Skeletal muscle can generate large amounts of force during eccentric contractions, which are characterized by reduced energy cost and a tendency to increase fascicle length (LF) and decrease pennation angle (PA). Macroscopic structural adaptations induced by training and based on eccentric contractions are different depending on the site of investigation, namely in the medial (M) and distal (D) portions, but it is unclear which specific molecular mechanisms regulate these different adaptations. The aim of this work was to investigate modifications in signaling pathways involved in protein synthesis, mitochondrial function and content, induced by moderate relative load eccentric strength training in young subjects. Eight young males aged 18-35 years underwent an 8-week eccentric (ECC) strength training protocol at a moderate load (60% maximal repetition). Both at the beginning and at the end of the training protocol, biopsies from the vastus lateralis muscle were taken at two sites, and histological evaluations and protein assays of molecular markers involved in pathways regulating muscle protein synthesis, mitochondrial volume and mitochondrial function, were performed. based on myosin heavy chains (MHC) and cluster of differentiation 31 (CD 31) – staining, following training, no histological changes were observed in the fiber-type distribuition, in fiber cross-sectional area (CSA) and capillarization (C/F). The only parameter which was significantly increased was the non-phosphorylated form of AKT at the distal site. Generally, these results could be explained by an insufficient mechanical loading unable to induce activation of the investigated molecular pathways and therefore unable to induce a change in protein expression. Future studies will need to understand whether moderate mechanical stress as well as different types of contractions, such as concentric contractions (CON), may induce different adaptations in different sites of the skeletal muscle. Finally, it might be interesting to replicate the same study in an elderly population in order to understand whether this mechanical stimulus is sufficient to counteract or reduce the structural and molecular changes typical of aging.
Il muscolo scheletrico può generare grandi quantità di forza durante le contrazioni eccentriche, le quali si contraddistinguono per un ridotto consumo energetico e per la tendenza ad aumentare la lunghezza del fascicolo (LF) e diminuire l’angolo di pennazione (PA). Gli adattamenti strutturali macroscopici indotti da allenamenti basati su contrazioni eccentriche sono diversi a seconda del sito studiato, ovvero nella porzione mediale (M) e distale (D) del muscolo vasto laterale, ma non è chiaro da quali specifici meccanismi molecolari questi differenti adattamenti derivino. L’obiettivo di questo lavoro è stato quello di investigare in soggetti giovani le modificazioni nelle vie di segnale coinvolte nel processo di sintesi proteica, di funzione e contenuto mitocondriale indotte da un allenamento di forza eccentrico a carico relativo moderato. Otto giovani maschi tra 18-35 anni sono stati sottoposti ad un protocollo di 8 settimane di allenamento eccentrico (ECC) ad un carico moderato (60% massima ripetizione). All’inizio e al termine del protocollo di allenamento, sono state eseguite biopsie del muscolo vasto laterale in due siti assieme a valutazioni istologiche e dosaggi proteici di marker molecolari coinvolti nelle vie di regolazione della sintesi proteica, del contenuto e della funzione mitocondriale nel muscolo scheletrico. A seguito di allenamento, non si sono osservate modificazioni istologiche nella distribuzione in fibre, basata su colorazioni indirizzate alle catene pesanti della miosina (MHC) e al cluster of differentiation 31 (CD31), nell’area di sezione trasversa delle fibre (CSA) e nella capillarizzazione (C/F). L’unico parametro ad essere aumentato in maniera significativa è stata la forma non fosforilata di AKT al sito distale. Generalmente, questi risultati potrebbero essere spiegati da un carico meccanico non sufficiente ad indurre un’attivazione delle vie molecolari indagate e un cambiamento dell’espressione proteica. Studi futuri dovranno indagare se uno stress meccanico moderato così come contrazioni di diversa tipologia, come quelle concentriche (CON), possano indurre risposte differenti in diversi siti del muscolo scheletrico. Infine, potrebbe essere interessante replicare lo stesso studio su una popolazione anziana per capire se questo stimolo meccanico sia sufficiente a contrastare o ridurre le modificazioni strutturali e molecolari tipiche dell’invecchiamento.
ADATTAMENTI STRUTTURALI E MOLECOLARI ALL’ALLENAMENTO ECCENTRICO: DIFFERENZE LOCO-REGIONALI NELLA PLASTICITA’ MUSCOLARE
DI STASIO, MASSIMILIANO
2022/2023
Abstract
Skeletal muscle can generate large amounts of force during eccentric contractions, which are characterized by reduced energy cost and a tendency to increase fascicle length (LF) and decrease pennation angle (PA). Macroscopic structural adaptations induced by training and based on eccentric contractions are different depending on the site of investigation, namely in the medial (M) and distal (D) portions, but it is unclear which specific molecular mechanisms regulate these different adaptations. The aim of this work was to investigate modifications in signaling pathways involved in protein synthesis, mitochondrial function and content, induced by moderate relative load eccentric strength training in young subjects. Eight young males aged 18-35 years underwent an 8-week eccentric (ECC) strength training protocol at a moderate load (60% maximal repetition). Both at the beginning and at the end of the training protocol, biopsies from the vastus lateralis muscle were taken at two sites, and histological evaluations and protein assays of molecular markers involved in pathways regulating muscle protein synthesis, mitochondrial volume and mitochondrial function, were performed. based on myosin heavy chains (MHC) and cluster of differentiation 31 (CD 31) – staining, following training, no histological changes were observed in the fiber-type distribuition, in fiber cross-sectional area (CSA) and capillarization (C/F). The only parameter which was significantly increased was the non-phosphorylated form of AKT at the distal site. Generally, these results could be explained by an insufficient mechanical loading unable to induce activation of the investigated molecular pathways and therefore unable to induce a change in protein expression. Future studies will need to understand whether moderate mechanical stress as well as different types of contractions, such as concentric contractions (CON), may induce different adaptations in different sites of the skeletal muscle. Finally, it might be interesting to replicate the same study in an elderly population in order to understand whether this mechanical stimulus is sufficient to counteract or reduce the structural and molecular changes typical of aging.È consentito all'utente scaricare e condividere i documenti disponibili a testo pieno in UNITESI UNIPV nel rispetto della licenza Creative Commons del tipo CC BY NC ND.
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https://hdl.handle.net/20.500.14239/16299