MDH1-mediated malate-aspartate NADH shuttle maintains the activity levels of fetal liver hematopoietic stem cells

Homeostatic regulation of NAD(H) and NADP(H) in cells

Nicotinamide adenine dinucleotide (NAD+)/reduced NAD+ (NADH) and nicotinamide adenine dinucleotide phosphate (NADP+)/reduced NADP+ (NADPH) are essential metabolites involved in multiple metabolic pathways and cellular processes. NAD+ and NADH redox couple plays a vital role in catabolic redox reactions, while NADPH is crucial for cellular anabolism and antioxidant responses. Maintaining NAD(H) and NADP(H) homeostasis is crucial for normal physiological activity and is tightly regulated through various mechanisms, such as biosynthesis, consumption, recycling, and conversion between NAD(H) and NADP(H). The conversions between NAD(H) and NADP(H) are controlled by NAD kinases (NADKs) and NADP(H) phosphatases [specifically, metazoan SpoT homolog-1 (MESH1) and nocturnin (NOCT)]. NADKs facilitate the synthesis of NADP+ from NAD+, while MESH1 and NOCT convert NADP(H) into NAD(H). In this review, we summarize the physiological roles of NAD(H) and NADP(H) and discuss the regulatory mechanisms governing NAD(H) and NADP(H) homeostasis in three key aspects: the transcriptional and posttranslational regulation of NADKs, the role of MESH1 and NOCT in maintaining NAD(H) and NADP(H) homeostasis, and the influence of the circadian clock on NAD(H) and NADP(H) homeostasis. In conclusion, NADKs, MESH1, and NOCT are integral to various cellular processes, regulating NAD(H) and NADP(H) homeostasis. Dysregulation of these enzymes results in various human diseases, such as cancers and metabolic disorders. Hence, strategies aiming to restore NAD(H) and NADP(H) homeostasis hold promise as novel therapeutic approaches for these diseases.

A negative feedback loop underlies the Warburg effect

Aerobic glycolysis, or the Warburg effect, is used by cancer cells for proliferation while producing lactate. Although lactate production has wide implications for cancer progression, it is not known how this effect increases cell proliferation and relates to oxidative phosphorylation. Here, we elucidate that a negative feedback loop (NFL) is responsible for the Warburg effect. Further, we show that aerobic glycolysis works as an amplifier of oxidative phosphorylation. On the other hand, quiescence is an important property of cancer stem cells. Based on the NFL, we show that both aerobic glycolysis and oxidative phosphorylation, playing a synergistic role, are required to achieve cell quiescence. Further, our results suggest that the cells in their hypoxic niche are highly proliferative yet close to attaining quiescence by increasing their NADH/NAD+ ratio through the severity of hypoxia. The findings of this study can help in a better understanding of the link among metabolism, cell cycle, carcinogenesis, and stemness.

The acetylation of MDH1 and IDH1 is associated with energy metabolism in acute liver failure

The liver is the main organ associated with metabolism. In our previous studies, we identified that the metabolic enzymes malate dehydrogenase 1 (MDH1) and isocitrate dehydrogenase 1 (IDH1) were differentially expressed in ALF. The aim of this study was to explore the changes in the acetylation of MDH1 and IDH1 and the therapeutic effect of histone deacetylase (HDAC) inhibitor in acute liver failure (ALF). Decreased levels of many metabolites were observed in ALF patients. MDH1 and IDH1 were decreased in the livers of ALF patients. The HDAC inhibitor ACY1215 improved the expression of MDH1 and IDH1 after treatment with MDH1-siRNA and IDH1-siRNA. Transfection with mutant plasmids and adeno-associated viruses, identified MDH1 K118 acetylation and IDH1 K93 acetylation as two important sites that regulate metabolism in vitro and in vivo.

