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Upregulated autophagy protects cardiomyocytes from oxidative stress-induced toxicity.

ABSTRACT: Autophagy is a cellular self-digestion process that mediates protein quality control and serves to protect against neurodegenerative disorders, infections, inflammatory diseases and cancer. Current evidence suggests that autophagy can selectively remove damaged organelles such as the mitochondria. Mitochondria-induced oxidative stress has been shown to play a major role in a wide range of pathologies in several organs, including the heart. Few studies have investigated whether enhanced autophagy can offer protection against mitochondrially-generated oxidative stress. We induced mitochondrial stress in cardiomyocytes using antimycin A (AMA), which increased mitochondrial superoxide generation, decreased mitochondrial membrane potential and depressed cellular respiration. In addition, AMA augmented nuclear DNA oxidation and cell death in cardiomyocytes. Interestingly, although oxidative stress has been proposed to induce autophagy, treatment with AMA did not result in stimulation of autophagy or mitophagy in cardiomyocytes. Our results showed that the MTOR inhibitor rapamycin induced autophagy, promoted mitochondrial clearance and protected cardiomyocytes from the cytotoxic effects of AMA, as assessed by apoptotic marker activation and viability assays in both mouse atrial HL-1 cardiomyocytes and human ventricular AC16 cells. Importantly, rapamycin improved mitochondrial function, as determined by cellular respiration, mitochondrial membrane potential and morphology analysis. Furthermore, autophagy induction by rapamycin suppressed the accumulation of ubiquitinylated proteins induced by AMA. Inhibition of rapamycin-induced autophagy by pharmacological or genetic interventions attenuated the cytoprotective effects of rapamycin against AMA. We propose that rapamycin offers cytoprotection against oxidative stress by a combined approach of removing dysfunctional mitochondria as well as by degrading damaged, ubiquitinated proteins. We conclude that autophagy induction by rapamycin could be utilized as a potential therapeutic strategy against oxidative stress-mediated damage in cardiomyocytes.

SUBMITTER: Dutta D

PROVIDER: S-EPMC3590254 | biostudies-other | 2013 Mar

REPOSITORIES: biostudies-other

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Upregulated autophagy protects cardiomyocytes from oxidative stress-induced toxicity.

Dutta Debapriya D Xu Jinze J Kim Jae-Sung JS Dunn William A WA Leeuwenburgh Christiaan C

Autophagy 20130108 3

Autophagy is a cellular self-digestion process that mediates protein quality control and serves to protect against neurodegenerative disorders, infections, inflammatory diseases and cancer. Current evidence suggests that autophagy can selectively remove damaged organelles such as the mitochondria. Mitochondria-induced oxidative stress has been shown to play a major role in a wide range of pathologies in several organs, including the heart. Few studies have investigated whether enhanced autophagy ...[more]

