Abstract
Sarcopenia, a loss of skeletal muscle mass and function, is prevalent in older people and associated with functional decline and mortality. Protein supplementation is necessary to maintain skeletal muscle mass and whey protein hydrolysates have the best nutrient quality among food proteins. In the first study, C57BL/6 mice were subjected to immobilization for 1 week to induce muscle atrophy. Then, mice were administered with four different whey protein hydrolysates for 2 weeks with continuous immobilization. Among them, soluble whey protein hydrolysate (WP-S) had the greatest increase in grip strength, muscle weight, and cross-sectional area of muscle fiber than other whey protein hydrolysates. To investigate the molecular mechanism, we conducted another experiment with the same experimental design. WP-S significantly promoted the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) pathway and inhibited the PI3K/Akt/forkhead box O (FoxO) pathway. In addition, it increased myosin heavy chain (MyHC) expression in both the soleus and quadriceps and changed MyHC isoform expressions. In conclusion, WP-S attenuated muscle atrophy induced by immobilization by enhancing the net protein content regulating muscle protein synthesis and degradation. Thus, it is a necessary and probable candidate for developing functional food to prevent sarcopenia.
Highlights
Skeletal muscle is the largest organ that constitutes approximately 40% of total body weight and conducts many important functions in the body
The total protein intake did not show a significant difference compared with the IM group, so we could interpret that the results of further experiments are caused by the administration of four different whey protein hydrolysates itself (Supplementary Figure S3)
At the end of the experiment, grip strength was decreased by 26.2% in the IM group compared to the normal group and it was significantly increased by 14.7% in the whey protein hydrolysate (WP-S) group (Figure 1A)
Summary
Skeletal muscle is the largest organ that constitutes approximately 40% of total body weight and conducts many important functions in the body. It enables individuals to move, supports the skeleton and organs, and regulates glucose homeostasis [1]. The loss of muscle mass causes discomfort in daily life and, even worse, exacerbates other metabolic diseases [2]. Skeletal muscle mass is regulated by the balance between muscle protein synthesis (MPS) and muscle protein degradation (MPD) [3]. A loss of muscle mass occurs when this balance is broken (MPS < MPD) and it can lead to muscle atrophy [4]. Sarcopenia is prevalent in older people and is associated with health and functional decline, disease and injury, quality of life, and even mortality
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