Crosstalk between DNA Damage Repair and Metabolic Regulation in Hematopoietic Stem Cells

Self-renewal and differentiation are two characteristics of hematopoietic stem cells (HSCs). Under steady physiological conditions, most primitive HSCs remain quiescent in the bone marrow (BM). They respond to different stimuli to refresh the blood system. The transition from quiescence to activation is accompanied by major changes in metabolism, a fundamental cellular process in living organisms that produces or consumes energy. Cellular metabolism is now considered to be a key regulator of HSC maintenance. Interestingly, HSCs possess a distinct metabolic profile with a preference for glycolysis rather than oxidative phosphorylation (OXPHOS) for energy production. Byproducts from the cellular metabolism can also damage DNA. To counteract such insults, mammalian cells have evolved a complex and efficient DNA damage repair (DDR) system to eliminate various DNA lesions and guard genomic stability. Given the enormous regenerative potential coupled with the lifetime persistence of HSCs, tight control of HSC genome stability is essential. The intersection of DDR and the HSC metabolism has recently emerged as an area of intense research interest, unraveling the profound connections between genomic stability and cellular energetics. In this brief review, we delve into the interplay between DDR deficiency and the metabolic reprogramming of HSCs, shedding light on the dynamic relationship that governs the fate and functionality of these remarkable stem cells. Understanding the crosstalk between DDR and the cellular metabolism will open a new avenue of research designed to target these interacting pathways for improving HSC function and treating hematologic disorders.

A novel HDAC6 inhibitor attenuate APAP-induced liver injury by regulating MDH1-mediated oxidative stress

Glutathione (GSH) depletion, mitochondrial damage, and oxidative stress have been implicated in the pathogenesis of acetaminophen (APAP) hepatotoxicity. Here, we demonstrated that the expression of histone deacetylase 6 (HDAC6) is highly elevated, whereas malate dehydrogenase 1 (MDH1) is downregulated in liver tissues and AML-12 cells induced by APAP. The therapeutic benefits of LT-630, a novel HDAC6 inhibitor on APAP-induced liver injury, were also substantiated. On this basis, we demonstrated that LT-630 improved the protein expression and acetylation level of MDH1. Furthermore, after overexpression of MDH1, an upregulated NADPH/NADP+ ratio and GSH level and decreased cell apoptosis were observed in APAP-stimulated AML-12 cells. Importantly, MDH1 siRNA clearly reversed the protection of LT-630 on APAP-stimulated AML-12 cells. In conclusion, LT-630 could ameliorate liver injury by modulating MDH1-mediated oxidative stress induced by APAP.

Transcription factor LHX9 (LIM Homeobox 9) enhances pyruvate kinase PKM2 activity to induce glycolytic metabolic reprogramming in cancer stem cells, promoting gastric cancer progression

BACKGROUND

Glycolytic metabolic reprogramming is a phenomenon in which cells undergo altered metabolic patterns during malignant transformation, mainly involving various aspects of glycolysis, electron transport chain, oxidative phosphorylation, and pentose phosphate pathway. This reprogramming phenomenon can be used as one of the markers of tumorigenesis and development. Pyruvate kinase is the third rate-limiting enzyme in the sugar metabolism process by specifically catalyzing the irreversible conversion of PEP to pyruvate.

PURPOSE

This study aimed to reveal the critical mediator(s) that regulate glycolytic metabolism reprogramming in gastric cancer and their underlying molecular mechanism and then explore the molecular mechanisms by which LHX9 may be involved in regulating gastric cancer (GC) progression.

METHODS

Firstly, we downloaded the GC and glycolysis-related microarray datasets from TCGA and MSigDB databases and took the intersection to screen out the transcription factor LHX9 that regulates GC glycolytic metabolic reprogramming. Software packages were used for differential analysis, single gene predictive analysis, and Venn diagram. In addition, an enrichment analysis of the glycolytic pathway was performed. Immunohistochemical staining was performed for LHX9 and PKM2 protein expression in 90 GC patients, and the association between their expressions was evaluated by Spearman's correlation coefficient method. Three human GC cell lines (AGS, NCI-N87, HGC-27) were selected for in vitro experimental validation. Flow cytometry was utilized to determine the stem cell marker CD44 expression status in GCSCs. A sphere formation assay was performed to evaluate the sphere-forming capabilities of GCSCs. In addition, RT-qPCR and Western blot experiments were employed to investigate the tumor stem cell markers OCT4 and SOX2 expression levels in GCSCs. Furthermore, a lentiviral expression vector was constructed to assess the impact of downregulating LHX9 or PKM2 on the glycolytic metabolic reprogramming of GCSCs. The proliferation, migration, and invasion of GCSCs were then detected by CCK-8, EdU, and Transwell assays. Subsequently, the mutual binding of LHX9 and PKM2 was verified using chromatin immunoprecipitation and dual luciferase reporter genes. In vivo experiments were verified by establishing a subcutaneous transplantation tumor model in nude mice, observing the size and volume of tumors in vivo in nude mice, and obtaining fresh tissues for subsequent experiments.

