Spermidine-mediated hypusination of translation factor EIF5A improves mitochondrial fatty acid oxidation and prevents non-alcoholic steatohepatitis progression

Mechanisms of metabolism-coupled protein modifications

Intricate coupling between metabolism and protein post-translational modifications (PTMs) has emerged as a fundamental aspect of cellular regulation. Recent studies demonstrate that protein modifications can originate from diverse metabolites, and that their regulation is closely tied to the cellular metabolic state. Here we explore recently uncovered PTMs, including the concept of 'modification of a modification', as well as associated feedback and feedforward regulatory mechanisms, in which modified proteins impact not only related metabolic pathways but also other signaling cascades affecting physiology and diseases. The recently uncovered role of nucleus-localized metabolic enzymes for histone modifications additionally highlights the importance of cell-compartment-specific metabolic states. We further comment on the utility of untargeted metabolomics and proteomics for previously unrecognized PTMs and associated metabolic patterns. Together, these advances have uncovered a dynamic interplay between metabolism and PTMs, offering new perspectives for understanding metabolic regulation and developing targeted therapeutic strategies.

Shared host genetic landscape of respiratory viral infection

Respiratory viruses represent a major global health burden. Although these viruses have different life cycles, they may depend on common host genetic factors, which could be targeted by broad-spectrum host-directed therapies. We used genome-wide CRISPR screens and advanced data analytics to map a network of host genes that support infection by nine human respiratory viruses [influenza A virus, parainfluenza virus, human rhinovirus, respiratory syncytial virus, human coronavirus (HCoV)-229E, HCoV-NL63, HCoV-OC43, Middle East respiratory syndrome-related coronavirus, and severe acute respiratory syndrome-related coronavirus 2]. We explored shared pathways using knowledge graphs to inform on pharmacological targets. We selected and validated STT3A/B proteins of the N-oligosaccharyltransferase complex as host targets of broad-spectrum antiviral small molecules. Our work highlights the commonalities of viral host genetic dependencies and the feasibility of using this information to develop broad-spectrum antiviral agents.

Structure-based identification of herbacetin and caffeic acid phenethyl ester as inhibitors of S-adenosylmethionine-dependent viral methyltransferase

Chikungunya (CHIKV) and dengue (DENV) viruses pose a public health risk and lack antiviral treatments. Structure-based molecular docking of a natural MTase substrates library identified herbacetin (HC) and caffeic acid phenethyl ester (CAPE) as potential CHIKV nsP1 and DENV NS5 MTase inhibitors. Binding affinities and MTase inhibition were confirmed using purified proteins. The crystal structure of DENV 3 NS5 MTase and CAPE complex revealed CAPE binding at viral RNA capping sites. Interestingly, HC and CAPE depleted polyamines crucial for RNA virus replication and decreased viral titer with IC50 values of ~ 13.44 and ~ 0.57 μm against CHIKV, and ~ 7.24 and ~ 1.01 μm against DENV 3, respectively. Polyamine addition did not reverse the antiviral effects, suggesting a dual inhibition mechanism. Impact statement This study reveals the antiviral potential of natural small molecules, Herbacetin (HC) and Caffeic acid phenethyl ester (CAPE) against Dengue and Chikungunya viruses. The molecules deplete polyamine levels and directly inhibit viral methyltransferases. This study opens new avenues for developing antiviral strategies that target both host factors and viral components.

The role of mitochondrial mRNA translation in cellular communication

Mitochondria are dynamic and heterogeneous organelles that rewire their network and metabolic functions in response to changing cellular needs. To this end, mitochondria integrate a plethora of incoming signals to influence cell fate and survival. A crucial and highly regulated node of cell-mitochondria communication is the translation of nuclear-encoded mitochondrial mRNAs. By controlling and monitoring the spatio-temporal translation of these mRNAs, cells can rapidly adjust mitochondrial function to meet metabolic demands, optimise ATP production and regulate organelle biogenesis and turnover. In this Review, we focus on how RNA-binding proteins that recognise nuclear-encoded mitochondrial mRNAs acutely modulate the rate of translation in response to nutrient availability. We further discuss the relevance of localised translation of these mRNAs for subsets of mitochondria in polarised cells. Finally, we highlight quality control mechanisms that monitor the translation process at the mitochondrial surface and their connections to mitophagy and stress responses. We propose that these processes collectively contribute to mitochondrial specialisation and signalling function.

NF-E2-related factor 1 suppresses the expression of a spermine oxidase and the production of highly reactive acrolein

Polyamines (putrescine, spermidine, and spermine) are among the most abundant intracellular small molecular metabolites, with concentrations at the mM level. The ratios of these three molecules remain constant under physiological conditions. Stress (i.e. polyamine overload, oxidative stress, aging, infection, etc.) triggers the catabolic conversion of spermine to spermidine, ultimately yielding acrolein and hydrogen peroxide. The potential of acrolein to induce DNA damage and protein denaturation is 1,000 times greater than that of reactive oxygen species. We have shown that these polyamine metabolic pathways also involve the nuclear factor erythroid-2-related factor 1 (NRF1) transcription factor. In our chemically-inducible, liver-specific Nrf1-knockout mice, the polyamine catabolic pathway dominated the anabolic pathway, producing free acrolein and accumulating acrolein-conjugated proteins in vivo. This metabolic feature implicates SMOX as an important causative enzyme. Chromatin immunoprecipitation and reporter assays confirmed that NRF1 directly suppressed Smox expression. This effect was also observed in vitro. Ectopic overexpression of SMOX increased the accumulation of free acrolein and acrolein-conjugated proteins. SMOX knockdown reversed the accumulation of free acrolein and acrolein-conjugated proteins. Our results show that NRF1 typically suppresses Smox expression when NRF1 is downregulated, SMOX is upregulated, and polyamine metabolic pathways are altered, producing low molecular weight polyamines and acrolein.

Harnessing Microalgae as Sustainable Cell Factories for Polyamine-Based Nanosilica for Biomedical Applications

Microalgae are microscopic unicellular organisms that inhabit marine, freshwater, and moist terrestrial ecosystems. The vast number and diversity of microalgal species provide a significant reservoir of biologically active compounds, highly promising for biomedical applications. Diatoms are unicellular eukaryotic algae belonging to the class Bacillariophyceae. They possess intricately structured silica-based cell walls, which contain long-chain polyamines that play important roles in the formation of silica. Long-chain polyamines are uncommon polyamines found only in organisms that produce biosilica. Diatomite, which is a marine sediment of the remains of the silica skeleton of diatoms, could be an abundant source of biogenic silica that can easily be converted to silica particles. This concise review focuses on the biofabrication of polyamine-based nanosilica from diatoms and highlights the possibility of utilizing diatom biosilica as a nanocarrier for drug and siRNA delivery, bioimaging, and bone tissue engineering. The challenges that may affect diatom production, including environmental stresses and climate change, are discussed together with the prospect of increasing diatom-based biosilica production with the desired nanostructures via genetic manipulation.

Regular exercise alleviates metabolic dysfunction-associated steatohepatitis through rescuing mitochondrial oxidative stress and dysfunction in liver

Metabolic dysfunction-associated steatohepatitis (MASH) is characterized by severe mitochondrial dysfunction, associated with the production of mitochondrial reactive oxygen species (mROS). The substantial generation of mROS in the MASH liver, resulting from lipid surplus and electron transport chain (ETC) overload, impairs mitochondrial structure and functionality, thereby contributing to the development of severe hepatic steatosis and inflammation. Regular exercise represents an effective strategy for the treatment of MASH. Understanding the effects of exercise on oxidative stress and mitochondrial function is essential for effective treatment of MASH. This article reviews the pathological alterations in mitochondrial β-oxidation, ETC efficiency and mROS production within MASH liver. Additionally, it discusses how exercise influences the redox state and mitochondrial quality control mechanisms-such as biogenesis, mitophagy, fusion, and fission-within the MASH liver. The article emphasizes the importance of in-depth studies on exercise-induced MASH mitigation through the enhancement of mitochondrial redox balance, quality control, and function. Exploring the relationship between exercise and hepatic mitochondria could provide valuable insights into identifying potential therapeutic targets for MASH.

