Metabolic Flexibility in Health and Disease

Is lean mass quantity or quality the determinant of maximal fat oxidation capacity? The potential mediating role of cardiorespiratory fitness

BACKGROUND

Impaired fat oxidation is linked to cardiometabolic risk. Maximal fat oxidation rate (MFO) reflects metabolic flexibility and is influenced by lean mass, muscle strength, muscle quality - defined as the ratio of strength to mass - and cardiorespiratory fitness. The relationship between these factors and fat oxidation is not fully understood. The aim is to analyze the associations of lean-mass, muscle strength and quality with fat oxidation parameters in young adults, considering the mediating role of VO2max.

METHODS

A cross-sectional observational study. Eighty-one adults (50 males, 31 females; age 22.8 ± 4.4, BMI 25.70 ± 5.75, lean-mass 54.19 ± 8.78, fat-mass 18.66 ± 11.32) Body composition assessment by bioimpedance determine fat and lean-mass. Indirect calorimetry at rest and exercise was used for the calculation of fat oxidation. An incremental exercise protocol in a cycle ergometer with two consecutive phases was performed. The first to determine MFO consisted of 3 min steps of 15W increments with a cadence of 60rpm. The test was stopped when RQ ≥ 1. After 5 min rest, a phase to detect VO2max began with steps of 15W/min until exhaustion. Muscular strength was assessed by handgrip dynamometry and the standing longitudinal jump test. A strength cluster was calculated with handgrip and long jump adjusted by sex and age. Data were analyzed using multiple linear regression and mediation analyses.

RESULTS

Total lean-mass and leg lean-mass were not associated with MFO. Long jump, relativized by lean-mass and by leg lean-mass have a standardized indirect effect on MFO of 0.50, CI: 0.32-0.70, on MFO/lean-mass 0.43, CI:0.27-0.60 and MFO/leg lean-mass 0.44, CI: 0.30-0.06, which VO2max mediated, VO2max/lean-mass and VO2max/leg lean-mass, respectively (all p < 0.01). The handgrip/arm lean-mass had an indirect effect of 0.25 (CI: 0.12-0.38) on MFO/leg lean-mass, with VO2max/leg lean-mass as the mediator (p < 0.01). The Cluster/lean-mass and Cluster/Extremities lean-mass have a standardized indirect effect on MFO/lean-mass (0.34, CI: 0.20-0.48) and MFO/leg lean-mass (0.44, CI: 0.28-0.60), mediated by VO2max/lean-mass and VO2max/leg lean-mass (p < 0.01).

CONCLUSIONS

Muscular strength and quality have an indirect effect on MFO mediated by VO2max. These findings suggest the importance of muscle quality on MFO.

The roles and functions of ergothioneine in metabolic diseases

The global prevalence of metabolic diseases is on the increase, and it has become a significant threat to the health and lives of individuals. Ergothioneine (EGT) is a natural betaine amino acid found in various foods, particularly mushrooms. EGT cannot be synthesized by mammals; it is absorbed into small intestinal epithelial cells by a cationic protein, the novel organic cation transporter 1 (OCTN1), and transported to certain organs including liver, spleen, kidney, lung, heart, eyes and brain. EGT has been reported to exhibit antioxidant, anti-inflammatory, anti-apoptotic, anti-aging, and metal-chelating effects. The unique chemical properties and biological functions of EGT position it as a promising candidate for the research and treatment of metabolic diseases. This review summarizes EGT's capacities, potential therapeutic effects on multiple metabolic diseases, and their specific mechanisms. Finally, we outline challenges for future research on EGT and aspire to establish it as a prospective therapeutic agent for metabolic diseases.

Glucose, glutamine, lactic acid and α‑ketoglutarate restore metabolic disturbances and atrophic changes in energy‑deprived muscle cells

Skeletal muscle atrophy is often triggered by catabolic conditions such as fasting, malnutrition and chronic diseases; however, the efficacy of nutritional supplementation in maintaining muscle mass and preventing muscle atrophy remains controversial. The present study aimed to compare the inhibitory effects of various nutritional substrates on starvation‑induced catabolic changes and muscle cell atrophy. C2C12 muscle cells were starved for up to 24 h in medium lacking serum and main nutrients (glucose, glutamine and pyruvate). To assess the effects of exogenous substrates, the cells were incubated in starvation medium and individually supplemented with each of the following nutrients: Glucose, amino acids, fatty acids, lactate or ketone bodies. The expression of each gene and protein was analyzed by reverse transcription‑quantitative PCR and western blotting, respectively. Mitochondrial activity was determined by MTT assay and cell morphology was observed by immunofluorescence staining. The results revealed that starvation for >3 h suppressed mitochondrial activity, and after 5 h of starvation, the expression levels of several metabolic genes were increased; however, the levels of most, with the exception of Scot and Cpt‑1b, were suppressed after 24 h. Protein degradation and a decrease in protein synthesis were observed after 5 h of starvation, followed by autophagy with morphological atrophy at 24 h. Supplementation with specific substrates, with the exception of leucine, such as glucose, glutamine, lactic acid or α‑ketoglutarate, attenuated the suppression of mitochondrial activity, and altered gene expression, protein degradation and myotube atrophy in starved myotubes. Furthermore, the decrease in intracellular ATP production after 24 h of starvation was reversed by restoring glycolysis in glucose‑treated cells, and via an increase in mitochondrial respiration in cells treated with glutamine, lactic acid or α‑ketoglutarate. In conclusion, increasing the availability of glucose, glutamine, lactic acid or α‑ketoglutarate may be beneficial for countering muscle atrophy associated with inadequate nutrient intake.

Elucidation of Mechanism of Action in Drug Invention: Using Stable Isotope Tracers to Unravel Biochemical Kinetics

The invention of a therapeutic begins by characterizing features that differentiate healthy versus diseased states; this often presents as changes in the concentration of an analyte. Examples include elevated blood glucose in diabetes, high cholesterol in heart disease, and protein aggregation in neurodegeneration. Analyte concentrations reflect the (im)balance of synthetic and degradation rates; as such, aberrant biochemical kinetics drive the changes in endpoint concentration that define disease biology. Therapeutics aim to reset the concentration of a disease marker via modulation of biochemical kinetics. This is easy to understand for drugs directly targeting an enzyme in a pathway but, although less obvious, this can also be at the core of protein: protein interactions. For instance, stimulation of the insulin receptor changes the flux of several biochemical substrates (across multiple tissues); similarly, modulation of proprotein convertase subtilisin/kexin type 9-low density lipoprotein (PCSK9-LDL) receptor interactions alters cholesterol trafficking. These classic examples underscore the importance of studying biochemical kinetics at a clinical level. Here, we discuss how kinetic studies link disease biology with mechanism of action elucidation and screening. This has an immediate impact on (i) enabling in vitro-in vivo correlations in early discovery, (ii) enhancing exposure-response models aiding in human dose prediction, and (iii) providing support for biomarker plans, including clinical diagnostics. Mechanism of action studies can also influence modality selection; e.g., knowledge regarding target kinetics is needed when making decisions surrounding the development of a reversible inhibitor vs. an irreversible covalent modifier, or an intervention that affects target levels such as those which enhance protein degradation or reduce protein synthesis.

Microenvironmental determinants of endothelial cell heterogeneity

During development, endothelial cells (ECs) undergo an extraordinary specialization by which generic capillary microcirculatory networks spanning from arteries to veins transform into patterned organotypic zonated blood vessels. These capillary ECs become specialized to support the cellular and metabolic demands of each specific organ, including supplying tissue-specific angiocrine factors that orchestrate organ development, maintenance of organ-specific functions and regeneration of injured adult organs. Here, we illustrate the mechanisms by which microenvironmental signals emanating from non-vascular niche cells induce generic ECs to acquire specific inter-organ and intra-organ functional attributes. We describe how perivascular, parenchymal and immune cells dictate vascular heterogeneity and capillary zonation, and how this system is maintained through tissue-specific signalling activated by vasculogenic and angiogenic factors and deposition of matrix components. We also discuss how perturbation of organotypic vascular niche cues lead to erasure of EC signatures, contributing to the pathogenesis of disease processes. We also describe approaches that use reconstitution of tissue-specific signatures of ECs to promote regeneration of damaged organs.

Targeting intramyocellular lipids to improve aging muscle function

Decline of skeletal muscle function in old age is a significant contributor to reduced quality of life, risk of injury, comorbidity and disability and even mortality. While this loss of muscle function has traditionally been attributed to sarcopenia (loss of muscle mass), it is now generally appreciated that factors other than mass play a significant role in age-related muscle weakness. One such factor gaining increased attention is the ectopic accumulation of lipids in skeletal muscle, in particular, intramyocellular lipids (IMCLs). It has been appreciated for some time that metabolic flexibility of several tissues/organs declines with age and may be related to accumulation of IMCLs in a "vicious cycle" whereby blunted metabolic flexibility promotes accumulation of IMCLs, which leases to lipotoxicity, which can then further impair metabolic flexibility. The standard interventions for addressing lipid accumulation and muscle weakness remain diet (caloric restriction) and exercise. However, long-term compliance with both interventions in older adults is low, and in the case of caloric restriction, may be inappropriate for many older adults. Accordingly, it is important, from a public health standpoint, to pursue potential pharmacological strategies for improving muscle function. Because of the success of incretin-analog drugs in addressing obesity, these medications may potentially reduce IMCLs in aging muscles and thus improve metabolic flexibility and improve muscle health. A contrasting potential pharmacological strategy for addressing these issues might be to enhance energy provision to stimulate metabolism by increasing NAD + availability, which is known to decline with age and has been linked to reduced metabolic flexibility. In this narrative review, we present information related to IMCL accumulation and metabolic flexibility in old age and how the two major lifestyle interventions, caloric restriction and exercise, can affect these factors. Finally, we discuss the potential benefits and risks of select pharmacologic interventions in older adults.

