Genetically Encoded ATP Biosensors for Direct Monitoring of Cellular ATP Dynamics

A guide to genetically-encoded redox biosensors: State of the art and opportunities

Genetically-encoded redox biosensors have become invaluable tools for monitoring cellular redox processes with high spatiotemporal resolution, coupling the presence of the redox-active analyte with a change in fluorescence signal that can be easily recorded. This review summarizes the available fluorescence recording methods and presents an in-depth classification of the redox biosensors, organized by the analytes they respond to. In addition to the fluorescent protein-based architectures, this review also describes the recent advances on fluorescent, chemigenetic-based redox biosensors and other emerging chemigenetic strategies. This review examines how these biosensors are designed, the biosensors sensing mechanism, and their practical advantages and disadvantages.

L-Theanine Prolongs the Lifespan by Activating Multiple Molecular Pathways in Ultraviolet C-Exposed Caenorhabditis elegans

L-theanine, a unique non-protein amino acid, is an important bioactive component of green tea. Previous studies have shown that L-theanine has many potent health benefits, such as anti-anxiety effects, regulation of the immune response, relaxing neural tension, and reducing oxidative damage. However, little is known concerning whether L-theanine can improve the clearance of mitochondrial DNA (mtDNA) damage in organisms. Here, we reported that L-theanine treatment increased ATP production and improved mitochondrial morphology to extend the lifespan of UVC-exposed nematodes. Mechanistic investigations showed that L-theanine treatment enhanced the removal of mtDNA damage and extended lifespan by activating autophagy, mitophagy, mitochondrial dynamics, and mitochondrial unfolded protein response (UPRmt) in UVC-exposed nematodes. In addition, L-theanine treatment also upregulated the expression of genes related to mitochondrial energy metabolism in UVC-exposed nematodes. Our study provides a theoretical basis for the possibility that tea drinking may prevent mitochondrial-related diseases.

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.

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.

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 production and consumption are highly compartmentalized in mammalian cells. Yet methods to measure acetyl-CoA in living cells are lacking. In this work, we engineer an acetyl-CoA biosensor from the bacterial protein PanZ and circularly permuted green fluorescent protein (cpGFP). We biochemically characterize the sensor and demonstrate its selectivity for acetyl-CoA over other CoA species. We then deploy the biosensor in E. coli and HeLa cells to demonstrate its utility in living cells. In E. coli, we show that the biosensor enables detection of rapid changes in acetyl-CoA levels. In human cells, we show that the biosensor enables subcellular detection and reveals the compartmentalization of acetyl-CoA metabolism.

Resveratrol Promotes Proliferation, Antioxidant Properties, and Progesterone Production in Yak (Bos grunniens) Granulosa Cells

Resveratrol (RES) is a class of natural polyphenolic compounds known for its strong anti-apoptotic and antioxidant properties. Granulosa cells (GCs) are one of the important components of ovarian follicles and play crucial roles in follicular development of follicles in the ovary. Here, we explored the effects of RES on the proliferation and functions of yak GCs. Firstly, we evaluated the effect of RES dose and time in culture on the viability of GCs, and then the optimum treatment protocol (10 μM RES, 36 h) was selected to analyze the effects of RES on the proliferation, cell cycle, apoptosis, malondialdehyde (MDA), glutathione (GSH), reactive oxygen species (ROS) accumulation, lipid droplet content, ATP production, and steroidogenesis of GCs, as well as the expression of related genes. The results show that RES treatment significantly (1) increased cell viability and proliferation and inhibited cell apoptosis by upregulating BCL-2 and SIRT1 genes and downregulating BAX, CASP3, P53, and KU70 genes; (2) increased the proportion of GCs in the S phase and upregulated CCND1, PCNA, CDK4, and CDK5 genes; (3) reduced ROS accumulation and MDA content and increased GSH content, as well as upregulating the relative expression levels of CAT, SOD2, and GPX1 genes; (4) decreased lipid droplet content and increased ATP production; (5) promoted progesterone (P4) secretion and the expression of P4 synthesis-related genes (StAR, HSD3B1, and CYP11A1); and (6) inhibited E2 secretion and CYP19A1 expression. These findings suggest that RES at 10 μM increases the proliferation and antioxidant properties, inhibits apoptosis, and promotes ATP production, lipid droplet consumption, and P4 secretion of yak GCs.

