ATP Production Rate Research Articles

The Role of Deuterium 2H in the Pathogenesis of Heart Failure as Deduced by Food Studies from Six Individual Cases

Heart failure results from the loss of structural integrity of the heart and/or a decrease in the rate of maximal ATP production. In cases of relatively preserved structural integrity, a decrease in ATP production in the mitochondria leads to a decrease in the cardiac stroke volume, thereby increasing the heart rate required to maintain the cardiac output. For many years, the exact location of this defect in the metabolic energy cycle remained elusive. Evidence is presented here to show that it is not a single metabolic substrate involved but rather the heavy isotope of hydrogen 2H, deuterium, that is jamming the ATP nanomotors slowing the rate of ATP production. During the digestion of a meal, the cardiac heart rate is shown to be very sensitive to the level of deuterium contained in the fatty acids recently consumed. During strenuous exercise in the fasting state, the enzyme adipose triglyceride lipase (ATGL) is found to mobilize the highest deuterium triglycerides more rapidly than the healthier lower deuterium triglycerides, converting the adipose tissue into a deuterium-depleted energy pool. This is believed to contribute to the low resting heart rates frequently observed in athletes. In vulnerable individuals, i.e., those weakened by disease(s) or space explorers in a weightless environment, the decreased ability to perform strenuous exercise leads to higher deuterium levels in their adipose tissue compromising their ATP production. In these individuals, maintaining healthy deuterium levels is best achieved by an increased intake of lower deuterium-containing foods.

Synthetic NAD(P)(H) Cycle for ATP Regeneration.

ATP is the energy currency of the cell and new methods for ATP regeneration will benefit a range of emerging biotechnology applications including synthetic cells. We designed and assembled a membraneless ATP-regenerating enzymatic cascade by exploiting the substrate specificities of selected NAD(P)(H)-dependent oxidoreductases combined with substrate-specific kinases. The enzymes in the NAD(P)(H) cycle were selected to avoid cross-reactions, and the cascade was driven by irreversible fuel oxidation. As a proof-of-concept, formate oxidation was chosen as the fueling reaction. ATP regeneration was accomplished via the phosphorylation of NADH to NADPH and the subsequent transfer of the phosphate to ADP by a reversible NAD+ kinase. The cascade was able to regenerate ATP at a high rate (up to 0.74 mmol/L/h) for hours, and >90% conversion of ADP to ATP using monophosphate was also demonstrated. The cascade was used to regenerate ATP for use in cell free protein synthesis reactions, and the ATP production rate was further enhanced when powered by the multistep oxidation of methanol. The NAD(P)(H) cycle provides a simple cascade for the in vitro regeneration of ATP without the need for a pH-gradient or costly phosphate donors.

IGF-1 Stimulates Glycolytic ATP Production in MCF-7L Cells.

The Insulin-like Growth Factor (IGF) system in breast cancer progression has been a matter of interest for decades, but targeting this system did not result in a successful clinical strategy. The system's complexity and homology of its two receptors-insulin receptor (IR) and type 1 insulin-like growth factor receptor (IGF-1R)-are possible causes. The IGF system maintains cell proliferation and also regulates metabolism, making it a pathway to explore. To understand the metabolic phenotype of breast cancer cells, we quantified their real-time ATP production rate upon acute stimulation with ligands-insulin-like growth factor 1 (1GF-1) and insulin. MCF-7L cells express both IGF-1R and IR, while tamoxifen-resistant MCF-7L (MCF-7L TamR) cells have downregulated IGF-1R with unchanged IR levels. Treating MCF-7L cells with 5 nM IGF-1 increased the glycolytic ATP production rate, while 10 nM insulin did not affect metabolism when compared with the control. Neither treatment altered ATP production in MCF-7L TamR cells. This study provides evidence of the relationship between metabolic dysfunction, cancer, and the IGF axis. In these cells, IGF-1R, and not IR, regulates ATP production.

Investigating the effects of 7-ketocholesterol on retinal pigment epithelium bioenergetics.

