The mitochondrial NAD+ transporter SLC25A51 is a fasting-induced gene affecting SIRT3 functions

The Roles of White Adipose Tissue and Liver NADPH in Dietary Restriction-Induced Longevity

Dietary restriction (DR) protocols frequently employ intermittent fasting. Following a period of fasting, meal consumption increases lipogenic gene expression, including that of NADPH-generating enzymes that fuel lipogenesis in white adipose tissue (WAT) through the induction of transcriptional regulators SREBP-1c and CHREBP. SREBP-1c knockout mice, unlike controls, did not show an extended lifespan on the DR diet. WAT cytoplasmic NADPH is generated by both malic enzyme 1 (ME1) and the pentose phosphate pathway (PPP), while liver cytoplasmic NADPH is primarily synthesized by folate cycle enzymes provided one-carbon units through serine catabolism. During the daily fasting period of the DR diet, fatty acids are released from WAT and are transported to peripheral tissues, where they are used for beta-oxidation and for phospholipid and lipid droplet synthesis, where monounsaturated fatty acids (MUFAs) may activate Nrf1 and inhibit ferroptosis to promote longevity. Decreased WAT NADPH from PPP gene knockout stimulated the browning of WAT and protected from a high-fat diet, while high levels of NADPH-generating enzymes in WAT and macrophages are linked to obesity. But oscillations in WAT [NADPH]/[NADP+] from feeding and fasting cycles may play an important role in maintaining metabolic plasticity to drive longevity. Studies measuring the WAT malate/pyruvate as a proxy for the cytoplasmic [NADPH]/[NADP+], as well as studies using fluorescent biosensors expressed in the WAT of animal models to monitor the changes in cytoplasmic [NADPH]/[NADP+], are needed during ad libitum and DR diets to determine the changes that are associated with longevity.

Liguzinediol potentiates the metabolic remodeling by activating the AMPK/SIRT3 pathway and represses Caspase-3/GSDME-mediated pyroptosis to ameliorate cardiotoxicity

BACKGROUND

Liguzinediol (Lig) has emerged as a promising candidate for mitigating Doxorubicin (DOX)-induced cardiotoxicity, a significant limitation in the clinical application of this widely used antineoplastic drug known for its efficacy. This study aimed to explore the effects and potential mechanisms underlying Lig's protective role against DOX-induced cardiotoxicity.

METHODS

C57BL/6 mice were treated with DOX. Cardiac function changes were observed by echocardiography. Cardiac structure changes were observed by HE and Masson staining. Immunofluorescence was applied to visualize the cardiomyocyte apoptosis. Western blotting was used to detect the expression levels of AMP-activated protein kinase (AMPK), sirtuin 3 (SIRT3), Caspase-3 and gasdermin E N-terminal fragment (GSDME-N). These experiments confirmed that Lig had an ameliorative effect on DOX-induced cardiotoxicity in mice.

RESULTS

The results demonstrated that Lig effectively countered myocardial oxidative stress by modulating intracellular levels of reactive oxygen species (ROS), malondialdehyde (MDA), and superoxide dismutase (SOD). Lig reduced levels of creatine kinase (CK) and lactate dehydrogenase (LDH), while ameliorating histopathological changes and improving electrocardiogram profiles in vivo. Furthermore, the study revealed that Lig activated the AMPK/SIRT3 pathway, thereby enhancing mitochondrial function and attenuating myocardial cell apoptosis. In experiments with H9C2 cells treated with DOX, co-administration of the AMPK inhibitor compound C (CC) led to a significant increase in intracellular ROS levels. Lig intervention reversed these effects, along with the downregulation of GSDME-N, interleukin-1β (IL-1β), and interleukin-6 (IL-6), suggesting a potential role of Lig in mitigating Caspase-3/GSDME-mediated pyroptosis.

CONCLUSION

The findings of this study suggest that Lig effectively alleviates DOX-induced cardiotoxicity through the activation of the AMPK/SIRT3 pathway, thereby presenting itself as a natural product with therapeutic potential for preventing DOX-associated cardiotoxicity. This novel approach may pave the way for the development of alternative strategies in the clinical management of DOX-induced cardiac complications.

SLC25A51 decouples the mitochondrial NAD+/NADH ratio to control proliferation of AML cells

SLC25A51 selectively imports oxidized NAD+ into the mitochondrial matrix and is required for sustaining cell respiration. We observed elevated expression of SLC25A51 that correlated with poorer outcomes in patients with acute myeloid leukemia (AML), and we sought to determine the role SLC25A51 may serve in this disease. We found that lowering SLC25A51 levels led to increased apoptosis and prolonged survival in orthotopic xenograft models. Metabolic flux analyses indicated that depletion of SLC25A51 shunted flux away from mitochondrial oxidative pathways, notably without increased glycolytic flux. Depletion of SLC25A51 combined with 5-azacytidine treatment limits expansion of AML cells in vivo. Together, the data indicate that AML cells upregulate SLC25A51 to decouple mitochondrial NAD+/NADH for a proliferative advantage by supporting oxidative reactions from a variety of fuels. Thus, SLC25A51 represents a critical regulator that can be exploited by cancer cells and may be a vulnerability for refractory AML.

