Purification and characterization of protein phosphatase type 2C in photoreceptors

Damage of guinea pig heart and arteries by a trioleate-enriched diet and of cultured cardiomyocytes by oleic acid

BACKGROUND

Mono-unsaturated fatty acids (MUFAs) like oleic acid have been shown to cause apoptosis of cultured endothelial cells by activating protein phosphatase type 2C alpha and beta (PP2C). The question arises whether damage of endothelial or other cells could be observed in intact animals fed with a trioleate-enriched diet.

METHODOLOGY/PRINCIPAL FINDINGS

Dunkin-Hartley guinea pigs were fed with a trioleate-enriched diet for 5 months. Advanced atherosclerotic changes of the aorta and the coronary arteries could not be seen but the arteries appeared in a pre-atherosclerotic stage of vascular remodelling. However, the weight and size of the hearts were lower than in controls and the number of apoptotic myocytes increased in the hearts of trioleate-fed animals. To confirm the idea that oleic acid may have caused this apoptosis by activation of PP2C, cultured cardiomyocytes from guinea pigs and mice were treated with various lipids. It was demonstrable that oleic acid dose-dependently caused apoptosis of cardiomyocytes from both species, yet, similar to previous experiments with cultured neurons and endothelial cells, stearic acid, elaidic acid and oleic acid methylester did not. The apoptotic effect caused by oleic acid was diminished when PP2C alpha and beta were downregulated by siRNA showing that PP2C was causally involved in apoptosis caused by oleic acid.

CONCLUSIONS/SIGNIFICANCE

The glycerol trioleate diet given to guinea pigs for 5 months did not cause marked atherosclerosis but clearly damaged the hearts by activating PP2C alpha and beta. The diet used with 24% (wt/wt) glycerol trioleate is not comparable to human diets. The detrimental role of MUFAs for guinea pig heart tissue in vivo is shown for the first time. Whether it is true for humans remains to be shown.

Unsaturated fatty acids isolated from human lipoproteins activate protein phosphatase type 2Cβ and induce apoptosis in endothelial cells

Activity of serine/threonine protein phosphatase type 2C is known to be stimulated by certain unsaturated fatty acids and this enzyme dephosphorylates Bad, thus acting on apoptosis. This prompted us to investigate endothelial cell death. Here, we present evidence for the presence of protein phosphatase type 2Cbeta (PP2Cbeta) in human umbilical vein endothelial cells (HUVECs) and report on colocalization of PP2Cbeta and Bad in the cytosol of endothelial cells. Lipophilic compounds that stimulated PP2Cbeta activity in vitro were found to induce cell death of HUVECs. Lipoproteins did neither influence PP2Cbeta activity nor affect cell behaviour. Lipoproteins treated with the lipoprotein lipase, however, stimulated the activity of PP2Cbeta at least 10-fold concomitantly triggering cell death. Analytical methods revealed that both effects - stimulation of PP2Cbeta and apoptosis - were caused by free fatty acids liberated from VLDL, LDL and HDL with oleic acid and linoleic acid as major constituents. The results provide novel insights in endothelial apoptosis and suggest that PP2Cbeta participates in the development and progress of atherosclerosis.