pH-Gated Succinate Secretion Regulates Muscle Remodeling in Response to Exercise

Exerkines: Benign adaptation for exercise and benefits for non-alcoholic fatty liver disease

Exercise has multiple beneficial effects on human metabolic health and is regarded as a "polypill" for various diseases. At present, the lack of physical activity usually causes an epidemic of chronic metabolic syndromes, including obesity, cardiovascular diseases, and non-alcoholic fatty liver disease (NAFLD). Remarkably, NAFLD is emerging as a serious public health issue and is associated with the development of cirrhosis and hepatocellular carcinoma. Unfortunately, specific drug therapies for NAFLD and its more severe form, non-alcoholic steatohepatitis (NASH), are currently unavailable. Lifestyle modification is the foundation of treatment recommendations for NAFLD and NASH, especially for exercise. There are under-appreciated organs that crosstalk to the liver during exercise such as muscle-liver crosstalk. Previous studies have reported that certain exerkines, such as FGF21, GDF15, irisin, and adiponectin, are beneficial for liver metabolism and have the potential to be targeted for NAFLD treatment. In addition, some of exerkines can be modified for the new proteins and get enhanced functions, like IL-6/IC7Fc. Another importance of exercise is the physiological adaptation that combats metabolic diseases. Thus, this review aims to summarize the known exerkines and utilize a multi-omics mining tool to identify more exerkines for the future research. Overall, understanding the mechanisms by which exercise-induced exerkines exert their beneficial effects on metabolic health holds promise for the development of novel therapeutic strategies for NAFLD and related diseases.

Determination of succinic acid and lactic acid in pigs' serum, intestinal contents, and meat by ultrahigh-performance liquid chromatography-tandem mass spectrometry

RATIONALE

Succinic acid and lactic acid have been associated with diarrhea in weaned piglets. The level of succinic acid and lactic acid in serum, meat, and intestinal contents is important to elucidate the mechanism of diarrhea in weaned piglets.

METHODS

A facile method was developed for the quantification of succinic acid and lactic acid in pigs' serum, intestinal contents, and meat using ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC/MS/MS). The serum samples underwent protein precipitation with methanol. The meat and intestinal contents were freeze-dried and homogenized using a tissue grinding apparatus. Methanol-water mixture (80:20, v/v) was used for homogenizing the meat, while water was used for homogenizing the intestinal contents. An additional step of protein precipitation with acetonitrile was required for the intestinal contents. The resulting solution was diluted with water before being analyzed by UHPLC/MS/MS. Separation of succinic acid and lactic acid could be achieved within 3 min using a Kinetic XB-C18 column.

RESULTS

The coefficients of variation for peak areas of succinic acid and lactic acid were less than 5.0%. The established method demonstrated good linearity as indicated by correlation coefficients exceeding 0.996. Additionally, satisfactory recoveries ranging from 88.58% to 108.8% were obtained. The detection limits (RS/N = 3) for succinic acid and lactic acid were determined to be 0.75 ng/mL and 0.02 μg/mL, respectively.

CONCLUSION

This method exhibited high sensitivity, simplicity in operation, and small sample weight, making it suitable for quantitative determination of succinic acid and lactic acid in pigs' serum, intestinal contents, and meat. The method developed will provide valuable technical support in studying the metabolic mechanisms of succinic acid and lactic acid in pigs.

Aging aggravates aortic aneurysm and dissection via miR-1204-MYLK signaling axis in mice

The mechanism by which aging induces aortic aneurysm and dissection (AAD) remains unclear. A total of 430 participants were recruited for the screening of differentially expressed plasma microRNAs (miRNAs). We found that miR-1204 is significantly increased in both the plasma and aorta of elder patients with AAD and is positively correlated with age. Cell senescence induces the expression of miR-1204 through p53 interaction with plasmacytoma variant translocation 1, and miR-1204 induces vascular smooth muscle cell (VSMC) senescence to form a positive feedback loop. Furthermore, miR-1204 aggravates angiotensin II-induced AAD formation, and inhibition of miR-1204 attenuates β-aminopropionitrile monofumarate-induced AAD development in mice. Mechanistically, miR-1204 directly targets myosin light chain kinase (MYLK), leading to the acquisition of a senescence-associated secretory phenotype (SASP) by VSMCs and loss of their contractile phenotype. MYLK overexpression reverses miR-1204-induced VSMC senescence, SASP and contractile phenotypic changes, and the decrease of transforming growth factor-β signaling pathway. Our findings suggest that aging aggravates AAD via the miR-1204-MYLK signaling axis.

An exercise physiologist's guide to metabolomics

The field of exercise physiology has undergone significant technological advancements since the pioneering works of exercise physiologists in the early to mid-20th century. Historically, the ability to detect metabolites in biofluids from exercising participants was limited to single-metabolite analyses. However, the rise of metabolomics, a discipline focused on the comprehensive analysis of metabolites within a biological system, has facilitated a more intricate understanding of metabolic pathways and networks in exercise. This review explores some of the pivotal technological and bioinformatic advancements that have propelled metabolomics to the forefront of exercise physiology research. Metabolomics offers a unique 'fingerprint' of cellular activity, offering a broader spectrum than traditional single-metabolite assays. Techniques, including mass spectrometry and nuclear magnetic resonance spectroscopy, have significantly improved the speed and sensitivity of metabolite analysis. Nonetheless, challenges persist, including study design and data interpretation issues. This review aims to serve as a guide for exercise physiologists to facilitate better research design, data analysis and interpretation within metabolomics. The potential of metabolomics in bridging the gap between genotype and phenotype is emphasised, underscoring the critical importance of careful study design and the selection of appropriate metabolomics techniques. Furthermore, the paper highlights the need to deeply understand the broader scientific context to discern meaningful metabolic changes. The emerging field of fluxomics, which seeks to quantify metabolic reaction rates, is also introduced as a promising avenue for future research.

Lactobacillus-derived protoporphyrin IX and SCFAs regulate the fiber size via glucose metabolism in the skeletal muscle of chickens

The gut microbiota contributes to skeletal muscle energy metabolism and is an indirect factor affecting meat quality. However, the role of specific gut microbes in energy metabolism and fiber size of skeletal muscle in chickens remains largely unknown. In this study, we first performed cecal microbiota transplantation from Chinese indigenous Jingyuan chickens (JY) to Arbor Acres chickens (AA), to determine the effects of microbiota on skeletal muscle fiber and energy metabolism. Then, we used metagenomics, gas chromatography, and metabolomics analysis to identify functional microbes. Finally, we validated the role of these functional microbes in regulating the fiber size via glucose metabolism in the skeletal muscle of chickens through feeding experiments. The results showed that the skeletal muscle characteristics of AA after microbiota transplantation tended to be consistent with that of JY, as the fiber diameter was significantly increased, and glucose metabolism level was significantly enhanced in the pectoralis muscle. L. plantarum, L. ingluviei, L. salivarius, and their mixture could increase the production of the microbial metabolites protoporphyrin IX and short-chain fatty acids, therefore increasing the expression levels of genes related to the oxidative fiber type (MyHC SM and MyHC FRM), mitochondrial function (Tfam and CoxVa), and glucose metabolism (PFK, PK, PDH, IDH, and SDH), thereby increasing the fiber diameter and density. These three Lactobacillus species could be promising probiotics to improve the meat quality of chicken.IMPORTANCEThis study revealed that the L. plantarum, L. ingluviei, and L. salivarius could enhance the production of protoporphyrin IX and short-chain fatty acids in the cecum of chickens, improving glucose metabolism, and finally cause the increase in fiber diameter and density of skeletal muscle. These three microbes could be potential probiotic candidates to regulate glucose metabolism in skeletal muscle to improve the meat quality of chicken in broiler production.

