Polyamines Control eIF5A Hypusination, TFEB Translation, and Autophagy to Reverse B Cell Senescence

Spermidine mitigates blue-light-induced corneal injury by alleviating oxidative stress and restoring autophagy impairment

This study investigated the protective efficacy of spermidine on corneal epithelium exposed to photodamage from artificial blue light (BL). After six weeks of BL exposure, the rabbit cornea exhibited epithelial injury and delayed wound healing accompanied by downregulation of spermidine, as identified through metabolomic analysis. Pathways related to autophagy and the antioxidant response were implicated in this process. In vitro, spermidine mitigated BL-induced reductions in viability and proliferation of human corneal epithelial cells, decreased cell death, and enhanced colony formation. Spermidine also partially reversed BL-induced mitochondrial dysfunction, oxidative stress and autophagy impairment. Furthermore, topical administration of spermidine eye drops reduced epithelial injury in the rabbit cornea under BL exposure, demonstrating benefits in promoting cell proliferation, accelerating wound healing, and maintaining antioxidant capacity and autophagy.

Quiescent cell re-entry is limited by macroautophagy-induced lysosomal damage

To maintain tissue homeostasis, many cells reside in a quiescent state until prompted to divide. The reactivation of quiescent cells is perturbed with aging and may underlie declining tissue homeostasis and resiliency. The unfolded protein response regulators IRE-1 and XBP-1 are required for the reactivation of quiescent cells in developmentally L1-arrested C. elegans. Utilizing a forward genetic screen in C. elegans, we discovered that macroautophagy targets protein aggregates to lysosomes in quiescent cells, leading to lysosome damage. Genetic inhibition of macroautophagy and stimulation of lysosomes via the overexpression of HLH-30 (TFEB/TFE3) synergistically reduces lysosome damage. Damaged lysosomes require IRE-1/XBP-1 for their repair following prolonged L1 arrest. Protein aggregates are also targeted to lysosomes by macroautophagy in quiescent cultured mammalian cells and are associated with lysosome damage. Thus, lysosome damage is a hallmark of quiescent cells, and limiting lysosome damage by restraining macroautophagy can stimulate their reactivation.

T-cell Senescence in the Tumor Microenvironment

T-cell senescence occurs in the tumor microenvironment (TME) and influences cancer outcomes as well as the effectiveness of immunotherapies. The TME triggers this T-cell senescence via multiple pathways, including persistent stimulation with tumor-associated antigens, altered metabolic pathways, and activation of chronic inflammatory responses. Senescent T cells exhibit characteristics such as genomic instability, loss of protein homeostasis, metabolic dysregulation, and epigenetic alterations. Direct cross-talk between senescent T cells and other immune cells further exacerbates the immunosuppressive TME. This immune-tumor cell interaction within the TME contributes to impaired tumor antigen recognition and surveillance by T cells. The presence of senescent T cells is often associated with poor prognosis and reduced efficacy of immunotherapies; thus, targeting the tumor-promoting mechanisms of T-cell senescence may provide novel insights into improving tumor immunotherapy and patient outcomes. This review explores the contributors to tumor-derived T-cell senescence, the link between T-cell senescence and tumor prognosis, and the potential for targeting T-cell senescence to enhance tumor immunotherapy.

Putrescine promotes maturation of oocytes from reproductively old mice via mitochondrial autophagy

RESEARCH QUESTION

Does putrescine (PUT) improve oocytes from reproductively old mice by promoting mitochondrial autophagy?

DESIGN

Germinal vesicle stage cumulus-oocyte complexes (COCs) were obtained from 9-month old female C57BL/6N mice and divided into control, PUT and difluoromethylornithine, inhibitor (DFMO) groups. These germinal vesicle COCs underwent mouse in-vitro maturation (IVM) culture to observe the extrusion of the first polar body in each group. Using JC-1, dichloro-dihydro-fluorescein diacetate fluorescent probes and a confocal microscope, the mitochondrial membrane potential integrity and reactive oxygen species levels were measured in metaphase II stage oocytes. The expression and cellular localization of the p53 protein were examined by immunofluorescence. Reverse transcription quantitative polymerase chain reaction was used to detect the activation of mitochondrial autophagy pathways. The potential mechanisms through which PUT improves oocytes from reproductively old mice were explored by single-cell transcriptomic analysis. Autophagosomes, autolysosomes and mitochondria in different groups were directly observed using transmission electron microscopy.

RESULTS

The addition of exogenous PUT can promote IVM of oocytes from reproductively old mice. It reduces oxidative stress by promoting the autophagy of damaged mitochondria, decreasing the levels of reactive oxygen species and increasing mitochondrial membrane potential. It affects the expression and subcellular localization of the p53 protein, and increases the expression of transcription factor EB, which may be the potential mechanism behind its promotion of autophagy.

CONCLUSION

The target and regulatory pathway of PUT in oocytes was clarified. Putrescine is an effective small molecule compound with significant potential for non-invasively improving the fertility of elderly women.

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.

Research progress on the microbial metabolism and transport of polyamines and their roles in animal gut homeostasis

Polyamines (putrescine, spermidine, and spermine) are aliphatic compounds ubiquitous in prokaryotes and eukaryotes. Positively charged polyamines bind to negatively charged macromolecules, such as nucleic acids and acidic phospholipids, and are involved in physiological activities including cell proliferation, differentiation, apoptosis and gene regulation. Intracellular polyamine levels are regulated by biosynthesis, catabolism and transport. Polyamines in the body originate from two primary sources: dietary intake and intestinal microbial metabolism. These polyamines are then transported into the bloodstream, through which they are distributed to various tissues and organs to exert their biological functions. Polyamines synthesized by intestinal microorganisms serve dual critical roles. First, they are essential for maintaining polyamine concentrations within the digestive tract. Second, through transcriptional and post-transcriptional mechanisms, these microbial-derived polyamines modulate the expression of genes governing key processes in intestinal epithelial cells-including proliferation, migration, apoptosis, and cell-cell interactions. Collectively, these regulatory effects help maintain intestinal epithelial homeostasis and ensure the integrity of the gut barrier. In addition, polyamines interact with the gut microbiota to maintain intestinal homeostasis by promoting microbial growth, biofilm formation, swarming, and endocytosis vesicle production, etc. Supplementation with polyamines has been demonstrated to be important in regulating host intestinal microbial composition, enhancing nutrient absorption, and improving metabolism and immunity. In this review, we will focus on recent advances in the study of polyamine metabolism and transport in intestinal microbes and intestinal epithelial cells. We then summarize the scientific understanding of their roles in intestinal homeostasis, exploring the advances in cellular and molecular mechanisms of polyamines and their potential clinical applications, and providing a rationale for polyamine metabolism as an important target for the treatment of intestinal-based diseases.