Tirzepatide did not impact metabolic adaptation in people with obesity, but increased fat oxidation

Tirzepatide, a glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 receptor agonist, promoted significant body weight reduction in the phase 3 clinical trials. We conducted a preclinical study and a phase 1 clinical trial (NCT04081337) to understand potential mechanisms mediating tirzepatide-induced weight loss in mice and people with obesity. In calorie-restricted, obese mice, chronic treatment with tirzepatide reduced the drop in energy expenditure that occurred in vehicle-treated and pair-fed mice, indicating that tirzepatide attenuated metabolic adaptation. Respiratory exchange ratio also decreased in tirzepatide-treated mice, indicating increased fat oxidation. In the clinical trial, tirzepatide appeared to have no impact on metabolic adaptation but led to increased fat oxidation and reductions in appetite and calorie intake during an ad libitum test meal (vs. placebo). This is the first study to provide insights into the mechanisms of action of tirzepatide on weight loss with respect to calorie intake, energy expenditure, and macronutrient utilization.

Investigating the role of adipose tissue in mobility and aging: design and methods of the Adipose Tissue ancillary to the Study of Muscle, Mobility, and Aging (SOMMA-AT)

BACKGROUND

Age-related changes in adipose tissue affect chronic medical diseases and mobility disability but mechanism remains poorly understood. The goal of this study is to define methods for phenotyping unique characteristics of adipose tissue from older adults.

METHODS

Older adults enrolled in study of muscle, mobility, and aging selected for the adipose tissue ancillary (SOMMA-AT; N = 210, 52.38% women, 76.12 ± 4.37 years) were assessed for regional adiposity by whole-body magnetic resonance (AMRA) and underwent a needle-aspiration biopsy of abdominal subcutaneous adipose tissue (ASAT). ASAT biopsies were flash frozen, fixed, or processed for downstream applications and deposited at the biorepository. Biopsy yields, qualitative features, adipocyte sizes, and concentration of adipokines secreted in ASAT explant conditioned media were measured. Inter-measure Spearman correlations were determined.

RESULTS

Regional, but not total, adiposity differed by sex: women had greater ASAT mass (8.20 ± 2.73 kg, p < .001) and biopsy yield (3.44 ± 1.81 g, p < .001) than men (ASAT = 5.95 ± 2.30 kg, biopsy = 2.30 ± 1.40 g). ASAT mass correlated with leptin (r = 0.54, p < .001) and not resistin (p = .248) and adiponectin (p = .353). Adipocyte area correlated with ASAT mass (r = 0.34, p < .001), BMI (r = 0.33, p < .001), adiponectin (r = -0.22, p = .005) and leptin (r = 0.18, p = .024) but not with resistin (p = .490).

CONCLUSION

In addition to the detailed ASAT biopsy processing in this report, we found that adipocyte area correlated with ASAT mass, and both measures related to some key adipokines in the explant conditioned media. These results, methods, and biological repositories underscore the potential of this unique cohort to impact the understanding of aging adipose biology on disease, disability, and other aging tissues.

Are Individuals With Type 2 Diabetes Metabolically Inflexible? A Systematic Review and Meta-Analysis

AIM

Type 2 diabetes (T2D) is characterised by insulin resistance and possibly by impaired metabolic flexibility, the latter referring to the body's ability to switch between fuel sources. This review systematically examines metabolic flexibility, measured by changes in the respiratory exchange ratio (ΔRER) during hyperinsulinaemic clamps, across lean, overweight/obese, and T2D populations.

METHODS

A comprehensive search of PubMed identified 65 studies meeting the inclusion criteria, with 35 using a ~40 mU/m2/min insulin infusion rate for accurate comparisons. These studies included 985 participants: 256 lean, 497 overweight/obese, and 232 T2D individuals. The differences in ΔRER between the three groups were meta-analysed.

RESULTS

Basal RER values did not significantly differ across groups, but insulin-stimulated ΔRER was higher in lean individuals compared to overweight/obese and T2D groups (ΔRER values 0.10, 0.07 and 0.07, respectively; p = 0.037) indicating greater metabolic flexibility in the lean group. However, high statistical heterogeneity in the ΔRER within-group results (I2 values: 92.3%-94.5%) suggests considerable variability among studies. A meta-regression analysis accounting for age, sex, and BMI indicated that only BMI was significantly associated with ΔRER. Factors contributing to the remaining heterogeneity likely include differences in participant characteristics (e.g., glycaemic control) and study design.

CONCLUSIONS

The review highlights the need for standardised data presentation in metabolic studies. Overall, metabolic flexibility appears more influenced by overweight status than T2D per se, challenging the notion of a distinct metabolic inflexibility threshold for T2D.

Optimized RNA sequencing deconvolution illustrates the impact of obesity and weight loss on cell composition of human adipose tissue

OBJECTIVE

Cellular heterogeneity of human adipose tissue is linked to the pathophysiology of obesity and may impact the response to energy restriction and changes in fat mass. Herein, we provide an optimized pipeline to estimate cellular composition in human abdominal subcutaneous adipose tissue (ASAT) bulk RNA sequencing (RNA-seq) datasets using a single-nuclei RNA-seq signature matrix.

METHODS

A deconvolution pipeline for ASAT was optimized by benchmarking publicly available algorithms using a signature matrix derived from ASAT single-nuclei RNA-seq data from 20 adults and then applied to estimate ASAT cell-type proportions in publicly available obesity and weight loss studies.

RESULTS

Individuals with obesity had greater proportions of macrophages and lower proportions of adipocyte subpopulations and vascular cells compared with lean individuals. Two months of diet-induced weight loss increased the estimated proportions of macrophages; however, 2 years of diet-induced weight loss reduced the estimated proportions of macrophages, thereby suggesting a biphasic nature of cellular remodeling of ASAT during weight loss.

CONCLUSIONS

Our optimized high-throughput pipeline facilitates the assessment of composition changes of highly characterized cell types in large numbers of ASAT samples using low-cost bulk RNA-seq. Our data reveal novel changes in cellular heterogeneity and its association with cardiometabolic health in humans with obesity and following weight loss.

Predicting Glycemic Control in Patients With Impaired Fasting Glucose With Fasting Respiratory Exchange Ratio

Context

Impaired metabolic flexibility is associated with prediabetes. However, its assessment with reference methods is impractical in routine clinical practice.

Objective

This study investigates the relationship between fasting respiratory exchange ratio (RER), measured through indirect calorimetry, and glucose metabolism in individuals with prediabetes.

Methods

The study involved 2 cohorts: (1) a cross-sectional cohort of 10 176 individuals to assess the association between fasting RER and glucose metabolism parameters, and (2) a matched longitudinal cohort of 86 patients with impaired fasting glucose, categorized into fat oxidation (RER < 0.775) and glucose oxidation (RER > 0.925) groups, to evaluate the impact of fasting RER on impaired fasting glucose resolution and fasting glucose after a 1-year lifestyle intervention.

Results

In the cross-sectional cohort, a higher fasting RER was associated with higher fasting glucose, insulin, and Homeostatic Model Assessment for Insulin Resistance. In the longitudinal cohort, the fat oxidation group showed a greater reduction in fasting glucose (+5.9; 95% CI 1.4, 10; P = .011) and a higher probability of achieving normal fasting glycemia (log(odds ratio) -0.89; 95% CI -1.8, -0.03; P = .046) after the intervention, despite similar weight loss between groups.

Conclusion

Our findings suggest that fasting RER, a readily accessible clinical measure, can provide valuable insights into glucose metabolism and impaired fasting glucose resolution. A lower fasting RER, indicative of a greater capacity for fat oxidation, is associated with improved glycemic control after a lifestyle intervention.

Tirzepatide reduces body weight by increasing fat utilization via the central nervous system-adipose tissue axis in male mice

AIMS

Tirzepatide, a dual glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptor agonist, demonstrates promise as a potent medication for obesity. However, the extent to which its weight-reducing effects go beyond suppressing appetite remains unclear. This study aimed to elucidate this by establishing a pair-fed control group, effectively eliminating the influence of reduced caloric intake.

MATERIALS AND METHODS

Mice fed on a chow diet or a high-fat diet received single or long-term intracerebroventricular (i.c.v.) injections of tirzepatide or vehicle. The vehicle-treated mice were pair-fed to the tirzepatide-treated group to avoid the impact induced by different caloric intakes. Body weight and food intake were monitored daily. Respiratory exchange ratio (RER) was determined in metabolic cages. Fat utilization was calculated based on RER. Parameters of lipid metabolism were evaluated.

RESULTS

Mice receiving i.c.v. administration of tirzepatide exhibited significant reductions in body weight and fat content compared with pair-fed controls. These effects were mediated by increased lipolytic capacity in white adipose tissue and enhanced thermogenesis in brown and beige adipose tissues, leading to decreased RER and increased lipid utilization. Mechanistic investigations revealed that these effects were primarily mediated by sympathetic nervous system innervation of adipose tissues. This innervation, in turn, might be associated with the neuronal activity changes in the dorsomedial hypothalamus and the nucleus of the solitary tract within the hindbrain.

CONCLUSIONS

These findings establish a critical role for tirzepatide in shifting the substrate preference to fat utilization through the central nervous system-adipose tissue axis, promoting weight loss independent of food intake.