Cellular succinate metabolism and signaling in inflammation: implications for therapeutic intervention

Succinate, traditionally viewed as a mere intermediate of the tricarboxylic acid (TCA) cycle, has emerged as a critical mediator in inflammation. Disruptions within the TCA cycle lead to an accumulation of succinate in the mitochondrial matrix. This excess succinate subsequently diffuses into the cytosol and is released into the extracellular space. Elevated cytosolic succinate levels stabilize hypoxia-inducible factor-1α by inhibiting prolyl hydroxylases, which enhances inflammatory responses. Notably, succinate also acts extracellularly as a signaling molecule by engaging succinate receptor 1 on immune cells, thus modulating their pro-inflammatory or anti-inflammatory activities. Alterations in succinate levels have been associated with various inflammatory disorders, including rheumatoid arthritis, inflammatory bowel disease, obesity, and atherosclerosis. These associations are primarily due to exaggerated immune cell responses. Given its central role in inflammation, targeting succinate pathways offers promising therapeutic avenues for these diseases. This paper provides an extensive review of succinate's involvement in inflammatory processes and highlights potential targets for future research and therapeutic possibilities development.

Glycolytic lactate in diabetic kidney disease

Lactate elevation is a well-characterized biomarker of mitochondrial dysfunction, but its role in diabetic kidney disease (DKD) is not well defined. Urine lactate was measured in patients with type 2 diabetes (T2D) in 3 cohorts (HUNT3, SMART2D, CRIC). Urine and plasma lactate were measured during euglycemic and hyperglycemic clamps in participants with type 1 diabetes (T1D). Patients in the HUNT3 cohort with DKD had elevated urine lactate levels compared with age- and sex-matched controls. In patients in the SMART2D and CRIC cohorts, the third tertile of urine lactate/creatinine was associated with more rapid estimated glomerular filtration rate decline, relative to first tertile. Patients with T1D demonstrated a strong association between glucose and lactate in both plasma and urine. Glucose-stimulated lactate likely derives in part from proximal tubular cells, since lactate production was attenuated with sodium-glucose cotransporter-2 (SGLT2) inhibition in kidney sections and in SGLT2-deficient mice. Several glycolytic genes were elevated in human diabetic proximal tubules. Lactate levels above 2.5 mM potently inhibited mitochondrial oxidative phosphorylation in human proximal tubule (HK2) cells. We conclude that increased lactate production under diabetic conditions can contribute to mitochondrial dysfunction and become a feed-forward component to DKD pathogenesis.

Metabolic Signaling in Cancer Metastasis

Metastases, which are the leading cause of death in patients with cancer, have metabolic vulnerabilities. Alterations in metabolism fuel the energy and biosynthetic needs of metastases but are also needed to activate cell state switches in cells leading to invasion, migration, colonization, and outgrowth in distant organs. Specifically, metabolites can activate protein kinases as well as receptors and they are crucial substrates for posttranslational modifications on histone and nonhistone proteins. Moreover, metabolic enzymes can have moonlighting functions by acting catalytically, mainly as protein kinases, or noncatalytically through protein-protein interactions. Here, we summarize the current knowledge on metabolic signaling in cancer metastasis.

SIGNIFICANCE

Effective drugs for the prevention and treatment of metastases will have an immediate impact on patient survival. To overcome the current lack of such drugs, a better understanding of the molecular processes that are an Achilles heel in metastasizing cancer cells is needed. One emerging opportunity is the metabolic changes cancer cells need to undergo to successfully metastasize and grow in distant organs. Mechanistically, these metabolic changes not only fulfill energy and biomass demands, which are often in common between cancer and normal but fast proliferating cells, but also metabolic signaling which enables the cell state changes that are particularly important for the metastasizing cancer cells.

Pulmonary succinate receptor 1 elevation in high-fat diet mice exacerbates lipopolysaccharides-induced acute lung injury via sensing succinate

BACKGROUND

Individuals with obesity have higher level of circulating succinate, which acts as a signaling factor that initiates inflammation. It is obscure whether succinate and succinate receptor 1 (SUCNR1) are involved in the process of obesity aggravating acute lung injury (ALI).

METHODS

The lung tissue and blood samples from patients with obesity who underwent lung wedgectomy or segmental resection were collected. Six-week-old male C57BL/6J mice were fed a high-fat diet for 12 weeks to induce obesity and lipopolysaccharides (LPS) were injected intratracheally (100 μg, 1 mg/ml) for 24 h to establish an ALI model. The pulmonary SUCNR1 expression and succinate level were measured. Exogenous succinate was supplemented to assess whether succinate exacerbated the LPS-induced lung injury. We next examined the cellular localization of pulmonary SUCNR1. Furthermore, the role of the succinate-SUCNR1 pathway in LPS-induced inflammatory responses in MH-s macrophages and obese mice was investigated.

RESULT

The pulmonary SUCNR1 expression and serum succinate level were significantly increased in patients with obesity and in HFD mice. Exogenous succinate supplementation significantly increased the severity of ALI and inflammatory response. SUCNR1 was mainly expressed on lung macrophages. In LPS-stimulated MH-s cells, knockdown of SUCNR1 expression significantly inhibited pro-inflammatory cytokines' expression, the increase of hypoxia-inducible factor-1α (HIF-1α) expression, inhibitory κB-α (IκB-α) phosphorylation, p65 phosphorylation and p65 translocation to nucleus. In obese mice, SUCNR1 inhibition significantly alleviated LPS-induced lung injury and decreased the HIF-1α expression and IκB-α phosphorylation.

CONCLUSION

The high expression of pulmonary SUCNR1 and serum succinate accumulation at least partly participate in the process of obesity aggravating LPS-induced lung injury.

Molecular insights of exercise therapy in disease prevention and treatment

Despite substantial evidence emphasizing the pleiotropic benefits of exercise for the prevention and treatment of various diseases, the underlying biological mechanisms have not been fully elucidated. Several exercise benefits have been attributed to signaling molecules that are released in response to exercise by different tissues such as skeletal muscle, cardiac muscle, adipose, and liver tissue. These signaling molecules, which are collectively termed exerkines, form a heterogenous group of bioactive substances, mediating inter-organ crosstalk as well as structural and functional tissue adaption. Numerous scientific endeavors have focused on identifying and characterizing new biological mediators with such properties. Additionally, some investigations have focused on the molecular targets of exerkines and the cellular signaling cascades that trigger adaption processes. A detailed understanding of the tissue-specific downstream effects of exerkines is crucial to harness the health-related benefits mediated by exercise and improve targeted exercise programs in health and disease. Herein, we review the current in vivo evidence on exerkine-induced signal transduction across multiple target tissues and highlight the preventive and therapeutic value of exerkine signaling in various diseases. By emphasizing different aspects of exerkine research, we provide a comprehensive overview of (i) the molecular underpinnings of exerkine secretion, (ii) the receptor-dependent and receptor-independent signaling cascades mediating tissue adaption, and (iii) the clinical implications of these mechanisms in disease prevention and treatment.