Spermine attenuates TGF-β-induced EMT by downregulating fibronectin

Epithelial-mesenchymal transition (EMT) is a highly dynamic cellular process that occurs in development, tissue repair, and cancer metastasis. As a master EMT inducer, transforming growth factor-beta (TGF-β) can activate the EMT program by regulating the expression of key EMT-related genes and triggering other required cellular changes. However, it is unclear whether cell metabolism is involved in TGF-β-induced EMT. Here, we characterized early metabolic changes in response to transient TGF-β stimulation in HaCaT cells and discovered that TGF-β signaling significantly reduces the intracellular polyamine pool. Exogenous addition of spermine, but not other polyamines, attenuates TGF-β-induced EMT. Mechanistically, spermine downregulates the extracellular matrix protein fibronectin. Furthermore, we found that TGF-β activates extracellular signal-regulated kinase to enhance the expression of spermine oxidase, which is responsible for the reduced spermine concentration. This action of TGF-β on EMT via the polyamine metabolism provides new insights into the mechanisms underlying EMT and might be exploited as a way to target the EMT program for therapy.

Spermidine restricts neonatal inflammation via metabolic shaping of polymorphonuclear myeloid-derived suppressor cells

Newborns exhibit a heightened vulnerability to inflammatory disorders due to their underdeveloped immune system, yet the underlying mechanisms remain poorly understood. Here we report that plasma spermidine is correlated with the maturity of human newborns and reduced risk of inflammation. Administration of spermidine led to the remission of neonatal inflammation in mice. Mechanistic studies revealed that spermidine enhanced the generation of polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) via downstream eIF5A hypusination. Genetic deficiency or pharmacological inhibition of deoxyhypusine synthase (DHPS), a key enzyme of hypusinated eIF5A (eIF5AHyp), diminished the immunosuppressive activity of PMN-MDSCs, leading to aggravated neonatal inflammation. The eIF5AHyp pathway was found to enhance the immunosuppressive function via histone acetylation-mediated epigenetic transcription of immunosuppressive signatures in PMN-MDSCs. These findings demonstrate the spermidine-eIF5AHyp metabolic axis as a master switch to restrict neonatal inflammation.

Genetic analyses of Myc and hypusine circuits in tumorigenesis

A prominent metabolic pathway induced by MYC family oncoproteins in cancer is the polyamine-hypusine circuit, which post-translationally modifies a specific lysine residue of eukaryotic translation initiation factor 5 A (eIF5A) with a unique amino acid coined hypusine [Nε-(4-amino-2-hydroxybutyl)lysine]. This modification occurs in a two-step process, whereby the aminobutyl group of the polyamine spermidine is covalently linked to lysine-50 of eIF5A via deoxyhypusine synthase (DHPS) to form the intermediate deoxyhypusinated eIF5A, which is subsequently hydoxylated by deoxyhypusine hydroxylase (DOHH) to form the fully mature eIF5AHyp. As a result, eIF5AHyp is elevated in MYC-driven cancers. Recently it has become evident that eIF5AHyp (i) plays key roles in the development, progression and maintenance of tumors; and (ii) eIF5AHyp functions are often tissue/cell context-specific. Thus, it is important to mechanistically assess how eIF5AHyp affects normal cells and tumorigenesis using suitable in vivo and ex vivo models. In this chapter, we describe the methods used in our laboratory to assess the effects of MYC-polyamine-hypusine axis on the development and maintenance of MYC-driven B-cell lymphoma. The goals of this chapter are twofold. First, we discuss genetic and cell biological approaches that can be applied to assess roles of eIF5AHyp on lymphoma and normal B cell development. Second, we discuss methods that can be used to assess the roles of eIF5AHyp on the growth and maintenance of lymphoma. Collectively, these approaches provide a template that can be applied to evaluate roles of any putative regulator of the development and/or maintenance of lymphoma.

Spermidine as a Potential Protective Agents Against Poly(I:C)-Induced Immune Response, Oxidative Stress, Apoptosis, and Testosterone Decrease in Yak Leydig Cells

Viral infections of the reproductive tract and testis in male yaks, often resulting from natural mating under grazing conditions, can lead to infertility due to Leydig cell (LC) apoptosis, immune activation, oxidative stress, and reduced testosterone production. Spermidine (SPD), a potential therapeutic agent with antioxidant and anti-aging properties, might alleviate oxidant stress, immune response, and virus infection caused by apoptosis. In this study, firstly testicular Leydig cells of yak were induced with Poly(I:C), the pathogen-associated molecular pattern of the dsRNA virus, as a pathogenic model at the cellular level. Secondly, immune response, apoptosis, oxidative stress, and testosterone synthesis were measured in LC with or without SPD culture medium. Finally, transcriptomic sequencing was utilized to investigate the molecular mechanisms underlying the protective effects of SPD. These results suggested Poly(I:C) damaged the function of Leydig cells, significantly decreased the concentration of testosterone, and induced immune response, oxidative stress, and cell apoptosis, while SPD significantly alleviated the immune response and oxidative stress, and then significantly inhibited cell apoptosis and restores testosterone production in LCs. Transcriptomic analysis revealed that SPD significantly alleviates inflammation and apoptosis induced by Poly(I:C), reducing immune response and cellular damage through the regulation of several key gene expressions. These findings suggest SPD has the potential ability to mitigate Poly(I:C)-induced immune response, oxidative stress, and apoptosis, and then restore testosterone production in Leydig cells, offering a promising strategy to protect and enhance male yak fertility after infection with dsRNA virus.

Mutation of an insulin-sensitive Drosophila insulin-like receptor mutant requires methionine metabolism reprogramming to extend lifespan

Insulin/insulin growth factor signaling is a conserved pathway that regulates lifespan across many species. Multiple mechanisms are proposed for how this altered signaling slows aging. To elaborate these causes, we recently developed a series of Drosophila insulin-like receptor (dInr) mutants with single amino acid substitutions that extend lifespan but differentially affect insulin sensitivity, growth and reproduction. Transheterozygotes of canonical dInr mutants (Type I) extend longevity and are insulin-resistant, small and weakly fecund. In contrast, a dominant mutation (dInr 353, Type II) within the Kinase Insert Domain (KID) robustly extends longevity but is insulin-sensitive, full-sized, and highly fecund. We applied transcriptome and metabolome analyses to explore how dInr 353 slows aging without insulin resistance. Type I and II mutants overlap in many pathways but also produce distinct transcriptomic profiles that include differences in innate immune and reproductive functions. In metabolomic analyses, the KID mutant dInr 353 reprograms methionine metabolism in a way that phenocopies dietary methionine restriction, in contrast to canonical mutants which are characterized by upregulation of the transsulfuration pathway. Because abrogation of S-adenosylhomocysteine hydrolase blocks the longevity benefit conferred by dInr 353, we conclude the methionine cycle reprogramming of Type II is sufficient to slow aging. Metabolomic analysis further revealed the Type II mutant is metabolically flexible: unlike aged wildtype, aged dInr 353 adults can reroute methionine toward the transsulfuration pathway, while Type I mutant flies upregulate the trassulfuration pathway continuously from young age. Altered insulin/insulin growth factor signaling has the potential to slow aging without the complications of insulin resistance by modulating methionine cycle dynamics.

