Composition of Muscle Fiber Types in Rat Rotator Cuff Muscles

Abstract

The rat is a suitable model to study human rotator cuff pathology owing to the similarities in morphological anatomy structure. However, few studies have reported the composition muscle fiber types of rotator cuff muscles in the rat. In this study, the myosin heavy chain (MyHC) isoforms were stained by immunofluorescence to show the muscle fiber types composition and distribution in rotator cuff muscles of the rat. It was found that rotator cuff muscles in the rat were of mixed fiber type composition. The majority of rotator cuff fibers labeled positively for MyHCII. Moreover, the rat rotator cuff muscles contained hybrid fibers. So, compared with human rotator cuff muscles composed partly of slow-twitch fibers, the majority of fast-twitch fibers in rat rotator cuff muscles should be considered when the rat model study focus on the pathological process of rotator cuff muscles after injury. Gaining greater insight into muscle fiber types in rotator cuff muscles of the rat may contribute to elucidate the mechanism of pathological change in rotator cuff muscles-related diseases. Anat Rec, 299:1397-1401, 2016. © 2016 Wiley Periodicals, Inc.

Progression of muscle loss and fat accumulation in a rabbit model of rotator cuff tear

“…In contrast, a rabbit RC model using the subscapularis muscle found no difference in MHC isoform composition after partial or complete tear creation, nor after denervation 33 . Furthermore, intact rat RC muscles are composed of less than 10% type I MHC, emphasizing that the shoulder musculature in this rodent model has a nearly completely fast‐twitch functionality that differs from human subjects 38 …”

“…33 Furthermore, intact rat RC muscles are composed of less than 10% type I MHC, emphasizing that the shoulder musculature in this rodent model has a nearly completely fast-twitch functionality that differs from human subjects. 38 Our evolving understanding of human RC pathophysiology also prompted the investigation of muscle degeneration as a separate finding from muscle atrophy. Whereas atrophy induced by unloading or inactivity can be nearly reversible with reloading, [39][40][41][42] muscle degeneration in the context of chronic human RC disease is a process of irreversible muscle damage and cell death.…”

Injection of Micronized Human Amnion/Chorion Membrane Results in Increased Early Supraspinatus Muscle Regeneration in a Chronic Model of Rotator Cuff Tear

“…S4 and supplemental text for details) are likely due to factors not related to muscle healing, such as the observed increase in use of the opposing uninjured limb. Perhaps increased use of the uninjured contralateral limb led to fiber type switching 2,43 , in which primarily larger, fast twitch fibers of the rat rotator cuff muscles 49 transitioned to smaller, slow twitch fibers.…”

Tenotomy-induced muscle atrophy is sex-specific and independent of NFκB

“…Under this assumption, the mass loss in a fiber (Δ m ) resulting from a decrease in fiber length (Δ FL ) and decrease in fiber CSA (Δ F CSA ) was calculated by multiplying the two and the density of muscle, ρ (Ward & Lieber, 2005). Then, the mass loss in the muscle was calculated by multiplying the mass loss in individual fiber types by the relative fraction of each fiber type (Rui et al ., 2016) and the decrease in fiber number (ΔFN), according to Equation 1. This equation assumes that the density of muscle and the relative fraction of each fiber type is unchanged following tenotomy.…”