Satellite cell content is specifically reduced in type II skeletal muscle fibers in the elderly

Abstract

Satellite cells (SC) are essential for skeletal muscle growth and repair. Because sarcopenia is associated with type II muscle fiber atrophy, we hypothesized that SC content is specifically reduced in the type II fibers in the elderly. A total of eight elderly (E; 76 Ϯ 1 yr) and eight young (Y; 20 Ϯ 1 yr) healthy males were selected. Muscle biopsies were collected from the vastus lateralis in both legs. ATPase staining and a pax7-antibody were used to determine fiber type-specific SC content (i.e., pax7-positive SC) on serial muscle cross sections. In contrast to the type I fibers, the proportion and mean cross-sectional area of the type II fibers were substantially reduced in E vs. Y. The number of SC per type I fiber was similar in E and Y. However, the number of SC per type II fiber was substantially lower in E vs. Y (0.044 Ϯ 0.003 vs. 0.080 Ϯ 0.007; P Ͻ 0.01). In addition, in the type II fibers, the number of SC relative to the total number of nuclei and the number of SC per fiber area were also significantly lower in E. This study is the first to show type II fiber atrophy in the elderly to be associated with a fiber type-specific decline in SC content. The latter is evident when SC content is expressed per fiber or per fiber area. The decline in SC content might be an important factor in the etiology of type II muscle fiber atrophy, which accompanies the loss of skeletal muscle with aging.

Genes and the ageing muscle: a review on genetic association studies

“…Sarcopenia can induce muscle weakness and reduced ability to produce rapid force, which are considered to be two of the most common risk factors associated with falls and loss of functional independence in older adults (Taaffe and Marcus 2000;Buchman et al 2007). Sarcopenia can be explained by several physiopathological factors including (a) progressive muscle denervation (Deschenes 2004;Saini et al 2009); (b) alterations in muscle protein turnover, specifically manifested by difficulty to increase protein synthesis (Kumar et al 2009); (c) malnutrition (Doherty 2003); (d) altered expression levels of anabolic hormones (Volpi et al 2004); (e) increased levels of pro-inflammatory cytokines (Kamel 2003); (f) increased oxidative stress (Howard et al 2007); (g) lower physical activity levels (Cesari and Pahor 2008) and (h) diminished number and function of satellite cells in skeletal muscles (Verdijk et al 2007). Concerning the latter, satellite cells are the main contributor to muscle maintenance, growth and repair (Anderson and Wozniak 2004).…”

“…Concerning the latter, satellite cells are the main contributor to muscle maintenance, growth and repair (Anderson and Wozniak 2004). Thus, a decline in the number of satellite cells (Kadi et al 2004;Renault et al 2002;Verdijk et al 2007) or their inability to become active and proliferate in response to anabolic stimuli (Conboy et al 2003;Conboy and Rando 2002) may contribute to the development of sarcopenia.…”

Age‐related changes in miR‐143‐3p:Igfbp5 interactions affect muscle regeneration

“…The availability and functionality of satellite cells determine effective regeneration. Aging‐related changes in satellite cell number and properties, such as susceptibility to apoptosis and ability to proliferate, have been shown in humans and rodents (Brack et al ., 2007; Collins et al ., 2007; Verdijk et al ., 2007). Moreover, the presence of senescent satellite cells in old mice and humans characterized by increased expression p16 INK4a and decreased phosphorylation of the retinoblastoma (RB) protein was shown (Sousa‐Victor et al ., 2014).…”

Age modifies respiratory complex I and protein homeostasis in a muscle type‐specific manner

“…The response to injury and atrophy varies with muscle fiber type. Type I muscle fibers may be more susceptible to atrophy from denervation and inactivity or microgravity (Grossman et al ., 1998; Patterson et al ., 2006), while type II fast‐twitch muscle fibers preferentially atrophy with age, sepsis, nutrient deprivation, and diabetes (Verdijk et al ., 2007; Jerkovic et al ., 2009; Picard et al ., 2011). Although the literature suggests that age‐related mitochondrial dysfunction is greater in fast‐twitch muscles, a mechanistic explanation of how the distinct composition and metabolic activity of muscle fiber type drive the specific sensitivity to various physiological insults has not been well defined.…”