Whole egg, but not egg white, ingestion induces mTOR colocalization with the lysosome after resistance exercise

Abstract

We have recently demonstrated that whole egg ingestion induces a greater muscle protein synthetic (MPS) response when compared with isonitrogenous egg white ingestion after resistance exercise in young men. Our aim was to determine whether whole egg or egg white ingestion differentially influenced colocalization of key regulators of mechanistic target of rapamycin complex 1 (mTORC1) as means to explain our previously observed divergent postexercise MPS response. In crossover trials, 10 healthy resistance-trained men (21 ± 1 yr; 88 ± 3 kg; body fat: 16 ± 1%; means ± SE) completed lower body resistance exercise before ingesting whole eggs (18 g protein, 17 g fat) or egg whites (18 g protein, 0 g fat). Muscle biopsies were obtained before exercise and at 120 and 300 min after egg ingestion to assess, by immunofluorescence, protein colocalization of key anabolic signaling molecules. After resistance exercise, tuberous sclerosis 2-Ras homolog enriched in brain (Rheb) colocalization decreased ( P < 0.01) at 120 and 300 min after whole egg and egg white ingestion with concomitant increases ( P < 0.01) in mTOR-Rheb colocalization. After resistance exercise, mTOR-lysosome-associated membrane protein 2 (LAMP2) colocalization significantly increased at 120 and 300 min only after whole egg ingestion ( P < 0.01), and mTOR-LAMP2 colocalization correlated with rates of MPS at rest and after exercise ( r = 0.40, P < 0.05). We demonstrated that the greater postexercise MPS response with whole egg ingestion is related in part to an enhanced recruitment of mTORC1-Rheb complexes to the lysosome during recovery. These data suggest nonprotein dietary factors influence the postexercise regulation of mRNA translation in human skeletal muscle.

Keywords: Rheb; TSC2; anabolic signaling; immunofluorescence; muscle protein synthesis.

Fig. 1.

Tuberous sclerosis 2 (TSC2) and mechanistic target of rapamycin (mTOR) colocalization with Ras homolog enriched in brain (Rheb) in response to whole eggs or egg whites following resistance exercise. Immunofluorescence quantification of mTOR/TSC2 (red) and Rheb (green) colocalization, displayed as a composite image (merge) and WGA (blue) (n = 10/condition). Yellow/orange regions represent TSC2 and Rheb (A) mTOR and Rheb colocalization (C). Each panel represents one subject from whole eggs and egg whites across the experimental time course. Group data are quantified and reported as TSC2 and Rheb colocalization (B) and mTOR and Rheb colocalization (D). Open circles represent whole eggs and closed circles represent egg whites. All data are presented relative to Fasted. Scale bar represents 100-μm area. Data are presented as means ± SE and were analyzed using two-way repeated-measures ANOVA. *P < 0.01, different from Fasted in same condition. Immunofluorescence image was obtained on a Leica DMI8 confocal microscope of mTOR (red) and Rheb (green) interaction, displayed as a composite image (merge) and WGA (blue) (E). Sections were viewed at ×60 1.30 numerical aperture oil immersion objective to visualize the signal being primarily intracellular and/or within the fiber junctions. Scale bar represents 20-μm area (E).

Fig. 2.

Mechanistic target of rapamycin (mTOR) colocalization with lysosome-associated membrane protein 2 (LAMP2) in response to whole eggs or egg whites after resistance exercise and mTOR-LAMP and phosphorylation of S6 kinase 1 (p-S6K1) against myofibrillar protein synthesis in response to whole eggs and egg whites. Immunofluorescence quantification of mTOR (red) and LAMP2 (green) colocalization, displayed as a composite image (merge) and wheat germ agglutinin (WGA; blue; n = 10/condition). Yellow/orange regions represent mTOR and LAMP2 colocalization (A). Each panel represents one subject from whole eggs and egg whites across the experimental time course. Group data are quantified and reported; open circles represent whole eggs and closed circles represent egg whites (B). Correlation analysis of mTOR-LAMP2 and myofibrillar fractional synthetic rate (FSR; C), p-S6K1 with myofibrillar FSR (D), and p-S6K1 with mTOR-LAMP2 (E). All data are presented relative to Fasted. Scale bar represents 100-μm area. Data are presented as means ± SE and were analyzed using two-way repeated-measures ANOVA. *P < 0.01, different from Fasted in whole eggs. AU, arbitrary units. [Myofibrillar FSR data from Ref. .]

Fig. 3.

Plasma cholecystokinin (CCK) and cholesterol availability in response to whole eggs or whites following resistance exercise. Total CCK (pg/ml) (A) and cholesterol (mg/dl) (B) were analyzed in response to whole eggs and egg whites (n = 10/condition); open circles represent whole eggs and closed circles represent egg whites. Data are presented as means ± SE and were analyzed using two-way repeated-measures ANOVA. AUC, area under the curve.