Six weeks of time-restricted eating improves basal fat oxidation and body composition but not fat oxidation during exercise in young males

BACKGROUND & AIMS

Time-restricted eating (TRE) is a type of intermittent fasting, requiring individuals to limit their eating timeframe to specific hours in the day, while maintaining a fasting period greater than 12 h. Fat oxidation (FOx) is a critical determinant in the pathophysiology of metabolic diseases, with impaired FOx contributing to conditions such as insulin resistance and obesity, whereas enhanced FOx is associated with improved metabolic health. However, the impact of the 16:8 TRE model on FOx remains largely unexplored. The aim of this study was to determine the effect of a 6-week TRE on resting and exercise substrate oxidation, body composition, and blood markers related to metabolic health.

METHODS

Thirty-three healthy, young males (age: 27.5 ± 6 years, body mass: 76.5 ± 8.4 kg, maximal oxygen uptake [V˙O2max]: 43.9 ± 6.6 mL·kg-1·min-1) were assigned to either TRE (n = 16) or control group (n = 17), with efforts to match baseline characteristics, including V˙O2max and body composition. The TRE group followed a 16:8 program for 6 weeks, while controls maintained their existing dietary habits. Body composition, blood glucose, insulin, blood lipids, resting substrate oxidation, and FOx during cycling at 40 % V˙O2max were assessed before and after the 6-week period. Data were analyzed using both intention-to-treat (ITT) and per-protocol approaches.

RESULTS

Thirty-three participants were included in the ITT analysis, while 31 participants were included in the per-protocol analysis. Compared to baseline, results showed a significant difference (p < 0.05) between TRE and control groups in body mass (TRE versus control) (Δ = -2.8 kg versus Δ = 0.7 kg), fat mass (Δ = -1.4 kg versus Δ = 0.4 kg), percent body fat (-1.7 % versus 0.4 %), lean mass (Δ = -1.4 kg versus Δ = 0.3 kg), and visceral adipose tissue mass (Δ = -39.7 g versus Δ = 46.4 g). There was a significant difference between TRE and control groups in resting respiratory exchange ratio (RER, Δ = -0.02 versus Δ = 0.02; p = 0.016), FOx (Δ = 0.33 mg·kg FFM-1·min-1versus Δ = -0.37 mg·kg FFM-1·min-1; p = 0.007), and carbohydrate oxidation (Δ = -0.39 mg·kg FFM-1·min-1versus Δ = 0.45 mg·kg FFM-1·min-1; p = 0.037) after the 6-week period. Exercise substrate oxidation and fasting blood glucose, insulin, triglycerides, total cholesterol, and high-density lipoprotein cholesterol did not significantly change over time in either group (p > 0.05).

CONCLUSIONS

In summary, a 6-week TRE significantly reduces body mass, fat mass, and resting RER as well as increases resting FOx in young, healthy males. However, it does not affect blood markers related to cardiometabolic health or exercise substrate oxidation. This trial was registered at https://clinicaltrials.gov/study/NCT06498102asNCT06498102.

Chlorogenic Acid Improves High-Fat Diet-Induced Skeletal Muscle Metabolic Disorders by Regulating Mitochondrial Function and Lactate Metabolism

Mitochondria are pivotal in sustaining skeletal muscle and the systemic metabolic balance. Chlorogenic acid (CA) is a common dietary antioxidant known for its ability to modulate metabolic homeostasis. This study aimed to investigate the impact of CA on high-fat diet (HFD)-induced mitochondrial dysfunction and metabolic disorder in skeletal muscle. C57BL/6J mice fed with a HFD were treated with CA for 12 weeks. The study assessed the overall glycolipid metabolic status, exercise performance, muscle fiber type, and antioxidant capacity of skeletal muscle in HFD-fed mice treated with CA. Results showed that CA reduced fat accumulation, improved exercise capacity, and enhanced mitochondrial performance in HFD-fed mice. Untargeted metabolomics analysis revealed that lactate metabolism and mitochondrial fatty acid oxidation (FAO) responded positively to CA intervention. Molecular mechanisms demonstrated that CA intervention improved mitochondrial biogenesis and function, promoting FAO and oxidative phosphorylation in mitochondria and ultimately reducing fat deposition in skeletal muscle induced by HFD feeding. Mechanistically, CA decreased HFD-induced lactate production and protein lactylation in skeletal muscle, highlighting the importance of the LDHA-lactate axis in mitochondrial function improvement by CA. Therefore, this study provides additional insights supporting the potential of CA as a natural dietary supplement for metabolic syndrome and associated disorders.

Anthropometric Trajectories and Dietary Compliance During a Personalized Ketogenic Program

BACKGROUND/OBJECTIVES

Ketogenic diets (KDs) have gained attention for their potential to promote weight loss and metabolic improvements. However, data on long-term body composition changes and adherence rates in real-world settings remain limited.

OBJECTIVE

This study aimed to assess the effects of a personalized ketogenic dietary program on anthropometric parameters over a 9-month period and to evaluate adherence across time.

METHODS

A total of 491 adults participated in a longitudinal intervention involving a structured ketogenic nutrition plan with follow-up at 3, 6, and 9 months. Body weight, fat mass (FM), skeletal muscle mass (SMM), and other composition metrics were measured at each visit.

RESULTS

Significant reductions in body weight (-12.6 kg) and fat mass (-10.3 kg) were observed after 3 months (p < 0.001), with minimal changes at 6 months and partial regain by Month 9. SMM remained relatively stable throughout the study. Retention dropped substantially after 3 months, dropping from 487 to 115 participants at Month 6 and 41 at Month 9. Despite this, participants who completed the program maintained significant anthropometric improvements.

CONCLUSIONS

A well-formulated ketogenic diet may promote rapid fat loss while preserving lean mass in the short term. However, long-term adherence poses significant challenges. Strategies to enhance dietary sustainability and retention are essential for maximizing the benefits of KDs in clinical practice.

Atypical gut microbial ecosystem from athletes with very high exercise capacity improves insulin sensitivity and muscle glycogen store in mice

Although the gut microbiota is known to act as a bridge between dietary nutrients and the body's energy needs, the interactions between the gut microbiota, host energy metabolism, and exercise capacity remain uncertain. Here, we characterized the gut microbiota ecosystem in a cohort of healthy normo-weight humans with highly heterogeneous aerobic exercise capacities and closely related body composition and food habits. While our data support the idea that the bacterial ecosystem appears to be modestly altered between individuals with low-to-high exercise capacities and close food habits, we report that gut bacterial α diversity, density, and functional richness are significantly reduced in athletes with very high exercise capacity. By using fecal microbiota transplantation, we report that the engraftment of gut microbiota from athletes with very high exercise capacity improves insulin sensitivity and muscle glycogen stores into transplanted mice, which highlights promising therapeutic perspectives in fecal transplantation from human donors selected based on exercise capacity traits.

Insulin resistance in type 2 diabetes mellitus

Insulin resistance is an integral pathophysiological feature of type 2 diabetes mellitus. Here, we review established and emerging cellular mechanisms of insulin resistance, their complex integrative features and their relevance to disease progression. While recognizing the heterogeneity of the elusive fundamental disruptions that cause insulin resistance, we endorse the view that effector mechanisms impinge on insulin receptor signalling and its relationship with plasma levels of insulin. We focus on hyperinsulinaemia and its consequences: acutely impaired but persistent insulin action, with reduced ability to lower glucose levels but preserved lipid synthesis and lipoprotein secretion. We emphasize the role of insulin sensitization as a therapeutic goal in type 2 diabetes mellitus.

Development of the MetFlex Index™: associations between cardiometabolic risk factors and fitness using a novel approach with blood lactate

Introduction

Cardiometabolic health is declining in the U.S. and anticipated to worsen over the next 30 years. Measurements of cardiometabolic health include blood metabolite profiles. One such metabolite is blood lactate. Lactate assessment is common in critical care and performance settings but less frequently used for the general population. The delayed onset of lactate accumulation during exercise may be an indicator of cardiometabolic health. Assessing lactate during a submaximal exercise test may assist in describing cardiometabolic health status in terms of metabolic fitness and metabolic flexibility.

Objectives

To introduce the MetFlex Index™ (MFI), a novel, scalable exercise-based and marker of cardiometabolic health, and to characterize its associations with routinely assessed cardiometabolic health risk factors.

Methods

Participants completed a submaximal test on a commercial stationary cycle following assessments of body composition, anthropometrics, vital signs, and a blood draw. Lactate was collected at each stage and the 1st and 2nd lactate thresholds were described. The MFI was calculated by using the power, in Watts, attained at the 1st lactate threshold relative to the participant's Body Mass Index (BMI).

Results

Data were collected on 827 participants (43 ± 13 years, 67% male, 72% overweight or obese). MFI peaked in the 30-39 year old cohort and decreased in subsequent decades. MFI was negatively associated with most markers of anthropometry, body composition, blood pressure, and was not associated with most blood metabolites.

Discussion

The MetFlex Index™ is a novel exercise-based approach using blood lactate to characterize skeletal muscle metabolism and is associated with several cardiometabolic health indices.

Loss of lysyl oxidase in adipose tissue ameliorates metabolic inflexibility induced by high-fat diet

OBJECTIVE

Systemic administration of β-aminopropionitrile to inhibit lysyl oxidase (Lox) activity improves metabolism, but it exhibits a broad spectrum of effects. Clarification of the role of Lox in adipose tissue metabolism under high-fat diet (HFD) conditions is needed.

METHODS

Mice with adipose tissue knockout of Lox (LoxAKO) and wild-type mice were subjected to a 16-week HFD regimen. A detailed evaluation encompassing adipose tissue, hepatic function, and systemic metabolism was conducted. RNA sequencing analysis was used to unravel the intricate mechanisms behind the metabolic enhancements in LoxAKO mice.