Arginine: at the crossroads of nitrogen metabolism

L-arginine is the most nitrogen-rich amino acid, acting as a key precursor for the synthesis of nitrogen-containing metabolites and an essential intermediate in the clearance of excess nitrogen. Arginine's side chain possesses a guanidino group which has unique biochemical properties, and plays a primary role in nitrogen excretion (urea), cellular signaling (nitric oxide) and energy buffering (phosphocreatine). The post-translational modification of protein-incorporated arginine by guanidino-group methylation also contributes to epigenetic gene control. Most human cells do not synthesize sufficient arginine to meet demand and are dependent on exogenous arginine. Thus, dietary arginine plays an important role in maintaining health, particularly upon physiologic stress. How cells adapt to changes in extracellular arginine availability is unclear, mostly because nearly all tissue culture media are supplemented with supraphysiologic levels of arginine. Evidence is emerging that arginine-deficiency can influence disease progression. Here, we review new insights into the importance of arginine as a metabolite, emphasizing the central role of mitochondria in arginine synthesis/catabolism and the recent discovery that arginine can act as a signaling molecule regulating gene expression and organelle dynamics.

Spermidine synthase promotes liver cancer progression in a paracrine manner by altering the macrophage immunometabolic state

PURPOSE

Understanding the molecular mechanisms of adaptive regulation in the tumor microenvironment is crucial for precision therapy in hepatocellular carcinoma (HCC). We hypothesized that cargo proteins carried by extracellular vesicles (EVs) released in a hypoxic microenvironment might promote HCC progression by remodeling tumor-associated macrophages (TAMs).

METHODS

EV protein analysis by label-free proteomics mass spectrometry of HCC cell lines of different tumor grades was performed. The promotional effect if spermidine synthase（SRM） on M2 polarized TAMs was further investigated using various biological approaches.

RESULTS

SRM expression was positively correlated with liver cancer progression in HCC cell lines, liver cancer samples, and nude mouse models. In a mouse model, SRM expression was positively correlated with TAM infiltration and liver cancer progression. Pan-cancer dataset analysis confirmed that SRM overexpression in HCC tumors is correlated with poor patient prognosis. However, a hypoxic microenvironment is an internal driving factor for exosomal SRM that participates in microenvironmental modifications. Moreover, we defined a hitherto unknown pattern of microenvironmental crosstalk involving SRM in EVs, whereby macrophages complete the phenotypic fate of M2 tumor-associated macrophages through SRM uptake.

CONCLUSION

SRM regulation within the immune microenvironment is metabolically driven. By upregulating spermidine, which serves as a substrate for eIF5A hypusination, excessive oxidative phosphorylation (OXPHOS) assembly is achieved. This, in turn, leads to the expression of immunosuppressive marker molecules and ultimately promotes liver cancer progression. SRM, which is enriched in the EVs of HCC cells under hypoxic conditions, acts as a potent regulator linking polyamine and energy metabolism in TAMs, thereby promoting liver cancer progression.

Maternal supplementation spermidine during gestation improves placental angiogenesis and reproductive performance of high prolific sows

Spermidine (SPD) is a widely recognized polyamine compound found in mammalian cells and plays a key role in various cellular processes. We propose that SPD may enhance placental vascular development in pregnant sows, leading to increased birth weight of piglets. Six hundred and nine sows at 60 days of gestation were randomly assigned into a basal diet (CON group), basal diet supplemented 10 mg/kg of SPD (SPD1 group), and basal diet supplemented 20 mg/kg of SPD (SPD2 group), respectively. Compared with the CON, SPD1 significantly increased the average number of healthy piglets per litter and the placental efficiency (P < .05), while the average number of mummified fetus per litter and the percentage of weak piglets significantly decreased (P < .05). In the plasma metabolomics, SPD content in plasma of sows (P = .075) and umbilical cord plasma of piglets (P = .078) had an increasing trend in response to SPD1. Furthermore, SPD1 increased the expression of the vascular endothelial cell marker protein, platelet endothelial cell adhesionmolecule-1 (PECAM-1/CD31) and the density of placental stromal vessels (P < .05). Moreover, as compared to CON, SPD2 significantly decreased the average number of mummified fetus per litter (P < .05), while the placental efficiency and the expression of amino acid transporter solute carrier (SLC) family 7, member7 (SLC7A7) and glucose transporters SLC2A2) and SLC5A4 in placental tissue significantly increased (P < .05). These results suggest that maternal supplementation of SPD during pregnancy increased healthy litter number, and promoted placental tissue development. Our findings provide evidence that maternal SPD has the potential to improve the production performance of sows.

Lactobacillus reuteri ZJ617 attenuates metabolic syndrome via microbiota-derived spermidine

Metabolic syndrome (MetS) is a difficult-to-manage disease that poses a significant risk to human health. Here, we show that the supplementation of Lactobacillus reuteri ZJ617 ameliorates symptoms of MetS in mice induced by the high-fat diet. L. reuteri ZJ617 modulates host metabolism by interacting with the microbiome, resulting in the production of spermidine synthesized by the microbiota. L. reuteri ZJ617 serves as a source of substrates for the microbiota to synthesize spermidine, hence preventing the decline of bacteria responsible for spermidine production. Spermidine treatment mimics the metabolic effects of L. reuteri ZJ617, whereas pharmacological inhibition of spermidine biosynthesis in mice abolishes these benefits. Our findings reveal the mechanism by which L. reuteri ZJ617 alleviates MetS symptoms and provide support for its potential use as a probiotic for promoting metabolic health.

Rescue of hippocampal synaptic plasticity and memory performance by Fingolimod (FTY720) in APP/PS1 model of Alzheimer's disease is accompanied by correction in metabolism of sphingolipids, polyamines, and phospholipid saturation composition

Previously, our metabolomic, transcriptomic, and genomic studies characterized the ceramide/sphingomyelin pathway as a therapeutic target in Alzheimer's disease, and we demonstrated that FTY720, a sphingosine-1-phospahate receptor modulator approved for treatment of multiple sclerosis, recovers synaptic plasticity and memory in APP/PS1 mice. To further investigate how FTY720 rescues the pathology, we performed metabolomic analysis in brain, plasma, and liver of trained APP/PS1 and wild-type mice. APP/PS1 mice showed area-specific brain disturbances in polyamines, phospholipids, and sphingolipids. Most changes were completely or partially normalized in FTY720-treated subjects, indicating rebalancing the "sphingolipid rheostat", reactivating phosphatidylethanolamine synthesis via mitochondrial phosphatidylserine decarboxylase pathway, and normalizing polyamine levels that support mitochondrial activity. Synaptic plasticity and memory were rescued, with spermidine synthesis in temporal cortex best corresponding to hippocampal CA3-CA1 plasticity normalization. FTY720 effects, also reflected in other pathways, are consistent with promotion of mitochondrial function, synaptic plasticity, and anti-inflammatory environment, while reducing pro-apoptotic and pro-inflammatory signals.

Beyond ATP: Metabolite Networks as Regulators of Physiological and Pathological Erythroid Differentiation

Hematopoietic stem cells (HSCs) possess the capacity for self-renewal and the sustained production of all mature blood cell lineages. It has been well established that a metabolic rewiring controls the switch of HSCs from a self-renewal state to a more differentiated state, but it is only recently that we have appreciated the importance of metabolic pathways in regulating the commitment of progenitors to distinct hematopoietic lineages. In the context of erythroid differentiation, an extensive network of metabolites, including amino acids, sugars, nucleotides, fatty acids, vitamins, and iron, is required for red blood cell (RBC) maturation. In this review, we highlight the multifaceted roles via which metabolites regulate physiological erythropoiesis as well as the effects of metabolic perturbations on erythroid lineage commitment and differentiation. Of note, the erythroid differentiation process is associated with an exceptional breadth of solute carrier (SLC) metabolite transporter upregulation. Finally, we discuss how recent research, revealing the critical impact of metabolic reprogramming in diseases of disordered and ineffective erythropoiesis, has created opportunities for the development of novel metabolic-centered therapeutic strategies.

