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Senolytics rescue blunted muscle hypertrophy in old mice

ABSTRACT: With aging, skeletal muscle plasticity is attenuated in response to exercise. Here, we report that senescent cells, identified using senescence markers senescence-associated β-Galactosidase (SA β-Gal) and p21 are very infrequent in resting muscle but emerge approximately two-weeks after a bout of resistance exercise in humans. We hypothesized that these cells contribute to blunted hypertrophic potential in old age. Using synergist ablation-induced mechanical overload of the plantaris muscle to model resistance training in adult (5-6 month) and old (23-24 month) male C57BL/6J mice, we found increased senescent cells in both age groups during hypertrophy. Consistent with the human data, there were negligible senescent cells in adult and old sham controls, but old mice had significantly more senescent cells 7- and 14-days following overload relative to young. Old mice had blunted whole muscle hypertrophy when compared to adult mice, along with smaller muscle fibers, specifically glycolytic Type 2x+2b fibers. To ablate senescent cells using a hit-and-run approach, old mice were treated with vehicle or a senolytic cocktail consisting of 5 mg/kg dasatinib and 50 mg/kg quercetin (D+Q) on day 7 and 10 during 14-days of overload; control mice underwent sham surgery with or without senolytic treatment. Old mice given D+Q had larger muscles and muscle fibers after 14 days of overload, fewer senescent cells when compared to vehicle-treated old mice, and changes in the expression of genes (i.e., Igf1, Ddit4, Mmp14) that are associated with hypertrophic growth . Our data collectively show that senescent cells emerge in human and mouse skeletal muscle following a hypertrophic stimulus, and that D+Q improves muscle growth in old mice.

ORGANISM(S): Mus musculus

PROVIDER: GSE195707 | GEO | 2022/05/29

REPOSITORIES: GEO

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Project description:Cellular senescence contributes to a variety of pathologies associated with aging and is implicated as a cellular state in which cancer cells can survive treatment. Reported senolytic drug treatments act through varying molecular mechanisms, but heterogeneous efficacy across the diverse contexts of cellular senescence indicates a need for predictive biomarkers of senolytic activity. Using multi-parametric analyses of commonly reported molecular features of the senescent phenotype, we assayed a variety of models, including malignant and nonmalignant cells, using several triggers of senescence induction and found no predictive power of these traditional senescence markers to identify senolytic drug sensitivity. We sought to identify novel drug targets in senescent cells that were insensitive to frequently implemented senolytic therapies, such as Navitoclax (ABT263), using quantitative mass spectrometry to measure changes in the senescent proteome, compared to cells which acquire an acute sensitivity to ABT263 with senescence induction. Inhibition of the antioxidant GPX4 or the Bcl-2 family member MCL-1 using small molecule compounds in combination with ABT263 significantly increased the induction of apoptosis in some, but not all, previously insensitive senescent cells. We then asked if we could use BH3 profiling to measure differences in mitochondrial apoptotic priming in these models of cellular senescence and predict sensitivity to the ABT263 or the combination of dasatinib and quercetin (D+Q). We found, despite being significantly less primed for apoptosis overall, the dependence of senescent mitochondria on BCL-xL was significantly correlated to senescent cell killing by both ABT263 and D+Q, despite no significant changes in the gene or protein expression of BCL-xL. However, our data caution against broad classification of drugs as globally senolytic and instead provide impetus for context-specific senolytic targets and propose BH3 profiling as an effective predictive biomarker.

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Senolytics rescue blunted muscle hypertrophy in old mice

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