KUS121, a VCP modulator, has an ameliorating effect on acute and chronic heart failure without calcium loading via maintenance of intracellular ATP levels.

AIMS: As heart failure (HF) progresses, ATP levels in myocardial cells decrease, and myocardial contractility also decreases. Inotropic drugs improve myocardial contractility but increase ATP consumption, leading to poor prognosis. Kyoto University Substance 121 (KUS121) is known to selectively inhibit the ATPase activity of valosin-containing protein, maintain cellular ATP levels, and manifest cytoprotective effects in several pathological conditions. The aim of this study is to determine the therapeutic effect of KUS121 on HF models. METHODS AND RESULTS: Cultured cell, mouse, and canine models of HF were used to examine the therapeutic effects of KUS121. The mechanism of action of KUS121 was also examined. Administration of KUS121 to a transverse aortic constriction (TAC)-induced mouse model of HF rapidly improved the left ventricular ejection fraction and improved the creatine phosphate/ATP ratio. In a canine model of high frequency-paced HF, administration of KUS121 also improved left ventricular contractility and decreased left ventricular end-diastolic pressure without increasing the heart rate. Long-term administration of KUS121 to a TAC-induced mouse model of HF suppressed cardiac hypertrophy and fibrosis. In H9C2 cells, KUS121 reduced ER stress. Finally, in experiments using primary cultured cardiomyocytes, KUS121 improved contractility and diastolic capacity without changing peak Ca2+ levels or contraction time. These effects were not accompanied by an increase in cyclic adenosine monophosphate or phosphorylation of phospholamban and ryanodine receptors. CONCLUSIONS: KUS121 ameliorated HF by a mechanism totally different from that of conventional catecholamines. We propose that KUS121 is a promising new option for the treatment of HF.

Survival and process outgrowth of human iPSC-derived cells expressing Purkinje cell markers in a mouse model for spinocerebellar degenerative disease.

Purkinje cells are the sole output neurons of the cerebellar cortex and play central roles in the integration of cerebellum-related motor coordination and memory. The loss or dysfunction of Purkinje cells due to cerebellar atrophy leads to severe ataxia. Here we used in vivo transplantation to examine the function of human iPS cell-derived cerebellar progenitors in adult transgenic mice in which Purkinje-specific cell death occurs due to cytotoxicity of polyglutamines. Transplantation using cerebellar organoids (42-48 days in culture), which are rich in neural progenitors, showed a viability of >50% 4 weeks after transplantation. STEM121+ grafted cells extended their processes toward the deep cerebellar nuclei, superior cerebellar peduncle, and vestibulocerebellar nuclei. The transplanted cells were mostly located in the white matter, and they were not found in the Purkinje cell layer. MAP2-positive fibers seen in the molecular layer of cerebellar cortex received VGluT2 inputs from climbing fibers. Transplanted neural progenitors overgrew in the host cerebellum but were suppressed by pretreatment with the γ-secretase inhibitor DAPT. Hyperproliferation was also suppressed by transplantation with more differentiated organoids (86 days in culture) or KIRREL2-positive cells purified by FACS sorting. Transplanted cells expressed Purkinje cell markers, GABA, CALB1 and L7, though they did not show fan-shaped morphology. We attempted to improve neuronal integration of stem cell-derived cerebellar progenitors by transplantation into the adult mouse, but this was not successfully achieved. Our findings in the present study contribute to regenerative medical application for cerebellar degeneration and provide new insights into cerebellar development in future.

A novel VCP modulator KUS121 exerts renoprotective effects in ischemia-reperfusion injury with retaining ATP and restoring ERAD-processing capacity.

