Novel aspects of age-protection by spermidine supplementation are associated with preserved telomere length

Spermidine protects cellular redox status and ionic homeostasis in D-galactose induced senescence and natural aging rat models

Impaired redox homeostasis is an important hallmark of aging. Among various anti-aging interventions, caloric restriction mimetics (CRMs) are the most effective in promoting health and longevity. The potential role of spermidine (SPD) as a CRM in modulating oxidative stress and redox homeostasis during aging remains unclear. This study aimed to investigate the protective effect of SPD in D-galactose (D-gal) accelerated induced senescence model and naturally aged rats. Young male rats (4 months), D-gal induced (500 mg/kg b. w., subcutaneously) aging model and naturally aged (22 months) rats were supplemented with SPD (10 mg/kg b. w., orally) for 6 weeks. The results showed that SPD supplementation suppresses the age induced increase in reactive oxygen species, lipid peroxidation and protein oxidation. Additionally, it increases the level of antioxidants, plasma membrane redox system in erythrocytes and membrane. These results also indicate that membrane transporter activity is correlated with the susceptibility of the erythrocyte towards oxidative damage. We therefore present evidence that SPD improves redox status and membrane impairments in erythrocytes in experimental and naturally aging rat models, however, more research is required to recommend a potential therapeutic role for SPD as an anti-aging intervention strategy.

Biosynthesis of the Functional Component Spermidine from Bacillus amyloliquefaciens by Iterative Integration Expression

Spermidine finds broad applications across both the nutraceutical and biomedical sectors. In this study, key regulatory genes affecting spermidine synthesis and efficient integration sites were identified to construct a chassis strain for green and sustainable spermidine production. First, the expression of argJ was increased, and the protein SAM2 was mutated to promote the synthesis of spermidine. Second, positional effects were examined in Bacillus amyloliquefaciens. Concurrently, bioinformatics analysis was conducted to uncover transport proteins Blt, YvdR, and Mta, as well as other key genes tcyJ, yxeM, appC, yngA, and orf03307 that affect spermidine synthesis. Ultimately, strain PM13 was constructed through the iterative integration of key genes, achieving a spermidine titer of 396.92 mg/L, 10.34 times higher than strain PM1. Furthermore, xylose fed-batch fermentation increased spermidine titer to 1.69 g/L, setting a new shake flask production record. In conclusion, this study amassed genetic resources and developed an integrated strain for efficient, stable spermidine synthesis.

Unveiling the novel role of spermidine in leaf senescence: A study of eukaryotic translation factor 5A-independent and dependent mechanisms

Senescence is a crucial and highly active process in plants, optimising resource allocation and promoting phenotypic plasticity under restricted conditions. It involves global metabolic reprogramming for the organised disintegration and remobilization of resources. Polyamines (PAs) are polycationic biogenic amines prevalent in all eukaryotes and are necessary for cell survival. The commonly used PAs in plants include putrescine, spermidine, and spermine. Notably, the leaf's expression of S-adenosylmethionine decarboxylase and spermidine synthase gene family transcripts significantly changes during senescence. This suggests these genes are critical in spermidine metabolism and may condition metabolic reprogramming. One key role of spermidine in eukaryotes is to provide the 4-aminobutyl group for the posttranslational modification of lysine in eukaryotic translation factor 5A (eIF5A). This modification is catalysed by two sequential enzymatic steps leading to the activation of eIF5A by converting lysine to the unusual amino acid hypusine. Although eIF5A is well characterised to be involved in the translation of proline-rich repeat proteins and other hard-to-read motifs, the biological role of eIF5A has recently been clarified only in mammals. It could be better described at the plant functional level. The expression patterns of eIF5A isoforms and genes encoding machinery responsible for hypusination, differ between induced and developmental leaf senescence. In this paper, we summarise the existing knowledge on spermidine-dependent senescence control mechanisms in plants, raising the possibility that spermidine could be an element of a biological switch controlling the onset of a different type of senescence in an eIF5A-independent and dependent manner.