RESULTS

Bioinformatics analysis revealed that LHX9 might be involved in the occurrence and development of GC through regulating glycolytic metabolism. High LHX9 expression could be used as a reference marker for prognosis prediction of GC patients. Clinical tissue assays revealed that LHX9 and PKM2 were highly expressed in GC tissues. Meanwhile, GC tissues also highly expressed glycolysis-associated protein GLUT1 and tumor cell stemness marker CD44. In vitro cellular assays showed that LHX9 could enhance its activity and induce glycolytic metabolic reprogramming in GCSCs through direct binding to PKM2. In addition, the knockdown of LHX9 inhibited PKM2 activity and glycolytic metabolic reprogramming and suppressed the proliferation, migration, and invasive ability of GCSCs. In vivo animal experiments further confirmed that the knockdown of LHX9 could reduce the tumorigenic ability of GCSCs in nude mice by inhibiting PKM2 activity and glycolytic metabolic reprogramming.

CONCLUSION

The findings suggest that both LHX9 and PKM2 are highly expressed in GCs, and LHX9 may induce the reprogramming of glycolytic metabolism through transcriptional activation of PKM2, enhancing the malignant biological properties of GCSCs and ultimately promoting GC progression.

l-Malic Acid Facilitates Stem Cell-Driven Intestinal Epithelial Renewal through the Amplification of β-Catenin Signaling by Targeting Frizzled7 in Chicks

l-Malic acid (l-MA) contributes to energy metabolism and nutrient digestion, which is an alternative to antibiotics for livestock; however, it is not clear whether l-MA can replace antibiotics to promote intestinal development in chicks. To investigate the effects of l-MA on intestinal stem cells (ISCs) driving epithelial renewal, we employed in vivo chick feeding experiments, chick intestinal organoid (IO) models, and in vitro chick intestinal epithelial cell models. The results showed that the feed conversion rate and diarrhea scores were decreased with improved jejunal morphology and barrier function in the 0.5% l-MA group. l-MA promoted the proliferation and differentiation of ISCs, inhibited the cell apoptosis, increased the IO formation efficiency, surface area, budding efficiency, and number of buds, suggesting that l-MA promoted the expansion of ISCs. Furthermore, l-MA treatment dramatically upregulated the Wnt/β-catenin signaling pathway in the jejunum. Importantly, Wnt transmembrane receptor Frizzled7 (FZD7) mRNA abundance was increased in response to dietary 0.5% l-MA. In addition, molecular docking analysis using Autodock software and isothermal titration calorimetry revealed that l-MA binds to Lys91 of FZD7 with high affinity, indicating a spontaneous interaction. The chick intestinal epithelial cells treated with 10 μM l-MA significantly increased cell viability, and the Wnt/β-catenin signaling pathway was activated, but l-MA failed to upregulate the Wnt/β-catenin signaling when treated with the FZD7-specific inhibitor Fz7-21 in chick intestinal epithelial cells, indicating that FZD7 is indispensable for l-MA activation of the Wnt/β-catenin signaling. Collectively, l-MA stimulated β-catenin signaling by targeting transmembrane receptor FZD7, which promoted ISC expansion and inhibited cell apoptosis to accelerate intestinal epithelial renewal in chicks.

Live-cell imaging reveals redox metabolic reprogramming during zygotic genome activation

Metabolic programming is deeply intertwined with early embryonic development including zygotic genome activation (ZGA), the polarization of zygotic cells, and cell fate commitment. It is crucial to establish a noninvasive imaging technology that spatiotemporally illuminates the cellular metabolism pathways in embryos to track developmental metabolism in situ. In this study, we used two high-quality genetically encoded fluorescent biosensors, SoNar for NADH/NAD+ and iNap1 for NADPH, to characterize the dynamic regulation of energy metabolism and redox homeostasis during early zygotic cleavage. Our imaging results showed that NADH/NAD+ levels decreased from the early to the late two-cell stage, whereas the levels of the reducing equivalent NADPH increased. Mechanistically, transcriptome profiling suggested that during the two-cell stage, zygotic cells downregulated the expression of genes involved in glucose uptake and glycolysis, and upregulated the expression of genes for pyruvate metabolism in mitochondria and oxidative phosphorylation, with a decline in the expression of two peroxiredoxin genes, Prdx1 and Prdx2. Collectively, with the establishment of in situ metabolic monitoring technology, our study revealed the programming of redox metabolism during ZGA.