Acute kidney injury (AKI) is a life-threatening condition and often progresses to chronic kidney disease or the development of other organ dysfunction even after recovery. Despite the increased recognition and high prevalence of AKI worldwide, there has been no established treatment so far. The aim of this study was to investigate the renoprotective effect of Kyoto University substance 121 (KUS121), a novel valosin-containing protein modulator, on AKI. In in vitro experiments, we evaluated cell viability and ATP levels of proximal tubular cells with or without KUS121 under endoplasmic reticulum (ER) stress conditions. In in vivo experiments, the effects of KUS121 were examined in mice with AKI caused by ischemia-reperfusion injury. ER-associated degradation (ERAD)-processing capacity was evaluated by quantification of the ERAD substrate CD3delta-YFP. KUS121 protected proximal tubular cells from cell death under ER stress. The apoptotic response was mitigated as indicated by the suppression of C/EBP homologous protein expression and caspase-3 cleavage, with maintained intracellular ATP levels by KUS121 administration. KUS121 treatment suppressed the elevation of serum creatinine and neutrophil gelatinase-associated lipocalin levels and attenuated renal tubular damage after ischemia-reperfusion. The expression of inflammatory cytokines in the kidney was also suppressed in the KUS121-treated group. Valosin-containing protein expression levels were not altered by KUS121 both in vitro and in vivo. KUS121 treatment restored ERAD-processing capacity associated with potentiation of its upstream pathway, phosphorylated inositol-requiring enzyme-1α, and spliced X box-binding protein-1. In conclusion, these findings indicate that KUS121 can protect renal tubular cells from ER stress-induced injury, suggesting that KUS121 could be a novel and promising therapeutic compound for ischemia-associated AKI.NEW & NOTEWORTHY Novel findings of this study are as follows: 1) Kyoto University substance 121 (KUS121), a novel valosin-containing protein (VCP) modulator, can reduce ATP consumption of VCP; 2) KUS121 reduced endoplasmic reticulum (ER) stress and improved cell viability in proximal tubular cells; 3) KUS121 exerted renoprotective effects against ischemia-reperfusion injury; and 4) KUS121 may prevent ischemic acute kidney injury with ATP retention and restoring ER-associated degradation capacity.

VCP relocalization limits mitochondrial activity, GSH depletion and ferroptosis during starvation in PC3 prostate cancer cells.

During periods of crisis, cells must compensate to survive. To this end, cells may need to alter the subcellular localization of crucial proteins. Here, we show that during starvation, VCP, the most abundant soluble ATPase, relocalizes and forms aggregate-like structures at perinuclear regions in PC3 prostate cancer cells. This movement is associated with a lowered metabolic state, in which mitochondrial activity and ROS production are reduced. VCP appears to explicitly sense glutamine levels, as removal of glutamine from complete medium triggered VCP relocalization and its addition to starvation media blunted VCP relocalization. Cells cultured in Gln(+) starvation media exhibited uniformly distributed VCP in the cytoplasm (free VCP) and underwent ferroptotic cell death, which was associated with a decrease in GSH levels. Moreover, the addition of a VCP inhibitor, CB-5083, in starvation media prevented VCP relocalization and triggered ferroptotic cell death. Likewise, expression of GFP-fused VCP proteins, irrespective of ATPase activities, displayed free VCP and triggered cell death during starvation. These results indicate that free VCP is essential for the maintenance of mitochondrial function and that PC3 cells employ a strategy of VCP self-aggregation to suppress mitochondrial activity in order to escape cell death during starvation, a novel VCP-mediated survival mechanism.

A VCP modulator, KUS121, as a promising therapeutic agent for post-traumatic osteoarthritis.

Post-traumatic osteoarthritis (PTOA) is a major cause which hinders patients from the recovery after intra-articular injuries or surgeries. Currently, no effective treatment is available. In this study, we showed that inhibition of the acute stage chondrocyte death is a promising strategy to mitigate the development of PTOA. Namely, we examined efficacies of Kyoto University Substance (KUS) 121, a valosin-containing protein modulator, for PTOA as well as its therapeutic mechanisms. In vivo, in a rat PTOA model by cyclic compressive loading, intra-articular treatments of KUS121 significantly improved the modified Mankin scores and reduced damaged-cartilage volumes, as compared to vehicle treatment. Moreover, KUS121 markedly reduced the numbers of TUNEL-, CHOP-, MMP-13-, and ADAMTS-5-positive chondrocytes in the damaged knees. In vitro, KUS121 rescued human articular chondrocytes from tunicamycin-induced cell death, in both monolayer culture and cartilage explants. It also significantly downregulated the protein or gene expression of ER stress markers, proinflammatory cytokines, and extracellular-matrix-degrading enzymes induced by tunicamycin or IL-1ß. Collectively, these results demonstrated that KUS121 protected chondrocytes from cell death through the inhibition of excessive ER stress. Therefore, KUS121 would be a new, promising therapeutic agent with a protective effect on the progression of PTOA.

Single-cell dynamics of pannexin-1-facilitated programmed ATP loss during apoptosis.

