Biology subjects

Field, M. S.

Publications and source records attributed to Field, M. S..

15 recordsLinked to original sources

bioRxiv2026

Maternal Folate Nutrition Programs Adult Hematopoietic Stem Cell Function Through Mitochondrial Remodeling

Folic acid fortification for the prevention of neural tube defects has been a cornerstone of public health policy for nearly three decades, but its broader consequences for other developing organ systems, particularly the hematopoietic system, are poorly studied. Hematopoietic stem cell (HSC) emergence overlaps developmentally with neural tube closure, and folate-dependent one-carbon metabolism is critical for nucleotide synthesis, cellular methylation, and redox balance, positioning folate as a candidate regulator of HSC programming. Using dietary models of maternal folate deficiency or supplementation in mice, we demonstrate that maternal folate acts as a dose-dependent developmental tuner of hematopoiesis, programming adult offspring HSC function through divergent mitochondrial and chromatin states. Maternal folate deficiency impaired adult HSC self-renewal, associated with mitochondrial defects, disrupted cristae, elevated proteotoxic stress and a stress-adapted chromatin landscape. In contrast, maternal folate supplementation enhanced HSC self-renewal accompanied by improved mitochondrial quality control and CDC42-associated organelle remodeling, and established chromatin states permissive for stem cell maintenance. Fetal HSC metabolomics identified shifts in one-carbon intermediates, pyruvate and lipid pools, suggesting that divergent fetal metabolic states provide substrate-level inputs that drive persistent and opposing chromatin programs in offspring HSCs. Our findings establish maternal folate availability as an unappreciated regulator of lifelong hematopoietic output demonstrating that a single maternal micronutrient, folate, is sufficient to program adult HSC function and regenerative capacity through persistent metabolic and mitochondrial programming.

cell biology↗

bioRxiv2026

Vitamin B12 Improves Skeletal Muscle Mitochondrial Biology in Aged Mice

Age-related skeletal muscle deterioration is a commonly reported disability among older adults, attributed to several factors including mitochondrial dysfunction, a major hallmark of aging. Therapies to attenuate or reverse mitochondrial decline are limited. Despite identified positive relationships between vitamin B12 (B12) and mitochondrial biology, the impact of B12 supplementation on skeletal muscle mitochondria, in advanced aged, has not been examined. Thus, the impact of B12 supplementation on skeletal muscle mitochondrial biology was examined in (i) aged female mice, given 12 weeks of B12 supplementation (SUPP) or vehicle control, and (ii) in human primary myotubes. In the mouse model, mitochondrial DNA and content were measured with PCR and citrate synthase activity, respectively; mitochondrial morphology was examined using transmission electron microscopy; mitochondrial function was examined using extracellular metabolic flux analysis; and proteins and pathway enrichment was identified with proteomics. In the cell model, ROS and glutathione was measured using luminescent assays. The results demonstrated that SUPP in aged mice increased muscle mitochondrial content and improved morphology. Further, differentially expressed proteins were enriched in TCA cycle, OXPHOS, and oxidative stress pathways. In the cell model, B12 supplementation reduced ROS levels. This is the first study, to our knowledge, examining the impact of B12 supplementation on skeletal muscle mitochondrial biology in aged female mice. Results suggest that B12 supplementation improves mitochondrial biology in aged female mice.

molecular biology↗

bioRxiv2025

Vitamin B12 supports skeletal muscle oxidative phosphorylation capacity in male mice

