Project description:Our study aimed to characterize sarcopenia in C57BL/6J mice using a clinically relevant definition and age range and investigate the underlying mechanisms leading to sarcopenia. Aged male C57BL/6J mice (23-32 months) were classified as non-sarcopenic (no deficit), probable sarcopenic (1 deficit), and sarcopenic (2-3 deficits) based on assessments of grip strength, muscle mass, and treadmill running time and using 2 standard deviations below the mean of the young (4-9 months) as cut-off points. A 9-22% prevalence of sarcopenia was identified in 23-26-month-old mice. Age-related declines in muscle function were more severe than in muscle mass and outcomes of all three assessments were positively correlated in aged mice. As sarcopenia progressed, there were decreases in specific force as well as fiber size and number of IIB skeletal muscle fibers. Mitochondrial biogenesis, oxidative capacity, and AMPK-autophagy signaling decreased significantly while no increase in atrogenes was detected. Our study is the first to characterize sarcopenia in C57BL/6J mice using a clinically relevant definition and highlights the different trajectories of age-related declines in muscle mass and function. These critical insights into the molecular changes associated with sarcopenia progression will facilitate future development of therapeutic interventions.
Project description:We investigated age-related changes in the transcriptional profile of skeletal muscle in 5 month old (young) and 25 month old (old) C57BL/6NHsd mice using high density oligonucleotide arrays (22,690 transcripts probed). We identified 712 transcripts that are differentially expressed in young (5 month old) and old (25-month old) mouse skeletal muscle. Caloric restriction (CR) completely or partially reversed 87% of the changes in expression. Examination of individual genes revealed a transcriptional profile indicative of increased p53 activity in the older muscle. To determine whether the increase in p53 activity is associated with transcriptional activation of apoptotic targets, we performed RT-PCR on four well known mediators of p53-induced apoptosis: puma, noxa, tnfrsf10b and bok. Expression levels for these proapoptotic genes increased significantly with age (P<0.05), while CR significantly lowered expression levels for these genes as compared to control fed old mice (P<0.05). Age-related induction of p53-related genes was observed in multiple tissues, but was not observed in SOD2+/- and GPX4+/- mice, suggesting that oxidative stress does not mediate the observed age-related increase in expression. Western blot analysis confirmed that protein levels for both p21 and GADD45a, two established transcriptional targets of p53, were higher in the older muscle tissue. These observations support a role for p53-mediated apoptotic activity in mammalian aging. Keywords: aging, calorie restriction, muscle, p53
Project description:We report RNA-seq of skeletal muscle (quadriceps) of young (6-month), old (24-month), and senolytic (Dasatinib + quercetin) treated mice
Project description:Transcriptional profiling of mouse Extensior Digitorum Longus muscle comparing control Wilde type (WT) C57BL/6J, 4 month old female with Calsequestrin 1-null muscles of the same age and gender without any treatment
Project description:Aging is associated with systemic chronic inflammation (inflammaging) that leads to impaired physiological functions and vulnerability to several diseases. However, underlying alterations in aged immune system resulting in gradual loss of immune fitness remain unclear. Using a combination of CD8 T cell transfer from young to old and from old to young mice and single-cell RNA sequencing, we characterized the age-associated alterations in CD8 T cells. We transferred 2 millions of purified CD8+ T cells pooled from 3 CD45.1 C57BL/6J 3 months old female mice (donor) by i.v. injection into CD45.2 C57BL/6J 24 months old female mouse (recipient) and sorted CD45.1+CD3e+CD8a+ and CD45.2+CD3e+CD8a+ T cells from the spleen 1 month post transfer to perform scRNA/TCR-seq.
Project description: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.
Project description:Pofut1 is an essential gene that glycosylates proteins containing EGF-like repeats, including Notch Receptors (NotchRs). Work in mice and in Drosophila has shown that O-fucosylation by Pofut1 is required for NotchR ligands to bind to and activate NotchRs. As such, Pofut1 deletion in skeletal myofibers allows for an analysis of potential functions and molecular changes of Pofut1 in skeletal muscle that derive from its expression in skeletal myofibers. In this study we compared gene expression profiles between quadriceps muscles in young (2 month) and old (17 month) mice where Protein O-fucosyltransferase 1 (Pofut1) was deleted specifically in skeletal myofibers via use of a human skeletal alpha actin Cre transgene (Scre) and a loxP flanked Pofut1 gene (SCreFF) and mice which bore the only the Scre transgene but did not have floxed Pofut1 alleles (SCre++).
Project description:Utilizing glycerol intramuscular injections in M. musculus provide a models of skeletal muscle damage followed by skeletal muscle regeneration. In particular, glycerol-induced muscle injury triggers accute activation of skeletal muscle stem cells, called satellite cells. However, aging dramatically impairs the regenerative capacity of satellite cells. We characterized genome-wide expression profiles of young and old satellite cells in the non-proliferative and activated state, freshly isolated to non-injured or damaged muscles, respectively. Our goal was to uncover new regulatory signaling specific to satellite cells entry into the activation and myogenic program that are affected with age. Satellite cells were isolated in either quiescent / non-proliferative or activated state from uninjured or 3 days after glycerol-induced injury of tibialis anterior, gastrocnemius and quadriceps, respectively. Young (2-4 months old) and old (20-24 months old) wildtype C57BL/6J male were used, with five to six biological replicates per group.
Project description:We subjected old (21-22 month) and young (3-4 month) male C57BL/6 mice to 45 min transient oclusion of the middle cerebral artery and obtained the brain four days later. We obtained bodipy+ microglia from the ischemic brain tissue by FACS.