Enhancement of NK Cell Cytotoxic Activity and Immunoregulatory Effects of a Natural Product Supplement Across a Wide Age Span: A 30-Day In Vivo Human Study

The purpose of this study was to examine whether supplementation of ultra- and nanofiltered colostrum-based products, combined with egg yolk extract, nicotinamide mononucleotide (NMN), quercetin, alpha-ketoglutarate, white button mushroom, and celery seed extracts (the formula was patented by 4Life Research Company, USA and named as AgePro), modulate the functional activity of natural killer (NK) cells in vivo. We found that this supplement, taken orally in two capsules twice a day for 30 days, significantly enhanced the cytotoxic activity of NK cells. This was evidenced by the increased NK cell-mediated killing of carboxyfluorescein diacetate succinimidyl ester (CFSE)-labeled K562 human myeloid leukemia cells. As expected, this effect was dependent on the ratio between the effector (E) (e.g., peripheral blood mononuclear cells (PBMCs)) and target (T) (e.g., K562) cells, illustrating maximal killing of K562 cells at a 50:1 E/T ratio. Of note, increased NK-mediated killing of K562 cells after taking AgePro correlated with increased perforin release, evidenced by the CD107a degranulation assay. In concordance with these findings, taking of AgePro for 1 month increased production of several cytokines and chemokines, including IL-1β, IL-1Rα, IL-6, IL-8, IL-10, IFN-γ, TNF-α, G-CSF, PDGF-AA, PDGF-AB/BB, GRO, MCP-1, MCP-3, and MIP-1α, in PBMCs co-cultured with K562 cells. Of note, increased production of the cytokines correlated with the activation state of PBMCs, as evidenced by increased expression of the surface activation markers (e.g., the interleukin-2 receptor alpha chain-CD25). A strong correlation was found between NK-based cytotoxic activity and the production of IL-1β, IL-6, TNF-α, and MIP-1α. Importantly, no increase in the aforementioned soluble factors and activation markers was detected in PBMCs cultured alone, thereby illustrating the potent immunoregulatory activity of AgePro only in the presence of the harmful target cells. Hematological parameters also remained unchanged over the entire study period. Collectively, we show herein the significant enhancement of the cytotoxic activity of NK cells against target tumor cells after taking AgePro for 1 month. Notably, this effect was observed for all age groups, including young, adult, and elderly participants. Moreover, a significant improvement in NK cytotoxic activity was also detected for participants with low basal (e.g., before taking AgePro) numbers of NK-mediated killing. The enhancement of NK-based cytotoxicity was associated with an increased release of several cytokines and chemokines involved in regulating a broad spectrum of mechanisms outside the cell-mediated cytotoxicity and killing of target cells. Of note, spontaneous activation of PBMCs, particularly NK cells, was not detected after taking AgePro. Given that spontaneous activation of autoreactive lymphocytes is a feature associated with autoimmunity and taking into account our data illustrating the AgePro-induced activation of NK cells detected only in the presence of the potentially harmful cells, we conclude that our innovative product exhibits potent immunoregulatory activity and high safety profile.

Spermidine Treatment Improves GRIN2B Loss-Of-Function, A Primary Disorder of Glutamatergic Neurotransmission

GRIN-related disorders (GRD) developmental and epileptic encephalopathies (DEEs) display a clinical spectrum including developmental delay, hypotonia, intellectual disability, epilepsy, and autistic traits. The presence of de novo pathogenic variants in the GRIN genes alters the N-methyl D-aspartate receptor (NMDAR) function, with a genotype-phenotype relationship. Despite recent advances to elucidate GRD pathophysiological mechanisms and to find treatments, to date, GRD therapeutic arms are still scarce and with limited efficacy. Herein, we investigated whether the natural polyamine spermine-positive allosteric modulators of GluN2B subunit-containing NMDARs-or its precursor spermidine might rescue NMDAR hypofunctionality. In heterologous cell systems, administration of spermine potentiated wild-type and loss-of-function (LoF) NMDAR-mediated currents and attenuated synaptic density deficits. Functionally, the putative therapeutic benefit of spermidine (spermine precursor) was assessed in constitutive Grin2b+/- heterozygous mice, a GRIN2B-LoF genetic murine model recapitulating GRD-like synaptic, motor, and cognitive alterations. Chronic spermidine administration in young adult Grin2b+/- mice partially rescued hippocampal long-term potentiation deficits in hippocampal slices of Grin2b+/- mice, supporting the cognitive improvement observed in behavioral phenotyping. Based on these preclinical findings, a case study was conducted in two pediatric patients harboring mild GRIN2B-LoF variants. Importantly, in line with preclinical findings, 18 months of spermidine treatment resulted in the amelioration of adaptive behavior (notably in the younger treated patient), with the absence of noticeable side effects. Overall, our findings provide both preclinical and clinical data supporting the benefit of spermidine for the treatment of GRD in individuals harboring GRIN2B-LoF variants.