Age-related macular degeneration (AMD) is associated with formation of drusen, clusters of lipids, and oxidized lipid products under the retinal pigment epithelium (RPE). 7-Ketocholesterol (7KC) is a form of oxidized cholesterol present in drusen and is hypothesized to play a role in AMD pathogenesis. The association of 7KC with cellular toxicity and inflammation, key elements of AMD pathology, has been demonstrated. However, the effects of 7KC on altering RPE bioenergetics, a potentially important pathologic process in AMD, are unclear. Herein, we describe the effects of non-lethal doses of 7KC on the bioenergetics and phenotype of RPE cells in culture. Metabolic analysis demonstrated a significant dose-dependent increase in total ATP production rates that was driven primarily by an increase in glycolysis. The increase in glycolysis was accompanied by an increase in glucose uptake and increased expression of hexokinase 1. Increased levels of Translocase of Outer Mitochondrial Membrane 20and NADH:Ubiquinone Oxidoreductase Core Subunit S1, Succinate dehydrogenase, Ubiquinol-Cytochrome C Reductase Core Protein 2, Cytochrome C Oxidase II, and ATP synthase subunit beta, proteins involved in oxidative phosphorylation (OXPHOS), were also seen. However, specific electron transport chain activity remained unchanged. 7KC-treated cells also demonstrated a change in cellular morphology with decreased expression of epithelial markers. In summary, 7KC has significant effects on the bioenergetics and morphology of RPE cells reflective of findings seen in clinical AMD.

A combined computational and functional approach identifies IGF2BP2 as a driver of chemoresistance in a wide array of pre-clinical models of colorectal cancer

AimChemoresistance is a major cause of treatment failure in colorectal cancer (CRC) therapy. In this study, the impact of the IGF2BP family of RNA-binding proteins on CRC chemoresistance was investigated using in silico, in vitro, and in vivo approaches.MethodsGene expression data from a well-characterized cohort and publicly available cross-linking immunoprecipitation sequencing (CLIP-Seq) data were collected. Resistance to chemotherapeutics was assessed in patient-derived xenografts (PDXs) and patient-derived organoids (PDOs). Functional studies were performed in 2D and 3D cell culture models, including proliferation, spheroid growth, and mitochondrial respiration analyses.ResultsWe identified IGF2BP2 as the most abundant IGF2BP in primary and metastastatic CRC, correlating with tumor stage in patient samples and tumor growth in PDXs. IGF2BP2 expression in primary tumor tissue was significantly associated with resistance to selumetinib, gefitinib, and regorafenib in PDOs and to 5-fluorouracil and oxaliplatin in PDX in vivo. IGF2BP2 knockout (KO) HCT116 cells were more susceptible to regorafenib in 2D and to oxaliplatin, selumitinib, and nintedanib in 3D cell culture. Further, a bioinformatic analysis using CLIP data suggested stabilization of target transcripts in primary and metastatic tumors. Measurement of oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) revealed a decreased basal OCR and an increase in glycolytic ATP production rate in IGF2BP2 KO. In addition, real-time reverse transcriptase polymerase chain reaction (qPCR) analysis confirmed decreased expression of genes of the respiratory chain complex I, complex IV, and the outer mitochondrial membrane in IGF2BP2 KO cells.ConclusionsIGF2BP2 correlates with CRC tumor growth in vivo and promotes chemoresistance by altering mitochondrial respiratory chain metabolism. As a druggable target, IGF2BP2 could be used in future CRC therapy to overcome CRC chemoresistance.

ANT2 Accelerates Cutaneous Wound Healing in Aged Skin by Regulating Energy Homeostasis and Inflammation

An effective healing response is critical to healthy aging. In particular, energy homeostasis has become increasingly recognized as a factor in effective skin regeneration. Adenine nucleotide translocase 2 (ANT2) is a mediator of ATP import into mitochondria for energy homeostasis. Although energy homeostasis and mitochondrial integrity are critical for wound healing, the role played by ANT2 in the repair process had not been elucidated to date. In our study, we found that ANT2 expression decreased in aged skin and cellular senescence. Interestingly, overexpression of ANT2 in aged mouse skin accelerated the healing of full-thickness cutaneous wounds. In addition, upregulation of ANT2 in replicative senescent human diploid dermal fibroblasts (HDFs) induced their proliferation and migration, which are critical processes in wound healing. Regarding energy homeostasis, ANT2 overexpression increased the ATP production rate by activating glycolysis and induced mitophagy. Notably, ANT2-mediated upregulation of HSPA6 in aged HDFs downregulated proinflammatory genes that mediate cellular senescence and mitochondrial damage. This study demonstrates a previously uncharacterized physiological role of ANT2 in skin wound healing via regulating cell proliferation, energy homeostasis and inflammation. Thus, our study links energy metabolism to skin homeostasis and reports to our knowledge previously unreported genetic factor that enhances wound healing in an aging model.

