Date of Graduation

5-2022

Document Type

Thesis

Degree Name

Master of Science in Food Science (MS)

Degree Level

Graduate

Department

Food Science

Advisor/Mentor

Jamie Baum

Committee Member

Yan Huang

Second Committee Member

Elisabet Børsheim

Third Committee Member

Sami Dridi

Keywords

aging, amino acids, essential amino acids, muscle, protein synthesis, sarcopenia

Abstract

Skeletal muscle (SM) is vital for both long term health and quality of life. Recent research suggests an increase in catabolic signals with age triggers pathologic conditions, such as sarcopenia. Although results from in vitro studies model how EAA can regulate muscle protein synthesis (MPS), the relevance of these models to muscle protein breakdown (MPB) and the presence of physiological EAA concentrations remains to be established. Therefore, the objective of this study was to determine the effects of a low, normal, and supra physiological dose of EAA (0.2, 1.0, and 3.0 x EAA) in a young (passages 2-10) and aging (passages 16-24) C2C12 murine muscle cell model. We hypothesized that increased levels of EAA will increase MPS in aging cells and suppress MPB via mTORC1 when compared to young cells. Myoblasts were seeded (1x105) into 6-well plates and differentiated into myotubes when they reached 80% confluency. Myotubes were serum and AA starved for 24 hours before receiving one of the following treatments: control (CON), 0.2 x EAA, 1.0 x EAA, 3.0 x EAA with or without rapamycin (100 nm; rapamycin (RAP) for 1, 6, and 24 hours. All treatments were performed in triplicate and then each experiment was repeated three times, yielding nine wells per treatment. Phosphorylation for phospho and total protein of p70 S6 kinase 1 (p70S6K1), 4E binding protein 1 (4EBP1), mechanistic target of rapamycin (mTOR), general control nonderepressible 2 (GCN2), eukaryotic initiation factor 2- alpha (eIF2α) and Sestrin 2 (SESN2) was measured using Western Blot analysis. RAP inhibited phosphorylation of MPS markers p70S6K1 and 4EBP1 in all treatments. Whereas the activation of GCN2 in young and old muscle cells is independent of the availability of EAA and mTORC1 activation. The phosphorylation of 4EBP1 increased (p<0.05) following 0.2 x EAA in young cells and 3.0 x EAA in old cells compared to CON. Phosphorylation of p70S6K1 increased (p<0.05) following 0.2, 1.0, and 3.0 x EAA in young cells compared to the CON. In conclusion, we demonstrated EAA can regulate pathways associated with sarcopenia and increase molecular markers related to MPS in young and old muscle cells. Therefore, it can be proposed increasing EAA may be effective for regulating the rate of MPS and MPB via the mTORC1 pathway in both young and aging muscle cells.

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