Training alters the distribution of perilipin proteins in muscle following acute free fatty acid exposure
Because the lipid droplet (LD)-associated perilipin (PLIN) proteins promote intramuscular triglyceride (IMTG) storage, we investigated the hypothesis that differential protein content of PLINs and their distribution with LDs may be linked to the diverse lipid storage in muscle between trained and sedentary individuals. Trained (n = 11) and sedentary (n = 10) subjects, matched for age, sex and body mass index, received either a 6 h lipid or glycerol infusion in the setting of a concurrent hyperinsulinaemic–euglycaemic clamp. Sequential muscle biopsies (0, 2 and 6 h) were analysed using confocal immunofluorescence microscopy for fibre type-specific IMTG content and PLIN associations with LDs. In both groups, lipid infusion increased IMTG content in type I fibres (trained: +62%, sedentary: +79%; P < 0.05) but did not affect PLIN protein content. At baseline, PLIN2 (+65%), PLIN3 (+105%) and PLIN5 (+53%; all P < 0.05) protein content was higher in trained compared to sedentary individuals. In trained individuals, lipid infusion increased the number of LDs associated with PLIN2 (+27%), PLIN3 (+73%) and PLIN5 (+40%; all P < 0.05) in type I fibres. By contrast, in sedentary individuals, lipid infusion only increased the number of LDs not associated with PLIN proteins. Acute free fatty acid elevation therefore induces a redistribution of PLIN proteins to an expanded LD pool in trained individuals only and this may be part of the mechanism that enables fatty acids to be stored in IMTG.