ObjectivesVitamin B12 plays a vital role in folate-mediated one-carbon metabolism (FOCM), a series of one-carbon transfer reactions that generate nucleotides (thymidylate (dTMP) and purines) and methionine. Inadequate levels of B12 impair FOCM, depressing de novo thymidylate (dTMP) synthesis, which in turn leads to uracil accumulation in DNA. This phenomenon has been well documented in nuclear DNA. Our previous work in liver tissue has shown that mitochondrial DNA (mtDNA) is more sensitive to FOCM impairments in that mtDNA exhibits elevated uracil levels before uracil concentrations in nuclear DNA change. However, the functional consequences of uracil accumulation in mtDNA are largely unknown. The purpose of this study was to determine how a functional B12 deficiency (induced by reduced levels of the B12-dependent enzyme methionine synthase (MTR)) and dietary B12 deficiency affects mtDNA integrity and mitochondrial function in energetic and mitochondria-rich tissues such as skeletal muscle. MethodsMale Mtr+/+ and Mtr+/- mice were weaned to either an AIN93G-based control (C) diet containing 25 {micro}g/kg vitamin B12 or a B12-deficient (-B12) diet containing 0 {micro}g/kg vitamin B12 to explore the effects of functional (Mtr+/-) and dietary B12 deficiency on muscle weight, uracil content in mtDNA, mtDNA content, and oxidative phosphorylation complex capacity in skeletal muscle. Aged (20-22mo) male C57BL6/N mice were acclimated to an AIN93G control diet four weeks, then received either weekly injections of saline (vehicle control [30 uL 0.9% NaCl]) or B12 (0.65mg per 30uL 0.9% NaCl) in each of two hindleg muscles [1.25 mg B12 total]) for 8 weeks. ResultsThe tibialis anterior (TA) muscle from Mtr+/-mice exhibited lowered maximal respiratory capacity of complex I, II, and IV of the electron transport chain than did TA from Mtr+/+ mice. Exposure to the -B12 diet lowered maximal capacity of complex I in red, mitochondrially rich muscle (soleus and mitochondria-rich portions of quadriceps and gastrocnemius) (p=0.02). Levels of uracil accumulation in mtDNA in red muscle and gastrocnemius were elevated [~]10 fold with exposure to -B12 diet (p=0.04 and p<0.001, respectively). In aged mice gastrocnemius complex IV activity increased with intramuscular B12 supplementation (p=0.04) ConclusionsExposure to a B12-deficient diet led to uracil accumulation in mtDNA and impaired maximal oxidative capacity in two different types of skeletal muscle. B12 supplementation improved complex IV maximal capacity in gastrocnemius from aged mice.

biochemistry↗

bioRxiv2024

Disruption of mitochondrial folate metabolism leads to mitochondrial DNA leakage and activation of apoptotic or inflammatory pathways

Folate-mediated one-carbon metabolism (FOCM) is required for the biosynthesis of purines, thymidylate (dTMP), and methionine. Maintenance of adequate cellular dTMP levels is essential to preserve the integrity of the nuclear and mitochondrial genomes. Inadequate dTMP production leads to uracil misincorporation into mitochondrial DNA (mtDNA) and impaired mitochondrial function. However, the mechanisms whereby uracil in mtDNA impairs mitochondrial function are uncharacterized. The release of mtDNA into the cytosol acts as a damage-associated molecular pattern (DAMP), resulting in inflammation and cell death. Previously, we reported that disrupting mitochondrial dTMP synthesis through serine hydroxymethyltransferase 2 (Shmt2) heterozygosity increases uracil in mtDNA and impairs mitochondrial function in mice. This study aimed to investigate whether impairment of mitochondrial FOCM through Shmt2 disruption leads to the release of mtDNA into the cytosol. Shmt2+/- MEF cells showed a > 2-fold increase in cytosolic mtDNA leakage compared to Shmt2+/+ cells (p<0.05). There was no significant difference in total mtDNA content between Shmt2+/+ and Shmt2+/- MEF cells. MEFs with decreased Shmt2 expression activated apoptosis by the ratio of cleaved caspase-3 to caspase-3. In addition, SHMT2 knock-out (SHMT2 KO) haploid chronic myeloid leukemia (HAP1) cells also exhibited increased cytosolic mtDNA content compared to the wild-type (WT) HAP1 cells. HAP1 lacking Shmt2 expression activated the cGAS/STING pathway, but suppressed apoptosis, compared to WT HAP1 cells. This study demonstrates that decreased Shmt2 expression leads to cytosolic mtDNA leakage and that the downstream effects of mtDNA leakage vary by cell type.

biochemistry↗

bioRxiv2024

Excess folic acid exposure increases uracil misincorporation into DNA in a tissue-specific manner in a mouse model of reduced methionine synthase expression

