Multiomics reveals glutathione metabolism as a driver of bimodality during stem cell aging

Longevity extension in rats via improved redox homeostasis with high carbohydrate diet intervention from weaning to adulthood: a comprehensive multi-omics study

Early dietary patterns potentially influence the health status and lifespan throughout adulthood and the entire lifespan. However, dietary behaviors are difficult for everyone to control during adolescence. It is even more important to study the effects of interventions of early dietary patterns on the lifespan under arbitrary feeding conditions. The research involves observing the survival status and lifespan of rats from weaning to adulthood with three different dietary patterns (a high-carbohydrate diet (HC), a high-protein diet (HP), and a high-fat diet (HF)) under ad libitum feeding conditions. The administration of high-carbohydrate diets leads to a significant extension of both median and maximum survival times (P < 0.05) in Wistar rats. Furthermore, it markedly enhanced the spatial memory capacity, mitigated the occurrence of liver and kidney pathological outcomes in elderly rats, and increased the abundance of gut microbiota improving amino acid metabolism. Additionally, feeding rats a high-carbohydrate diet improved glutathione (GSH) synthesis and recycling and activated the expression and upregulation of the lifespan-related proteins Foxo3a/Sirt3 and the key metabolic enzyme GPX-4. The high-carbohydrate diet from weaning to adulthood may potentially extend the lifespan by enhancing rat systemic glutathione synthesis, recycling, and improving the redox state pathway.

Cystine/glutamate antiporter xCT controls skeletal muscle glutathione redox, bioenergetics and differentiation

Cysteine, the rate-controlling amino acid in cellular glutathione synthesis is imported as cystine, by the cystine/glutamate antiporter, xCT, and subsequently reduced to cysteine. As glutathione redox is important in muscle regeneration in aging, we hypothesized that xCT exerts upstream control over skeletal muscle glutathione redox, metabolism and regeneration. Bioinformatic analyses of publicly available datasets revealed that expression levels of xCT and GSH-related genes are inversely correlated with myogenic differentiation genes. Muscle satellite cells (MuSCs) isolated from Slc7a11sut/sut mice, which harbour a mutation in the Slc7a11 gene encoding xCT, required media supplementation with 2-mercaptoethanol to support cell proliferation but not myotube differentiation, despite persistently lower GSH. Slc7a11sut/sut primary myotubes were larger compared to WT myotubes, and also exhibited higher glucose uptake and cellular oxidative capacities. Immunostaining of myogenic markers (Pax7, MyoD, and myogenin) in cardiotoxin-damaged tibialis anterior muscle fibres revealed greater MuSC activation and commitment to differentiation in Slc7a11sut/sut muscle compared to WT mice, culminating in larger myofiber cross-sectional areas at 21 days post-injury. Slc7a11sut/sut mice subjected to a 5-week exercise training protocol demonstrated enhanced insulin tolerance compared to WT mice, but blunted muscle mitochondrial biogenesis and respiration in response to exercise training. Our results demonstrate that the absence of xCT inhibits cell proliferation but promotes myotube differentiation by regulating cellular metabolism and glutathione redox. Altogether, these results support the notion that myogenesis is a redox-regulated process and may help inform novel therapeutic approaches for muscle wasting and dysfunction in aging and disease.

Metabolomic changes in culture media with varying passage numbers of pig muscle stem cell culture for cultured meat production

