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.
Keywords Adipose-differentiation related protein (ADRP) - Intramyocellular lipids (IMCL) - PAT-proteins - Fluorescence microscopy - Skeletal muscle