BackgroundFolate and vitamin B12 (B12) are cofactors in folate-mediated one-carbon metabolism (FOCM), a metabolic network that supports synthesis of nucleotides (including thymidylate, or dTMP) and methionine. FOCM impairments such as a deficiency or imbalance of cofactors can perturb dTMP synthesis, causing uracil misincorporation into DNA. ObjectiveThe purpose of this study was to determine how reduced expression of the B12-dependent enzyme methionine synthase (MTR) and excess dietary folic acid interact to affect folate distribution and markers of genome stability in mouse tissues. MethodsHeterozygous Mtr knockout mice (Mtr+/-) model the FOCM-specific effects of B12 deficiency. Folate accumulation and vitamer distribution, genomic uracil levels, and phosphorylated histone {gamma}H2AX immunostaining were measured in male Mtr+/+ and Mtr+/- mice weaned to either a folate-sufficient control (C) diet (2 mg/kg folic acid) or a high folic acid (HFA) diet (20 mg/kg folic acid) for 7 weeks. ResultsExposure to the HFA diet led to tissue-specific patterns of folate accumulation, with plasma, colon, kidney, and skeletal muscle exhibiting increased folate concentrations compared to control. Liver total folate did not differ. Though unmetabolized folic acid (UMFA) increased 10-fold in mouse plasma with HFA diet, UMFA accounted for less than 0.2% of total folate in liver and colon tissue. Exposure to HFA diet resulted in a shift in folate distribution in colon tissue with higher 5-methyl-THF and lower formyl-THF than in control mice. Mtr heterozygosity did not impact folate accumulation or distribution in any tissue. Mice on HFA diet exhibited higher uracil in genomic DNA and {gamma}H2AX foci in colon. Similar differences were not seen in liver. ConclusionsThis study demonstrates that folic acid, even when consumed at high doses, does not meaningfully accumulate in mouse tissues, although high-dose folic acid shifts folate distribution and increases uracil accumulation in genomic DNA in colon tissue.

biochemistry↗

bioRxiv2024

Late-life dietary folate restriction reduces biosynthetic processes without compromising healthspan in mice

Folate is a vitamin required for cell growth and is present in fortified foods in the form of folic acid to prevent congenital abnormalities. The impact of low folate status on life-long health is poorly understood. We found that limiting folate levels with the folate antagonist methotrexate increased the lifespan of yeast and worms. We then restricted folate intake in aged mice and measured various health metrics, metabolites, and gene expression signatures. Limiting folate intake decreased anabolic biosynthetic processes in mice and enhanced metabolic plasticity. Despite reduced serum folate levels in mice with limited folic acid intake, these animals maintained their weight and adiposity late in life, and we did not observe adverse health outcomes. These results argue that the effectiveness of folate dietary interventions may vary depending on an individuals age and sex. A higher folate intake is advantageous during the early stages of life to support cell divisions needed for proper development. However, a lower folate intake later in life may result in healthier aging.

molecular biology↗

bioRxiv2023

C2C12 muscle myotubes, but not kidney proximal tubule HK-2 cells, elevate erythritol synthesis in response to oxidative stress

BackgroundAs a biomarker, elevated serum erythritol predicts type 2 diabetes and cardiovascular disease onset. Erythritol was recently shown to be a product of human glucose metabolism through the pentose phosphate pathway. The regulation of erythritol synthesis from glucose has been explored in cancer cells, but not in non-transformed cells. ObjectiveThe kidneys and skeletal muscle have increased erythritol content in response to dietary sucrose, which suggests that they may significantly contribute to circulating erythritol levels. In the present study, we evaluated if conditions that promote erythritol synthesis in cancer cells are consistent in skeletal muscle and kidney cells. MethodsC2C12 myotubules were used as a model for skeletal muscle and HK-2 human proximal tubule cells were used to model kidney. C2C12 cells were exposed to high-or low-glucose conditions. Both C2C12 and HK-2 cells were exposed to the free radical generator menadione, then intracellular reactive oxygen species (ROS) and erythritol were measured. Intracellular sorbitol levels were also measured because increased polyol flux is also observed after exposure to excess glucose and oxidative stress. ResultsIntracellular erythritol was significantly elevated in C2C12 cells following both high glucose and menadione treatment. In contrast, HK-2 cells did not increase erythritol synthesis in response to oxidative stress. Generation of ROS through hydrogen peroxide (H2O2) exposure elevated sorbitol levels in both C2C12 and HK-2 cells, whereas generation of radicals with menadione treatment did not affect sorbitol production in either cell type. ConclusionsThese findings highlight that the factors contributing to elevated erythritol synthesis vary between cell types. More specifically, these studies demonstrate that muscle cells increase erythritol synthesis in response to both high glucose in culture medium and oxidative stress, whereas kidney cells increase erythritol synthesis only in response to high glucose.