RESULTS

Compared with the control, although there was no difference in body weight, LoxAKO mice exhibited an improved metabolic phenotype, including enhanced insulin sensitivity, improved glucose tolerance, and reduced liver steatosis, along with reduced adipose tissue inflammation and fibrosis. LoxAKO mice showed increased thermogenic activity in brown adipose tissue with increased uncoupling protein 1 (UCP1) expression and oxygen consumption rate. Additionally, RNA sequencing analysis revealed that adipose deletion of Lox might facilitate the metabolic processing of glucose, branched-chain amino acids, and fatty acids in brown adipose tissue.

CONCLUSIONS

These findings indicate that adipocyte Lox deletion improves metabolic adaptability under an HFD, highlighting Lox as a promising therapeutic target for obesity-associated metabolic disorders.

Effects of 10 weeks of walking-based exercise training on resting substrate oxidation in postmenopausal women with obesity

BACKGROUND AND AIMS

Accumulating evidence supports the effectiveness of moderate-intensity aerobic training on metabolic health, with limited studies investigating change in resting substrate oxidation. The aim of this study was to explore whether 10 weeks of walking-based aerobic training would alter substrate oxidation in postmenopausal women with obesity.

METHODS AND RESULTS

Twenty-four postmenopausal women with obesity who were assigned into the control (n = 12) or exercise groups (n = 12) undertook a 10-week aerobic training program (3 d·week-1) that involved walking exercises at 50-70% of heart rate reserve on a treadmill, with exercise volume increased from 25 to 40 min·day-1. Resting metabolic rate (RMR) and body composition were measured pre- and post-training. Whole-body substrate oxidation was calculated using respiratory data collected during RMR measurement via indirect calorimetry. No significant change was noted (p > 0.05) in resting fat oxidation and carbohydrate oxidation in the exercise group. Resting respiratory exchange ratio and RMR did not alter in response to the training program (p > 0.05).

CONCLUSION

Our results show that a 10-week of moderate-intensity aerobic training does not modify substrate oxidation in postmenopausal women with obesity.

Nutritional Importance of a Liana Species for a Population of Bornean Orangutans

OBJECTIVES

Temporal variation in food availability can pose nutritional challenges to primates. Characterizing the nutritional content of the non-preferred foods that primates switch to, termed fallback foods, is useful for identifying the nutritional challenges of lean periods, the nutritional limits of what primates can subsist on, and physiological adaptations. We explored the temporal patterning and the nutritional contribution of food items for Bornean orangutans (Pongo pygmaeus wurmbii) at Tuanan, Indonesia, with particular attention to the liana, Bowringia callicarpa.

MATERIALS AND METHODS

We quantified the nutritional contribution of food items to the diet of wild orangutans over 18 years. We modeled the relationship between preferred food availability and the nutritional contribution of Bowringia.

RESULTS

Bowringia played an outsize role in the feeding time and nutritional intake of orangutans. It can be characterized as a fallback food because it is increasingly consumed when preferred tree fruits are less available. Its immature leaves are particularly important as the greatest source of protein and energy. However, the nonprotein energy-to-protein ratio of Bowringia is extremely low, and overreliance on it would bring orangutans away from their estimated nutritional intake target.

DISCUSSION

Despite its high energy and protein content, Bowringia is a nutritionally imbalanced food. Fallback food quality should thus be evaluated based on the ability to bring an animal toward its nutritional goal rather than nutrient density. We propose that orangutans are preadapted to falling back on protein-dense foods and the great abundance of Bowringia has contributed to the high population density of orangutans at Tuanan.

Validation of a novel approach to assess metabolic flexibility to a high-fat meal in a whole-body room calorimeter

OBJECTIVE

Metabolic inflexibility to Western high-fat diets may contribute to the obesity epidemic. However, validated methods for assessing metabolic flexibility (MetFlex) to high-fat meals are currently lacking. The purpose of this study was to evaluate the reliability of a novel approach for determining MetFlex to a high-fat meal and to compare it with the gold standard for measuring MetFlex to high-carbohydrate loads.

METHODS

Eight healthy adults were enrolled in our study, which consisted of the following two assessments of MetFlex: 1) MetFlex to fat, via two overnight stays in a metabolic chamber separated by 5 to 7 days; and 2) Metflex to carbohydrates, via a two-step hyperinsulinemic-euglycemic clamp measured >5 days later.

RESULTS

Participants were predominantly White and male, with mean (SD) age of 29.4 (6.3) years and BMI of 25.4 (4.1) kg/m2. MetFlex to fat displayed satisfactory test-retest reliability (intraclass correlation coefficient > 0.70) for several outcomes but showed no correlation to MetFlex measured during the clamp.

CONCLUSIONS

Overnight changes in substrate oxidation following a high-fat dinner meal represent a unique aspect of MetFlex that cannot be captured using more conventional methods. Our findings warrant prospective studies to determine whether these parameters are predictive of the development of obesity or metabolic dysfunction.

Using Metabolic Testing to Personalize Behavioral Obesity Treatment

Background

There are large individual differences in weight loss and maintenance. Metabolic testing can provide phenotypical information that can be used to personalize treatment so that people remain in negative energy balance during weight loss and remain in energy balance during maintenance. Behavioral testing can assess the reinforcing value and change in the temporal window related to the personalized diet and exercise program to motivate people to maintain engagement in healthier eating and activity programs.

Objective

Provide an expository overview of how metabolic testing can be used to personalize weight control. Ideas about incorporating behavioral economic concepts are also included.

Methods

A broad overview of how resting metabolic rate, thermic effect of food and respiratory quotient can be used to improve weight control. Also discussed are behavioral economic principles that can maximize adherence to diet and activity protocols.

Results

Research suggests that measuring metabolic rate can be used to set calorie goals for weight loss and maintenance, thermic effect of food to increase energy expenditure, and respiratory quotient to guide macronutrient composition of the diet and maximize fat loss. Developing programs that foster a strong motivation to eat healthier and be active can maximize treatment success.

Conclusion

Incorporating metabolic measures can personalize behavioral weight loss programs, and the use of behavioral economic principles can increase the probability of adherence and long-term success in weight control.

Metabolic Flexibility as a Candidate Mechanism for the Development of Postoperative Morbidity

BACKGROUND

This study investigates the role of metabolic flexibility in determining perioperative outcomes. Metabolic flexibility, a key feature of metabolic health, is the ability to efficiently switch between different fuel sources (predominantly carbohydrates and fats) depending on energy demands and availability. Given the rapidly changing physiological conditions in the perioperative period, we hypothesized that good metabolic adaptability could mitigate postoperative complications.

METHODS

We conducted a retrospective observational study utilizing a prospectively collected, single-center preoperative cardiopulmonary exercise testing (CPET) database of patients undergoing a range of major surgeries between 2012 and 2022. On day 3, patients were categorized into 3 groups based on their Postoperative Morbidity Survey (POMS) scores: 0 to 1, 2, and 3 to 6. Metabolic flexibility was evaluated through measurements of fat and carbohydrate oxidation during exercise testing (CPET). Associations were explored between metabolic flexibility, cardiorespiratory fitness, and postoperative outcomes.

RESULTS

Of 585 patients, those with no or low postoperative day 3 morbidity (POMS 0-1; n = 204) demonstrated significantly higher fat oxidation early in exercise before anaerobic threshold (fatty acid oxidation [FATox] area under the curve [AUC] 826 [578-1147]) compared to both POMS 2 (658 [448-922; n = 268]) and POMS 3 to 6 (608 [414-845; n = 113]); both P < .001. POMS 0 to 1 patients also had more effective carbohydrate utilization at peak exercise intensity. Higher postoperative morbidity (POMS) categories were associated with diminished metabolic flexibility characterized by a reduced ability to switch between metabolic substrates-carbohydrate oxidation (CHOox) POMS 0 to 1 group AUC 10277 (interquartile range [IQR] 7773-13358) compared to POMS 2 AUC 8356 (IQR 6548-10377) and POMS 3 to 6 AUC 6696 (IQR 473-9392); both P < .001. Reduced metabolic flexibility correlated with increased postoperative complications and an extended hospital stay.

CONCLUSIONS

Metabolic flexibility may be a pivotal factor in determining postoperative outcomes. Patients with greater metabolic adaptability had fewer complications and shorter hospitalization by 4 days on average. This suggests that preoperative metabolic conditioning-something potentially achieved by targeted prehabilitation-could be linked to surgical recovery. Future research should focus on prospective studies to confirm these relationships and explore underlying mechanisms. If confirmed, metabolic flexibility assessments could be integrated into routine preoperative evaluation to better predict and improve patient outcomes.

Exercise Testing for Metabolic Flexibility: Time for Protocol Standardization

Metabolic syndrome (MetS) is a combination of risk factors that contribute to the development of many of today's chronic diseases. Rates of MetS continue to increase and it is now considered a worldwide epidemic. As with many chronic diseases it may take years for symptoms and the effects of MetS to manifest into severe health problems. Therefore, early detection is paramount A recently proposed method for the early detection of MetS is the assessment of an individual's metabolic flexibility during exercise. Metabolic flexibility is defined as the ability of the body to switch between energy substrates, primarily fats and carbohydrates, to produce energy and meet metabolic demand. This provides an indication of mitochondrial health, the possible beginning point of early insulin resistance and the development of MetS.Although there is widespread use of exercise and expired gas analysis to determine metabolic flexibility, there is no consensus on the appropriate guidelines, protocol, or interpretation of the subsequent data. Studies have used a variety of different protocols involving maximal and submaximal tests with step protocols ranging from 2 to 10 min, differences in data averaging, analysis, and stoichiometric equations, as well as variations in nutritional status of participants, and mode of exercise. This has led to considerable variation in reported results. Although the use of exercise to determine metabolic flexibility and act as a possible marker of early mitochondrial dysfunction holds significant promise, more work is required to determine the optimal protocol for clinical and research purposes.

