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Abstract
ABSTRACTProlonged high-fat diets (HFDs) can cause intramyocellular lipid (IMCL) accumulation that may negatively affect muscle function. We investigated the duration of a HFD required to instigate these changes, and whether the effects are muscle specific and aggravated in older age. Muscle morphology was determined in the soleus, extensor digitorum longus (EDL) and diaphragm muscles of female CD-1 mice from 5 groups: young fed a HFD for 8 weeks (YS-HFD, n=16), young fed a HFD for 16 weeks (YL-HFD, n=28) and young control (Y-Con, n=28). The young animals were 20 weeks old at the end of the experiment. Old (70 weeks) female CD-1 mice received either a normal diet (O-Con, n=30) or a HFD for 9 weeks (OS-HFD, n=30). Body mass, body mass index and intramyocellular lipid (IMCL) content increased in OS-HFD (P≤0.003). In the young mice, this increase was seen in YL-HFD and not YS-HFD (P≤0.006). The soleus and diaphragm fibre cross-sectional area (FCSA) in YL-HFD was larger than that in Y-Con (P≤0.004) while OS-HFD had a larger soleus FCSA compared with that of O-Con after only 9 weeks on a HFD (P<0.001). The FCSA of the EDL muscle did not differ significantly between groups. The oxidative capacity of fibres increased in young mice only, irrespective of HFD duration (P<0.001). High-fat diet-induced morphological changes occurred earlier in the old animals than in the young, and adaptations to HFD were muscle specific, with the EDL being least responsive.
Highlights
More than 1.9 billion adults over the age of 18 are overweight or obese (WHO, 2018)
The 79 week old female mice are a model of early ageing, where survival is 50% (Navarro et al, 2002) and the muscles show morphological changes suggestive of early ageing (Messa et al, 2019), further supported by a significant decline in soleus and extensor digitorum longus (EDL) specific tension and specific power compared with 10 week old animals (Hill et al, 2018)
In the present study, we evaluated whether morphological changes induced by a high-fat diets (HFDs) differed between the soleus, EDL and diaphragm and whether the adaptations differed between young-adult (20 weeks) and old mice (79 weeks)
Summary
More than 1.9 billion adults (approximately 24.6% of the world’s population) over the age of 18 are overweight or obese (WHO, 2018). Under obesogenic conditions, such as excessive and prolonged consumption of high-fat diets (HFDs), energy intake exceeds. In addition to the negative effects of systemic inflammation and insulin resistance associated with obesity (Cesari et al, 2005) on myogenesis and muscle function, muscular lipid accumulation itself can compromise excitation–contraction coupling, metabolism and contractile function of skeletal muscle (Bonen et al, 2015; Choi et al, 2016; Hancock et al, 2008; Montgomery et al, 2017; Tallis et al, 2018). It has been reported that the age-related loss of muscle strength is greater in obese than in non-obese women (Tomlinson et al, 2014)
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