The Yeast-Fermented Garlic and a Balance of Spermine/Spermidine Activates Autophagy via EGR1 Transcriptional Factor

Spermine (SPM) and spermidine (SPD) are polyamines found in all organisms, and their concentrations can be regulated by ingestion. We demonstrated that yeast-fermented garlic (YF) extract significantly increased autophag flux in OUMS-36T-1 and HeLa cells expressing the fluorescent probe (GFP-LC3-RFP-LC3ΔG). YF-induced increase of autophagy occurred independently of mTORC1 signaling, and RNA-sequencing analysis revealed that EGR1 was the most significantly altered gene in YF-treated OUMS-36T-1 cells. YF-treated EGR1-deficient HAP1 cells displayed reduced autophagic flux (p < 0.05). YF-induced increasing of autophagic flux occurred via a specific SPM/SPD ratio. HAP1 cells treated with equivalent amounts of SPD or SPM as that found in YF did not increase autophagic flux (p > 0.05); however, treatment with SPD and SPM in the same ratio as that found in YF increased autophagic flux (p < 0.05). This specific SPM/SPD ratio reduced MG132-induced proteostress via EGR1-dependent pathways (p < 0.05). Thus, the SPM/SPD balance may regulate autophagy via EGR1-dependent pathways, and controlling this balance may provide a strategy to maintain cellular homeostasis.

eIF5A downregulated by mechanical overloading delays chondrocyte senescence and osteoarthritis by regulating the CREBBP-mediated Notch pathway

Aims

To examine how eukaryotic translation initiation factor 5A (eIF5A) regulates osteoarthritis (OA) during mechanical overload and the specific mechanism.

Methods

Histological experiments used human bone samples and C57BL/6J mice knee samples. All cell experiments were performed using mice primary chondrocytes. Messenger RNA (mRNA) sequencing was performed on chondrocytes treated with 20% cyclic tensile strain for 24 hours. Western blot (WB) and quantitative polymerase chain reaction were employed to detect relevant indicators of cartilage function in chondrocytes. We created the destabilization of the medial meniscus (DMM) model and the mechanical overload-induced OA model and injected with overexpressing eIF5A adenovirus (eIF5A-ADV). Cartilage degeneration was evaluated using Safranin O/Fast Green staining. Relative protein levels were ascertained by immunohistochemistry (IHC) and immunofluorescence (IF) staining.

Results

After OA initiation, eIF5A caused an upregulation of type II collagen (COL2) and a downregulation of matrix metalloproteinase 13 (MMP13), P16, and P21, which postponed the aggravation of OA. Further sequencing and experimental findings revealed that eIF5A knockdown accelerated the progression of OA by boosting the expression of histone acetyltransferase cyclic-adenosine monophosphate response element binding protein (CREB)-binding protein (CREBBP) to mediate activation of the Notch pathway.

Conclusion

Our findings identified a crucial functional mechanism for the onset of OA, and suggest that intra-articular eIF5A injections might be a useful therapeutic strategy for OA treatment.

Polyamine metabolism and anti-tumor immunity

Growing attention has been directed toward the critical role of polyamines in the tumor microenvironment and immune regulation. Polyamines, primarily comprising putrescine, spermidine, and spermine, are tightly regulated through coordinated biosynthesis, catabolism, and transport, with distinct metabolic patterns between normal and cancerous tissues. Emerging evidence highlights the pivotal role of polyamine metabolism in tumor initiation, progression, and metastasis. This review aims to elucidate the differences in polyamine biosynthesis, transport, and catabolism between normal and cancerous tissues, as well as the associated alterations in tumor epigenetic modifications and resistance to immune checkpoint blockade driven by polyamine metabolism. Polyamine metabolism influences both tumor cells and the tumor microenvironment by modulating immune cell phenotypes-shifting them towards either tumor suppression or immune evasion within the tumor immune microenvironment. Additionally, polyamine metabolism impacts immunotherapy through its regulation of key enzymes. This review also explores potential therapeutic targets and summarizes the roles of polyamine inhibitors in combination with immunotherapy for cancer treatment, offering a novel perspective on therapeutic strategies.

Polyamine biosynthesis dysregulation in Alzheimer's disease and Down syndrome cellular models

BACKGROUND

Individuals with Down Syndrome (DS) frequently develop early onset Alzheimer's disease (AD) with pathological hallmarks closely resembling AD due to several triplicated genes on chromosome 21. Polyamines are small, organic molecules that play a pivotal role for growth and differentiation, and a dysregulation of polyamine pathways is implicated in AD pathology. However, their role in DS-associated AD is unclear.

METHODS

We analyzed polyamines and their metabolite levels in mouse hippocampal cells and human DS-AD and AD hippocampal tissue and assessed the effects of the ODC inhibitor difluoromethylornithine (DFMO) on Aβ42 aggregation and protein expression in DS fibroblasts.

RESULTS

Amyloid-β42 increased polyamine levels via ornithine decarboxylase (ODC) activation in a dose-dependent manner. DFMO reduced Aβ42 aggregation, decreased amyloid precursor protein (APP) levels, and normalized proteins linked to AD pathology in DS fibroblasts. Polyamine levels were elevated in DS-AD hippocampal tissue, with colocalization of ODC and Aβ42 aggregates.

CONCLUSION

These findings suggest that polyamine biosynthesis may exacerbate Aβ42 toxicity and APP expression, contributing to AD progression in DS. The ability of DFMO to reduce Aβ42 aggregation and restore protein homeostasis presents the polyamine pathway as a therapeutic target for DS-AD management.

Fungi, immunosenescence and cancer

Fungal microbes are a small but immunoreactive component of the human microbiome, which may influence cancer development, progression and therapeutic response. Immunosenescence is a process of immune dysfunction that occurs with aging, including lymphoid organ remodeling, contributing to alterations in the immune system in the elderly, which plays a critical role in many aspects of cancer. There is evidence for the interactions between fungi and immunosenescence in potentially regulating cancer progression and remodeling the tumor microenvironment (TME). In this review, we summarize potential roles of commensal and pathogenic fungi in modulating cancer-associated processes and provide more-detailed discussions on the mechanisms of which fungi affect tumor biology, including local and distant regulation of the TME, modulating antitumor immune responses and interactions with neighboring bacterial commensals. We also delineate the features of immunosenescence and its influence on cancer development and treatment, and highlight the interactions between fungi and immunosenescence in cancer. We discuss the prospects and challenges for harnessing fungi and immunosenescence in cancer diagnosis and/or treatment. Considering the limited understanding and techniques in conducting such research, we also provide our view on how to overcome challenges faced by the exploration of fungi, immunosenescence and their interactions on tumor biology.

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.

Age-related TFEB downregulation in proximal tubules causes systemic metabolic disorders and occasional apolipoprotein A4-related amyloidosis

With the aging of society, the incidence of chronic kidney disease (CKD), a common cause of death, has been increasing. Transcription factor EB (TFEB), the master transcriptional regulator of the autophagy/lysosomal pathway, is regarded as a promising candidate for preventing various age-related diseases. However, whether TFEB in the proximal tubules plays a significant role in elderly patients with CKD remains unknown. First, we found that nuclear TFEB localization in proximal tubular epithelial cells (PTECs) declined with age in both mice and humans. Next, we generated PTEC-specific Tfeb-deficient mice and bred them for up to 24 months. We found that TFEB deficiency in the proximal tubules caused metabolic disorders and occasionally led to apolipoprotein A4 (APOA4) amyloidosis. Supporting this result, we identified markedly decreased nuclear TFEB localization in the proximal tubules of elderly patients with APOA4 amyloidosis. The metabolic disturbances were accompanied by mitochondrial dysfunction due to transcriptional changes involved in fatty acid oxidation and oxidative phosphorylation pathways, as well as decreased mitochondrial clearance. This decreased clearance was reflected by the accumulation of mitochondria-lysosome-related organelles, which depended on lysosomal function. These results shed light on the presumptive mechanisms of APOA4 amyloidosis pathogenesis and provide a therapeutic strategy for CKD-related metabolic disorders and APOA4 amyloidosis.

