Associating Inulin with a Pea Protein Improves Fast-Twitch Skeletal Muscle Mass and Muscle Mitochondrial Activities in Old Rats

Abstract

Aging is associated with a decline in muscle mass and function, leading to increased risk for mobility limitations and frailty. Dietary interventions incorporating specific nutrients, such as pea proteins or inulin, have shown promise in attenuating age-related muscle loss. This study aimed to investigate the effect of pea proteins given with inulin on skeletal muscle in old rats. Old male rats (20 months old) were randomly assigned to one of two diet groups for 16 weeks: a 'PEA' group receiving a pea-protein-based diet, or a 'PEA + INU' group receiving the same pea protein-based diet supplemented with inulin. Both groups showed significant postprandial stimulation of muscle p70 S6 kinase phosphorylation rate after consumption of pea proteins. However, the PEA + INU rats showed significant preservation of muscle mass with time together with decreased MuRF1 transcript levels. In addition, inulin specifically increased PGC1-α expression and key mitochondrial enzyme activities in the plantaris muscle of the old rats. These findings suggest that dietary supplementation with pea proteins in combination with inulin has the potential to attenuate age-related muscle loss. Further research is warranted to explore the underlying mechanisms and determine the optimal dosage and duration of intervention for potential translation to human studies.

Keywords: inulin; mitochondrial activity; pea protein; protein synthesis; sarcopenia; skeletal muscle.

Figure 1

Protein synthesis rate, p70 S6 kinase phosphorylation rate, and expression of ubiquitin-proteasome pathway markers in plantaris muscles of fasted and postprandial old rats fed either PEA or PEA + INU diets. All rats were fasted overnight. PEA rats and PEA + INU rats were randomly divided into groups that either were kept in the fasted state or given a nutrient mixture by oral gavage (postprandial state). (A) Absolute synthesis rate was measured by tracer enrichment in plantaris muscles after incubation with L-[¹³C₆] phenylalanine. (B,C) Ratio of phosphorylated p70 S6 kinase to total p70 S6 kinase content in the same plantaris muscles was determined by Western-blotting. Gene expressions of the two ubiquitin E3 ligases MAFbx (D) and MuRF1 (E) were assessed by quantitative RT-PCR. Data are expressed as means ± SEM. * significantly different from PEA rats at identical nutritional status (fasted or postprandial) at p < 0.05. # significantly different from the same rat group in the fasted state at p < 0.05. ### significantly different from the same rat group rats in the fasted state at p < 0.001. A.U.: arbitrary units. M: Mix of all samples. PEA rat group at the fasted state, n = 8; PEA rat group at the postprandial state, n = 6; PEA + INU rat group at the fasted state, n = 7; PEA + INU rat group at the postprandial state, n = 5.

Figure 2

Mitochondrial function and biogenesis in plantaris muscles of PEA and PEA + INU old rats. (A) Mitochondrial function was assessed by measuring complex 1, citrate synthase, and 3-hydroxyacyl-CoA dehydrogenase (HAD) activity in plantaris muscles. Enzyme activities were expressed as fold change vs. the value found for the PEA rat group. (B) Mitochondrial biogenesis was determined by measuring PGC1α mRNA expression using quantitative RT-PCR and was expressed as fold change vs. value found for the PEA rat group. Data are expressed as means ± SEM. * significantly different from PEA rats at p < 0.05. ** significantly different from PEA rats at p < 0.01. (A.U.): arbitrary units. PEA rat group, n = 14; PEA + INU rat group, n = 12.