O-GlcNAc regulates the mitochondrial integrated stress response by regulating ATF4

Ibtihal M Alghusen; Marisa S Carman; Heather Wilkins; Sophiya John Ephrame; Amy Qiang; Wagner B Dias; Halyna Fedosyuk; Aspin R Denson; Russell H Swerdlow; Chad Slawson

doi:10.3389/fnagi.2023.1326127

O-GlcNAc regulates the mitochondrial integrated stress response by regulating ATF4

Front Aging Neurosci. 2023 Dec 18:15:1326127. doi: 10.3389/fnagi.2023.1326127. eCollection 2023.

Authors

Ibtihal M Alghusen¹, Marisa S Carman¹, Heather Wilkins^{1

2

3}, Sophiya John Ephrame¹, Amy Qiang¹, Wagner B Dias¹, Halyna Fedosyuk¹, Aspin R Denson¹, Russell H Swerdlow^{1

2

3}, Chad Slawson^{1

3}

Affiliations

¹ School of Medicine, Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS, United States.
² Department of Neurology, University of Kansas Medical Center, Kansas City, KS, United States.
³ University of Kansas Alzheimer's Disease Research Center, University of Kansas Medical Center, Kansas City, KS, United States.

Abstract

Background: Accumulation of mitochondrial dysfunctional is a hallmark of age-related neurodegeneration including Alzheimer's disease (AD). Impairment of mitochondrial quality control mechanisms leading to the accumulation of damaged mitochondria and increasing neuronal stress. Therefore, investigating the basic mechanisms of how mitochondrial homeostasis is regulated is essential. Herein, we investigate the role of O-GlcNAcylation, a single sugar post-translational modification, in controlling mitochondrial stress-induced transcription factor Activating Transcription Factor 4 (ATF4). Mitochondrial dysfunction triggers the integrated stress response (ISR^mt), in which the phosphorylation of eukaryotic translation initiation factor 2α results in the translation of ATF4.

Methods: We used patient-derived induced pluripotent stem cells, a transgenic mouse model of AD, SH-SY5Y neuroblastoma and HeLa cell-lines to examine the effect of sustained O-GlcNAcase inhibition by Thiamet-G (TMG) on ISR^mt using biochemical analyses.

Results: We show that TMG elevates ATF4 protein levels upon mitochondrial stress in SH-SY5Y neuroblastoma and HeLa cell-lines. An indirect downstream target of ATF4 mitochondrial chaperone glucose-regulated protein 75 (GRP75) is significantly elevated. Interestingly, knock-down of O-GlcNAc transferase (OGT), the enzyme that adds O-GlcNAc, in SH-SY5Y increases ATF4 protein and mRNA expression. Additionally, ATF4 target gene Activating Transcription Factor 5 (ATF5) is significantly elevated at both the protein and mRNA level. Brains isolated from TMG treated mice show elevated levels of ATF4 and GRP75. Importantly, ATF4 occupancy increases at the ATF5 promoter site in brains isolated from TMG treated mice suggesting that O-GlcNAc is regulating ATF4 targeted gene expression. Interestingly, ATF4 and GRP75 are not induced in TMG treated familial Alzheimer's Disease mice model. The same results are seen in a human in vitro model of AD.

Conclusion: Together, these results indicate that in healthy conditions, O-GlcNAc regulates the ISRmt through regulating ATF4, while manipulating O-GlcNAc in AD has no effect on ISR^mt.

Keywords: Alzheimer’s disease; O-GlcNAc; activating transcription factor 4 (ATF4); integrated stress response; mitochondrial stress.

Abstract

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