biochemistry↗

bioRxiv2023

Vitamin B12 status and folic acid supplementation influence mitochondrial heteroplasmy levels in mice as they age.

One-carbon metabolism is a complex network of metabolic reactions that are essential for cellular function including DNA synthesis. Vitamin B12 and folate are micronutrients that are utilized in this pathway and their deficiency can result in the perturbation of one-carbon metabolism and subsequent perturbations in DNA replication and repair. This effect has been well characterized in nuclear DNA but to date, mitochondrial DNA (mtDNA) has not been investigated extensively. Mitochondrial variants have been associated with several inherited and age-related disease states; therefore, the study of factors that impact heteroplasmy are important for advancing our understanding of the mitochondrial genomes impact on human health. Heteroplasmy studies require robust and efficient mitochondrial DNA enrichment to carry out in-depth mtDNA sequencing. Many of the current methods for mtDNA enrichment can introduce biases and false positive results. Here we use a method that overcomes these limitations and have applied it to assess mitochondrial heteroplasmy in mouse models of altered one-carbon metabolism. Vitamin B12 deficiency was found to cause increased levels of mitochondrial DNA heteroplasmy across all tissues that were investigated. Folic acid supplementation also contributed to elevated mitochondrial DNA heteroplasmy across all mouse tissues investigated. Heteroplasmy analysis of human data from the Framingham Heart Study suggested a potential sex-specific effect of folate and vitamin B12 status on mitochondrial heteroplasmy. This is a novel relationship that may have broader consequences for our understanding of one-carbon metabolism, mitochondrial related disease and the influence of nutrients on DNA mutation rates. Significance StatementUsing a sensitive method for mitochondrial heteroplasmy analysis, we show that both vitamin B12 and folic acid can impact mitochondrial DNA mutation. This effect requires further investigation of the potential impact on humans.

molecular biology↗

bioRxiv2022

Elevated plasma and urinary erythritol is a biomarker of excess simple carbohydrate intake in mice

BackgroundElevated serum erythritol is a predictive biomarker of diabetes and cardiovascular incidence and complications. Erythritol is synthesized endogenously from glucose, but little is known regarding the origin of elevated circulating erythritol in vivo. ObjectiveIn vitro evidence indicates that intracellular erythritol is elevated by high-glucose cell culture conditions and that final step of erythritol synthesis is catalyzed by the enzymes SORD and ADH1. The purpose of this study was to determine if dietary intake and/or diet-induced obesity (DIO) affect erythritol synthesis in mice, and if this relationship is modified by loss of the enzymes SORD or ADH1. MethodsFirst, 8-week-old, male Sord+/+, Sord-/-, Adh1+/+, and Adh1-/- mice were fed either low-fat diet (LFD) with 10% fat-derived calories or DIO high-fat diet (HFD) with 60% fat-derived calories for 8 weeks. Plasma and tissue erythritol were measured using GC-MS. Second, wild-type 8-week-old C57BL/6J mice were fed LFD or HFD with plain drinking water or 30% sucrose water for 8 weeks. Blood glucose and plasma and urinary erythritol were measured in non-fasted and fasted samples. Tissue erythritol was measured following sacrifice. Finally, Sord+/+ and Sord-/- mice were fed LFD with 30% sucrose water for two weeks, then non-fasted plasma, urine, and tissue erythritol were quantified. ResultsPlasma and tissue erythritol were not impacted by loss of Sord or Adh1 on LFD or HFD. In wild-type mice, consumption of 30% sucrose water significantly elevated plasma and urinary erythritol on both LFD and HFD compared to plain water. Sord genotype did not affect plasma or urinary erythritol in response to sucrose feeding, but Sord-/- mice had reduced kidney erythritol content compared to wildtype littermates in response to sucrose. ConclusionsSucrose intake, not high-fat diet, elevates erythritol synthesis and excretion in mice. Loss of ADH1 or SORD does not significantly impact erythritol levels in mice.

