The effects of long-term lactate and high-intensity interval training (HIIT) on brain neuroplasticity of aged mice

Extensive research has confirmed numerous advantages of exercise for promoting brain health. More recent studies have proposed the potential benefits of lactate, the by-product of exercise, in various aspects of brain function and disorders. However, there remains a gap in understanding the effects of lactate dosage and its impact on aged rodents. The present study first examined the long-term effects of three different doses of lactate intervention (2000 mg/kg, 1000 mg/kg, and 500 mg/kg) and high-intensity interval training (HIIT) on aging mice (20-22 months) as the 1st experiment. Subsequently, in the 2nd experiment, we investigated the long-term effects of 500 mg/kg lactate intervention and HIIT on brain neuroplasticity in aged mice (25-27 months). The results of the 1st experiment demonstrated that both HIIT and different doses of lactate intervention (500 mg/kg and 2000 mg/kg) positively impacted the neuroplasticity biomarker VEGF in the hippocampus of aging mice. Subsequently, the 2nd experiment revealed that long-term HIIT significantly improved the performance of mice in open-field, novel object recognition, and passive avoidance tests. However, lactate intervention did not significantly affect these behavioral tests. Moreover, compared to the control group, both HIIT and lactate intervention positively influenced the angiogenesis signaling pathway (p/t-AKT/ENOS/VEGF), mitochondrial biomarker (SDHA), and metabolic protein (p/t-CREB, p/t-HSL, and LDH) in the hippocampus of aged mice. Notably, only lactate intervention significantly elevated the BDNF (PGC-1α, SIRT1, and BDNF) signaling pathway and metabolic content (lactate and pyruvate). In the end, long-term HIIT and lactate intervention failed to change the protein expression of p/t-MTOR, iNOS, nNOS, HIF-1α, SYNAPSIN, SIRT3, NAMPT, CS, FNDC5 and Pan Lactic aid-Lysine in the hippocampus of aged mice. In summary, the present study proved that long-term HIIT and lactate treatment have positive effects on the brain functions of aged mice, suggesting the potential usage of lactate as a therapeutic strategy in neurodegenerative diseases in the elderly population.

Intramuscular mitochondrial and lipid metabolic changes of rats after regular high-intensity interval training (HIIT) of different training periods

BACKGROUND

High-intensity Interval Training (HIIT) is a time-efficient form of exercise and has gained popularity in recent years. However, at molecular level, the understanding about the effects of HIIT is not comprehensive, and even less is elucidated about HIIT of different training duration cycles, although different durations always lead to different post-training consequences.

METHOD

In this study, by training SD rats using HIIT protocols lasting for different training duration cycles, we investigated the adaptive response of intramuscular triglyceride abundance as well as mitochondrial and lipid metabolic changes after HIIT training (2, 4, 6, 8, and 10 weeks). We selected 72 h after the last session of training as the time point of sacrifice.

RESULTS

The suppressed activation of the cAMP-PKA pathway indicates that skeletal muscle was in the recovery phase at this time point. Intramuscular triglyceride abundance was significantly elevated after 2, 4, and 10 weeks of HIIT. However, the lipid metabolism-related proteins inconsistently changed in a chaotic trend (see Table 1). The expression levels of PGC1-α and COX IV decreased after 2 and 4 weeks of training and raised after 6 and 8 weeks of training. The expression level of citrate synthase (CS) decreased after 2, 4, 8, and 10 weeks of training, and showed an upward trend after 6 weeks of training. While the activity of CS decreased after 2 and 8 weeks of training and showed an upward trend after 6 weeks of HIIT.

CONCLUSION

Given the abovementioned changing trends, we propose two speculations: (A) the damaged mitochondria oxidation capacity might be one of the causes of IMTG accumulation observed after 2 and 4 weeks of HIIT. This phase might be similar to the condition of type 2 diabetes. (B) after 6-week HIIT, mitochondria function and biogenesis might be improved and the IMTG contents declined to baseline. This might be explained as: mitochondrial enhancement increased the capacity of lipid oxidation and then offset the increase in IMTG achieved during the first 4 weeks. For HIIT Rat Modelling, if the aim is to observe HIIT-induced positive effects, caution should be exercised when considering 2 and 4 weeks of training under our HIIT frame. Also, implementing six-week training is at least effective for mitochondrial enhancement when using similar HIIT frame of this study.

Acute and chronic effects of high-intensity interval training (HIIT) on postexercise intramuscular lipid metabolism in rats

Recovery from exercise refers to the period between the end of a bout of exercise and the subsequent return to a resting or recovered state. It is a dynamic period in which many physiological changes occur. A large amount of research has evaluated the effect of training on intramuscular lipid metabolism. However, data are limited regarding intramuscular lipid metabolism during the recovery period. In this study, lipid metabolism-related proteins were examined after a single bout of exercise in a time-dependent way to explore the mechanism of how exercise induces intramuscular lipid metabolism adaptation. Firstly, all rats in the exercise group underwent a five-week training protocol (HIIT, five times/week), and then performed a more intense HIIT session after 72 h of the last-time five-week training. After that, rats were sampled in a time-dependent way, including 0 h, 6 h, 12 h, 24 h, 48 h, 72 h, and 96 h following the acute training session. Our results discovered that five weeks of HIIT increased the content of intramuscular triglyceride (IMTG) and enhanced the lipolytic and lipogenesis-related proteins in skeletal muscle. Furthermore, IMTG content decreased immediately post HIIT and gradually increased to baseline levels 48 h postexercise, continuing to over-recover up to 96 h postexercise. Following acute exercise, lipolytic-related proteins showed an initial increase (6-12 h) before decreasing during recovery. Conversely, lipogenesis-related proteins decreased following exercise (6-12 h), then increased in the recovery period. Based on the changes, we speculate that skeletal muscle is predominated by lipid oxidative at the first 12 h postexercise. After this period, lipid synthesis-related proteins increased, which may be the result of body recovery. Together, these results may provide insight into how the lipid metabolism-related signaling changes after chronic and acute HIIT and how protein levels lipid metabolism correlates to IMTG recovery.