Mitochondrial oxidative capacity and NAD+ biosynthesis are reduced in human sarcopenia across ethnicities

The causes of impaired skeletal muscle mass and strength during aging are well-studied in healthy populations. Less is known on pathological age-related muscle wasting and weakness termed sarcopenia, which directly impacts physical autonomy and survival. Here, we compare genome-wide transcriptional changes of sarcopenia versus age-matched controls in muscle biopsies from 119 older men from Singapore, Hertfordshire UK and Jamaica. Individuals with sarcopenia reproducibly demonstrate a prominent transcriptional signature of mitochondrial bioenergetic dysfunction in skeletal muscle, with low PGC-1α/ERRα signalling, and downregulation of oxidative phosphorylation and mitochondrial proteostasis genes. These changes translate functionally into fewer mitochondria, reduced mitochondrial respiratory complex expression and activity, and low NAD+ levels through perturbed NAD+ biosynthesis and salvage in sarcopenic muscle. We provide an integrated molecular profile of human sarcopenia across ethnicities, demonstrating a fundamental role of altered mitochondrial metabolism in the pathological loss of skeletal muscle mass and function in older people.

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Policy information about availability of computer code Data collection RNA seq and nanoString data were collected using the vendor's software Illumina HiSeq 2500 and nanoString nSolver version 3.

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All statistical analyses concerning RNA-seq data were conducted in R version 3.3.3 using relevant Bioconductor packages (e.g. limma 3.30.13, edgeR 3.16.5). Co-expression networks were defined using the WGCNA 1.51 package in R. Pathway enrichment analysis was performed using CAMERA querying gene sets annotated in MSigDB v5.2. Protein interaction networks were generated using STRING version 10 (http://string-db.org/). Functional enrichment analysis to decipher functionally grouped gene ontology and biological process using ClueGO. GraphPad Prism Software 7, Cytoscape version 3.5.1 were also used.
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April 2018
Data Policy information about availability of data All manuscripts must include a data availability statement. This statement should provide the following information, where applicable: -Accession codes, unique identifiers, or web links for publicly available datasets -A list of figures that have associated raw data -A description of any restrictions on data availability The unprocessed transcriptomic data of this study have been deposited in the Gene Expression Omnibus under accession numbers GSE111006, GSE111010, GSE111016 and integrated in the series GSE111017. Other datasets analysed during the current study are available from the corresponding authors on reasonable request. Due to ethical concerns, supporting clinical data cannot be made openly available. The MEMOSA team can provide the data on request subject to appropriate approvals, after a formal application to the Oversight Group of the different cohorts through their respective corresponding author.

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We Data exclusions 40 samples were analyzed in the Singapore and Hertfordshire sarcopenia studies (SSS and HSS) and 39 samples in the Jamaica sarcopenia study (JSS). One sample from SSS was excluded from RNA sequencing analyses as it did not reach the expecting sequencing depth of 35 millions of uniquely mapped paired reads and only remaining samples with sufficient muscle biopsy material were analyzed in the SSS mitochondrial validation assays (expression, activity and NAD).

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The RNAseq results from SSS were validated using Nanostring on the same samples. These results were further validated at a pathway level in two other collections of human muscle biopsies from HSS and JSS. Functional validation by measuring mitochondrial protein expression and mitochondrial complex activity was performed in the SSS.
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