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Molecular Analysis of Endothelial-mesenchymal Transition Induced by Transforming Growth Factor-β Signaling
Published on: August 3, 2018
Mitophagy is primarily due to alternative autophagy and requires the MAPK1 and MAPK14 signaling pathways
Yuko Hirota1, Shun-ichi Yamashita, Yusuke Kurihara
1a Laboratory of Biosignaling ; Niigata University Graduate School of Medical and Dental Sciences ; Niigata , Japan.
Abstract:
In cultured cells, not many mitochondria are degraded by mitophagy induced by physiological cellular stress. We observed mitophagy in HeLa cells using a method that relies on the pH-sensitive fluorescent protein Keima. With this approach, we found that mitophagy was barely induced by carbonyl cyanide m-chlorophenyl hydrazone treatment, which is widely used as an inducer of PARK2/Parkin-related mitophagy, whereas a small but modest amount of mitochondria were degraded by mitophagy under conditions of starvation or hypoxia. Mitophagy induced by starvation or hypoxia was marginally suppressed by knockdown of ATG7 and ATG12, or MAP1LC3B, which are essential for conventional macroautophagy. In addition, mitophagy was efficiently induced in Atg5 knockout mouse embryonic fibroblasts. However, knockdown of RAB9A and RAB9B, which are essential for alternative autophagy, but not conventional macroautophagy, severely suppressed mitophagy. Finally, we found that the MAPKs MAPK1/ERK2 and MAPK14/p38 were required for mitophagy. Based on these findings, we conclude that mitophagy in mammalian cells predominantly occurs through an alternative autophagy pathway, requiring the MAPK1 and MAPK14 signaling pathways.
Insights
Mitophagy, the degradation of mitochondria, primarily uses an alternative pathway in mammalian cells, not the conventional macroautophagy. This process requires specific MAPK signaling pathways for efficient mitochondrial turnover.
Area of Science:
- Cell Biology
- Autophagy Research
- Mitochondrial Dynamics
Background:
- Mitophagy is crucial for cellular health, but the specific pathways involved in physiological stress remain unclear.
- Conventional macroautophagy and alternative autophagy pathways are known mechanisms for cellular degradation.
Purpose of the Study:
- To investigate the predominant pathway of mitophagy induced by physiological stress in mammalian cells.
- To identify the key molecular players and signaling pathways regulating mitophagy.
Main Methods:
- Utilized pH-sensitive fluorescent protein Keima in HeLa cells to monitor mitophagy.
- Employed gene knockdown techniques for ATG7, ATG12, MAP1LC3B, RAB9A, and RAB9B.
- Examined mitophagy in Atg5 knockout mouse embryonic fibroblasts.
- Assessed the role of MAPKs (MAPK1/ERK2 and MAPK14/p38) in mitophagy.
Main Results:
- Mitophagy was minimally induced by carbonyl cyanide m-chlorophenyl hydrazone but modestly induced by starvation or hypoxia.
- Knockdown of conventional macroautophagy genes had marginal effects, while knockdown of RAB9A/B severely suppressed mitophagy.
- Mitophagy was efficiently induced in Atg5 knockout cells.
- MAPK1/ERK2 and MAPK14/p38 signaling pathways were found to be essential for mitophagy.
Conclusions:
- Mammalian mitophagy predominantly occurs via an alternative autophagy pathway, distinct from conventional macroautophagy.
- The alternative mitophagy pathway critically depends on RAB9A/B and MAPK signaling (MAPK1/ERK2 and MAPK14/p38).
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