Bisphenol F exposure induces depression-like changes: Roles of the kynurenine metabolic pathway along the "liver-brain" axis

Bisphenol F (BPF), one of the major alternatives of Bisphenol A (BPA), is becoming extensively used in industrial production with great harm to human beings and environment. Recent studies have revealed that environmental exposure is crucial to the initiation and development of depression. Thereby, the aim the present study is to ascertain the correlationship between the BPF exposure and depression occurrence. In the current study, BPF strikingly triggered depression-like changes in mice through the sucrose preference test (SPT), tail suspension test (TST) and forced swim test (FST), accompanied by the perturbation of the kynurenine (KYN) metabolic pathway along the "liver-brain" axis. Mechanistically, the neurotransmitters from the tryptophan metabolic pathway were converted to the toxic KYN pathway after BPF treatment. With the ELISA assay, it revealed that the toxic KYN metabolites, including KYN and 3-hydroxykynurenine (3-HK), were strikingly increased in the mouse brains which was ascribed to the enhanced expression of the rate-limiting enzymes Indoleamine 2,3-dioxygenase (IDO1) and Kynurenine 3-monooxygenase (KMO) respectively. Interestingly, the increased brain KYN induced by BPF was also validated partially from the periphery, since the ELISA and western blotting results indicated the significantly increased KYN in the serum and L-type amino acid transporter 1 (LAT1) in the brain, the key transporter responsible for KYN and 3-HK crossing the blood-brain barrier. Intriguingly, the liver-derived KYN metabolic pathway was the important source of the peripheral KYN and 3-HK, as BPF substantially enhanced hepatic IDO1, Tryptophan, 2, 3-dioxygenase (TDO2), and KMO levels indicated by western blotting. This study is the first to delineate previously unrecognized BPF-induced depression by regulating the KYN metabolic pathway along the "liver-brain" axis; therefore, targeting LAT1 or hepatic KYN signaling may provide a potentially unique therapeutic intervention in BPF-induced depression.

SIRT3 alleviates high glucose-induced chondrocyte injury through the promotion of autophagy and suppression of apoptosis in osteoarthritis progression

A growing amount of epidemiological evidence proposes diabetes mellitus (DM) to be an independent risk factor for osteoarthritis (OA). Sirtuin 3 (SIRT3), which is mainly located in mitochondria, belongs to the family of nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylases and is involved in the physiological and pathological processes of cell regulation. The aim of this study was to investigate the effects of SIRT3 on diabetic OA and underlying mechanisms in the prevention of type 2 DM (T2DM)-induced articular cartilage damage. High-fat and high-sugar diets combined with streptozotocin (STZ) injection were used for establishing an experimental T2DM rat model. The destabilization of medial meniscus (DMM) surgery was applied to induce the rat OA model. Primary rat chondrocytes were cultivated with a concentration of gradient glucose. Treatment with intra-articular injection of SIRT3 overexpression lentivirus was achieved in vivo, and intervention with SIRT3 knockdown was performed using siRNA transfection in vitro. High glucose content was found to activate inflammatory response, facilitate apoptosis, downregulate autophagy, and exacerbate mitochondrial dysfunction in a dose-dependent manner in rat chondrocytes, which can be deteriorated by SIRT3 knockdown. In addition, articular cartilage damage was found to be more severe in T2DM-OA rats than in DMM-induced OA rats, which can be mitigated by the intra-articular injection of SIRT3 overexpression lentivirus. Targeting SIRT3 is a potential therapeutic strategy for the alleviation of diabetic OA.

Kynurenine in IDO1high cancer cell-derived extracellular vesicles promotes angiogenesis by inducing endothelial mitophagy in ovarian cancer

BACKGROUND

Mitophagy, a prominent cellular homeostasis process, has been implicated in modulating endothelial cell function. Emerging evidence suggests that extracellular vesicles (EVs) participate in intercellular communication, which could modulate tumor angiogenesis, a hallmark of ovarian cancer (OC) progression. However, the underlying mechanisms through how EVs regulate endothelial mitophagy associated with tumor angiogenesis during OC development remain obscure.

METHODS

The effect of cancer cell-derived EVs on endothelial mitophagy and its correlation with tumor angiogenesis and OC development were explored by in vitro and in vivo experiments. Multi-omics integration analysis was employed to identify potential regulatory mechanisms of cancer cell-derived EVs on endothelial mitophagy, which is involved in tumor angiogenesis associated with OC development. These insights were then further corroborated through additional experiments. An orthotopic OC mouse model was constructed to assess the antiangiogenic and therapeutic potential of the Indoleamine 2,3 dioxygenase-1 (IDO1) inhibitor.