Optimizing metabolic health with digital twins

A hallmark of subclinical metabolic decline is impaired metabolic flexibility, which refers to the ability to switch fuel utilization between glucose and fat according to energy demand and substrate availability. Herein, we propose optimizing metabolic health with digital twins that model an individual's metabolic flexibility profile to gamify the process of health optimization and predict long-term health outcomes. We explore key characteristics of this approach from technological and socioeconomical perspectives, with the objective of reducing the burden from metabolic disorders through driving behavior change and early detection of metabolic decline.

High-content screening identifies ganoderic acid A as a senotherapeutic to prevent cellular senescence and extend healthspan in preclinical models

Accumulated senescent cells during the aging process are a key driver of functional decline and age-related disorders. Here, we identify ganoderic acid A (GAA) as a potent anti-senescent compound with low toxicity and favorable drug properties through high-content screening. GAA, a major natural component of Ganoderma lucidum, possesses broad-spectrum geroprotective activity across various species. In C. elegans, GAA treatment extends lifespan and healthspan as effectively as rapamycin. Administration of GAA also mitigates the accumulation of senescent cells and physiological decline in multiple organs of irradiation-stimulated premature aging mice, natural aged mice, and western diet-induced obese mice. Notably, GAA displays a capability to enhance physical function and adapts to conditional changes in metabolic demand as mice aged. Mechanistically, GAA directly binds to TCOF1 to maintain ribosome homeostasis and thereby alleviate cellular senescence. These findings suggest a feasible senotherapeutic strategy for protecting against cellular senescence and age-related pathologies.

Prehabilitation: Do We Need Metabolic Flexibility?

BACKGROUND

Metabolic flexibility, the capacity to switch between energy sources in response to changing physiological demands, emerges as a critical determinant of perioperative resilience. In the context of surgery, where metabolic demands are high and energy homeostasis is disrupted, patients with metabolic inflexibility may experience worse outcomes due to impaired immune responses and heightened insulin resistance, resulting in prolonged recovery times.

SUMMARY

This article explores the implications of metabolic flexibility in the perioperative period and examines the potential for prehabilitation strategies, such as targeted exercise and nutritional interventions, to improve patient readiness for surgery. Cardiopulmonary exercise testing is discussed as a valuable assessment tool for metabolic flexibility, capable of providing insights into a patient's fuel adaptability and overall metabolic health preoperatively. Evidence suggests that targeted exercise and nutritional strategies can enhance mitochondrial function, improve nutrient-sensing pathways, and increase substrate oxidation, which may reduce perioperative complications and support immune resilience.

KEY MESSAGES

Future research should prioritise refining methods to identify metabolically inflexible patients and tailoring prehabilitation interventions to optimise metabolic flexibility. Enhancing perioperative metabolic readiness is important for populations vulnerable to metabolic dysfunction, such as those with obesity, diabetes, and cancer. Aligning metabolic optimisation with surgical recovery demands may help establish new standards in perioperative care and improve patient outcomes.

Therapeutic assessment of a novel mitochondrial complex I inhibitor in in vitro and in vivo models of Alzheimer's disease

Despite recent approval of monoclonal antibodies that reduce amyloid (Aβ) accumulation, the development of disease-modifying strategies targeting the underlying mechanisms of Alzheimer's disease (AD) is urgently needed. We demonstrate that mitochondrial complex I (mtCI) represents a druggable target, where its weak inhibition activates neuroprotective signaling, benefiting AD mouse models with Aβ and p-Tau pathologies. Rational design and structure-activity relationship studies yielded novel mtCI inhibitors profiled in a drug discovery funnel designed to address their safety, selectivity, and efficacy. The new lead compound C458 is highly protective against Aβ toxicity, has favorable pharmacokinetics, and has minimal off-target effects. C458 exhibited excellent brain penetrance, activating neuroprotective pathways with a single dose. Preclinical studies in APP/PS1 mice were conducted via functional tests, metabolic assessment, in vivo 31P-NMR spectroscopy, blood cytokine panels, ex vivo electrophysiology, and Western blotting. Chronic oral administration improved long-term potentiation, reduced oxidative stress and inflammation, and enhanced mitochondrial biogenesis, antioxidant signaling, and cellular energetics. These studies provide further evidence that the restoration of mitochondrial function and brain energetics in response to mild energetic stress represents a promising disease-modifying strategy for AD.

Isolating the acute metabolic effects of carbohydrate restriction on postprandial metabolism with or without energy restriction: a crossover study

Low-carbohydrate diets and intermittent energy restriction may offer metabolic advantages in fuel utilisation, that are independent of weight loss. The underlying mechanisms for these effects are unclear but may involve extensions of the catabolic phase and/or attenuation of insulin secretion. To address this gap, we aimed to investigate the independent acute metabolic effect of carbohydrate restriction at varying energy levels. Twelve, (six female) healthy overweight/obese participants (27.3 ± 1.8 years; 25.2 ± 1.6 kg/m2) completed this three-way study. Volunteers followed three diets for one day (36 h, covering the intervention day and overnight fasting), separated by 5-day washout: a normal carbohydrate, energy-balanced diet (nEB, 55% CHO), a low-carbohydrate, energy-balanced diet (LCEB, 50 g/day CHO), and a low-carbohydrate, energy-restricted diet (LC25, 50 g/day CHO with 75% energy restriction). Fasting and serial postprandial (360 min) measurements to a mixed test meal were collected the following morning. Additionally, subjective appetite responses and two-day subsequent ad libitum food intake was assessed. Both low-carbohydrate with and without energy restriction diets induced comparable decrease in triacylglycerol iAUC (p = 0.02, p = 0.04, respectively), and respiratory quotient (both p < 0.01) along with increase in non-esterified fatty acids (both p < 0.01) and 3-hydroxybutyrate (p = 0.001, p = 0.01, respectively) levels. Compared to a non-restricted carbohydrate, energy-balanced diet, postprandial glucose levels significantly increased in the LCEB arm (p = 0.024) and showed a rising trend in the LC25 arm (p = 0.07). Neither insulin responses nor resting, and diet-induced thermogenesis were significantly altered by variations in energy or carbohydrate content. These findings demonstrate that carbohydrate restriction, without altering energy intake, can elicit effects similar to those observed in short-term fasting. As such we propose a strategy of repeated carbohydrate restriction cycles alone may be an emerging alternative approach for the enhancement of cardiometabolic health, warranting further investigation.

Dietary timing enhances exercise by modulating fat-muscle crosstalk via adipocyte AMPKα2 signaling

Feeding rhythms regulate exercise performance and muscle energy metabolism. However, the mechanisms regulating adipocyte functions remain unclear. Here, using multi-omics analyses, involving (phospho-)proteomics and lipidomics, we found that day-restricted feeding (DRF) regulates diurnal rhythms of the mitochondrial proteome, neutral lipidome, and nutrient-sensing pathways in mouse gonadal white adipose tissue (GWAT). Adipocyte-specific knockdown of Prkaa2 (the gene encoding AMPKα2) impairs physical endurance. This defect is associated with altered rhythmicity in acyl-coenzyme A (CoA) metabolism-related genes, a loss of rhythmicity in the GWAT lipidome, and circadian remodeling of serum metabolites-in particular, lactate and succinate. We also found that adipocyte Prkaa2 regulates muscle clock genes during DRF. Notably, oral administration of the AMPK activator C29 increases endurance and muscle functions in a time-of-day manner, which requires intact adipocyte AMPKα2 signaling. Collectively, our work defines adipocyte AMPKα2 signaling as a critical regulator of circadian metabolic coordination between fat and muscle, thereby enhancing exercise performance.

Changes in plasma cytokines following a 60-h fast are not influenced by the addition of exercise despite elevated ketones in healthy young adults

Immunometabolic processes maintain physiological homeostasis and are implicated in various chronic diseases. Fasting and exercise independently alter metabolic and immunological processes; their combination could provide insights into immunometabolic interactions. Using a randomized crossover design, 15 healthy adults (six females, nine males, 26.5 ± 4.3 years) fasted for 60 h with and without the addition of a 3 h cycling bout (65%-80% VO2 peak). Fasting alone (FAST) and with exercise (FEX) reduced plasma glucose, insulin, respiratory exchange ratio, and increased β-hydroxybutyrate (BHB; all p < 0.01). FEX elicited more rapid changes in glucose and BHB and higher BHB concentrations at 60 h (all p < 0.01). Both conditions decreased circulating TNF-⍺ concentrations and increased IL-10 (p < 0.01), although the increase in IL-10 appeared to be driven by the FEX condition (p = 0.03). IL-6 concentrations tended to increase in both conditions (p = 0.1). Total white blood cell count remained unchanged after 60 h in both conditions, with only modest changes in some leukocyte subpopulations. Collectively, the observed changes in circulating cytokine concentrations support an overall anti-inflammatory effect of prolonged fasting, while the maintenance of leukocyte concentrations suggests immune function is not compromised. Despite greater metabolic strain, the addition of prolonged exercise did not appear to augment changes in systemic cytokines and leukocytes.

Effect of Menaquinone-7 (MK-7) Supplementation on Anthropometric Measurements, Glycemic Indices, and Lipid Profiles: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

BACKGROUND

Menaquinone-7 (MK-7) is a type of vitamin K that has a longer half-life and stays in the body for a more extended period compared to other types of vitamin K. Recently, the effects of this vitamin on body weight, glycemic control, and lipid profiles have garnered much attention.

AIM OF THE REVIEW

This systematic review and meta-analysis were performed to evaluate the effects of MK-7 on anthropometric measurements, glycemic indices, and lipid profiles.

METHODS

A systematic search via appropriate keywords was conducted in electronic databases including PubMed, Scopus, Web of Science, and Google Scholar up to October 2023 to obtain relevant original articles. The quality of studies was evaluated using the Cochrane Collaboration tool. Six original articles met our criteria and were included in the analysis.