Mechanisms and therapeutic targets of mitochondria in the progression of metabolic dysfunction-associated steatotic liver disease

Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) includes liver disease processes from simple fatty liver to nonalcoholic steatohepatitis, which may progress to liver fibrosis, cirrhosis, and even hepatocellular carcinoma (HCC). As the incidence of HCC derived from viral hepatitis decreases, MASLD has emerged as a significant health threat, driven by lifestyle changes and rising obesity rates among patients. The pathogenesis of MASLD is complex, involving factors such as insulin resistance, gut microbiota imbalance, and genetic and epigenetic factors. In recent years, the role of mitochondrial dysfunction in MASLD has gained significant attention, involving β-oxidation imbalance, oxidative stress increase, mitophagy defects, and mitochondrial DNA (mtDNA) mutations. This article reviews the pathophysiological mechanisms of mitochondrial dysfunction in MASLD, diagnostic methods, and potential therapeutic strategies. By synthesizing current research findings, the review aims to highlight the critical role of mitochondrial dysfunction as a target for future diagnostic and therapeutic interventions. This focus could pave the way for innovative clinical strategies, ultimately improving treatment options and patient prognosis in MASLD.

Insights into eukaryotic translation initiation factor 5A: Its role and mechanisms in protein synthesis

The protein synthesis within eukaryotic cells is a complex process involving various translation factors. Among these factors, eukaryotic translation initiation factor 5 A (eIF5A) emerges as a crucial translation factor with high evolutionary conservation. eIF5A is unique as it is the only protein in eukaryotic cells containing the hypusine modification. Initially presumed to be a translation initiation factor, eIF5A was subsequently discovered to act mainly during the translation elongation phase. Notably, eIF5A facilitates the translation of peptide sequences containing polyproline stretches and exerts a universal regulatory effect on the elongation and termination phases of protein synthesis. Additionally, eIF5A indirectly affects various physiological processes within the cell by modulating the translation of specific proteins. This review provides a comprehensive overview of the structure, physiological functions, various post-translational modifications of eIF5A, and its association with various human diseases. The comparison between eIF5A and its bacterial homolog, EF-P, extends the discussion to the evolutionary conservation of eIF5A. This highlights its significance across different domains of life.

CircHIPK3 regulates cementoblast differentiation via the miR-10b-5p/DOHH/NF-κB axis

BACKGROUND

Intact cementum is vital for tooth stability and health. Cementoblasts, which line the root surface, are responsible for cementum formation. Recent evidence suggests that circular RNAs (circRNAs) are involved in various cellular functions and may have clinical applications. Although circHIPK3 has been shown to participate in osteogenesis, its role in cementoblast differentiation and mineralization is not well understood.

METHODS

The ring structure of circHIPK3 was confirmed using Sanger sequencing and an actinomycin D assay. Subcellular localization of circHIPK3 was assessed using a nucleus-cytoplasm separation assay. RT-qPCR was employed to analyze circHIPK3 expression during cementoblast differentiation and following TNF-α treatment. In vivo, periapical lesions were induced in mouse mandibular first molars to mimic an inflammatory environment, and circHIPK3 expression was evaluated. The interaction of the circHIPK3/miR-10b-5p/DOHH axis was explored through RNA pull-down assays, bioinformatics analysis, and dual-luciferase reporter assays. The effects on cementoblast differentiation and mineralization were assessed by measuring osteogenic markers, alkaline phosphatase (ALP) activity, ALP staining, and alizarin red S staining.

RESULTS

CircHIPK3 was predominantly located in the cytoplasm of cementoblasts, and its expression was significantly upregulated during cementoblast differentiation. Knockdown of circHIPK3 inhibited cementoblast differentiation and mineralization, whereas its overexpression promoted these processes. Mechanistically, circHIPK3 upregulated DOHH expression by sponging miR-10b-5p, thereby enhancing cementoblast differentiation and mineralization. The NF-κB pathway was found to act downstream of the circHIPK3/miR-10b-5p/DOHH axis in these processes. Additionally, circHIPK3 expression was significantly downregulated in inflammatory environments both in vitro and in vivo. Forced overexpression of circHIPK3 mitigated the inhibitory effects of TNF-α on cementoblast differentiation and mineralization.

CONCLUSION

CircHIPK3 acts as a positive regulator of cementoblast differentiation and mineralization through the miR-10b-5p/DOHH/NF-κB axis, playing a crucial role in both normal and pathological cementogenesis.

Postbiotics as Antiinflammatory and Immune-Modulating Bioactive Compounds in Metabolic Dysfunction-Associated Steatotic Liver Disease

Postbiotics, defined as products or metabolic byproducts secreted by live bacteria or released after bacterial lysis, are emerging as promising therapeutic agents for metabolic dysfunction-associated steatotic liver disease (MASLD). This review explores the antiinflammatory and immunomodulatory properties of various postbiotics, including exopolysaccharides, lipoteichoic acid, short-chain fatty acids, hydrogen sulfide, polyamines, tryptophan derivatives, and polyphenol metabolites. These compounds have demonstrated potential in mitigating steatotic liver infiltration, reducing inflammation, and slowing fibrosis progression in preclinical studies. Notably, postbiotics exert their beneficial effects by modulating gut microbiota composition, enhancing intestinal barrier function, optimizing lipid metabolism, reducing hepatic inflammation and steatosis, and exhibiting hepatoprotective properties. However, translating these findings into clinical practice requires well-designed trials to validate efficacy and safety, standardize production and characterization, and explore personalized approaches and synergistic effects with other therapeutic modalities. Despite challenges, the unique biological properties of postbiotics, such as enhanced safety compared to probiotics, make them attractive candidates for developing novel nutritional interventions targeting the multifactorial pathogenesis of MASLD. Further research is needed to establish their clinical utility and potential to improve liver and systemic outcomes in this increasingly prevalent condition.

Spermidine mitigates ferroptosis in free fatty acid-induced AML-12 cells through the ATF4/SLC7A11/GCLM/GPX4 pathway

Non-alcoholic fatty liver disease (NAFLD) is a prominent cause of chronic liver disease worldwide. Spermidine (SPD), a naturally occurring polyamine, has shown potential in alleviating the accumulation of hepatic lipids and reducing NAFLD symptoms in overweight mice. Nonetheless, the specific mechanisms through which SPD exerts its effects remain largely unknown. This study seeks to explore the protective effects of SPD on NAFLD and to clarify the underlying mechanisms. An in vitro model of NAFLD was established by inducing steatosis in AML-12 cells through the use of free fatty acids (FFAs). Our experimental results demonstrate that SPD significantly reduces NAFLD development induced by FFAs. This reduction is primarily achieved through the inhibition of cellular ferroptosis, as evidenced by decreased levels of Fe2+, malondialdehyde (MDA), and reactive oxygen species (ROS). Additionally, SPD was found to enhance cellular activity and ameliorate mitochondrial dysfunction and oxidative stress caused by FFA exposure. Further mechanistic studies have revealed that SPD upregulates the expression of solute transporter family 7a member 11 (SLC7A11), glutamate-cysteine ligase modifier subunit (GCLM), and glutathione peroxidase (GPX4). This upregulation is mediated by the activation of activating transcription factor 4 (ATF4). Knockdown experiments of ATF4 confirmed that its inhibition reverses the upregulation of SLC7A11, GCLM, and GPX4, thereby negating the protective effects of SPD. In conclusion, our findings suggest that SPD mitigates NAFLD by modulating the ATF4/SLC7A11/GCLM/GPX4 signaling pathway, resulting in the suppression of ferroptosis and the improvement of cellular health. These insights provide a novel molecular mechanism and identify potential therapeutic targets for the treatment of NAFLD.