biochemistry↗

bioRxiv2022

Reduced methionine synthase (Mtr) expression creates a functional vitamin B12 deficiency that leads to uracil accumulation in mouse mitochondrial DNA

Adequate thymidylate (dTMP or the "T" base in DNA) levels are essential for stability of mitochondrial DNA (mtDNA) and nuclear DNA (nDNA). Folate and vitamin B12 (B12) are essential cofactors in folate-mediated one carbon metabolism (FOCM), a metabolic network which supports synthesis of nucleotides (including dTMP) and methionine. Perturbations in FOCM impair dTMP synthesis, causing misincorporation of uracil (or a "U" base) into DNA. During B12 deficiency, cellular folate accumulates as 5-methyltetrahdryfolate (5-methyl-THF), limiting nucleotide synthesis. The purpose of this study was to determine how B12 deficiency and dietary folate interact to affect mtDNA integrity and mitochondrial function in mouse liver. Mice expressing reduced methionine synthase (Mtr) levels were used to create a functional B12 deficiency. Folate accumulation, uracil levels, mtDNA content, and oxidative phosphorylation capacity were measured in male Mtr+/+ and Mtr+/- mice weaned onto either a folate-sufficient control diet (2 mg/kg folic acid, C) or a folate-deficient diet (FD, lacking folic acid) for 7 weeks. Mtr heterozygosity led to increased liver 5-methyl-THF levels. Mtr+/- mice consuming the C diet also exhibited a 40-fold increase in uracil in liver mtDNA. However, the combination of Mtr heterozygosity and exposure to the FD diet partially alleviated the level of uracil accumulation in mtDNA. Furthermore, Mtr+/- mice exhibited a 25% decrease in liver mtDNA content and a 20% decrease in maximal oxygen consumption rates. Impairments in mitochondrial FOCM are known to lead to increased uracil in mtDNA. This study demonstrates that impaired cytosolic dTMP synthesis also leads to increased uracil in mtDNA.

biochemistry↗

bioRxiv2022

Impairments in SHMT2 expression or cellular folate availability reduce oxidative phosphorylation and pyruvate kinase activity

BackgroundSerine hydroxymethyltransferase 2 (SHMT2) catalyzes the reversible conversion of tetrahydrofolate (THF) and serine producing THF-conjugated one-carbon units and glycine in the mitochondria. Biallelic SHMT2 variants were identified in humans and suggested to alter the proteins active site, potentially disrupting enzymatic function. SHMT2 expression has also been shown to decrease with aging in human fibroblasts. Immortalized cells models of total SHMT2 loss or folate deficiency exhibit decreased oxidative capacity and impaired mitochondrial complex I assembly and protein levels, suggesting folate-mediated one-carbon metabolism (FOCM) and the oxidative phosphorylation system are functionally coordinated. This study examined the role of SHMT2 and folate availability in regulating mitochondrial function, energy metabolism, and cellular proliferative capacity in both heterozygous and homozygous cell models of reduced SHMT2 expression. MethodsPrimary mouse embryonic fibroblasts (MEF) were isolated from a C57Bl/6 dam crossed with a heterozygous Shmt2+/- male to generate Shmt2+/+ (wild-type) or Shmt2+/- (HET) MEF cells. In addition, haploid chronic myeloid leukemia cells (HAP1, wild-type) or HAP1 cells lacking SHMT2 expression ({Delta}SHMT2) were cultured for 4 doublings in either low-folate or folate-sufficient culture media. Cells were examined for proliferation, total folate levels, mtDNA content, protein levels of pyruvate kinase and PGC1, pyruvate kinase enzyme activity, mitochondrial membrane potential, and mitochondrial function. ResultsHomozygous loss of SHMT2 in HAP1 cells impaired cellular folate accumulation and altered mitochondrial DNA content, membrane potential, and basal respiration. Formate rescued proliferation in HAP1, but not {Delta}SHMT2, cells cultured in low-folate medium. Pyruvate kinase activity and protein levels were impaired in {Delta}SHMT2 cells and in MEF cells exposed to low-folate medium. Mitochondrial biogenesis protein levels were elevated in Shmt2+/- MEF cells, while mitochondrial mass was increased in both homozygous and heterozygous models of SHMT2 loss. ConclusionsThe results from this study indicate disrupted mitochondrial FOCM impairs mitochondrial folate accumulation and respiration, glycolytic activity, and cellular proliferation. These changes persist even after a potentially compensatory increase in mitochondrial biogenesis as a result of decreased SHMT2 levels.

