Extracellular pH regulates autophagy via the AMPK–ULK1 pathway in rat cardiomyocytes

Zhao, Liping; Cui, Lin; Jiang, Xupin; Zhang, Junhui; Zhu, Minghua; Jia, Jiezhi; Zhang, Qiong; Zhang, Jiaping; Zhang, Dongxia; Huang, Yuesheng

doi:10.1002/1873-3468.12359

Cited by 18 publications

(12 citation statements)

References 48 publications

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“…In the present study, there was a trend for a decrease in p-AMPK relative abundance in the low pH condition (p = 0.098). Consistent with our study, Zhao et al (42) observed that an acidic pH decreased p-AMPK relative abundance, whilst an alkaline pH increased p-AMPK relative abundance in cultured cardiomyocytes (42). Another study in cultured fibroblasts also found that an acidic or low pH decreased p-AMPK relative abundance (3).…”

Section: Discussionsupporting

confidence: 91%

“…In this study we examined the response of genes and proteins known to have a role in mitochondrial biogenesis to physiologically-relevant changes in pH and lactate (12), which did not negatively affect cell viability. While greater, non-physiological changes may have produced different results, greater changes have also been reported to negatively affect cell viability (42). By changing the media pH we were able to also alter the intracellular pH (Figure 1).…”

Section: Discussionmentioning

confidence: 90%

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A physiological drop in pH decreases mitochondrial respiration, and HDAC and Akt signaling, in L6 myocytes

Genders

Martin

McGee

et al. 2019

American Journal of Physiology-Cell Physiology

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Exercise stimulates mitochondrial biogenesis and increases mitochondrial respiratory function and content. However, during high-intensity exercise muscle pH can decrease below pH 6.8 with a concomitant increase in lactate concentration. This drop in muscle pH is associated with reduced exercise-induced mitochondrial biogenesis, while increased lactate may act as a signaling molecule to affect mitochondrial biogenesis. Therefore, in this study we wished to determine the impact of altering pH and lactate concentration in L6 myotubes on genes and proteins known to be involved in mitochondrial biogenesis. We also examined mitochondrial respiration in response to these perturbations. Differentiated L6 myotubes were exposed to normal (pH 7.5)-, low (pH 7.0)-, or high (pH 8.0)-pH media with and without 20 mM sodium l-lactate for 1 and 6 h. Low pH and 20 mM sodium l-lactate resulted in decreased Akt (Ser473) and AMPK (T172) phosphorylation at 1 h compared with controls, while at 6 h the nuclear localization of histone deacetylase 5 (HDAC5) was decreased. When the pH was increased both Akt (Ser473) and AMPK (T172) phosphorylation was increased at 1 h. Overall increased lactate decreased the nuclear content of HDAC5 at 6 h. Exposure to both high- and low-pH media decreased basal mitochondrial respiration, ATP turnover, and maximum mitochondrial respiratory capacity. These data indicate that muscle pH affects several metabolic signaling pathways, including those required for mitochondrial function.

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Section: Discussionsupporting

confidence: 91%

Section: Discussionmentioning

confidence: 90%

A physiological drop in pH decreases mitochondrial respiration, and HDAC and Akt signaling, in L6 myocytes

Genders

Martin

McGee

et al. 2019

American Journal of Physiology-Cell Physiology

View full text Add to dashboard Cite

show abstract

“…In the present study, there was a decrease in p-AMPK relative abundance in the low pH with lactate condition, as well as a trend towards increased phosphorylation with a higher pH. Consistent with our study, Zhao et al [31] observed that an acidic pH decreased p-AMPK relative abundance, whilst an alkaline pH increased p-AMPK relative abundance in cultured cardiomyocytes [31]. Another study in cultured fibroblasts also found that an acidic or low pH decreased p-AMPK relative abundance [33].…”

Section: Discussionsupporting

confidence: 93%

“…In this study we examined the response of genes and proteins known to have a role in mitochondrial biogenesis to physiologically-relevant changes in pH and lactate [14], which did not negatively affect cell viability. While greater, non-physiological changes may have produced different results, greater changes have also been reported to negatively affect cell viability [31]. By changing the media pH we were able to also alter the intracellular pH ( Figure 1).…”

Section: Discussionmentioning

confidence: 90%

A physiological drop in pH decreases mitochondrial respiration, and AMPK and Akt signalling, in L6 myocytes

