Abstract
Aging is characterized by a progressive decline of skeletal muscle (SM) mass and strength which may lead to sarcopenia in older persons. To date, a limited number of studies have been performed in the old SM looking at the whole, complex network of the extracellular matrix (i.e., matrisome) and its aging-associated changes. In this study, skeletal muscle proteins were isolated from whole gastrocnemius muscles of adult (12 mo.) and old (24 mo.) mice using three sequential extractions, each one analyzed by liquid chromatography with tandem mass spectrometry. Muscle sections were investigated using fluorescence- and transmission electron microscopy. This study provided the first characterization of the matrisome in the old SM demonstrating several statistically significantly increased matrisome proteins in the old vs. adult SM. Several proteomic findings were confirmed and expanded by morphological data. The current findings shed new light on the mutually cooperative interplay between cells and the extracellular environment in the aging SM. These data open the door for a better understanding of the mechanisms modulating myocellular behavior in aging (e.g., by altering mechano-sensing stimuli as well as signaling pathways) and their contribution to age-dependent muscle dysfunction.
Highlights
Skeletal muscle (SM) is necessary for locomotion, but it plays important roles in several physiological processes such as bone homeostasis, thermogenesis, and metabolism of amino acids, glucose, and lipids [1,2]
Samples of gastrocnemius muscle were subjected to three sequential extractions, each one being analyzed by LC-mass spectrometry (MS)/MS
Phosphate buffer saline (PBS) was used to solubilize hydrophilic proteins (PBS extract), and the insoluble part was treated with a combination of urea (U) and thiourea (T) to extract hydrophobic molecules such as membrane proteins, myofibrillar, and part of extracellular matrix (ECM) proteins
Summary
Skeletal muscle (SM) is necessary for locomotion, but it plays important roles in several physiological processes such as bone homeostasis, thermogenesis, and metabolism of amino acids, glucose, and lipids [1,2]. The extracellular matrix (ECM) is composed of different groups of macromolecules such as collagens, non-collagenous glycoproteins (e.g., laminin, tenascin, and fibronectin), glycosaminoglycans (e.g., heparan sulfate), and proteoglycans (e.g., biglycan and lumican) [12]. These macromolecules bind to each other and to cells through integrins, sarcoglycan complex, and dystroglycan to form an intricate network sending biochemical signals to myofibres. ECM is affected by the aging process in terms of turnover and ratio of specific components, the balance between synthesis and degradation of components, modifications in cellular behavior through altered cell-matrix interactions, and changes in mechano-sensing pathways. Until now, a limited number of investigations have been performed in the aging SM looking at the matrisome as the whole complex network of ECM molecules
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