Mitochondrial Ca2+ dynamics differ between the left and right ventricles in murine and porcine hearts

Despite their differences in metabolism, mechanics, and developmental origin, the right ventricle (RV) is often assumed to function similarly to the left ventricle (LV). Specifically, though Ca 2+ transport into mitochondria is well established to play a crucial role in matching cardiac energy production to demand, little is known regarding whether mitochondrial Ca 2+ (mtCa 2+ ) handling is distinct in the RV and LV. Our objective was to test the hypothesis that the regulation of mtCa 2+ differs in the RV and LV. By isolating mitochondria from RV and LV free wall tissues from wild-type mice and healthy pigs, we compared several parameters indicative of Ca 2+ -regulated mitochondrial function. Basal mtCa 2+ levels were higher in RV mitochondria than in LV mitochondria. When successive boluses of Ca 2+ were administered to isolated mitochondria, RV mitochondria took up fewer Ca 2+ boluses, showing lower Ca 2+ retention capacity. RV mitochondria displayed relatively more protein carbonylation, suggesting oxidative stress. Interestingly, ATP production rate was higher in RV mitochondria relative to LV mitochondria; however, only LV mitochondria exhibited an increase in ATP production rate in the presence of Ca 2+ . We also compared the protein expression of the subunits of the mitochondrial Ca 2+ uniporter complex (MCUC) and the mitochondrial Na+/Ca 2+ exchanger (NCLX) and found that levels of the MCUC subunit Essential MCU Regulator (EMRE) and NCLX were higher in the LV than the RV, potentially facilitating more dynamic Ca 2+ transport in and out of LV mitochondria. Collectively, these data suggest that mtCa 2+ is calibrated to higher but more static levels in the RV, whereas in the LV basal mtCa 2+ is lower to ensure dynamic range for physiological stimuli to increase mitochondrial bioenergetics, corresponding to the larger changes in workload experienced by the LV. This study was supported by the National Institutes of Health (1K22HL137901 to Julia C. Liu) and by the Department of Integrative Biology and Physiology (to Jae Hwi Sung). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

GLUT1 is redundant in hypoxic and glycolytic nucleus pulposus cells of the intervertebral disc.

Glycolysis is central to homeostasis of nucleus pulposus (NP) cells in the avascular intervertebral disc. Since the glucose transporter, GLUT1, is a highly enriched phenotypic marker of NP cells, we hypothesized that it is vital for the development and postnatal maintenance of the disc. Surprisingly, primary NP cells treated with 2 well-characterized GLUT1 inhibitors maintained normal rates of glycolysis and ATP production, indicating intrinsic compensatory mechanisms. We showed in vitro that NP cells mitigated GLUT1 loss by rewiring glucose import through GLUT3. Of note, we demonstrated that substrates, such as glutamine and palmitate, did not compensate for glucose restriction resulting from dual inhibition of GLUT1/3, and inhibition compromised long-term cell viability. To investigate the redundancy of GLUT1 function in NP, we generated 2 NP-specific knockout mice: Krt19CreERT Glut1fl/fl and Foxa2Cre Glut1fl/fl. There were no apparent defects in postnatal disc health or development and maturation in mutant mice. Microarray analysis verified that GLUT1 loss did not cause transcriptomic alterations in the NP, supporting that cells are refractory to GLUT1 loss. These observations provide the first evidence to our knowledge of functional redundancy in GLUT transporters in the physiologically hypoxic intervertebral disc and underscore the importance of glucose as the indispensable substrate for NP cells.

Relationship between anticancer sensitivities and cellular respiration properties in 5-fluorouracil-resistant HCT116 human colorectal cancer cells.