Genders

Martin

McGee

et al. 2018

Preprint

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Exercise stimulates mitochondrial biogenesis and increases mitochondrial respiratory function and content. However, during high-intensity exercise muscle pH can decrease below pH 6.8 with a concomitant increase in lactate concentration. This drop in muscle pH is associated with reduced exercise-induced mitochondrial biogenesis, whilst increased lactate may act as a signaling molecule to affect mitochondrial biogenesis. Therefore, in this study we wished to determine the impact of altering pH and lactate concentration in L6 myotubes on genes and proteins known to be involved in mitochondrial biogenesis. We also examined mitochondrial respiration in response to these perturbations. Differentiated L6 myotubes were exposed to normal (pH 7.5), low (pH 7.0) or high pH (pH 8.0) media with and without 20 mM sodium L-lactate for 1 and 6 h. Low pH and 20 mM Sodium L-Lactate resulted in decreased Akt (Ser473) and AMPK (T172) phosphorylation at 1 h compared to controls, whilst at 6 h the nuclear localisation of HDAC5 was decreased. When the pH was increased both Akt (Ser473) and AMPK (T172) phosphorylation was increased at 1 h. Overall increased lactate decreased the nuclear content of HDAC5 at 6 h. Exposure to both high and low pH media significantly decreased basal mitochondrial respiration, ATP turnover, and maximum mitochondrial respiratory capacity. These data indicate that muscle pH affects several metabolic signalling pathways, including those required for mitochondrial function.

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“…33 Subsequently, AMPK is activated and phosphorylates ULK1 (ATG1) and mTORC1. 34 mTORC1 is an inhibitor of autophagy, and its phosphorylation by AMPK removes the inhibitory effect on autophagosome formation. Alternatively, we showed previously that sustained HG concentrations activate HIF-1 α activity in rMC1 cells.…”

Section: Discussionmentioning

confidence: 99%

TXNIP regulates mitophagy in retinal Müller cells under high-glucose conditions: implications for diabetic retinopathy

et al. 2017

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Thioredoxin-interacting protein (TXNIP) is involved in oxidative stress and apoptosis in diabetic retinopathy. However, the role of TXNIP in the removal of damaged mitochondria (MT) via mitophagy, a process of macroautophagy, remains unexplored. Here we investigate the associated cellular and molecular mechanisms underlying mitophagy in retinal cells under diabetic conditions. For this, we maintained a rat Müller cell line (rMC1) under high-glucose (25 mM, HG) or low-glucose (5.5 mM, LG) condition for 5 days. Our data reveal that HG upregulates TXNIP in the cytosol as well as in the MT. Moreover, mitochondrial oxidative stress and membrane depolarization occur under prolonged hyperglycemia leading to fragmentation. These damaged MT are targeted to lysosome for mitophagic degradation, as is evident by co-localization of mitochondrial protein COXIV, a subunit of cytochrome c oxidase, with autophagosome marker LC3BII and the lysosomal membrane protein LAMP2A. In addition, under HG conditions, there is an accumulation of dynamin-related fission protein Drp1 and E3 ubiquitin ligase Parkin in damaged MT, suggesting their roles in mitochondrial fragmentation and ubiquitination, respectively, which is absent in LG conditions. Subsequently, ubiquitin receptors, optineurin and p62/sequestrome 1, bind to the damaged MT and target them to LC3BII autophagosomes. Conversely, TXNIP knockout via CRISPR/Cas9 and TXNIP gRNA prevents the HG-induced mitochondrial damage and mitophagy in rMC1. Last, TXNIP level is also significantly upregulated in the diabetic rat retina in vivo and induces radial glial fibrillary acidic protein expression, a marker for Müller glia activation, and the formation of LC3BII puncta, which are prevented by intravitreal injection of TXNIP siRNA. Therefore, TXNIP represents a potential target for preventing ocular complications of diabetes.

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Extracellular pH regulates autophagy via the AMPK–ULK1 pathway in rat cardiomyocytes

Cited by 18 publications

References 48 publications

A physiological drop in pH decreases mitochondrial respiration, and HDAC and Akt signaling, in L6 myocytes

A physiological drop in pH decreases mitochondrial respiration, and HDAC and Akt signaling, in L6 myocytes

A physiological drop in pH decreases mitochondrial respiration, and AMPK and Akt signalling, in L6 myocytes

TXNIP regulates mitophagy in retinal Müller cells under high-glucose conditions: implications for diabetic retinopathy

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