RESULTS

Statistical analysis showed that MK-7 had a desirable effect on inulin (SMD= -0.56; 95 % CI: -0.77, -0.36; P = 0.000, I2 = 84 %, P = 0.000), HbA1c (SMD=-0.32; 95 % CI: -0.55, -0.09; P = 0.007, I2 = 86.8 %, P = 0.000), and homeostatic Model Assessment for Insulin Resistance (HOMA-IR) (SMD= -0.56; 95 % CI: -0.76, -0.35; P = 0.000, I2 = 84.3 %, P = 0.000). Additionally, subgroup analysis revealed negligible effects of MK-7 on total cholesterol (TC), insulin, HbA1c, and HOMA-IR in both genders of patients who received ≤ 90 mg MK-7 for less than 12 weeks. However, MK-7 didn't have any meaningful effect on other factors.

CONCLUSION

Based on the findings of the present systematic review and meta-analysis, MK-7 may have beneficial effects on glycemic control and TC, although further highly qualified original research is needed for a consistent conclusion.

Single-cell RNA transcriptome uncovers distinct developmental trajectories in the embryonic skeletal muscle of Daheng broiler and Tibetan chicken

Different chicken breeds exhibit distinct muscle phenotypes resulting from selective breeding, but little is known about the molecular mechanisms responsible for this phenotypic difference. Skeletal muscle is composed of a large number of heterogeneous cell populations. Differences in differentiation and interaction of cell populations play a key role in the difference of skeletal muscle phenotype. In the current study, we performed a single-cell RNA sequencing (scRNA-seq) on the leg muscle of Daheng broiler (DH, cultivated breed) and Tibetan chicken (TC, native breed) at embryonic (E) 10, E14 and E18. A comprehensive cell atlas of embryonic chicken skeletal muscle, consisting of 29,579 high-quality cells representing 6 distinct cell types was built. The differentiation trajectory of Myoblasts and fibro-adipogenic progenitors (FAPs) was constructed through pseudotemporal trajectory analysis. Our results revealed the different developmental trajectories and dynamic gene expression profiles in 3 subtypes of myoblasts and 5 FAPs subtypes of the two chicken breeds. Tibetan chicken showed earlier embryonic myogenesis and less myoblasts compared with Daheng broiler. By comparing the switch status and switch time of genes in the two breeds, SNRPG,SNRPE,EIF4EBP1 and HSP90AB1 were considered as potentially critical genes for embryonic myogenesis, and the genes MYOG,MYBPH,APOA1, and MGP played dominant roles in the embryonic adipogenesis. Intercellular interaction networks showed that strong and complex intercellular communication was contained during embryonic skeletal muscle growth and development. These findings revealed the differences of molecular mechanisms in the skeletal muscle development between TC and DH chickens. Our data provide a better understanding of skeletal muscle developmental differences between cultivated and native breeds and valuable information for genetic breeding of chicken.

Zone 2 Intensity: A Critical Comparison of Individual Variability in Different Submaximal Exercise Intensity Boundaries

Introduction: Endurance athletes often utilize low-intensity training, commonly defined as Zone 2 (Z2) within a five-zone intensity model, for its potential to enhance aerobic adaptations and metabolic efficiency. This study aimed at evaluating intra- and interindividual variability of commonly used Z2 intensity markers to assess their precision in reflecting physiological responses during training. Methods: Fifty cyclists (30 males and 20 females) performed both an incremental ramp and a step test in a laboratory setting, during which the power output, heart rate, blood lactate, ventilation, and substrate utilization were measured. Results: Analysis revealed substantial variability in Z2 markers, with the coefficients of variation (CV) ranging from 6% to 29% across different parameters. Ventilatory Threshold 1 (VT1) and maximal fat oxidation (FatMax) showed strong alignment, whereas fixed percentages of HRmax and blood lactate thresholds exhibited wide individual differences. Discussion: Standardized markers for Z2, such as fixed percentages of HRmax, offer practical simplicity but may inaccurately reflect metabolic responses, potentially affecting training outcomes. Given the considerable individual variability, particularly in markers with high CVs, personalized Z2 prescriptions based on physiological measurements such as VT1 and FatMax may provide a more accurate approach for aligning training intensities with metabolic demands. This variability highlights the need for individualized low-intensity training prescriptions to optimize endurance adaptations in cyclists, accommodating differences in physiological profiles and improving training specificity.

Male mouse skeletal muscle lacking HuR shows enhanced glucose disposal at a young age

Introduction

Metabolic flexibility is the ability of a system to switch between metabolic substrates. Human and murine skeletal muscle tissues and cells with decreased activity of the regulatory RNA-binding protein, human antigen R (HuR), have decreased capacity for fat oxidation, and thus decreased metabolic flexibility. In this study, we aimed to assess the preference for carbohydrates in mice lacking HuR in skeletal muscle.

Methods

Experiments were performed on weight-matched control and HuR knockout mice of both sexes. Palmitate and pyruvate oxidation were performed in mouse muscle following the release of 14CO2. In vivo glucose and lipid uptake were assayed in mouse tissue following nonmetabolizable 3H-2-deoxyglucose or 14C-bromopalmitate injection. Transcriptomic analyses were performed in the skeletal muscle of all mice, followed by qPCR validation of select genes. Serum lactate and glucose levels were measured in mice via tail nick, and the muscle glycogen level was measured through colorimetric assay. Indirect calorimetry was used to measure respiratory exchange ratios.

Results

Male muscle-specific HuR knockout mice showed increased glucose uptake relative to controls, specifically in skeletal muscle, and have increased muscle glycogen content. These mice also displayed greater respiratory exchange ratios than controls. None of these differences were noted in females. Transcriptomics showed far more differences between male and female mice than between control and HuR knockout mice. However, differential gene expression between male and female mice was diminished by 50% following the removal of HuR. Male HuR knockout mouse skeletal muscle had increased glycolytic gene expression relative to controls but showed no difference relative to females of the same genotype. Both palmitate and pyruvate oxidation were decreased in the skeletal muscle of male HuR knockout mice relative to controls, and serum lactate levels were increased. No notable differences were seen in females between genotypes.

Discussion

The increase in the markers of glucose utilization with decreased HuR activity in male mice may indicate a switch toward glycolysis as compensation for decreased fat oxidation. These results continue to highlight a sex dependence on HuR as a driver of fat oxidation in mouse skeletal muscle while also indicating that muscle itself shows greater ambiguity between males and females following the removal of HuR.

Independent influence of type 2 diabetes on reduced cardiopulmonary fitness in patients after percutaneous coronary intervention: a cross-sectional study

Previous studies have found a significant association between type 2 diabetes (T2DM) and impaired cardiopulmonary fitness (CRF); however, little evidence was shown in patients after percutaneous coronary intervention (PCI). This study aimed to evaluate the independent effects of T2DM on CRF in patients who have undergone successful percutaneous coronary intervention (PCI) and received guideline-directed medical therapy. Additionally, we explored whether this association is influenced by factors such as demographic features, physical activity level, duration of diabetes, time from index PCI, and history of occlusion myocardial infarction. We retrospectively analyzed data from post-PCI patients who consecutively visited the Cardiac Rehabilitation Center at Beijing Anzhen Hospital between September 2023 and July 2024. To isolate the impact of T2DM on cardiovascular fitness, we implemented strict exclusion criteria for confounding comorbidities, particularly heart failure. Cardiorespiratory fitness was quantified through gold-standard measures: peak oxygen uptake (VO2max) and metabolic equivalents (METs). Baseline characteristics were compared between patients with T2DM and non-diabetic patients (DM group vs. non-DM group). A multivariable regression model was used to evaluate the independent effect of T2DM on CRF, adjusting for confounding factors such as demographic features, physical activity level, duration of diabetes, time since index PCI, and residual comorbidities. Subgroup analyses and interaction tests were performed to assess the impact of T2DM across different subgroups. 201 patients (150 non-DM and 51 DM patients) were included in the final analysis. Hypertension was significantly more prevalent in DM patients (68.6 vs. 42.7%, p = 0.001), while other comorbidities, anthropometric measurements, lifestyle factors, and time from index PCI showed no significant differences between groups (all p > 0.05). Multivariate logistic regression analyses demonstrated significant negative associations between T2DM and both VO2max and METs. After adjusting for basic demographic and lifestyle factors (Model 1), T2DM was inversely associated with VO2max (β=-98.3, 95% CI -193.4 to -3.3, p = 0.044) and METs (β=-0.4, 95% CI -0.8 to -0.0, p = 0.05). These negative associations remained robust and became stronger in Model 2, which further adjusted for physical activity status, hypertension, hyperlipidemia, history of occlusion myocardial infarction, time from index PCI, DM duration, and using beta-blockers, showing more pronounced inverse relationships with both VO2max (β=-212.3, 95% CI -389.4 to -35.3, p = 0.02) and METs (β=-0.9, 95% CI -1.6 to -0.2, p = 0.014). Subgroup analyses indicated consistent inverse associations, with no significant effect modification based on sex, age, body mass index (BMI), time since the index PCI, physical activity status, or a history of occlusion myocardial infarction. Our study demonstrates that T2DM is an independent negative predictor of CRF in post-PCI patients, with consistent findings across various subgroups and robust results after adjusting for confounding factors. These findings underscore the importance of CRF assessment in post-PCI patients and highlight the need for targeted interventions to improve CRF in individuals with T2DM.

