Loss of mitochondrial transcription factor A in neural stem cells leads to immature brain development and triggers the activation of the integral stress response in vivo.

Rintaro Kuroda,Hitoshi Endo,Kenji Kuroiwa,Kaoru Tominaga,Hiroko Hayakawa,Nobuhiko Ohno,Tom Kouki,Eiji Sakashita,Katsumi Kasashima,Kensuke Kawai,Wenhui Hu

doi:10.1371/journal.pone.0255355

Abstract

Mitochondrial dysfunction is significantly associated with neurological deficits and age-related neurological diseases. While mitochondria are dynamically regulated and properly maintained during neurogenesis, the manner in which mitochondrial activities are controlled and contribute to these processes is not fully understood. Mitochondrial transcription factor A (TFAM) contributes to mitochondrial function by maintaining mitochondrial DNA (mtDNA). To clarify how mitochondrial dysfunction affects neurogenesis, we induced mitochondrial dysfunction specifically in murine neural stem cells (NSCs) by inactivating Tfam. Tfam inactivation in NSCs resulted in mitochondrial dysfunction by reducing respiratory chain activities and causing a severe deficit in neural differentiation and maturation both in vivo and in vitro. Brain tissue from Tfam-deficient mice exhibited neuronal cell death primarily at layer V and microglia were activated prior to cell death. Cultured Tfam-deficient NSCs showed a reduction in reactive oxygen species produced by the mitochondria. Tfam inactivation during neurogenesis resulted in the accumulation of ATF4 and activation of target gene expression. Therefore, we propose that the integrated stress response (ISR) induced by mitochondrial dysfunction in neurogenesis is activated to protect the progression of neurodegenerative diseases.

Highlights

Mitochondria are highly dynamic organelles that contribute to cellular energy metabolism by generating ATP through oxidative phosphorylation (OXPHOS) according to energy demands [1]
The results suggest that mitochondrial dysfunction caused by mitochondrial DNA (mtDNA) defects induces integrated stress response (ISR) activation in the brain which prevents the progression of neurodegeneration
Tfam cKO mice are born at the expected ratio but exhibit postnatal lethality All mice were born with the expected Mendelian ratio independently of their genotypes and Tfam cKO (Tfamfl/fl; Nestin-Cre+) mice could not be distinguished from the others at birth

Summary

Introduction

Mitochondria are highly dynamic organelles that contribute to cellular energy metabolism by generating ATP through oxidative phosphorylation (OXPHOS) according to energy demands [1]. ATP production by mitochondria is important for maintaining neuronal function and activity, but it is severely compromised in mitochondrial disease patients [17,18,19,20]. Because massive neuronal cell death at end stages and excitotoxic stress conditions were observed in MILON mice, mitochondrial activities are important for maintaining proper neuronal activities in this model. We examined the role of mitochondria during neurogenesis using mice exhibiting conditional Tfam inactivation in nestin-expressing NSCs. Tfam-deficient mice were viable and indistinguishable from control littermates at birth. NSCs cultured as neurospheres from Tfam-deficient mouse brains exhibited defective growth characteristics and their neural differentiation ability was severely compromised. We showed that the integrated stress response (ISR) was activated in Tfam-deficient brains and NSCs in response to reduced mitochondrial activity. The results suggest that mitochondrial dysfunction caused by mtDNA defects induces ISR activation in the brain which prevents the progression of neurodegeneration

Materials and methods

Results

Discussion