biochemistry↗

bioRxiv2022

Erythritol synthesis in human cells is elevated in response to oxidative stress and regulated by the non-oxidative pentose phosphate pathway

Erythritol is a predictive biomarker of cardiometabolic diseases and is produced from glucose metabolism through the pentose phosphate pathway (PPP). Little is known regarding the regulation of endogenous erythritol synthesis in humans. In the present study, we investigated the stimuli that promote erythritol synthesis in human cells and characterized potential points of regulation along the PPP. Human A549 lung carcinoma cells were chosen for their known ability to synthesize erythritol. A549 cells were treated with potential substrates for erythritol production, including glucose, fructose, and glycerol. Using siRNA knockdown, we assessed the necessity of enzymes G6PD, TKT, TALDO, and SORD for erythritol synthesis. We also used position-specific 13C-glucose tracers to determine whether the carbons for erythritol synthesis are derived directly from glycolysis or through the oxidative PPP. Finally, we assessed if erythritol synthesis responds to oxidative stress using chemical and genetic models. Intracellular erythritol was directly associated with media glucose concentration. In addition, siRNA knockdown of TKT or SORD inhibited erythritol synthesis, whereas siG6PD did not. Both chemically induced oxidative stress and constitutive activation of the antioxidant response transcription factor NRF2 elevated intracellular erythritol. Our findings indicate that erythritol synthesis is proportional to flux through the PPP and is regulated by non-oxidative PPP enzymes.

biochemistry↗

bioRxiv2021

Reduced Shmt2 expression impairs mitochondrial folate accumulation and respiration, and leads to uracil accumulation in mouse mitochondrial DNA

BackgroundAdequate cellular thymidylate (dTMP) pools are essential for preservation of nuclear and mitochondrial genome stability. Previous studies have indicated that disruption in dTMP synthesis in the nucleus leads to increased uracil misincorporation into DNA affecting genome stability. To date, the effects of impaired mitochondrial dTMP synthesis in non- transformed tissues have been understudied. ObjectiveThis study aimed to determine the effects of decreased serine hydroxymethyltransferase 2 (Shmt2) expression and dietary folate deficiency on mitochondrial DNA integrity and mitochondrial function in mouse tissues. MethodsLiver mitochondrial DNA (mtDNA) content, and uracil content in liver mtDNA was measured in Shmt2+/- and Shmt2+/+ mice weaned onto either a folate-sufficient control diet (2 mg/kg folic acid, C) or a modified diet lacking folic acid (0 mg/kg folic acid, FD) for 7 wks. Shmt2+/- and Shmt2+/+ mouse embryonic fibroblasts (MEF cells) were cultured in defined culture medium containing either 0 or 25 nM folate to assess proliferative capacity and mitochondrial function. ResultsShmt2+/- mice exhibited 48-67% reduction in SHMT2 protein levels in tissues. Interestingly, Shmt2+/- mice consuming the folate-sufficient C diet exhibited a 25% reduction in total folate in liver mitochondria. There was also a >20-fold increase in uracil in liver mtDNA in Shmt2+/- mice consuming the C diet, and dietary folate deficiency also increased uracil content in mouse liver mtDNA from both Shmt2+/+ and Shmt2+/- mice. Furthermore, decreased Shmt2 expression in MEF cells reduced cell proliferation, mitochondrial membrane potential, and oxygen consumption rate. ConclusionsThis study demonstrates that Shmt2 heterozygosity and dietary folate deficiency impair mitochondrial dTMP synthesis, as evidenced by the increased uracil in mtDNA. In addition, Shmt2 heterozygosity impairs mitochondrial function in MEF cells. These findings suggest that elevated uracil in mtDNA may impair mitochondrial function.

