Interleukin-6 potentiates endurance training adaptation and improves functional capacity in old mice

Liver lipid metabolism, oxidative stress, and inflammation in glutamine-supplemented ob/ob mice

Glutamine availability may be reduced in chronic diseases, such as type 2 diabetes mellitus (T2DM)-induced by obesity. Herein, the antioxidant, anti-inflammatory and lipid metabolism effects of chronic oral glutamine supplementation in its free and dipeptide form were assessed in ob/ob mice. Adult male C57BL/6J ob/ob mice were supplemented with L-alanyl-L-glutamine (DIP) or free L-glutamine (GLN) in the drinking water for 40 days, whilst C57BL/6J Wild-type lean (WT) and control ob/ob mice (CTRL) received fresh water only. Plasma and tissue (skeletal muscle and liver) glutamine levels, and insulin resistance parameters (e.g., GTT, ITT, insulin) were determined. Oxidative stress (e.g., GSH system, Nrf2 translocation), inflammatory (e.g., NFkB translocation, TNF-α gene expression) and lipid metabolism parameters (e.g., plasma and liver triglyceride levels, SRBP-1, FAS, ACC, and ChRBP gene expression) were also analyzed. CTRL ob/ob mice showed lower glutamine levels in plasma and tissue, as well as increased insulin resistance and fat in the liver. Conversely, chronic DIP supplementation restored glutamine levels in plasma and tissues, improved glucose homeostasis and reduced plasma and liver lipid levels. Also, Nrf2 restoration, reduced NFkB translocation, and lower TNF-α gene expression was observed in the DIP group. Interestingly, chronic free GLN only increased muscle glutamine stores but reduced overall insulin resistance, and attenuated plasma and liver lipid metabolic biomarkers. The results presented herein indicate that restoration of body glutamine levels reduces oxidative stress and inflammation in obese and T2DM ob/ob mice. This effect attenuated hepatic lipid metabolic changes observed in obesity.

Aging Skeletal Muscles: What Are the Mechanisms of Age-Related Loss of Strength and Muscle Mass, and Can We Impede Its Development and Progression?

As we age, we lose muscle strength and power, a condition commonly referred to as sarcopenia (ICD-10-CM code (M62.84)). The prevalence of sarcopenia is about 5-10% of the elderly population, resulting in varying degrees of disability. In this review we emphasise that sarcopenia does not occur suddenly. It is an aging-induced deterioration that occurs over time and is only recognised as a disease when it manifests clinically in the 6th-7th decade of life. Evidence from animal studies, elite athletes and longitudinal population studies all confirms that the underlying process has been ongoing for decades once sarcopenia has manifested. We present hypotheses about the mechanism(s) underlying this process and their supporting evidence. We briefly review various proposals to impede sarcopenia, including cell therapy, reducing senescent cells and their secretome, utilising targets revealed by the skeletal muscle secretome, and muscle innervation. We conclude that although there are potential candidates and ongoing preclinical and clinical trials with drug treatments, the only evidence-based intervention today for humans is exercise. We present different exercise programmes and discuss to what extent the interindividual susceptibility to developing sarcopenia is due to our genetic predisposition or lifestyle factors.

Combined physical exercise re-synchronizes expression of Bmal1 and REV-ERBα and up-regulates apoptosis and metabolism in the prostate during aging

BACKGROUND

Aging increases the prevalence of prostate cancer. The circadian clock coordinates metabolism, cell cycle, and tumor suppressor p53. Although physical exercise has several effects on preventing prostate diseases, its effect on regulating genes and proteins of the circadian rhythm of the prostate needs to be better evaluated. The present study verified expression of REV-ERBα (Nr1d1), Bmal1, apoptosis, tumor suppressors, energetic metabolism markers, and androgen receptors in the prostatic microenvironment in 18-month-old mice submitted to combined physical training.