SUCNR1 regulates insulin secretion and glucose elevates the succinate response in people with prediabetes

Pancreatic β-cell dysfunction is a key feature of type 2 diabetes, and novel regulators of insulin secretion are desirable. Here we report that the succinate receptor (SUCNR1) is expressed in β-cells and is up-regulated in hyperglycemic states in mice and humans. We found that succinate acts as a hormone-like metabolite and stimulates insulin secretion via a SUCNR1-Gq-PKC-dependent mechanism in human β-cells. Mice with β-cell-specific Sucnr1 deficiency exhibit impaired glucose tolerance and insulin secretion on a high-fat diet, indicating that SUCNR1 is essential for preserving insulin secretion in diet-induced insulin resistance. Patients with impaired glucose tolerance show an enhanced nutritional-related succinate response, which correlates with the potentiation of insulin secretion during intravenous glucose administration. These data demonstrate that the succinate/SUCNR1 axis is activated by high glucose and identify a GPCR-mediated amplifying pathway for insulin secretion relevant to the hyperinsulinemia of prediabetic states.

Mitochondrial heterogeneity and adaptations to cellular needs

Although it is well described that mitochondria are at the epicentre of the energy demands of a cell, it is becoming important to consider how each cell tailors its mitochondrial composition and functions to suit its particular needs beyond ATP production. Here we provide insight into mitochondrial heterogeneity throughout development as well as in tissues with specific energy demands and discuss how mitochondrial malleability contributes to cell fate determination and tissue remodelling.

Lactate-induced metabolic remodeling and myofiber type transitions via activation of the Ca2+-NFATC1 signaling pathway

Lactate can serve as both an energy substrate and a signaling molecule, exerting diverse effects on skeletal muscle physiology. Due to the apparently positive effects, it would be interesting to consider it as a sports supplement. However, the mechanism behind these effects are yet to be comprehensively understood. In this study, we observed that lactate administration could improve the ability of antifatigue, and we further found that lactate upregulated the expression of myosin heavy chain (MYHC I) and MYHC IIa, while downregulating the expression of MYHC IIb. Besides, transcriptomics and metabolomics revealed significant changes in the metabolic profile of gastrocnemius muscle following lactate administration. Furthermore, lactate enhanced the activities of metabolic enzymes, including HK, LDHB, IDH, SDM, and MDH, and promoted the expression of lactate transport-related proteins MCT1 and CD147, thereby improving the transport and utilization of lactate in both vivo and vitro. More importantly, lactate administration increased cellular Ca2+ concentration and facilitated nuclear translocation of nuclear factor of activated T cells (NFATC1) in myotubes, whereas inhibition of NFATC1 significantly attenuated the effects of lactate treatment on NFATC1 nuclear translocation and MyHC expression. Our results elucidate the ability of lactate to induce metabolic remodeling in skeletal muscle and promote myofiber-type transitions by activating the Ca2+-NFATC1 signaling pathway. This study is useful in exploring the potential of lactate as a nutritional supplement for skeletal muscle adaptation and contributing to a mechanistic understanding of the central role of lactate in exercise physiology.

Ergothioneine boosts mitochondrial respiration and exercise performance via direct activation of MPST

Ergothioneine (EGT) is a diet-derived, atypical amino acid that accumulates to high levels in human tissues. Reduced EGT levels have been linked to age-related disorders, including neurodegenerative and cardiovascular diseases, while EGT supplementation is protective in a broad range of disease and aging models in mice. Despite these promising data, the direct and physiologically relevant molecular target of EGT has remained elusive. Here we use a systematic approach to identify how mitochondria remodel their metabolome in response to exercise training. From this data, we find that EGT accumulates in muscle mitochondria upon exercise training. Proteome-wide thermal stability studies identify 3-mercaptopyruvate sulfurtransferase (MPST) as a direct molecular target of EGT; EGT binds to and activates MPST, thereby boosting mitochondrial respiration and exercise training performance in mice. Together, these data identify the first physiologically relevant EGT target and establish the EGT-MPST axis as a molecular mechanism for regulating mitochondrial function and exercise performance.

Transcriptome analysis of Kluyveromyces marxianus under succinic acid stress and development of robust strains

Kluyveromyces marxianus has become an attractive non-conventional yeast cell factory due to its advantageous properties such as high thermal tolerance and rapid growth. Succinic acid (SA) is an important platform molecule that has been applied in various industries such as food, material, cosmetics, and pharmaceuticals. SA bioproduction may be compromised by its toxicity. Besides, metabolite-responsive promoters are known to be important for dynamic control of gene transcription. Therefore, studies on global gene transcription under various SA concentrations are of great importance. Here, comparative transcriptome changes of K. marxianus exposed to various concentrations of SA were analyzed. Enrichment and analysis of gene clusters revealed repression of the tricarboxylic acid cycle and glyoxylate cycle, also activation of the glycolysis pathway and genes related to ergosterol synthesis. Based on the analyses, potential SA-responsive promoters were investigated, among which the promoter strength of IMTCP2 and KLMA_50231 increased 43.4% and 154.7% in response to 15 g/L SA. In addition, overexpression of the transcription factors Gcr1, Upc2, and Ndt80 significantly increased growth under SA stress. Our results benefit understanding SA toxicity mechanisms and the development of robust yeast for organic acid production. KEY POINTS: • Global gene transcription of K. marxianus is changed by succinic acid (SA) • Promoter activities of IMTCP2 and KLMA_50123 are regulated by SA • Overexpression of Gcr1, Upc2, and Ndt80 enhanced SA tolerance.

Exercise increases TCA intermediate concentrations during low-calorie diet independent of insulin resistance among women with obesity

Tricarboxylic acid cycle intermediates (TCAi) have been proposed to act as myokines that influence energy metabolism. We determined if 2-weeks of low-calorie diet with interval exercise (LCD + INT) would increase TCAi more than a low-calorie diet (LCD). Twenty-three women were randomized to 2-weeks of LCD (n = 12, 48.4 ± 2.5 years, 37.8 ± 1.5 kg/m2, ~1200 kcal/d) or LCD + INT (n = 11, 47.6 ± 4.3 years, 37.9 ± 2.3 kg/m2; 60 min/d supervised INT of 3 min 90% & 50% HRpeak). TCAi and amino acids (AA) were measured at 0 min of a 75 g OGTT, while glucose, insulin, and FFA were obtained at 0, 30, 60, 90, 120, and 180 min to assess total area under the curve (tAUC180min) and insulin resistance (IR; tAUC180min of Glucose × Insulin). Fuel use (indirect calorimetry) was also collected at 0, 60, 120, and 180 min as was fitness (VO2peak) and body composition (BodPod). Treatments reduced weight (p < 0.001), fasting RER (p = 0.01), and IR (p = 0.03), although LCD + INT increased VO2peak (p = 0.02) and maintained RER tAUC180min (p = 0.05) versus LCD. Treatments increased FFA tAUC180min (p = 0.005), cis-aconitate, isocitrate, and succinate (p ≤ 0.02), as well as reduced phenylalanine and tryptophan, cysteine (p ≤ 0.005). However, LCD + INT increased malate, citrate, α-ketoglutarate, and alanine more than LCD (p ≤ 0.04). Thus, INT enhanced LCD effects on some TCAi in women with obesity independent of IR.

