Journal
JOURNAL OF VETERINARY MEDICAL SCIENCE
Volume 83, Issue 11, Pages 1764-1771Publisher
JAPAN SOC VET SCI
DOI: 10.1292/jvms.21-0408
Keywords
3D reconstruction; mitochondria; slow-/fast-twitch muscle; ultrastructure; wooden breast syndrome
Categories
Funding
- Japan Society for the Promotion of Science [18K05941, 17K08067]
- Rakuno Gakuen University Research Fund [2021-04]
- Cooperative Study Program of the National Institute for Physiological Sciences
- Grants-in-Aid for Scientific Research [18K05941, 17K08067] Funding Source: KAKEN
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This study compared the mitochondrial properties of different muscle fiber types, revealing that slow-twitch and fast-twitch fibers have distinct mitochondrial structures to adapt to oxidative respiration and muscle damage requirements. The fast-twitch fibers in broiler chickens' pectoralis major muscles were found to have a low capacity for maintaining mitochondrial health.
Typical skeletal muscles are composed of mixed muscle fiber types, which are classified as slow-twitch (type I) and fast-twitch (type II) fibers, whereas pectoralis major muscles (PMs) in broiler chickens are 100% composed of type IIb fast-twitch fibers. Since metabolic properties differ among muscle fiber types, the combination of muscle fiber types is involved in physiological functions and pathological conditions in skeletal muscles. In this study, using serial block-face scanning electron microscopy, we compared three-dimensional (3D) mitochondrial properties in type IIb fibers in broiler PMs and those in type I fibers of broiler gastrocnemius muscles (GMs) heterogeneously composed of slow- and fast-twitch muscle fibers. In type I fibers in the GMs, elongated mitochondria with numerous interconnections to form a substantial network among myofibrils were observed. Along with lipid droplets sandwiched by mitochondria, these features are an adaptation to effective oxidative respiration and constant oxidative damage in slow-twitch muscle fibers. In contrast, type IIb fibers in the PMs showed small and ellipsoid-shaped mitochondria with few interconnections and no lipid droplets, forming a sparse network. The mitochondrial spatial network comprises of active mitochondrial dynamics to reduce mitochondrial damage; therefore, type IIb fibers possess physiologically low capacity to maintain mitochondrial wellness due to static mitochondrial dynamics. Based on 3D mitochondrial properties, we discussed the contrasting physiological functions between type I and IIb fibers and proposed a high contractile power and low stress resistance as unique physiological properties of broiler PMs.
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