METHODS

C57BL/6 J mice were divided into 2 groups: 6 months-old (n = 10) and 18 months-old, (n = 20). The 18-month-old animals were divided into 2 subgroups: sedentary (n = 10, 18 m Sed) and submitted to combined physical training (n = 10, 18 m TR). Combined physical training protocol was performed by running on the treadmill (40-60 % of incremental load test) and climbing strength training (40-50 % of maximum repetition test), consisting of 5×/week (3 days aerobic and 2 days strength) for 3 weeks. The prostate was prepared for Western blot and RT-qPCR analysis, and the plasm was prepared for the biochemistry analysis.

RESULTS

Combined physical exercise during aging led to increased levels of Bmal1 and decreased levels of REV-ERBα in the prostate. These results were accompanied by a reduction in the AMPK/SIRT1/PGC-1α proteins and an increase in the PI3K/AKT and p53/PTEN/caspase 3 pathways, promoting apoptotic potential.

CONCLUSION

These findings suggest that strength and aerobic physical exercise may be preventive in the development of preneoplastic molecular alterations and age-related features by re-synchronizes Bmal1 and REV-ERBα in prostatic tissues.

The gut mucin-microbiota interactions: a missing key to optimizing endurance performance

Endurance athletes offer unique physiology and metabolism compared to sedentary individuals. Athletes training at high intensities for prolonged periods are at risk for gastrointestinal disturbances. An important factor in endurance performance is the integrity and function of the gut barrier, which primarily depends on heavily O-glycosylated mucins. Emerging evidence shows a complex bidirectional dialogue between glycans on mucins and gut microorganisms. This review emphasizes the importance of the crosstalk between the gut microbiome and host mucus mucins and some of the mechanisms underlying this symbiosis. The contribution of mucin glycans to the composition and functionality of the gut microbiome is discussed, as well as the persuasive impact of the gut microbiome on mucin composition, thickness, and immune and metabolic functions. Lastly, we propose natural and synthetic glycans supplements to improve intestinal mucus production and barrier function, offering new opportunities to enhance endurance athletes' performance and gut health.

The Molecular Mechanisms of Fuel Utilization during Exercise

Exercise is widely recognized for its positive impact on human health and well-being. The process of utilizing substrates in skeletal muscle during exercise is intricate and governed by complex mechanisms. Carbohydrates and lipids serve as the primary fuel sources for skeletal muscle during exercise. It is now understood that fuel selection during exercise is not solely determined by physical activity itself but is also influenced by the overall metabolic state of the body. The balance between lipid and carbohydrate utilization significantly affects exercise capacity, including endurance, fatigue, and overall performance. Therefore, comprehensively understanding the regulation of substrate utilization during exercise is of utmost importance. The aim of this review is to provide an extensive overview of the current knowledge regarding the pathways involved in the regulation of substrate utilization during exercise. By synthesizing existing research, we can gain a holistic perspective on the intricate relationship between exercise, metabolism, and fuel selection. This advanced understanding has the potential to drive advancements in the field of exercise science and contribute to the development of personalized exercise strategies for individuals looking to optimize their performance and overall health.

Impaired age-associated mitochondrial translation is mitigated by exercise and PGC-1α

Sarcopenia, the age-related loss of skeletal muscle mass and function, can dramatically impinge on quality of life and mortality. While mitochondrial dysfunction and imbalanced proteostasis are recognized as hallmarks of sarcopenia, the regulatory and functional link between these processes is underappreciated and unresolved. We therefore investigated how mitochondrial proteostasis, a crucial process that coordinates the expression of nuclear- and mitochondrial-encoded mitochondrial proteins with supercomplex formation and respiratory activity, is affected in skeletal muscle aging. Intriguingly, a robust mitochondrial translation impairment was observed in sarcopenic muscle, which is regulated by the peroxisome proliferator-activated receptor γ coactivator 1 α (PGC-1α) with the estrogen-related receptor α (ERRα). Exercise, a potent inducer of PGC-1α activity, rectifies age-related reduction in mitochondrial translation, in conjunction with quality control pathways. These results highlight the importance of mitochondrial proteostasis in muscle aging, and elucidate regulatory interactions that underlie the powerful benefits of physical activity in this context.

