Age‐Dependent Effects on Functional Aspects in Human Satellite Cells

Abstract

In humans aging is a complex process that determines many physical and metabolic alterations correlated to the accumulation of oxidative damage in different tissues. Sarcopenia is an age-related nonpathological condition that includes a progressive loss of mass and strength in skeletal muscle, associated with a decline in the fibers' functional capability. This condition could be correlated to abnormal reactive oxygen species (ROS) accumulation with consequent fiber oxidative damage. This complex situation is not only evident in mature muscle fibers but also in muscle resident satellite cells (involved in fiber damage repairing) in which some functional parameters, at least for that concerns the Ca(2+) homeostasis, seem to be modified. In fact, our data show that there is an age-dependent increase of lipid peroxidation, in cultured myotubes (differentiated and fused satellite cells) after 7 days of in vitro differentiation. In these substrates also the capacity of these cells to produce Ca(2+) transient in response to various stimuli (ATP, caffeine, nicotine, KCl) is, sometimes, drastically modified. In particular, the presence of an age-dependent defective status of excitation-contraction (EC) coupling apparatus is supported by a single cell Ca(2+) analysis obtained from myotubes (derived from aged muscles) in the presence of 40 mM caffeine or 40 mM KCl. The alkaloid presence induces a complete emptying of ryanodine-dependent calcium stores indicating a probable integrity both of SR-terminal cisternae and/or the specific Ca(2+) channel known as RyR1. However, if a sarcolemmal depolarization is induced by the addition of 40 mM KCl in the experimental medium then Ca(2+) release RyR1-dependent can be observed only if Ca(2+) is present in the experimental solution. These results suggest that the EC uncoupling status could be due to the alteration of the interaction between RyR and DHPR. The two receptors are present and functionally active in myotubes from aged donors but they are probably still not in the right localization. These results suggest that during donor's life the satellite cells undergo an aging process similar to the one observed in skeletal muscle tissue, even if they are in a quiescence status for most of the time.

Molecular basis of the myogenic profile of aged human skeletal muscle satellite cells during differentiation

“…The increase in membrane lipid peroxidation (Beccafico et al, 2007) related to alterations in antioxidant enzyme activities (GPX and GST) (Fanò et al, 2001), reported previously by our group, was confirmed by the transcriptional profile reported in this study showing alterations in the expression patterns of genes encoding antioxidant enzymes. This condition leads to increased membrane rigidity (Fulle et al, 2005), and together with other factors, may be responsible for insufficient ability to fuse into myotubes noted during in vitro myogenesis of elderly satellite cells.…”

“…In addition, MMP1 is involved in specific protein substrate digestion of the extracellular matrix, and is fundamental in facilitating cellular migration when myocytes fuse and form myotubes (Saffarian et al, 2004). These results are consistent with the increase in membrane rigidity in myotubes of the elderly (Fulle et al, 2005) that may be attributed to enhanced lipid peroxidation (Beccafico et al, 2007), increasing the difficulty of migration and fusion. Therefore, the lower motility of senescent myoblasts and myotubes, 17 also observed by other investigators (Renault et al, 2000), may be attributed to increase in extracellular matrix deposition.…”

“…This condition leads to increased membrane rigidity (Fulle et al, 2005), and together with other factors, may be responsible for insufficient ability to fuse into myotubes noted during in vitro myogenesis of elderly satellite cells. The oxidative stress-induced state may also underlie the inability of elderly cells to align calcium channels (calcium release units, CRU) correctly during myogenesis, and thus uncouple the E-C mechanism in a way that prevents the correct development of stimulus-response coupling, as reported previously (Beccafico et al, 2007).…”

“…In fact, our data revealed an age-dependent increase in lipid peroxidation in cultured myotubes. In these substrates, the capacity of satellite cells to generate Ca 2+ transients in response to various physiological or pharmacological stimuli is significantly modified (Beccafico et al, 2007).…”

“…To ascertain whether these morphological alterations and previously reported functional changes (Beccafico et al, 2007;Fulle et al, 2005) in aged myotubes could be associated to gene expression changes, we performed a series of experiments to analyze the transcriptional profile during the early steps of the differentiation program (0, 4, 24 and 72 h). We assessed genes obtained from SAM analysis (see Experimental Procedures) according to  and false discovery rates reported in Table 1.…”