Complex Correlations Between Desmin Content, Myofiber Types, and Innervation Patterns in the Human Extraocular...

Area of Science:

• Muscle biology
• Neuroscience
• Cellular and cytoskeletal organization

Background:

• Human extraocular muscles (EOMs) exhibit unique physiological properties.
• Understanding the cytoskeletal organization of EOMs is crucial for comprehending their function.

Purpose of the Study:

• To investigate the relationship between desmin distribution and distinct innervation patterns in human EOMs.
• To explore potential signaling mechanisms between neuromuscular junctions (NMJs) and myofibers in EOMs.

Main Methods:

• Immunohistochemistry was employed on EOM samples.
• Antibodies against desmin, vimentin, myosin heavy chain (MyHC) isoforms, and acetylcholine receptor (AChR) subunits were used.
• Neuromuscular junctions (NMJs) were identified using α-bungarotoxin or antibodies against neurofilament and synaptophysin.

Main Results:

• Desmin was largely present in myofibers but showed reduced or absent presence near single en plaque NMJs.
• Desmin presence varied in MyHCsto/I myofibers depending on NMJ type (en grappe vs. spiral endings).
• Desmin distribution was inconsistent in MyHCeom myofibers with multiterminal en plaque endings, independent of AChR subunits or EOM layer. Vimentin did not compensate for desmin absence.

Conclusions:

• Human EOMs possess a more intricate cytoskeletal framework compared to other skeletal muscles.
• The findings imply the existence of additional signaling pathways connecting NMJs to myofibers in EOMs.