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Impaired inhibition of eIF4E-BP1 in skeletal muscle impacts stretch-shortening contraction maladaptation with age.
Baker BA; Hollander MS; Cutlip RG
Med Sci Sports Exerc 2011 May; 43(5)(Suppl 1):52
Specific molecular signaling mechanisms governing protein synthesis/degradation in skeletal muscle, which results in known adaptation or maladaptation following mechanical loading with aging are largely unknown. Purpose: The purpose of this study was to determine the morphological localization, distribution, and quantity of eIF4E and its regulator eIF4E-BP1 (regulators of the initiation of protein translation and the inhibition of initiation of protein translation, respectively) and their collective influence/s on young and old skeletal muscle of rats following chronic high-intensity mechanical loading via stretch-shortening contractions (SSCs). Methods: Left dorsiflexor muscles of young (12 weeks, N=6) and old (30 months, N=6) Fischer Brown Norway Hybrid rats, were loaded 3 times/week for 4.5-weeks using a protocol of 80 maximal SSCs per exposure in vivo. Transverse sections of the tibialis anterior muscle midbelly were cut and prepared for eIF4E and eIF4E-BP1 immunofluorescence and quantified via microscopy/imaging using standard stereology and densitometry. RESULTS: The % volume density of fibers per muscle section and the % affected area of eIF4E-BP1 both decreased significantly (approximately 16% and approximately 83%; p < 0.05 and p < 0.01), respectively) in young rats following SSC loading. Interestingly, following SSC loading the % affected area of eIF4E labeling remained elevated by approximately 150% (p < 0.05) in old compared with young rats following SSC loading. Furthermore, the % affected area of eIF4E-BP1 remained elevated by approximately 400% (p < 0.01) following SSC loading in old compared with young rats following SSC loading, while the % volume density also remained elevated by approximately 32% (p < 0.01) in old versus young rats. CONCLUSIONS: Our data suggest that SSC loading adaptation/maladaptation is significantly impacted by the distribution and quantity of eIF4E-BP1 and its regulation on the initiation of protein translation via sequestration of eIF4E. Collectively, these findings indicate that eIF4EBP1 may exert a chronic inhibitory effect on the availability of eIF4E to contribute to protein translation/synthesis in skeletal muscle of aged populations following repetitive mechanical loading.
Musculoskeletal-system-disorders; Musculoskeletal-system; Muscle-physiology; Muscle-function; Age-factors; Laboratory-animals; Animal-studies; Animals; Author Keywords: eIF4E; eIF4E-BP1; Protein Translation; Aging; Stretch-Shortening Contractions
Issue of Publication
Medicine and Science in Sports and Exercise
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