Dietary intake of polyamines in a Spanish adult population: Age-dependent correlation with Healthy Eating Index and Dietary Inflammatory Index scores

OBJECTIVES

A healthy and balanced diet is crucial to maintaining optimal health. Understanding the benefits of different food components is essential. The polyamine spermidine is linked to age-related disease protection, but daily intakes and whether these vary with age are unknown. This study aimed to determine polyamine intake in a Mediterranean diet population and its association with participants' age and Healthy Eating Index (HEI) and Dietary Inflammatory Index (DII) scores.

METHODS

A database was created with references concerning polyamine content in foods to determine the daily intake of foods frequently consumed by 203 participants (84 males and 119 females), ages 18 to 90 y, using a nutritional survey (VioScreen) that includes HEI and DII scores.

RESULTS

The participants' characteristics were as reported in the corresponding 2020 Spanish nutritional survey. Two-thirds demonstrated moderate to high adherence to the Mediterranean diet. The mean HEI score was 74.45 (out of 100), and the mean DII was -1.94 (anti-inflammatory). The median intake of polyamines was 45.59 mg/d/person (mean, 46.89 mg/d/person, 410.57 µmol/d/person), without sex differences. After normalizing the intake per kilocalorie, the Kruskal-Wallis test showed significant differences among age groups for total polyamines ingested, putrescine, and spermidine. The intake of putrescine and spermidine was significantly higher in the 60 to 69 age group compared with the 24 to 59 and 18 to 23 age groups, respectively. HEI scores were positively correlated with polyamine intake, whereas DII scores were negatively correlated.

CONCLUSIONS

Polyamine intake was higher than reported in other populations, did not decrease based on age, and was associated with healthy eating and anti-inflammatory foods.

Targeting lysosomal quality control as a therapeutic strategy against aging and diseases

Previously, lysosomes were primarily referred to as the digestive organelles and recycling centers within cells. Recent discoveries have expanded the lysosomal functional scope and revealed their critical roles in nutrient sensing, epigenetic regulation, plasma membrane repair, lipid transport, ion homeostasis, and cellular stress response. Lysosomal dysfunction is also found to be associated with aging and several diseases. Therefore, function of macroautophagy, a lysosome-dependent intracellular degradation system, has been identified as one of the updated twelve hallmarks of aging. In this review, we begin by introducing the concept of lysosomal quality control (LQC), which is a cellular machinery that maintains the number, morphology, and function of lysosomes through different processes such as lysosomal biogenesis, reformation, fission, fusion, turnover, lysophagy, exocytosis, and membrane permeabilization and repair. Next, we summarize the results from studies reporting the association between LQC dysregulation and aging/various disorders. Subsequently, we explore the emerging therapeutic strategies that target distinct aspects of LQC for treating diseases and combatting aging. Lastly, we underscore the existing knowledge gap and propose potential avenues for future research.

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 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.

Unlocking longevity: the role of telomeres and its targeting interventions

Average life expectancy has been steadily increasing in developed countries worldwide. These demographic changes are associated with an ever-growing social and economic strain to healthcare systems as well as society. The aging process typically manifests as a decline in physiological and cognitive functions, accompanied by a rise in chronic diseases. Consequently, strategies that both mitigate age-related diseases and promote healthy aging are urgently needed. Telomere attrition, characterized by the shortening of telomeres with each cell division, paradoxically serves as both a protective mechanism and a contributor to tissue degeneration and age-related ailments. Based on the essential role of telomere biology in aging, research efforts aim to develop approaches designed to counteract telomere attrition, aiming to delay or reduce age-related diseases. In this review, telomere biology and its role in aging and age-related diseases is summarized along with recent approaches to interfere with telomere shortening aiming at well- and healthy-aging as well as longevity. As aging research enters a new era, this review emphasizes telomere-targeting therapeutics, including telomerase activators and tankyrase inhibitors, while also exploring the effects of antioxidative and anti-inflammatory agents, along with indirectly related approaches like statins.