ATP is essential for all living cells. However, how dead cells lose ATP has not been well investigated. In this study, we developed new FRET biosensors for dual imaging of intracellular ATP level and caspase-3 activity in single apoptotic cultured human cells. We show that the cytosolic ATP level starts to decrease immediately after the activation of caspase-3, and this process is completed typically within 2 hr. The ATP decrease was facilitated by caspase-dependent cleavage of the plasma membrane channel pannexin-1, indicating that the intracellular decrease of the apoptotic cell is a 'programmed' process. Apoptotic cells deficient of pannexin-1 sustained the ability to produce ATP through glycolysis and to consume ATP, and did not stop wasting glucose much longer period than normal apoptotic cells. Thus, the pannexin-1 plays a role in arresting the metabolic activity of dead apoptotic cells, most likely through facilitating the loss of intracellular ATP.

Safety and effectiveness of a novel neuroprotectant, KUS121, in patients with non-arteritic central retinal artery occlusion: An open-label, non-randomized, first-in-humans, phase 1/2 trial.

Kyoto University Substance (KUS) 121, an ATPase inhibitor of valosin-containing protein, is a novel neuroprotectant. We tested the safety and effectiveness of KUS121 in patients with acute central retinal artery occlusion (CRAO). We conducted an investigator-initiated, first-in-humans, phase 1/2 clinical trial. Nine patients with non-arteritic CRAO symptoms lasting for 4-48 h were enrolled. These patients received daily intravitreal injections of KUS121 for 3 days: 25 µg (low-dose) in the first three patients and 50 µg (high-dose) in the next six patients. The primary endpoint was the safety of the drug. As a secondary endpoint, pharmacokinetics was evaluated. Other key secondary endpoints were changes in best-corrected visual acuity (BCVA), measured using the Early Treatment Diabetic Retinopathy Study chart, visual field scores, and retinal sensitivities between baseline and week 12; and decimal BCVA at week 12. Administration of KUS121 did not result in serious adverse events. All nine patients (100%) showed significant improvement of BCVA. Average readable letter counts, visual field scores, and retinal sensitivities also improved. Decimal BCVA at week 12 was better than 0.1 in four patients (44%) and equal to or better than 0.05 in seven patients (78%). This first-in-humans clinical trial provides support for the safety and efficacy of intravitreal KUS121 injection. To substantiate the safety and effectiveness for patients with acute CRAO, further larger scale clinical studies will be needed.

Cardioprotective Effects of VCP Modulator KUS121 in Murine and Porcine Models of Myocardial Infarction.

No effective treatment is yet available to reduce infarct size and improve clinical outcomes after acute myocardial infarction by enhancing early reperfusion therapy using primary percutaneous coronary intervention. The study showed that Kyoto University Substance 121 (KUS121) reduced endoplasmic reticulum stress, maintained adenosine triphosphate levels, and ameliorated the infarct size in a murine cardiac ischemia and reperfusion injury model. The study confirmed the cardioprotective effect of KUS121 in a porcine ischemia and reperfusion injury model. These findings confirmed that KUS121 is a promising novel therapeutic agent for myocardial infarction in conjunction with primary percutaneous coronary intervention.

Ellagic acid, extracted from Sanguisorba officinalis, induces G1 arrest by modulating PTEN activity in B16F10 melanoma cells.

In Chinese medicine, herbal medicine is commonly used to treat individuals suffering from many types of diseases. We thus expected that some herbal medicines would contain promising compounds for cancer chemotherapy. Indeed, we found that Sanguisorba officinalis extracts strongly inhibit the growth of B16F10 melanoma cells, and we identified ellagic acid (EA) as the responsible ingredient. B16F10 cells treated with EA exhibited strong G1 arrest accompanied by accumulation of p53, followed by inactivation of AKT. Addition of a PTEN inhibitor, but not a p53 inhibitor, abrogated the EA-induced AKT inactivation and G1 arrest. The PTEN inhibitor also diminished EA-induced p53 accumulation. Furthermore, EA apparently increased the protein phosphatase activity of PTEN, as demonstrated by the reduced phosphorylation level of FAK, a protein substrate of PTEN. Furthermore, an in vitro PTEN phosphatase assay on PIP3 showed the direct modulation of PTEN activity by EA. These results suggest that EA functions as an allosteric modulator of PTEN, enhancing its protein phosphatase activity while inhibiting its lipid phosphatase activity. It is notable that a combination of EA and cisplatin, a widely used chemotherapy agent, dramatically enhanced cell death in B16F10 cells, suggesting a promising strategy in chemotherapy.

KUS121, a valosin-containing protein modulator, attenuates ischemic stroke via preventing ATP depletion.