Autophagy and lysosomal dysfunction in diabetes and its complications

Autophagy is critical for energy homeostasis and the function of organelles such as endoplasmic reticulum (ER) and mitochondria. Dysregulated autophagy due to aging, environmental factors, or genetic predisposition can be an underlying cause of not only diabetes through β-cell dysfunction and metabolic inflammation, but also diabetic complications such as diabetic kidney diseases (DKDs). Dysfunction of lysosomes, effector organelles of autophagic degradation, due to metabolic stress or nutrients/metabolites accumulating in metabolic diseases is also emerging as a cause or aggravating element in diabetes and its complications. Here, we discuss the etiological role of dysregulated autophagy and lysosomal dysfunction in diabetes and a potential role of autophagy or lysosomal modulation as a new avenue for treatment of diabetes and its complications.

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.

The nutrient-sensing Rag-GTPase complex in B cells controls humoral immunity via TFEB/TFE3-dependent mitochondrial fitness

Germinal center (GC) formation, which is an integrant part of humoral immunity, involves energy-consuming metabolic reprogramming. Rag-GTPases are known to signal amino acid availability to cellular pathways that regulate nutrient distribution such as the mechanistic target of rapamycin complex 1 (mTORC1) pathway and the transcription factors TFEB and TFE3. However, the contribution of these factors to humoral immunity remains undefined. Here, we show that B cell-intrinsic Rag-GTPases are critical for the development and activation of B cells. RagA/RagB deficient B cells fail to form GCs, produce antibodies, and to generate plasmablasts during both T-dependent (TD) and T-independent (TI) humoral immune responses. Deletion of RagA/RagB in GC B cells leads to abnormal dark zone (DZ) to light zone (LZ) ratio and reduced affinity maturation. Mechanistically, the Rag-GTPase complex constrains TFEB/TFE3 activity to prevent mitophagy dysregulation and maintain mitochondrial fitness in B cells, which are independent of canonical mTORC1 activation. TFEB/TFE3 deletion restores B cell development, GC formation in Peyer's patches and TI humoral immunity, but not TD humoral immunity in the absence of Rag-GTPases. Collectively, our data establish the Rag GTPase-TFEB/TFE3 pathway as a likely mTORC1 independent mechanism to coordinating nutrient sensing and mitochondrial metabolism in B cells.

Probiotics and their metabolite spermidine enhance IFN-γ+CD4+ T cell immunity to inhibit hepatitis B virus

The therapeutic potential of commensal microbes and their metabolites is promising in the functional cure of chronic hepatitis B virus (HBV) infection, which is defined as hepatitis B surface antigen (HBsAg) loss. Here, using both specific-pathogen-free and germ-free mice, we report that probiotics significantly promote the decline of HBsAg and inhibit HBV replication by enhancing intestinal homeostasis and provoking intrahepatic interferon (IFN)-γ+CD4+ T cell immune response. Depletion of CD4+ T cells or blockage of IFN-γ abolishes probiotics-mediated HBV inhibition. Specifically, probiotics-derived spermidine accumulates in the gut and transports to the liver, where it exhibits a similar anti-HBV effect. Mechanistically, spermidine enhances IFN-γ+CD4+ T cell immunity by autophagy. Strikingly, administration of probiotics in HBV patients reveals a preliminary trend to accelerate the decline of serum HBsAg. In conclusion, probiotics and their derived spermidine promote HBV clearance via autophagy-enhanced IFN-γ+CD4+ T cell immunity, highlighting the therapeutic potential of probiotics and spermidine for the functional cure of HBV patients.

Unveiling the Longevity Potential of Natural Phytochemicals: A Comprehensive Review of Active Ingredients in Dietary Plants and Herbs

Ancient humans used dietary plants and herbs to treat disease and to pursue eternal life. Today, phytochemicals in dietary plants and herbs have been shown to be the active ingredients, some of which have antiaging and longevity-promoting effects. Here, we summarize 210 antiaging phytochemicals in dietary plants and herbs, systematically classify them into 8 groups. We found that all groups of phytochemicals can be categorized into six areas that regulate organism longevity: ROS levels, nutrient sensing network, mitochondria, autophagy, gut microbiota, and lipid metabolism. We review the role of these processes in aging and the molecular mechanism of the health benefits through phytochemical-mediated regulation. Among these, how phytochemicals promote longevity through the gut microbiota and lipid metabolism is rarely highlighted in the field. Our understanding of the mechanisms of phytochemicals based on the above six aspects may provide a theoretical basis for the further development of antiaging drugs and new insights into the promotion of human longevity.

Spermidine Associated with Gut Microbiota Protects Against MRSA Bloodstream Infection by Promoting Macrophage M2 Polarization

Methicillin-resistant Staphylococcus aureus (MRSA) is a major human pathogen that causes various diseases. Extensive researches highlight the significant role of gut microbiota and its metabolites, particularly spermidine, in infectious diseases. However, the immunomodulatory mechanisms of spermidine in MRSA-induced bloodstream infection remain unclear. Here, we confirmed the protective effects of spermidine in bloodstream infection in mice. Spermidine reduced the bacterial load and expression of inflammatory factors by shifting the macrophage phenotype to an anti-inflammatory phenotype, ultimately prolonging the survival of the infected mice. The protective effect against MRSA infection may rely on the elevated expression of protein tyrosine phosphatase nonreceptor 2 (PTPN2). Collectively, these findings confirm the immunoprotective effects of spermidine via binding to PTPN2 in MRSA bloodstream infection, providing new ideas for the treatment of related infectious diseases.

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.

Putrescine can inhibit germinal center B cell differentiation by inducing reactive oxygen species generation

ABSTRACT

Polyamine synthesis and abnormal regulation of B cell differentiation occur concurrently in various diseases. We investigated whether putrescine could suppress germinal center B cell (GCB) differentiation by inducing reactive oxygen species (ROS) generation. The results of flow cytometry analysis revealed that putrescine did not affect B cell apoptosis and cell cycle. The results of RT-qPCR and western blotting revealed that putrescine could inhibit CD79a phosphorylation rather than total expression. Using an O2K high-resolution respirometer, we illustrated that putrescine increased the oxygen consumption rate in the basal mitochondrial respiration stage, ATP-coupled respiration stage, and maximum respiration stage. Similarly, it also elevated ROS generation across stages in B cells and reduced the proportion of GCB cells. Meanwhile, ROS scavenging by SOD could reverse such inhibitory effects on GCB cells. We concluded that putrescine could inhibit the differentiation of GCB cells by reducing CD79a phosphorylation and increasing ROS levels in GCB cells.

