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Long ‐ term, but not short ‐ term high ‐ fat diet induces fiber composition changes and impaired contractile force in mouse fast ‐ twitch skeletal muscle

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ABSTRACT

In this study, we investigated the effects of a short‐term and long‐term high‐fat diet (HFD) on morphological and functional features of fast‐twitch skeletal muscle. Male C57BL/6J mice were fed a HFD (60% fat) for 4 weeks (4‐week HFD) or 12 weeks (12‐week HFD). Subsequently, the fast‐twitch extensor digitorum longus muscle was isolated, and the composition of muscle fiber type, expression levels of proteins involved in muscle contraction, and force production on electrical stimulation were analyzed. The 12‐week HFD, but not the 4‐week HFD, resulted in a decreased muscle tetanic force on 100 Hz stimulation compared with control (5.1 ± 1.4 N/g in the 12‐week HFD vs. 7.5 ± 1.7 N/g in the control group; P < 0.05), whereas muscle weight and cross‐sectional area were not altered after both HFD protocols. Morphological analysis indicated that the percentage of type IIx myosin heavy chain fibers, mitochondrial oxidative enzyme activity, and intramyocellular lipid levels increased in the 12‐week HFD group, but not in the 4‐week HFD group, compared with controls (P < 0.05). No changes in the expression levels of calcium handling‐related proteins and myofibrillar proteins (myosin heavy chain and actin) were detected in the HFD models, whereas fast‐troponin T‐protein expression was decreased in the 12‐week HFD group, but not in the 4‐week HFD group (P < 0.05). These findings indicate that a long‐term HFD, but not a short‐term HFD, impairs contractile force in fast‐twitch muscle fibers. Given that skeletal muscle strength largely depends on muscle fiber type, the impaired muscle contractile force by a HFD might result from morphological changes of fiber type composition.

No MeSH data available.


Morphometric changes of muscles after a high‐fat diet. Composition (A and B), cross‐sectional area (C and D), succinate dehydrogenase (SDH) activity (E and F), and intramyocellular lipid levels determined by Oil Red O staining (G and H) of extensor digitorum longus muscles in control mice (CONT) and high‐fat diet‐fed mice (HFD; left: 4 weeks; right: 12 weeks). succinate dehydrogenase (SDH) and Oil Red O staining are graphically represented by arbitrary units of optical density (O.D.), with higher values representing more intense staining, normalized to a percentage of the overall mean control value for each graph (% of CONT). Values are means ± SE (n = 3–7). *Significant difference between CONT and HFD groups (P < 0.05).
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phy213250-fig-0004: Morphometric changes of muscles after a high‐fat diet. Composition (A and B), cross‐sectional area (C and D), succinate dehydrogenase (SDH) activity (E and F), and intramyocellular lipid levels determined by Oil Red O staining (G and H) of extensor digitorum longus muscles in control mice (CONT) and high‐fat diet‐fed mice (HFD; left: 4 weeks; right: 12 weeks). succinate dehydrogenase (SDH) and Oil Red O staining are graphically represented by arbitrary units of optical density (O.D.), with higher values representing more intense staining, normalized to a percentage of the overall mean control value for each graph (% of CONT). Values are means ± SE (n = 3–7). *Significant difference between CONT and HFD groups (P < 0.05).

Mentions: In EDL muscles from the 12‐week HFD group, but not the 4‐week HFD group, there was an increased percentage of MHC type IIa/x fibers, mainly at the expense of decreased type IIb fibers, compared with those from the CONT group (Fig. 4, A and B), whereas total cross‐sectional areas were unchanged in both HFD groups (Fig. 4, C and D). SDH activity was unchanged in the 4‐week HFD group (108.8 ± 8.8 O.D. in the 4‐week HFD vs 98.9 ± 3.4 O.D. in the CONT group; P > 0.05; Fig. 4E), but the 12‐week HFD group showed evidence of significantly increased SDH activity in total fiber analysis (P > 0.05; Fig. 4F). Furthermore, in the 12‐week HFD, but not in the 4‐week HFD group (P < 0.05; Fig. 4G), increased IMCL levels were observed in all type II fiber types compared with the CONT group (P < 0.05; Fig. 4H).


