Accumulation of neutral lipids by human skin fibroblasts: differential effects of saturated and unsaturated fatty acids.

The accumulation of neutral lipids by human skin fibroblasts grown in medium supplemented with fatty acids has been investigated. GM-10 cells incorporated exogenous fatty acids into both phospholipids and neutral lipids. More [14C]oleate, linoleate, or linolenate was incorporated into triacylglycerol than was [14C]palmitate or stearate. Supplementation of medium containing delipidized serum with unsaturated fatty acids resulted in far more stimulation of [14C]glycerol incorporation into triacylglycerol than did supplementation with saturated fatty acids. Palmitate- and stearate-fed cells incorporated sizable amounts of [14C] fatty acids and [14C]glycerol into diacylglycerol as well as triacylglycerol, especially at higher fatty acid concentrations. Increased oleate supplementation from 10-300 microM resulted in increased triacyglycerol synthesis and accumulation of discrete cytoplasmic lipid droplets; palmitate concentrations above 70 microgram were toxic. Micrographs of the palmitate-fed cells showed electron translucent slits, suggesting solid depositions of saturated fat, rather than the discrete osmiophilic droplets found in oleate-fed cells. Although GM-10 cells can synthesize fully saturated triacylglycerols, these data suggest that in cells fed saturated fatty acids, solid depositions of neutral lipids may sequester diacylglycerols and thus limit triacylglycerol synthesis.