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Comparison of murine masticatory and limb skeletal muscle

ABSTRACT: Distinctions between craniofacial and axial muscles exist from the onset of development and throughout adulthood. The masticatory muscles are a specialized group of craniofacial muscles that retain embryonic fiber properties throughout adulthood, suggesting that the developmental origin of these muscles may govern a pattern of expression that differs from limb muscles. To determine the extent of these differences, expression profiling of total RNA isolated from the masseter and tibialis anterior (TA) muscles of adult female mice was performed, which identified transcriptional changes in unanticipated functional classes of genes in addition to those associated with fiber type. In particular, the masseters displayed a reduction of transcripts associated with load-sensing and anabolic processes, and heightened expression of genes associated with stress. Consistent with these observations were a significantly smaller fiber cross-sectional area in masseters, significantly elevated load-sensing signaling (phosphorylated Focal Adhesion Kinase (FAK)), and increased apoptotic index in masseters compared to TA muscles. Based on these results, we hypothesize that masticatory muscles may sense and respond to load differently than limb muscles, where the drive for anabolic processes is reduced, and cell stress mediated processes are enhanced. These results establish a novel classification for the masseter muscle in the spectrum of skeletal muscle allotypes, and may provide insight into the molecular basis for specific muscle-related pathologies associated with masticatory muscles. Keywords: skeletal muscle, developmental origin, craniofacial muscles

ORGANISM(S): Mus musculus

PROVIDER: GSE11114 | GEO | 2008/05/09

SECONDARY ACCESSION(S): PRJNA107007

REPOSITORIES: GEO

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Project description:Purpose: Despite demonstrating that the overall effect of long-term rapamycin-treatment is overwhelmingly positive in aging skeletal muscle, we observed muscle-specificity in the responsiveness to rapamycin, leading us to hypothesize that the primary drivers of age-related muscle loss and therefore effective intervention strategies may differ between muscles. To address this question and dissect the key signaling nodes associated with mTORC1-driven muscle aging, we created a comprehensive multi-muscle gene expression atlas in adult, sarcopenic and rapamycin-treated mice using RNA-seq. Methods: To examine the impact of long-term rapamycin treatment, male C57BL/6 mice were fed encapsulated rapamycin incorporated into a standardized AIN93M diet at 42 ppm (i.e. mg per kg of food), corresponding to a dose of ~4 mg·kg-1·day-1, from 15- to 30-months of age. This dose of rapamycin has been shown to extend lifespan maximally in male C57BL/6 mice. We performed RNA-seq on gastrocnemius (GAS), tibialis anterior (TA), triceps brachii (TRI) and soleus (SOL) muscles from each of six mice for 10m, 30m and 30mRM groups. The four muscle types were chosen to encompass fore- and hindlimb locations (e.g. TRI and GAS); slow and fast contraction properties (e.g. SOL and GAS); anterior and posterior positioning (e.g. TA and GAS) and the extent of protection by rapamycin (TA and TRI: protected; SOL: partiallly protected; GAS: not protected). Results: Age-related gene expression changes were remarkably consistent across the four different muscles, varying only in magnitude. Despite having the smallest age-related muscle loss of the four muscles, TA had the strongest age-related gene expression response which was associated with an increased reinnervation response. Despite the strong between-muscle commonality of age-related changes, gene expression responses to prolonged rapamycin treatment differed substantially between muscles. Rapamycin partially reversed many age-related changes in mRNA expression in the TA and TRI, but not in SOL or GAS muscle. Principle component analysis (PCA) showed that rapamycin had common 'anti-aging' effects on all muscles, while also exerting muscle-specific pro-aging effects on muscles not protected by rapamycin. Conclusions: Sustained, muscle fiber-specific mTORC1 activity drives sarcopenia-like gene expression programs, and the hyperactive mTORC1 seen in sarcopenic muscle may therefore contribute to sarcopenia.

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Comparison of murine masticatory and limb skeletal muscle

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