophilic complex is enriched in mouse brain synaptosomes

ALS2/alsin, the causative gene product for a number of juvenile recessive motor neuron diseases, acts as a guanine nucleotide exchange factor (GEF) for Rab5, regulating early endosome trafficking and matura-tion. It has been demonstrated that ALS2 forms a tetramer, and this oligomerization is essential for its GEF activity and endosomal localization in established cancer cells. However, despite that ALS2 defi-ciency is implicated in neurological diseases, neither the subcellular distribution of ALS2 nor the form of its complex in the central nervous system (CNS) has been investigated. In this study, we showed that ALS2 in the brain was enriched both in synaptosomal and cytosolic fractions, while those in the liver were almost exclusively present in cytosolic fraction by differential centrifugation. Gel filtration chro-matography revealed that cytosolic ALS2 prepared both from the brain and liver formed a tetramer. Remarkably, synaptosomal ALS2 existed as a high-molecular weight complex in addition to a tetramer. Such complex was also observed not only in embryonic brain but also several neuronal and glial cultures, but not in fibroblast-derived cell lines. Thus, the high-molecular weight ALS2 complex represents a unique form of ALS2-homophilic oligomers in the CNS, which may play a role in the maintenance of neural function.(c) 2022 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/).

Automated summary

ALS2 functions as a guanine nucleotide exchange factor for Rab5 and plays a role in regulating early endosome trafficking. ALS2 is enriched in synaptosomal and cytosolic fractions in the brain, while it is mainly present in the cytosolic fraction in the liver. Both brain and liver cytosolic ALS2 form a tetramer, and synaptosomal ALS2 exists as a high-molecular weight complex in addition to a tetramer. This unique form of ALS2-homophilic oligomers may be involved in the maintenance of neural function.