All cellular membranes have the functionality of generating and maintaining the gradients of electrical and electrochemical potentials. Such potentials were generally thought to be an essential but ...homeostatic contributor to complex bacterial behaviors. Recent studies have revised this view, and we now know that bacterial membrane potential is dynamic and plays signaling roles in cell–cell interaction, adaptation to antibiotics, and sensation of cellular conditions and environments. These discoveries argue that bacterial membrane potential dynamics deserve more attention. Here, we review the recent studies revealing the signaling roles of bacterial membrane potential dynamics. We also introduce basic biophysical theories of the membrane potential to the microbiology community and discuss the needs to revise these theories for applications in bacterial electrophysiology.
Bacterial membrane potential is dynamic, with the ability to hyperpolarize and depolarize.The dynamics of bacterial membrane potential mediate signaling at the single-cell and biofilm levels.Bacterial electrophysiology is different from neural electrophysiology because of the size of bacteria and their membrane structure.Techniques have been developed and utilized to measure bacterial membrane potential quantitatively and temporally.
Mitochondria are essential regulators of cellular energy and metabolism, and have a crucial role in sustaining the growth and survival of cancer cells. A central function of mitochondria is the ...synthesis of ATP by oxidative phosphorylation, known as mitochondrial bioenergetics. Mitochondria maintain oxidative phosphorylation by creating a membrane potential gradient that is generated by the electron transport chain to drive the synthesis of ATP
. Mitochondria are essential for tumour initiation and maintaining tumour cell growth in cell culture and xenografts
. However, our understanding of oxidative mitochondrial metabolism in cancer is limited because most studies have been performed in vitro in cell culture models. This highlights a need for in vivo studies to better understand how oxidative metabolism supports tumour growth. Here we measure mitochondrial membrane potential in non-small-cell lung cancer in vivo using a voltage-sensitive, positron emission tomography (PET) radiotracer known as 4-
Ffluorobenzyl-triphenylphosphonium (
F-BnTP)
. By using PET imaging of
F-BnTP, we profile mitochondrial membrane potential in autochthonous mouse models of lung cancer, and find distinct functional mitochondrial heterogeneity within subtypes of lung tumours. The use of
F-BnTP PET imaging enabled us to functionally profile mitochondrial membrane potential in live tumours.
Mitochondrial membrane potential (ΔΨ
) is a universal selective indicator of mitochondrial function and is known to play a central role in many human pathologies, such as diabetes mellitus, cancer ...and Alzheimer's and Parkinson's diseases. Here, we report the design, synthesis and several applications of mitochondria-activatable luciferin (MAL), a bioluminescent probe sensitive to ΔΨ
, and partially to plasma membrane potential (ΔΨ
), for non-invasive, longitudinal monitoring of ΔΨ
in vitro and in vivo. We applied this new technology to evaluate the aging-related change of ΔΨ
in mice and showed that nicotinamide riboside (NR) reverts aging-related mitochondrial depolarization, revealing another important aspect of the mechanism of action of this potent biomolecule. In addition, we demonstrated application of the MAL probe for studies of brown adipose tissue (BAT) activation and non-invasive in vivo assessment of ΔΨ
in animal cancer models, opening exciting opportunities for understanding the underlying mechanisms and for discovery of effective treatments for many human pathologies.
Mitochondrial function, a key indicator of cell health, can be assessed by monitoring changes in mitochondrial membrane potential (MMP). Cationic fluorescent dyes are commonly used tools to assess ...MMP. We used a water-soluble mitochondrial membrane potential indicator (m-MPI) to detect changes in MMP in HepG2 cells. A homogenous cell-based MMP assay was optimized and performed in a 1536-well plate format to screen several compound libraries for mitochondrial toxicity by evaluating the effects of chemical compounds on MMP.
Biological effects of high fluence low-power (HFLP) lasers have been reported for some time, yet the molecular mechanisms procuring cellular responses remain obscure. A better understanding of the ...effects of HFLP lasers on living cells will be instrumental for the development of new experimental and therapeutic strategies. Therefore, we investigated sub-cellular mechanisms involved in the laser interaction with human hepatic cell lines. We show that mitochondria serve as sub-cellular “sensor” and “effector” of laser light non-specific interactions with cells. We demonstrated that despite blue and red laser irradiation results in similar apoptotic death, cellular signaling and kinetic of biochemical responses are distinct. Based on our data, we concluded that blue laser irradiation inhibited cytochrome c oxidase activity in electron transport chain of mitochondria. Contrary, red laser triggered cytochrome c oxidase excessive activation. Moreover, we showed that Bcl-2 protein inhibited laser-induced toxicity by stabilizing mitochondria membrane potential. Thus, cells that either overexpress or have elevated levels of Bcl-2 are protected from laser-induced cytotoxicity. Our findings reveal the mechanism how HFLP laser irradiation interfere with cell homeostasis and underscore that such laser irradiation permits remote control of mitochondrial function in the absence of chemical or biological agents.