RESULTS

Cancer cell-derived EVs promoted tumor angiogenesis via the activation of endothelial mitophagy, contributing to the growth and metastasis of OC. The aberrantly high expression of IDO1 mediated abnormal tryptophan metabolism in cancer cells and promoted the secretion of L-kynurenine (L-kyn)-enriched EVs, with associated high levels of L-kyn in EVs isolated from both the tumor tissues and patient plasma in OC. EVs derived from IDO1high ovarian cancer cells elevated nicotinamide adenine dinucleotide (NAD +) levels in endothelial cells via delivering L-kyn. Besides, IDO1high ovarian cancer cell-derived EVs upregulated sirt3 expression in endothelial cells by increasing acetylation modification. These findings are crucial for promoting endothelial mitophagy correlated with tumor angiogenesis. Notably, both endothelial mitophagy and tumor angiogenesis could be suppressed by the IDO1 inhibitor in the orthotopic OC mouse model.

CONCLUSIONS

Together, our findings unveil a mechanism of mitophagy in OC angiogenesis and indicate the clinical relevance of EV enriched L-kyn as a potential biomarker for tumorigenesis and progression. Additionally, IDO1 inhibitors might become an alternative option for OC adjuvant therapy.

Layered mechanisms regulating the human mitochondrial NAD+ transporter SLC25A51

SLC25A51 is the primary mitochondrial NAD+ transporter in humans and controls many local reactions by mediating the influx of oxidized NAD+. Intriguingly, SLC25A51 lacks several key features compared with other members in the mitochondrial carrier family, thus its molecular mechanism has been unclear. A deeper understanding would shed light on the control of cellular respiration, the citric acid cycle, and free NAD+ concentrations in mammalian mitochondria. This review discusses recent insights into the transport mechanism of SLC25A51, and in the process highlights a multitiered regulation that governs NAD+ transport. The aspects regulating SLC25A51 import activity can be categorized as contributions from (1) structural characteristics of the transporter itself, (2) its microenvironment, and (3) distinctive properties of the transported ligand. These unique mechanisms further evoke compelling new ideas for modulating the activity of this transporter, as well as new mechanistic models for the mitochondrial carrier family.

A big picture of the mitochondria-mediated signals: From mitochondria to organism

Mitochondria, well-known for years as the powerhouse and biosynthetic center of the cell, are dynamic signaling organelles beyond their energy production and biosynthesis functions. The metabolic functions of mitochondria, playing an important role in various biological events both in physiological and stress conditions, transform them into important cellular stress sensors. Mitochondria constantly communicate with the rest of the cell and even from other cells to the organism, transmitting stress signals including oxidative and reductive stress or adaptive signals such as mitohormesis. Mitochondrial signal transduction has a vital function in regulating integrity of human genome, organelles, cells, and ultimately organism.

The autophagy-NAD axis in longevity and disease

Autophagy is an intracellular degradation pathway that recycles subcellular components to maintain metabolic homeostasis. NAD is an essential metabolite that participates in energy metabolism and serves as a substrate for a series of NAD+-consuming enzymes (NADases), including PARPs and SIRTs. Declining levels of autophagic activity and NAD represent features of cellular ageing, and consequently enhancing either significantly extends health/lifespan in animals and normalises metabolic activity in cells. Mechanistically, it has been shown that NADases can directly regulate autophagy and mitochondrial quality control. Conversely, autophagy has been shown to preserve NAD levels by modulating cellular stress. In this review we highlight the mechanisms underlying this bidirectional relationship between NAD and autophagy, and the potential therapeutic targets it provides for combatting age-related disease and promoting longevity.

Cellular and Mitochondrial NAD Homeostasis in Health and Disease

The mitochondrion has a unique position among other cellular organelles due to its dynamic properties and symbiotic nature, which is reflected in an active exchange of metabolites and cofactors between the rest of the intracellular compartments. The mitochondrial energy metabolism is greatly dependent on nicotinamide adenine dinucleotide (NAD) as a cofactor that is essential for both the activity of respiratory and TCA cycle enzymes. The NAD level is determined by the rate of NAD synthesis, the activity of NAD-consuming enzymes, and the exchange rate between the individual subcellular compartments. In this review, we discuss the NAD synthesis pathways, the NAD degradation enzymes, and NAD subcellular localization, as well as NAD transport mechanisms with a focus on mitochondria. Finally, the effect of the pathologic depletion of mitochondrial NAD pools on mitochondrial proteins' post-translational modifications and its role in neurodegeneration will be reviewed. Understanding the physiological constraints and mechanisms of NAD maintenance and the exchange between subcellular compartments is critical given NAD's broad effects and roles in health and disease.

Principles and functions of metabolic compartmentalization

Metabolism has historically been studied at the levels of whole cells, whole tissues and whole organisms. As a result, our understanding of how compartmentalization-the spatial and temporal separation of pathways and components-shapes organismal metabolism remains limited. At its essence, metabolic compartmentalization fulfils three important functions or 'pillars': establishing unique chemical environments, providing protection from reactive metabolites and enabling the regulation of metabolic pathways. However, how these pillars are established, regulated and maintained at both the cellular and systemic levels remains unclear. Here we discuss how the three pillars are established, maintained and regulated within the cell and discuss the consequences of dysregulation of metabolic compartmentalization in human disease. Organelles are increasingly emerging as 'command-and-control centres' and the increased understanding of metabolic compartmentalization is revealing new aspects of metabolic homeostasis, with this knowledge being translated into therapies for the treatment of cancer and certain neurodegenerative diseases.