Novel deoxyhypusine synthase (DHPS) inhibitors target hypusination-induced vasculogenic mimicry (VM) against malignant melanoma

Vasculogenic mimicry (VM) contributes factor to the poor prognosis of malignant melanoma. Developing deoxyhypusine synthase (DHPS) inhibitors against melanoma VM is clinically essential. In this study, we optimized and synthesized a series of compounds based on the candidate structure, and the hit compound 7k was identified through enzyme assay and cell viability inhibition screening. Both inside and outside the cell, 7k's ability to target DHPS and its high affinity were demonstrated. Molecular dynamics and point mutation indicated that mutations of K329 or V129 in DHPS abolish 7k's inhibitory activity. Using PCR arrays, solid-state antibody microarrays, and angiogenesis assays investigated 7k's impact on melanoma cells to reveal that DHPS regulates melanoma VM by promoting FGFR2 and c-KIT expression. Surprisingly, 7k was discovered to inhibit MC1R-mediated melanin synthesis in the zebrafish. Pharmacokinetic evaluations demonstrated 7k's favorable properties, and xenograft models evidenced its notable anti-melanoma efficacy, achieving a TGI of 73 %. These results highlighted DHPS as key in melanoma VM formation and confirmed 7k's potential as a novel anti-melanoma agent.

Polyamine metabolism in macrophage-adipose tissue function and homeostasis

Intracellular metabolism is a crucial regulator of macrophage function. Recent evidence revealed that the polyamine pathway and subsequent hypusination of eukaryotic initiation factor 5A (eIF5A) are master regulators of immune cell functions. In brown adipose tissue (BAT), macrophages show an impressive degree of heterogenicity, with specific subsets supporting adaptive thermogenesis during cold exposure. In this review, we discuss the impact of polyamine metabolism on macrophage diversity and function, with a particular focus on their role in adipose tissue homeostasis. Thus, we highlight the exploration of how polyamine metabolism in macrophages contributes to BAT homeostasis as an attractive and exciting new field of research.

Esrra regulates Rplp1-mediated translation of lysosome proteins suppressed in metabolic dysfunction-associated steatohepatitis and reversed by alternate day fasting

OBJECTIVE

Currently, little is known about the mechanism(s) regulating global and specific protein translation during metabolic dysfunction-associated steatohepatitis (MASH; previously known as non-alcoholic steatohepatitis, NASH).

METHODS

Unbiased label-free quantitative proteome, puromycin-labelling and polysome profiling were used to understand protein translation activity in vitro and in vivo.

RESULTS

We observed a global decrease in protein translation during lipotoxicity in human primary hepatocytes, mouse hepatic AML12 cells, and livers from a dietary mouse model of MASH. Interestingly, proteomic analysis showed that Rplp1, which regulates ribosome and translation pathways, was one of the most downregulated proteins. Moreover, decreased Esrra expression and binding to the Rplp1 promoter, diminished Rplp1 gene expression during lipotoxicity. This, in turn, reduced global protein translation and Esrra/Rplp1-dependent translation of lysosome (Lamp2, Ctsd) and autophagy (sqstm1, Map1lc3b) proteins. Of note, Esrra did not increase its binding to these gene promoters or their gene transcription, confirming its regulation of their translation during lipotoxicity. Notably, hepatic Esrra-Rplp1-dependent translation of lysosomal and autophagy proteins also was impaired in MASH patients and liver-specific Esrra knockout mice. Remarkably, alternate day fasting induced Esrra-Rplp1-dependent expression of lysosomal proteins, restored autophagy, and reduced lipotoxicity, inflammation, and fibrosis in hepatic cell culture and in vivo models of MASH.

CONCLUSIONS

Esrra regulation of Rplp1-mediated translation of lysosome/autolysosome proteins was downregulated during MASH. Alternate day fasting activated this novel pathway and improved MASH, suggesting that Esrra and Rplp1 may serve as therapeutic targets for MASH. Our findings also provided the first example of a nuclear hormone receptor, Esrra, to not only regulate transcription but also protein translation, via induction of Rplp1.

Increased hepatic putrescine levels as a new potential factor related to the progression of metabolic dysfunction-associated steatotic liver disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a chronic liver condition that often progresses to more advanced stages, such as metabolic dysfunction-associated steatohepatitis (MASH). MASH is characterized by inflammation and hepatocellular ballooning, in addition to hepatic steatosis. Despite the relatively high incidence of MASH in the population and its potential detrimental effects on human health, this liver disease is still not fully understood from a pathophysiological perspective. Deregulation of polyamine levels has been detected in various pathological conditions, including neurodegenerative diseases, inflammation, and cancer. However, the role of the polyamine pathway in chronic liver disorders such as MASLD has not been explored. In this study, we measured the expression of liver ornithine decarboxylase (ODC1), the rate-limiting enzyme responsible for the production of putrescine, and the hepatic levels of putrescine, in a preclinical model of MASH as well as in liver biopsies of patients with obesity undergoing bariatric surgery. Our findings reveal that expression of ODC1 and the levels of putrescine, but not spermidine nor spermine, are elevated in hepatic tissue of both diet-induced MASH mice and patients with biopsy-proven MASH compared with control mice and patients without MASH, respectively. Furthermore, we found that the levels of putrescine were positively associated with higher aspartate aminotransferase concentrations in serum and an increased SAF score (steatosis, activity, fibrosis). Additionally, in in vitro assays using human HepG2 cells, we demonstrate that elevated levels of putrescine exacerbate the cellular response to palmitic acid, leading to decreased cell viability and increased release of CK-18. Our results support an association between the expression of ODC1 and the progression of MASLD, which could have translational relevance in understanding the onset of this disease. © 2024 The Pathological Society of Great Britain and Ireland.

P53-dependent hypusination of eIF5A affects mitochondrial translation and senescence immune surveillance

Cellular senescence is characterized by a permanent growth arrest and is associated with tissue aging and cancer. Senescent cells secrete a number of different cytokines referred to as the senescence-associated secretory phenotype (SASP), which impacts the surrounding tissue and immune response. Here, we find that senescent cells exhibit higher rates of protein synthesis compared to proliferating cells and identify eIF5A as a crucial regulator of this process. Polyamine metabolism and hypusination of eIF5A play a pivotal role in sustaining elevated levels of protein synthesis in senescent cells. Mechanistically, we identify a p53-dependent program in senescent cells that maintains hypusination levels of eIF5A. Finally, we demonstrate that functional eIF5A is required for synthesizing mitochondrial ribosomal proteins and monitoring the immune clearance of premalignant senescent cells in vivo. Our findings establish an important role of protein synthesis during cellular senescence and suggest a link between eIF5A, polyamine metabolism, and senescence immune surveillance.

Autophagy and hepatic lipid metabolism: mechanistic insight and therapeutic potential for MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD) originates from a homeostatic imbalance in hepatic lipid metabolism. Increased fat deposition in the liver of people suffering from MASLD predisposes them to develop further metabolic derangements, including diabetes mellitus, metabolic dysfunction-associated steatohepatitis (MASH), and other end-stage liver diseases. Unfortunately, only limited pharmacological therapies exist for MASLD to date. Autophagy, a cellular catabolic process, has emerged as a primary mechanism of lipid metabolism in mammalian hepatocytes. Furthermore, preclinical studies with autophagy modulators have shown promising results in resolving MASLD and mitigating its progress into deleterious liver pathologies. In this review, we discuss our current understanding of autophagy-mediated hepatic lipid metabolism, its therapeutic modulation for MASLD treatment, and current limitations and scope for clinical translation.

