Myosin heavy chain composition in normal and atrophic equine laryngeal muscle.

The study investigates how the composition of myosin heavy chain (MHC) isoforms, proteins that determine muscle contraction properties, differ in the laryngeal muscles of horses diagnosed with a laryngeal condition called left laryngeal hemiplegia and in healthy ones. The results show that affected horses have higher expression of type IIB MHC and lower expression of type I MHC in atrophying muscles, which may be useful for future strategies addressing muscle regeneration.

Background

• The research focuses on myosin heavy chain (MHC) isoforms in laryngeal muscles. Myosin heavy chains are crucial constituents of muscle tissue, affecting the contractile properties and type of muscle fibers.
• The expression of these isoforms is modulated by neural input and function, therefore changes in their distribution can indicate muscle denervation or reinnervation.
• The study was conducted using laryngeal muscle samples from healthy horses and those suffering from left laryngeal hemiplegia, a condition caused by recurrent laryngeal neuropathy. The muscles, thyroarytenoideus (TA) and cricoarytenoideus dorsalis (CAD), will be analysed to reveal the pattern of MHC isoform expression.

Methodology

• The research obtained laryngeal muscles from 7 horses with left laryngeal hemiplegia and 2 normal horses. The muscle tissues were frozen and prepared for histological evaluation.
• These tissues were assessed for atrophy (muscle damage) and fiber type composition to see if there’s a change in the muscle fiber types distribution.
• The MHC isoform expression was determined using a method called sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), which is used to separate proteins based upon their sizes.

Findings

• The study observed histologic atrophy in all atrophic muscles and some right-sided muscles of 3 affected horses, as well as the left TA of 1 normal horse.
• A loss or clustering of type I muscle fibers was noticed in the left-sided laryngeal muscles in all but one affected horse, as well as in right-sided muscles of two affected horses, and in the left TA of one normal horse.
• SDS-PAGE results revealed the existence of two bands corresponding to type I and type IIB myosin isoforms in the CAD and TA muscles of two normal horses.
• Compared to normal horses, affected ones showed an increased expression of type IIB MHC isoform and a decreased expression of type I MHC isoform in atrophic muscles.

Conclusion

• This study provides important insights on the changes in MHC isoforms’ composition in the laryngeal muscles of horses affected with left laryngeal hemiplegia.
• The finding of increased type IIB and decreased type I MHC expression in affected muscles can potentially aid in understanding the changes at a cellular level in denervated or reinnervated conditions.
• Such knowledge may be useful in developing future strategies for muscle reinnervation or regeneration, thus contributing to a better understanding of laryngeal muscle pathology.