High stearoyl-CoA desaturase protein and activity levels in simian virus 40 transformed-human lung fibroblasts.

The precise role of monounsaturated fatty acid (MUFA) synthesis in cell proliferation and programmed cell death remains unknown. The strong correlation of high levels of MUFA and neoplastic phenotype suggest that the regulation of stearoyl CoA desaturase (SCD) must play a significant role in cancer development. In this study, the levels of SCD protein and activity were investigated in normal (WI38) and SV40-transformed (SV40-WI38) human lung fibroblasts. Thus, the activity of SCD on exogenous [14C]stearic acid and endogenous [14C]acetate-labeled fatty acids was increased by 2.2- and 2.6-fold, respectively, in SV40-WI38 compared to WI38 fibroblasts. Concomitantly, a 3.3-fold increase in SCD protein content was observed in SV40-transformed cells. Cell transformation also led to high levels of MUFA, which was paralleled by a more fluid membrane environment. Furthermore, the levels of PPAR-gamma, a well-known activator of SCD expression, were highly increased in SV40-transformed fibroblasts. SCD activity appeared linked to the events of programmed cell death, since incubations with 40 microM etoposide induced apoptosis in SV40 cells, and led to a decrease in fatty acid synthesis, SCD activity and in MUFA cellular levels. Taken together, these results suggest that SCD protein and activity levels are associated with the events of neoplastic cell transformation and programmed cell death.

Phosphatidylcholine deficiency upregulates enzymes of triacylglycerol metabolism in CHO cells.

We studied the regulation of triacylglycerol (TAG) metabolism by phosphatidylcholine (PC) in CHO MT58 cells, which are deficient in PC synthesis because of a temperature-sensitive CTP:phosphocholine cytidylyltransferase. At the permissive growth temperature (34 degrees C), these cells contained 49% less TAG and 30% less PC than wild-type CHO K1 cells. Treatment with dipalmitoylphosphatidylcholine normalized both the PC and TAG levels. Despite low TAG levels, the incorporation of [14C]oleate into TAG was increased in CHO MT58 cells. The in vitro de novo synthesis of TAG and the activity of diacylglycerol acyltransferase were 90% and 34% higher, respectively. Two other key enzyme activities in TAG synthesis, acyl-CoA synthetase and mitochondrial glycerol-3-phosphate acyltransferase (GPAT), increased by 48% and 2-fold, respectively, and mitochondrial GPAT mRNA increased by approximately 4-fold. Additionally, TAG hydrolysis was accelerated in CHO MT58 cells, and in vitro lipolytic activity increased by 68%. These studies suggest that a homeostatic mechanism increases TAG synthesis and recycling in response to PC deficiency. TAG recycling produces diacylglycerol and fatty acids that can be substrates for de novo PC synthesis and for lysophosphatidylcholine (lysoPC) acylation. In CHO MT58 cells, in which de novo PC synthesis is blocked, lysoPC acylation with fatty acid originating from TAG may represent the main pathway for generating PC.

Lipid metabolism in the embryos of diabetic rats during early organogenesis: modulatory effect of prostaglandin E2.

The purpose of this work was to evaluate de novo lipid biosynthesis and the lipid profile, and to study the effect of prostaglandin E2 (PGE2; prostaglandin has previously been found to be involved in diabetes embryopathy) on lipid metabolism in embryos from control and streptozotocin-induced diabetic rats during organogenesis. Increased levels of triacylglycerols were found in embryos of diabetic rats compared with controls, whereas no differences were detected in the levels of cholesterol, cholesterylester, phosphatidylcholine and phosphatidylethanolamine. When the de novo synthesis of lipids in the embryo was studied using [14C]acetate as a tracer, a diminished rate of incorporation of [14C]acetate into the evaluated lipid classes was detected in the diabetic embryo compared with controls. Addition of PGE2 did not modify the incorporation of [14C]acetate into any of the lipid species of control embryos, but enhanced the incorporation of [14C]acetate into triacylglycerol, cholesterylesters, phosphatidylcholine and phosphatidylethanolamine of embryos from diabetic rats. The study's results show alterations in both synthesis and concentrations of lipids in the embryos of diabetic rats. Interestingly, the results demonstrate that the addition of PGE2, a prostaglandin that reverses the embryonic morphological abnormalities induced by diabetes, prevents disturbances in embryo lipid synthesis caused by diabetes.