Selecting the primary cells in an optimal state for cultured meat production is a crucial challenge in commercializing cultured meat. We investigated the metabolomic changes in culture media according to passage numbers for indirectly assessing the state of primary cells. Pig skeletal muscle stem cells (PSCs) harvested from the biceps femoris muscles of 7-d-old crossbred pigs (Landrace × Yorkshire × Duroc, LYD) were used for cell characterization. Fresh media (FM) and spent media (SM) of PSCs during passages 1 to 3 in vitro culture were prepared for metabolomics analysis. SM was collected on the third day of proliferation for each passage of PSCs. Cell characterization analysis revealed that the proliferation rate was highest at passage 2; however, a significant loss of expression of myogenic marker genes was observed at passage 3. Based on metabolomic profiles of culture media, FM and SM groups (SM1, SM2, and SM3) were clearly separated by partial least squares-discriminant analysis. A total of seven differentially abundant metabolites (DAMs) were identified from FM and SM for each passage, based on the following criteria: P < 0.05, fold change > 1.5 or < 0.66, and a variable importance in projection score > 1.5. All seven DAMs and their interconnected metabolites might be primarily used as substrates for energy production and most of them were relatively abundant in SM3. Among the seven DAMs, the three potential biomarkers (γ-glutamyl-L-leucine, cytosine, and ketoleucine), which showed significant changes exclusively in SM3, each had an area under the curve value of 1. Therefore, monitoring the levels of these key metabolites in culture media could serve as a quality control measure for cultured meat production by enabling the indirect detection of suboptimal PSCs based on their proliferation ability.

Epigenetic erosion of H4K20me1 induced by inflammation drives aged stem cell ferroptosis

Aging is associated with a decline in stem cell functionality and number across the organism. In this study, we aimed to further unravel Muscle Stem Cells (MuSCs) aging by assessing how systemic factors influence MuSC fate decisions through long-term epigenetic landscape remodelling. As aging is intricately linked to a pro-inflammatory shift, we studied the epigenetic effects of inflammatory signals in MuSCs and measured decreased H4K20me1 levels. This loss disrupts MuSC quiescence, largely through epigenetic silencing of Notch target genes. In the setting of inflammatory signals or aging, the lack of Kmt5a and the subsequent absence of de novoH4K20me1 culminate in cell death by ferroptosis. Aged MuSCs manifest abnormal iron metabolism and reduced Gpx4 levels, resulting in the accumulation of intracellular iron, increased reactive oxygen species, genomic instability, and lipid peroxidation. We showed that ferroptosis is the predominant mode of cell death in aged MuSCs, with remarkably high levels of lipid peroxidation; a phenomenon we also observed in aged hematopoietic stem cells. Implementing preventative strategies to inhibit systemic inflammation prevented aged MuSC ferroptosis, preserving their numbers and regenerative capabilities. This intervention significantly enhanced aged muscle regeneration and strength recovery and extended both lifespan and healthspan in mice. This study delineates a previously underappreciated fate trajectory for stem cell aging, and offers meaningful insights into the treatment of age-related disorders.

TDDFT study on a fluorescent probe for distinguishing analogous thiols based on smiles rearrangement

The complete excited-state sensing mechanism of a fluorescent probe capable of distinguishing cysteine/homocysteine and glutathione from analogous biological thiols has been investigated. Using a TDDFT method, the nature of the fluorescence differences in the detection of thiols by the probe has been explained at the molecular level. Calculation results imply that the probe undergoes photoinduced electron transfer (PET) from the fluorophore to the nitrobenzooxadiazole (NBD)-based acceptor in the excited state. In the presence of a thiol, the NBD moiety is cleaved and the red fluorescence emission of the fluorophore is enhanced through inhibition of the PET process. The sulfur-substituted NBD-thiol product is predisposed to undergo excited-state torsion, leading to fluorescence quenching. However, for cysteine and homocysteine, their appropriate distances lead to Smiles rearrangements with relatively low activation energies (26.60 kJ/mol and 42.94 kJ/mol, respectively) and the emission of a distinct green fluorescence at ambient temperature. It has been theoretically confirmed that the distance between two reactive sites, such as sulfhydryl and amino moieties, can be used to distinguish different thiols, thus providing rational support for the control of fluorescence activity and the design of probe molecules.