Natural Autophagy Activators to Fight Age-Related Diseases

The constant increase in the elderly population presents significant challenges in addressing new social, economic, and health problems concerning this population. With respect to health, aging is a primary risk factor for age-related diseases, which are driven by interconnected molecular hallmarks that influence the development of these diseases. One of the main mechanisms that has attracted more attention to aging is autophagy, a catabolic process that removes and recycles damaged or dysfunctional cell components to preserve cell viability. The autophagy process can be induced or deregulated in response to a wide range of internal or external stimuli, such as starvation, oxidative stress, hypoxia, damaged organelles, infectious pathogens, and aging. Natural compounds that promote the stimulation of autophagy regulatory pathways, such as mTOR, FoxO1/3, AMPK, and Sirt1, lead to increased levels of essential proteins such as Beclin-1 and LC3, as well as a decrease in p62. These changes indicate the activation of autophagic flux, which is known to be decreased in cardiovascular diseases, neurodegeneration, and cataracts. The regulated administration of natural compounds offers an adjuvant therapeutic alternative in age-related diseases; however, more experimental evidence is needed to support and confirm these health benefits. Hence, this review aims to highlight the potential benefits of natural compounds in regulating autophagy pathways as an alternative approach to combating age-related diseases.

Spermidine-eIF5A axis is essential for muscle stem cell activation via translational control

Adult skeletal muscle stem cells, also known satellite cells (SCs), are quiescent and activate in response to injury. However, the activation mechanisms of quiescent SCs (QSCs) remain largely unknown. Here, we investigated the metabolic regulation of SC activation by identifying regulatory metabolites that promote SC activation. Using targeted metabolomics, we found that spermidine acts as a regulatory metabolite to promote SC activation and muscle regeneration in mice. Mechanistically, spermidine activates SCs via generating hypusinated eIF5A. Using SC-specific eIF5A-knockout (KO) and Myod-KO mice, we further found that eIF5A is required for spermidine-mediated SC activation by controlling MyoD translation. More significantly, depletion of eIF5A in SCs results in impaired muscle regeneration in mice. Together, the findings of our study define a novel mechanism that is essential for SC activation and acts via spermidine-eIF5A-mediated MyoD translation. Our findings suggest that the spermidine-eIF5A axis represents a promising pharmacological target in efforts to activate endogenous SCs for the treatment of muscular disease.

A review on polyamines as promising next-generation neuroprotective and anti-aging therapy

Neurodegenerative disorders are diseases characterized by progressive degeneration of neurons and associated structures and are a major global issue growing more widespread as the global population's average age increases. Despite several investigations on their etiology, the specific cause of these disorders remains unknown. However, there are few symptomatic therapies to treat these disorders. Polyamines (PAs) (putrescine, spermidine, and spermine) are being studied for their role in neuroprotection, aging and cognitive impairment. They are ubiquitous polycations which have relatively higher concentrations in the brain and possess pleiotropic biochemical activities, including regulation of gene expression, ion channels, mitochondria Ca2+ transport, autophagy induction, programmed cell death, and many more. Their cellular content is tightly regulated, and substantial evidence indicates that their altered levels and metabolism are strongly implicated in aging, stress, cognitive dysfunction, and neurodegenerative disorders. In addition, dietary polyamine supplementation has been reported to induce anti-aging effects, anti-oxidant effects, and improve locomotor abnormalities, and cognitive dysfunction. Thus, restoring the polyamine level is considered a promising pharmacological strategy to counteract neurodegeneration. This review highlights PAs' physiological role and the molecular mechanism underpinning their proposed neuroprotective effect in aging and neurodegenerative disorders.

Spermidine is essential for fasting-mediated autophagy and longevity

Caloric restriction and intermittent fasting prolong the lifespan and healthspan of model organisms and improve human health. The natural polyamine spermidine has been similarly linked to autophagy enhancement, geroprotection and reduced incidence of cardiovascular and neurodegenerative diseases across species borders. Here, we asked whether the cellular and physiological consequences of caloric restriction and fasting depend on polyamine metabolism. We report that spermidine levels increased upon distinct regimens of fasting or caloric restriction in yeast, flies, mice and human volunteers. Genetic or pharmacological blockade of endogenous spermidine synthesis reduced fasting-induced autophagy in yeast, nematodes and human cells. Furthermore, perturbing the polyamine pathway in vivo abrogated the lifespan- and healthspan-extending effects, as well as the cardioprotective and anti-arthritic consequences of fasting. Mechanistically, spermidine mediated these effects via autophagy induction and hypusination of the translation regulator eIF5A. In summary, the polyamine-hypusination axis emerges as a phylogenetically conserved metabolic control hub for fasting-mediated autophagy enhancement and longevity.

DHPS-Mediated Hypusination Regulates METTL3 Self-m6A-Methylation Modification to Promote Melanoma Proliferation and the Development of Novel Inhibitors

Discovering new treatments for melanoma will benefit human health. The mechanism by which deoxyhypusine synthase (DHPS) promotes melanoma development remains elucidated. Multi-omics studies have revealed that DHPS regulates m6A modification and maintains mRNA stability in melanoma cells. Mechanistically, DHPS activates the hypusination of eukaryotic translation initiation factor 5A (eIF5A) to assist METTL3 localizing on its mRNA for m6A modification, then promoting METTL3 expression. Structure-based design, synthesis, and activity screening yielded the hit compound GL-1 as a DHPS inhibitor. Notably, GL-1 directly inhibits DHPS binding to eIF5A, whereas GC-7 cannot. Based on the clarification of the mode of action of GL-1 on DHPS, it is found that GL-1 can promote the accumulation of intracellular Cu2+ to induce apoptosis, and antibody microarray analysis shows that GL-1 inhibits the expression of several cytokines. GL-1 shows promising antitumor activity with good bioavailability in a xenograft tumor model. These findings clarify the molecular mechanisms by which DHPS regulates melanoma proliferation and demonstrate the potential of GL-1 for clinical melanoma therapy.

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.

TFEB activation hallmarks antigenic experience of B lymphocytes and directs germinal center fate decisions

Ligation of the B cell antigen receptor (BCR) initiates humoral immunity. However, BCR signaling without appropriate co-stimulation commits B cells to death rather than to differentiation into immune effector cells. How BCR activation depletes potentially autoreactive B cells while simultaneously primes for receiving rescue and differentiation signals from cognate T lymphocytes remains unknown. Here, we use a mass spectrometry-based proteomic approach to identify cytosolic/nuclear shuttling elements and uncover transcription factor EB (TFEB) as a central BCR-controlled rheostat that drives activation-induced apoptosis, and concurrently promotes the reception of co-stimulatory rescue signals by supporting B cell migration and antigen presentation. CD40 co-stimulation prevents TFEB-driven cell death, while enhancing and prolonging TFEB's nuclear residency, which hallmarks antigenic experience also of memory B cells. In mice, TFEB shapes the transcriptional landscape of germinal center B cells. Within the germinal center, TFEB facilitates the dark zone entry of light-zone-residing centrocytes through regulation of chemokine receptors and, by balancing the expression of Bcl-2/BH3-only family members, integrates antigen-induced apoptosis with T cell-provided CD40 survival signals. Thus, TFEB reprograms antigen-primed germinal center B cells for cell fate decisions.