Reduced adenosine triphosphate (ATP) levels in ischemic stroke constitute an upstream contributor to neuronal cell death. We have recently created a small chemical, named Kyoto University Substance 121 (KUS121), which can reduce cellular ATP consumption. In this study, we examined whether KUS121 has neuroprotective effects in rodent cerebral ischemia models. We evaluated cell viability and ATP levels in vitro after oxygen glucose deprivation (OGD) in rat cortical primary neuronal cultures incubated with or without KUS121. We found that KUS121 protected neurons from cell death under OGD by preventing ATP depletion. We also used in vivo ischemic stroke models of transient distal middle cerebral artery occlusion in C57BL/6 and B-17 mice. Administration of KUS121 in these models improved functional deficits and reduced brain infarction volume after transient focal cerebral ischemia in both C57BL/6 and B-17 mice. These results indicate that KUS121 could be a novel type of neuroprotective drug for ischemic stroke.

Emodin, as a mitochondrial uncoupler, induces strong decreases in adenosine triphosphate (ATP) levels and proliferation of B16F10 cells, owing to their poor glycolytic reserve.

Many types of cancer cells show a characteristic increase in glycolysis, which is called the "Warburg effect." By screening plant extracts, we identified one that decreases cellular adenosine triphosphate (ATP) levels and suppresses proliferation of malignant melanoma B16F10 cells, but not of noncancerous MEF cells. We showed that its active ingredient is emodin, which showed strong antiproliferative effects on B16F10 cells both in vitro and in vivo. Moreover, we also found that emodin can function as a mitochondrial uncoupler. Consistently, three known mitochondrial uncouplers also displayed potent antiproliferative effects and preferential cellular ATP reduction in B16F10 cells, but not in MEF cells. These uncouplers provoked comparable mitochondrial uncoupling in both cell types, but they manifested dramatically different cellular effects. Namely in MEF cells, these uncouplers induced three to fivefold increases in glycolysis from the basal state, and this compensatory activation appeared to be responsible for the maintenance of cellular ATP levels. In contrast, B16F10 cells treated with the uncouplers showed less than a twofold enhancement of glycolysis, which was not sufficient to compensate for the decrease of ATP production. Together, these results raise the possibility that uncouplers could be effective therapeutic agents specifically for cancer cells with prominent "Warburg effect."

PPARα-Mediated Positive-Feedback Loop Contributes to Cold Exposure Memory.

Fluctuations in food availability and shifts in temperature are typical environmental changes experienced by animals. These environmental shifts sometimes portend more severe changes; e.g., chilly north winds precede the onset of winter. Such telltale signs may be indicators for animals to prepare for such a shift. Here we show that HEK293A cells, cultured under starvation conditions, can "memorize" a short exposure to cold temperature (15 °C), which was evidenced by their higher survival rate compared to cells continuously grown at 37 °C. We refer to this phenomenon as "cold adaptation". The cold-exposed cells retained high ATP levels, and addition of etomoxir, a fatty acid oxidation inhibitor, abrogated the enhanced cell survival. In our standard protocol, cold adaptation required linoleic acid (LA) supplementation along with the activity of Δ-6-desaturase (D6D), a key enzyme in LA metabolism. Moreover, supplementation with the LA metabolite arachidonic acid (AA), which is a high-affinity agonist of peroxisome proliferator-activated receptor-alpha (PPARα), was able to underpin the cold adaptation, even in the presence of a D6D inhibitor. Cold exposure with added LA or AA prompted a surge in PPARα levels, followed by the induction of D6D expression; addition of a PPARα antagonist or a D6D inhibitor abrogated both their expression, and reduced cell survival to control levels. We also found that the brief cold exposure transiently prevents PPARα degradation by inhibiting the ubiquitin proteasome system, and starvation contributes to the enhancement of PPARα activity by inhibiting mTORC1. Our results reveal an innate adaptive positive-feedback mechanism with a PPARα-D6D-AA axis that is triggered by a brief cold exposure in cells. "Cold adaptation" could have evolved to increase strength and resilience against imminent extreme cold temperatures.

In vivo targeted single-nucleotide editing in zebrafish.

To date, several genome editing technologies have been developed and are widely utilized in many fields of biology. Most of these technologies, if not all, use nucleases to create DNA double-strand breaks (DSBs), raising the potential risk of cell death and/or oncogenic transformation. The risks hinder their therapeutic applications in humans. Here, we show that in vivo targeted single-nucleotide editing in zebrafish, a vertebrate model organism, can be successfully accomplished with the Target-AID system, which involves deamination of a targeted cytidine to create a nucleotide substitution from cytosine to thymine after replication. Application of the system to two zebrafish genes, chordin (chd) and one-eyed pinhead (oep), successfully introduced premature stop codons (TAG or TAA) in the targeted genomic loci. The modifications were heritable and faithfully produced phenocopies of well-known homozygous mutants of each gene. These results demonstrate for the first time that the Target-AID system can create heritable nucleotide substitutions in vivo in a programmable manner, in vertebrates, namely zebrafish.

