A genetically encoded single-wavelength sensor for imaging cytosolic and cell surface ATP

State of the art indicators for imaging purinergic dynamics in vitro and in vivo

Purinergic neurotransmission, a dynamic signaling system using adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine (ADO), uridine diphosphate (UDP), and others, plays a crucial role in brain function. Purinergic signaling is involved in regulating synaptic communication to influence sleep and neuroprotection; malfunction of purinergic signaling contributes to various neurological disorders like pain, epilepsy, and depression. Effective detection methods are crucial for a comprehensive understanding of the multifaceted roles of purinergic signaling in the brain. This review sheds light on advancements in fluorescent indicators, a powerful toolkit for visualizing purinergic activities in living animals. We explore the diverse applications of these indicators in studying purinergic transmission both in health and in diseases. Despite their current strengths, we emphasize the need for continuous development of fluorescent indicators to achieve an even more comprehensive, specific, and quantitative detection of purinergic signaling.

KUS121, a novel VCP modulator, attenuates atherosclerosis development by reducing ER stress and inhibiting glycolysis through the maintenance of ATP levels in endothelial cells

BACKGROUND AND AIMS

Endoplasmic reticulum (ER) stress pathways contribute to atherosclerosis progression. Recently, we developed Kyoto University Substance (KUS) 121, which selectively inhibits ATPase activities of valosin-containing protein (VCP), consequently conserving intracellular ATP consumption and mitigating ER stress. This study evaluated the efficacy of KUS121 in atherosclerosis.

METHODS AND RESULTS

KUS121 was administered daily to Apoe-/- mice fed a Western diet (WD) for 8 weeks. KUS121 treatment resulted in a 40-50 % reduction in atherosclerosis progression. Interestingly, we observed that C/EBP homologous protein (Chop), a well-established ER stress marker, was predominantly expressed in plaque endothelium. In human EA.hy926 endothelial cells, KUS121 prevented ER stress-induced apoptosis and downregulated the Inositol-requiring enzyme 1 alpha (IRE1α)-associated inflammatory pathways. Consistent with these in vitro findings, KUS121 treatment significantly reduced endothelial apoptosis, as shown by TUNEL and cleaved caspase-3 staining, and inflammation, as demonstrated by immunostaining of Nuclear factor kappa B (NF-κB) and Intercellular adhesion molecule (Icam) 1 at plaque endothelium. We also demonstrated that KUS121 maintained ATP levels in EA.hy926 cells and atherosclerotic plaque lesions using single-wavelength and the FRET-based fluorescent ATP sensors. Supplementation of intracellular ATP by methyl pyruvate attenuated ER stress-induced apoptotic and inflammatory pathways in endothelial cells, similar to KUS121. Besides affecting ER stress, KUS121 also reduced inflammation even without ER stress by inhibiting glycolysis through increased intracellular ATP levels in LPS-treated EA.hy926 cells.

CONCLUSIONS

KUS121 can be a new therapeutic option for atherosclerotic diseases by maintaining intracellular ATP levels, leading to the attenuation of ER stress and glycolysis in plaque endothelium.

Mechanical Modulation, Physiological Roles, and Imaging Innovations of Intercellular Calcium Waves in Living Systems

Long-range intercellular communication is essential for multicellular biological systems to regulate multiscale cell-cell interactions and maintain life. Growing evidence suggests that intercellular calcium waves (ICWs) act as a class of long-range signals that influence a broad spectrum of cellular functions and behaviors. Importantly, mechanical signals, ranging from single-molecule-scale to tissue-scale in vivo, can initiate and modulate ICWs in addition to relatively well-appreciated biochemical and bioelectrical signals. Despite these recent conceptual and experimental advances, the full nature of underpinning mechanotransduction mechanisms by which cells convert mechanical signals into ICW dynamics remains poorly understood. This review provides a systematic analysis of quantitative ICW dynamics around three main stages: initiation, propagation, and regeneration/relay. We highlight the landscape of upstream molecules and organelles that sense and respond to mechanical stimuli, including mechanosensitive membrane proteins and cytoskeletal machinery. We clarify the roles of downstream molecular networks that mediate signal release, spread, and amplification, including adenosine triphosphate (ATP) release, purinergic receptor activation, and gap junction (GJ) communication. Furthermore, we discuss the broad pathophysiological implications of ICWs, covering pathophysiological processes such as cancer metastasis, tissue repair, and developmental patterning. Finally, we summarize recent advances in optical imaging and artificial intelligence (AI)/machine learning (ML) technologies that reveal the precise spatial-temporal-functional dynamics of ICWs and ATP waves. By synthesizing these insights, we offer a comprehensive framework of ICW mechanobiology and propose new directions for mechano-therapeutic strategies in disease diagnosis, cancer immunotherapies, and drug discovery.

Exploring the role of mitochondrial dysfunction and aging in COVID-19-Related neurological complications

The COVID-19 pandemic, caused by SARS-CoV-2, posed a tremendous challenge to healthcare systems globally. Severe COVID-19 infection was reported to be associated with altered immunometabolism and cytokine storms, contributing to poor clinical outcomes and in many cases resulting in mortality. Despite promising preclinical results, many drugs have failed to show efficacy in clinical trials, highlighting the need for novel approaches to combat the virus and its severe manifestations. Mitochondria, crucial for aerobic respiration, play a pivotal role in modulating immunometabolism and neuronal function, making their compromised capability as central pathological mechanism contributing to the development of neurological complications in COVID-19. Dysregulated mitochondrial dynamics can lead to uncontrolled immune responses, underscoring the importance of mitochondrial regulation in shaping clinical outcomes. Aging further accelerates mitochondrial dysfunction, compounding immune dysregulation and neurodegeneration, making older adults particularly vulnerable to severe COVID-19 and its neurological sequelae. COVID-19 infection impairs mitochondrial oxidative phosphorylation, contributing to the long-term neurological complications associated with the disease. Additionally, recent reports also suggest that up to 30% of COVID-19 patients experience lingering neurological issues, thereby highlighting the critical need for further research into mitochondrial pathways to mitigate long-tern neurological consequences of Covid-19. This review examines the role of mitochondrial dysfunction in COVID-19-induced neurological complications, its connection to aging, and potential biomarkers for clinical diagnostics. It also discusses therapeutic strategies aimed at maintaining mitochondrial integrity to improve COVID-19 outcomes.

An optical BOD biosensor based on intracellular ATP measurements in genetically modified Saccharomyces cerevisiae

A biosensor for biochemical oxygen demand (BOD) was developed based on intracellular 5'-adenosine triphosphate (ATP) measurements in Saccharomyces cerevisiae. Intracellular ATP was measured using an engineered protein named ATeam, comprising a bacterial F0F1-ATP synthase ε subunit sandwiched between cyan fluorescent protein and mVenus, a modified yellow fluorescent protein. Because the binding of ATP to ATeam induces changes in the fluorescence spectra owing to Fӧrster resonance energy transfer, S. cerevisiae expressing ATeam is expected to show spectral changes owing to the intracellular ATP produced by the metabolism of the BOD sample. A glycogen phosphorylase knockout S. cerevisiae strain expressing ATeam was prepared, and the fluorescence spectra of the strain were analyzed. Changes in the fluorescence spectra of glucose in the medium were observed, which exhibited a linear relationship with the glucose concentration (0-100 mg/L, R2 = 0.970). Responses to lactose, fructose, sucrose, Glu, Asp, His, and Gly were evaluated and compared with typical BOD measurements. The results of this comparison suggest that a BOD biosensor based on intracellular ATP can be used for BOD measurements. A BOD standard solution comprising glucose and glutamic acid (GGA) was calibrated across a concentration range of 0 to 100 mg/L. Finally, simulated real samples were prepared using real pond water and GGA was measured. The correlation between the BOD value evaluated using intracellular ATP and that evaluated using the 5-day BOD test showed a linear relationship with R2 = 0.944.