5-Fluorouracil (5-FU) is widely used for colorectal cancer (CRC) treatment; however, continuous treatment of CRC cells with 5-FU can result in acquired resistance, and the underlying mechanism of 5-FU resistance remains unclear. We previously established an acquired 5-FU-resistant CRC cell line, HCT116RF10 , and examined its biological features and 5-FU resistance mechanisms. In this study, we evaluated the 5-FU sensitivity and cellular respiration dependency of HCT116RF10 cells and parental HCT116 cells under conditions of high- and low-glucose concentrations. Both HCT116RF10 and parental HCT116 cells were more sensitive to 5-FU under low-glucose conditions compared with high-glucose conditions. Interestingly, HCT116RF10 and parental HCT116 cells exhibited altered cellular respiration dependence for glycolysis and mitochondrial respiration under high- and low-glucose conditions. Additionally, HCT116RF10 cells showed a markedly decreased ATP production rate compared with HCT116 cells under both high- and low-glucose conditions. Importantly, glucose restriction significantly reduced the ATP production rate for both glycolysis and mitochondrial respiration in HCT116RF10 cells compared with HCT116 cells. The ATP production rates in HCT116RF10 and HCT116 cells were reduced by approximately 64% and 23%, respectively, under glucose restriction, suggesting that glucose restriction may be effective at enhancing 5-FU chemotherapy. Overall, these findings shed light on 5-FU resistance mechanisms, which may lead to improvements in anticancer treatment strategies.

FTY720-P, a Biased S1PR Ligand, Increases Mitochondrial Function through STAT3 Activation in Cardiac Cells.

FTY720 is an FDA-approved sphingosine derivative drug for the treatment of multiple sclerosis. This compound blocks lymphocyte egress from lymphoid organs and autoimmunity through sphingosine 1-phosphate (S1P) receptor blockage. Drug repurposing of FTY720 has revealed improvements in glucose metabolism and metabolic diseases. Studies also demonstrate that preconditioning with this compound preserves the ATP levels during cardiac ischemia in rats. The molecular mechanisms by which FTY720 promotes metabolism are not well understood. Here, we demonstrate that nanomolar concentrations of the phosphorylated form of FTY720 (FTY720-P), the active ligand of S1P receptor (S1PR), activates mitochondrial respiration and the mitochondrial ATP production rate in AC16 human cardiomyocyte cells. Additionally, FTY720-P increases the number of mitochondrial nucleoids, promotes mitochondrial morphology alterations, and induces activation of STAT3, a transcription factor that promotes mitochondrial function. Notably, the effect of FTY720-P on mitochondrial function was suppressed in the presence of a STAT3 inhibitor. In summary, our results suggest that FTY720 promotes the activation of mitochondrial function, in part, through a STAT3 action.

Abstract 3694: Metabolic response in human cervical cancer cells to modifications in bioavailable ATP

Abstract Introduction: Cancer cells utilize a markedly reduced oxidative phosphorylation (OXPHOS) when experiencing conditions of high oxygen stress (Warburg Effect/aerobic glycolysis), a phenomenon first studied by Otto Warburg. While there have been many discoveries associated with metabolic differences across cancer cells, one of the most common alterations is the primary means of generating ATP. The importance of deciphering these cellular decisions will enable an understanding of the multifaceted role ATP has in cancer proliferation, senescence, and chemotherapeutic resistance. The use of synthetic protein DX, a man-made ATP chelator with high specificity and affinity, is a proposed method of investigating the metabolic response in cancer cells. Hypothesis: Following DX expression, HeLa cells respond to energy stress (reduced intracellular ATP) via metabolic adaptations, specifically inducing the spare respiratory capacity. Methods: The impact of DX on cell viability was determined using a tetrazolium-based colorimetric cell viability assay and a caspase 3/7 assay. To correlate phenotypic/viability change with DX activity, bioavailable ATP levels were measured at specific time points following DX expression. Additionally, the relative contribution of glycolysis and OXPHOS to the total ATP production rate was measured using the label-free XF Real Time ATP Rate Assay and XF Cell Mito Stress Test (XFe96 Seahorse, Agilent Technologies) over time post DX expression. To determine the impact of ATP stress on mitochondrial and nuclear content, both were quantified following DX-expression. Results: In a time- and dose- dependent manner, DX negatively impacted cell growth and induced cell death via apoptosis, at a time concomitant with a decrease in bioavailable ATP. In response to DX over time, the total ATP production rates in HeLa cells significantly decreased. Importantly, this reduction in the rate of ATP production was associated with a significant downregulation in both OXPHOS and glycolysis. Conclusion: Advances in synthetic biology have allowed for the intentional design of artificial proteins that maintain function in vivo. These proteins can be developed into powerful investigative tools to study biological questions, such as cellular decisions involved in cancer cell metabolism. In response to DX-potentiated ATP stress, the significant reduction in both glycolysis and oxidative phosphorylation suggests metabolic downregulation is required to maintain HeLa cell viability. Citation Format: Parth K. Jayaswal, Taha Muhammad, Ashley Brown, Jeffrey Norris, Shaleen B. Korch. Metabolic response in human cervical cancer cells to modifications in bioavailable ATP. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3694.

