| Summary: | Ectopic lipid accumulation in skeletal muscle is linked with insulin resistance and type 2 diabetes (T2D). Neutral lipid is stored as lipid droplets, which are coated by lipid droplet coat proteins. One important class of these proteins are the perilipins. Little research has focused on perilipin 3 (PLIN3) and coatomer gtp-ases, theorized to be involved in PLIN3 directed lipid oxidation.
Under lipolytic stimulation with epinephrine or palmitate, forskolin, and ionomysin (PFI), primary human myotubes taken from health non-T2D donors showed increased protein content levels of PLIN3. Concordantly, following endurance exercise in non-T2D malesan experimental paradigm shown to increase lipolysislevels of PLIN3 protein were increased and associated with changes in both in vivo and ex vivo lipid oxidation. In both primary myotubes and in muscle tissue from the exercise bout, several coatomer gtp-ases were significantly altered. From a second clinical investigation, PLIN3 muscle protein content was associated with in vivo and ex vivo lipid oxidation under resting conditions in non-T2D males. Similarly, knockdown of PLIN3 in primary human myotubes using siRNA showed frank reductions in lipid oxidation. Cross-sectionally, PFI treatment in myotubes from sedentary and T2D donors increased expression levels of PLIN3 and ARFRP1, while myotubes from active donors increased expression of PLIN5. When myotubes from all three cohorts were treated with brefeldin A, an inhibitor of the coatomer gtp-ase ARF1, lipid oxidation was decreased in sedentary and T2D donors, but not in active donors. This suggests a role for PLIN3 and coatomer-gtpases in lipid oxidation and a potential alternate pathway for lipid oxidation in sedentary non-T2D and T2D individuals, not seen in active individuals.
In women with polycystic ovary syndrome (PCOS), a condition associated with insulin resistance, we discovered that PLIN3 expression in adipose is naturally knocked down when compared to weight-matched controls, along with reduced levels of lipid oxidation. Sixteen weeks of exercise training stimulated expression of PLIN3 in women with PCOS, concomitantly with increases in lipid oxidation. These results give credence to the myotube knockdown experiment that a naturally occurring absence of PLIN3 is associated with reduced lipid oxidation, which is rescued with aerobic exercise.
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