Sarcopenia is a common age-related disease characterized by a gradual decline in muscle mass, strength, and function. Usually, individuals may begin to experience related symptoms around the age of 40, and the progression of the disease will accelerate after the age of 75 (Roubenoff&Hughes, 2000). Muscle atrophy has a significant impact on the elderly population, leading to disability, weakness, and reduced quality of life (Rong et al., 2020); Manrique Espinoza et al., 2017). The underlying causes of this disease are complex and involve multiple factors. Dysregulation of signaling pathways, especially disruption of mitochondrial homeostasis, can impair the energy generation ability of muscle cells, which is associated with the onset of sarcopenia (Boengle et al., 2017); Yin et al., 2021). Although sarcopenia has a significant impact on the elderly population, there are currently no approved drug interventions specifically targeting this disease. This highlights the urgent need to find other methods to prevent or slow down the progression of muscle wasting.
The School of Life Sciences at Nanchang University, in collaboration with the Kunming Institute of Zoology, Chinese Academy of Sciences, published an article titled "Histone β - hydroxybutyrylation is critical in reversal of sarcopenia" in Aging Cell. Through research on nematodes and mouse models, it was found that β - hydroxybutyric acid (β - HB) can induce histone β - hydroxybutyrylation (KbHB), enhance mitochondrial function, and improve muscle and motor function, providing a new direction for the treatment of sarcopenia.
Research background:
Muscle atrophy is associated with aging and can lead to a decrease in muscle mass and function, and there is currently a lack of effective drug treatment. Interventions such as calorie restriction (CR), ketogenic diet (KD), and exercise can alleviate muscle atrophy and increase β - HB levels, but the role of β - HB in this process is not yet clear.
Research content and conclusion:
1. The relationship between β - HB and muscle mass: Analysis of BXD mouse strains revealed a positive correlation between β - HB production ability and muscle mass, with a decrease in β - HB production ability in mice, primates, and humans with age.
2. The effect of β - HB on changes in muscle atrophy in vitro: In vitro experiments, β - HB dose dependently prevented TNF - α - induced decrease in C2C12 myotube MyHC protein levels and inhibited changes in muscle atrophy in vitro.
3. The effect of β - HB on muscle function and fiber in elderly mice: Supplementing 23 month old mice with β - HB can enhance their exercise endurance and coordination ability, increase the relative weight and cross-sectional area of the gastrocnemius muscle, and improve muscle function and fiber structure.
4. The effect of β - HB on the motor function and muscle fiber integrity of elderly nematodes: In the experiment of elderly nematodes, β - HB can dose dependently improve their motor function, increase the level of myo3 protein in muscle fibers, and improve muscle fiber integrity.
5. The effect of enhancing endogenous β - HB production capacity: Overexpression of HMGS-1, the rate limiting enzyme for β - HB production in nematodes, can improve motor function in elderly nematodes, indicating that increasing endogenous β - HB production capacity can help improve muscle atrophy.
6. The effect of β - HB on mitochondrial function: β - HB can enhance mitochondrial related gene transcription, increase the oxygen consumption rate of C2C12 myotubes, improve the quantity and morphology of mitochondria in elderly nematodes, and enhance mitochondrial function.
7. The role of histone β - hydroxybutyrylation: β - HB can induce an increase in histone Kbhbb modification in C2C12 myotubes. ChIP seq results showed that H3K9bhb modification can significantly increase the enrichment of mitochondrial related gene loci. Inhibiting p300 (histone Kbhbtransferase) will eliminate the upregulation of β - HB on mitochondrial related gene expression, indicating that β - HB enhances mitochondrial related gene transcription by inducing Kbhb-dependent epigenetic modifications.
8. The role of histone Kbhbb in reversing muscle atrophy: Inhibiting or silencing p300 eliminates the protective effect of β - HB on C2C12 myotube MyHC expression. In the experiment of elderly nematodes, inhibiting histone Kbhbb also eliminates the improvement effect of β - HB and overexpression of HMGS-1 on motor function and muscle fiber structure, indicating that histone Kbhbb is crucial in β - HB reversing muscle atrophy.
9. Relationship between CR and Histone Kbhb: CR dietary intervention in mice was found to reduce body weight and fat mass ratio, increase lean meat mass ratio and relative skeletal muscle mass, increase β - HB levels, and increase H3K9bhb levels and downstream gene expression in mouse skeletal muscle. This suggests that the beneficial effects of CR on skeletal muscle and muscle atrophy may be partially achieved by increasing β - HB and skeletal muscle histone Kbhb levels.
Equipment used in the experiment:
Treadmill Test
The mouse treadmill test uses the KW-PT small animal treadmill (Nanjing Calvin Biotechnology Co., Ltd.), which is equipped with a charged metal grille behind the treadmill movement belt. If the mouse stops running, the grille will apply an electric shock to it. During testing, the mice were placed on a treadmill with an initial tilt angle of 10 °. The treadmill speed gradually increases, starting at 8 m/min, then increases to 16 m/min after 10 minutes, increases to 24 m/min after 20 minutes, and stops testing at 30 minutes. Record the number of electric shocks received by mice during the 30 minute test period and plot the relationship between running distance and exhaustion time.
Rotary testing
The mouse rotary fatigue tester used in the experiment is KW-6C type (Nanjing Calvin Biotechnology Co., Ltd.), equipped with an automatic timer and a drop sensor. During the test, place the mouse on the rotating rod apparatus with an initial speed set at 6 m/min. Then, gradually increase the rotating rod speed by 2 m/min until the mouse becomes fatigued and falls off. Record the time and distance that mice persist on the spinning stick before falling, in order to measure their motor coordination and endurance.
Grasp force measurement
Evaluate the upper limb grip of mice using the mouse grip tester KW-ZL-1 (Nanjing Calvin Biotechnology Co., Ltd.). During testing, grab the mouse's tail and lift it up, guiding the mouse to grasp the sturdy mesh connected to the digital force gauge. Then gently pull the mouse's tail back until it releases the grip. At this point, the tension reading displayed on the digital force gauge is the grip force. Each mouse was tested continuously for 5 times, and the average maximum gripping force of its limb muscles was calculated (in grams).
Research limitations and prospects:
There are limitations to the research, such as the inability to evaluate the long-term side effects of β - HB supplements in short-term studies, the need to validate animal experiment results in humans, and insufficient assessment of the effects of diet, exercise, and individual metabolic differences. Long term research and clinical trials are needed in the future to further explore the role of β - HB.