Natural products and mitochondrial allies in colorectal cancer therapy

Colorectal cancer (CRC) is a globally prevalent malignancy with a high potential for metastasis. Existing cancer treatments have limitations, including drug resistance and adverse effects. Researchers are striving to develop effective therapies to address these challenges. Impressively, contemporary research has discovered that many natural products derived from foods, plants, insects, and marine invertebrates can suppress the progression, metastasis, and invasion of CRC. In this review, we conducted a comprehensive search of the CNKI, PubMed, Embase, and Web of Science databases from inception to April 2023 to evaluate the efficacy of natural products targeting mitochondria to fight against CRC. Mitochondria are intracellular energy factories involved in cell differentiation, signal transduction, cell cycle regulation, apoptosis, and tumorigenesis. The identified natural products have been classified and summarized based on their mechanisms of action. These findings indicate that natural products can induce apoptosis in colorectal cancer cells by inhibiting the mitochondrial respiratory chain, ROS elevation, disruption of mitochondrial membrane potential, the release of pro-apoptotic factors, modulation of the Bcl-2 protein family to facilitate cytochrome c release, induction of apoptotic vesicle activity by activating the caspase protein family, and selective targeting of mitochondrial division. Furthermore, diverse apoptotic signaling pathways targeting mitochondria, such as the MAPK, p53, STAT3, JNK and AKT pathway, have been triggered by natural products. Natural products such as diosgenin, allopurinol, and clausenidin have demonstrated low toxicity, high efficacy, and multi-targeted properties. Mitochondria-targeting natural products have great potential for overcoming the challenges of CRC therapy.

Lobetyolin inhibits cell proliferation and induces cell apoptosis by downregulating ASCT2 in gastric cancer

Gastric cancer (GC) is a heterogeneous disease and is the fifth most common cancer worldwide. Lobetyolin, as a bioactive ingredient extracted from Codonopsis pilosula (Franch.) Nannf., has been reported to exert anti-tumor effects in several cancer types. This study was aimed to investigate the role of lobetyolin in GC and the associated mechanism. MKN-45 and MKN-28 cells were incubated with concentrations of lobetyolin for 24 h. The viability and survival of GC cells were evaluated by performing MTT assay. Glutamine uptake, Adenosine Triphosphate, reactive oxygen species (ROS), and glutathione levels were measured by corresponding kits. Apoptosis and mitochondrial membrane potential of GC cells were determined by flow cytometry. Alanine, serine, cysteine-preferring transporter 2 (ASCT2) and the AKT/GSK3β/c-Myc pathway protein levels were examined by western blotting. Xenograft model and immunohistochemical staining were used to evaluate the pharmacological effects of lobetyolin in mice in vivo. We found that lobetyolin treatment suppressed the proliferative capacity of both MKN-45 and MKN-28 cells in a concentration-dependent manner. Lobetyolin reduced the uptake of glutamine and downregulated the expression levels of ASCT2 in GC cells and xenograft tumors. Lobetyolin effectively restrained the growth of tumors in vivo. In addition, lobetyolin induced the accumulation of ROS to attenuate mitochondria-mediated apoptosis via downregulation of ASCT2 expression. Lobetyolin promoted the phosphorylation of c-Myc and suppressed the phosphorylation of GSK3β and AKT in both MKN-45 and MKN-28 cells. The level of total Nrf2 protein was reduced after lobetyolin treatment. Overall, lobetyolin exerts anti-cancer effects by repressing cell proliferation and inducing cell apoptosis via downregulation of ASCT2 in GC.