Exogenously and Endogenously Sequential Regulation of DNA Nanodevices Enables Organelle-Specific Signal Amplification in Subcellular ATP Profiling

Adenosine triphosphate (ATP), the primary energy currency in cells, is dynamically regulated across different subcellular compartments. The ATP interplay between mitochondria and endoplasmic reticulum (ER) underscores their coordinated roles in various biochemical processes, highlighting the necessity for precise profiling of subcellular ATP dynamics. Here we present an exogenously and endogenously dual-regulated DNA nanodevice for spatiotemporally selective, subcellular-compartment specific signal amplification in ATP sensing. The system allows for exogenous NIR light-controlled spatiotemporal localization and activation of the aptamer sensor in mitochondria or ER, while a specific endogenous enzyme in the organelles further drives signal amplification via the consumption of molecular beacon fuels, resulting in significantly enhanced sensitivity and spatial precision for the subcellular ATP profiling in the organelle of interest. Furthermore, we demonstrate the application of this system for robust monitoring of ATP fluctuations in mitochondria and ER following drug interventions. This advancement provides a powerful tool for improving our understanding of cellular energetics at the subcellular level and holds potential for the development of targeted therapeutics.

Principles and Design of Molecular Tools for Sensing and Perturbing Cell Surface Receptor Activity

Cell-surface receptors are vital for controlling numerous cellular processes with their dysregulation being linked to disease states. Therefore, it is necessary to develop tools to study receptors and the signaling pathways they control. This Review broadly describes molecular approaches that enable 1) the visualization of receptors to determine their localization and distribution; 2) sensing receptor activation with permanent readouts as well as readouts in real time; and 3) perturbing receptor activity and mimicking receptor-controlled processes to learn more about these processes. Together, these tools have provided valuable insight into fundamental receptor biology and helped to characterize therapeutics that target receptors.

Harmine promotes axon regeneration through enhancing glucose metabolism

Axon regeneration requires a substantial mitochondrial energy supply. However, injured mature neurons often fail to regenerate due to their inability to meet these elevated energy demands. Our findings indicate that harmine compensates for the energy deficit following axonal injury by enhancing the coupling between glucose metabolism and mitochondrial homeostasis, thereby promoting axon regeneration. Notably, harmine facilitates mitochondrial biogenesis and enhances mitophagy, ensuring efficient mitochondrial turnover, and energy supply. Thus, harmine plays a crucial role in enhancing glucose metabolism to maintain mitochondrial function, demonstrating significant potential in treating mature neuronal axon injuries and sciatic nerve injuries.

Live MSCs Characterizer Displays Stemness and Differentiation Using Colorful LV-cp Biosensors

Mesenchymal stem cells (MSCs) have garnered significant attention in biomedical research due to their accessibility and remarkable differentiation potential. However, the lack of efficient and convenient living cell monitoring methods limits their widespread application in tissue engineering and stem cell therapy. Therefore, we present progress in the development of a novel series of fluorescent protein (FP) sensors based on turn-on fluorescent protein biosensors (Turn-on FPBs), termed the LV-cp biosensor system (novel live cell permuted fluorescent protein biosensors). Utilizing phage display technology to screen for affinity peptides specifically targeting MSCs and chondrocytes, the LV-cp were engineered by subcloning these peptides into permuted fluorescent proteins, thereby integrating the fluorescence activation mechanism with the affinity peptides and achieving highly accurate detection and identification of these two cell types using living cells as "fluorescence keys." This system provides a simplified, nontoxic method to replace traditional antibody kits, and strong fluorescence signals can be obtained through various fluorescence detection devices. In addition, the LV-cp biosensors enabled dynamic observation of MSCs differentiation into chondrocytes through changes in the cell fluorescence colors.

Genetically Encoded Single-Wavelength Sensor with High Specificity for Imaging ATP in Living Cells

Adenosine 5'-triphosphate (ATP) plays an essential role in regulating many metabolic activities. Therefore, developing tools to directly measure ATP in real time will help us understand its underlying functions. Here, we report an optimized genetically encoded ATP sensor (OAS1.0) with a high specificity for ATP detection. OAS1.0 can be genetically targeted to specific cell types and subcellular compartments to monitor ATP production and consumption. We also used OAS1.0 to visualize metabolic-activity-dependent changes in ATP in normal and tumor cell lines and ATP consumption during the virus-host interaction process. OAS1.0 also worked well with a Ca2+ sensor to concurrently monitor ATP and Ca2+ dynamics in living cells. Thus, OAS1.0 represents a promising tool for ATP imaging under both physiological and pathophysiological conditions.

A genetically encoded fluorescent biosensor for visualization of acetyl-CoA in live cells

Acetyl-coenzyme A is a central metabolite that participates in many cellular pathways. Evidence suggests that acetyl-CoA metabolism is highly compartmentalized in mammalian cells. Yet methods to measure acetyl-CoA in living cells are lacking. Herein, we engineered an acetyl-CoA biosensor from the bacterial protein PanZ and circularly permuted green fluorescent protein (cpGFP). The sensor, "PancACe," has a maximum change of ∼2-fold and a response range of ∼10 μM-2 mM acetyl-CoA. We demonstrated that the sensor has a greater than 7-fold selectivity over coenzyme A, butyryl-CoA, malonyl-CoA, and succinyl-CoA, and a 2.3-fold selectivity over propionyl-CoA. We expressed the sensor in E. coli and showed that it enables detection of rapid changes in acetyl-CoA levels. By localizing the sensor to either the cytoplasm, nucleus, or mitochondria in human cells, we showed that it enables subcellular detection of changes in acetyl-CoA levels, the magnitudes of which agreed with an orthogonal PicoProbe assay.

Solute carriers: The gatekeepers of metabolism

Solute carrier (SLC) proteins play critical roles in maintaining cellular and organismal homeostasis by transporting small molecules and ions. Despite a growing body of research over the past decade, physiological substrates and functions of many SLCs remain elusive. This perspective outlines key challenges in studying SLC biology and proposes an evidence-based framework for defining SLC substrates. To accelerate the deorphanization process, we explore systematic technologies, including human genetics, biochemistry, and computational and structural approaches. Finally, we suggest directions to better understand SLC functions beyond substrate identification in physiology and disease.