Monitoring NAD(H) and NADP(H) dynamics during organismal development with genetically encoded fluorescent biosensors

Cell metabolism plays vital roles in organismal development, but it has been much less studied than transcriptional and epigenetic control of developmental programs. The difficulty might be largely attributed to the lack of in situ metabolite assays. Genetically encoded fluorescent sensors are powerful tools for noninvasive metabolic monitoring in living cells and in vivo by highly spatiotemporal visualization. Among all living organisms, the NAD(H) and NADP(H) pools are essential for maintaining redox homeostasis and for modulating cellular metabolism. Here, we introduce NAD(H) and NADP(H) biosensors, present example assays in developing organisms, and describe promising prospects for how sensors contribute to developmental biology research.

Gadus morhua Eggs Sialoglycoprotein Prevent Estrogen Deficiency-Induced High Bone Turnover by Controlling OPG/RANKL/TRAF6 Pathway and Serum Metabolism

In recent years, the development of safe and effective anti-osteoporosis factors has attracted extensive attention. In this study, an estrogen-deficient osteoporosis rat model was employed to study the improving mechanism of sialoglycoprotein isolated from Gadus morhua eggs (Gds) against osteoporosis. The results showed that compared with OVX, Gds ameliorated the trabecular microstructure, especially the increased trabecular thickness, decreased trabecular separation, and enhanced the trabecular number. The analysis of qRT-PCR and western blotting found that Gds reduced bone resorption by inhibiting RANKL-induced osteoclastogenesis. The LC-MS/MS was used to investigate serum metabolism, and the enrichment metabolites were analyzed by the KEGG pathway. The results revealed that the Gds significantly altered the fat anabolism pathway, which includes ovarian steroidogenesis pathway and arachidonic acid metabolism pathway. Altogether, Gds could improve osteoporosis by suppressing high bone turnover via controlling OPG/RANKL/TRAF6 pathway, which is implicated with ovarian steroidogenesis pathway and arachidonic acid metabolism pathway. These findings indicated that Gds could be a candidate factor for anti-osteoporosis.

Genetically encoded biosensors for evaluating NAD+/NADH ratio in cytosolic and mitochondrial compartments

The ratio of oxidized to reduced NAD (NAD+/NADH) sets intracellular redox balance and antioxidant capacity. Intracellular NAD is compartmentalized and the mitochondrial NAD+/NADH ratio is intricately linked to cellular function. Here, we report the monitoring of the NAD+/NADH ratio in mitochondrial and cytosolic compartments in live cells by using a modified genetic biosensor (SoNar). The fluorescence signal of SoNar targeted to mitochondria (mt-SoNar) or cytosol (ct-SoNar) responded linearly to physiological NAD+/NADH ratios in situ. NAD+/NADH ratios in cytosol versus mitochondria responded rapidly, but differently, to acute metabolic perturbations, indicating distinct NAD pools. Subcellular NAD redox balance regained homeostasis via communications through malate-aspartate shuttle. Mitochondrial and cytosolic NAD+/NADH ratios are influenced by NAD+ precursor levels and are distinctly regulated under pathophysiological conditions. Compartment-targeted biosensors and real-time imaging allow assessment of subcellular NAD+/NADH redox signaling in live cells, enabling future mechanistic research of NAD redox in cell biology and disease development.

