Fatty acids modulate protein kinase C activation in porcine vascular smooth muscle cells independently of their effect on de novo diacylglycerol synthesis

Aims/hypothesis. Diabetes-induced activation of protein kinase C has been a ssociated with the development of vascular complications. Elevated de novo diacylglycerol synthesis has been postulated to underlie this protein kinas e C activation. Diabetes also increases the circulating concentrations of n on-esterified fatty acids, which are immediate precursors of diacylglycerol through the de novo pathway. We hypothesized that increased fatty acids co ntribute to de novo diacylglycerol synthesis and activation of protein kina se C in vascular cells. Methods. Primary cultures of porcine carotid smooth muscle cells were expos ed to fatty acids, bound to albumin in physiologic ratios. Diacylglycerol a nd triacylglycerol were measured in extracts of these cells. Protein kinase C activation was measured as membrane translocation with isoform-specific antibodies. Results. Saturated fatty acids caused considerable accumulation of diacylgl ycerol through de novo synthesis. Unsaturated fatty acids increased triacyl glycerol,but not diacylglycerol, Platelet-derived growth factor activated t he alpha, epsilon and zeta protein kinase C isoforms. Activation of the alp ha and zeta isoforms was amplified by oleate pretreatment but inhibited by palmitate. In the absence of growth factor stimulation, neither palmitate n or oleate had any effect on the membrane/cytosol distribution of any protei n kinase C isoform. Conclusion/interpretation. Saturated fatty acids elicited de novo diacylgly cerol synthesis in vascular smooth muscle cells without activating protein kinase C. Effects of fatty acids on protein kinase C activation by platelet -derived growth factor did not correlate with the effects on de novo diacyl glycerol synthesis. These results indicate that de novo diacylglycerol synt hesis is, by itself, insufficient to activate protein kinase C.