Analysis of mitochondrial function in human induced pluripotent stem cells from patients with mitochondrial diabetes due to the A3243G mutation.

We previously established human induced pluripotent stem (iPS) cells in two diabetic patients from different families with the mitochondrial A3243G mutation and isolated isogenic iPS cell clones with either undetectable or high levels of the mutation in both patients. In the present study, we analyzed the mitochondrial functions of two mutation-undetectable and two mutation-high clones in each patient through four methods to assess complex I activity, mitochondrial membrane potential, mitochondrial respiration, and mitochondrial ATP production. In the first patient, complex I activity, mitochondrial respiration, and mitochondrial ATP production were decreased in the mutation-high clones compared with the mutation-undetectable clones, and mitochondrial membrane potential was decreased in a mutation-high clone compared with a mutation-undetectable clone. In the second patient, complex I activity was decreased in one mutation-high clone compared with the other clones. The other parameters showed no differences in any clones. In addition, the complex I activity and mitochondrial respiration of the mutation-undetectable clones from both patients were located in the range of those of iPS cells from healthy subjects. The present study suggests that the mitochondrial function of the mutation-undetectable iPS cell clones obtained from two patients with the A3243G mutation is comparable to the control iPS cells.

ATP Maintenance via Two Types of ATP Regulators Mitigates Pathological Phenotypes in Mouse Models of Parkinson's Disease.

Parkinson's disease is assumed to be caused by mitochondrial dysfunction in the affected dopaminergic neurons in the brain. We have recently created small chemicals, KUSs (Kyoto University Substances), which can reduce cellular ATP consumption. By contrast, agonistic ligands of ERRs (estrogen receptor-related receptors) are expected to raise cellular ATP levels via enhancing ATP production. Here, we show that esculetin functions as an ERR agonist, and its addition to culture media enhances glycolysis and mitochondrial respiration, leading to elevated cellular ATP levels. Subsequently, we show the neuroprotective efficacies of KUSs, esculetin, and GSK4716 (an ERRγ agonist) against cell death in Parkinson's disease models. In the surviving neurons, ATP levels and expression levels of α-synuclein and CHOP (an ER stress-mediated cell death executor) were all rectified. We propose that maintenance of ATP levels, by inhibiting ATP consumption or enhancing ATP production, or both, would be a promising therapeutic strategy for Parkinson's disease.

BTeam, a Novel BRET-based Biosensor for the Accurate Quantification of ATP Concentration within Living Cells.

ATP levels may represent fundamental health conditions of cells. However, precise measurement of intracellular ATP levels in living cells is hindered by the lack of suitable methodologies. Here, we developed a novel ATP biosensor termed "BTeam". BTeam comprises a yellow fluorescent protein (YFP), the ATP binding domain of the ε subunit of the bacterial ATP synthase, and an ATP-nonconsuming luciferase (NLuc). To attain emission, BTeam simply required NLuc substrate. BTeam showed elevated bioluminescence resonance energy transfer efficiency upon ATP binding, resulted in the emission spectra changes correlating with ATP concentrations. By using values of YFP/NLuc emission ratio to represent ATP levels, BTeam achieved steady signal outputs even though emission intensities were altered. With this biosensor, we succeeded in the accurate quantification of intracellular ATP concentrations of a population of living cells, as demonstrated by detecting the slight distribution in the cytosol (3.7-4.1 mM) and mitochondrial matrix (2.4-2.7 mM) within some cultured cell lines. Furthermore, BTeam allowed continuous tracing of cytosolic ATP levels of the same cells, as well as bioluminescent imaging of cytosolic ATP dynamics within individual cells. This simple and accurate technique should be an effective method for quantitative measurement of intracellular ATP concentrations.

Nuclear pyruvate kinase M2 complex serves as a transcriptional coactivator of arylhydrocarbon receptor.

