Myosin heavy chain composition in normal and atrophic equine laryngeal muscle.
Authors: Adreani C M, Li Z B, Lehar M, Southwood L L, Habecker P L, Flint P W, Parente E J
Journal: Veterinary pathology
Summary
# Editorial Summary: Myosin Heavy Chain Composition in Equine Laryngeal Muscle Atrophy Recurrent laryngeal neuropathy (RLN) causes denervation and atrophy of the intrinsic laryngeal muscles in horses, but the molecular changes underlying this pathology have been poorly characterised. Researchers analysed muscle tissue from seven horses with naturally occurring left-sided laryngeal hemiplegia and two controls, examining both histological features and myosin heavy chain (MHC) isoform expression in the thyroarytenoideus and cricoarytenoideus dorsalis muscles using SDS-PAGE protein analysis and light microscopy. Atrophic muscles from affected horses demonstrated a clear shift in fibre type composition: type I MHC expression decreased whilst type IIB MHC expression increased, accompanied by selective loss of type I fibres and fibre type grouping on histology. Notably, microscopic abnormalities were detected in some contralateral (right-sided) muscles that appeared grossly normal, suggesting subclinical pathology may be more widespread than previously recognised. These findings illuminate the cellular mechanisms of RLN-induced muscle degeneration and have important implications for developing regenerative therapies—understanding how denervation alters the muscle phenotype at the molecular level is essential for designing future interventions aimed at restoring normal fibre composition and contractile function to compromised laryngeal muscles.
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Practical Takeaways
- •Laryngeal hemiplegia causes measurable cellular changes in muscle fiber composition that shift toward fast-twitch glycolytic fibers, which may affect long-term muscle recovery potential
- •Grossly normal laryngeal muscles can still show microscopic denervation changes, meaning subclinical nerve damage may be more widespread than clinical signs suggest
- •Understanding these cellular-level changes may inform future treatment strategies for laryngeal muscle regeneration or reinnervation therapies
Key Findings
- •Atrophic laryngeal muscles showed increased type IIB myosin heavy chain expression and decreased type I expression compared to normal muscles
- •Fiber type grouping and loss of type I fibers occurred in left-sided laryngeal muscles of all but one affected horse
- •Histologic abnormalities were present in some grossly normal-appearing laryngeal muscles from affected horses, indicating subclinical denervation changes
- •Both thyroarytenoideus and cricoarytenoideus dorsalis muscles demonstrated similar patterns of MHC isoform shifts in response to denervation