A Genetically Encoded Fluorescent Biosensor for Intracellular Measurement of Malonyl-CoA

Malonyl-CoA is the essential building block of fatty acids and regulates cell function through protein malonylation and allosteric regulation of signaling networks. Accordingly, the production and use of malonyl-CoA is finely tuned by the cellular energy status. Most studies of malonyl-CoA dynamics rely on bulk approaches that take only a snapshot of the average metabolic state of a population of cells, missing out on heterogeneous differences in malonyl-CoA and fatty acid biosynthesis that could be occurring among a cell population. To overcome this limitation, we have developed a genetically encoded fluorescent protein-based biosensor for malonyl-CoA that can be used to capture malonyl-CoA dynamics in single cells. This biosensor, termed Malibu (malonyl-CoA intracellular biosensor to understand dynamics), exhibits an excitation-ratiometric change in response to malonyl-CoA binding. We first used Malibu to monitor malonyl-CoA dynamics during inhibition of fatty acid biosynthesis using cerulenin in Escherichia coli, observing an increase in Malibu response in a time- and dose-dependent manner. In HeLa cells, we used Malibu to monitor the impact of fatty acid biosynthesis inhibition on malonyl-CoA dynamics in single cells, finding that two inhibitors of fatty acid biosynthesis, cerulenin and orlistat, which inhibit different steps of fatty acid biosynthesis, increase malonyl-CoA levels. Altogether, we have developed a new genetically encoded biosensor for malonyl-CoA, which can be used to study malonyl-CoA dynamics in single cells, providing an unparalleled view into fatty acid biosynthesis.

Genetically Encoded Fluorogenic DNA Aptamers for Imaging Metabolite in Living Cells

Genetically encoded fluorescent protein and fluorogenic RNA sensors are indispensable tools for imaging biomolecules in cells. To expand the toolboxes and improve the generalizability and stability of this type of sensor, we report herein a genetically encoded fluorogenic DNA aptamer (GEFDA) sensor by linking a fluorogenic DNA aptamer for dimethylindole red with an ATP aptamer. The design enhances red fluorescence by 4-fold at 650 nm in the presence of ATP. Additionally, upon dimerization, it improves the signal-to-noise ratio by 2-3 folds. We further integrated the design into a plasmid to create a GEFDA sensor for sensing ATP in live bacterial and mammalian cells. This work expanded genetically encoded sensors by employing fluorogenic DNA aptamers, which offer enhanced stability over fluorogenic proteins and RNAs, providing a novel tool for real-time monitoring of an even broader range of small molecular metabolites in biological systems.

Tracheal tuft cells release ATP and link innate to adaptive immunity in pneumonia

Tracheal tuft cells shape immune responses in the airways. While some of these effects have been attributed to differential release of either acetylcholine, leukotriene C4 and/or interleukin-25 depending on the activating stimuli, tuft cell-dependent mechanisms underlying the recruitment and activation of immune cells are incompletely understood. Here we show that Pseudomonas aeruginosa infection activates mouse tuft cells, which release ATP via pannexin 1 channels. Taste signaling through the Trpm5 channel is essential for bacterial tuft cell activation and ATP release. We demonstrate that activated tuft cells recruit dendritic cells to the trachea and lung. ATP released by tuft cells initiates dendritic cell activation, phagocytosis and migration. Tuft cell stimulation also involves an adaptive immune response through recruitment of IL-17A secreting T helper cells. Collectively, the results provide a molecular framework defining tuft cell dependent regulation of both innate and adaptive immune responses in the airways to combat bacterial infection.

Outer mitochondrial membrane E3 Ub ligase MARCH5 controls de novo peroxisome biogenesis

We report that the outer mitochondrial membrane (OMM)-associated E3 Ub ligase MARCH5 is vital for generating mitochondria-derived pre-peroxisomes. In human immortalized cells, MARCH5 knockout leads to the accumulation of immature peroxisomes, reduced fatty-acid-induced peroxisomal biogenesis, and abnormal peroxisome biogenesis in MARCH5/Pex14 and MARCH5/Pex3 dko cells. Upon fatty-acid-induced peroxisomal biogenesis, MARCH5 redistributes to peroxisomes, and ubiquitination activity-deficient mutants of MARCH5 accumulate on peroxisomes containing high levels of the OMM protein Tom20 (mitochondria-derived pre-peroxisomes). Similarly, depletion of peroxisome biogenesis factor Pex14 leads to the accumulation of MARCH5- and Tom20-positive pre-peroxisomes, whereas no peroxisomes are detected in MARCH5/Pex14 dko cells. Inconsistent with MARCH5 merely acting as a quality factor, mitochondrial decline is not evident in tested models. Furthermore, reduced expression of peroxisomal proteins is detected in MARCH5-/- cells, whereas some of these proteins are stabilized in peroxisome biogenesis deficiency models lacking MARCH5 expression. Thus, MARCH5 is central for mitochondria-dependent peroxisome biogenesis.

FRET-Based Sensor for Measuring Adenine Nucleotide Binding to AMPK

AMP-activated protein kinase (AMPK) has evolved to detect a critical increase in cellular AMP/ATP and ADP/ATP concentration ratios as a signal for limiting energy supply. Such energy stress then leads to AMPK activation and downstream events that maintain cellular energy homeostasis. AMPK activation by AMP, ADP, or pharmacological activators involves a conformational switch within the AMPK heterotrimeric complex. We have engineered an AMPK-based sensor, AMPfret, which translates the activating conformational switch into a fluorescence signal, based on increased fluorescence resonance energy transfer (FRET) between donor and acceptor fluorophores. Here we describe how this sensor can be used to analyze direct AMPK activation by small molecules in vitro using a fluorimeter, or to estimate changes in the energy state of cells using standard fluorescence or confocal microscopy.

Live imaging of paracrine signaling: Advances in visualization and tracking techniques

Live imaging techniques have revolutionized our understanding of paracrine signaling, a crucial form of cell-to-cell communication in biological processes. This review examines recent advances in visualizing and tracking paracrine factors through four key stages: secretion from producing cells, diffusion through extracellular space, binding to target cells, and activation of intracellular signaling within target cells. Paracrine factor secretion can be directly visualized by fluorescent protein tagging to ligand, or indirectly by visualizing the cleavage of the transmembrane pro-ligands or plasma membrane fusion of endosomes comprising the paracrine factors. Diffusion of paracrine factors has been studied using techniques such as fluorescence correlation spectroscopy (FCS), fluorescence recovery after photobleaching (FRAP), fluorescence decay after photoactivation (FDAP), and single-molecule tracking. Binding of paracrine factors to target cells has been visualized through various biosensors, including GPCR-activation-based (GRAB) sensors and Förster resonance energy transfer (FRET) probes for receptor tyrosine kinases. Finally, activation of intracellular signaling is monitored within the target cells by biosensors for second messengers, transcription factors, and so on. In addition to the imaging tools, the review also highlights emerging optogenetic and chemogenetic tools for triggering the release of paracrine factors, which is essential for associating the paracrine factor secretion to biological outcomes during the bioimaging of paracrine factor signaling.Key words: paracrine signaling, live imaging, biosensors, optogenetics, chemogenetics.

Noncanonical role of ALAS1 as a heme-independent inhibitor of small RNA-mediated silencing

microRNAs (miRNAs) and small interfering RNAs (siRNAs) are 21- to 22-nucleotide RNAs that guide Argonaute-class effectors to targets for repression. In this work, we uncover 5-aminolevulinic acid synthase 1 (ALAS1), the initiating enzyme for heme biosynthesis, as a general repressor of miRNA accumulation. Although heme is known to be a positive cofactor for the nuclear miRNA processing machinery, ALAS1-but not other heme biosynthesis enzymes-limits the assembly and activity of Argonaute complexes under heme-replete conditions. This involves a cytoplasmic role for ALAS1, previously considered inactive outside of mitochondria. Moreover, conditional depletion of ALAS activity from mouse hepatocytes increases miRNAs and enhances siRNA-mediated knockdown. Notably, because ALAS1 is the target of a Food and Drug Administration-approved siRNA drug, agents that suppress ALAS may serve as adjuvants for siRNA therapies.

