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Perilipin 3 Differentially Regulates Skeletal Muscle Lipid Oxidation in Active, Sedentary, and Type 2 Diabetic Males.

CONTEXT
The role of perilipin 3 (PLIN3) on lipid oxidation is not fully understood.


OBJECTIVE
We aimed to 1) determine whether skeletal muscle PLIN3 protein content is associated with lipid oxidation in humans, 2) understand the role of PLIN3 in lipid oxidation by knocking down PLIN3 protein content in primary human myotubes, and 3) compare PLIN3 content and its role in lipid oxidation in human primary skeletal muscle cultures established from sedentary, healthy lean (leans), type 2 diabetic (T2D), and physically active donors.


DESIGN, PARTICIPANTS, AND INTERVENTION
This was a clinical investigation of 29 healthy, normoglycemic males and a cross-sectional study using primary human myotubes from five leans, four T2D, and four active donors. Energy expenditure, whole-body lipid oxidation, PLIN3 protein content in skeletal muscle tissue, and ex vivo muscle palmitate oxidation were measured. Myotubes underwent lipolytic stimulation (palmitate, forskolin, inomycin [PFI] cocktail), treatment with brefeldin A (BFA), and knockdown of PLIN3 using siRNA.


SETTING
Experiments were performed in a Biomedical Research Institute.


MAIN OUTCOME MEASURES
Protein content, 24-hour respiratory quotient (RQ), and ex vivo/in vitro lipid oxidations.


RESULTS
PLIN3 protein content was associated with 24-h RQ (r = -0.44; P = .02) and skeletal muscle-specific ex vivo palmitate oxidation (r = 0.61; P = .02). PLIN3 knockdown showed drastic reductions in lipid oxidation in myotubes from leans. Lipolytic stimulation increased PLIN3 protein in cells from leans over T2Ds with little expression in active participants. Furthermore, treatment with BFA, known to inhibit coatomers that associate with PLIN3, reduced lipid oxidation in cells from lean and T2D, but not in active participants.


CONCLUSIONS
Differential expression of PLIN3 and BFA sensitivity may explain differential lipid oxidation efficiency in skeletal muscle among these cohorts.