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Many different tissues and cell types exhibit regulated secretion of lipoprotein lipase (LPL). However, the sorting of LPL in the trans Golgi network has not, hitherto, been understood in detail. Here, we characterize the role of SorLA (officially known as SorLA-1 or sortilin-related receptor) in the intracellular trafficking of LPL. We found that LPL bound to SorLA under neutral and acidic conditions, and in cells this binding mainly occurred in vesicular structures. SorLA expression changed the subcellular distribution of LPL so it became more concentrated in endosomes. From the endosomes, LPL was further routed to the lysosomes, which resulted in a degradation of newly synthesized LPL. Consequently, an 80% reduction of LPL activity was observed in cells that expressed SorLA. By analogy, SorLA regulated the vesicle-like localization of LPL in primary neuronal cells. Thus, LPL binds to SorLA in the biosynthetic pathway and is subsequently transported to endosomes. As a result of this SorLA mediated-transport, newly synthesized LPL can be routed into specialized vesicles and eventually sent to degradation, and its activity thereby regulated.

Metabolically healthy skeletal muscle is characterized by the ability to switch easily between glucose and fat oxidation, whereas loss of this ability seems to be related to insulin resistance. The aim of this study was to investigate whether different fatty acids (FAs) and the LXR ligand T0901317 affected metabolic switching in human skeletal muscle cells (myotubes). Pretreatment of myotubes with eicosapentaenoic acid (EPA) increased suppressibility, the ability of glucose to suppress FA oxidation, and metabolic flexibility, the ability to increase FA oxidation when changing from “fed” to “fasted” state. Adaptability, the capacity to increase FA oxidation with increasing FA availability, was increased after pretreatment with EPA, linoleic acid (LA) and palmitic acid (PA). T0901317 counteracted the effect of EPA on suppressibility and adaptability, but did not affect these parameters alone. EPA itself accumulated less, however, EPA, LA, OA and T0901317 increased the number of lipid droplets (LDs) in myotubes, whereas LD size and mitochondria amount were independent of pretreatment. Microarray analysis showed that EPA regulated more genes than the other FAs. Some pathways involved in carbohydrate metabolism were induced only by EPA. The present study suggests a possible favorable effect of EPA on skeletal muscle metabolic switching and glucose utilization., Metabolically healthy skeletal muscle is characterized by the ability to switch easily between glucose and fat oxidation, whereas loss of this ability seems to be related to insulin resistance. The aim of this study was to investigate whether different fatty acids (FAs) and the LXR ligand T0901317 affected metabolic switching in human skeletal muscle cells (myotubes). Pretreatment of myotubes with eicosapentaenoic acid (EPA) increased suppressibility, the ability of glucose to suppress FA oxidation, and metabolic flexibility, the ability to increase FA oxidation when changing from “fed” to “fasted” state. Adaptability, the capacity to increase FA oxidation with increasing FA availability, was increased after pretreatment with EPA, linoleic acid (LA) and palmitic acid (PA). T0901317 counteracted the effect of EPA on suppressibility and adaptability, but did not affect these parameters alone. EPA itself accumulated less, however, EPA, LA, OA and T0901317 increased the number of lipid droplets (LDs) in myotubes, whereas LD size and mitochondria amount were independent of pretreatment. Microarray analysis showed that EPA regulated more genes than the other FAs. Some pathways involved in carbohydrate metabolism were induced only by EPA. The present study suggests a possible favorable effect of EPA on skeletal muscle metabolic switching and glucose utilization.