The mechanisms underlying alterations in muscle lipid metabolism in
obesity are poorly understood. The primary aim of this study was to compare the abundance and/or activities of key
proteins that regulate intramyocellular
triglyceride (IMTG) concentration in the skeletal muscle obtained from obese (OB; n = 8, BMI 38 ± 1 kg/m(2)) and nonobese (NOB; n = 9, BMI 23 ± 1 kg/m(2)) women. IMTG concentration was nearly twofold greater in OB vs. NOB subjects (75 ± 15 vs. 40 ± 8 μmol/g dry wt, P < 0.05). In contrast, the activity and
protein abundance of key
enzymes that regulate the esterification of IMTG (i.e.,
glycerol-3-
phosphate acyltransferase and
diacylglycerol acyltransferase) were not elevated. We also found no differences between groups in muscle adipose
triglyceride lipase and
hormone-sensitive lipase (HSL)
protein abundance and no differences in phosphorylation of specific sites known to affect HSL activity. However, we did find the elevated IMTG in
obesity to be accompanied by a greater abundance of the
fatty acid transporter FAT/CD36 in the membrane fraction of muscle from OB vs. NOB subjects (P < 0.05), suggestive of an elevated
fatty acid transport capacity. Additionally,
protein abundance of the
lipid-trafficking
protein perilipin 3 was lower (P < 0.05) in muscle from OB vs. NOB when expressed relative to IMTG content. Our findings indicate that the elevated IMTG content found in obese women was not due to an upregulation of key lipogenic
proteins or to the suppression of lipolytic
proteins. The impact of a low
perilipin protein abundance relative to the amount of IMTG in
obesity remains to be clarified.