• BMB Reports
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• v.50 no.6
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• pp.299-307
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• 2017

Mitophagy is a process of selective removal of damaged or unnecessary mitochondria using autophagic machinery. Mitophagy plays an essential role in maintaining mitochondrial quality control and homeostasis. Mitochondrial dysfunctions and defective mitophagy in neurodegenerative diseases, cancer, and metabolic diseases indicate a close link between human disease and mitophagy. Furthermore, recent studies showing the involvement of mitophagy in differentiation and development, suggest that mitophagy may play a more active role in controlling cellular functions. A better understanding of mitophagy will provide insights about human disease and offer novel chance for treatment. This review mainly focuses on the recent implications for mitophagy in human diseases and normal physiology.

• Journal of Ginseng Research
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• v.46 no.2
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• pp.266-274
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• 2022

Colon cancer, the third most frequent occurred cancer, has high mortality and extremely poor prognosis. Ginsenoside, the active components of traditional Chinese herbal medicine Panax ginseng, exerts antitumor effect in various cancers, including colon cancer. However, the detailed molecular mechanism of Ginsenoside in the tumor suppression have not been fully elucidated. Here, we chose the representative ginsenoside Rg3 and reported for the first time that Rg3 induces mitophagy in human colon cancer cells, which is responsible for its anticancer effect. Rg3 treatment leads to mitochondria damage and the formation of mitophagosome; when autophagy is inhibited, the clearance of damaged mitochondria can be reversed. Next, our results showed that Rg3 treatment activates the PINK1-Parkin signaling pathway and recruits Parkin and ubiquitin proteins to mitochondria to induce mitophagy. GO analysis of Parkin targets showed that Parkin interacts with a large number of mitochondrial proteins and regulates the molecular function of mitochondria. The cellular energy metabolism enzyme GAPDH is validated as a novel substrate of Parkin, which is ubiquitinated by Parkin. Moreover, GAPDH participates in the Rg3-induced mitophagy and regulates the translocation of Parkin to mitochondria. Functionally, Rg3 exerts the inhibitory effect through regulating the nonglycolytic activity of GAPDH, which could be associated with the cellular oxidative stress. Thus, our results revealed GAPDH ubiquitination by Parkin as a crucial mechanism for mitophagy induction that contributes to the tumor-suppressive function of ginsenoside, which could be a novel treatment strategy for colon cancer.

• The Korean Journal of Physiology and Pharmacology
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• v.24 no.3
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• pp.223-232
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• 2020

Sesamin, a lipid-soluble lignin originally isolated from sesame seeds, which induces cancer cell apoptosis and autophagy. In the present study, has been reported that sesamin induces apoptosis via several pathways in human lung cancer cells. However, whether mitophagy is involved in sesamin induced lung cancer cell apotosis remains unclear. This study, the anticancer activity of sesamin in lung cancer was studied by reactive oxygen species (ROS) and mitophagy. A549 cells were treated with sesamin, and cell viability, migration ability, and cell cycle were assessed using the CCK8 assay, scratch-wound test, and flow cytometry, respectively. ROS levels, mitochondrial membrane potential, and apoptosis were examined by flow cytometric detection of DCFH-DA fluorescence and by using JC-1 and TUNEL assays. The results indicated that sesamin treatment inhibited the cell viability and migration ability of A549 cells and induced G₀/G₁ phase arrest. Furthermore, sesamin induced an increase in ROS levels, a reduction in mitochondrial membrane potential, and apoptosis accompanied by an increase in cleaved caspase-3 and cleaved caspase-9. Additionally, sesamin triggered mitophagy and increased the expression of PINK1 and translocation of Parkin from the cytoplasm to the mitochondria. However, the antioxidant N-acetyl-L-cysteine clearly reduced the oxidative stress and mitophagy induced by sesamin. Furthermore, we found that cyclosporine A (an inhibitor of mitophagy) decreased the inhibitory effect of sesamin on A549 cell viability. Collectively, our data indicate that sesamin exerts lethal effects on lung cancer cells through the induction of ROS-mediated mitophagy and mitochondrial apoptosis.

• Molecules and Cells
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• v.40 no.7
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• pp.503-514
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• 2017

Nicotinamide (NAM) plays essential roles in physiology through facilitating $NAD^+$ redox homeostasis. Importantly, at high doses, it protects cells under oxidative stresses, and has shown therapeutic effectiveness in a variety of disease conditions. In our previous studies, NAM lowered reactive oxygen species (ROS) levels and extended cellular life span in primary human cells. In the treated cells, levels of $NAD^+/NADH$ and SIRT1 activity increased, while mitochondrial content decreased through autophagy activation. The remaining mitochondria were marked with low superoxide levels and high membrane potentials (${\Delta}_{{\Psi}m}$); we posited that the treatment of NAM induced an activation of mitophagy that is selective for depolarized mitochondria, which produce high levels of ROS. However, evidence for the selective mitophagy that is mediated by SIRT1 has never been provided. This study sought to explain the mechanisms by which NAM lowers ROS levels and increases ${\Delta}_{{\Psi}m}$. Our results showed that NAM and SIRT1 activation exert quite different effects on mitochondrial physiology. Furthermore, the changes in ROS and ${\Delta}_{{\Psi}m}$ were not found to be mediated through autophagy or SIRT activation. Rather, NAM suppressed superoxide generation via a direct reduction of electron transport, and increased ${\Delta}_{{\Psi}m}$ via suppression of mitochondrial permeability transition pore formation. Our results dissected the effects of cellular $NAD^+$ redox modulation, and emphasized the importance of the $NAD^+/NADH$ ratio in the mitochondria as well as the cytosol in maintaining mitochondrial quality.