Abstract 3969: Screening of kinase inhibitors as bioenergetic metabolism modulator using the XF Real-Time ATP Rate Assay

Abstract Cancer cells are metabolically reprogrammed through tumor initiation and progression, and there are increasing developments in cancer therapies exploiting the potential metabolic vulnerability. A better understanding of cancer cell metabolic regulation can also contribute to modulating the harsh tumor microenvironment, which strongly affects the efficacy of emerging anti-cancer immunotherapies. As one of the critical contributors to cancer therapy design, there is increasing demand for time-efficient and reliable analytic tools when searching for drugs and genes modulating cancer cell metabolism. The XF Real-Time ATP Rate Assay measures ATP production from glycolysis and mitochondrial respiration simultaneously and provides a quantitative overview of the bioenergetic phenotype of the cells. By using ATP production rate as a universal unit of bioenergetic metabolism, this assay quickly detects metabolic modulations induced by chemical stimuli or genetic modifications. It allows the identification of potential targets for therapy design. In this study, we used the Seahorse XF Pro Analyzer combined with the XF ATP Rate assay to screen 80 kinase inhibitors for the suppressive effects on energy metabolism and/or inducing a metabolic phenotype shift in THP-1 cells, a monocytic leukemia cell line, using PBMC as the control. We identified four mitochondrial and two glycolytic suppressors using the screening and dose-response views available in Seahorse Analytics, a cloud-based data analysis tool for Seahorse XF assays. These compounds showed moderate or no effects on the net ATP production rates but induced a significant shift in the metabolic phenotype of THP-1 cells. Among the selected kinase inhibitors, AG-879 (ErbB2 inhibitor), SU-1498 (VEGFR inhibitor), and U-0126 (MEK1/2 inhibitor) showed the most potent inhibitory effect on mitochondrial energy production in THP-1 cells. Dose-response studies indicated that SU-1498 and U-0126 have higher potency in THP-1 than PBMC, and thus they can be considered good cancer-cell targets for mitochondrial suppressors. In contrast, AG-879 showed a similar or higher inhibitory effect on PBMC even though it is the most potent mitochondrial suppressor among the selected compounds. These results demonstrate that the XF Real-Time ATP Rate Assay can be used as a primary assay for screening and validating drug candidate(s) targeting the bioenergetic metabolism of cancer cells. Citation Format: Yoonseok Kam, Lisa Winer, Natalia Romero. Screening of kinase inhibitors as bioenergetic metabolism modulator using the XF Real-Time ATP Rate Assay. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3969.

Abstract 6032: Exploiting metabolic vulnerabilities of ovarian cancer with upregulated succinate dehydrogenase