Telomeres: Dysfunction, Maintenance, Aging and Cancer

Aging has emerged at the forefront of scientific research due to the growing social and economic costs associated with the growing aging global population. The defining features of aging involve a variety of molecular processes and cellular systems, which are interconnected and collaboratively contribute to the aging process. Herein, we analyze how telomere dysfunction potentially amplifies or accelerates the molecular and biochemical mechanisms underpinning each feature of aging and contributes to the emergence of age-associated illnesses, including cancer and neurodegeneration, via the perspective of telomere biology. Furthermore, the recently identified novel mechanistic actions for telomere maintenance offer a fresh viewpoint and approach to the management of telomeres and associated disorders. Telomeres and the defining features of aging are intimately related, which has implications for therapeutic and preventive approaches to slow aging and reduce the prevalence of age-related disorders.

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.

Toxicology of pharmaceutical and nutritional longevity compounds

Aging is the most prominent risk factor for many diseases, which is considered to be a complicated biological process. The rate of aging depends on the effectiveness of important mechanisms such as the protection of DNA from free radicals, which protects the structural and functional integrity of cells and tissues. In any organism, not all organs may age at the same rate. Slowing down primary aging and reaching maximum lifespan is the most basic necessity. In this process, it may be possible to slow down or stabilise some diseases by using the compounds for both dietary and pharmacological purposes. Natural compounds with antioxidant and anti-inflammatory effects, mostly plant-based nutraceuticals, are preferred in the treatment of age-related chronic diseases and can also be used for other diseases. An increasing number of long-term studies on synthetic and natural compounds aim to elucidate preclinically and clinically the mechanisms underlying being healthy and prolongation of life. To delay age-related diseases and prolong the lifespan, it is necessary to take these compounds with diet or pharmaceuticals, along with detailed toxicological results. In this review, the most promising and utilised compounds will be highlighted and it will be discussed whether they have toxic effects in short/long-term use, although they are thought to be used safely.

Sex differences in pharmacological interventions and their effects on lifespan and healthspan outcomes: a systematic review

With an increasing aging population, the burden of age-related diseases magnifies. To alleviate this burden, geroprotection has been an area of intense research focus with the development of pharmacological interventions that target lifespan and/or healthspan. However, there are often sex differences, with compounds mostly tested in male animals. Given the importance of considering both sexes in preclinical research, this neglects potential benefits for the female population, as interventions tested in both sexes often show clear sexual dimorphisms in their biological responses. To further understand the prevalence of sex differences in pharmacological geroprotective intervention studies, we performed a systematic review of the literature according to the PRISMA guidelines. Seventy-two studies met our inclusion criteria and were classified into one of five subclasses: FDA-repurposed drugs, novel small molecules, probiotics, traditional Chinese medicine, and antioxidants, vitamins, or other dietary supplements. Interventions were analyzed for their effects on median and maximal lifespan and healthspan markers, including frailty, muscle function and coordination, cognitive function and learning, metabolism, and cancer. With our systematic review, we found that twenty-two out of sixty-four compounds tested were able to prolong both lifespan and healthspan measures. Focusing on the use of female and male mice, and on comparing their outcomes, we found that 40% of studies only used male mice or did not clarify the sex. Notably, of the 36% of pharmacologic interventions that did use both male and female mice, 73% of these studies showed sex-specific outcomes on healthspan and/or lifespan. These data highlight the importance of studying both sexes in the search for geroprotectors, as the biology of aging is not the same in male and female mice. Systematic Review Registration: [website], identifier [registration number].

Changes in the Localization of Polyamine Spermidine in the Rat Retina with Age

Polyamines (PAs) in the nervous system has a key role in regeneration and aging. Therefore, we investigated age-related changes in the expression of PA spermidine (SPD) in the rat retina. Fluorescent immunocytochemistry was used to evaluate the accumulation of SPD in retinae from rats of postnatal days 3, 21, and 120. Glial cells were identified using glutamine synthetase (GS), whereas DAPI, a marker of cell nuclei, was used to differentiate between retinal layers. SPD localization in the retina was strikingly different between neonates and adults. In the neonatal retina (postnatal day 3-P3), SPD is strongly expressed in practically all cell types, including radial glia and neurons. SPD staining showed strong co-localization with the glial marker GS in Müller Cells (MCs) in the outer neuroblast layer. In the weaning period (postnatal day 21-P21), the SPD label was strongly expressed in all MCs, but not in neurons. In early adulthood (postnatal day 120-P120), SPD was localized in MCs only and was co-localized with the glial marker GS. A decline in the expression of PAs in neurons was observed with age while glial cells accumulated SPD after the differentiation stage (P21) and during aging in MC cellular endfoot compartments.

