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High Levels of ROS Impair Lysosomal Acidity and Autophagy Flux in Glucose-Deprived Fibroblasts by Activating ATM and
Seon Beom Song1, Eun Seong Hwang1
1Department of Life Science, University of Seoul, Dongdaemun-gu, Seoulsiripdae-ro 163, Seoul 02504, Korea.
Abstract:
Under glucose deprivation, cells heavily mobilize oxidative phosphorylation to maintain energy homeostasis. This leads to the generation of high levels of ATP, as well as reactive oxygen species (ROS), from mitochondria. In nutrient starvation, autophagy is activated, likely to facilitate resource recycling, but recent studies suggest that autophagy flux is inhibited in cells undergoing glucose deprivation. In this study, we analyzed the status of autophagic flux in glucose-deprived human fibroblasts. Although lysosomes increased in quantity due in part to an increase of biogenesis, a large population of them suffered low acidity in the glucose-deprived cells. Autophagosomes also accumulated due to poor autolysis in these cells. A treatment of antioxidants not only restored lysosomal acidity but also released the flux blockade. The inhibition of ataxia telangiectasia mutated (ATM) serine/threonine kinase, which is activated by ROS, also attenuated the impairment of lysosomal acidity and autophagic flux, suggesting an effect of ROS that might be mediated through ATM activation. In addition, the activity of extracellular signal-regulated kinase (Erk) increased upon glucose deprivation, but this was also compromised by a treatment of antioxidants. Furthermore, the Erk inhibitor treatment also alleviated the failure in lysosomal acidity and autophagic flux. These together indicate that, upon glucose deprivation, cells undergo a failure of autophagy flux through an impairment of lysosomal acidity and that a high-level ROS-induced activation of Erk and ATM is involved in this impairment.
Insights
Glucose deprivation impairs cellular autophagy by reducing lysosomal acidity, leading to autophagosome accumulation. Antioxidants and inhibitors of ATM and Erk signaling restore lysosomal function and autophagy flux.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Cells mobilize oxidative phosphorylation for energy homeostasis under glucose deprivation, producing ATP and reactive oxygen species (ROS).
- Autophagy is typically activated during nutrient starvation for resource recycling, but recent studies indicate its flux is inhibited during glucose deprivation.
- Understanding the mechanisms of autophagy inhibition under glucose deprivation is crucial for cellular energy and stress response research.
Purpose of the Study:
- To analyze the status of autophagic flux in glucose-deprived human fibroblasts.
- To investigate the role of lysosomal acidity, reactive oxygen species (ROS), ataxia telangiectasia mutated (ATM) kinase, and extracellular signal-regulated kinase (Erk) in the observed autophagy impairment.
Main Methods:
- Analysis of autophagic flux in glucose-deprived human fibroblasts.
- Assessment of lysosomal quantity and acidity.
- Treatment with antioxidants, ATM inhibitors, and Erk inhibitors.
- Monitoring of autophagosome accumulation and autolysis.
Main Results:
- Glucose deprivation led to increased lysosome biogenesis but decreased lysosomal acidity and autophagosome accumulation due to poor autolysis.
- Antioxidant treatment restored lysosomal acidity and released the autophagy flux blockade.
- Inhibition of ROS-activated ATM kinase attenuated lysosomal acidity impairment and autophagic flux inhibition.
- Increased Erk activity upon glucose deprivation was compromised by antioxidants and its inhibition alleviated lysosomal acidity and autophagy defects.
Conclusions:
- Glucose deprivation causes autophagy flux failure in human fibroblasts, characterized by impaired lysosomal acidity.
- High levels of ROS-induced activation of Erk and ATM signaling pathways are involved in the impairment of lysosomal acidity and subsequent autophagy failure.
- Targeting ROS, ATM, and Erk signaling may offer therapeutic strategies for conditions involving impaired autophagy due to glucose deprivation.
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