Abstract Ovarian cancer remains the deadliest of all gynecologic malignancies nationwide due to limited therapeutic options and chemotherapy resistance. The response to chemotherapy is substantially influenced by the high metabolic flexibility of ovarian cancer cells, which allows the cells to reprogram their metabolism and survive the treatment. Better understanding mechanisms regulating ovarian tumor metabolism could be exploited to develop new improved therapies. Our work demonstrated that the upregulation of mitochondrial enzyme succinate dehydrogenase (SDHA) is particularly prevalent (~20% of patients) in ovarian carcinoma and contributes to high energy tumor metabolism and cell survival. We observed that SDHA overexpressing ovarian cancer cells showed improved ability to survive and generate colonies in anchorage-independent conditions, which is an important feature of ovarian tumor cells surviving and spreading in peritoneal fluid (ascites). Proteomics data revealed that the SDHA overexpressing tumor cells showed reduced levels of proteins promoting anaerobic glycolysis (LDHA and HIF1α), and increased levels of mitochondrial pyruvate carrier (MPC) proteins. In addition, our tracer-based metabolomics data revealed that the elevated SDHA stimulates glutaminolysis by increasing mitochondrial glutamine supply fueling the TCA cycle with essential metabolites. We also demonstrated that the overexpression of SDHA is associated with a significant increase of OXPHOS and ATP production rate. Further, we reasoned that the SDHA overexpressing tumor cells could be particularly vulnerable to drugs disrupting glucose and/or glutamine metabolism. We performed a drug screening and identified an anti-metabolic compound shikonin known to disrupt glucose and amino acid metabolism. In in vitro studies, shikonin exhibited a profound anti-tumor efficacy and selectivity towards SDHA overexpressing tumor cells superior to that observed with chemotherapy. Importantly, our in vivo study validated the in vitro observations, and showed that shikonin is highly effective in suppressing SDHA overexpressing patient-derived tumor growth. In summary, the unique metabolic state of ovarian cancer associated with SDHA amplification could be successfully targetable offering a potential new treatment strategy for ovarian cancer patients. Citation Format: Lin Wang, Magdalena Bulicz, Patryk Mucha, Michael Kinter, Atul Pranay, Timothy M. Griffin, Benjamin F. Miller, Magdalena Bieniasz. Exploiting metabolic vulnerabilities of ovarian cancer with upregulated succinate dehydrogenase [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6032.

Low-dose of caffeine alleviates high altitude pulmonary edema via regulating mitochondrial quality control process in AT1 cells.

Backgrounds: High-altitude pulmonary edema (HAPE) is a life-threatening disease without effective drugs. Caffeine is a small molecule compound with antioxidant biological activity used to treat respiratory distress syndrome. However, it is unclear whether caffeine plays a role in alleviating HAPE. Methods: We combined a series of biological experiments and label-free quantitative proteomics analysis to detect the effect of caffeine on treating HAPE and explore its mechanism in vivo and in vitro. Results: Dry and wet weight ratio and HE staining of pulmonary tissues showed that the HAPE model was constructed successfully, and caffeine relieved pulmonary edema. The proteomic results of mice lungs indicated that regulating mitochondria might be the mechanism by which caffeine reduced HAPE. We found that caffeine blocked the reduction of ATP production and oxygen consumption rate, decreased ROS accumulation, and stabilized mitochondrial membrane potential to protect AT1 cells from oxidative stress damage under hypoxia. Caffeine promoted the PINK1/parkin-dependent mitophagy and enhanced mitochondrial fission to maintain the mitochondria quality control process. Conclusion: Low-dose of caffeine alleviated HAPE by promoting PINK1/parkin-dependent mitophagy and mitochondrial fission to control the mitochondria quality. Therefore, caffeine could be a potential treatment for HAPE.

Metformin induces mitochondrial fission and reduces energy metabolism by targeting respiratory chain complex I in hepatic stellate cells to reverse liver fibrosis.

The activation and proliferation of hepatic stellate cells (HSCs) are critical processes for the treatment of liver fibrosis. It is necessary to identify effective drugs for the treatment of liver fibrosis and elucidate their mechanisms of action. Metformin can inhibit HSCs; however, no systematic studies demonstrating the effects of metformin on mitochondria in HSCs have been reported. This study demonstrated that metformin induces mitochondrial fission by phosphorylating AMPK/DRP1 (S616) in HSCs to decrease the expression of α-SMA and collagen. Additionally, metformin repressed the total ATP production rate, especially the production rate of ATP produced through mitochondrial oxidative phosphorylation, by inhibiting the enzymatic activity of complex I. Further analysis revealed that metformin strongly constrained the transcription of mitochondrial genes (ND1-ND6 and ND4L) that encode the core subunits of respiratory chain I. Upregulation of the mRNA expression of HK2 and GLUT1 slightly enhanced glycolysis. Additionally, metformin increased mitochondrial DNA (mtDNA) copy number to suppress the proliferation and activation of HSCs, indicating that mtDNA copy number can alter the fate of HSCs. In conclusion, metformin can induce mitochondrial fragmentation and low-level energy metabolism in HSCs, thereby suppressing HSCs activation and proliferation to reverse liver fibrosis.

