Yuyang Miao

ROS and Autophagy: Interactions and Molecular Regulatory Mechanisms

Abstract Reactive oxygen species (ROS) and antioxidant ingredients are a series of crucial signaling molecules in oxidative stress response. Under some pathological conditions such as traumatic brain injury, ischemia/reperfusion, and hypoxia in tumor, the relative excessive accumulation of ROS could break cellular homeostasis, resulting in oxidative stress and mitochondrial dysfunction. Meanwhile, autophagy is also induced. In this process, oxidative stress could promote the formation of autophagy. Autophagy, in turn, may contribute to reduce oxidative damages by engulfing and degradating oxidized substance. This short review summarizes these interactions between ROS and autophagy in related pathological conditions referred to as above with a focus on discussing internal regulatory mechanisms. The tight interactions between ROS and autophagy reflected in two aspects: the induction of autophagy by oxidative stress and the reduction of ROS by autophagy. The internal regulatory mechanisms of autophagy by ROS can be summarized as transcriptional and post-transcriptional regulation, which includes various molecular signal pathways such as ROS–FOXO3–LC3/BNIP3–autophagy, ROS–NRF2–P62–autophagy, ROS–HIF1–BNIP3/NIX–autophagy, and ROS–TIGAR–autophagy. Autophagy also may regulate ROS levels through several pathways such as chaperone-mediated autophagy pathway, mitophagy pathway, and P62 delivery pathway, which might provide a further theoretical basis for the pathogenesis of the related diseases and still need further research.

Crosstalk of autophagy and apoptosis: Involvement of the dual role of autophagy under ER stress

Endoplasmic reticulum (ER) stress is a common cellular stress response that is triggered by a variety of conditions that disturb cellular homeostasis, and induces cell apoptosis. Autophagy, an important and evolutionarily conserved mechanism for maintaining cellular homeostasis, is closely related to the apoptosis induced by ER stress. There are common upstream signaling pathways between autophagy and apoptosis induced by ER stress, including PERK/ATF4, IRE1α, ATF6, and Ca2+. Autophagy can not only block the induction of apoptosis by inhibiting the activation of apoptosis‐associated caspase which could reduce cellular injury, but also help to induce apoptosis. In addition, the activation of apoptosis‐related proteins can also inhibit autophagy by degrading autophagy‐related proteins, such as Beclin‐1, Atg4D, Atg3, and Atg5. Although the interactions of different autophagy‐ and apoptosis‐related proteins, and also common upstream signaling pathways have been found, the potential regulatory mechanisms have not been clearly understood. In this review, we summarize the dual role of autophagy, and the interplay and potential regulatory mechanisms between autophagy and apoptosis under ER stress condition.

The dual role of autophagy under hypoxia-involvement of interaction between autophagy and apoptosis

Abstract Hypoxia is one of severe cellular stress and it is well known to be associated with a worse outcome since a lack of oxygen accelerates the induction of apoptosis. Autophagy, an important and evolutionarily conserved mechanism for maintaining cellular homeostasis, is closely related to the apoptosis caused by hypoxia. Generally autophagy blocks the induction of apoptosis and inhibits the activation of apoptosis-associated caspase which could reduce cellular injury. However, in special cases, autophagy or autophagy-relevant proteins may help to induce apoptosis, which could aggravate cell damage under hypoxia condition. In addition, the activation of apoptosis-related proteins–caspase can also degrade autophagy-related proteins, such as Atg3, Atg4, Beclin1 protein, inhibiting autophagy. Although the relationship between autophagy and apoptosis has been known for rather complex for more than a decade, the underlying regulatory mechanisms have not been clearly understood. This short review discusses and summarizes the dual role of autophagy and the interaction and molecular regulatory mechanisms between autophagy and apoptosis under hypoxia.

Sirt1: Role Under the Condition of Ischemia/Hypoxia.

Silent information regulator factor 2-related enzyme 1 (sirtuin 1, Sirt1) is a nicotinamide adenine dinucleotide-dependent deacetylase, which can deacetylate histone and non-histone proteins and other transcription factors, and is involved in the regulation of many physiological functions, including cell senescence, gene transcription, energy balance, and oxidative stress. Ischemia/hypoxia injury remains an unresolved and complicated situation in the diseases of ischemia stroke, heart failure, and coronary heart disease, especially among the old folks. Studies have demonstrated that aging could enhance the vulnerability of brain, heart, lung, liver, and kidney to ischemia/hypoxia injury and the susceptibility in old folks to ischemia/hypoxia injury might be associated with Sirt1. In this review, we mainly summarize the role of Sirt1 in modulating pathways against energy depletion and its involvement in oxidative stress, apoptosis, and inflammation under the condition of ischemia/hypoxia.

Crosstalk of ER stress-mediated autophagy and ER-phagy: involvement of UPR and the core autophagy machinery.

Endoplasmic reticulum (ER) stress, a common cellular stress response, is closely related to the activation of autophagy that is an important and evolutionarily conserved mechanism for maintaining cellular homeostasis. Autophagy induced by ER stress mainly includes the ER stress‐mediated autophagy and ER‐phagy. The ER stress‐mediated autophagy is characterized by the generation of autophagosomes that include worn‐out proteins, protein aggregates, and damaged organelles. While the autophagosomes of ER‐phagy selectively include ER membranes, and the double membranes also derive, at least in part, from the ER. The signaling pathways of IRE1α, PERK, ATF6, and Ca2+ are necessary for the activation of ER stress‐mediated autophagy, while the receptor‐mediated selective ER‐phagy degrades the ER is Atg40/FAM134B. The ER stress‐mediated autophagy and ER‐phagy not only have differences, but also have connections. The activation of ER‐phagy requires the core autophagy machinery, and the ER‐phagy may be a branch of ER stress‐mediated autophagy that selectively targets the ER. However, the determined factors that control the changeover switch between ER stress‐mediated autophagy and ER‐phagy are largely obscure, which may be associated with the type of cells and the extent of stimulation. This review summarized the crosstalk between ER stress‐mediated autophagy and ER‐phagy and their signaling networks. Additionally, we discussed the possible factors that influence the type of autophagy induced by ER stress.