Depletion of SAM leading to loss of heterochromatin drives muscle stem cell ageing

The global loss of heterochromatin during ageing has been observed in eukaryotes from yeast to humans, and this has been proposed as one of the causes of ageing. However, the cause of this age-associated loss of heterochromatin has remained enigmatic. Here we show that heterochromatin markers, including histone H3K9 di/tri-methylation and HP1, decrease with age in muscle stem cells (MuSCs) as a consequence of the depletion of the methyl donor S-adenosylmethionine (SAM). We find that restoration of intracellular SAM in aged MuSCs restores heterochromatin content to youthful levels and rejuvenates age-associated features, including DNA damage accumulation, increased cell death, and defective muscle regeneration. SAM is not only a methyl group donor for transmethylation, but it is also an aminopropyl donor for polyamine synthesis. Excessive consumption of SAM in polyamine synthesis may reduce its availability for transmethylation. Consistent with this premise, we observe that perturbation of increased polyamine synthesis by inhibiting spermidine synthase restores intracellular SAM content and heterochromatin formation, leading to improvements in aged MuSC function and regenerative capacity in male and female mice. Together, our studies demonstrate a direct causal link between polyamine metabolism and epigenetic dysregulation during murine MuSC ageing.

How is Big Data reshaping preclinical aging research?

The exponential scientific and technological progress during the past 30 years has favored the comprehensive characterization of aging processes with their multivariate nature, leading to the advent of Big Data in preclinical aging research. Spanning from molecular omics to organism-level deep phenotyping, Big Data demands large computational resources for storage and analysis, as well as new analytical tools and conceptual frameworks to gain novel insights leading to discovery. Systems biology has emerged as a paradigm that utilizes Big Data to gain insightful information enabling a better understanding of living organisms, visualized as multilayered networks of interacting molecules, cells, tissues and organs at different spatiotemporal scales. In this framework, where aging, health and disease represent emergent states from an evolving dynamic complex system, context given by, for example, strain, sex and feeding times, becomes paramount for defining the biological trajectory of an organism. Using bioinformatics and artificial intelligence, the systems biology approach is leading to remarkable advances in our understanding of the underlying mechanism of aging biology and assisting in creative experimental study designs in animal models. Future in-depth knowledge acquisition will depend on the ability to fully integrate information from different spatiotemporal scales in organisms, which will probably require the adoption of theories and methods from the field of complex systems. Here we review state-of-the-art approaches in preclinical research, with a focus on rodent models, that are leading to conceptual and/or technical advances in leveraging Big Data to understand basic aging biology and its full translational potential.

Overcoming muscle stem cell aging

Reduced muscle strength and mass is one of the hallmarks of physiological aging in humans and can result in severe impairment of the quality of life. In part this is caused by a functional loss of the highly specialized muscle stem cells (MuSCs), which in healthy conditions provide maintenance, growth, and regeneration. Recent progress in understanding of the stem cell niche and results from single cell technologies reveal exciting insights at unprecedented detail into MuSCs and muscle biology during aging. Here, we review this field and discuss the implications of current findings with a focus on cellular reprogramming approaches as a novel therapeutic avenue for age-related muscle decline.

The roles of miRNAs in adult skeletal muscle satellite cells

Satellite cells are bona fide muscle stem cells that are indispensable for successful post-natal muscle growth and regeneration after severe injury. These cells also participate in adult muscle adaptation in several capacities. MicroRNAs (miRNAs) are post-transcriptional regulators of mRNA that are implicated in several aspects of stem cell function. There is evidence to suggest that miRNAs affect satellite cell behavior in vivo during development and myogenic progenitor behavior in vitro, but the role of miRNAs in adult skeletal muscle satellite cells is less studied. In this review, we provide evidence for how miRNAs control satellite cell function with emphasis on satellite cells of adult skeletal muscle in vivo. We first outline how miRNAs are indispensable for satellite cell viability and control the phases of myogenesis. Next, we discuss the interplay between miRNAs and myogenic cell redox status, senescence, and communication to other muscle-resident cells during muscle adaptation. Results from recent satellite cell miRNA profiling studies are also summarized. In vitro experiments in primary myogenic cells and cell lines have been invaluable for exploring the influence of miRNAs, but we identify a need for novel genetic tools to further interrogate how miRNAs control satellite cell behavior in adult skeletal muscle in vivo.