Mechanisms of spermidine-induced autophagy and geroprotection

Aging involves the systemic deterioration of all known cell types in most eukaryotes. Several recently discovered compounds that extend the healthspan and lifespan of model organisms decelerate pathways that govern the aging process. Among these geroprotectors, spermidine, a natural polyamine ubiquitously found in organisms from all kingdoms, prolongs the lifespan of fungi, nematodes, insects and rodents. In mice, it also postpones the manifestation of various age-associated disorders such as cardiovascular disease and neurodegeneration. The specific features of spermidine, including its presence in common food items, make it an interesting candidate for translational aging research. Here, we review novel insights into the geroprotective mode of action of spermidine at the molecular level, as we discuss strategies for elucidating its clinical potential.

Critical Role of Astrocytic Polyamine and GABA Metabolism in Epileptogenesis

Accumulating evidence indicate that astrocytes are essential players of the excitatory and inhibitory signaling during normal and epileptiform activity via uptake and release of gliotransmitters, ions, and other substances. Polyamines can be regarded as gliotransmitters since they are almost exclusively stored in astrocytes and can be released by various mechanisms. The polyamine putrescine (PUT) is utilized to synthesize GABA, which can also be released from astrocytes and provide tonic inhibition on neurons. The polyamine spermine (SPM), synthesized form PUT through spermidine (SPD), is known to unblock astrocytic Cx43 gap junction channels and therefore facilitate astrocytic synchronization. In addition, SPM released from astrocytes may also modulate neuronal NMDA, AMPA, and kainate receptors. As a consequence, astrocytic polyamines possess the capability to significantly modulate epileptiform activity. In this study, we investigated different steps in polyamine metabolism and coupled GABA release to assess their potential to control seizure generation and maintenance in two different epilepsy models: the low-[Mg2+] model of temporal lobe epilepsy in vitro and in the WAG/Rij rat model of absence epilepsy in vivo. We show that SPM is a gliotransmitter that is released from astrocytes and significantly contributes to network excitation. Importantly, we found that inhibition of SPD synthesis completely prevented seizure generation in WAG/Rij rats. We hypothesize that this antiepileptic effect is attributed to the subsequent enhancement of PUT to GABA conversion in astrocytes, leading to GABA release through GAT-2/3 transporters. This interpretation is supported by the observation that antiepileptic potential of the Food and Drug Administration (FDA)-approved drug levetiracetam can be diminished by specifically blocking astrocytic GAT-2/3 with SNAP-5114, suggesting that levetiracetam exerts its effect by increasing surface expression of GAT-2/3. Our findings conclusively suggest that the major pathway through which astrocytic polyamines contribute to epileptiform activity is the production of GABA. Modulation of astrocytic polyamine levels, therefore, may serve for a more effective antiepileptic drug development in the future.

The Role of Polyamines in the Mechanisms of Cognitive Impairment

Abstract—As the population ages, age-related cognitive impairments are becoming an increasingly pressing problem. Currently, the role of polyamines (putrescine, spermidine, and spermine) in the pathogenesis of cognitive impairments of various origin is actively discussed. It was shown that the content of polyamines in the brain tissue decreases with age. Exogenous administration of polyamines makes it possible to avoid cognitive impairment and/or influence the pathogenetic processes associated with disease progression. There are 3 known ways that polyamines can enter the human body: food, synthesis by intestinal bacteria, and biosynthesis in the body. Currently, one of the most promising approaches to the prevention of cognitive impairment is the use of foods with a high content of polyamines, as well as the use of various probiotics that affect intestinal bacteria that synthesize polyamines. Since 2018, in a number of European countries projects have been launched aimed at evaluation of the impact of a diet high in polyamines on cognitive processes. The review, based on analysis of modern scientific literature and the authors' own data, presents material on the effect of polyamines on cognitive processes and the role of polyamines in the regulation of neurotransmitter processes, and discusses the role of polyamines in cognitive disorders in mental and neurological diseases.