Ageing-related bone and immunity changes: insights into the complex interplay between the skeleton and the immune system

Ageing as a natural irreversible process inherently results in the functional deterioration of numerous organ systems and tissues, including the skeletal and immune systems. Recent studies have elucidated the intricate bidirectional interactions between these two systems. In this review, we provide a comprehensive synthesis of molecular mechanisms of cell ageing. We further discuss how age-related skeletal changes influence the immune system and the consequent impact of immune system alterations on the skeletal system. Finally, we highlight the clinical implications of these findings and propose potential strategies to promote healthy ageing and reduce pathologic deterioration of both the skeletal and immune systems.

Identifying polyamine related biomarkers in diagnosis and treatment of ulcerative colitis by integrating bulk and single-cell sequencing data

Ulcerative colitis (UC) is a chronic inflammatory disorder of the colon, and its pathogenesis remains unclear. Polyamine metabolic enzymes play a crucial role in UC. In this study, we aimed to identify pivotal polyamine-related genes (PRGs) and explore the underlying mechanism between PRGs and the disease status and therapeutic response of UC. We analyzed mRNA-sequencing data and clinical information of UC patients from the GEO database and identified NNMT, PTGS2, TRIM22, TGM2, and PPARG as key PRGs associated with active UC using differential expression analysis and weighted gene co-expression network analysis (WCGNA). Receiver operator characteristic curve (ROC) analysis confirmed the accuracy of these key genes in UC and colitis-associated colon cancer (CAC) diagnosis, and we validated their relationship with therapeutic response in external verification sets. Additionally, single-cell analysis revealed that the key PRGs were specific to certain immune cell types, emphasizing the vital role of intestinal tissue stem cells in active UC. The results were validated in vitro and in vivo experiments, including the colitis mice model and CAC mice model. In conclusion, these key PRGs effectively predict the progression of UC patients and could serve as new pharmacological biomarkers for the therapeutic response of UC.

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.

Role of canonical and noncanonical autophagy pathways in shaping the life journey of B cells

Autophagy is a regulated intracellular catabolic process by which invading pathogens, damaged organelles, aggregated proteins, and other macromolecules are degraded in lysosomes. It has been widely appreciated that autophagic activity plays an important role in regulating the development, fate determination, and function of cells in the immune system, including B lymphocytes. Autophagy encompasses several distinct pathways that have been linked to B cell homeostasis and function. While B cell presentation of major histocompatibility complex (MHC) class II-restricted cytosolic antigens to T cells involves both macroautophagy and chaperone-mediated autophagy (CMA), plasma cells and memory B cells mainly rely on macroautophagy for their survival. Emerging evidence indicates that core autophagy factors also participate in processes related to yet clearly distinct from classical autophagy. These autophagy-related pathways, referred to as noncanonical autophagy or conjugation of ATG8 to single membranes (CASM), contribute to B cell homeostasis and functions, including MHC class II-restricted antigen presentation to T cells, germinal center formation, plasma cell differentiation, and recall responses. Dysregulation of B cell autophagy has been identified in several autoimmune and autoinflammatory diseases such as systemic lupus erythematosus, rheumatoid arthritis, and inflammatory bowel disease. In this review, we discuss recent advances in understanding the role of canonical and noncanonical autophagy in B cells, including B cell development and maturation, antigen processing and presentation, pathogen-specific antibody responses, cytokine secretion, and autoimmunity. Unraveling the molecular mechanisms of canonical and noncanonical autophagy in B cells will improve our understanding of B cell biology, with implications for the development of autophagy-based immunotherapies.

The Many Faces of Hypusinated eIF5A: Cell Context-Specific Effects of the Hypusine Circuit and Implications for Human Health

The unique amino acid hypusine [Nε-(4-amino-2-hydroxybutyl)lysine] is exclusively formed on the translational regulator eukaryotic initiation factor 5A (eIF5A) via a process coined hypusination. Hypusination is mediated by two enzymes, deoxyhypusine synthase (DHPS) and deoxyhypusine hydroxylase (DOHH), and hypusinated eIF5A (eIF5AHyp) promotes translation elongation by alleviating ribosome pauses at amino acid motifs that cause structural constraints, and it also facilitates translation initiation and termination. Accordingly, eIF5AHyp has diverse biological functions that rely on translational control of its targets. Homozygous deletion of Eif5a, Dhps, or Dohh in mice leads to embryonic lethality, and heterozygous germline variants in EIF5A and biallelic variants in DHPS and DOHH are associated with rare inherited neurodevelopmental disorders, underscoring the importance of the hypusine circuit for embryonic and neuronal development. Given the pleiotropic effects of eIF5AHyp, a detailed understanding of the cell context-specific intrinsic roles of eIF5AHyp and of the chronic versus acute effects of eIF5AHyp inhibition is necessary to develop future strategies for eIF5AHyp-targeted therapy to treat various human health problems. Here, we review the most recent studies documenting the intrinsic roles of eIF5AHyp in different tissues/cell types under normal or pathophysiological conditions and discuss these unique aspects of eIF5AHyp-dependent translational control.

In vitro and in vivo studies on exogenous polyamines and α-difluoromethylornithine to enhance bone formation and suppress osteoclast differentiation

Exogenous polyamines, including putrescine (PUT), spermidine (SPD), and spermine (SPM), and the irreversible inhibitor of the rate-limiting enzyme ornithine decarboxylase (ODC) of polyamine biosynthesis, α-difluoromethylornithine (DFMO), are implicated as stimulants for bone formation. We demonstrate in this study the osteogenic potential of exogenous polyamines and DFMO in human osteoblasts (hOBs), murine monocyte cell line RAW 264.7, and an ovariectomized rat model. The effect of polyamines and DFMO on hOBs and RAW 264.7 cells was studied by analyzing gene expression, alkaline phosphatase (ALP) activity, tartrate-resistant acid phosphatase (TRAP) activity, and matrix mineralization. Ovariectomized rats were treated with polyamines and DFMO and analyzed by micro computed tomography (micro CT). The mRNA level of the early onset genes of osteogenic differentiation, Runt-related transcription factor 2 (Runx2) and ALP, was significantly elevated in hOBs under osteogenic conditions, while both ALP activity and matrix mineralization were enhanced by exogenous polyamines and DFMO. Under osteoclastogenic conditions, the gene expression of both receptor activator of nuclear factor-κB (RANK) and nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1) was reduced, and TRAP activity was suppressed by exogenous polyamines and DFMO in RAW 264.7 cells. In an osteoporotic animal model of ovariectomized rats, SPM and DFMO were found to improve bone volume in rat femurs, while trabecular thickness was increased in all treatment groups. Results from this study provide in vitro and in vivo evidence indicating that polyamines and DFMO act as stimulants for bone formation, and their osteogenic effect may be associated with the suppression of osteoclastogenesis.

