apoptosis of cells may occur as a result of muscle atrophy.
which may occur as a result of muscle atrophy?
apoptosis of cells
muscle atrophy is defined as a decrease in the mass of the muscle; it can be a partial or complete wasting away of muscle, and is most commonly experienced when persons suffer temporary disabling circumstances such as being restricted in movement and/or confined to bed as when hospitalized. when a muscle atrophies, this leads to muscle weakness, since the ability to exert force is related to mass. modern medicine's understanding of the quick onset of muscle atrophy is a major factor behind the practice of getting hospitalized patients out of bed and moving about as active as possible as soon as is feasible, despite sutures, wounds, broken bones, and pain.
muscle atrophy
as presented above, skeletal muscle atrophy involves an imbalance between the processes that control protein synthesis (also known as protein translation) and those that control protein breakdown. when the two processes are in synchrony, muscle mass is stable. however, if there is an imbalance such that the protein synthetic pathway is decreased relative to that of the rate of degradation, muscle atrophy will occur. in the case of skeletal muscle atrophy in response to spaceflight or hs, a decrease in the capacity for synthesis as well as an increase in the processes that regulate degradation seem to occur, creating a rapid net degradation response to the unloading stimulus. on the basis of the available information, such a scenario is thought to involve the following chain of events. at the onset of unloading involving a wide range of models including spaceflight, a decrease in transcriptional and/or pre-translational activity occurs in skeletal muscle that affects the type i and iia mhc genes as well as the actin gene. this results in a reduced level of both pre-mrna and mrna pools (the latter being a substrate for protein translation) for these three proteins. together, mhc and actin provide the bulk of the myofibril fraction that accounts for most of the protein in the muscle cell. concomitantly, a decrease occurs in the activity of key protein kinase enzyme systems (constituting the pi3kinase/akt/mtor pathway), which regulates the protein synthetic apparatus controlling protein translation. this alteration, in combination with a smaller amount of mrna substrate, collectively contributes to a reduction in the net capacity for protein synthesis. occurring simultaneously with this process is the up-regulation of a set of genes that encode proteins that play a regulatory role in augmenting protein degradation. these include the myostatin gene, the atrogin 1 gene, and a gene called muscle ring finger protein, referred to as murf. myostatin is an antigrowth transcription factor, which is thought to negatively modulate the genes that promote growth. atrogin and murf are e3 ligases that are responsible for ubiquinating target proteins to mark them for degradation in a system designated as the proteasome. this murf protein has been reported to be a key regulator for specifically targeting breakdown of the type i and type iia mhc proteins.
reduced muscle mass, strength and performance in space