Adipophilin distribution and colocalisation with lipid droplets in skeletal muscle
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Intramyocellular lipids (IMCL) are stored as discrete lipid droplets which are associated with a number of proteins. The lipid droplet-associated protein adipophilin (the human orthologue of adipose differentiation-related protein) is ubiquitously expressed and is one of the predominant lipid droplet-proteins in skeletal muscle. The aim of this study was to investigate the subcellular distribution of adipophilin in human muscle fibres and to measure the colocalisation of adipophilin with IMCL. Muscle biopsies from six lean male cyclists (BMI 23.4 ± 0.4, aged 31 ± 2 years, W max 346 ± 8) were stained for myosin heavy chain type 1, IMCL, adipophilin and mitochondria using immunofluorescence and viewed with widefield and confocal fluorescence microscopy. The present study shows that like IMCL, the adipophilin content is ~twofold greater in type I skeletal muscle fibres and is situated in the areas between the mitochondrial network. Colocalisation analysis demonstrated that 61 ± 2% of IMCL contain adipophilin. Although the majority of adipophilin is contained within IMCL, 36 ± 4% of adipophilin is not associated with IMCL. In conclusion, this study indicates that the IMCL pool is heterogenous, as the majority but not all IMCL contain adipophilin.
KeywordsAdipose-differentiation related protein (ADRP) Intramyocellular lipids (IMCL) PAT-proteins Fluorescence microscopy Skeletal muscle
The study was performed at the Wellcome Trust Clinical Research Facility, Queen Elizabeth Hospital, and we thank Heather Jones and Joanna Finney for nursing support during the study. The antibody against myosin (human slow fibres, A4.840) used in the study was developed by Dr. Blau and was obtained from the Developmental Studies Hybridoma Bank developed under the auspices of the NICHD and maintained by The University of Iowa, Department of Biological Sciences, Iowa City, IA 52242.
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