Bioinspired Supramolecular Hydrogel from Design to Applications

Nature offers a wealth of opportunities to solve scientific and technological issues based on its unique structures and function. The dynamic non-covalent interaction is considered to be the main base of living functions of creatures including humans, animals, and plants. Supramolecular hydrogels formed by non-covalent bonding interactions has become a unique platform for constructing promising materials for medicine, energy, electronic, and biological substitute. In this review, the self-assemble principle of supramolecular hydrogels is summarized. Next, the stimulation of external environment that triggers the assembly or disassembly of supramolecular hydrogels are recapitulated, including temperature, mechanics, light, pH, ions, etc. The main applications of bioinspired supramolecular hydrogels in terms of bionic objects including humans, animals, and plants are also described. Although so many efforts are done for revealing the synergized mechanism of the function and non-covalent interactions on the supramolecular hydrogel, the complexity and variability between stimulus and non-covalent bonding in the supramolecular system still require impeccable theories. As an outlook, the bioinspired supramolecular hydrogel is just beginning to exhibit its great potential in human life, offering significant opportunities in drug delivery and screening, implantable devices and substitutions, tissue engineering, micro-fluidic devices, and biosensors.

Metabolomic response to acute resistance exercise in healthy older adults by 1H-NMR

BACKGROUND

The favorable health-promoting adaptations to exercise result from cumulative responses to individual bouts of physical activity. Older adults often exhibit anabolic resistance; a phenomenon whereby the anabolic responses to exercise and nutrition are attenuated in skeletal muscle. The mechanisms contributing to age-related anabolic resistance are emerging, but our understanding of how chronological age influences responsiveness to exercise is incomplete. The objective was to determine the effects of healthy aging on peripheral blood metabolomic response to a single bout of resistance exercise and whether any metabolites in circulation are predictive of anabolic response in skeletal muscle.

METHODS

Thirty young (20-35 years) and 49 older (65-85 years) men and women were studied in a cross-sectional manner. Participants completed a single bout of resistance exercise consisting of eight sets of 10 repetitions of unilateral knee extension at 70% of one-repetition maximum. Blood samples were collected before exercise, immediately post exercise, and 30-, 90-, and 180-minutes into recovery. Proton nuclear magnetic resonance spectroscopy was used to profile circulating metabolites at all timepoints. Serial muscle biopsies were collected for measuring muscle protein synthesis rates.

RESULTS

Our analysis revealed that one bout of resistance exercise elicits significant changes in 26 of 33 measured plasma metabolites, reflecting alterations in several biological processes. Furthermore, 12 metabolites demonstrated significant interactions between exercise and age, including organic acids, amino acids, ketones, and keto-acids, which exhibited distinct responses to exercise in young and older adults. Pre-exercise histidine and sarcosine were negatively associated with muscle protein synthesis, as was the pre/post-exercise fold change in plasma histidine.

CONCLUSIONS

This study demonstrates that while many exercise-responsive metabolites change similarly in young and older adults, several demonstrate age-dependent changes even in the absence of evidence of sarcopenia or frailty.

TRIAL REGISTRATION

Clinical trial registry: ClinicalTrials.gov NCT03350906.

Effects of Succinate on Growth Performance, Meat Quality and Lipid Synthesis in Bama Miniature Pigs

Succinate, one of the intermediates of the tricarboxylic acid cycle, is now recognized to play a role in a broad range of physiological and pathophysiological settings, but its role in adipogenesis is unclear. Our study used Bama miniature pigs as a model to explore the effects of succinate on performance, meat quality, and fat formation. The results showed that adding 1% succinate significantly increased the average daily gain, feed/gain ratio, eye muscle area, and body fat content (p < 0.05), but had no effect on feed intake. Further meat quality analysis showed that succinate increased the marbling score and intramuscular fat content of longissimus dorsi muscle (LM), while decreasing the shear force and the cross-sectional area of LM (p < 0.05). Metabolomics analysis of LM revealed that succinate reshaped levels of fatty acids, triglycerides, glycerophospholipids, and sphingolipids in LM. Succinate promotes adipogenic differentiation in porcine primary preadipocytes. Finally, dietary succinate supplementation increased succinylation modification rather than acetylation modification in the adipose tissue pool. This study elucidated the effects of succinate on the growth and meat quality of pigs and its mechanism of action and provided a reference for the role of succinate in the nutrition and metabolism of pigs.

Targeting Mitochondria for Cancer Treatment

There is an increasing accumulation of data on the exceptional importance of mitochondria in the occurrence and treatment of cancer, and in all lines of evidence for such participation, there are both energetic and non-bioenergetic functional features of mitochondria. This analytical review examines three specific features of adaptive mitochondrial changes in several malignant tumors. The first feature is characteristic of solid tumors, whose cells are forced to rebuild their energetics due to the absence of oxygen, namely, to activate the fumarate reductase pathway instead of the traditional succinate oxidase pathway that exists in aerobic conditions. For such a restructuring, the presence of a low-potential quinone is necessary, which cannot ensure the conventional conversion of succinate into fumarate but rather enables the reverse reaction, that is, the conversion of fumarate into succinate. In this scenario, complex I becomes the only generator of energy in mitochondria. The second feature is the increased proliferation in aggressive tumors of the so-called mitochondrial (peripheral) benzodiazepine receptor, also called translocator protein (TSPO) residing in the outer mitochondrial membrane, the function of which in oncogenic transformation stays mysterious. The third feature of tumor cells is the enhanced retention of certain molecules, in particular mitochondrially directed cations similar to rhodamine 123, which allows for the selective accumulation of anticancer drugs in mitochondria. These three features of mitochondria can be targets for the development of an anti-cancer strategy.

Carnosine regulation of intracellular pH homeostasis promotes lysosome-dependent tumor immunoevasion

Tumor cells and surrounding immune cells undergo metabolic reprogramming, leading to an acidic tumor microenvironment. However, it is unclear how tumor cells adapt to this acidic stress during tumor progression. Here we show that carnosine, a mobile buffering metabolite that accumulates under hypoxia in tumor cells, regulates intracellular pH homeostasis and drives lysosome-dependent tumor immune evasion. A previously unrecognized isoform of carnosine synthase, CARNS2, promotes carnosine synthesis under hypoxia. Carnosine maintains intracellular pH (pHi) homeostasis by functioning as a mobile proton carrier to accelerate cytosolic H+ mobility and release, which in turn controls lysosomal subcellular distribution, acidification and activity. Furthermore, by maintaining lysosomal activity, carnosine facilitates nuclear transcription factor X-box binding 1 (NFX1) degradation, triggering galectin-9 and T-cell-mediated immune escape and tumorigenesis. These findings indicate an unconventional mechanism for pHi regulation in cancer cells and demonstrate how lysosome contributes to immune evasion, thus providing a basis for development of combined therapeutic strategies against hepatocellular carcinoma that exploit disrupted pHi homeostasis with immune checkpoint blockade.

Monocarboxylate transporters facilitate succinate uptake into brown adipocytes

Uptake of circulating succinate by brown adipose tissue (BAT) and beige fat elevates whole-body energy expenditure, counteracts obesity and antagonizes systemic tissue inflammation in mice. The plasma membrane transporters that facilitate succinate uptake in these adipocytes remain undefined. Here we elucidate a mechanism underlying succinate import into BAT via monocarboxylate transporters (MCTs). We show that succinate transport is strongly dependent on the proportion that is present in the monocarboxylate form. MCTs facilitate monocarboxylate succinate uptake, which is promoted by alkalinization of the cytosol driven by adrenoreceptor stimulation. In brown adipocytes, we show that MCT1 primarily facilitates succinate import. In male mice, we show that both acute pharmacological inhibition of MCT1 and congenital depletion of MCT1 decrease succinate uptake into BAT and consequent catabolism. In sum, we define a mechanism of succinate uptake in BAT that underlies its protective activity in mouse models of metabolic disease.