Spermidine Synthase Localization in Retinal Layers: Early Age Changes

Polyamine (PA) spermidine (SPD) plays a crucial role in aging. Since SPD accumulates in glial cells, particularly in Müller retinal cells (MCs), the expression of the SPD-synthesizing enzyme spermidine synthase (SpdS) in Müller glia and age-dependent SpdS activity are not known. We used immunocytochemistry, Western blot (WB), and image analysis on rat retinae at postnatal days 3, 21, and 120. The anti-glutamine synthetase (GS) antibody was used to identify glial cells. In the neonatal retina (postnatal day 3 (P3)), SpdS was expressed in almost all progenitor cells in the neuroblast. However, by day 21 (P21), the SpdS label was pronouncedly expressed in multiple neurons, while GS labels were observed only in radial Müller glial cells. During early cell adulthood, at postnatal day 120 (P120), SpdS was observed solely in ganglion cells and a few other neurons. Western blot and semi-quantitative analyses of SpdS labeling showed a dramatic decrease in SpdS at P21 and P120 compared to P3. In conclusion, the redistribution of SpdS with aging indicates that SPD is first synthesized in all progenitor cells and then later in neurons, but not in glia. However, MCs take up and accumulate SPD, regardless of the age-associated decrease in SPD synthesis in neurons.

Non-linear associations of serum spermidine with type 2 diabetes mellitus and fasting plasma glucose: a cross-sectional study

Background

Previous animal experiments have demonstrated the potential of spermidine to mitigate glucose intolerance, insulin resistance, and hyperinsulinemia. However, there remains a scarcity of epidemiological evidence supporting these findings. Therefore, we aimed to elucidate the associations of serum spermidine with T2DM and FPG.

Materials and methods

The cross-sectional study was conducted from June to August 2019 in the rural areas of Fuxin County, Liaoning Province, China. A total of 4,437 participants were included in the study. The serum spermidine was detected using high-performance liquid chromatography with a fluorescence detector. FPG was measured using the hexokinase method. T2DM was defined as participants with a FPG level of 7.0 mmol/L or greater, or self-reported diagnosis of diabetes by a doctor. Restricted cubic spline model and piecewise linear regression model were used to explore the associations of serum spermidine with T2DM and FPG, respectively.

Results

The mean (SD) age of the participants was 59.3 (10.0) years, with 622 out of 4,437 participants being defined as T2DM. The serum spermidine in participants stratified by age and BMI categories was significantly different, with p values of 0.006 and 0.001, respectively. Among all the participants, the association of serum spermidine with T2DM was J-shaped. The log (spermidine) was negatively associated with T2DM (OR = 0.68, 95% CI: 0.52 to 0.92, p = 0.01) below the inflection point, while log (spermidine) was not significantly associated with T2DM (OR = 1.97, 95% CI: 0.93 to 4.15, p = 0.07) above the inflection point. Among the participants without T2DM, the association of serum spermidine with FPG was inverted J-shaped. The log (spermidine) was positively associated with FPG (β = 0.13, 95% CI: 0.05 to 0.21, p = 0.001) below the inflection point, while log (spermidine) was negatively associated with FPG (β = -0.29, 95% CI: -0.42 to -0.16, p < 0.001) above the inflection point.

Conclusion

In conclusion, non-linear associations of serum spermidine with T2DM and FPG were found in the cross-sectional study in Chinese rural adults. This provided insights into the use of spermidine for the prevention of T2DM, highlighting the potential role in public health prevention strategies of spermidine.

Reduction of spermine synthase enhances autophagy to suppress Tau accumulation

Precise polyamine metabolism regulation is vital for cells and organisms. Mutations in spermine synthase (SMS) cause Snyder-Robinson intellectual disability syndrome (SRS), characterized by significant spermidine accumulation and autophagy blockage in the nervous system. Emerging evidence connects polyamine metabolism with other autophagy-related diseases, such as Tauopathy, however, the functional intersection between polyamine metabolism and autophagy in the context of these diseases remains unclear. Here, we altered SMS expression level to investigate the regulation of autophagy by modulated polyamine metabolism in Tauopathy in Drosophila and human cellular models. Interestingly, while complete loss of Drosophila spermine synthase (dSms) impairs lysosomal function and blocks autophagic flux recapitulating SRS disease phenotype, partial loss of dSms enhanced autophagic flux, reduced Tau protein accumulation, and led to extended lifespan and improved climbing performance in Tauopathy flies. Measurement of polyamine levels detected a mild elevation of spermidine in flies with partial loss of dSms. Similarly, in human neuronal or glial cells, partial loss of SMS by siRNA-mediated knockdown upregulated autophagic flux and reduced Tau protein accumulation. Importantly, proteomics analysis of postmortem brain tissue from Alzheimer's disease (AD) patients showed a significant albeit modest elevation of SMS level. Taken together, our study uncovers a functional correlation between polyamine metabolism and autophagy in AD: SMS reduction upregulates autophagy, suppresses Tau accumulation, and ameliorates neurodegeneration and cell death. These findings provide a new potential therapeutic target for AD.

Glutamine-derived aspartate is required for eIF5A hypusination-mediated translation of HIF-1α to induce the polarization of tumor-associated macrophages

Tumor-associated macrophages (TAMs) are vital contributors to the growth, metastasis, and therapeutic resistance of various cancers, including hepatocellular carcinoma (HCC). However, the exact phenotype of TAMs and the mechanisms underlying their modulation for therapeutic purposes have not been determined. Here, we present compelling evidence that glutamine-derived aspartate in TAMs stimulates spermidine production through the polyamine synthesis pathway, thereby increasing the translation efficiency of HIF-1α via eIF5A hypusination. Consequently, augmented translation of HIF-1α drives TAMs to undergo an increase glycolysis and acquire a metabolic phenotype distinct from that of M2 macrophages. Finally, eIF5A levels in tumor stromal lesions were greater than those in nontumor stromal lesions. Additionally, a higher degree of tumor stromal eIF5A hypusination was significantly associated with a more advanced tumor stage. Taken together, these data highlight the potential of inhibiting hypusinated eIF5A by targeting glutamine metabolism in TAMs, thereby opening a promising avenue for the development of novel therapeutic approaches for HCC.

Low-Molecular Weight Compounds that Extend the Chronological Lifespan of Yeasts, Saccharomyces cerevisiae, and Schizosaccharomyces pombe

Yeast is an excellent model organism for research for regulating aging and lifespan, and the studies have made many contributions to date, including identifying various factors and signaling pathways related to aging and lifespan. More than 20 years have passed since molecular biological perspectives are adopted in this research field, and intracellular factors and signal pathways that control aging and lifespan have evolutionarily conserved from yeast to mammals. Furthermore, these findings have been applied to control the aging and lifespan of various model organisms by adjustment of the nutritional environment, genetic manipulation, and drug treatment using low-molecular weight compounds. Among these, drug treatment is easier than the other methods, and research into drugs that regulate aging and lifespan is consequently expected to become more active. Chronological lifespan, a definition of yeast lifespan, refers to the survival period of a cell population under nondividing conditions. Herein, low-molecular weight compounds are summarized that extend the chronological lifespan of Saccharomyces cerevisiae and Schizosaccharomyces pombe, along with their intracellular functions. The low-molecular weight compounds are also discussed that extend the lifespan of other model organisms. Compounds that have so far only been studied in yeast may soon extend lifespan in other organisms.