Aspartate availability limits hematopoietic stem cell function during hematopoietic regeneration

The electron transport chain promotes aspartate synthesis, which is required for cancer cell proliferation. However, it is unclear whether aspartate is limiting in normal stem cells. We found that mouse hematopoietic stem cells (HSCs) depend entirely on cell-autonomous aspartate synthesis, which increases upon HSC activation. Overexpression of the glutamate/aspartate transporter, Glast, or deletion of glutamic-oxaloacetic transaminase 1 (Got1) each increased aspartate levels in HSCs/progenitor cells and increased the function of HSCs but not colony-forming progenitors. Conversely, deletion of Got2 reduced aspartate levels and the function of HSCs but not colony-forming progenitors. Deletion of Got1 and Got2 eliminated HSCs. Isotope tracing showed aspartate was used to synthesize asparagine and purines. Both contributed to increased HSC function as deletion of asparagine synthetase or treatment with 6-mercaptopurine attenuated the increased function of GLAST-overexpressing HSCs. HSC function is thus limited by aspartate, purine, and asparagine availability during hematopoietic regeneration.

Malate-Aspartate Shuttle Plays an Important Role in LPS-Induced Neuroinflammation of Mice Due to its Effect on STAT3 Phosphorylation

Neuroinflammation is a key pathological factor in numerous neurological disorders. Cumulating evidence has indicated critical roles of NAD⁺/NADH metabolism in multiple major diseases, while the role of malate-aspartate shuttle (MAS) - a major NADH shuttle - in inflammation has remained unclear. In this study we investigated the roles of MAS in LPS-induced neuroinflammation both in vivo and in vitro. Immunofluorescence staining, Western blot assay and Real-time PCR assays were conducted to determine the activation of Iba-1, the protein levels of iNOS and COX2 and the mRNA levels of IL-1β, IL-6, and TNF-α in vivo, showing that both pre-treatment and post-treatment of aminooxyacetic acid (AOAA) - an MAS inhibitor - profoundly decreased the LPS-induced neuroinflammation in mice. BV2 microglia was also used as a cellular model to investigate the mechanisms of this finding, in which such assays as Western blot assay and nitrite assay. Our study further indicated that AOAA produced its effects on LPS-induced microglial activation by its effects on MAS: Pyruvate treatment reversed the effects of AOAA on the cytosolic NAD⁺/NADH ratio, which also restored the LPS-induced activation of the AOAA-treated microglia. Moreover, the lactate dehydrogenase (LDH) inhibitor GSK2837808A blocked the effects of pyruvate on the AOAA-produced decreases in both the cytosolic NAD⁺/NADH ratio and LPS-induced microglial activation. Our study has further suggested that AOAA produced inhibition of LPS-induced microglial activation at least partially by decreasing STAT3 phosphorylation. Collectively, our findings have indicated AOAA as a new and effective drug for inhibiting LPS-induced neuroinflammation. Our study has also indicated that MAS is a novel mediator of LPS-induced neuroinflammation due to its capacity to modulate LPS-induced STAT3 phosphorylation, which has further highlighted a critical role of NAD⁺/NADH metabolism in inflammation.

Warburg-like Metabolic Reprogramming in Aging Intestinal Stem Cells Contributes to Tissue Hyperplasia

In many tissues, stem cell (SC) proliferation is dynamically adjusted to regenerative needs. How SCs adapt their metabolism to meet the demands of proliferation and how changes in such adaptive mechanisms contribute to age-related dysfunction remain poorly understood. Here, we identify mitochondrial Ca²⁺ uptake as a central coordinator of SC metabolism. Live imaging of genetically encoded metabolite sensors in intestinal SCs (ISCs) of Drosophila reveals that mitochondrial Ca²⁺ uptake transiently adapts electron transport chain flux to match energetic demand upon proliferative activation. This tight metabolic adaptation is lost in ISCs of old flies, as declines in mitochondrial Ca²⁺ uptake promote a “Warburg-like” metabolic reprogramming toward aerobic glycolysis. This switch mimics metabolic reprogramming by the oncogene Ras^V12 and enhances ISC hyperplasia. Our data identify a critical mechanism for metabolic adaptation of tissue SCs and reveal how its decline sets aging SCs on a metabolic trajectory reminiscent of that seen upon oncogenic transformation.

Morris et al. uncover a Ca²⁺-mediated adjustment of mitochondrial electron transport chain flux that links increased ATP production to proliferation in Drosophila intestinal stem cells. Declines in mitochondrial Ca²⁺ uptake in aging stem cells promote a Warburg-like metabolic reprogramming reminiscent of that observed upon oncogenic transformation.