MiR-130a-3p regulates FUNDC1-mediated mitophagy by targeting GJA1 in myocardial ischemia/reperfusion injury

Understanding the complex pathogenesis in myocardial ischemia/reperfusion (I/R) injury (IRI) is an urgent problem in clinical trials. Increasing pieces of evidence have suggested that miRNAs are involved in the occurrence and development of heart diseases by regulating mitochondria-related gene expression. Mitochondria have been acknowledged as the key triggers of cardiac I/R injury. However, the potential impact of miR-130a on mitochondria remains unclear in myocardial IRI. Exploring the regulatory mechanism of miR-130a on mitochondria may provide a new target for IRI therapy. In the present study, we found that miR-130a significantly increased in acute myocardial infarction (AMI) patients and myocardial I/R rats. MiR-130a could downregulate the viability of cardiomyocytes and the knockdown of miR-130a could protect the viability of cardiomyocytes under hypoxia-reoxygenation (HR). Over-expression of miR-130a resulted in mitochondrial dysfunction. It was evidenced by decreases in mitochondrial ATP production, mitochondrial membrane potential (MMP), and an increase in reactive oxygen species (ROS) production. However, suppression of miR-130a could protect against mitochondrial damage, show elevation of mitochondrial ATP production rate and MMP, and reduce ROS production. We further explored the effect of miR-130a on the mitochondrial quality control (QMC) system by determining mitochondrial-protein-specific proteases and analyzed mitochondrial morphology by fluorescence imaging and electron microscopy, respectively. It was noted that miR-130a could suppress mitochondrial fusion and FUNDC1-mediated mitophagy to accelerate myocardial IRI. Moreover, we investigated the potential miR-130a targeted mitochondria-related genes to understand the regulatory mechanism of miR-130a in the setting of myocardial IRI. It was revealed that miR-130a targeted GJA1, and GJA1 rescued IRI by enhancing ATP production rate and oxidative phosphorylation, meanwhile protecting cell viability, MMP, and activating mitophagy. In addition, the knockdown of miR-130a significantly activated FUNDC1-mediated mitophagy, while the knockdown of GJA1 reversed the relevant response. Collectively, our findings suggest that miR-130a regulates FUNDC1-mediated mitophagy by targeting GJA1 in myocardial IRI.

Effect of light fluctuations on photosynthesis and metabolic flux in Synechocystis sp. PCC 6803.

In nature, photosynthetic organisms are exposed to fluctuating light, and their physiological systems must adapt to this fluctuation. To maintain homeostasis, these organisms have a light fluctuation photoprotective mechanism, which functions in both photosystems and metabolism. Although the photoprotective mechanisms functioning in the photosystem have been studied, it is unclear how metabolism responds to light fluctuations within a few seconds. In the present study, we investigated the metabolic response of Synechocystis sp. PCC 6803 to light fluctuations using 13 C-metabolic flux analysis. The light intensity and duty ratio were adjusted such that the total number of photons or the light intensity during the low-light phase was equal. Light fluctuations affected cell growth and photosynthetic activity under the experimental conditions. However, metabolic flux distributions and cofactor production rates were not affected by the light fluctuations. Furthermore, the estimated ATP and NADPH production rates in the photosystems suggest that NADPH-consuming electron dissipation occurs under fluctuating light conditions. Although we focused on the water-water cycle as the electron dissipation path, no growth effect was observed in an flv3-disrupted strain under fluctuating light, suggesting that another path contributes to electron dissipation under these conditions.