Oxidative stress and metabolism meet epigenetic modulation in physical exercise

Physical exercise is established as an important factor of health and generally is recommended for its positive effects on several tissues, organs, and systems. These positive effects come from metabolic adaptations that also include oxidative eustress, in which physical activity increases ROS production and antioxidant mechanisms, although this depends on the intensity of the exercise. Muscle metabolism through mechanisms such as aerobic and anaerobic glycolysis, tricarboxylic acid cycle, and oxidative lipid metabolism can produce metabolites and co-factors which directly impact the epigenetic machinery. In this review, we clearly reinforce the evidence that exercise regulates several epigenetic mechanisms and explain how these mechanisms can be regulated by metabolic products and co-factors produced during exercise. In fact, recent evidence has demonstrated the importance of epigenetics in the gene expression changes implicated in metabolic adaptation after exercise. Importantly, intermediates of the metabolism generated by continuous, acute, moderate, or strenuous exercise control the activity of epigenetic enzymes, therefore turning on or turning off the gene expression of specific programs which can lead to physiological adaptations after exercise.

Type 2 diabetes and succinate: unmasking an age-old molecule

Beyond their conventional roles in intracellular energy production, some traditional metabolites also function as extracellular messengers that activate cell-surface G-protein-coupled receptors (GPCRs) akin to hormones and neurotransmitters. These signalling metabolites, often derived from nutrients, the gut microbiota or the host's intermediary metabolism, are now acknowledged as key regulators of various metabolic and immune responses. This review delves into the multi-dimensional aspects of succinate, a dual metabolite with roots in both the mitochondria and microbiome. It also connects the dots between succinate's role in the Krebs cycle, mitochondrial respiration, and its double-edge function as a signalling transmitter within and outside the cell. We aim to provide an overview of the role of the succinate-succinate receptor 1 (SUCNR1) axis in diabetes, discussing the potential use of succinate as a biomarker and the novel prospect of targeting SUCNR1 to manage complications associated with diabetes. We further propose strategies to manipulate the succinate-SUCNR1 axis for better diabetes management; this includes pharmacological modulation of SUCNR1 and innovative approaches to manage succinate concentrations, such as succinate administration and indirect strategies, like microbiota modulation. The dual nature of succinate, both in terms of origins and roles, offers a rich landscape for understanding the intricate connections within metabolic diseases, like diabetes, and indicates promising pathways for developing new therapeutic strategies.

Mexidol, Cytoflavin, and succinic acid derivatives as antihypoxic, anti-ischemic metabolic modulators, and ergogenic aids in athletes and consideration of their potential as performance enhancing drugs

Emoxypine (ethylmethylhydroxypyridine) is a synthetic derivative of vitamin B6 . Emoxypine succinate is a registered drug in Russia and Ukraine under various trade names including Mexidol, Mexicor, and Armadin Long. Mexidol demonstrates antihypoxic and anti-ischemic effects and also modulates metabolism. The use of Mexidol by Russian athletes has been confirmed in the past. Current use by athletes is unknown as this drug is not monitored or included in drug testing protocol. Metabotropic and antihypoxic effects of Mexidol were compared to the effects of meldonium or trimetazidine, both of which are included on the World Anti-Doping Agency (WADA) Prohibited List in category S4.4. Metabolic Modulators. The conjugation of emoxypine with succinate elevates the therapeutic effectiveness of the Mexidol formulation as succinic acid itself has important impacts to consider despite being a common food additive and drug excipient. Other succinic acid salts like ammonium succinate, found as dietary supplement, have been patented as performance enhancers. Available research on healthy subjects suggests that combinations of selected 3-substituted pyridine derivatives with succinate including Mexidol and a related drug Cytoflavin can enhance the performance of athletes. Cytoflavin is a multi-component formula containing meglumine sodium succinate, nicotinamide (vitamin B3 ), inosine (riboxin), and riboflavin. Other related succinate-based drugs include Remaxol, Reamberin, and Cogitum. Mexidol and Cytoflavin and related substances exhibit similar biological effects as drugs on the WADA Prohibited List, and if they are used for performance enhancement by athletes, they could be worthy of consideration as prohibited substances in sport.

Size matters: the biochemical logic of ligand type in endocrine crosstalk

The endocrine system is a fundamental type of long-range cell-cell communication that is important for maintaining metabolism, physiology, and other aspects of organismal homeostasis. Endocrine signaling is mediated by diverse blood-borne ligands, also called hormones, including metabolites, lipids, steroids, peptides, and proteins. The size and structure of these hormones are fine-tuned to make them bioactive, responsive, and adaptable to meet the demands of changing environments. Why has nature selected such diverse ligand types to mediate communication in the endocrine system? What is the chemical, signaling, or physiologic logic of these ligands? What fundamental principles from our knowledge of endocrine communication can be applied as we continue as a field to uncover additional new circulating molecules that are claimed to mediate long-range cell and tissue crosstalk? This review provides a framework based on the biochemical logic behind this crosstalk with respect to their chemistry, temporal regulation in physiology, specificity, signaling actions, and evolutionary development.

Molecular Insights From Multiomics Studies of Physical Activity

Physical activity confers systemic health benefits and provides powerful protection against disease. There has been tremendous interest in understanding the molecular effectors of exercise that mediate these physiologic effects. The modern growth of multiomics technologies-including metabolomics, proteomics, phosphoproteomics, lipidomics, single-cell RNA sequencing, and epigenomics-has provided unparalleled opportunities to systematically investigate the molecular changes associated with physical activity on an organism-wide scale. Here, we discuss how multiomics technologies provide new insights into the systemic effects of physical activity, including the integrative responses across organs as well as the molecules and mechanisms mediating tissue communication during exercise. We also highlight critical unanswered questions that can now be addressed using these high-dimensional tools and provide perspectives on fertile future research directions.

Need for speed: Human fast-twitch mitochondria favor power over efficiency

OBJECTIVE

Human skeletal muscle consists of a mixture of slow- and fast-twitch fibers with distinct capacities for contraction mechanics, fermentation, and oxidative phosphorylation. While the divergence in mitochondrial volume favoring slow-twitch fibers is well established, data on the fiber type-specific intrinsic mitochondrial function and morphology are highly limited with existing data mainly being generated in animal models. This highlights the need for more human data on the topic.

METHODS

Here, we utilized THRIFTY, a rapid fiber type identification protocol to detect, sort, and pool fast- and slow-twitch fibers within 6 h of muscle biopsy sampling. Respiration of permeabilized fast- and slow-twitch fiber pools was then analyzed with high-resolution respirometry. Using standardized western blot procedures, muscle fiber pools were subsequently analyzed for control proteins and key proteins related to respiratory capacity.

RESULTS

Maximal complex I+II respiration was 25% higher in human slow-twitch fibers compared to fast-twitch fibers. However, per mitochondrial volume, the respiratory rate of mitochondria in fast-twitch fibers was approximately 50% higher for complex I+II, which was primarily mediated through elevated complex II respiration. Furthermore, the abundance of complex II protein and proteins regulating cristae structure were disproportionally elevated in mitochondria of the fast-twitch fibers. The difference in intrinsic respiratory rate was not reflected in fatty acid-or complex I respiration.

CONCLUSION

Mitochondria of human fast-twitch muscle fibers compensate for their lack of volume by substantially elevating intrinsic respiratory rate through increased reliance on complex II.