New Insights into the Roles and Mechanisms of Spermidine in Aging and Age-Related Diseases

High incidences of morbidity and mortality associated with age-related diseases among the elderly population are a socio-economic challenge. Aging is an irreversible and inevitable process that is a risk factor for pathological progression of diverse age-related diseases. Spermidine, a natural polyamine, plays a critical role in molecular and cellular interactions involved in various physiological and functional processes. Spermidine has been shown to modulate aging, suppress the occurrence and severity of age-related diseases, and prolong lifespan. However, the precise mechanisms through which spermidine exerts its anti-aging effects have not been established. In this review, we elucidate on the mechanisms and roles underlying the beneficial effects of spermidine in aging from a molecular and cellular perspective. Moreover, we provide new insights into the promising potential diagnostic and therapeutic applications of spermidine in aging and age-related diseases.

Autophagy and the hallmarks of aging

Autophagy, an essential cellular process that mediates degradation of proteins and organelles in lysosomes, has been tightly linked to cellular quality control for its role as part of the proteostasis network. The current interest in identifying the cellular and molecular determinants of aging, has highlighted the important contribution of malfunctioning of autophagy with age to the loss of proteostasis that characterizes all old organisms. However, the diversity of cellular functions of the different types of autophagy and the often reciprocal interactions of autophagy with other determinants of aging, is placing autophagy at the center of the aging process. In this work, we summarize evidence for the contribution of autophagy to health- and lifespan and provide examples of the bidirectional interplay between autophagic pathways and several of the so-called hallmarks of aging. This central role of autophagy in aging, and the dependence on autophagy of many geroprotective interventions, has motivated a search for direct modulators of autophagy that could be used to slow aging and extend healthspan. Here, we review some of those ongoing therapeutic efforts and comment on the potential of targeting autophagy in aging.

Caloric Restriction Mimetics in Nutrition and Clinical Trials

The human diet and dietary patterns are closely linked to the health status. High-calorie Western-style diets have increasingly come under scrutiny as their caloric load and composition contribute to the development of non-communicable diseases, such as diabetes, cancer, obesity, and cardiovascular disorders. On the other hand, calorie-reduced and health-promoting diets have shown promising results in maintaining health and reducing disease burden throughout aging. More recently, pharmacological Caloric Restriction Mimetics (CRMs) have gained interest of the public and scientific community as promising candidates that mimic some of the myriad of effects induced by caloric restriction. Importantly, many of the CRM candidates activate autophagy, prolong life- and healthspan in model organisms and ameliorate diverse disease symptoms without the need to cut calories. Among others, glycolytic inhibitors (e.g., D-allulose, D-glucosamine), hydroxycitric acid, NAD+ precursors, polyamines (e.g., spermidine), polyphenols (e.g., resveratrol, dimethoxychalcones, curcumin, EGCG, quercetin) and salicylic acid qualify as CRM candidates, which are naturally available via foods and beverages. However, it is yet unclear how these bioactive substances contribute to the benefits of healthy diets. In this review, we thus discuss dietary sources, availability and intake levels of dietary CRMs. Finally, since translational research on CRMs has entered the clinical stage, we provide a summary of their effects in clinical trials.

Common Muscle Metabolic Signatures Highlight Arginine and Lysine Metabolism as Potential Therapeutic Targets to Combat Unhealthy Aging

Biological aging research is expected to reveal modifiable molecular mechanisms that can be harnessed to slow or possibly reverse unhealthy trajectories. However, there is first an urgent need to define consensus molecular markers of healthy and unhealthy aging. Established aging hallmarks are all linked to metabolism, and a ‘rewired’ metabolic circuitry has been shown to accelerate or delay biological aging. To identify metabolic signatures distinguishing healthy from unhealthy aging trajectories, we performed nontargeted metabolomics on skeletal muscles from 2-month-old and 21-month-old mice, and after dietary and lifestyle interventions known to impact biological aging. We hypothesized that common metabolic signatures would highlight specific pathways and processes promoting healthy aging, while revealing the molecular underpinnings of unhealthy aging. Here, we report 50 metabolites that commonly distinguished aging trajectories in all cohorts, including 18 commonly reduced under unhealthy aging and 32 increased. We stratified these metabolites according to known relationships with various aging hallmarks and found the greatest associations with oxidative stress and nutrient sensing. Collectively, our data suggest interventions aimed at maintaining skeletal muscle arginine and lysine may be useful therapeutic strategies to minimize biological aging and maintain skeletal muscle health, function, and regenerative capacity in old age.