Vascular ATGL-dependent lipolysis and the activation of cPLA2-PGI2 pathway protect against postprandial endothelial dysfunction.

Adipose triglyceride lipase (ATGL) is involved in lipolysis and displays a detrimental pathophysiological role in cardio-metabolic diseases. However, the organo-protective effects of ATGL-induced lipolysis were also suggested. The aim of this work was to characterize the function of lipid droplets (LDs) and ATGL-induced lipolysis in the regulation of endothelial function. ATGL-dependent LDs hydrolysis and cytosolic phospholipase A2 (cPLA2)-derived eicosanoids production were studied in the aorta, endothelial and smooth muscle cells exposed to exogenous oleic acid (OA) or arachidonic acid (AA). Functional effects of ATGL-dependent lipolysis and subsequent activation of cPLA2/PGI2 pathway were also studied in vivo in relation to postprandial endothelial dysfunction.The formation of LDs was invariably associated with elevated production of endogenous AA-derived prostacyclin (PGI2). In the presence of the inhibitor of ATGL or the inhibitor of cytosolic phospholipase A2, the production of eicosanoids was reduced, with a concomitant increase in the number of LDs. OA administration impaired endothelial barrier integrity in vitro that was further impaired if OA was given together with ATGL inhibitor. Importantly, in vivo, olive oil induced postprandial endothelial dysfunction that was significantly deteriorated by ATGL inhibition, cPLA2 inhibition or by prostacyclin (IP) receptor blockade.In summary, vascular LDs formation induced by exogenous AA or OA was associated with ATGL- and cPLA2-dependent PGI2 production from endogenous AA. The inhibition of ATGL resulted in an impairment of endothelial barrier function in vitro. The inhibition of ATGL-cPLA2-PGI2 dependent pathway resulted in the deterioration of endothelial function upon exposure to olive oil in vivo. In conclusion, vascular ATGL-cPLA2-PGI2 dependent pathway activated by lipid overload and linked to LDs formation in endothelium and smooth muscle cells has a vasoprotective role by counterbalancing detrimental effects of lipid overload on endothelial function.

Identification of a biochemical marker for endothelial dysfunction using Raman spectroscopy.

In the present work, we propose the spectroscopic approach to identify biochemical alterations in endothelial dysfunction. The method is based on the quantification of the ratio of phenylalanine (Phe) to tyrosine (Tyr) contents in the endothelium. The synthesis of Tyr from Phe requires the presence of tetrahydrobiopterin (BH4) as a cofactor of phenylalanine hydroxylase (PAH). Limitation of BH4 availability in the endothelium is a hallmark endothelial nitric oxide synthase (eNOS) dysfunction that may also lead to PAH dysfunction and a fall in Tyr contents. Using Raman spectra, the ratio of marker bands of Tyr to Phe was calculated and the pathological state of the endothelium was detected. We provide evidence that Phe/Tyr ratio analysis by Raman spectroscopy discriminate endothelial dysfunction in ApoE/LDLR(-/-) mice as compared to control mice.

Biochemical changes of the endothelium in the murine model of NO-deficient hypertension.

The main spectral differences between the biochemical compositions of the vascular endothelium of control, hypertensive NO-deficient, and NO-deficient mice supplemented with nitrate were studied using Raman microimaging. A significantly different Raman signature of the endothelium in these three groups in the 1200-1400 cm(-1) region was assigned to the α-helix and ß-sheet alterations in the protein secondary structure upon the development of hypertension. The second pronounced biochemical marker of endothelium alterations was the lipid to protein ratio. A lower intensity of the band at 2940 cm(-1) relative to the feature at 1007 cm(-1) in the endothelium in hypertension compared to the control indicated a decrease of the lipid content relative to proteins during the progress of the pathology. The nitrate-based treatment partially reversed the effects of hypertension. The nitrate supplementation restored the lipid to protein ratio in the endothelium to the control level, while the changes in the secondary structure of proteins were irreversible upon nitrate administration.