Abstract
Differences in the protein composition of fast- and slow-twitch muscle may be maintained by different rates of protein turnover. We investigated protein turnover rates in slow-twitch soleus and fast-twitch plantaris of male Wistar rats (body weight 412 ± 69 g). Animals were assigned to four groups (n = 3, in each), including a control group (0 d) and three groups that received deuterium oxide (D2O) for either 10 days, 20 days or 30 days. D2O administration was initiated by an intraperitoneal injection of 20 μL of 99% D2O-saline per g body weight, and maintained by provision of 4% (v/v) D2O in the drinking water available ad libitum. Soluble proteins from harvested muscles were analysed by liquid chromatography–tandem mass spectrometry and identified against the SwissProt database. The enrichment of D2O and rate constant (k) of protein synthesis was calculated from the abundance of peptide mass isotopomers. The fractional synthesis rate (FSR) of 44 proteins in soleus and 34 proteins in plantaris spanned from 0.58%/day (CO1A1: Collagen alpha-1 chain) to 5.40%/day NDRG2 (N-myc downstream-regulated gene 2 protein). Eight out of 18 proteins identified in both muscles had a different FSR in soleus than in plantaris (p < 0.05).
Highlights
Skeletal muscle exhibits a broad phenotypic range depending on its anatomical location and function within each organism
The characteristic differences in protein abundance between fast- and slow-twitch muscle may be the result of differences in protein synthesis, which can be studied in vivo via biosynthetic labelling using radio- or stable-isotope-labelled amino acids
We reported the total proportion of protein synthesised after 14 days rather than rate constants of protein-specific synthesis
Summary
Skeletal muscle exhibits a broad phenotypic range depending on its anatomical location and function within each organism. Proteomes 2020, 8, 10 on this theme reported proteome profiles of single fibres extracted from human muscle classified by their dominant MyHC isoform [8] Such analyses provide the fundamental basis for physiological genomic studies aiming to establish links between the proteome and muscle function. The characteristic differences in protein abundance between fast- and slow-twitch muscle may be the result of differences in protein synthesis, which can be studied in vivo via biosynthetic labelling using radio- or stable-isotope-labelled amino acids. We aimed to verify differences in protein-specific FSR in slow and fast muscle using bottom-up proteomics and we performed semi-log plot analysis over a time series of peptide mass isotopomer data rather than MIDA calculations. Data were analysed by semi-log plot and peptides with poor fitting (R2 < 0.85) data were excluded from further analysis, consistent with our recent work [19]
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