The role of polyamine metabolism in cellular function and physiology

Polyamines are molecules with multiple amino groups that are essential for cellular function. The major polyamines are putrescine, spermidine, spermine, and cadaverine. Polyamines are important for posttranscriptional regulation, autophagy, programmed cell death, proliferation, redox homeostasis, and ion channel function. Their levels are tightly controlled. High levels of polyamines are associated with proliferative pathologies such as cancer, whereas low polyamine levels are observed in aging, and elevated polyamine turnover enhances oxidative stress. Polyamine metabolism is implicated in several pathophysiological processes in the nervous, immune, and cardiovascular systems. Currently, manipulating polyamine levels is under investigation as a potential preventive treatment for several pathologies, including aging, ischemia/reperfusion injury, pulmonary hypertension, and cancer. Although polyamines have been implicated in many intracellular mechanisms, our understanding of these processes remains incomplete and is a topic of ongoing investigation. Here, we discuss the regulation and cellular functions of polyamines, their role in physiology and pathology, and emphasize the current gaps in knowledge and potential future research directions.

Hypusine Signaling Promotes Pulmonary Vascular Remodeling in Pulmonary Arterial Hypertension

Rationale: The ubiquitous polyamine spermidine is essential for cell survival and proliferation. One important function of spermidine is to serve as a substrate for hypusination, a posttranslational modification process that occurs exclusively on eukaryotic translation factor 5A (eIF5A) and ensures efficient translation of various gene products. Pulmonary arterial hypertension (PAH) is a life-threatening disease characterized by progressive obliteration of the small pulmonary arteries (PAs) caused by excessive proliferation of PA smooth muscle cells (PASMCs) and suppressed apoptosis. Objectives: To characterize the role of hypusine signaling in PAH. Methods: Molecular, genetic, and pharmacological approaches were used both in vitro and in vivo to investigate the role of hypusine signaling in pulmonary vascular remodeling. Measurements and Main Results: Hypusine forming enzymes-deoxyhypusine synthase (DHPS) and deoxyhypusine hydroxylase (DOHH)-and hypusinated eukaryotic translation factor 5A are overexpressed in distal PAs and isolated PASMCs from PAH patients and animal models. In vitro, inhibition of DHPS using N1-guanyl-1,7-diaminoheptane or shRNA resulted in a decrease in PAH-PASMC resistance to apoptosis and proliferation. In vivo, inactivation of one allele of Dhps targeted to smooth muscle cells alleviates PAH in mice, and its pharmacological inhibition significantly decreases pulmonary vascular remodeling and improves hemodynamics and cardiac function in two rat models of established PAH. With mass spectrometry, hypusine signaling is shown to promote the expression of a broad array of proteins involved in oxidative phosphorylation, thus supporting the bioenergetic requirements of cell survival and proliferation. Conclusions: These findings support inhibiting hypusine signaling as a potential treatment for PAH.

Examining the Pathogenesis of MAFLD and the Medicinal Properties of Natural Products from a Metabolic Perspective

Metabolic-associated fatty liver disease (MAFLD), characterized primarily by hepatic steatosis, has become the most prevalent liver disease worldwide, affecting approximately two-fifths of the global population. The pathogenesis of MAFLD is extremely complex, and to date, there are no approved therapeutic drugs for clinical use. Considerable evidence indicates that various metabolic disorders play a pivotal role in the progression of MAFLD, including lipids, carbohydrates, amino acids, and micronutrients. In recent years, the medicinal properties of natural products have attracted widespread attention, and numerous studies have reported their efficacy in ameliorating metabolic disorders and subsequently alleviating MAFLD. This review aims to summarize the metabolic-associated pathological mechanisms of MAFLD, as well as the natural products that regulate metabolic pathways to alleviate MAFLD.

The lack of PPARα exacerbated the progression of non-alcoholic steatohepatitis in mice with spleen deficiency syndrome by triggering an inflammatory response

Background

In addition to abnormal liver inflammation, the main symptoms of non-alcoholic steatohepatitis (NASH) are often accompanied by gastrointestinal digestive dysfunction, consistent with the concept of spleen deficiency (SD) in traditional Chinese medicine. As an important metabolic sensor, whether peroxisome proliferator-activated receptor alpha (PPARα) participates in regulating the occurrence and development of NASH with SD (NASH-SD) remains to be explored.

Methods

Clinical liver samples were collected for RNA-seq analysis. C57BL/6J mice induced by folium sennae (SE) were used as an SD model. qPCR analysis was conducted to evaluate the inflammation and metabolic levels of mice. PPARα knockout mice (PPARαko) were subjected to SE and methionine-choline-deficient (MCD) diet to establish the NASH-SD model. The phenotype of NASH and the inflammatory indicators were measured using histopathologic analysis and qPCR as well.

Results

The abnormal expression of PPARα signaling, coupled with metabolism and inflammation, was found in the results of RNA-seq analysis from clinical samples. SD mice showed a more severe inflammatory response in the liver evidenced by the increases in macrophage biomarkers, inflammatory factors, and fibrotic indicators in the liver. qPCR results also showed differences in PPARα between SD mice and control mice. In PPARαko mice, further evidence was found that the lack of PPARα exacerbated the inflammatory response phenotype as well as the lipid metabolism disorder in NASH-SD mice.

Conclusion

The abnormal NR signaling accelerated the vicious cycle between lipotoxicity and inflammatory response in NAFLD with SD. Our results provide new evidence for nuclear receptors as potential therapeutic targets for NAFLD with spleen deficiency.

Polyamine-mediated ferroptosis amplification acts as a targetable vulnerability in cancer

Targeting ferroptosis, an iron-dependent form of regulated cell death triggered by the lethal overload of lipid peroxides, in cancer therapy is impeded by our limited understanding of the intersection of tumour's metabolic feature and ferroptosis vulnerability. In the present study, arginine is identified as a ferroptotic promoter using a metabolites library. This effect is mainly achieved through arginine's conversion to polyamines, which exerts their potent ferroptosis-promoting property in an H2O2-dependent manner. Notably, the expression of ornithine decarboxylase 1 (ODC1), the critical enzyme catalysing polyamine synthesis, is significantly activated by the ferroptosis signal--iron overload--through WNT/MYC signalling, as well as the subsequent elevated polyamine synthesis, thus forming a ferroptosis-iron overload-WNT/MYC-ODC1-polyamine-H2O2 positive feedback loop that amplifies ferroptosis. Meanwhile, we notice that ferroptotic cells release enhanced polyamine-containing extracellular vesicles into the microenvironment, thereby further sensitizing neighbouring cells to ferroptosis and accelerating the "spread" of ferroptosis in the tumour region. Besides, polyamine supplementation also sensitizes cancer cells or xenograft tumours to radiotherapy or chemotherapy through inducing ferroptosis. Considering that cancer cells are often characterized by elevated intracellular polyamine pools, our results indicate that polyamine metabolism exposes a targetable vulnerability to ferroptosis and represents an exciting opportunity for therapeutic strategies for cancer.

NAD metabolic therapy in metabolic dysfunction-associated steatotic liver disease: Possible roles of gut microbiota

Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly named non-alcoholic fatty liver disease (NAFLD), is induced by alterations of hepatic metabolism. As a critical metabolites function regulator, nicotinamide adenine dinucleotide (NAD) nowadays has been validated to be effective in the treatment of diet-induced murine model of MASLD. Additionally, gut microbiota has been reported to have the potential to prevent MASLD by dietary NAD precursors metabolizing together with mammals. However, the underlying mechanism remains unclear. In this review, we hypothesized that NAD enhancing mitochondrial activity might reshape a specific microbiota signature, and improve MASLD progression demonstrated by fecal microbiota transplantation. Here, this review especially focused on the mechanism of Microbiota-Gut-Liver Axis together with NAD metabolism for the MASLD progress. Notably, we found significant changes in Prevotella associated with NAD in a gut microbiome signature of certain MASLD patients. With the recent researches, we also inferred that Prevotella can not only regulate the level of NAD pool by boosting the carbon metabolism, but also play a vital part in regulating the branched-chain amino acid (BCAA)-related fatty acid metabolism pathway. Altogether, our results support the notion that the gut microbiota contribute to the dietary NAD precursors metabolism in MASLD development and the dietary NAD precursors together with certain gut microbiota may be a preventive or therapeutic strategy in MASLD management.

