Droplets of triglycerides and other lipid species stored within the cytoplasm of muscle fibers, specifically skeletal muscle cells. While a normal energy reserve for muscle contraction, excessive accumulation of these lipids is strongly correlated with impaired insulin signaling and the development of insulin resistance in muscle tissue. This accumulation serves as a significant biomarker and mechanistic link in the pathophysiology of type 2 diabetes.
Origin
The term is derived from its anatomical location: intra- (within), myo- (muscle), and cellular (cell), combined with lipids (fats). The clinical significance of these fat droplets became evident with the use of advanced magnetic resonance spectroscopy (MRS) techniques, which allowed for the non-invasive quantification of this specific fat depot. Research in metabolic endocrinology has focused on the role of this ectopic fat in systemic insulin resistance.
Mechanism
High levels of intramyocellular lipids lead to insulin resistance primarily through the accumulation of specific lipid metabolites, such as diacylglycerols and ceramides. These metabolites interfere with the insulin signaling cascade by activating various serine/threonine kinases, which in turn phosphorylate the insulin receptor substrate (IRS) proteins at inhibitory sites. This phosphorylation blocks the normal downstream signaling of the insulin receptor, preventing the translocation of GLUT4 transporters to the cell membrane and thereby impairing glucose uptake into the muscle cell.
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