PMID: 23298947

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Project description:Diastolic heart failure (HF) i.e., "HF with preserved ejection fraction" (HF-preserved EF) accounts for up to 50% of all HF presentations; however there have been no therapeutic advances. This stems in part from an incomplete understanding about HF-preserved EF. Hypertension is the major cause of HF-preserved EF whilst HF-preserved EF is also highly associated with obesity. Similarly, excessive reactive oxygen species (ROS), i.e., oxidative stress occurs in hypertension and obesity, sensitizing the heart to the renin-angiotensin-aldosterone system, inducing autophagic type-II programmed cell death and accelerating the propensity to adverse cardiac remodeling, diastolic dysfunction and HF. Adiponectin (APN), an adipokine, mediates cardioprotective actions but it is unknown if APN modulates cardiomyocyte autophagy. We tested the hypothesis that APN ameliorates oxidative stress-induced autophagy in cardiomyocytes. Isolated adult rat ventricular myocytes were pretreated with recombinant APN (30 µg/mL) followed by 1mM hydrogen peroxide (H2O2) exposure. Wild type (WT) and APN-deficient (APN-KO) mice were infused with angiotensin (Ang)-II (3.2 mg/kg/d) for 14 days to induced oxidative stress. Autophagy-related proteins, mTOR, AMPK and ERK expression were measured. H2O2 induced LC3I to LC3II conversion by a factor of 3.4±1.0 which was abrogated by pre-treatment with APN by 44.5±10%. However, neither H2O2 nor APN affected ATG5, ATG7, or Beclin-1 expression. H2O2 increased phospho-AMPK by 49±6.0%, whilst pretreatment with APN decreased phospho-AMPK by 26±4%. H2O2 decreased phospho-mTOR by 36±13%, which was restored by APN. ERK inhibition demonstrated that the ERK-mTOR pathway is involved in H2O2-induced autophagy. Chronic Ang-II infusion significantly increased myocardial LC3II/I protein expression ratio in APN-KO vs. WT mice. These data suggest that excessive ROS caused cardiomyocyte autophagy which was ameliorated by APN by inhibiting an H2O2-induced AMPK/mTOR/ERK-dependent mechanism. These findings demonstrate the anti-oxidant potential of APN in oxidative stress-associated cardiovascular diseases, such as hypertension-induced HF-preserved EF.

Project description:Skin cells are vulnerable to oxidative stress-induced senescence, which may lead to abnormal aging or aging-related disorders. Therefore, strategies that can ameliorate oxidative stress-induced senescence are expected to protect skin from damage, holding the promise of treating skin diseases in the clinic. This study aims to investigate whether caffeine, a well-known purine alkaloid, is able to prevent skin from oxidative stress-induced senescence, and to explore the underlying molecular mechanisms. Methods: A free radical inducer 2,2'-Azobis (2-amidinopropane) dihydrochloride (AAPH) was used to induce oxidative stress and cellular senescence in both transformed skin cells and in normal human epidermal keratinocytes (NHEKs). Ultraviolet (UV) irradiation was established as the in vivo oxidative stress model in mouse skin tissues. Cellular senescence was determined by SA β-galactosidase staining, immunofluorescence and western blotting. Activation of autophagy was confirmed by western blotting, immunofluorescence, and transmission electron microscopy. Reactive oxygen species (ROS) detection by commercial kits, gene knockdown by RNA interference (RNAi) and receptor activation/inactivation by agonist/antagonist treatment were applied in mechanistic experiments. Results: We report that AAPH induced senescence in both transformed skin cells and in NHEKs. Similarly, UV irradiation induced senescence in mouse skin tissues. Remarkably, low dose of caffeine (<10 μM) suppressed cellular senescence and skin damage induced by AAPH or UV. Mechanistically, caffeine facilitated the elimination of ROS by activating autophagy. Using a combination of RNAi and chemical treatment, we demonstrate that caffeine activates autophagy through a series of sequential events, starting from the inhibition of its primary cellular target adenosine A2a receptor (A2AR) to an increase in the protein level of Sirtuin 3 (SIRT3) and to the activation of 5' adenosine monophosphate-activated protein kinase (AMPK). Oral administration of caffeine increased the protein level of SIRT3, induced autophagy, and reduced senescence and tissue damage in UV-irradiated mouse skin. On the other hand, co-administration with autophagy inhibitors attenuated the protective effect of caffeine on UV-induced skin damage in mice. Conclusion: The results reveal that caffeine protects skin from oxidative stress-induced senescence through activating the A2AR/SIRT3/AMPK-mediated autophagy. Our study not only demonstrated the beneficial effect of caffeine using both in vitro and in vivo models, but also systematically investigated the underlying molecular mechanisms. These discoveries implicate the potential of caffeine in the protection of skin disease.

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Upregulated autophagy protects cardiomyocytes from oxidative stress-induced toxicity.

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Upregulated autophagy protects cardiomyocytes from oxidative stress-induced toxicity.

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