Huanglian Jiedu Wan intervened with "Shi-Re Shanghuo" syndrome through regulating immune balance mediated by biomarker succinate

With increasing stress in daily life and work, subhealth conditions induced by "Shi-Re Shanghuo" syndrome was gradually universal. "Huanglian Jiedu Wan" (HLJDW) was the first new syndrome Chinese medicine approved for the treatment of "Shi-Re Shanghuo" with promising clinical efficacy. Preliminary small-sample clinical studies have identified some notable biomarkers (succinate, 4-hydroxynonenal, etc.). However, the correlation and underlying mechanism between these biomarkers of HLJDW intervention on "Shi-Re Shanghuo" syndrome remained ambiguous. Therefore, this study was designed as a randomized, double-blind, multicenter, placebo-controlled Phase II clinical trial, employing integrated analysis techniques such as non-targeted and targeted metabolomics, salivary microbiota, proteomics, parallel peaction monitoring, molecular docking and surface plasmon resonance (SPR). The results of the correlation analysis indicated that HLJDW could mediate the balance between inflammation and immunity through succinate produced via host and microbial source to intervene "Shi-Re Shanghuo" syndrome. Further through the HIF1α/MMP9 pathway, succinate regulated downstream arachidonic acid metabolism, particularly the lipid peroxidation product 4-hydroxynonenal. Finally, an animal model of recurrent oral ulcers induced by "Shi-Re Shang Huo" was established and HLJDW was used for intervention, key essential indicators (succinate, glutamine, 4-hydroxynonenal, arachidonic acid metabolism) essential in the potential pathway HIF1α/MMP9 discovered in clinical practice were validated. The results were found to be consistent with our clinical findings. Taken together, succinate was observed as an important signal that triggered immune responses, which might serve as a key regulatory metabolic switch or marker of "Shi-Re Shanghuo" syndrome treated with HLJDW.

Physiological and molecular predictors of cycling sprint performance

The study aimed to identify novel muscle phenotypic factors that could determine sprint performance using linear regression models including the lean mass of the lower extremities (LLM), myosin heavy chain composition (MHC), and proteins and enzymes implicated in glycolytic and aerobic energy generation (citrate synthase, OXPHOS proteins), oxygen transport and diffusion (myoglobin), ROS sensing (Nrf2/Keap1), antioxidant enzymes, and proteins implicated in calcium handling. For this purpose, body composition (dual-energy X-ray absorptiometry) and sprint performance (isokinetic 30-s Wingate test: peak and mean power output, Wpeak and Wmean ) were measured in young physically active adults (51 males and 10 females), from which a resting muscle biopsy was obtained from the musculus vastus lateralis. Although females had a higher percentage of MHC I, SERCA2, pSer16 /Thr17 -phospholamban, and Calsequestrin 2 protein expressions (all p < 0.05), and 18.4% lower phosphofructokinase 1 protein expression than males (p < 0.05), both sexes had similar sprint performance when it was normalized to body weight or LLM. Multiple regression analysis showed that Wpeak could be predicted from LLM, SDHB, Keap1, and MHC II % (R 2  = 0.62, p < 0.001), each variable contributing to explain 46.4%, 6.3%, 4.4%, and 4.3% of the variance in Wpeak , respectively. LLM and MHC II % explained 67.5% and 2.1% of the variance in Wmean , respectively (R 2  = 0.70, p < 0.001). The present investigation shows that SDHB and Keap1, in addition to MHC II %, are relevant determinants of peak power output during sprinting.

Basic Mechanisms of Immunometabolites in Shaping the Immune Response

BACKGROUND

Innate immune cells play a crucial role in responding to microbial infections, but their improper activation can also drive inflammatory disease. For this reason, their activation state is governed by a multitude of factors, including the metabolic state of the cell and, more specifically, the individual metabolites which accumulate intracellularly and extracellularly. This relationship is bidirectional, as innate immune cell activation by pathogen-associated molecular patterns causes critical changes in cellular metabolism.

SUMMARY

In this review, we describe the emergence of various "immunometabolites." We outline the general characteristics of these immunometabolites, the conditions under which they accumulate, and their subsequent impact on immune cells. We delve into well-studied metabolites of recent years, such as succinate and itaconate, as well as newly emerging immunometabolites, such as methylglyoxal.

KEY MESSAGES

We hope that this review may be used as a framework for further studies dissecting the mechanisms by which immunometabolites regulate the immune system and provide an outlook to harnessing these mechanisms in the treatment of inflammatory diseases.

Health position paper and redox perspectives on reactive oxygen species as signals and targets of cardioprotection

The present review summarizes the beneficial and detrimental roles of reactive oxygen species in myocardial ischemia/reperfusion injury and cardioprotection. In the first part, the continued need for cardioprotection beyond that by rapid reperfusion of acute myocardial infarction is emphasized. Then, pathomechanisms of myocardial ischemia/reperfusion to the myocardium and the coronary circulation and the different modes of cell death in myocardial infarction are characterized. Different mechanical and pharmacological interventions to protect the ischemic/reperfused myocardium in elective percutaneous coronary interventions and coronary artery bypass grafting, in acute myocardial infarction and in cardiotoxicity from cancer therapy are detailed. The second part keeps the focus on ROS providing a comprehensive overview of molecular and cellular mechanisms involved in ischemia/reperfusion injury. Starting from mitochondria as the main sources and targets of ROS in ischemic/reperfused myocardium, a complex network of cellular and extracellular processes is discussed, including relationships with Ca2+ homeostasis, thiol group redox balance, hydrogen sulfide modulation, cross-talk with NAPDH oxidases, exosomes, cytokines and growth factors. While mechanistic insights are needed to improve our current therapeutic approaches, advancements in knowledge of ROS-mediated processes indicate that detrimental facets of oxidative stress are opposed by ROS requirement for physiological and protective reactions. This inevitable contrast is likely to underlie unsuccessful clinical trials and limits the development of novel cardioprotective interventions simply based upon ROS removal.

Acetate and succinate benefit host muscle energetics as exercise-associated post-biotics

Recently, the gut microbiome has emerged as a potent modulator of exercise-induced systemic adaptation and appears to be crucial for mediating some of the benefits of exercise. This study builds upon previous evidence establishing a gut microbiome-skeletal muscle axis, identifying exercise-induced changes in microbiome composition. Metagenomics sequencing of fecal samples from non-exercise-trained controls or exercise-trained mice was conducted. Biodiversity indices indicated exercise training did not change alpha diversity. However, there were notable differences in beta-diversity between trained and untrained microbiomes. Exercise significantly increased the level of the bacterial species Muribaculaceae bacterium DSM 103720. Computation simulation of bacterial growth was used to predict metabolites that accumulate under in silico culture of exercise-responsive bacteria. We identified acetate and succinate as potential gut microbial metabolites that are produced by Muribaculaceae bacterium, which were then administered to mice during a period of mechanical overload-induced muscle hypertrophy. Although no differences were observed for the overall muscle growth response to succinate or acetate administration during the first 5 days of mechanical overload-induced hypertrophy, acetate and succinate increased skeletal muscle mitochondrial respiration. When given as post-biotics, succinate or acetate treatment may improve oxidative metabolism during muscle hypertrophy.