Drug targets regulate systemic metabolism and provide new horizons to treat nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH), is the advanced stage of nonalcoholic fatty liver disease (NAFLD) with rapidly rising global prevalence. It is featured with severe hepatocyte apoptosis, inflammation and hepatic lipogenesis. The drugs directly targeting the processes of steatosis, inflammation and fibrosis are currently under clinical investigation. Nevertheless, the long-term ineffectiveness and remarkable adverse effects are well documented, and new concepts are required to tackle with the root causes of NASH progression. We critically assess the recently validated drug targets that regulate the systemic metabolism to ameliorate NASH. Thermogenesis promoted by mitochondrial uncouplers restores systemic energy expenditure. Furthermore, regulation of mitochondrial proteases and proteins that are pivotal for intracellular metabolic homeostasis normalize mitochondrial function. Secreted proteins also improve systemic metabolism, and NASH is ameliorated by agonizing receptors of secreted proteins with small molecules. We analyze the drug design, the advantages and shortcomings of these novel drug candidates. Meanwhile, the structural modification of current NASH therapeutics significantly increased their selectivity, efficacy and safety. Furthermore, the arising CRISPR-Cas9 screen strategy on liver organoids has enabled the identification of new genes that mediate lipid metabolism, which may serve as promising drug targets. In summary, this article discusses the in-depth novel mechanisms and the multidisciplinary approaches, and they provide new horizons to treat NASH.

Dietary polyamines promote intestinal adaptation in an experimental model of short bowel syndrome

Intestinal adaptation does not necessarily recover absorptive capacity in short bowel syndrome (SBS), sometimes resulting in intestinal failure-associated liver disease (IFALD). Additionally, its therapeutic options remain limited. Polyamines (spermidine and spermine) are known as one of the autophagy inducers and play important roles in promoting the weaning process; however, their impact on intestinal adaptation is unknown. The aim of this study was to investigate the impact of polyamines ingestion on adaptation and hepatic lipid metabolism in SBS. We performed resection of two-thirds of the small intestine in male Lewis rats as an SBS model. They were allocated into three groups and fed different polyamine content diets (0%, 0.01%, 0.1%) for 30 days. Polyamines were confirmed to distribute to remnant intestine, whole blood, and liver. Villous height and number of Ki-67-positive cells in the crypt area increased with the high polyamine diet. Polyamines increased secretory IgA and mucin content in feces, and enhanced tissue Claudin-3 expression. In contrast, polyamines augmented albumin synthesis, mitochondrial DNA copy number, and ATP storage in the liver. Moreover, polyamines promoted autophagy flux and activated AMP-activated protein kinase with suppression of lipogenic gene expression. Polyamines ingestion may provide a new therapeutic option for SBS with IFALD.

Polyamine Signal through HCC Microenvironment: A Key Regulator of Mitochondrial Preservation and Turnover in TAMs

Hepatocellular carcinoma (HCC) is the most common primary liver cancer, and, with increasing research on the tumor immune microenvironment (TIME), the immunosuppressive micro-environment of HCC hampers further application of immunotherapy, even though immunotherapy can provide survival benefits to patients with advanced liver cancer. Current studies suggest that polyamine metabolism is not only a key metabolic pathway for the formation of immunosuppressive phenotypes in tumor-associated macrophages (TAMs), but it is also profoundly involved in mitochondrial quality control signaling and the energy metabolism regulation process, so it is particularly important to further investigate the role of polyamine metabolism in the tumor microenvironment (TME). In this review, by summarizing the current research progress of key enzymes and substrates of the polyamine metabolic pathway in regulating TAMs and T cells, we propose that polyamine biosynthesis can intervene in the process of mitochondrial energy metabolism by affecting mitochondrial autophagy, which, in turn, regulates macrophage polarization and T cell differentiation. Polyamine metabolism may be a key target for the interactive dialog between HCC cells and immune cells such as TAMs, so interfering with polyamine metabolism may become an important entry point to break intercellular communication, providing new research space for developing polyamine metabolism-based therapy for HCC.

Exosomal EIF5A derived from Lewis lung carcinoma induced adipocyte wasting in cancer cachexia

Cancer cachexia is a systemic inflammation-driven syndrome, characterized by muscle atrophy and adipose tissue wasting, with progressive weight loss leading to serious impairment of physiological function. Extracellular vesicles (EVs) derived from cancer cells play a significant role in adipocyte lipolysis, yet the mechanism remain uneclucidated. In this study, EVs derived from Lewis lung carcinoma (LLC) cells were extracted and characterized. 3T3-L1 and HIB1B adipocytes were cultured with conditioned medium or EVs from LLC, and LLC cells were used to establish a cancer cachexia mouse model. EVs derived from LLC cells were taken up by 3T3-L1 and HIB1B adipocytes, and derived exosomal EIF5A protein-induced lipolysis of adipocytes. High level of EIF5A was expressed in EVs from LLC cells, exosomal EIF5A is linked to lipid metabolism. Elevated expression of EIF5A is associated with shorter overall survival in lung cancer patients. Western blots, glycerol release and Oil red O staining assays were used to evaluate lipolysis of adipocytes. The reduction of lipolysis in 3T3-L1 and HIB1B adipocytes is achieved through silencing EIF5A or treating with pharmacologic inhibitor GC7 in vitro, and suppressing the expression of EIF5A in LLC cells by infected with shRNA or GC7 treatment partly alleviated white and brown adipose tissue lipolysis in vivo. Mechanistically, EIF5A directly binds with G protein-coupled bile acid receptor 1 (GPBAR1) mRNA to promote its translation and then activates cAMP response element binding protein (CREB) signaling pathway to induce lipolysis. This study demonstrates that exosomal EIF5A from LLC cells, with hypusinated EIF5A, has a lipolytic effect on adipocyte and adipose tissues in cancer cachexia model. Exosomal EIF5A could be involved in lipolysis and these findings indicate that a novel regulator and potential target for cachexia treatment.

ZHX2 emerges as a negative regulator of mitochondrial oxidative phosphorylation during acute liver injury

Mitochondria dysfunction contributes to acute liver injuries, and mitochondrial regulators, such as PGC-1α and MCJ, affect liver regeneration. Therefore, identification of mitochondrial modulators may pave the way for developing therapeutic strategies. Here, ZHX2 is identified as a mitochondrial regulator during acute liver injury. ZHX2 both transcriptionally inhibits expression of several mitochondrial electron transport chain genes and decreases PGC-1α stability, leading to reduction of mitochondrial mass and OXPHOS. Loss of Zhx2 promotes liver recovery by increasing mitochondrial OXPHOS in mice with partial hepatectomy or CCl4-induced liver injury, and inhibition of PGC-1α or electron transport chain abolishes these effects. Notably, ZHX2 expression is higher in liver tissues from patients with drug-induced liver injury and is negatively correlated with mitochondrial mass marker TOM20. Delivery of shRNA targeting Zhx2 effectively protects mice from CCl4-induced liver injury. Together, our data clarify ZHX2 as a negative regulator of mitochondrial OXPHOS and a potential target for developing strategies for improving liver recovery after acute injuries.

