ESCRT Proteins Control the Dendritic Morphology of Developing and Mature Hippocampal Neurons.

The proper shape of dendritic arbors of different types of neurons determines their proper communication within neuronal networks. The shape of dendritic arbors is acquired during a complex and multistep process called dendritogenesis. In most cases, once proper morphology is achieved, it remains stable throughout the lifespan, with the exception of rare events during which dendrites are abruptly pruned. The endosomal sorting complex required for transport (ESCRT) is multisubunit machinery that is involved in various cellular processes when membrane scission is needed. ESCRT subcomplexes regulate dendrite pruning in Drosophila neurons. However, the contribution of ESCRT components to the dendritogenesis of mammalian neurons and control of dendrite stability remains poorly defined. In the present study, we found that ESCRT-0, ESCRT-I, ESCRT-II, and ESCRT-III and Vps4 are required for proper dendrite morphology under basal culture conditions and for accelerated dendritogenesis in response to phosphoinositide 3-kinase (PI3K) activation. The knockdown of Vps28 (ESCRT-I) and Vps25 (ESCRT-II) resulted in downregulation of the activity of mechanistic/mammalian target of rapamycin complex 1. We also demonstrated that Vps28, Vps24, and Vps25 are required for dendrite stabilization in mature neurons.

Kainic Acid Induces mTORC1-Dependent Expression of Elmo1 in Hippocampal Neurons.

Epileptogenesis is a process triggered by initial environmental or genetic factors that result in epilepsy and may continue during disease progression. Important parts of this process include changes in transcriptome and the pathological rewiring of neuronal circuits that involves changes in neuronal morphology. Mammalian/mechanistic target of rapamycin (mTOR) is upregulated by proconvulsive drugs, e.g., kainic acid, and is needed for progression of epileptogenesis, but molecular aspects of its contribution are not fully understood. Since mTOR can modulate transcription, we tested if rapamycin, an mTOR complex 1 inhibitor, affects kainic acid-evoked transcriptome changes. Using microarray technology, we showed that rapamycin inhibits the kainic acid-induced expression of multiple functionally heterogeneous genes. We further focused on engulfment and cell motility 1 (Elmo1), which is a modulator of actin dynamics and therefore could contribute to pathological rewiring of neuronal circuits during epileptogenesis. We showed that prolonged overexpression of Elmo1 in cultured hippocampal neurons increased axonal growth, decreased dendritic spine density, and affected their shape. In conclusion, data presented herein show that increased mTORC1 activity in response to kainic acid has no global effect on gene expression. Instead, our findings suggest that mTORC1 inhibition may affect development of epilepsy, by modulating expression of specific subset of genes, including Elmo1, and point to a potential role for Elmo1 in morphological changes that accompany epileptogenesis.