Dysregulation of Glutamine Transporter SNAT1 in Rett Syndrome Microglia: A Mechanism for Mitochondrial Dysfunction and Neurotoxicity

Lee-Way Jin, Makoto Horiuchi, Heike Wulff, Xiao Bo Liu, Gino A Cortopassi, Jeffrey D. Erickson, Izumi Maezawa

Research output: Contribution to journalArticle

38 Citations (Scopus)

Abstract

Rett syndrome (RTT) is an autism spectrum disorder caused by loss-of-function mutations in the gene encoding MeCP2, an epigenetic modulator that binds the methyl CpG dinucleotide in target genes to regulate transcription. Previously, we and others reported a role of microglia in the pathophysiology of RTT. To understand the mechanism of microglia dysfunction in RTT, we identified a MeCP2 target gene, SLC38A1, which encodes a major glutamine transporter (SNAT1), and characterized its role in microglia. We found that MeCP2 acts as a microglia-specific transcriptional repressor of SNAT1. Because glutamine is mainly metabolized in the mitochondria, where it is used as an energy substrate and a precursor for glutamate production, we hypothesize that SNAT1 overexpression in MeCP2-deficient microglia would impair the glutamine homeostasis, resulting in mitochondrial dysfunction as well as microglial neurotoxicity because of glutamate overproduction. Supporting this hypothesis, we found that MeCP2 downregulation or SNAT1 overexpression in microglia resulted in (1) glutamine-dependent decrease in microglial viability, which was corroborated by reduced microglia counts in the brains of MECP2 knock-out mice; (2) proliferation of mitochondria and enhanced mitochondrial production of reactive oxygen species; (3) increased oxygen consumption but decreased ATP production (an energy-wasting state); and (4) overproduction of glutamate that caused NMDA receptor-dependent neurotoxicity. The abnormalities could be rectified by mitochondria-targeted expression of catalase and a mitochondria-targeted peptide antioxidant, Szeto-Schiller 31. Our results reveal a novel mechanism via which MeCP2 regulates bioenergetic pathways in microglia and suggest a therapeutic potential of mitochondria-targeted antioxidants for RTT.

Original languageEnglish (US)
Pages (from-to)2516-2529
Number of pages14
JournalJournal of Neuroscience
Volume35
Issue number6
DOIs
StatePublished - 2015

Fingerprint

Rett Syndrome
Microglia
Glutamine
Mitochondria
Glutamic Acid
Antioxidants
Genes
N-Methyl-D-Aspartate Receptors
Epigenomics
Knockout Mice
Oxygen Consumption
Catalase
Energy Metabolism
Reactive Oxygen Species
Homeostasis
Down-Regulation
Adenosine Triphosphate
Peptides
Mutation
Brain

Keywords

  • Glutamate
  • Glutamine
  • Microglia
  • Mitochondria
  • Rett
  • Transporter

ASJC Scopus subject areas

  • Neuroscience(all)

Cite this

Dysregulation of Glutamine Transporter SNAT1 in Rett Syndrome Microglia : A Mechanism for Mitochondrial Dysfunction and Neurotoxicity. / Jin, Lee-Way; Horiuchi, Makoto; Wulff, Heike; Liu, Xiao Bo; Cortopassi, Gino A; Erickson, Jeffrey D.; Maezawa, Izumi.

In: Journal of Neuroscience, Vol. 35, No. 6, 2015, p. 2516-2529.

Research output: Contribution to journalArticle

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abstract = "Rett syndrome (RTT) is an autism spectrum disorder caused by loss-of-function mutations in the gene encoding MeCP2, an epigenetic modulator that binds the methyl CpG dinucleotide in target genes to regulate transcription. Previously, we and others reported a role of microglia in the pathophysiology of RTT. To understand the mechanism of microglia dysfunction in RTT, we identified a MeCP2 target gene, SLC38A1, which encodes a major glutamine transporter (SNAT1), and characterized its role in microglia. We found that MeCP2 acts as a microglia-specific transcriptional repressor of SNAT1. Because glutamine is mainly metabolized in the mitochondria, where it is used as an energy substrate and a precursor for glutamate production, we hypothesize that SNAT1 overexpression in MeCP2-deficient microglia would impair the glutamine homeostasis, resulting in mitochondrial dysfunction as well as microglial neurotoxicity because of glutamate overproduction. Supporting this hypothesis, we found that MeCP2 downregulation or SNAT1 overexpression in microglia resulted in (1) glutamine-dependent decrease in microglial viability, which was corroborated by reduced microglia counts in the brains of MECP2 knock-out mice; (2) proliferation of mitochondria and enhanced mitochondrial production of reactive oxygen species; (3) increased oxygen consumption but decreased ATP production (an energy-wasting state); and (4) overproduction of glutamate that caused NMDA receptor-dependent neurotoxicity. The abnormalities could be rectified by mitochondria-targeted expression of catalase and a mitochondria-targeted peptide antioxidant, Szeto-Schiller 31. Our results reveal a novel mechanism via which MeCP2 regulates bioenergetic pathways in microglia and suggest a therapeutic potential of mitochondria-targeted antioxidants for RTT.",
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