Polyamine metabolite spermidine rejuvenates oocyte quality by enhancing mitophagy during female reproductive aging

Advanced age is a primary risk factor for female infertility due to reduced ovarian reserve and declining oocyte quality. However, as an important contributing factor, the role of metabolic regulation during reproductive aging is poorly understood. Here, we applied untargeted metabolomics to identify spermidine as a critical metabolite in ovaries to protect oocytes against aging. In particular, we found that the spermidine level was reduced in ovaries of aged mice and that supplementation with spermidine promoted follicle development, oocyte maturation, early embryonic development and female fertility of aged mice. By microtranscriptomic analysis, we further discovered that spermidine-induced recovery of oocyte quality was mediated by enhancement of mitophagy activity and mitochondrial function in aged mice, and this mechanism of action was conserved in porcine oocytes under oxidative stress. Altogether, our findings suggest that spermidine supplementation could represent a therapeutic strategy to ameliorate oocyte quality and reproductive outcome in cis-gender women and other persons trying to conceive at an advanced age. Future work is needed to test whether this approach can be safely and effectively translated to humans.

Polyamines in Ovarian Aging and Disease

Ovarian aging and disease-related decline in fertility are challenging medical and economic issues with an increasing prevalence. Polyamines are a class of polycationic alkylamines widely distributed in mammals. They are small molecules essential for cell growth and development. Polyamines alleviate ovarian aging through various biological processes, including reproductive hormone synthesis, cell metabolism, programmed cell death, etc. However, an abnormal increase in polyamine levels can lead to ovarian damage and promote the development of ovarian disease. Therefore, polyamines have long been considered potential therapeutic targets for aging and disease, but their regulatory roles in the ovary deserve further investigation. This review discusses the mechanisms by which polyamines ameliorate human ovarian aging and disease through different biological processes, such as autophagy and oxidative stress, to develop safe and effective polyamine targeted therapy strategies for ovarian aging and the diseases.

Recent updates on the role of the gut-liver axis in the pathogenesis of NAFLD/NASH, HCC, and beyond

The gut and the liver are anatomically and physiologically connected, and this connection is called the "gut-liver axis," which exerts various influences on liver physiology and pathology. The gut microbiota has been recognized to trigger innate immunity and modulate the liver immune microenvironment. Gut microbiota influences the physiological processes in the host, such as metabolism, by acting on various signaling receptors and transcription factors through their metabolites and related molecules. The gut microbiota has also been increasingly recognized to modulate the efficacy of immune checkpoint inhibitors. In this review, we discuss recent updates on gut microbiota-associated mechanisms in the pathogenesis of chronic liver diseases such as NAFLD and NASH, as well as liver cancer, in light of the gut-liver axis. We particularly focus on gut microbial metabolites and components that are associated with these liver diseases. We also discuss the role of gut microbiota in modulating the response to immunotherapy in liver diseases.

Lipidomics Workflow for Analyzing Lipid Profiles Using Multiple Reaction Monitoring (MRM) in Liver Homogenate of Mice with Non-alcoholic Steatohepatitis (NASH)

Non-alcoholic steatohepatitis (NASH) is a condition characterized by inflammation and hepatic injury/fibrosis caused by the accumulation of ectopic fats in the liver. Recent advances in lipidomics have allowed the identification and characterization of lipid species and have revealed signature patterns of various diseases. Here, we describe a lipidomics workflow to assess the lipid profiles of liver homogenates taken from a NASH mouse model. The protocol described below was used to extract and analyze the metabolites from the livers of mice with NASH by liquid chromatography-mass spectrometry (LC-MS); however, it can be applied to other tissue homogenate samples. Using this method, over 1,000 species of lipids from five classes can be analyzed in a single run on the LC-MS. Also, partial elucidation of the identity of neutral lipid (triacylglycerides and diacylglycerides) aliphatic chains can be performed with this simple LC-MS setup. Key features Over 1,000 lipid species (sphingolipids, cholesteryl esters, neutral lipids, phospholipids, fatty acids) are analyzed in one run. Analysis of liver lipids in non-alcoholic steatohepatitis (NASH) mouse model. Normal-phase chromatography coupled to a triple quadrupole mass spectrometer.

Molecular targets of spermidine: implications for cancer suppression

Spermidine is a ubiquitous, natural polyamine with geroprotective features. Supplementation of spermidine extends the lifespan of yeast, worms, flies, and mice, and dietary spermidine intake correlates with reduced human mortality. However, the crucial role of polyamines in cell proliferation has also implicated polyamine metabolism in neoplastic diseases, such as cancer. While depleting intracellular polyamine biosynthesis halts tumor growth in mouse models, lifelong external spermidine administration in mice does not increase cancer incidence. In contrast, a series of recent findings points to anti-neoplastic properties of spermidine administration in the context of immunotherapy. Various molecular mechanisms for the anti-aging and anti-cancer properties have been proposed, including the promotion of autophagy, enhanced translational control, and augmented mitochondrial function. For instance, spermidine allosterically activates mitochondrial trifunctional protein (MTP), a bipartite protein complex that mediates three of the four steps of mitochondrial fatty acid (β-oxidation. Through this action, spermidine supplementation is able to restore MTP-mediated mitochondrial respiratory capacity in naïve CD8⁺ T cells to juvenile levels and thereby improves T cell activation in aged mice. Here, we put this finding into the context of the previously described molecular target space of spermidine.

Arginine metabolism regulates human erythroid differentiation through hypusination of eIF5A

Metabolic programs contribute to hematopoietic stem and progenitor cell (HSPC) fate, but it is not known whether the metabolic regulation of protein synthesis controls HSPC differentiation. Here, we show that SLC7A1/cationic amino acid transporter 1-dependent arginine uptake and its catabolism to the polyamine spermidine control human erythroid specification of HSPCs via the activation of the eukaryotic translation initiation factor 5A (eIF5A). eIF5A activity is dependent on its hypusination, a posttranslational modification resulting from the conjugation of the aminobutyl moiety of spermidine to lysine. Notably, attenuation of hypusine synthesis in erythroid progenitors, by the inhibition of deoxyhypusine synthase, abrogates erythropoiesis but not myeloid cell differentiation. Proteomic profiling reveals mitochondrial translation to be a critical target of hypusinated eIF5A, and accordingly, progenitors with decreased hypusine activity exhibit diminished oxidative phosphorylation. This affected pathway is critical for eIF5A-regulated erythropoiesis, as interventions augmenting mitochondrial function partially rescue human erythropoiesis under conditions of attenuated hypusination. Levels of mitochondrial ribosomal proteins (RPs) were especially sensitive to the loss of hypusine, and we find that the ineffective erythropoiesis linked to haploinsufficiency of RPS14 in chromosome 5q deletions in myelodysplastic syndrome is associated with a diminished pool of hypusinated eIF5A. Moreover, patients with RPL11-haploinsufficient Diamond-Blackfan anemia as well as CD34+ progenitors with downregulated RPL11 exhibit a markedly decreased hypusination in erythroid progenitors, concomitant with a loss of mitochondrial metabolism. Thus, eIF5A-dependent protein synthesis regulates human erythropoiesis, and our data reveal a novel role for RPs in controlling eIF5A hypusination in HSPCs, synchronizing mitochondrial metabolism with erythroid differentiation.

Dietary Supplementation with Putrescine Improves Growth Performance and Meat Quality of Wenchang Chickens

This study was to investigate the effects of dietary supplementation with putrescine on the growth performance and meat quality of chickens. A total of 480 eighty-day-old female Wenchang chickens were randomly assigned into four groups, with 8 replications per group and 15 animals per replicate. The chickens in the control group (Con) were fed a basal diet; the 3 experimental groups were fed a basal diet with 0.01%, 0.03%, and 0.05% putrescine, respectively. The experiment lasted for 40 days. The results showed that dietary supplementation with 0.05% putrescine increased (p < 0.05) the final body weight and average daily weight gain, and decreased the ratio of feed intake to the body weight gain of Wenchang chickens. Dietary supplementation with putrescine decreased the concentrations of putrescine, spermidine, and spermine in serum (p < 0.05). The contents of methionine, phenylalanine, lysine, aspartic acid, tyrosine, total essential amino acids, and total amino acids in breast muscle were higher (p < 0.05) in 0.03% and 0.05% groups than those in Con group. However, the contents of undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, arachidic acid, docosanoic acid, tricosanic acid, lignoceric acid, erucic acid, cis-11,14,17-eicosatrienoate, linoleic acid, and total n-6 monounsaturated fatty acids in breast muscle were lower (p < 0.05) in 0.03% and 0.05% groups than those in Con group. In addition, putrescine supplementation decreased (p < 0.05) the ratio of n-6/n-3 polyunsaturated fatty acids in breast meat. Overall, dietary supplementation with 0.05% putrescine enhanced the growth performance and meat quality of Wenchang chickens.