Autophagy, a double-edged sword for oral tissue regeneration

BACKGROUND

Oral health is of fundamental importance to maintain systemic health in humans. Stem cell-based oral tissue regeneration is a promising strategy to achieve the recovery of impaired oral tissue. As a highly conserved process of lysosomal degradation, autophagy induction regulates stem cell function physiologically and pathologically. Autophagy activation can serve as a cytoprotective mechanism in stressful environments, while insufficient or over-activation may also lead to cell function dysregulation and cell death.

AIM OF REVIEW

This review focuses on the effects of autophagy on stem cell function and oral tissue regeneration, with particular emphasis on diverse roles of autophagy in different oral tissues, including periodontal tissue, bone tissue, dentin pulp tissue, oral mucosa, salivary gland, maxillofacial muscle, temporomandibular joint, etc. Additionally, this review introduces the molecular mechanisms involved in autophagy during the regeneration of different parts of oral tissue, and how autophagy can be regulated by small molecule drugs, biomaterials, exosomes/RNAs or other specific treatments. Finally, this review discusses new perspectives for autophagy manipulation and oral tissue regeneration.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Overall, this review emphasizes the contribution of autophagy to oral tissue regeneration and highlights the possible approaches for regulating autophagy to promote the regeneration of human oral tissue.

Spermidine - an old molecule with a new age-defying immune function

Polyamines - putrescine, spermidine, and spermine - are widely distributed aliphatic compounds known to regulate important biological processes in prokaryotic and eukaryotic cells. Therefore, spermidine insufficiency is associated with various physio-pathological processes, such as aging and cancers. Recent advances in immuno-metabolism and immunotherapy shed new light on the role of spermidine in immune cell regulation and anticancer responses. Here, we review novel works demonstrating that spermidine is produced by collective metabolic pathways of gut bacteria, bacteria-host co-metabolism, and by the host cells, including activated immune cells. We highlight the effectiveness of spermidine in enhancing antitumor responses in aged animals otherwise nonresponsive to immune checkpoint therapy and propose that spermidine supplementation could be used to enhance the efficacy of anti-PD-1 treatment.

Insights into vaccines for elderly individuals: from the impacts of immunosenescence to delivery strategies

Immunosenescence increases the risk and severity of diseases in elderly individuals and leads to impaired vaccine-induced immunity. With aging of the global population and the emerging risk of epidemics, developing adjuvants and vaccines for elderly individuals to improve their immune protection is pivotal for healthy aging worldwide. Deepening our understanding of the role of immunosenescence in vaccine efficacy could accelerate research focused on optimizing vaccine delivery for elderly individuals. In this review, we analyzed the characteristics of immunosenescence at the cellular and molecular levels. Strategies to improve vaccination potency in elderly individuals are summarized, including increasing the antigen dose, preparing multivalent antigen vaccines, adding appropriate adjuvants, inhibiting chronic inflammation, and inhibiting immunosenescence. We hope that this review can provide a review of new findings with regards to the impacts of immunosenescence on vaccine-mediated protection and inspire the development of individualized vaccines for elderly individuals.

Metabolic control of mitophagy

Mitochondrial dysfunction is a major hallmark of ageing and related chronic disorders. Controlled removal of damaged mitochondria by the autophagic machinery, a process known as mitophagy, is vital for mitochondrial homeostasis and cell survival. The central role of mitochondria in cellular metabolism places mitochondrial removal at the interface of key metabolic pathways affecting the biosynthesis or catabolism of acetyl-coenzyme A, nicotinamide adenine dinucleotide, polyamines, as well as fatty acids and amino acids. Molecular switches that integrate the metabolic status of the cell, like AMP-dependent protein kinase, protein kinase A, mechanistic target of rapamycin and sirtuins, have also emerged as important regulators of mitophagy. In this review, we discuss how metabolic regulation intersects with mitophagy. We place special emphasis on the metabolic regulatory circuits that may be therapeutically targeted to delay ageing and mitochondria-associated chronic diseases. Moreover, we identify outstanding knowledge gaps, such as the ill-defined distinction between basal and damage-induced mitophagy, which must be resolved to boost progress in this area.

Rag-GTPase-TFEB/TFE3 axis controls B cell mitochondrial fitness and humoral immunity independent of mTORC1

During the humoral immune response, B cells undergo rapid metabolic reprogramming with a high demand for nutrients, which are vital to sustain the formation of the germinal centers (GCs). Rag-GTPases sense amino acid availability to modulate the mechanistic target of rapamycin complex 1 (mTORC1) pathway and suppress transcription factor EB (TFEB) and transcription factor enhancer 3 (TFE3), members of the microphthalmia (MiT/TFE) family of HLH-leucine zipper transcription factors. However, how Rag-GTPases coordinate amino acid sensing, mTORC1 activation, and TFEB/TFE3 activity in humoral immunity remains undefined. Here, we show that B cell-intrinsic Rag-GTPases are critical for the development and activation of B cells. RagA/RagB deficient B cells fail to form GCs, produce antibodies, and generate plasmablasts in both T-dependent (TD) and T-independent (TI) humoral immune responses. Deletion of RagA/RagB in GC B cells leads to abnormal dark zone (DZ) to light zone (LZ) ratio and reduced affinity maturation. Mechanistically, the Rag-GTPase complex constrains TFEB/TFE3 activity to prevent mitophagy dysregulation and maintain mitochondrial fitness in B cells, which are independent of canonical mTORC1 activation. TFEB/TFE3 deletion restores B cell development, GC formation in Peyer's patches and TI humoral immunity, but not TD humoral immunity in the absence of Rag-GTPases. Collectively, our data establish Rag-GTPase-TFEB/TFE3 axis as an mTORC1 independent mechanism to coordinating nutrient sensing and mitochondrial metabolism in B cells.

The nutrient-sensing Rag-GTPase complex in B cells controls humoral immunity via TFEB/TFE3-dependent mitochondrial fitness

During the humoral immune response, B cells undergo rapid metabolic reprogramming with a high demand for nutrients, which are vital to sustain the formation of the germinal centers (GCs). Rag-GTPases sense amino acid availability to modulate the mechanistic target of rapamycin complex 1 (mTORC1) pathway and suppress transcription factor EB (TFEB) and transcription factor enhancer 3 (TFE3), members of the microphthalmia (MiT/TFE) family of HLH-leucine zipper transcription factors. However, how Rag-GTPases coordinate amino acid sensing, mTORC1 activation, and TFEB/TFE3 activity in humoral immunity remains undefined. Here, we show that B cell-intrinsic Rag-GTPases are critical for the development and activation of B cells. RagA/RagB deficient B cells fail to form GCs, produce antibodies, and generate plasmablasts in both T-dependent (TD) and T-independent (TI) humoral immune responses. Deletion of RagA/RagB in GC B cells leads to abnormal dark zone (DZ) to light zone (LZ) ratio and reduced affinity maturation. Mechanistically, the Rag-GTPase complex constrains TFEB/TFE3 activity to prevent mitophagy dysregulation and maintain mitochondrial fitness in B cells, which are independent of canonical mTORC1 activation. TFEB/TFE3 deletion restores B cell development, GC formation in Peyer's patches and TI humoral immunity, but not TD humoral immunity in the absence of Rag-GTPases. Collectively, our data establish Rag-GTPase-TFEB/TFE3 pathway as an mTORC1 independent mechanism to coordinating nutrient sensing and mitochondrial metabolism in B cells.