Shear stress-stimulated AMPK couples endothelial cell mechanics, metabolism and vasodilation

Endothelial cells respond to mechanical force by stimulating cellular signaling, but how these pathways are linked to elevations in cell metabolism and whether metabolism supports the mechanical response remains poorly understood. Here, we show that the application of force to endothelial cells stimulates VE-cadherin to activate liver kinase B1 (LKB1; also known as STK11) and AMP-activated protein kinase (AMPK), a master regulator of energy homeostasis. VE-cadherin-stimulated AMPK increases eNOS (also known as NOS3) activity and localization to the plasma membrane, reinforcement of the actin cytoskeleton and cadherin adhesion complex, and glucose uptake. We present evidence for the increase in metabolism being necessary to fortify the adhesion complex, actin cytoskeleton and cellular alignment. Together, these data extend the paradigm for how mechanotransduction and metabolism are linked to include a connection to vasodilation, thereby providing new insight into how diseases involving contractile, metabolic and vasodilatory disturbances arise.

Ciliary length regulation by intraflagellar transport in zebrafish

How cells regulate the size of their organelles remains a fundamental question in cell biology. Cilia, with their simple structure and surface localization, provide an ideal model for investigating organelle size control. However, most studies on cilia length regulation are primarily performed on several single-celled organisms. In contrast, the mechanism of length regulation in cilia across diverse cell types within multicellular organisms remains a mystery. Similar to humans, zebrafish contain diverse types of cilia with variable lengths. Taking advantage of the transparency of zebrafish embryos, we conducted a comprehensive investigation into intraflagellar transport (IFT), an essential process for ciliogenesis. By generating a transgenic line carrying Ift88-GFP transgene, we observed IFT in multiple types of cilia with varying lengths. Remarkably, cilia exhibited variable IFT speeds in different cell types, with longer cilia exhibiting faster IFT speeds. This increased IFT speed in longer cilia is likely not due to changes in common factors that regulate IFT, such as motor selection, BBSome proteins, or tubulin modification. Interestingly, longer cilia in the ear cristae tend to form larger IFT compared to shorter spinal cord cilia. Reducing the size of IFT particles by knocking down Ift88 slowed IFT speed and resulted in the formation of shorter cilia. Our study proposes an intriguing model of cilia length regulation via controlling IFT speed through the modulation of the size of the IFT complex. This discovery may provide further insights into our understanding of how organelle size is regulated in higher vertebrates.

Affinity Peptide-Based Circularly Permuted Fluorescent Protein Biosensors for Non-Small Cell Lung Cancer Diagnosis

Non-small cell lung cancer (NSCLC) is the predominant form of lung cancer and poses a significant public health challenge. Early detection is crucial for improving patient outcomes, with serum biomarkers such as carcinoembryonic antigen (CEA), squamous cell carcinoma antigen (SCCAg), and cytokeratin fragment 19 (CYFRA 21-1) playing a critical role in early screening and pathological classification of NSCLC. However, due to being mainly based on corresponding antibody binding reactions, existing detection technologies for these serum biomarkers have shortcomings such as complex operations, high false positive rates, and high costs. This study aimed to develop new methods for detecting CEA, SCCAg, and CYFRA 21-1 to assist in the diagnosis of NSCLC. Affinity peptides of CEA, SCCAg, and CYFRA 21-1, respectively, were screened by phage display technology, and the peptides' binding affinities were determined by enzyme-linked immunosorbent assay and biolayer interferometry. Peptides with high affinity were then integrated as binding domains into biosensors by fusing them with circularly permuted fluorescent proteins (cpFPs) through genetic coding. The resulting biosensors, C4 biosensor for CEA, S1 biosensor for SCCAg, and Y3 biosensor for CYFRA 21-1, demonstrated robust sensitivity and specificity even at concentrations as low as 1 ng/mL for their respective tumor markers. When applied to clinical samples and recalibrated for the upper limit of normal concentrations, the biosensors exhibited enhanced sensitivity and specificity for NSCLC diagnosis. This study introduced innovative biosensors for the detection of CEA, SCCAg, and CYFRA 21-1, providing a highly sensitive, specific, rapid, and cost-effective diagnostic alternative that could significantly improve NSCLC screening rates.

TND1128, a 5-deazaflavin derivative with auto-redox ability, facilitates polarization of mitochondrial membrane potential (ΔΨm) and on-demand ATP synthesis in mice brain slices

TND1128, a 5-deazaflavin derivative, is a drug with self-redox ability. We examined the effect of TND1128 on the level of mitochondrial membrane potential (ΔΨm), which is the most critical motive power for the biosynthesis of ATP. We prepared brain slices from mice pretreated with TND1128 (0.1-10 mg/kg, intraperitoneally) and detected ΔΨm level with JC-1, a fluorescence ΔΨm indicator. We further examined the depolarization of ΔΨm under 5-min exposure to 25 mM KCl-ACSF (25K-ACSF), which activated neuronal voltage-dependent Ca2+ channels. We evaluated the effect of TND1128 by using the inverse number of the ΔΨm value as the ATP synthesis index (ASI). The level of ΔΨm increased significantly by 24-h pretreatment with TND1128 (10 mg/kg), and significantly higher depolarization of the ΔΨm was observed with 25K-ACSF exposure than in non-treated control. We found a significant decrease in 25K-ACSF induced [Ca2+]c and [Ca2+]m levels in the TND1128-pretreated preparations. We confirmed the dose and time-dependent facilitatory effects of TND1128 on the ASI. This study suggested that TND1128 could be incorporated into the TCA cycle and electron transfer chains to facilitate the polarization of ΔΨm and activate on-demand ATP synthesis. TND1128 might rescue neurons in various brain diseases caused by energy defects. (198).

Molecular Spies in Action: Genetically Encoded Fluorescent Biosensors Light up Cellular Signals

Cellular function is controlled through intricate networks of signals, which lead to the myriad pathways governing cell fate. Fluorescent biosensors have enabled the study of these signaling pathways in living systems across temporal and spatial scales. Over the years there has been an explosion in the number of fluorescent biosensors, as they have become available for numerous targets, utilized across spectral space, and suited for various imaging techniques. To guide users through this extensive biosensor landscape, we discuss critical aspects of fluorescent proteins for consideration in biosensor development, smart tagging strategies, and the historical and recent biosensors of various types, grouped by target, and with a focus on the design and recent applications of these sensors in living systems.

Elucidating the spatiotemporal dynamics of glucose metabolism with genetically encoded fluorescent biosensors

Glucose metabolism has been well understood for many years, but some intriguing questions remain regarding the subcellular distribution, transport, and functions of glycolytic metabolites. To address these issues, a living cell metabolic monitoring technology with high spatiotemporal resolution is needed. Genetically encoded fluorescent sensors can achieve specific, sensitive, and spatiotemporally resolved metabolic monitoring in living cells and in vivo, and dozens of glucose metabolite sensors have been developed recently. Here, we highlight the importance of tracking specific intermediate metabolites of glycolysis and glycolytic flux measurements, monitoring the spatiotemporal dynamics, and quantifying metabolite abundance. We then describe the working principles of fluorescent protein sensors and summarize the existing biosensors and their application in understanding glucose metabolism. Finally, we analyze the remaining challenges in developing high-quality biosensors and the huge potential of biosensor-based metabolic monitoring at multiple spatiotemporal scales.