Characterization of the effect of the GLUT-1 inhibitor BAY-876 on T cells and macrophages

Increased aerobic glycolysis is a metabolic hallmark of proinflammatory leukocytes including macrophages and T cells. To take up glucose from the environment and fuel glycolysis, activated leukocytes upregulate the glucose transporter GLUT1. The orally bioavailable selective GLUT1 inhibitor BAY-876 was developed primarily as an anti-tumor drug. Our study assessed its activity on activated macrophages and CD4+ T cells. BAY-876 significantly attenuated glucose uptake by cultured CD4+ T cells and macrophages by 41% and 15%, respectively. Extracellular flux analysis of activated CD4+ T cells in vitro showed that BAY-876 significantly decreases glycolytic proton flux rate and lactate production, effects that are accompanied by an increased oxidative phosphorylation-mediated ATP production rate, leaving intracellular ATP levels per cell unchanged. However, GLUT1 inhibition reduced CD4+ T cell proliferation without compromising cell viability and reduced IFN-γ secretion by 20%. Moreover, TNF secretion from macrophages was reduced by 27%. We conclude that GLUT1-specific inhibitors, like BAY-876, deserve further in vivo testing in a broad range of (auto-) inflammatory disease models.

Molecular mechanism of reversed temperature-dependence of ATP synthesis in glacier ice worms.

The F0F1 ATP synthase enzyme is highly conserved across species. The F0F1 is a reversible motor, where the clockwise rotation of the rotor portion of F0 (known as the c-ring and present in the membrane embedded F0 domain) produces ATP and the counter-clockwise rotation induces ATP hydrolysis. In a surprising contrast with temperate organisms, glacier ice worms display elevated ATP levels as temperatures decline. The increased energy expenditure is used as a strategy for survival at cold temperatures, but the mechanism is unknown. To investigate the underlying mechanism of elevated ATP levels in glacier ice worms, we investigated the effects of temperature on the dynamics of the F0F1 ATP synthase of glacier ice worms compared to their temperate counterparts. More specifically, an ice worm-specific, 18 amino acid extension with regularly spaced histidine residues was previously found to be fused to the carboxy terminal of the ATP6 subunit generating a proton shuttling domain projecting away from the F0 exit pore. The role of this C-terminal extension in the temperature dependance ATP synthesis in ice worms is undetermined. We conducted all-atomistic MD simulations of the F0 domain subunits at different temperatures and used earthworms as a control to evaluate the effect of sequence on temperature dependence. We also measured the rotational diffusion of the c-ring as a function of temperature to evaluate the change in the rotation angles of the c-ring around the z axis in clock- and counter-clockwise directions. The ATP6 subunit is attached to the c-ring at the proton exit site. This suggests that the change in the c-ring rotational diffusion, as a function of temperature, can affect the ATP6 conformation, which likely affects the rate of ATP production.

Molecular mechanism of glycolytic assembly on mitochondria through O-GlcNAcylation.

Glucose is the primary fuel of cells, and its metabolism starts with the activity of the first rate-limiting enzyme Hexokinase (HK). HK1 is the dominant isoform in the brain and is mainly localized near the mitochondrial outer membrane. The positioning of HK1 on mitochondria is critical because it couples two energy generation pathways: Glycolysis and mitochondrial oxidative phosphorylation. Here, we report a new molecular mechanism that regulates HK1 activity and mitochondrial localization via the metabolic sensor enzyme O-GlcNAc transferase (OGT). OGT catalyzes a reversible post-translational modification by adding a GlcNAc sugar moiety to serine and threonine residues (O-GlcNAcylation). By combining experiments and molecular simulations, this study shows that the dynamical modification of HK1 with O-GlcNAcylation at its regulatory domain disrupts the product, G6P, from binding to this non-catalytic domain. We further demonstrate that G6P binding to the non-catalytic domain plays a role in controlling mitochondrial localization through electrostatic repulsion due to the additional negative charge from G6P. In addition, we demonstrated that O-GlcNAc modification induces a conformational change which increases mitochondrial HK1 and enhances glycolytic and mitochondrial ATP production rates. By computing binding affinities of the O-GlcNAc modified and unmodified HK1, we see that the O-GlcNAcylation decreases G6P and increases ATP binding to HK1. Furthermore, by mutating the O-GlcNAcylation site of HK1, we see a decrease in both glycolytic and mitochondrial ATP production rate and dysfunction of presynaptic vesicle releasing in neurons. Our findings may reveal key molecular pathways that couple neuronal metabolism to mitochondrial function via OGT and how their dysregulation leads to neurological disorders.