biochemistry↗

bioRxiv2021

Chronic dietary erythritol exposure elevates fasting plasma erythritol levels but does not cause weight gain or modify glucose homeostasis in mice

ObjectiveErythritol is both a common non-nutritive sweetener (NNS) and an endogenous product of glucose metabolism. Recent reports indicate that elevated plasma erythritol is a predictive biomarker of cardiometabolic disease onset and complications. Although short-term erythritol consumption has been evaluated, the effect of chronically elevated circulating erythritol on adiposity and glucose metabolism has not. This study investigated the effect of longer-term erythritol consumption on weight gain and glucose tolerance, and the interaction between dietary composition and erythritol supplementation on these parameters. Methods8-week-old and 20-week-old C57BL/6J mice were randomized to consume low-fat diet (LFD), high-fat diet (HFD), LFD with 40g/kg erythritol (LFD+ERY), and HFD with 40g/kg erythritol (HFD+ERY) groups. After 8 weeks, plasma erythritol, body weight and composition, food intake, glucose tolerance, and brown adipose tissue (BAT) uncoupling protein 1 (UCP1) expression were measured. ResultsPlasma erythritol was elevated 40-fold in mice consuming LFD+ERY or HFD+ERY relative to mice consuming LFD or HFD, respectively. Liver and kidney tissue contained higher levels of erythritol than adipose. Unexpectedly, there was no effect of erythritol supplementation on body weight or glucose tolerance in 8- or 20-week-old mice fed LFD+ERY, or in 8-week-old mice fed HFD+ERY. In 20-week-old mice fed HFD+ERY, there was a significant interaction between erythritol and body weight (p<0.0001) compared to controls, but the main effect of diet was not significant. We also found no effect of chronic erythritol consumption on BAT UCP1 expression. ConclusionProlonged erythritol consumption did not significantly impact body weight, composition, or glucose tolerance. This suggests that dietary erythritol does not contribute to the development of cardiometabolic disease.

biochemistry↗

bioRxiv2019

Serine and glycine are essential for human muscle progenitor cell population expansion

Skeletal muscle regeneration is reliant on a population of muscle specific adult stem cells (muscle progenitor cells; MPCs). During regeneration, the MPC population undergoes a transient and rapid period of population expansion, which is necessary to repair damaged myofibers and restore muscle homeostasis. Much research has focused on the age-related accumulation of negative regulators of regeneration, while the age-related decline of nutrient and metabolic determinants of the regenerative process needs examination. We hypothesized that older individuals, a population that is at risk for protein malnutrition, have diminished availability of amino acids that are necessary for MPC function. Here, we identified that levels of the non-essential amino acid serine are reduced in the skeletal muscle of healthy, older individuals. Furthermore, using stable-isotope tracing studies, we demonstrate that primary, human MPCs (hMPCs) exhibit a limited capacity for de novo biosynthesis of serine and the closely related amino acid glycine. We identified that serine and glycine are essential for hMPC proliferation and, therefore, population expansion. Serine and glycine were necessary to support synthesis of the intracellular antioxidant glutathione, and restriction of serine and glycine was sensed in an EIF2-dependent manner resulting in cell cycle arrest in G0/G1. In conclusion, we elucidate that, despite an absolute requirement of serine/glycine for hMPC proliferation, availability of serine in the skeletal muscle microenvironment is limited to the hMPCs of healthy older adults and is a likely underlying mechanism for impaired skeletal muscle regeneration with advancing age.\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=176 SRC=\"FIGDIR/small/833798v1_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (32K):\norg.highwire.dtl.DTLVardef@438298org.highwire.dtl.DTLVardef@32f66dorg.highwire.dtl.DTLVardef@1d08aeeorg.highwire.dtl.DTLVardef@511c7f_HPS_FORMAT_FIGEXP M_FIG Graphical Abstract C_FIG

cell biology↗