Intracellular Mg2+ concentrations are differentially regulated in the sperm head and mid-piece in acrosome reaction inducing conditions

The sperm ability to fertilize involves the regulation of ATP levels. Because inside cells, ATP is complexed with Mg2+ ions, changes in ATP levels result in changes in intracellular Mg2+ concentration ([Mg2+]i), which can be followed using intracellular Mg2+ sensors such as Mag-520. In this work, we tested conditions known to decrease sperm ATP such as starvation and capacitation. As expected, in these conditions [Mg2+]i increased in all cell compartments. In contrast, when ATP increases, such as adding nutrients to starved sperm, [Mg2+]i significantly decreases in all compartments. On the other hand, when the acrosome reaction was induced, either with progesterone or with ionomycin, [Mg2+]i was differentially regulated in the head and mid-piece. While Mag-520 fluorescence increased in the sperm mid-piece, it decreased in the head. These changes were observed in capacitated as well as in starved sperm but not in sperm incubated in conditions that do not support capacitation. Changes in [Mg2+]i were still observed when the sperm were incubated in high extracellular Mg2+ suggesting that this decrease is not due to Mg2+ efflux. Interestingly, the progesterone and ionomycin effects on [Mg2+]i were abolished on sperm incubated in Ca2+-free media. Altogether, these results indicate that [Mg2+]i is regulated in sperm during capacitation and acrosomal reaction, and suggest that these measurements can serve to evaluate ATP levels in real time.

De novo designed YK peptides forming reversible amyloid for synthetic protein condensates in mammalian cells

In mammalian cells, protein condensates underlie diverse cell functions. Intensive synthetic biological research has been devoted to fabricating liquid droplets using de novo peptides/proteins designed from scratch in test tubes or bacterial cells. However, the development of de novo sequences for synthetic droplets forming in eukaryotes is challenging. Here, we report YK peptides, comprising 9-15 residues of alternating repeats of tyrosine and lysine, which form reversible amyloid-like fibrils accompanied by binding with poly-anion species such as ATP. By genetically tagging the YK peptide, superfolder GFPs assemble into artificial liquid-like droplets in living cells. Rational design of the YK system allows fine-tuning of the fluidity and construction of multi-component droplets. The YK system not only facilitates intracellular reconstitution of simplified models for natural protein condensates, but it also provides a toolbox for the systematic creation of droplets with different dynamics and composition for in situ evaluation.

Non-Invasive On-Off Fluorescent Biosensor for Endothelial Cell Detection

For rapid and convenient detection of living endothelial cells (ECs) specifically without immunostaining, we developed a biosensor based on turn-on fluorescent protein, named LV-EcpG. It includes a high-affinity peptide E12P obtained through phage display technology for specifically recognizing ECs and a turn-on EGFP fused with two linker peptides. The "on-off" switching mechanism of this genetically encoded fluorescent protein-based biosensor (FPB) ensured that fluorescence signals were activated only when binding with ECs, thus enabling these FPB characters for direct, visual, and non-invasive detection of ECs. Its specificity and multicolor imaging capability established LV-EcpG as a powerful tool for live EC research, with significant potential for diagnosing and treating cardiovascular diseases and tumor angiogenesis.

ZnS and Reduced Graphene Oxide Nanocomposite-Based Non-Enzymatic Biosensor for the Photoelectrochemical Detection of Uric Acid

In this work, we report a study of a zinc sulfide (ZnS) nanocrystal and reduced graphene oxide (RGO) nanocomposite-based non-enzymatic uric acid biosensor. ZnS nanocrystals with different morphologies were synthesized through a hydrothermal method, and both pure nanocrystals and related ZnS/RGO were characterized with SEM, XRD and an absorption spectrum and resistance test. It was found that compared to ZnS nanoparticles, the ZnS nanoflakes had stronger UV light absorption ability at the wavelength of 280 nm of UV light. The RGO significantly enhanced the electron transfer efficiency of the ZnS nanoflakes, which further led to a better photoelectrochemical property of the ZnS/RGO nanocomposites. The ZnS nanoflake/RGO nanocomposite-based biosensor showed an excellent uric acid detecting sensitivity of 534.5 μA·cm-2·mM-1 in the linear range of 0.01 to 2 mM and a detection limit of 0.048 μM. These results will help to improve non-enzymatic biosensor properties for the rapid and accurate clinical detection of uric acid.

A Genetically Encoded Fluorescent Biosensor for Intracellular Measurement of Malonyl-CoA

Malonyl-CoA is the essential building block of fatty acids and regulates cell function through protein malonylation and allosteric regulation of signaling networks. Accordingly, the production and use of malonyl-CoA is finely tuned by the cellular energy status. Most studies of malonyl-CoA dynamics rely on bulk approaches that take only a snapshot of the average metabolic state of a population of cells, missing out on dynamic changes in malonyl-CoA and fatty acid biosynthesis that could be occurring within a single cell. To overcome this limitation, we have developed a genetically encoded fluorescent protein-based biosensor for malonyl-CoA that can be used to capture malonyl-CoA dynamics in single cells. This biosensor, termed Malibu (malonyl-CoA intracellular biosensor to understand dynamics), exhibits an excitation-ratiometric change in response to malonyl-CoA binding. We first used Malibu to monitor malonyl-CoA dynamics during inhibition of fatty acid biosynthesis using cerulenin in E. coli, observing an increase in Malibu response in a time- and dose-dependent manner. In HeLa cells, we used Malibu to monitor the impact of fatty acid biosynthesis inhibition on malonyl-CoA dynamics in single cells, finding that two inhibitors of fatty acid biosynthesis, cerulenin and orlistat, which inhibit different steps of fatty acid biosynthesis, increase malonyl-CoA levels. Altogether, we have developed a new genetically encoded biosensor for malonyl-CoA, which can be used to sensitively study malonyl-CoA dynamics in single cells, providing an unparalleled view into fatty acid biosynthesis.

Organization of a functional glycolytic metabolon on mitochondria for metabolic efficiency

Glucose, the primary cellular energy source, is metabolized through glycolysis initiated by the rate-limiting enzyme hexokinase (HK). In energy-demanding tissues like the brain, HK1 is the dominant isoform, primarily localized on mitochondria, and is crucial for efficient glycolysis-oxidative phosphorylation coupling and optimal energy generation. This study unveils a unique mechanism regulating HK1 activity, glycolysis and the dynamics of mitochondrial coupling, mediated by the metabolic sensor enzyme O-GlcNAc transferase (OGT). OGT catalyses reversible O-GlcNAcylation, a post-translational modification influenced by glucose flux. Elevated OGT activity induces dynamic O-GlcNAcylation of the regulatory domain of HK1, subsequently promoting the assembly of the glycolytic metabolon on the outer mitochondrial membrane. This modification enhances the mitochondrial association with HK1, orchestrating glycolytic and mitochondrial ATP production. Mutation in HK1's O-GlcNAcylation site reduces ATP generation in multiple cell types, specifically affecting metabolic efficiency in neurons. This study reveals a previously unappreciated pathway that links neuronal metabolism and mitochondrial function through OGT and the formation of the glycolytic metabolon, providing potential strategies for tackling metabolic and neurological disorders.