Intracellular energy production and distribution in hypoxia

The hydrolysis of ATP is the primary source of metabolic energy for eukaryotic cells. Under physiological conditions, cells generally produce more than sufficient levels of ATP to fuel the active biological processes necessary to maintain homeostasis. However, mechanisms underpinning the distribution of ATP to subcellular microenvironments with high local demand remain poorly understood. Intracellular distribution of ATP in normal physiological conditions has been proposed to rely on passive diffusion across concentration gradients generated by ATP producing systems such as the mitochondria and the glycolytic pathway. However, subcellular microenvironments can develop with ATP deficiency due to increases in local ATP consumption. Alternatively, ATP production can be reduced during bioenergetic stress during hypoxia. Mammalian cells therefore need to have the capacity to alter their metabolism and energy distribution strategies to compensate for local ATP deficits while also controlling ATP production. It is highly likely that satisfying the bioenergetic requirements of the cell involves the regulated distribution of ATP producing systems to areas of high ATP demand within the cell. Recently, the distribution (both spatially and temporally) of ATP-producing systems has become an area of intense investigation. Here, we review what is known (and unknown) about intracellular energy production and distribution and explore potential mechanisms through which this targeted distribution can be altered in hypoxia, with the aim of stimulating investigation in this important, yet poorly understood field of research.

Antibody gene transfer treatment drastically improves epidermal pathology in a keratitis ichthyosis deafness syndrome model using male mice

BACKGROUND

Keratitis ichthyosis deafness (KID) syndrome is a rare disorder caused by hemichannel (HC) activating gain-of-function mutations in the GJB2 gene encoding connexin (Cx) 26, for which there is no cure, or current treatments based upon the mechanism of disease causation.

METHODS

We applied Adeno Associated Virus (AAV) mediated mAb gene transfer (AAVmAb) to treat the epidermal features of KID syndrome with a well-characterized HC blocking antibody using male mice of a murine model that replicates the skin pathology of the human disease.

FINDINGS

We demonstrate that in vivo AAVmAb treatment significantly reduced the size and thickness of KID lesions, in addition to blocking activity of mutant HCs in the epidermis in vivo. We also show that AAVmAb treatment eliminated abnormal keratinocyte proliferation and enlarged cell size, decreased apoptosis, and restored the normal distribution of keratin expression.

INTERPRETATION

Our findings reinforce the critical role played by increased HC activity in the skin pathology associated with KID syndrome. They also underscore the clinical potential of anti-HC mAbs coupled with genetic based delivery systems for treating the underlying mechanistic basis of this disorder. Inhibition of HC activity is an ideal therapeutic target in KID syndrome, and the genetic delivery of mAbs targeted against mutant HCs could form the basis of new therapeutic interventions to treat this incurable disease.

FUNDING

Fondazione Telethon grant GGP19148 and University of Padova grant Prot. BIRD187130 to FM; Foundation for Ichthyosis and Related Skin Types (FIRST) and National Institutes of Health grant EY 026911 to TWW.

Real-Time Visualization of Cytosolic and Mitochondrial ATP Dynamics in Response to Metabolic Stress in Cultured Cells

Adenosine 5' triphosphate (ATP) is the energy currency of life, which is produced in mitochondria (~90%) and cytosol (less than 10%). Real-time effects of metabolic changes on cellular ATP dynamics remain indeterminate. Here we report the design and validation of a genetically encoded fluorescent ATP indicator that allows for real-time, simultaneous visualization of cytosolic and mitochondrial ATP in cultured cells. This dual-ATP indicator, called smacATPi (simultaneous mitochondrial and cytosolic ATP indicator), combines previously described individual cytosolic and mitochondrial ATP indicators. The use of smacATPi can help answer biological questions regarding ATP contents and dynamics in living cells. As expected, 2-deoxyglucose (2-DG, a glycolytic inhibitor) led to substantially decreased cytosolic ATP, and oligomycin (a complex V inhibitor) markedly decreased mitochondrial ATP in cultured HEK293T cells transfected with smacATPi. With the use of smacATPi, we can also observe that 2-DG treatment modestly attenuates mitochondrial ATP and oligomycin reduces cytosolic ATP, indicating the subsequent changes of compartmental ATP. To evaluate the role of ATP/ADP carrier (AAC) in ATP trafficking, we treated HEK293T cells with an AAC inhibitor, Atractyloside (ATR). ATR treatment attenuated cytosolic and mitochondrial ATP in normoxia, suggesting AAC inhibition reduces ADP import from the cytosol to mitochondria and ATP export from mitochondria to cytosol. In HEK293T cells subjected to hypoxia, ATR treatment increased mitochondrial ATP along with decreased cytosolic ATP, implicating that ACC inhibition during hypoxia sustains mitochondrial ATP but may not inhibit the reversed ATP import from the cytosol. Furthermore, both mitochondrial and cytosolic signals decrease when ATR is given in conjunction with 2-DG in hypoxia. Thus, real-time visualization of spatiotemporal ATP dynamics using smacATPi provides novel insights into how cytosolic and mitochondrial ATP signals respond to metabolic changes, providing a better understanding of cellular metabolism in health and disease.