Unveiling the molecular legacy of transient insulin resistance: Implications for hepatic metabolic adaptability

BACKGROUND & AIMS

Insulin plays a central role in coordinating metabolic flexibility (MetF). Insulin resistance (IR) can impair MetF, contributing to type 2 diabetes and obesity. Transient IR episodes, like gestational diabetes or stress-induced hyperglycemia, also heighten the risk of later diabetes development. While the health significance of transient IR is well established, we aimed to better understand the heretofore poorly understood molecular processes that occur after such episodes.

METHODS

To do this, we characterized the hepatic response to a high-fat diet challenge in mice previously exposed to a transient IR episode. We integrated transcriptomic, epigenomic, lipidomic, and molecular clock assessments to provide a molecular basis for the observed dysregulations.

RESULTS

Our study shows that temporarily blocking the insulin receptor in young mice leads to later-life liver issues by hindering PPARα-mediated adaptation to a high-fat diet. This is linked to decreased histone active marks at PPARα sites and reduced endogenous PPARα ligands. Transient insulin receptor blockade also altered the liver's molecular clock, particularly affecting PPARα transcriptional responsiveness.

CONCLUSIONS

Seemingly reversible metabolic challenges in early adulthood may predispose the liver to exacerbated metabolic dysfunctions when confronted with chronic challenges later in life.

IMPACT AND IMPLICATIONS

While the health significance of transient insulin resistance is well established, the molecular processes that occur after such episodes are poorly understood. This study thus provides a circadian molecular paradigm for a later-in-life alteration of liver metabolic flexibility following a previous episode of insulin resistance and calls for particular attention to be paid to detecting transient episodes of insulin resistance as they occur in patients with gestational diabetes or stress-induced hyperglycemia. By extension, any transient exposure to compounds altering circadian rhythmicity, such as anti-depressants, might predispose to a compromised metabolic response to an unbalanced diet later in life.

Type 2 diabetes mellitus' impact on heart failure patients' exercise tolerance: a focus on maximal fat oxidation during exercise

Objective

To explore the impact of type 2 diabetes mellitus (T2DM) on exercise tolerance and fat oxidation capacity in patients with heart failure (HF).

Methods

We retrospectively analyzed 108 Chinese patients with HF who were divided into a diabetic group (T2DM group, n = 47) and a non-diabetic group (non-T2DM group, n = 61). All subjects completed cardiopulmonary exercise testing (CPX). We determined their fat oxidation (FATox) by indirect calorimetry.

Results

In the HF patients, the peak oxygen uptake (VO2) value was 14.76 ± 3.27 ml/kg/min in the T2DM group and 17.76 ± 4.64 ml/kg/min in the non-T2DM group. After adjusting for age, sex, body mass index (BMI), log N-terminal pro-B type natriuretic peptide (log NT-proBNP), left ventricular ejection fraction (LVEF), hemoglobin, renal function, coronary heart disease and hypertension, the peak VO2 was lower in the T2DM group compared to the non-T2DM group with a mean difference (MD) of -2.0 ml/kg/min [95% confidence interval (CI), -3.18 to -0.82, P < 0.01]. The VO2 at anaerobic threshold (AT VO2) was also lower in the T2DM group than in the non-T2DM group, with a MD of -1.11 ml/kg/min (95% CI -2.04 to -0.18, P < 0.05). Regarding the fat oxidation capacity during CPX, the T2DM group's maximal fat oxidation (MFO) was lower than that of the non-T2DM group (0.143 ± 0.055 vs. 0.169 ± 0.061 g/min, P < 0.05). In addition, the T2DM group had lower FATox at exercise intensity levels of 40% (P < 0.05) and 50% (P < 0.05) of peak VO2, compared to the non-T2DM group.

Conclusions

T2DM is associated with a decrease in exercise tolerance and fat oxidation capacity in patients with heart failure. Thus, it could be useful to develop exercises of appropriate intensity to optimize physical and metabolic health.

Genetically predicted basal metabolic rate and infectious diseases: a Mendelian randomization study

BACKGROUND

The causal relationship between basal metabolic rate (BMR) and infectious diseases remains elusive. This study aims to clarify this association.

METHODS

This study analyzed genome-wide association studies (GWASs) data from the UK Biobank and FinnGen cohorts to investigate the association between BMR and infectious diseases in European populations. Mendelian randomization (MR) analysis was initially employed, followed by multivariable Mendelian randomization (MVMR) to account for potential confounders. Mediation analysis further confirmed significant relationships. Sensitivity analyses were conducted to validate the study findings.

RESULTS

Using two sample MR, genetically predicted BMR was positively linked to skin and soft tissue infections (SSTIs) (OR: 1.31, 95% CI: 1.18-1.47, P < .001), osteomyelitis (OR: 1.95, 95% CI: 1.36-2.80, P < .001) (1.36 ± 2.80), all-cause infections (OR: 1.36, 95% CI: 1.26-1.48, P < .001) and sepsis (OR: 1.36, 95% CI: 1.23-1.51, P < .001). MVMR analysis confirmed BMR's direct causal effect on SSTIs, osteomyelitis, all-cause infections, and sepsis, except for BMI and other factors affecting osteomyelitis. Mediation analysis revealed VAT as a mediator in the linkage between BMR and SSTIs and all-cause infections. HbA1c mediated the path from BMR to osteomyelitis, while CRP and BMI exhibited mediation effects in the BMR-all-cause infections relationship.

CONCLUSION

The study revealed a significant link between increased BMR and elevated risks of SSTIs, osteomyelitis, and bacterial infections, highlighting the intricate BMR-immune connection and its implications for disease control. Key message What is already known on this topic:  High BMR is positively correlated with COVID-19 and associated with proinflammatory and immunological activation, but the relationship between BMR and other infectious diseases remains largely unexplored. What this study adds:  Higher BMR significantly raises the risk of SSTIs, osteomyelitis, all-cause infections, and sepsis. VAT, HbA1c, CRP, and BMI may mediate the BMR-infection relationship. How this study might affect research, practice, or policy:  A higher BMR may be a valuable indicator associated with an increased risk for SSTIs, osteomyelitis, and sepsis. Modulating BMR might hold promise as a clinically relevant intervention to prevent specific infectious diseases.

Moderating carbohydrate digestion rate in mice promotes fat oxidation and metabolic flexibility revealed through a new approach to assess metabolic substrate utilization

PURPOSE

Superior metabolic flexibility, or the ability to efficiently switch between oxidation of carbohydrate and fat, is inversely associated with obesity and type 2 diabetes. The influence of dietary factors on metabolic flexibility is incompletely understood. This study examined the impact of dietary carbohydrate digestion rate on metabolic flexibility and metabolic substrate utilization.

METHODS

We employed percent relative cumulative frequency (PRCF) analyses coupled with a new application of modeling using the Mixed Weibull Cumulative Distribution function to examine respiratory exchange ratio (RER) data from adult wild-type mice and mice lacking the mucosal maltase-glucoamylase enzyme (Mgam) under different dietary carbohydrate conditions, with diets matched for total carbohydrate contents and containing different ratios of slowly digestible starch (SDS) and resistant starch (RS), or that were high in sucrose or fat. Fungal amyloglucosidase (AMG) was administered in drinking water to increase carbohydrate digestion rate. We devised a Metabolic Flexibility Factor (MFF) to quantitate metabolic flexibility for each dietary condition and mouse genotype, with higher MFF indicating higher metabolic flexibility.

RESULTS

Diets high in SDS exhibited lower average RER and higher metabolic flexibility (MFF) than diets high in resistant starch, sucrose, or fat. Diets containing high and intermediate amounts of SDS led to a more complete shift to fat oxidation. While mouse genotype had minimal effects on substrate oxidation and MFF, AMG supplementation shifted substrate utilization to carbohydrate oxidation and generally decreased MFF.

CONCLUSIONS

Consumption of slowly digestible carbohydrates improved measures of metabolic substrate utilization at the whole-body level in adult mice.

A Drosophila holidic diet optimized for growth and development

Diets composed of chemically pure components (holidic diets) are useful for determining the metabolic roles of individual nutrients. For the model organism Drosophila melanogaster, existing holidic diets are unable to support the rapid growth characteristic of the larval stage. Here, we use a nutrient co-optimization strategy across more than 50 diet variants to design HolFast, a holidic medium tailored to fast larval growth and development. We identify dietary amino acid ratios optimal for developmental speed but show that they compromise survival unless vitamins and sterols are co-optimized. Rapid development on HolFast is not improved by adding fatty acids, but it is dependent upon their de novo synthesis in the fat body via fatty acid synthase (FASN). HolFast outperforms other holidic diets, supporting rates of growth and development close to those of yeast-based diets and, under germ-free conditions, identical. HolFast has wide applications in nutritional and metabolic studies of Drosophila development.

The interplay of NAD and hypoxic stress and its relevance for ageing

Nicotinamide adenine dinucleotide (NAD) is an essential regulator of cellular metabolism and redox processes. NAD levels and the dynamics of NAD metabolism change with increasing age but can be modulated via the diet or medication. Because NAD metabolism is complex and its regulation still insufficiently understood, achieving specific outcomes without perturbing delicate balances through targeted pharmacological interventions remains challenging. NAD metabolism is also highly sensitive to environmental conditions and can be influenced behaviorally, e.g., by exercise. Changes in oxygen availability directly and indirectly affect NAD levels and may result from exposure to ambient hypoxia, increased oxygen demand during exercise, ageing or disease. Cellular responses to hypoxic stress involve rapid alterations in NAD metabolism and depend on many factors, including age, glucose status, the dose of the hypoxic stress and occurrence of reoxygenation phases, and exhibit complex time-courses. Here we summarize the known determinants of NAD-regulation by hypoxia and evaluate the role of NAD in hypoxic stress. We define the specific NAD responses to hypoxia and identify a great potential of the modulation of NAD metabolism regarding hypoxic injuries. In conclusion, NAD metabolism and cellular hypoxia responses are strongly intertwined and together mediate protective processes against hypoxic insults. Their interactions likely contribute to age-related changes and vulnerabilities. Targeting NAD homeostasis presents a promising avenue to prevent/treat hypoxic insults and - conversely - controlled hypoxia is a potential tool to regulate NAD homeostasis.