• Molecules and Cells
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• v.39 no.2
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• pp.87-95
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• 2016

Sirt1 is the most prominent and extensively studied member of sirtuins, the family of mammalian class III histone deacetylases heavily implicated in health span and longevity. Although primarily a nuclear protein, Sirt1's deacetylation of Peroxisome proliferator-activated receptor Gamma Coactivator-$1{\alpha}$ (PGC-$1{\alpha}$) has been extensively implicated in metabolic control and mitochondrial biogenesis, which was proposed to partially underlie Sirt1's role in caloric restriction and impacts on longevity. The notion of Sirt1's regulation of PGC-$1{\alpha}$ activity and its role in mitochondrial biogenesis has, however, been controversial. Interestingly, Sirt1 also appears to be important for the turnover of defective mitochondria by mitophagy. I discuss here evidences for Sirt1's regulation of mitochondrial biogenesis and turnover, in relation to PGC-$1{\alpha}$ deacetylation and various aspects of cellular physiology and disease.

• Herbal Formula Science
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• v.28 no.1
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• pp.15-27
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• 2020

Objectives : We selected three herb-combined remedies, Bigihwan (BGH), Daechilgitang (DCGT) and Mokwhyangbinranghwan (MHBRH), through Donguibogam text-mining analysis, and evaluated their anti-cancer effects on human hepatocellular carcinoma Hep3B cells. Methods : Cytotoxicity was assessed by an MTT assay. Apoptosis rate, autophagy and ROS level were detected by flow cytometry. The autophagy was also observed by Cyto-ID staining fluorescence microscopy. The expression of autophagy, mitophagy and pexophagy regulatory proteins was detected by Western blot analysis. Results : BGH showed the strongest effect among the three prescriptions in inhibiting Hep3B cell viability, which was associated with the induction of apoptosis and autophagy. Autophagy blockers improved cell viability and reduced apoptosis after BGH and DCGT treatments, indicating that autophagy by these prescriptions enhanced Hep3B cells against their cytotoxicity. However, MHBRH enhanced the reduction of cell viability and apoptosis by autophagy blockers. Induction of autophagy by BGH treatment was associated with mitophagy due to mitochondrial dysfunction than DCGT and MHBRH-treated cells. In addition, induction of apoptosis by BGH treatment was ROS-dependent and showed the possibility of pexophagy involvement. Conclusion : Although further studies need to be conducted to study the efficacy and mechanism of accurate anticancer activity, the present results will serve as important sources of understanding the mechanism of action of herbal remedies prescribed for liver disease as documented in Donguibogam.

• Molecules and Cells
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• v.46 no.11
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• pp.655-663
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• 2023

Autophagy dysfunction is associated with human diseases and conditions including neurodegenerative diseases, metabolic issues, and chronic infections. Additionally, the decline in autophagic activity contributes to tissue and organ dysfunction and aging-related diseases. Several factors, such as down-regulation of autophagy components and activators, oxidative damage, microinflammation, and impaired autophagy flux, are linked to autophagy decline. An autophagy flux impairment (AFI) has been implicated in neurological disorders and in certain other pathological conditions. Here, to enhance our understanding of AFI, we conducted a comprehensive literature review of findings derived from two well-studied cellular stress models: glucose deprivation and replicative senescence. Glucose deprivation is a condition in which cells heavily rely on oxidative phosphorylation for ATP generation. Autophagy is activated, but its flux is hindered at the autolysis step, primarily due to an impairment of lysosomal acidity. Cells undergoing replicative senescence also experience AFI, which is also known to be caused by lysosomal acidity failure. Both glucose deprivation and replicative senescence elevate levels of reactive oxygen species (ROS), affecting lysosomal acidification. Mitochondrial alterations play a crucial role in elevating ROS generation and reducing lysosomal acidity, highlighting their association with autophagy dysfunction and disease conditions. This paper delves into the underlying molecular and cellular pathways of AFI in glucose-deprived cells, providing insights into potential strategies for managing AFI that is driven by lysosomal acidity failure. Furthermore, the investigation on the roles of mitochondrial dysfunction sheds light on the potential effectiveness of modulating mitochondrial function to overcome AFI, offering new possibilities for therapeutic interventions.