Remote ischemic preconditioning prevents high-altitude cerebral edema by enhancing glucose metabolic reprogramming

AIMS

Incidence of acute mountain sickness (AMS) ranges from 40%-90%, with high-altitude cerebral edema (HACE) representing a life-threatening end stage of severe AMS. However, practical and convenient preventive strategies for HACE are lacking. Remote ischemic preconditioning (RIPC) has demonstrated preventive effects on ischemia- or hypoxia-induced cardiovascular and cerebrovascular diseases. This study aimed to investigate the potential molecular mechanism of HACE and the application of RIPC in preventing HACE onset.

METHODS

A hypobaric hypoxia chamber was used to simulate a high-altitude environment of 7000 meters. Metabolomics and metabolic flux analysis were employed to assay metabolite levels. Transcriptomics and quantitative real-time PCR (q-PCR) were used to investigate gene expression levels. Immunofluorescence staining was performed on neurons to label cellular proteins. The fluorescent probes Mito-Dendra2, iATPSnFR1.0, and CMTMRos were used to observe mitochondria, ATP, and membrane potential in cultured neurons, respectively. TUNEL staining was performed to detect and quantify apoptotic cell death. Hematoxylin and eosin (H&E) staining was utilized to analyze pathological changes, such as tissue swelling in cerebral cortex samples. The Rotarod test was performed to assess motor coordination and balance in rats. Oxygen-glucose deprivation (OGD) of cultured cells was employed as an in vitro model to simulate the hypoxia and hypoglycemia induced by RIPC in animal experiments.

RESULTS

We revealed a causative perturbation of glucose metabolism in the brain preceding cerebral edema. Ischemic preconditioning treatment significantly reprograms glucose metabolism, ameliorating cell apoptosis and hypoxia-induced energy deprivation. Notably, ischemic preconditioning improves mitochondrial membrane potential and ATP production through enhanced glucose-coupled mitochondrial metabolism. In vivo studies confirm that RIPC alleviates cerebral edema, reduces cell apoptosis induced by high-altitude hypoxia, and improves motor dysfunction resulting from cerebral edema.

CONCLUSIONS

Our study elucidates the metabolic basis of HACE pathogenesis. This study provides a new strategy for preventing HACE that RIPC reduces brain edema through reprogramming metabolism, highlighting the potential of targeting metabolic reprogramming for neuroprotective interventions in neurological diseases caused by ischemia or hypoxia.

Epilepsy insights revealed by intravital functional optical imaging

Despite an abundance of pharmacologic and surgical epilepsy treatments, there remain millions of patients suffering from poorly controlled seizures. One approach to closing this treatment gap may be found through a deeper mechanistic understanding of the network alterations that underly this aberrant activity. Functional optical imaging in vertebrate models provides powerful advantages to this end, enabling the spatiotemporal acquisition of individual neuron activity patterns across multiple seizures. This coupled with the advent of genetically encoded indicators, be them for specific ions, neurotransmitters or voltage, grants researchers unparalleled access to the intact nervous system. Here, we will review how in vivo functional optical imaging in various vertebrate seizure models has advanced our knowledge of seizure dynamics, principally seizure initiation, propagation and termination.

Enhanced cellular longevity arising from environmental fluctuations

Cellular longevity is regulated by both genetic and environmental factors. However, the interactions of these factors in the context of aging remain largely unclear. Here, we formulate a mathematical model for dynamic glucose modulation of a core gene circuit in yeast aging, which not only guided the design of pro-longevity interventions but also revealed the theoretical principles underlying these interventions. We introduce the dynamical systems theory to capture two general means for promoting longevity-the creation of a stable fixed point in the "healthy" state of the cell and the "dynamic stabilization" of the system around this healthy state through environmental oscillations. Guided by the model, we investigate how both of these can be experimentally realized by dynamically modulating environmental glucose levels. The results establish a paradigm for theoretically analyzing the trajectories and perturbations of aging that can be generalized to aging processes in diverse cell types and organisms.

Neuronal activity-driven O-GlcNAcylation promotes mitochondrial plasticity

Neuronal activity is an energy-intensive process that is largely sustained by instantaneous fuel utilization and ATP synthesis. However, how neurons couple ATP synthesis rate to fuel availability is largely unknown. Here, we demonstrate that the metabolic sensor enzyme O-linked N-acetyl glucosamine (O-GlcNAc) transferase regulates neuronal activity-driven mitochondrial bioenergetics in hippocampal and cortical neurons. We show that neuronal activity upregulates O-GlcNAcylation in mitochondria. Mitochondrial O-GlcNAcylation is promoted by activity-driven glucose consumption, which allows neurons to compensate for high energy expenditure based on fuel availability. To determine the proteins that are responsible for these adjustments, we mapped the mitochondrial O-GlcNAcome of neurons. Finally, we determine that neurons fail to meet activity-driven metabolic demand when O-GlcNAcylation dynamics are prevented. Our findings suggest that O-GlcNAcylation provides a fuel-dependent feedforward control mechanism in neurons to optimize mitochondrial performance based on neuronal activity. This mechanism thereby couples neuronal metabolism to mitochondrial bioenergetics and plays a key role in sustaining energy homeostasis.

Upstream alternative polyadenylation in SCN5A produces a short transcript isoform encoding a mitochondria-localized NaV1.5 N-terminal fragment that influences cardiomyocyte respiration

SCN5A encodes the cardiac voltage-gated Na+ channel, NaV1.5, that initiates action potentials. SCN5A gene variants cause arrhythmias and increased heart failure risk. Mechanisms controlling NaV1.5 expression and activity are not fully understood. We recently found a well-conserved alternative polyadenylation (APA) signal downstream of the first SCN5A coding exon. This yields a SCN5A-short transcript isoform expressed in several species (e.g. human, pig, and cat), though rodents lack this upstream APA. Reanalysis of transcriptome-wide cardiac APA-seq and mRNA-seq data shows reductions in both upstream APA usage and short/full-length SCN5A mRNA ratios in failing hearts. Knock-in of the human SCN5A APA sequence into mice is sufficient to enable expression of SCN5A -short transcript, while significantly decreasing expression of full-length SCN5A mRNA. Notably, SCN5A -short transcript encodes a novel protein (NaV1.5-NT), composed of an N-terminus identical to NaV1.5 and a unique C-terminus derived from intronic sequence. AAV9 constructs were able to achieve stable NaV1.5-NT expression in mouse hearts, and western blot of human heart tissues showed bands co-migrating with NaV1.5-NT transgene-derived bands. NaV1.5-NT is predicted to contain a mitochondrial targeting sequence and localizes to mitochondria in cultured cardiomyocytes and in mouse hearts. NaV1.5-NT expression in cardiomyocytes led to elevations in basal oxygen consumption rate, ATP production, and mitochondrial ROS, while depleting NADH supply. Native PAGE analyses of mitochondria lysates revealed that NaV1.5-NT expression resulted in increased levels of disassembled complex V subunits and accumulation of complex I-containing supercomplexes. Overall, we discovered that APA-mediated regulation of SCN5A produces a short transcript encoding NaV1.5-NT. Our data support that NaV1.5-NT plays a multifaceted role in influencing mitochondrial physiology: 1) by increasing basal respiration likely through promoting complex V conformations that enhance proton leak, and 2) by increasing overall respiratory efficiency and NADH consumption by enhancing formation and/or stability of complex I-containing respiratory supercomplexes, though the specific molecular mechanisms underlying each of these remain unresolved.