Impact of Bmal1 Rescue and Time-Restricted Feeding on Liver and Muscle Proteomes During the Active Phase in Mice

Molecular clocks and daily feeding cycles support metabolism in peripheral tissues. Although the roles of local clocks and feeding are well defined at the transcriptional level, their impact on governing protein abundance in peripheral tissues is unclear. Here, we determine the relative contributions of local molecular clocks and daily feeding cycles on liver and muscle proteomes during the active phase in mice. LC-MS/MS was performed on liver and gastrocnemius muscle harvested 4 h into the dark phase from WT, Bmal1 KO, and dual liver- and muscle-Bmal1-rescued mice under either ad libitum feeding or time-restricted feeding during the dark phase. Feeding-fasting cycles had only minimal effects on levels of liver proteins and few, if any, on the muscle proteome. In contrast, Bmal1 KO altered the abundance of 674 proteins in liver and 80 proteins in muscle. Local rescue of liver and muscle Bmal1 restored ∼50% of proteins in liver and ∼25% in muscle. These included proteins involved in fatty acid oxidation in liver and carbohydrate metabolism in muscle. For liver, proteins involved in de novo lipogenesis were largely dependent on Bmal1 function in other tissues (i.e., the wider clock system). Proteins regulated by BMAL1 in liver and muscle were enriched for secreted proteins. We found that the abundance of fibroblast growth factor 1, a liver secreted protein, requires BMAL1 and that autocrine fibroblast growth factor 1 signaling modulates mitochondrial respiration in hepatocytes. In liver and muscle, BMAL1 is a more potent regulator of dark phase proteomes than daily feeding cycles, highlighting the need to assess protein levels in addition to mRNA when investigating clock mechanisms. The proteome is more extensively regulated by BMAL1 in liver than in muscle, and many metabolic pathways in peripheral tissues are reliant on the function of the clock system as a whole.

Exercise metabolism and adaptation in skeletal muscle

Viewing metabolism through the lens of exercise biology has proven an accessible and practical strategy to gain new insights into local and systemic metabolic regulation. Recent methodological developments have advanced understanding of the central role of skeletal muscle in many exercise-associated health benefits and have uncovered the molecular underpinnings driving adaptive responses to training regimens. In this Review, we provide a contemporary view of the metabolic flexibility and functional plasticity of skeletal muscle in response to exercise. First, we provide background on the macrostructure and ultrastructure of skeletal muscle fibres, highlighting the current understanding of sarcomeric networks and mitochondrial subpopulations. Next, we discuss acute exercise skeletal muscle metabolism and the signalling, transcriptional and epigenetic regulation of adaptations to exercise training. We address knowledge gaps throughout and propose future directions for the field. This Review contextualizes recent research of skeletal muscle exercise metabolism, framing further advances and translation into practice.

Exercise in cold: Friend than foe to cardiovascular health

Exercise has been proven to benefit human health comprehensively regardless of the intensity, time, or environment. Recent studies have found that combined exercise with a cold environment displays a synergistical beneficial effect on cardiovascular system compared to exercise in thermoneutral environment. Cold environment leads to an increase in body heat loss, and has been considered a notorious factor for cardiovascular system. Exercise in cold increases the stress of cardiovascular system and risks of cardiovascular diseases, but increases the body tolerance to detrimental insults and benefits cardiovascular health. The biological effects and its underlying mechanisms of exercise in cold are complex and not well studied. Evidence has shown that exercise in cold exerts more noticeable effects on sympathetic nervous activation, bioenergetics, anti-oxidative capacity, and immune response compared to exercise in thermoneutral environment. It also increases the secretion of a series of exerkines, including irisin and fibroblast growth factor 21, which may contribute to the cardiovascular benefits induced by exercise in cold. Further well-designed studies are needed to advance the biological effects of exercise in cold. Understanding the mechanisms underlying the benefits of exercise in cold will help prescribe cold exercise to those who can benefit from it.

Extensive profiling of histidine-containing dipeptides reveals species- and tissue-specific distribution and metabolism in mice, rats, and humans

AIM

Histidine-containing dipeptides (HCDs) are pleiotropic homeostatic molecules with potent antioxidative and carbonyl quenching properties linked to various inflammatory, metabolic, and neurological diseases, as well as exercise performance. However, the distribution and metabolism of HCDs across tissues and species are still unclear.

METHODS

Using a sensitive UHPLC-MS/MS approach and an optimized quantification method, we performed a systematic and extensive profiling of HCDs in the mouse, rat, and human body (in n = 26, n = 25, and n = 19 tissues, respectively).

RESULTS

Our data show that tissue HCD levels are uniquely produced by carnosine synthase (CARNS1), an enzyme that was preferentially expressed by fast-twitch skeletal muscle fibres and brain oligodendrocytes. Cardiac HCD levels are remarkably low compared to other excitable tissues. Carnosine is unstable in human plasma, but is preferentially transported within red blood cells in humans but not rodents. The low abundant carnosine analogue N-acetylcarnosine is the most stable plasma HCD, and is enriched in human skeletal muscles. Here, N-acetylcarnosine is continuously secreted into the circulation, which is further induced by acute exercise in a myokine-like fashion.

CONCLUSION

Collectively, we provide a novel basis to unravel tissue-specific, paracrine, and endocrine roles of HCDs in human health and disease.

Preventing mitochondrial reverse electron transport as a strategy for cardioprotection

In the context of myocardial infarction, the burst of superoxide generated by reverse electron transport (RET) at complex I in mitochondria is a crucial trigger for damage during ischaemia/reperfusion (I/R) injury. Here we outline the necessary conditions for superoxide production by RET at complex I and how it can occur during reperfusion. In addition, we explore various pathways that are implicated in generating the conditions for RET to occur and suggest potential therapeutic strategies to target RET, aiming to achieve cardioprotection.

The metabolic interplay between dietary carbohydrate and exercise and its role in acute appetite regulation in males: a randomized controlled study

An understanding of the metabolic determinants of postexercise appetite regulation would facilitate development of adjunctive therapeutics to suppress compensatory eating behaviours and improve the efficacy of exercise as a weight-loss treatment. Metabolic responses to acute exercise are, however, dependent on pre-exercise nutritional practices, including carbohydrate intake. We therefore aimed to determine the interactive effects of dietary carbohydrate and exercise on plasma hormonal and metabolite responses and explore mediators of exercise-induced changes in appetite regulation across nutritional states. In this randomized crossover study, participants completed four 120 min visits: (i) control (water) followed by rest; (ii) control followed by exercise (30 min at ∼75% of maximal oxygen uptake); (iii) carbohydrate (75 g maltodextrin) followed by rest; and (iv) carbohydrate followed by exercise. An ad libitum meal was provided at the end of each 120 min visit, with blood sample collection and appetite assessment performed at predefined intervals. We found that dietary carbohydrate and exercise exerted independent effects on the hormones glucagon-like peptide 1 (carbohydrate, 16.8 pmol/L; exercise, 7.4 pmol/L), ghrelin (carbohydrate, -48.8 pmol/L; exercise: -22.7 pmol/L) and glucagon (carbohydrate, 9.8 ng/L; exercise, 8.2 ng/L) that were linked to the generation of distinct plasma 1 H nuclear magnetic resonance metabolic phenotypes. These metabolic responses were associated with changes in appetite and energy intake, and plasma acetate and succinate were subsequently identified as potential novel mediators of exercise-induced appetite and energy intake responses. In summary, dietary carbohydrate and exercise independently influence gastrointestinal hormones associated with appetite regulation. Future work is warranted to probe the mechanistic importance of plasma acetate and succinate in postexercise appetite regulation. KEY POINTS: Carbohydrate and exercise independently influence key appetite-regulating hormones. Temporal changes in postexercise appetite are linked to acetate, lactate and peptide YY. Postexercise energy intake is associated with glucagon-like peptide 1 and succinate levels.