Long ‐ term, but not short ‐ term high ‐ fat diet induces fiber composition changes and impaired contractile force in mouse fast ‐ twitch skeletal muscle
Morphometric changes of muscles after a high‐fat diet. Composition (A and B), cross‐sectional area (C and D), succinate dehydrogenase (SDH) activity (E and F), and intramyocellular lipid levels determined by Oil Red O staining (G and H) of extensor digitorum longus muscles in control mice (CONT) and high‐fat diet‐fed mice (HFD; left: 4 weeks; right: 12 weeks). succinate dehydrogenase (SDH) and Oil Red O staining are graphically represented by arbitrary units of optical density (O.D.), with higher values representing more intense staining, normalized to a percentage of the overall mean control value for each graph (% of CONT). Values are means ± SE (n = 3–7). *Significant difference between CONT and HFD groups (P < 0.05).
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phy213250-fig-0004: Morphometric changes of muscles after a high‐fat diet. Composition (A and B), cross‐sectional area (C and D), succinate dehydrogenase (SDH) activity (E and F), and intramyocellular lipid levels determined by Oil Red O staining (G and H) of extensor digitorum longus muscles in control mice (CONT) and high‐fat diet‐fed mice (HFD; left: 4 weeks; right: 12 weeks). succinate dehydrogenase (SDH) and Oil Red O staining are graphically represented by arbitrary units of optical density (O.D.), with higher values representing more intense staining, normalized to a percentage of the overall mean control value for each graph (% of CONT). Values are means ± SE (n = 3–7). *Significant difference between CONT and HFD groups (P < 0.05).
Mentions: In EDL muscles from the 12‐week HFD group, but not the 4‐week HFD group, there was an increased percentage of MHC type IIa/x fibers, mainly at the expense of decreased type IIb fibers, compared with those from the CONT group (Fig. 4, A and B), whereas total cross‐sectional areas were unchanged in both HFD groups (Fig. 4, C and D). SDH activity was unchanged in the 4‐week HFD group (108.8 ± 8.8 O.D. in the 4‐week HFD vs 98.9 ± 3.4 O.D. in the CONT group; P > 0.05; Fig. 4E), but the 12‐week HFD group showed evidence of significantly increased SDH activity in total fiber analysis (P > 0.05; Fig. 4F). Furthermore, in the 12‐week HFD, but not in the 4‐week HFD group (P < 0.05; Fig. 4G), increased IMCL levels were observed in all type II fiber types compared with the CONT group (P < 0.05; Fig. 4H).

View Article: PubMed Central - PubMed

ABSTRACT

In this study, we investigated the effects of a short&#8208;term and long&#8208;term high&#8208;fat diet (HFD) on morphological and functional features of fast&#8208;twitch skeletal muscle. Male C57BL/6J mice were fed a HFD (60% fat) for 4&nbsp;weeks (4&#8208;week HFD) or 12&nbsp;weeks (12&#8208;week HFD). Subsequently, the fast&#8208;twitch extensor digitorum longus muscle was isolated, and the composition of muscle fiber type, expression levels of proteins involved in muscle contraction, and force production on electrical stimulation were analyzed. The 12&#8208;week HFD, but not the 4&#8208;week HFD, resulted in a decreased muscle tetanic force on 100&nbsp;Hz stimulation compared with control (5.1&nbsp;&plusmn;&nbsp;1.4&nbsp;N/g in the 12&#8208;week HFD vs. 7.5&nbsp;&plusmn;&nbsp;1.7&nbsp;N/g in the control group; P&nbsp;&lt;&nbsp;0.05), whereas muscle weight and cross&#8208;sectional area were not altered after both HFD protocols. Morphological analysis indicated that the percentage of type IIx myosin heavy chain fibers, mitochondrial oxidative enzyme activity, and intramyocellular lipid levels increased in the 12&#8208;week HFD group, but not in the 4&#8208;week HFD group, compared with controls (P&nbsp;&lt;&nbsp;0.05). No changes in the expression levels of calcium handling&#8208;related proteins and myofibrillar proteins (myosin heavy chain and actin) were detected in the HFD models, whereas fast&#8208;troponin T&#8208;protein expression was decreased in the 12&#8208;week HFD group, but not in the 4&#8208;week HFD group (P&nbsp;&lt;&nbsp;0.05). These findings indicate that a long&#8208;term HFD, but not a short&#8208;term HFD, impairs contractile force in fast&#8208;twitch muscle fibers. Given that skeletal muscle strength largely depends on muscle fiber type, the impaired muscle contractile force by a HFD might result from morphological changes of fiber type composition.

No MeSH data available.