MC4R Localizes at Excitatory Postsynaptic and Peri-Postsynaptic Sites of Hypothalamic Neurons in Primary Culture

The melanocortin-4 receptor (MC4R) is a G protein-coupled receptor (GPCR) that is expressed in several brain locations encompassing the hypothalamus and the brainstem, where the receptor controls several body functions, including metabolism. In a well-defined pathway to decrease appetite, hypothalamic proopiomelanocortin (POMC) neurons localized in the arcuate nucleus (Arc) project to MC4R neurons in the paraventricular nuclei (PVN) to release the natural MC4R agonist α-melanocyte-stimulating hormone (α-MSH). Arc neurons also project excitatory glutamatergic fibers to the MC4R neurons in the PVN for a fast synaptic transmission to regulate a satiety pathway potentiated by α-MSH. By using super-resolution microscopy, we found that in hypothalamic neurons in a primary culture, postsynaptic density protein 95 (PSD95) colocalizes with GluN1, a subunit of the ionotropic N-methyl-D-aspartate receptor (NMDAR). Thus, hypothalamic neurons form excitatory postsynaptic specializations. To study the MC4R distribution at these sites, tagged HA-MC4R under the synapsin promoter was expressed in neurons by adeno-associated virus (AAV) gene transduction. HA-MC4R immunofluorescence peaked at the center and in proximity to the PSD95- and NMDAR-expressing sites. These data provide morphological evidence that MC4R localizes together with glutamate receptors at postsynaptic and peri-postsynaptic sites.

Advances in the Synthesis and Physiological Metabolic Regulation of Nicotinamide Mononucleotide

Nicotinamide mononucleotide (NMN), the direct precursor of nicotinamide adenine dinucleotide (NAD+), is involved in the regulation of many physiological and metabolic reactions in the body. NMN can indirectly affect cellular metabolic pathways, DNA repair, and senescence, while also being essential for maintaining tissues and dynamic metabolic equilibria, promoting healthy aging. Therefore, NMN has found many applications in the food, pharmaceutical, and cosmetics industries. At present, NMN synthesis strategies mainly include chemical synthesis and biosynthesis. Despite its potential benefits, the commercial production of NMN by organic chemistry approaches faces environmental and safety problems. With the rapid development of synthetic biology, it has become possible to construct microbial cell factories to produce NMN in a cost-effective way. In this review, we summarize the chemical and biosynthetic strategies of NMN, offering an overview of the recent research progress on host selection, chassis cell optimization, mining of key enzymes, metabolic engineering, and adaptive fermentation strategies. In addition, we also review the advances in the role of NMN in aging, metabolic diseases, and neural function. This review provides comprehensive technical guidance for the efficient biosynthesis of NMN as well as a theoretical basis for its application in the fields of food, medicine, and cosmetics.

Priming central sound processing circuits through induction of spontaneous activity in the cochlea before hearing onset

Sensory systems experience a period of intrinsically generated neural activity before maturation is complete and sensory transduction occurs. Here we review evidence describing the mechanisms and functions of this 'spontaneous' activity in the auditory system. Both ex vivo and in vivo studies indicate that this correlated activity is initiated by non-sensory supporting cells within the developing cochlea, which induce depolarization and burst firing of groups of nearby hair cells in the sensory epithelium, activity that is conveyed to auditory neurons that will later process similar sound features. This stereotyped neural burst firing promotes cellular maturation, synaptic refinement, acoustic sensitivity, and establishment of sound-responsive domains in the brain. While sensitive to perturbation, the developing auditory system exhibits remarkable homeostatic mechanisms to preserve periodic burst firing in deaf mice. Preservation of this early spontaneous activity in the context of deafness may enhance the efficacy of later interventions to restore hearing.

ATP biosensor reveals microbial energetic dynamics and facilitates bioproduction

Adenosine-5'-triphosphate (ATP), the primary energy currency in cellular processes, drives metabolic activities and biosynthesis. Despite its importance, understanding intracellular ATP dynamics' impact on bioproduction and exploiting it for enhanced bioproduction remains largely unexplored. Here, we harness an ATP biosensor to dissect ATP dynamics across different growth phases and carbon sources in multiple microbial strains. We find transient ATP accumulations during the transition from exponential to stationary growth phases in various conditions, coinciding with fatty acid (FA) and polyhydroxyalkanoate (PHA) production in Escherichia coli and Pseudomonas putida, respectively. We identify carbon sources (acetate for E. coli, oleate for P. putida) that elevate steady-state ATP levels and boost FA and PHA production. Moreover, we employ ATP dynamics as a diagnostic tool to assess metabolic burden, revealing bottlenecks that limit limonene bioproduction. Our results not only elucidate the relationship between ATP dynamics and bioproduction but also showcase its value in enhancing bioproduction in various microbial species.

Fueling the heartbeat: Dynamic regulation of intracellular ATP during excitation-contraction coupling in ventricular myocytes

The heart beats approximately 100,000 times per day in humans, imposing substantial energetic demands on cardiac muscle. Adenosine triphosphate (ATP) is an essential energy source for normal function of cardiac muscle during each beat, as it powers ion transport, intracellular Ca2+ handling, and actin-myosin cross-bridge cycling. Despite this, the impact of excitation-contraction coupling on the intracellular ATP concentration ([ATP]i) in myocytes is poorly understood. Here, we conducted real-time measurements of [ATP]i in ventricular myocytes using a genetically encoded ATP fluorescent reporter. Our data reveal rapid beat-to-beat variations in [ATP]i. Notably, diastolic [ATP]i was <1 mM, which is eightfold to 10-fold lower than previously estimated. Accordingly, ATP-sensitive K+ (KATP) channels were active at physiological [ATP]i. Cells exhibited two distinct types of ATP fluctuations during an action potential: net increases (Mode 1) or decreases (Mode 2) in [ATP]i. Mode 1 [ATP]i increases necessitated Ca2+ entry and release from the sarcoplasmic reticulum (SR) and were associated with increases in mitochondrial Ca2+. By contrast, decreases in mitochondrial Ca2+ accompanied Mode 2 [ATP]i decreases. Down-regulation of the protein mitofusin 2 reduced the magnitude of [ATP]i fluctuations, indicating that SR-mitochondrial coupling plays a crucial role in the dynamic control of ATP levels. Activation of β-adrenergic receptors decreased [ATP]i, underscoring the energetic impact of this signaling pathway. Finally, our work suggests that cross-bridge cycling is the largest consumer of ATP in a ventricular myocyte during an action potential. These findings provide insights into the energetic demands of EC coupling and highlight the dynamic nature of ATP concentrations in cardiac muscle.

