Combined Effect of Dietary Phosphorus and Structured Exercise on Skeletal Muscle Degradation in Rats

Abstract

Phosphorus (P) has been associated with the availability of cellular energy. Protein metabolism, including both synthesis and degradation, requires energy in the form of ATP. Hence, P might impact protein metabolism through its association with ATP. Moreover, several studies have shown that dietary phosphorus content affects energy expenditure (EE). Most of the EE in the body is related to Lean Body Mass (LBM), and it is known that protein synthesis and degradation are major regulators of muscle mass. Previously, it has been shown that P intake higher than normal might increase protein synthesis, and in order to complete the image, we aim in this thesis to examine the individual and combined effect of dietary P and moderate-intensity running exercise routine on muscle degradation in rats.

Researchers, who studied protein homeostasis, have for a long time ignored the role of degradation. In eukaryotic cells, two major pathways—the ubiquitin-proteasome pathway and lysosomal proteolysis—mediate protein degradation. In this thesis, we will focus on studying parameters involved in the ubiquitin-proteasome pathway which are Forkhead box O 3 (FOXO3) and the catalytic sites of the Proteasome: Proteasome β1 (PSMB1) and Proteasome β5 (PSMB5).

After receiving approval from Institutional Animal Care and Use Committee of the American University of Beirut, two experiments were performed, Low Phosphorus (LP) (0.1%P, 0.2%P, and 0.3% P) and High Phosphorus (HP) (0.3%P, 0.6%P, and 1.2% P) diets. In each experiment, male rats were randomly divided into 3 groups (n=8), in which a sedentary or moderate-intensity exercise routine (30 minutes 5 days a week) was implemented. Following sacrifice, parameters involved in protein degradation from the ubiquitin-proteasome pathway, FOXO3, PSMB1, and PSMB5, were measured in gastrocnemius muscle using the following three techniques: Immunohistochemistry, Immunofluorescence, and Western Blot.

. With respect to PSMB1 and PSMB5, despite the fact that there was a significant change, however the pattern of values was inconsistent in response to P or/and E. In reference to FOXO3, the expression did not differ in response to exercise, however it increased as the intake of P increased. In conclusion, these collective results demonstrate that P ingestion above the standard level of 0.3%P may increase protein degradation in muscle.