Restoring polyamine levels by supplementation of spermidine modulates hepatic immune landscape in murine model of NASH

AIMS

To determine if changes in polyamines metabolism occur during non-alcoholic steatohepatitis (NASH) in human patients and mice, as well as to assess systemic and liver-specific effects of spermidine administration into mice suffering from advanced NASH.

MATERIALS AND METHODS

Human fecal samples were collected from 50 healthy and 50 NASH patients. For the preclinical studies C57Bl6/N male mice fed GAN or NIH-31 diet for 6 months were ordered from Taconic and liver biopsy was performed. Based on severity of liver fibrosis, body composition and body weight, the mice from both dietary groups were randomized into another two groups: half receiving 3 mM spermidine in drinking water, half normal water for subsequent 12 weeks. Body weight was measured weekly and glucose tolerance and body composition were assessed at the end. Blood and organs were collected during necropsy, and intrahepatic immune cells were isolated for flow cytometry analysis.

RESULTS

Metabolomic analysis of human and murine feces confirmed that levels of polyamines decreased along NASH progression. Administration of exogenous spermidine to the mice from both dietary groups did not affect body weight, body composition or adiposity. Moreover, incidence of macroscopic hepatic lesions was higher in NASH mice receiving spermidine. On the other hand, spermidine normalized numbers of Kupffer cells in the livers of mice suffering from NASH, although these beneficial effects did not translate into improved liver steatosis or fibrosis severity.

CONCLUSION

Levels of polyamines decrease during NASH in mice and human patients but spermidine administration does not improve advanced NASH.

New K50R mutant mouse models reveal impaired hypusination of eif5a2 with alterations in cell metabolite landscape

The eukaryotic translation initiation factor 5A1 (eIF5A1) and 5A2 (eIF5A2) are important proteins in a variety of physiological and pathophysiological processes and their function has been linked to neurodevelopmental disorders, cancer, and viral infections. Here, we report two new genome-edited mouse models, generated using a CRISPR-Cas9 approach, in which the amino acid residue lysine 50 is replaced with arginine 50 (K50R) in eIF5A1 or in the closely related eIF5A2 protein. This mutation prevents the spermidine-dependent post-translational formation of hypusine, a unique lysine derivative that is necessary for activation of eIF5A1 and eIF5A2. Mouse brain lysates from homozygous eif5a2-K50R mutant mice (eif5a2K50R/K50R) confirmed the absence of hypusine formation of eIF5A2, and metabolomic analysis of primary mouse dermal fibroblasts revealed significant alterations in the metabolite landscape compared to controls including increased levels of tryptophan, kyrunenine, pyridoxine, nicotinamide adenine dinucleotide, riboflavin, flavin adenine dinucleotide, pantothenate, and coenzyme A. Further supported by new publicly available bioinformatics data, these new mouse models represent excellent in vivo models to study hypusine-dependent biological processes, hypusination-related disorders caused by eIF5A1 and eIF5A2 gene aberrations or mRNA expression dysregulation, as well as several major human cancer types and potential therapies.

Translational Control of Metabolism and Cell Cycle Progression in Hepatocellular Carcinoma

The liver is a metabolic hub characterized by high levels of protein synthesis. Eukaryotic initiation factors, eIFs, control the first phase of translation, initiation. Initiation factors are essential for tumor progression and, since they regulate the translation of specific mRNAs downstream of oncogenic signaling cascades, may be druggable. In this review, we address the issue of whether the massive translational machinery of liver cells contributes to liver pathology and to the progression of hepatocellular carcinoma (HCC); it represents a valuable biomarker and druggable target. First, we observe that the common markers of HCC cells, such as phosphorylated ribosomal protein S6, belong to the ribosomal and translational apparatus. This fact is in agreement with observations that demonstrate a huge amplification of the ribosomal machinery during the progression to HCC. Some translation factors, such as eIF4E and eIF6, are then harnessed by oncogenic signaling. In particular, the action of eIF4E and eIF6 is particularly important in HCC when driven by fatty liver pathologies. Indeed, both eIF4E and eIF6 amplify at the translational level the production and accumulation of fatty acids. As it is evident that abnormal levels of these factors drive cancer, we discuss their therapeutic value.

The interplay between nonalcoholic fatty liver disease and atherosclerotic cardiovascular disease

Therapeutic approaches that lower circulating low-density lipoprotein (LDL)-cholesterol significantly reduced the burden of cardiovascular disease over the last decades. However, the persistent rise in the obesity epidemic is beginning to reverse this decline. Alongside obesity, the incidence of nonalcoholic fatty liver disease (NAFLD) has substantially increased in the last three decades. Currently, approximately one third of world population is affected by NAFLD. Notably, the presence of NAFLD and particularly its more severe form, nonalcoholic steatohepatitis (NASH), serves as an independent risk factor for atherosclerotic cardiovascular disease (ASCVD), thus, raising interest in the relationship between these two diseases. Importantly, ASCVD is the major cause of death in patients with NASH independent of traditional risk factors. Nevertheless, the pathophysiology linking NAFLD/NASH with ASCVD remains poorly understood. While dyslipidemia is a common risk factor underlying both diseases, therapies that lower circulating LDL-cholesterol are largely ineffective against NASH. While there are no approved pharmacological therapies for NASH, some of the most advanced drug candidates exacerbate atherogenic dyslipidemia, raising concerns regarding their adverse cardiovascular consequences. In this review, we address current gaps in our understanding of the mechanisms linking NAFLD/NASH and ASCVD, explore strategies to simultaneously model these diseases, evaluate emerging biomarkers that may be useful to diagnose the presence of both diseases, and discuss investigational approaches and ongoing clinical trials that potentially target both diseases.

The pleiotropic roles of eIF5A in cellular life and its therapeutic potential in cancer

Protein synthesis is dysregulated in the majority of cancers and this process therefore provides a good therapeutic target. Many novel anti-cancer agents are directed to target the initiation stage of translation, however, translation elongation also holds great potential as a therapeutic target. The elongation factor eIF5A that assists the formation of peptidyl bonds during the elongation process is of considerable interest in this regard. Overexpression of eIF5A has been linked with the development of a variety of cancers and inhibitors of the molecule have been proposed for anti-cancer clinical applications. eIF5A is the only protein in the cell that contains the post-translational modification hypusine. Hypusination is a two-step enzymatic process catalysed by the Deoxyhypusine Synthase (DHPS) and Deoxyhypusine Hydroxylase (DOHH). In addition, eIF5A can be acetylated by p300/CBP-associated factor (PCAF) which leads to translocation of the protein to the nucleus and its deactivation. In addition to the nucleus, eIF5A has been found in the mitochondria and the endoplasmic reticulum (ER) with eIF5A localisation related to function from regulation of mitochondrial activity and apoptosis to maintenance of ER integrity and control of the unfolded protein response (UPR). Given the pleiotropic functions of eIF5A and by extension the hypusination enzymes, this system is being considered as a target for a range of cancers including multiple myeloma, B-Cell lymphoma, and neuroblastoma. In this review, we explore the role of eIF5A and discuss the therapeutic strategies that are currently developing both in the pre- and the clinical stage.