Development of the IMP biosensor for rapid and stable analysis of IMP concentrations in fermentation broth

IMP (inosinic acid) is a crucial intermediate in the purine metabolic pathway and is continuously synthesized in all cells. Besides its role as a precursor for DNA and RNA, IMP also plays a critical or essential role in cell growth, energy storage, conversion, and metabolism. In our study, we utilized the circularly permuted fluorescent protein (cpFP) and IMP dehydrogenase to screen and develop the IMP biosensor, IMPCP1. By introducing a mutation in the catalytically active site of IMPCP1, from Cys to Ala, we disrupted its ability to catalyze IMP while retaining its capability to bind to IMP without affecting the IMP concentration in the sample. To immobilize IMPCP1, we employed the SpyCatcher/SpyTag system and securely attached it to Magarose-Epoxy, resulting in the development of the IMP rapid test kit, referred to as IMPTK. The biosensor integrated into IMPTK offers enhanced stability, resistance to degradation activity, and specific recognition of IMP. It is also resistant to peroxides and temperature changes. IMPTK serves as a rapid and stable assay for analyzing IMP concentrations in fermentation broth. Within the linear range of IMP concentrations, it can be utilized as a substitute for HPLC. The IMPTK biosensor provides a reliable and efficient alternative for monitoring IMP levels, offering advantages such as speed, stability, and resistance to environmental factors.

Neurotransmitter accumulation and Parkinson's disease-like phenotype caused by anion channelrhodopsin opto-controlled astrocytic mitochondrial depolarization in substantia nigra pars compacta

Parkinson's disease (PD) is a mitochondria-related neurodegenerative disease characterized by locomotor deficits and loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNc). Majority of PD research primarily focused on neuronal dysfunction, while the roles of astrocytes and their mitochondria remain largely unexplored. To bridge the gap and investigate the roles of astrocytic mitochondria in PD progression, we constructed a specialized optogenetic tool, mitochondrial-targeted anion channelrhodopsin, to manipulate mitochondrial membrane potential in astrocytes. Utilizing this tool, the depolarization of astrocytic mitochondria within the SNc in vivo led to the accumulation of γ-aminobutyric acid (GABA) and glutamate in SNc, subsequently resulting in excitatory/inhibitory imbalance and locomotor deficits. Consequently, in vivo calcium imaging and interventions of neurotransmitter antagonists demonstrated that GABA accumulation mediated movement deficits of mice. Furthermore, 1 h/day intermittent astrocytic mitochondrial depolarization for 2 weeks triggered spontaneous locomotor dysfunction, α-synuclein aggregation, and the loss of DA neurons, suggesting that astrocytic mitochondrial depolarization was sufficient to induce a PD-like phenotype. In summary, our findings suggest the maintenance of proper astrocytic mitochondrial function and the reinstatement of a balanced neurotransmitter profile may provide a new angle for mitigating neuronal dysfunction during the initial phases of PD.

iATPSnFR2: A high-dynamic-range fluorescent sensor for monitoring intracellular ATP

We developed a significantly improved genetically encoded quantitative adenosine triphosphate (ATP) sensor to provide real-time dynamics of ATP levels in subcellular compartments. iATPSnFR2 is a variant of iATPSnFR1, a previously developed sensor that has circularly permuted superfolder green fluorescent protein (GFP) inserted between the ATP-binding helices of the ε-subunit of a bacterial F0-F1 ATPase. Optimizing the linkers joining the two domains resulted in a ~fivefold to sixfold improvement in the dynamic range compared to the previous-generation sensor, with excellent discrimination against other analytes, and affinity variants varying from 4 µM to 500 µM. A chimeric version of this sensor fused to either the HaloTag protein or a suitable spectrally separated fluorescent protein provides an optional ratiometric readout allowing comparisons of ATP across cellular regions. Subcellular targeting the sensor to nerve terminals reveals previously uncharacterized single-synapse metabolic signatures, while targeting to the mitochondrial matrix allowed direct quantitative probing of oxidative phosphorylation dynamics.

Mechanical activation of VE-cadherin stimulates AMPK to increase endothelial cell metabolism and vasodilation

Endothelia cells respond to mechanical force by stimulating cellular signaling, but how these pathways are linked to elevations in cell metabolism and whether metabolism supports the mechanical response remains poorly understood. Here, we show that application of force to VE-cadherin stimulates liver kinase B1 (LKB1) to activate AMP-activated protein kinase (AMPK), a master regulator of energy homeostasis. VE-cadherin stimulated AMPK increases eNOS activity and localization to the plasma membrane as well as reinforcement of the actin cytoskeleton and cadherin adhesion complex, and glucose uptake. We present evidence for the increase in metabolism being necessary to fortify the adhesion complex, actin cytoskeleton, and cellular alignment. Together these data extend the paradigm for how mechanotransduction and metabolism are linked to include a connection to vasodilation, thereby providing new insight into how diseases involving contractile, metabolic, and vasodilatory disturbances arise.

Modular Engineering of Aptamer-Based Nanobiotechnology for Conditional Control of ATP Sensing

Dynamic changes of intracellular, extracellular, and subcellular adenosine triphosphates (ATPs) have fundamental interdependence with the physio-pathological states of cells. Spatially selective in situ imaging of such ATP dynamics offers valuable mechanistic insights into the related biological activities. Despite significant advances in the design of aptamer sensors for ATP detection, the dearth of methods that enable precise ATP imaging in specific cellular locations remains a challenge in this field. This review focuses on the modular engineering of regulatable sensing technology via the integration of aptamer probe designs with advanced functional nanomaterials, allowing conditional control of ATP sensing and imaging with high spatial precision from subcellular organelles to living animals. Highlighting the recent advances in the design of photo-triggered nanosensors for spatiotemporally controlled ATP imaging, endogenously-triggered ATP sensing in a cell-selective manner, and spatially-controlled nanodevices for ATP imaging in specific organelles and extracellular microenvironments. Emphasis will be put on elucidating the principles of how nanotechnology can be applied to regulate the spatial precision of aptamer-based ATP sensing activities. The authors envision that this perspective provides insights into the engineering of aptamer-based nanobiotechnology for opening new frontiers in precise molecular sensing and other bio-applications.

Imaging of extracellular and intracellular ATP in pancreatic beta cells reveals correlation between glucose metabolism and purinergic signalling

Adenosine triphosphate (ATP) is a universal energy molecule and yet cells release it and extracellular ATP is an important signalling molecule between cells. Monitoring of ATP levels outside of cells is important for our understanding of physiological and pathophysiological processes in cells/tissues. Here, we focus on pancreatic beta cells (INS-1E) and test the hypothesis that there is an association between intra- and extracellular ATP levels which depends on glucose provision. We imaged real-time changes in extracellular ATP in pancreatic beta cells using two sensors tethered to extracellular aspects of the plasma membrane (eATeam3.10, iATPSnFR1.0). Increase in glucose induced fast micromolar ATP release to the cell surface, depending on glucose concentrations. Chronic pre-treatment with glucose increased the basal ATP signal. In addition, we co-expressed intracellular ATP sensors (ATeam1.30, PercevalHR) in the same cultures and showed that glucose induced fast increases in extracellular and intracellular ATP. Glucose and extracellular ATP stimulated glucose transport monitored by the glucose sensor (FLII12Pglu-700uDelta6). In conclusion, we propose that in beta cells there is a dynamic relation between intra- and extracellular ATP that depends on glucose transport and metabolism and these processes may be tuned by purinergic signalling. Future development of ATP sensors for imaging may aid development of novel approaches to target extracellular ATP in, for example, type 2 diabetes mellitus therapy.