Females display relatively preserved muscle quality compared with males during the onset and early stages of C26-induced cancer cachexia

Cancer cachexia is clinically defined by involuntary weight loss >5% in <6 mo, primarily affecting skeletal muscle. Here, we aimed to identify sex differences in the onset of colorectal cancer cachexia with specific consideration to skeletal muscle contractile and metabolic functions. Eight-weeks old BALB/c mice (69 males, 59 females) received subcutaneous C26 allografts or PBS vehicle. Tumors were developed for 10-, 15-, 20-, or 25 days. Muscles and organs were collected, in vivo muscle contractility, protein synthesis rate, mitochondrial function, and protein turnover markers were assessed. One-way ANOVA within sex and trend analysis between sexes were performed, P < 0.05. Gastrocnemius and tibialis anterior (TA) muscles became atrophic in male mice at 25 days, whereas female mice exhibited no significant differences in muscle weights at endpoints despite presenting hallmarks of cancer cachexia (fat loss, hepatosplenomegaly). We observed lowered muscle contractility and protein synthesis concomitantly to muscle mass decay in males, with higher proteolytic markers in muscles of both sexes. mRNA of Opa1 was lower in TA, whereas Bnip3 was higher in gastrocnemius after 25 days in male mice, with no significant effect in female mice. Our data suggest relative protections to skeletal muscle in females compared with males despite other canonical signs of cancer cachexia and increased protein degradation markers; suggesting we should place onus upon nonmuscle tissues during early stages of cancer cachexia in females. We noted potential protective mechanisms relating to skeletal muscle contractile and mitochondrial functions. Our findings underline possible heterogeneity in onset of cancer cachexia between biological sexes, suggesting the need for sex-specific approaches to treat cancer cachexia.NEW & NOTEWORTHY Our study demonstrates biological-sex differences in phenotypic characteristics of cancer cachexia between male and female mice, whereby females display many common characteristics of cachexia (gonadal fat loss and hepatosplenomegaly), protein synthesis markers alterations, and common catabolic markers in skeletal muscle despite relatively preserved muscle mass in early-stage cachexia compared with males. Mechanisms of cancer cachexia appear to differ between sexes. Data suggest need to place onus of early cancer cachexia detection and treatment on nonmuscle tissues in females.

Muscle-Brain crosstalk in cognitive impairment

Sarcopenia is an age-related, involuntary loss of skeletal muscle mass and strength. Alzheimer's disease (AD) is the most common cause of dementia in elderly adults. To date, no effective cures for sarcopenia and AD are available. Physical and cognitive impairments are two major causes of disability in the elderly population, which severely decrease their quality of life and increase their economic burden. Clinically, sarcopenia is strongly associated with AD. However, the underlying factors for this association remain unknown. Mechanistic studies on muscle-brain crosstalk during cognitive impairment might shed light on new insights and novel therapeutic approaches for combating cognitive decline and AD. In this review, we summarize the latest studies emphasizing the association between sarcopenia and cognitive impairment. The underlying mechanisms involved in muscle-brain crosstalk and the potential implications of such crosstalk are discussed. Finally, future directions for drug development to improve age-related cognitive impairment and AD-related cognitive dysfunction are also explored.

Physiological role of cytokines in the regulation of mammalian metabolism

The innate cytokine system is involved in the response to excessive food intake. In this review, we highlight recent advances in our understanding of the physiological role of three prominent cytokines, interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF), in mammalian metabolic regulation. This recent research highlights the pleiotropic and context-dependent functions in the immune-metabolic interplay. IL-1β is activated in response to overloaded mitochondrial metabolism, stimulates insulin secretion, and allocates energy to immune cells. IL-6 is released by contracting skeletal muscle and adipose tissue and directs energy from storing tissues to consuming tissues. TNF induces insulin resistance and prevents ketogenesis. Additionally, the therapeutic potential of modulating the activity of each cytokine is discussed.

