Abstract
Mechanistic target of rapamycin (mTOR) resides as two complexes within skeletal muscle. mTOR complex 1 [mTORC1-regulatory associated protein of mTOR (Raptor) positive] regulates skeletal muscle growth, whereas mTORC2 [rapamycin-insensitive companion of mTOR (Rictor) positive] regulates insulin sensitivity. To examine the regulation of these complexes in human skeletal muscle, we utilized immunohistochemical analysis to study the localization of mTOR complexes before and following protein-carbohydrate feeding (FED) and resistance exercise plus protein-carbohydrate feeding (EXFED) in a unilateral exercise model. In basal samples, mTOR and the lysosomal marker lysosomal associated membrane protein 2 (LAMP2) were highly colocalized and remained so throughout. In the FED and EXFED states, mTOR/LAMP2 complexes were redistributed to the cell periphery [wheat germ agglutinin (WGA)-positive staining] (time effect; P = 0.025), with 39% (FED) and 26% (EXFED) increases in mTOR/WGA association observed 1 h post-feeding/exercise. mTOR/WGA colocalization continued to increase in EXFED at 3 h (48% above baseline) whereas colocalization decreased in FED (21% above baseline). A significant effect of condition (P = 0.05) was noted suggesting mTOR/WGA colocalization was greater during EXFED. This pattern was replicated in Raptor/WGA association, where a significant difference between EXFED and FED was noted at 3 h post-exercise/feeding (P = 0.014). Rictor/WGA colocalization remained unaltered throughout the trial. Alterations in mTORC1 cellular location coincided with elevated S6K1 kinase activity, which rose to a greater extent in EXFED compared with FED at 1 h post-exercise/feeding (P < 0.001), and only remained elevated in EXFED at the 3 h time point (P = 0.037). Collectively these data suggest that mTORC1 redistribution within the cell is a fundamental response to resistance exercise and feeding, whereas mTORC2 is predominantly situated at the sarcolemma and does not alter localization.
Highlights
Resulting in a positive net protein balance (NPB) [5]
Complex 1 contains mechanistic target of rapamycin (mTOR), regulatory associated protein of mTOR (Raptor), G protein -subunit-like (GL), proline-rich Akt1 substrate 1 of 40 kDa (PRAS40), and DEP domain-containing mTOR-interacting protein (DEPTOR) [4], and is believed to activate protein synthetic machinery [1], whereas complex 2 is composed of mTOR, rapamycin-insensitive companion of mTOR (Rictor), DEPTOR, GL, stress-activated protein kinase interacting protein 1 (Sin1), and protein observed with Rictor (Protor) and is implicated in insulin sensitivity and actin cytoskeleton dynamics [4]
Utilizing a within-subject design, we report that a combination of unilateral resistance exercise and protein-carbohydrate feeding elicits a greater mTOR translocation toward the cell
Summary
Resulting in a positive net protein balance (NPB) [5] Such elevations in MPS are underpinned by the activation of the conserved serine/threonine kinase, mechanistic target of rapamycin (mTOR). A similar mechanism has been reported in rodent skeletal muscle, where eccentric contractions of the tibialis anterior muscle induce mTOR-lysosome colocalization [13] in parallel to increases in mTORC1 activity [inferred by the phosphorylation of ribosomal protein S6 kinase 1 threonine 389 (S6K1Thr389)]. Together these data infer an importance of mTOR-lysosome colocalization in the activation of molecular pathways implicated in protein synthesis. We hypothesized this translocation would be specific to mTORC1
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
