## 3 eIF3f and mTOR in Skeletal Muscle Function
Importantly, studies with immunofluorescence approaches found a new cellular trafficking involving mTORC1/eIF3f during exercise [171]. In humans, mTOR was found to co-localize with the lysosomal-associated membrane protein (LAMP2) at rest, suggesting that mTOR is located close to the late-lysosome in skeletal muscle [172]. A single bout of resistance exercise increased the translocation of mTOR/LAMP2 complex at the cell membrane near to the blood capillaries [172]. However, it was previously indicated that mTORC1 recruitment to the lysosome membranes is essential to rise mTOR kinase activity, especially because the mTORC1 activator RHEB is contained in a membrane-bound compartment of the lysosome [16, 173, 174, 175]. Importantly, the authors also found that the interaction between mTOR and eIF3f increased at the cell membrane after exercise and this response was enhanced in a fed state (20g protein/ 40 g carbohydrate/ 1 g fat) [172]. That probably explains the increase of S6K1 kinase activity and protein synthesis enhancement observed after exercise with amino acids ingestion [176, 177, 17]. Accordingly, mTORC1 translocation to lysosomes is known to be mediated by Regulator-Rag complex and plays a pivotal role in amino acid signaling related to mTORC1 [174]. Of note, a reduction of TSC2 abundance at the cell membrane was also observed after exercise with a dissociation from RHEB [172]. These results strongly suggest that this newly identified trafficking contributes to higher activation of mTOR signaling. Interestingly, recent data reinforced our knowledge on the influence of nutritional state after exercise on mTOR/eIF3f trafficking and adaptations to resistance training. Indeed, it was reported that the ingestion of whole eggs after resistance exercise promotes a higher stimulation of protein synthesis compared to consumption of egg whites only [178]. A more pronounced mTOR localization at the lysosome was observed after whole eggs consumption [179]. Among the multiple candidates involved in mTOR trafficking after whole egg ingestion, PA and low-density lipoprotein (LDL)-derived cholesterol have been suggested [178]. The first one can be generated via the novo synthesis by phosphatidylcholine, oleic acid, and diacylglycerol [180, 181]. Egg yolks also contain LDL-derived cholesterol known to have a role in mTORC1 recruitment to the lysosome through SLC38A9-Niemann-Pick C1 signaling complex [182]. Altogether, these data suggest that whole egg ingestion could promote a higher mRNA translation compared to egg white. However, even if these acute outcomes may suggest that whole eggs consumption could maximize gains in skeletal muscle mass, longitudinal data recently failed to support this assumption [183]. A recent study compared the effect of daily whole egg vs. egg white ingestion during 12 weeks of resistance training in humans [183]. The authors found that, when protein intake was equalized, the effects of whole egg and egg white on body weight, fat mass, skeletal muscle mass, and strength, and the expression of fibroblast growth factor 2, follistatin, transforming growth factor-beta1, activin 1, and myostatin were similar. Thus, optimizing acute protein synthesis with nutritional strategies does not necessarily support long-term adaptations in skeletal muscle. Finally, another recent study assessed the effects of a habitual high-protein diet on response to an acute resistance exercise and muscle protein synthesis [184]. The authors found that a four-week high-protein diet (crude protein \(\approx\) 52%) does not influence resting mTORC1 activity nor muscle protein synthesis, as well as in response to a single bout of resistance exercise. However, higher muscle mass and lower fat mass were found with habitual high-protein diet compared to control, but with a concomitant impairment in glucose metabolism-related proteins [184]. Consistent with this result, long-term habitual high-protein intake may promote insulin resistance and whole body glucose intolerance [185].