Where is striated muscle

This adaptation is initially beneficial but sustained cardiac hypertrophy eventually results in impaired cardiac function, partially due to cell death caused by apoptosis Dorn, STARS is increased in several models of cardiac hypertrophy and myopathy.

The transient increase in STARS gene expression was observed prior to any detectable increase in LV mass which did not occur until at least 4 days post banding. This suggests that STARS may detect the initial mechanical stress and its activation would signal to mechanisms that directly cause the cardiac remodeling response to LVH. However, this cardiac hypertrophy only occurs when the mice are subjected to pressure overload.

A similar observation has been made in humans with STARS mRNA significantly higher in human hearts with idiopathic cardiomyopathy when compared to normal control hearts Kuwahara et al. While the mechanism behind this cardiomyocyte hypertrophy was not established, STARS overexpression did not affect proliferation, but it did reduce chemically induced apoptosis Koekemoer et al.

STARS may also regulate muscle cell hypertrophy by influencing protein synthesis and degradation, however, this has not been experimentally determined.

These observations suggest that STARS is an early marker of cardiac remodeling in response to increased mechanical stress. The fact that endogenous STARS is rapidly and transiently increased in response to external stress signals suggests that it may have a protective and a physiological adaptive role in muscle cells. The adaptation of skeletal muscle to changes in mechanical stress, such as muscle contraction or immobilization, requires the sensing and the transduction of the extracellular stress signals into the cell in order to generate the appropriate physiological response.

Our group first observed that STARS mRNA levels significantly increased in the vastus lateralis muscle following 8 weeks of hypertrophy-inducing resistance exercise training in humans Lamon et al. With respect to acute single-bout exercise, STARS gene expression increases fold when measured 3 h after eccentric exercise MacNeil et al. Work from our group has also shown that STARS mRNA and protein levels are increased 3 h following an acute bout of single-leg endurance exercise; both returning to basal levels 24 h post-exercise Wallace et al.

This transient increase in STARS following contraction-induced mechanical stress may provide a protective mechanism to reduce the risk of contractile damage to the sarcomere or be required to activate intracellular signals responsible for muscle adaptation to exercise. Limb immobilization drastically reduces the exposure of skeletal muscle to mechanical stress factors. However, a reduction in muscle weight was not observed until 48 h post intervention Giger et al.

Whether the decrease in STARS is a cause or a consequence of muscle wasting is yet to be established. We have observed that reducing mechanical stress due to cessation of exercise training for 8 weeks results in a loss of muscle mass and a reduction in STARS mRNA Lamon et al. As STARS binds and stabilizes actin and the sarcomere, it has been suggested that it protects against contraction-induced damage Arai et al. Muscle from older animals is more susceptible to contraction-induced damage, partially due to a mechanically compromised sarcomeric structure that is less able to withstand stretch Lynch et al.

Older muscle also repairs less efficiently which is attributed to its reduced capacity to promote satellite cell activation, proliferation, and differentiation, thereby contributing to its impaired regenerative capacity and reduced muscle mass Grounds, ; Welle, The reduction in STARS in older muscle may be a factor contributing to the increased susceptibility of contraction-induced muscle damage as well as its attenuated muscle cell proliferation and repair. STARS gene expression is upregulated in skeletal muscle of patients with type 2 diabetes when compared with healthy family members Jin et al.

Knock-down of STARS in L6 myotubes enhances insulin signaling, as measured by increased insulin stimulated Akt phosphorylation as well as basal and insulin-stimulated glucose uptake Jin et al. Presently, it is difficult to determine if the increase in STARS in diabetic muscle is a consequence of or directly contributes to insulin resistance.

The local intracollateral over expression of STARS ameliorates collateral conductance in rabbits following femoral artery ligature.

Furthermore, identification of the downstream molecules activated by STARS that regulate proliferation is required. STARS may play an important role in sensing mechanical stress and up-regulating important pathways controlling muscle growth and regeneration. Continual adaptations such as growth, repair, and maintenance of cardiac, smooth, and skeletal muscle are required throughout the lifespan for the maintenance of healthy living and longevity. For healthy adaptation to occur the muscle cells must be able to detect the extracellular stress signals and efficiently transmit them to appropriate intracellular transcriptional programs.

The STARS protein appears to be a key player in the detection and transmission of adaptive stress signals in muscle cells. However, forced chronic overexpression of STARS appears to make the muscle cells hypersensitive to adaptive external stress and may result in a maladaptive response. These observations suggest that if STARS was to be considered a therapeutic target to enhance muscle growth and repair then it would require a precise and conditional method of induction or suppression.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The lymphatic system is also elucidated elaborately here Skip to content Main Navigation Search. Dictionary Articles Tutorials Biology Forum.

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