We show that regenerating planarians’ normal anterior-posterior pattern can be permanently rewritten by a brief perturbation of endogenous bioelectrical networks. Temporary modulation of regenerative ...bioelectric dynamics in amputated trunk fragments of planaria stochastically results in a constant ratio of regenerates with two heads to regenerates with normal morphology. Remarkably, this is shown to be due not to partial penetrance of treatment, but a profound yet hidden alteration to the animals’ patterning circuitry. Subsequent amputations of the morphologically normal regenerates in water result in the same ratio of double-headed to normal morphology, revealing a cryptic phenotype that is not apparent unless the animals are cut. These animals do not differ from wild-type worms in histology, expression of key polarity genes, or neoblast distribution. Instead, the altered regenerative bodyplan is stored in seemingly normal planaria via global patterns of cellular resting potential. This gradient is functionally instructive, and represents a multistable, epigenetic anatomical switch: experimental reversals of bioelectric state reset subsequent regenerative morphology back to wild-type. Hence, bioelectric properties can stably override genome-default target morphology, and provide a tractable control point for investigating cryptic phenotypes and the stochasticity of large-scale epigenetic controls.
Reduction of mitochondrial membrane potential (Δψm) is a hallmark of mitochondrial dysfunction. It activates adaptive responses in organisms from yeast to human to rewire metabolism, remove ...depolarized mitochondria, and degrade unimported precursor proteins. It remains unclear how cells maintain Δψm, which is critical for maintaining iron‐sulfur cluster (ISC) synthesis, an indispensable function of mitochondria. Here, we show that yeast oxidative phosphorylation mutants deficient in complex III, IV, V, and mtDNA, respectively, exhibit activated stress responses and progressive reduction of Δψm. Extensive omics analyses of these mutants show that these mutants progressively activate adaptive responses, including transcriptional downregulation of ATP synthase inhibitor Inh1 and OXPHOS subunits, Puf3‐mediated upregulation of import receptor Mia40 and global mitochondrial biogenesis, Snf1/AMPK‐mediated upregulation of glycolysis and repression of ribosome biogenesis, and transcriptional upregulation of cytoplasmic chaperones. These adaptations disinhibit mitochondrial ATP hydrolysis, remodel mitochondrial proteome, and optimize ATP supply to mitochondria to convergently maintain Δψm, ISC biosynthesis, and cell proliferation.
Synopsis
Oxidative phosphorylation deficiency causes mitochondrial membrane potential (Δψm) reduction and activates transcriptional and post‐transcriptional adaptions to maintain Δψm.
OXPHOS deficient mitochondria hydrolyze ATP to maintain Δψm.
OXPHOS deficiency represses Inh1 transcription to enhance mitochondrial ATP hydrolysis.
OXPHOS deficiency optimizes ATP metabolism by Snf1‐mediated enhancement of glycolysis and repression of ribosome biogenesis.
OXPHOS deficiency hyper‐phosphorylates Puf3 to promote mitochondrial biogenesis.
Oxidative phosphorylation deficiency causes mitochondrial membrane potential (Δψm) reduction and activates transcriptional and post‐transcriptional adaptions to maintain Δψm.
Membrane potential is a fundamental property of biological cells. Changes in membrane potential characterize a vast number of vital biological processes, such as the activity of neurons and ...cardiomyocytes, tumorogenesis, cell-cycle progression, etc. A common strategy to record membrane potential changes that occur in the process of interest is to utilize organic dyes or genetically-encoded voltage indicators with voltage-dependent fluorescence. Sensors are introduced into target cells, and alterations of fluorescence intensity are recorded with optical methods. Techniques that allow recording relative changes of membrane potential and do not take into account fluorescence alterations due to factors other than membrane voltage are already widely used in modern biological and biomedical studies. Such techniques have been reviewed previously in many works. However, in order to investigate a number of processes, especially long-term processes, the measured signal must be corrected to exclude the contribution from voltage-independent factors or even absolute values of cell membrane potential have to be evaluated. Techniques that enable such measurements are the subject of this review.
SIRT1, an NAD-dependent deacetylase, plays a role in regulation of autophagy. SIRT1 increases mitochondrial function and reduces oxidative stress, and has been linked to age-related reactive oxygen ...species (ROS) generation, which is highly dependent on mitochondrial metabolism. H2O2 induces oxidative stress and autophagic cell death through interference with Beclin 1 and the mTOR signaling pathways. We evaluated connections between SIRT1 activity and induction of autophagy in murine (m) and human (h) embryonic stem cells (ESCs) upon ROS challenge. Exogenous H2 O2 (1 mM) induced apoptosis and autophagy in wild-type (WT) and Sirt1-/- mESCs. High concentrations of H2O2 (1 mM) induced more apoptosis in Sirt1-/-, than in WT mESCs. However, addition of 3-methyladenine, a widely used autophagy inhibitor, in combination with H2O2 induced more cell death in WT than in Sirt1-/- mESCs. Decreased induction of autophagy in Sirt1-/- mESCs was demonstrated by decreased conversion of LC3-I to LC3-II, lowered expression of Beclin-1, and decreased LC3 punctae and LysoTracker staining. H2O2 induced autophagy with loss of mitochondrial membrane potential and disruption of mitochondrial dynamics in Sirt1-/- mESCs. Increased phosphorylation of P70/85-S6 kinase and ribosomal S6 was noted in Sirt1-/- mESCs, suggesting that SIRT1 regulates the mTOR pathway. Consistent with effects in mESCs, inhibition of SIRT1 using Lentivirus-mediated SIRT1 shRNA in hESCs demonstrated that knockdown of SIRT1 decreased H2O2-induced autophagy. This suggests a role for SIRT1 in regulating autophagy and mitochondria function in ESCs upon oxidative stress, effects mediated at least in part by the class III PI3K/Beclin 1 and mTOR pathways.
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