Adreani C M, Li Z B, Lehar M, Southwood L L, Habecker P L, Flint P W, Parente E J
Department of Clinical Studies, New Bolton Center, 382 West Street Road, Kennett Square, PA 19348, USA.
Vet Pathol. 2006 Nov;43(6):881-9. doi: 10.1354/vp.43-6-881.
The myosin heavy chain (MHC) composition of a given muscle determines the contractile properties and, therefore, the fiber type distribution of the muscle. MHC isoform expression in the laryngeal muscle is modulated by neural input and function, and it represents the cellular level changes that occur with denervation and reinnervation of skeletal muscle. The objective of this study was to evaluate the pattern of MHC isoform expression in laryngeal muscle harvested from normal cadavers and cadavers with naturally occurring left laryngeal hemiplegia secondary to recurrent laryngeal neuropathy. Left and right thyroarytenoideus (TA) and cricoarytenoideus dorsalis (CAD) were obtained from 7 horses affected with left-sided intrinsic laryngeal muscle atrophy and from 2 normal horses. Frozen sections were evaluated histologically for degree of atrophy and fiber type composition. MHC isoform expression was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of muscle protein. Histologic atrophy was seen in all atrophic muscles and some right-sided muscles of 3 affected horses, as well as the left TA of 1 normal horse. Fiber type grouping or loss of type I muscle fibers was observed in the left-sided laryngeal muscles in all but 1 affected horse, as well as in the right muscles of 2 affected horses, and the left TA of 1 normal horse. SDS-PAGE showed 2 bands corresponding to the type I and type IIB myosin isoforms in the CAD and TA of the 2 normal horses. Affected horses demonstrated a trend toward increased expression of the type IIB isoform and decreased expression of the type I isoform in atrophic muscles. This study confirmed the presence of histologic abnormalities in grossly normal equine laryngeal muscle, and it demonstrated an increased expression of type IIB MHC with a concurrent decreased expression of type I MHC in affected muscles. Evaluation of muscle fiber changes at the cellular level under denervated and reinnervated conditions may aid in assessing future strategies for reinnervation or regeneration of atrophic laryngeal muscle.
特定肌肉的肌球蛋白重链（MHC）组成决定了其收缩特性，进而决定了肌肉的纤维类型分布。喉肌中MHC同工型的表达受神经输入和功能的调节，它代表了骨骼肌去神经支配和重新神经支配时发生的细胞水平变化。本研究的目的是评估从正常尸体以及因喉返神经病变继发自然发生左侧喉偏瘫的尸体获取的喉肌中MHC同工型的表达模式。从7匹患有左侧喉内肌萎缩的马和2匹正常马获取左、右甲杓肌（TA）和环杓后肌（CAD）。对冰冻切片进行组织学评估，以确定萎缩程度和纤维类型组成。通过肌肉蛋白的十二烷基硫酸钠-聚丙烯酰胺凝胶电泳（SDS-PAGE）来确定MHC同工型的表达。在所有萎缩肌肉以及3匹患病马的一些右侧肌肉和1匹正常马的左侧TA中均观察到组织学萎缩。除1匹患病马外，在所有左侧喉肌以及2匹患病马的右侧肌肉和1匹正常马的左侧TA中均观察到纤维类型分组或I型肌纤维丢失。SDS-PAGE显示2匹正常马的CAD和TA中有对应于I型和IIB型肌球蛋白同工型的两条带。患病马在萎缩肌肉中呈现出IIB型同工型表达增加而I型同工型表达减少的趋势。本研究证实了大体正常的马喉肌中存在组织学异常，并且表明在患病肌肉中IIB型MHC表达增加，同时I型MHC表达减少。评估去神经支配和重新神经支配条件下细胞水平的肌纤维变化可能有助于评估未来萎缩喉肌重新神经支配或再生的策略。