IL-6 signaling in acute exercise and chronic training: Potential consequences for health and athletic performance

The cytokine interleukin-6 (IL-6) is involved in a diverse set of physiological processes. Traditionally, IL-6 has been thought of in terms of its inflammatory actions during the acute phase response and in chronic conditions such as rheumatoid arthritis and obesity. However, IL-6 is also an important signaling molecule during exercise, being acutely released from working muscle fibers with increased exercise duration, intensity, and muscle glycogen depletion. In this context, IL-6 enables muscle-organ crosstalk, facilitating a coordinated response to help maintain muscle energy homeostasis, while also having anti-inflammatory actions. The range of actions of IL-6 can be explained by its dichotomous signaling pathways. Classical signaling involves IL-6 binding to a cell-surface receptor (mbIL-6R; present on only a small number of cell types) and is the predominant signaling mechanism during exercise. Trans-signaling involves IL-6 binding to a soluble version of its receptor (sIL-6R), with the resulting complex having a much greater half-life and the ability to signal in all cell types. Trans-signaling drives the inflammatory actions of IL-6 and is the predominant pathway in disease. A single nucleotide polymorphism (rs2228145) on the IL-6R gene can modify the classical/trans-signaling balance through increasing the levels of sIL-6R. This SNP has clinical significance, having been linked to inflammatory conditions such as rheumatoid arthritis and type 1 diabetes, as well as to the severity of symptoms experienced with COVID-19. This review will describe how acute exercise, chronic training and the rs2228145 SNP can modify the IL-6 signaling pathway and the consequent implications for health and athletic performance.

Interleukin-6 potentiates endurance training adaptation and improves functional capacity in old mice

BACKGROUND

Interventions to preserve functional capacities at advanced age are becoming increasingly important. So far, exercise provides the only means to counteract age-related decrements in physical performance and muscle function. Unfortunately, the effectiveness of exercise interventions in elderly populations is hampered by reduced acceptance and compliance as well as disuse complications. We therefore studied whether application of interleukin-6 (IL-6), a pleiotropic myokine that is induced by skeletal muscle activity and exerts broad systemic effects in response to exercise, affects physical performance and muscle function alone or in combination with training in aged mice.

METHODS

Sedentary old male mice (Sed+Saline, n = 15) were compared with animals that received recombinant IL-6 (rIL-6) in an exercise-mimicking pulsatile manner (Sed+IL-6, n = 16), were trained with a moderate-intensity, low-volume endurance exercise regimen (Ex+Saline, n = 13), or were exposed to a combination of these two interventions (Ex+IL-6, n = 16) for 12 weeks. Before and at the end of the intervention, mice underwent a battery of tests to quantify endurance performance, muscle contractility in situ, motor coordination, and gait and metabolic parameters.

RESULTS

Mice exposed to enhanced levels of IL-6 during endurance exercise bouts showed superior improvements in endurance performance (33% more work and 12% greater peak power compared with baseline), fatigue resistance in situ (P = 0.0014 vs. Sed+Saline; P = 0.0199 vs. Sed+IL-6; and P = 0.0342 vs. Ex+Saline), motor coordination (rotarod performance, P = 0.0428), and gait (gait speed, P = 0.0053) following training. Pulsatile rIL-6 treatment in sedentary mice had only marginal effects on glucose tolerance and some gait parameters. No increase in adverse events or mortality related to rIL-6 treatment was observed.

CONCLUSIONS

Administration of rIL-6 paired with treadmill running bouts potentiates the adaptive response to a moderate-intensity low-volume endurance exercise regimen in old mice, while being safe and well tolerated.