• Journal of Life Science
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• v.30 no.5
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• pp.460-467
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• 2020

Hepatocellular carcinoma (HCC) is one of the most commonly diagnosed cancers in the word. Although radiation and chemotherapy are generally effective, there are various side effects that greatly limit the effectiveness of these treatments. Therefore, traditional herbs may have potential as important resources for the discovery of liver cancer therapeutics. In this study, we selected three Korean herbal medicine formulas from the Donguibogam, namely Bigihwan (BGH), Daechilgithang (DCGT), and Mokwhyangbinranghwan (MHBRH), and evaluated their anti-cancer effects on HCC cells. According to our results of three ethanol extracts, BGH was more effective at suppressing HCC growth than DCGT or MHBRH. Furthermore, flow cytometry analysis showed that inhibition of HCC proliferation by the three extracts was associated with the induction of apoptosis and autophagy. In particular, BGH significantly increased mitochondrial impairment and showed the possibility of inducing mitophagy in comparison with the other two extracts. BGH prominently upregulated the levels of microtubule-associated protein light chain-3 which was accompanied by a decrease in the expression of anti-apoptotic Bcl-2 without altering the expression of pro-apoptotic Bax. In addition, the levels of PTEN-induced kinase 1 were also markedly increased in BGH-treated HCC cells. Moreover, autophagy blocking improved cell viability and reduced apoptosis after the three treatments, indicating that autophagy by these extracts enhances HCC cells against cytotoxicity. In conclusion, our findings show that BGH demonstrates the highest anti-cancer activity among the three formulas and inhibits the proliferation of HCC cells through autophagy induction.

• Biomolecules & Therapeutics
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• v.27 no.6
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• pp.530-539
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• 2019

Brain aging is an inevitable process characterized by structural and functional changes and is a major risk factor for neurodegenerative diseases. Most brain aging studies are focused on neurons and less on astrocytes which are the most abundant cells in the brain known to be in charge of various functions including the maintenance of brain physical formation, ion homeostasis, and secretion of various extracellular matrix proteins. Altered mitochondrial dynamics, defective mitophagy or mitochondrial damages are causative factors of mitochondrial dysfunction, which is linked to age-related disorders. Etoposide is an anti-cancer reagent which can induce DNA stress and cellular senescence of cancer cell lines. In this study, we investigated whether etoposide induces senescence and functional alterations in cultured rat astrocytes. Senescence-associated ${\beta}$-galactosidase (SA-${\beta}$-gal) activity was used as a cellular senescence marker. The results indicated that etoposide-treated astrocytes showed cellular senescence phenotypes including increased SA-${\beta}$-gal-positive cells number, increased nuclear size and increased senescence-associated secretory phenotypes (SASP) such as IL-6. We also observed a decreased expression of cell cycle markers, including PhosphoHistone H3/Histone H3 and CDK2, and dysregulation of cellular functions based on wound-healing, neuronal protection, and phagocytosis assays. Finally, mitochondrial dysfunction was noted through the determination of mitochondrial membrane potential using tetramethylrhodamine methyl ester (TMRM) and the measurement of mitochondrial oxygen consumption rate (OCR). These data suggest that etoposide can induce cellular senescence and mitochondrial dysfunction in astrocytes which may have implications in brain aging and neurodegenerative conditions.

• BMB Reports
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• v.56 no.12
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• pp.663-668
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• 2023

C-reactive protein (CRP) is an inflammatory marker and risk factor for atherosclerosis and cardiovascular diseases. However, the mechanism through which CRP induces myocardial damage remains unclear. This study aimed to determine how CRP damages cardiomyocytes via the change of mitochondrial dynamics and whether survivin, an anti-apoptotic protein, exerts a cardioprotective effect in this process. We treated H9c2 cardiomyocytes with CRP and found increased intracellular ROS production and shortened mitochondrial length. CRP treatment phosphorylated ERK1/2 and promoted increased expression, phosphorylation, and translocation of DRP1, a mitochondrial fission-related protein, from the cytoplasm to the mitochondria. The expression of mitophagy proteins PINK1 and PARK2 was also increased by CRP. YAP, a transcriptional regulator of PINK1 and PARK2, was also increased by CRP. Knockdown of YAP prevented CRP-induced increases in DRP1, PINK1, and PARK2. Furthermore, CRP-induced changes in the expression of DRP1 and increases in YAP, PINK1, and PARK2 were inhibited by ERK1/2 inhibition, suggesting that ERK1/2 signaling is involved in CRP-induced mitochondrial fission. We treated H9c2 cardiomyocytes with a recombinant TAT-survivin protein before CRP treatment, which reduced CRP-induced ROS accumulation and reduced mitochondrial fission. CRP-induced activation of ERK1/2 and increases in the expression and activity of YAP and its downstream mitochondrial proteins were inhibited by TAT-survivin. This study shows that mitochondrial fission occurs during CRP-induced cardiomyocyte damage and that the ERK1/2-YAP axis is involved in this process, and identifies that survivin alters these mechanisms to prevent CRP-induced mitochondrial damage.