Everything about Satellite Cells totally explained
Satellite cells are mononuclear
progenitor cells found in mature
muscle between the
basal lamina and
sarcolemma. Satellite cells are able to differentiate and fuse to augment existing
muscle fibres and to form new fibres. These cells are involved in the normal growth of muscle, as well as regeneration following injury or
disease.
In undamaged muscle, the majority of satellite cells are
quiescent; they neither differentiate nor undergo cell division. In response to mechanical strain, satellite cells become
activated. Activated satellite cells initially proliferate as skeletal
myoblasts before undergoing myogenic
differentiation.
Genetic markers of satellite cells
All satellite cells express a number of distinctive
genetic markers including
Pax7 and
syndecan 4. Quiescent satellite cells can also express markers common to
stem cells.
Activated satellite cells express myogenic transcription factors, such as
MyoD and
Myf5. They also begin expressing muscle-specific filament proteins such as
desmin as they differentiate.
Function in muscular repair
When muscle cells undergo injury, quiescent satellite cells are released from beneath the
basal lamina. While normally in a post-
mitotic state, they become activated and re-enter the
cell cycle. Proliferating myoblasts then undergo myogenic differentiation, becoming post-mitotic, and form new myotubes and fuse with existing muscle fibres. This leads to repair of the injured site.
The presence of
fibroblasts during muscle repair can lead to the formation of
scar tissue that can lead to impaired muscle function.
Plasticity
Upon minimal stimulation, satellite cells
in vitro or
in vivo will undergo a myogenic differentiation program.
Some research is underway to investigate the potential for satellite cells to differentiate into other cell types. One application for this would be cardiac
cell therapy, should muscle satellite cells be able to be converted into viable
cardiac muscle cells.
Satellite cells can also be converted
in vitro into bone and cartilage cells, via the application of osteogenic
bone morphogenetic proteins or
transforming growth factor-beta.
Regulation
Satellite cells are regulated by
myogenic regulatory factors, such as
MyoD,
Myf5,
myogenin, and
MRF4.
MEF2 family transcription factors can also promote myogenic differentiation.
There is also research indicating that satellite cells are negatively regulated by a protein called
myostatin. Increased levels of myostatin up-regulate a
cyclin-dependent kinase inhibitor called p21 and thereby induce the differentiation of satellite cells.
Satellite cells are commonly linked to aid in muscular hypertrophy.
Further Information
Get more info on 'Satellite Cells'.
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