Pyruvate kinase M2 (PKM2) and pyruvate dehydrogenase complex (PDC) regulate production of acetyl-CoA, which functions as an acetyl donor in diverse enzymatic reactions, including histone acetylation. However, the mechanism by which the acetyl-CoA required for histone acetylation is ensured in a gene context-dependent manner is not clear. Here we show that PKM2, the E2 subunit of PDC and histone acetyltransferase p300 constitute a complex on chromatin with arylhydrocarbon receptor (AhR), a transcription factor associated with xenobiotic metabolism. All of these factors are recruited to the enhancer of AhR-target genes, in an AhR-dependent manner. PKM2 contributes to enhancement of transcription of cytochrome P450 1A1 (CYP1A1), an AhR-target gene, acetylation at lysine 9 of histone H3 at the CYP1A1 enhancer. Site-directed mutagenesis of PKM2 indicates that this enhancement of histone acetylation requires the pyruvate kinase activity of the enzyme. Furthermore, we reveal that PDC activity is present in nuclei. Based on these findings, we propose a local acetyl-CoA production system in which PKM2 and PDC locally supply acetyl-CoA to p300 from abundant PEP for histone acetylation at the gene enhancer, and our data suggest that PKM2 sensitizes AhR-mediated detoxification in actively proliferating cells such as cancer and fetal cells.

Identification of a New Type of Covalent PPARγ Agonist using a Ligand-Linking Strategy.

Peroxisome proliferator-activated receptor γ (PPARγ) is a ligand-activated transcription factor that plays an important role in adipogenesis and glucose metabolism. The ligand-binding pocket (LBP) of PPARγ has a large Y-shaped cavity with multiple subpockets where multiple ligands can simultaneously bind and cooperatively activate PPARγ. Focusing on this unique property of the PPARγ LBP, we describe a novel two-step cell-based strategy to develop PPARγ ligands. First, a combination of ligands that cooperatively activates PPARγ was identified using a luciferase reporter assay. Second, hybrid ligands were designed and synthesized. For proof of concept, we focused on covalent agonists, which activate PPARγ through a unique activation mechanism regulated by a covalent linkage with the Cys285 residue in the PPARγ LBP. Despite their biological significance and pharmacological potential, few covalent PPARγ agonists are known except for endogenous fatty acid metabolites. With our strategy, we determined that plant-derived cinnamic acid derivatives cooperatively activated PPARγ by combining with GW9662, an irreversible antagonist. GW9662 covalently reacts with the Cys285 residue. A docking study predicted that a cinnamic acid derivative can bind to the open cavity in GW9662-bound PPARγ LBP. On the basis of the putative binding mode, structures of both ligands were linked successfully to create a potent PPARγ agonist, which enhanced the transactivation potential of PPARγ at submicromolar levels through covalent modification of Cys285. Our approach could lead to the discovery of novel high-potency PPARγ agonists.

VCP/Cdc48 rescues the growth defect of a GPI10 mutant in yeast.

We identified a yeast mutant with temperature-sensitive growth defects that were rescued by VCP expression. The mutation occurred in GPI10, which encodes a mannosyl transferase for glycosylphosphatidylinositol anchor formation in the endoplasmic reticulum, and caused a Gly469Glu substitution in Gpi10. The mutant exhibited increased unfolded protein response, which was partially rescued by VCP or Cdc48, and showed sensitivity against cell-wall stressors, which were not rescued by VCP. These results suggest a potential link between VCP/Cdc48 and Gpi10 functions in the control of cell growth.

Diversity in ATP concentrations in a single bacterial cell population revealed by quantitative single-cell imaging.

Recent advances in quantitative single-cell analysis revealed large diversity in gene expression levels between individual cells, which could affect the physiology and/or fate of each cell. In contrast, for most metabolites, the concentrations were only measureable as ensemble averages of many cells. In living cells, adenosine triphosphate (ATP) is a critically important metabolite that powers many intracellular reactions. Quantitative measurement of the absolute ATP concentration in individual cells has not been achieved because of the lack of reliable methods. In this study, we developed a new genetically-encoded ratiometric fluorescent ATP indicator "QUEEN", which is composed of a single circularly-permuted fluorescent protein and a bacterial ATP binding protein. Unlike previous FRET-based indicators, QUEEN was apparently insensitive to bacteria growth rate changes. Importantly, intracellular ATP concentrations of numbers of bacterial cells calculated from QUEEN fluorescence were almost equal to those from firefly luciferase assay. Thus, QUEEN is suitable for quantifying the absolute ATP concentration inside bacteria cells. Finally, we found that, even for a genetically-identical Escherichia coli cell population, absolute concentrations of intracellular ATP were significantly diverse between individual cells from the same culture, by imaging QUEEN signals from single cells.