Aberrant neuronal differentiation and inhibition of dendrite outgrowth resulting from endoplasmic reticulum stress.

Koichi Kawada,Yasunobu Okuma,Masayuki Kaneko,Ryo Saito,Seisuke Mimori,Yasuyuki Nomura,Takaaki Iekumo

doi:10.1002/jnr.23389

Abstract

Neural stem cells (NSCs) play an essential role in development of the central nervous system. Endoplasmic reticulum (ER) stress induces neuronal death. After neuronal death, neurogenesis is generally enhanced to repair the damaged regions. However, it is unclear whether ER stress directly affects neurogenesis-related processes such as neuronal differentiation and dendrite outgrowth. We evaluated whether neuronal differentiation and dendrite outgrowth were regulated by HRD1, a ubiquitin ligase that was induced under mild conditions of tunicamycin-induced ER stress. Neurons were differentiated from mouse embryonic carcinoma P19 cells by using retinoic acid. The differentiated cells were cultured for 8 days with or without tunicamycin and HRD1 knockdown. The ER stressor led to markedly increased levels of ER stress. ER stress increased the expression levels of neuronal marker βIII-tubulin in 8-day-differentiated cells. However, the neurites of dendrite marker microtubule-associated protein-2 (MAP-2)-positive cells appeared to retract in response to ER stress. Moreover, ER stress markedly reduced the dendrite length and MAP-2 expression levels, whereas it did not affect the number of surviving mature neurons. In contrast, HRD1 knockdown abolished the changes in expression of proteins such as βIII-tubulin and MAP-2. These results suggested that ER stress caused aberrant neuronal differentiation from NSCs followed by the inhibition of neurite outgrowth. These events may be mediated by increased HRD1 expression.

Highlights

New neurons are generated in specific regions of the mammalian brain throughout adult life
To investigate whether endoplasmic reticulum (ER) stress was induced by 10 ng/ml tunicamycin, we performed an immunoblot assay with the anti-KDEL and anti-GADD 153 (C/EBP homologous protein [CHOP]) antibodies to determine glucose-regulated protein (GRP) 94 and GRP78 expression
GRP94, GRP78, and CHOP are molecular chaperones whose expression levels are known to increase with ER stress

Summary

Introduction

New neurons are generated in specific regions of the mammalian brain throughout adult life. NSCs generate rapidly proliferating neural progenitor cells that differentiate to produce thousands of new neurons each day in the adult mammalian brain (Abrous et al, 2005). The regulation of neuronal differentiation and neurite outgrowth plays a pivotal role in adult brain homeostasis and embryonic development. A variety of stressors affect ER function and result in an accumulation of unfolded proteins in the ER lumen. Under such conditions, known as ER stress, the unfolded protein response, which consists of translational. We previously demonstrated that HRD1 promotes ubiquitination and degradation of Parkinassociated endothelin receptor-like receptor (Pael-R), a substrate for Parkin, and suppresses Pael-R-induced ER stress and apoptosis (Omura et al, 2006). Mutations in this gene are known to cause a familial form of Parkinson’s disease known as autosomal recessive juvenile Parkinson’s disease

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