Phenome-Wide Investigation of the Causal Associations Between Pre-Pregnancy Obesity Traits and Gestational Diabetes: A Two-Sample Mendelian Randomization Analyses

Pre-pregnancy obesity was associated with gestational diabetes in observational studies, but whether this relationship is causal remains to be determined. To evaluate whether pre-pregnancy obesity traits causally affect gestational diabetes risk, a two-sample Mendelian randomization (MR) analysis was performed utilizing summary-level statistics from published genome-wide association studies (GWAS). Obesity-related traits included body mass index (BMI), overweight, obesity, obesity class 1, obesity class 2, obesity class 3, childhood obesity, waist circumference (WC), hip circumference (HC), waist-to-hip ratio (WHR), percent liver fat, visceral adipose tissue volume, abdominal subcutaneous adipose tissue volume. Effect estimates were evaluated using the inverse-variance weighting method. Weighted median, MR-Egger, simple mode, and weighted mode were performed as sensitivity analyses. Genetically predicted pre-pregnancy BMI [odds ratio (OR) = 1.68; 95% confidence interval (CI): 1.45-1.95; P = 9.13 × 10-12], overweight (OR = 1.49; 95% CI: 1.21-1.85; P = 2.06 × 10-4), obesity (OR = 1.25; 95% CI: 1.18-1.33; P = 8.01 × 10-13), obesity class 1 (OR = 1.31; 95% CI: 1.17-1.46; P = 1.49 × 10-6), obesity class 2 (OR = 1.26; 95% CI: 1.16-1.37; P = 5.23 × 10-8), childhood obesity (OR = 1.33; 95% CI: 1.23-1.44; P = 4.06 × 10-12), and WHR (OR = 2.35; 95% CI: 1.44-3.83; P = 5.89 × 10-4) were associated with increased risk of gestational diabetes. No significant association was observed with obesity class 3, WC, HC, percent liver fat, visceral adipose tissue volume, or abdominal subcutaneous adipose tissue volume. Similar results were observed in sensitivity analyses. Therefore, genetically predicted pre-pregnancy obesity traits may increase the risk of gestational diabetes. Weight control before pregnancy may be beneficial to prevent gestational diabetes.

Effects of Aerobic Exercise on Blood Lipids in People with Overweight or Obesity: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

This study aimed to investigate the effects of aerobic exercise (AE) on triglyceride (TG), total cholesterol (TC), high-density lipoprotein (HDL), and low-density lipoprotein (LDL) levels in people with overweight or obesity. Searches were performed in PubMed, Scopus, Cochrane, and Web of Science, covering data up to 27 October 2023. A meta-analysis was conducted to determine the standardized mean difference (SMD) and 95% confidence interval. Nineteen studies met the inclusion criteria. AE significantly improved blood lipids in people with overweight or obesity (TG: SMD = -0.54; p < 0.00001; TC: SMD = -0.24; p = 0.003; HDL: SMD = 0.33; p = 0.003; LDL: SMD = -0.42; p = 0.0005). Both moderate-intensity and vigorous-intensity AE demonstrated significant impacts in reducing TC, TG, and LDL, whereas only moderate-intensity exercise significantly elevated HDL. Additionally, AE significantly optimized blood lipids in those with overweight, with TG being the only parameter showing improvement in individuals with obesity. Moreover, continuous AE notably improved HDL and TG, while interval AE significantly reduced TG, TC, and LDL. Lastly, a clear positive correlation emerged between the duration of the intervention and the decrease in LDL, and a distinct negative correlation was observed between session duration and the reduction of LDL.

Pachymic acid promotes brown/beige adipocyte differentiation and lipid metabolism in preadipocytes 3T3-L1 MBX

OBJECTIVES

To investigate the effect of pachymic acid on brown/beige adipocyte differentiation and lipid metabolism in preadipocytes 3T3-L1 MBX.

METHODS

The brown cocktail method was employed to induce 3T3-L1 MBX cells to differentiate into beige adipocytes. The impact of pachymic acid on the viability of 3T3-L1 MBX preadipocytes was evaluated using the CCK-8 assay. The formation of lipid droplets following treatment with pachymic acid was observed through oil red O staining, and the content of lipids in differentiated cells was determined. The expression levels of key browning genes, including uncoupling protein (Ucp) 1, the peroxisome proliferation-activating receptor gamma coactivator (Pgc)-1α, and the transcription factor containing PR domain 16 (Prdm16) were detected by quantitative reverse transcription polymerase chain reaction. The expression of sterol regulatory element binding protein (Srebp) 1c, acetyl-CoA carboxylase (Acc), fatty acid synthetase (Fas), and steroid-sensitive lipase (Hsl), fatty triglyceride hydrolase (Atgl), and carnitine palmitoyl transferase (Cpt) 1 of lipolysis-related genes were also examined.

RESULTS

The 3T3-L1 MBX was induced in vitro to form beige adipocytes with high expression of key browning genes, including Ucp1, Pgc-1α, Prdm16, and beige adipose-marker genes, including Cd137, Tbx1, and Tmem26. The concentration range of 0-80 μM pachymic acid was non-cytotoxic to 3T3-L1 MBX. Pachymic acid treatment significantly inhibited the differentiation of 3T3-L1 MBX, resulting in a notable decrease in lipid accumulation content (P<0.01). Additionally, there was a marked increase in the expression of key browning genes and their proteins, such as Ucp1, Pgc-1α, and Prdm16, while the expressions of fat synthesis-related genes Srebp1c, Acc and Fas were significantly decreased (all P<0.05). The expressions of lipolysis-related genes, including Hsl, Atgl, and Cpt1, were significantly increased (all P<0.05). Besides, treating with 20 μmol/L pachymic acid showed the most pronounced effect.

CONCLUSIONS

Pachymic acid can inhibit fat synthesis and promote lipid decomposition by regulating the brown formation and lipid differentiation of 3T3-L1 MBX preadipocytes.

The effects of regular exercise on cognitive and cardiometabolic health in testicular cancer survivors subjected to platinum-based chemotherapy

BACKGROUND

Platinum-based chemotherapy provides curative treatment to more than 95% of patients with testicular germ cell tumor but it has negative cardiometabolic and neurological effects. Regular exercise can alleviate late chemotherapy-related toxicities. We examined the impact of a 6-month supervised aerobic-strength training on cognitive and cardiometabolic health and residual level of platinum in cancer survivors.

METHODS

Twenty-eight middle-aged (42.1 ± 7.6 years) testicular germ cell tumor survivors subjected to platinum-based chemotherapy (1-8 cycles, 0-24 years ago) were recruited into exercise (n = 20) and control (n = 8) groups. Effects of 6-month exercise training on the whole-body and muscle metabolism, cognitive functions, cardiopulmonary fitness, residual plasma platinum, and plasma adiponectin were examined.

RESULTS

Exercise intervention improved cardiopulmonary fitness and cognitive functions, reduced residual plasma platinum, visceral adiposity and muscle lipids, improved glucose (glycosylated hemoglobin) and lipid (high-density lipoprotein cholesterol) metabolism, and enhanced dynamics of muscle post-exercise phosphocreatine recovery. Exercise-related decline in plasma platinum was paralleled by decline of muscle glycerophosphocholines and by the enhanced metabolic flexibility during low-intensity exercise, and predicted training-induced increase in cognitive functions.

CONCLUSIONS

The 6-month exercise intervention resulted in improved cognitive and cardiometabolic health in testicular germ cell tumor survivors, which was paralleled by reduced plasma platinum, providing evidence that structured supervised exercise brings multiple health benefits to testicular germ cell tumor survivors.

Altered mitochondria-associated ER membrane (MAM) function shifts mitochondrial metabolism in amyotrophic lateral sclerosis (ALS)

Mitochondrial function is modulated by its interaction with the endoplasmic reticulum (ER). Recent research indicates that these contacts are disrupted in familial models of amyotrophic lateral sclerosis (ALS). We report here that this impairment in the crosstalk between mitochondria and the ER impedes the use of glucose-derived pyruvate as mitochondrial fuel, causing a shift to fatty acids to sustain energy production. Over time, this deficiency alters mitochondrial electron flow and the active/dormant status of complex I in spinal cord tissues, but not in the brain. These findings suggest mitochondria-associated ER membranes (MAM domains) play a crucial role in regulating cellular glucose metabolism and that MAM dysfunction may underlie the bioenergetic deficits observed in ALS.

Pantothenate kinase 4 controls skeletal muscle substrate metabolism

Metabolic flexibility in skeletal muscle is essential for maintaining healthy glucose and lipid metabolism, and its dysfunction is closely linked to metabolic diseases. Exercise enhances metabolic flexibility, making it an important tool for discovering mechanisms that promote metabolic health. Here we show that pantothenate kinase 4 (PanK4) is a new conserved exercise target with high abundance in muscle. Muscle-specific deletion of PanK4 impairs fatty acid oxidation which is related to higher intramuscular acetyl-CoA and malonyl-CoA levels. Elevated acetyl-CoA levels persist regardless of feeding state and are associated with whole-body glucose intolerance, reduced insulin-stimulated glucose uptake in glycolytic muscle, and impaired glucose uptake during exercise. Conversely, increasing PanK4 levels in glycolytic muscle lowers acetyl-CoA and enhances glucose uptake. Our findings highlight PanK4 as an important regulator of acetyl-CoA levels, playing a key role in both muscle lipid and glucose metabolism.