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Molecular mechanisms behind the accumulation of lipid that occurs after skeletal muscle injury
Author(s) -
Gumucio Jonathan,
Rittman Danielle,
McDonagh Brian,
Mendias Christopher
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1244.8
Subject(s) - skeletal muscle , lipid metabolism , sarcomere , lipidomics , lipid droplet , microbiology and biotechnology , mitochondrion , biology , chemistry , biochemistry , medicine , endocrinology , myocyte
Myosteatosis is the accumulation of lipid that occurs after skeletal muscle injury or in certain chronic neuromuscular or metabolic diseases. Muscle fiber atrophy and fibrosis often accompany myosteatosis. The amount of lipid accumulation is negatively correlated with skeletal muscle functional capacity, but the causes of myosteatosis are unknown. To gain a greater understanding of the ontogeny of myosteatosis, we induced a severe injury to the rotator cuff musculature in rats, isolated tissues 10, 30 or 60 days after tear, and used a combination of RNA sequencing and shotgun lipidomics to identify global changes in gene expression and lipid content in injured muscles. The RNA sequencing data and shotgun lipidomics results were then analyzed by Ingenuity Pathway Analysis (IPA, Qiagen) software to determine the biochemical pathways involved in myosteatosis. Samples were also prepared for electron microscopy and single muscle fiber contractility. Following muscle injury, there was a time dependent increase in total lipid content, largely due to a dramatic rise in triacylglyceride species. Interestingly, genes related to lipid synthesis (DGAT1, DGAT2) and lipid breakdown (LPL, HSL) were largely downregulated over time. IPA of RNASeq data predicted increased mitochondrial dysfunction and oxidative stress, and decreased lipid oxidation to be highly associated with myosteatosis at all time points. Genes related to lipid utilization and mitochondrial function (CPT1/2, SDH, COXIV) were also decreased with time. From electron micrographs, there was increased subsarcolemmal mitochondria at all time points after injury and dramatic sarcomere streaming at 30d and 60d compared to controls. Additionally, there was an increase in carbonylated proteins at 60d. At 30 and 60d, IPA predicted increased inflammatory pathways in chronically torn rotator cuff muscles compared to controls, and there was an overall increase in inflammatory gene markers (IL6, IL1b, COX1) at all time points. These changes corresponded to a time dependent decrease in muscle fiber specific force production, or muscle fiber maximum isometric force normalized to cross sectional area. Combined, these data suggest that the accumulation of lipid that occurs after muscle injury is likely due to a decrease in lipid utilization and breakdown rather than an increase in lipid synthesis. Sustained mitochondrial dysfunction and oxidative stress may result in the increased lipid infiltration and atrophy of muscle fibers over time. While further investigation is necessary, this study provided important insight into the development of myosteatosis and identifying potential therapeutic targets to improve muscle regeneration. Support or Funding Information This work was supported by NIH grants (R01AR063649 and F31AR065931)