Antimicrobial effect of sorbic acid-loaded chitosan/tripolyphosphate nanoparticles on Pseudomonas aeruginosa

Sorbic acid-loaded chitosan/tripolyphosphate nanoparticles (SANs) have previously been shown to exert both antibacterial and antioxidant effects on Chinese sausage. In this study, the minimum inhibitory concentrations (MICs) of SANs against two Pseudomonas aeruginosa strains were determined. The blank control group (BC) served as the negative control, while the chitosan/tripolyphosphate nanoparticles (CTNs) group and free sorbic acid (SA) group served as the positive controls. Tests conducted under five different pH conditions (5/6/7/8/9) revealed that the SANs exhibited a good bacteriostatic effect against P. aeruginosa. Variations in the metabolism, cell membrane or cell wall integrity, and morphology of P. aeruginosa were measured to evaluate the effects of SANs on their intracellular and extracellular components. The MIC of SANs for the two P. aeruginosa strains was determined to be 150 μg/mL. SANs delayed the growth of P. aeruginosa and severely damaged both its inner and outer cell membranes. The heteromorphism of the bacteria as observed by field emission scanning electron microscopy (FESEM), verified the aforementioned results. The results showed SANs could effectively inhibit the growth of P. aeruginosa and exert antibacterial ability in a wider range of acid-base environments. This study broadens the application of SANs in food processing and provides experimental basis.

Application of the Luminescent luxCDABE Gene for the Rapid Screening of Antibacterial Substances Targeting Pseudomonas aeruginosa

Pseudomonas aeruginosa (P. aeruginosa) is a typical Gram-negative bacterium that can cause the spoilage of catered food products. Using a luminescent reporter gene (luxCDABE), this study sought to construct a cell-based biosensor (PAO1-CE) to rapidly screen antibacterial substances against P. aeruginosa. A total of six antibiotics belonging to five categories were used as the model test substances. The results of the bioluminescence detection method were verified using traditional antibacterial research assessments. The correlation coefficient of the regression equation fitting the data generated using this method was greater than 0.98, supporting the credibility of this approach. Additionally, the EC₅₀ of each of the antibiotics assessed in this study was lower than the 1/2 MIC determined by conventional means. All six of the antibiotics caused varying degrees of damage to the cell membrane and cell wall of P. aeruginosa. Importantly, this novel method helped shorten the time necessary for active-compound detection and could be used for high-throughput detection, which would also help improve the detection efficiency. The application of this method towards the discovery of novel antibacterial compounds targeting P. aeruginosa holds substantial promise for greatly improving the efficiency of compound discovery.

Study on the toxic effects of sodium pentachlorophenol (PCP-Na) on razor clam (Sinonovacula constricta)

Currently, research on toxic effects of PCP Na is greatly insufficient. The aim of this study is to explore the toxic effects of PCP-Na for better conducting future work on PCP-Na toxicology. For this purpose, S. constricta adults were exposed to PCP-Na for toxicity testing. The results showed that PCP-Na could easily bioaccumulate in S. constricta and significantly affected both phrase I and II metabolism enzymes. Meanwhile, PCP-Na strongly activated antioxidant system and caused PC, LPO and DNA damage. In addition, neurotoxicity and immunotoxicity of PCP-Na was demonstrated in this study. Interestingly, we observed that PCP-Na significantly affected the expression of genes of electron transport chain and induced key enzymes of glycolysis, indicating that PCP-Na may act as an uncoupler of oxidative phosphorylation, interfering with energy supply and causing energy compensation. This study is the first to fully analyze and provide a new perspective on the toxicity of PCP-Na.