Metabolic Signatures of Performance in Elite World Tour Professional Male Cyclists

BACKGROUND AND OBJECTIVE

Metabolomics studies of recreational and elite athletes have been so far limited to venipuncture-dependent blood sample collection in the setting of controlled training and medical facilities. However, limited to no information is currently available to determine if findings in laboratory settings are translatable to a real-world scenario in elite competitions. The goal of this study was to define molecular signatures of exertion under controlled exercise conditions and use these signatures as a framework for assessing cycling performance in a World Tour competition.

METHODS

To characterize molecular profiles of exertion in elite athletes during cycling, we performed metabolomics analyses on blood isolated from 28 international-level, elite, World Tour professional male athletes from a Union Cycliste Internationale World Team taken before and after a graded exercise test to volitional exhaustion and before and after a long aerobic training session. Moreover, established signatures were then used to characterize the metabolic physiology of five of these cyclists who were selected to represent the same Union Cycliste Internationale World Team during a seven-stage elite World Tour race.

RESULTS

Using dried blood spot collection to circumvent logistical hurdles associated with field sampling, these studies defined metabolite signatures and fold change ranges of anaerobic or aerobic exertion in elite cyclists, respectively. Blood profiles of lactate, carboxylic acids, fatty acids, and acylcarnitines differed between exercise modes. The graded exercise test elicited significant two- to three-fold accumulations in lactate and succinate, in addition to significant elevations in free fatty acids and acylcarnitines. Conversely, the long aerobic training session elicited a larger magnitude of increase in fatty acids and acylcarnitines without appreciable increases in lactate or succinate. Comparable signatures were revealed after sprinting and climbing stages, respectively, in a World Tour race. In addition, signatures of elevated fatty acid oxidation capacity correlated with competitive performance.

CONCLUSIONS

Collectively, these studies provide a unique view of alterations in the blood metabolome of elite athletes during competition and at the peak of their performance capabilities. Furthermore, they demonstrate the utility of dried blood sampling for omics analysis, thereby enabling molecular monitoring of athletic performance in the field during training and competition.

Complex II Biology in Aging, Health, and Disease

Aging is associated with a decline in mitochondrial function which may contribute to age-related diseases such as neurodegeneration, cancer, and cardiovascular diseases. Recently, mitochondrial Complex II has emerged as an important player in the aging process. Mitochondrial Complex II converts succinate to fumarate and plays an essential role in both the tricarboxylic acid (TCA) cycle and the electron transport chain (ETC). The dysfunction of Complex II not only limits mitochondrial energy production; it may also promote oxidative stress, contributing, over time, to cellular damage, aging, and disease. Intriguingly, succinate, the substrate for Complex II which accumulates during mitochondrial dysfunction, has been shown to have widespread effects as a signaling molecule. Here, we review recent advances related to understanding the function of Complex II, succinate signaling, and their combined roles in aging and aging-related diseases.

Reverse-ChIP Techniques for Identifying Locus-Specific Proteomes: A Key Tool in Unlocking the Cancer Regulome

A phenotypic hallmark of cancer is aberrant transcriptional regulation. Transcriptional regulation is controlled by a complicated array of molecular factors, including the presence of transcription factors, the deposition of histone post-translational modifications, and long-range DNA interactions. Determining the molecular identity and function of these various factors is necessary to understand specific aspects of cancer biology and reveal potential therapeutic targets. Regulation of the genome by specific factors is typically studied using chromatin immunoprecipitation followed by sequencing (ChIP-Seq) that identifies genome-wide binding interactions through the use of factor-specific antibodies. A long-standing goal in many laboratories has been the development of a 'reverse-ChIP' approach to identify unknown binding partners at loci of interest. A variety of strategies have been employed to enable the selective biochemical purification of sequence-defined chromatin regions, including single-copy loci, and the subsequent analytical detection of associated proteins. This review covers mass spectrometry techniques that enable quantitative proteomics before providing a survey of approaches toward the development of strategies for the purification of sequence-specific chromatin as a 'reverse-ChIP' technique. A fully realized reverse-ChIP technique holds great potential for identifying cancer-specific targets and the development of personalized therapeutic regimens.

Organism-wide, cell-type-specific secretome mapping of exercise training in mice

There is a significant interest in identifying blood-borne factors that mediate tissue crosstalk and function as molecular effectors of physical activity. Although past studies have focused on an individual molecule or cell type, the organism-wide secretome response to physical activity has not been evaluated. Here, we use a cell-type-specific proteomic approach to generate a 21-cell-type, 10-tissue map of exercise training-regulated secretomes in mice. Our dataset identifies >200 exercise training-regulated cell-type-secreted protein pairs, the majority of which have not been previously reported. Pdgfra-cre-labeled secretomes were the most responsive to exercise training. Finally, we show anti-obesity, anti-diabetic, and exercise performance-enhancing activities for proteoforms of intracellular carboxylesterases whose secretion from the liver is induced by exercise training.

A critical role for heme synthesis and succinate in the regulation of pluripotent states transitions

Using embryonic stem cells (ESCs) in regenerative medicine or in disease modeling requires a complete understanding of these cells. Two main distinct developmental states of ESCs have been stabilized in vitro, a naïve pre-implantation stage and a primed post-implantation stage. Based on two recently published CRISPR-Cas9 knockout functional screens, we show here that the exit of the naïve state is impaired upon heme biosynthesis pathway blockade, linked in mESCs to the incapacity to activate MAPK- and TGFβ-dependent signaling pathways after succinate accumulation. In addition, heme synthesis inhibition promotes the acquisition of 2 cell-like cells in a heme-independent manner caused by a mitochondrial succinate accumulation and leakage out of the cell. We further demonstrate that extracellular succinate acts as a paracrine/autocrine signal, able to trigger the 2C-like reprogramming through the activation of its plasma membrane receptor, SUCNR1. Overall, this study unveils a new mechanism underlying the maintenance of pluripotency under the control of heme synthesis.

Extracellular Succinate: A Physiological Messenger and a Pathological Trigger

When tissues are under physiological stresses, such as vigorous exercise and cold exposure, skeletal muscle cells secrete succinate into the extracellular space for adaptation and survival. By contrast, environmental toxins and injurious agents induce cellular secretion of succinate to damage tissues, trigger inflammation, and induce tissue fibrosis. Extracellular succinate induces cellular changes and tissue adaptation or damage by ligating cell surface succinate receptor-1 (SUCNR-1) and activating downstream signaling pathways and transcriptional programs. Since SUCNR-1 mediates not only pathological processes but also physiological functions, targeting it for drug development is hampered by incomplete knowledge about the characteristics of its physiological vs. pathological actions. This review summarizes the current status of extracellular succinate in health and disease and discusses the underlying mechanisms and therapeutic implications.

Depletion of creatine phosphagen energetics with a covalent creatine kinase inhibitor

Creatine kinases (CKs) provide local ATP production in periods of elevated energetic demand, such as during rapid anabolism and growth. Thus, creatine energetics has emerged as a major metabolic liability in many rapidly proliferating cancers. Whether CKs can be targeted therapeutically is unknown because no potent or selective CK inhibitors have been developed. Here we leverage an active site cysteine present in all CK isoforms to develop a selective covalent inhibitor of creatine phosphagen energetics, CKi. Using deep chemoproteomics, we discover that CKi selectively engages the active site cysteine of CKs in cells. A co-crystal structure of CKi with creatine kinase B indicates active site inhibition that prevents bidirectional phosphotransfer. In cells, CKi and its analogs rapidly and selectively deplete creatine phosphate, and drive toxicity selectively in CK-dependent acute myeloid leukemia. Finally, we use CKi to uncover an essential role for CKs in the regulation of proinflammatory cytokine production in macrophages.