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Caloric restriction combined with immobilization as translational model for sarcopenia expressing key-pathways of human pathology

ABSTRACT: Abstract Background: The prevalence of sarcopenia is increasing and effective interventions are required to prevent or reverse age-related muscle loss. However it is often challenging expensive and time-consuming to develop and test the effectiveness of such interventions. Furthermore translational animal models that adequately mimic underlying physiological pathways are scarce. Strong predictors for the incidence of sarcopenia include a sedentary life-style and malnutrition. Therefore our objective was to investigate the translational value of three potential mouse models for sarcopenia namely partial immobilized caloric restricted (CR) and a combination (immobilized & CR) model. Methods: C57BL/6J mice were calorically restricted (-40%) and/or one hindleg was immobilized for two weeks to induce loss of muscle mass and function. Muscle mass function and diameter and distribution of slow (type 1) and fast ( type 2) myofibers were compared to those of young control (4 months) and old reference mice (21 months). Transcriptome analysis of quadriceps muscle was performed to identify underlying pathways and were compared with those being expressed in aged human vastus lateralis muscle-biopsies using a meta-analysis of five different human studies. Results: Caloric restriction induced overall loss of lean body mass (-15% p<0.001) whereas immobilization decreased muscle strength (-28% p<0.001) and muscle mass of hindleg muscles specifically (on average -25% p<0.001). The proportion of slow myofibers increased with aging in mice (+5% p<0.05) and this was not recapitulated by the CR and/or immobilization models. The diameter of fast myofibers decreased with aging (-7% p<0.05) and this was mimicked by all models. Transcriptome analysis revealed that the combination of CR and immobilization recapitulated more pathways characteristic for human muscle-aging (73%) than naturally aged (21 months old) mice (45%). These pathways included critical pathways relevant for protein synthesis/ breakdown (mitochondrial) metabolism neurology and the vascular system. Conclusions: The combination model exhibits loss of both muscle mass (due to CR) and function (due to immobilization) and has a remarkable similarity with pathways underlying human sarcopenia. Our results demonstrate that naturally aging up to 21 months in mice only partially recapitulates the human pathology with fewer overlapping pathways than the combination model. These findings underline that external factors such as sedentary behavior and malnutrition are key elements of a translational mouse model and favor the combination model as a rapid model for testing the treatments against sarcopenia.

ORGANISM(S): Mus musculus

PROVIDER: GSE213148 | GEO | 2022/12/16

REPOSITORIES: GEO

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Project description:Mitochondrial dysfunction caused by mitochondrial (mtDNA) deletions have been associated with skeletal muscle atrophy and myofiber loss. However, whether such defects occurring in myofibers cause sarcopenia is unclear. Also, the contribution of mtDNA alterations in muscle stem cells (MuSCs) to sarcopenia remain to be investigated. We expressed a dominant-negative variant of the mitochondrial helicase, which induces mtDNA alterations, specifically in differentiated myofibers (K320Eskm mice) and MuSCs (K320Emsc mice), respectively, and investigated their impact on muscle structure and function by immunohistochemistry, analysis of mtDNA and respiratory chain content, muscle transcriptome and functional tests. K320Eskm mice at 24 months of age had higher levels of mtDNA deletions compared to controls in soleus (SOL, 0.07673 % vs 0.00015 %, p=0.0167), extensor digitorium longi (EDL, 0.0649 vs 0.000925, p= 0.0015) and gastrocnemius (GAS, 0.09353 vs 0.000425, p=0.0004). K320Eskm mice revealed a progressive increase in the proportion of cytochrome c oxidase deficient fibers (COX-) in cross sections, reaching a maximum of 3.03%, 4.36%, 13.58% and 17.08% in EDL, SOL, tibialis anterior (TA) and GAS, respectively. However, mice did not show accelerated loss of muscle mass, muscle strength or physical performance. Histological analyses revealed ragged red fibers but also stimulated regeneration, indicating activation of MuSCs. RNAseq demonstrated enhanced expression of genes associated with protein synthesis, but also degradation, as well as muscle fiber differentiation and cell proliferation. In contrast, 7 days after destruction by cardiotoxin, regenerating TA of K320Emsc mice showed 30% of COX- fibers. Notably, regenerated muscle showed dystrophic changes, increased fibrosis (2.5% vs 1.6%, p=0.0003), increased abundance of fat cells (2.76% vs 0.23%, p=0.0144) and reduced muscle mass (regenerated TA: 40.0mg vs 60.2mg, p=0.0171). In contrast to muscles from K320Eskm mice, freshly isolated MuSCs from aged K320Emsc mice were completely devoid of mtDNA alterations. However, after passaging, mtDNA copy number as well as respiratory chain subunits and p62 levels gradually decreased.Taken together, accumulation of large-scale mtDNA alterations in myofibers alone is not sufficient to cause sarcopenia. Expression of K320E is tolerated in quiescent MuSCs, but progressively leads to mtDNA and respiratory chain depletion upon activation, in vivo and in vitro, possibly caused by an increased mitochondrial removal. Altogether, our results suggest that the accumulation of mtDNA alterations in myofibers activates regeneration during aging, which leads to sarcopenia if such alterations have expanded in MuSCs as well.

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Caloric restriction combined with immobilization as translational model for sarcopenia expressing key-pathways of human pathology

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