title: Mouse soleus (slow) muscle shows greater intramyocellular lipid droplet accumulation than EDL (fast) muscle: fiber type-specific analysis.
abstract: Skeletal muscle is the main tissue of lipid metabolism and accordingly is critical for homeostasis and energy production; however, the determinants of lipid accumulation in skeletal muscle are unknown. Here, we examined whether the soleus muscle (predominantly slow-twitch fibers) has a higher lipid accumulation capacity than that of the extensor digitorum longus (EDL, predominantly fast-twitch fibers) muscle in mice. Soleus and EDL muscles were harvested from male C57BL/6J mice. The mRNA levels of genes involved in fatty acid import and triglyceride synthesis and accumulation were examined in soleus and EDL muscles. The intramyocellular lipid (IMCL) droplets of muscle cross sections and isolated single fibers were visualized by staining with BODIPY493/503, and fiber types were determined by immunofluorescent detection of myosin heavy chain (MyHC) isoforms. We detected higher mRNA expression of genes related to lipid accumulation in the soleus than the EDL. We also observed a marked increase of IMCL in single fibers from the soleus, but not the EDL, after treatment with a high-fat diet plus denervation. Interestingly, greater accumulation of IMCL droplets was observed in type 2A and 2X fibers (MyHC2A- and MyHC2X-positive fibers) than type 1 fibers (MyHC1-positive fibers) in soleus muscles. These results suggest that the soleus contains more IMCL owing to the higher population of type 2A fibers, and the difference in lipid accumulation between the soleus and EDL could depend on fiber type composition.
authors.affiliation: Department of Bioresource Sciences, Faculty of Agriculture, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan.|Department of Animal Science, School of Veterinary Medicine, Kitasato University, Towada, 034-8628, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Komiya
authors.affiliation: Department of Food Nutrition, Fukuoka Women's Junior College, Dazaifu, 818-0193, Japan.
authors.forename: Shoko
authors.initials: S
authors.lastname: Sawano
authors.affiliation: Department of Bioresource Sciences, Faculty of Agriculture, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Mashima
authors.affiliation: Department of Bioresource Sciences, Faculty of Agriculture, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan.
authors.forename: Riho
authors.initials: R
authors.lastname: Ichitsubo
authors.affiliation: Department of Bioresource Sciences, Faculty of Agriculture, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan.
authors.forename: Mako
authors.initials: M
authors.lastname: Nakamura
authors.affiliation: Department of Bioresource Sciences, Faculty of Agriculture, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan.
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Tatsumi
authors.affiliation: Department of Bioresource Sciences, Faculty of Agriculture, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan.
authors.forename: Yoshihide
authors.initials: Y
authors.lastname: Ikeuchi
authors.affiliation: Department of Bioresource Sciences, Faculty of Agriculture, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan. mizunoya.wataru.185@m.kyushu-u.ac.jp.
authors.forename: Wataru
authors.identifier: 0000-0002-2258-1964
authors.initials: W
authors.lastname: Mizunoya
mesh_terms: D000818:Animals; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism*; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*
keywords: Fast-twitch fiber; Intramyocellular lipid (IMCL); Muscle fiber type; Skeletal muscle; Slow-twitch fiber