Heterogeneity of chemical composition of lipid droplets in endothelial inflammation and apoptosis.

Lipid droplets (LDs) play regulatory role in various cells but their significance in endothelial pathophysiology is still not well understood. Here, we studied LDs in in situ endothelial cells (ECs) in isolated blood vessels stimulated with pro-inflammatory or pro-apoptotic stimuli using Raman and fluorescence imaging. Endothelial inflammation induced by murine TNF-α (mTNF-α) was featured by overexpression of ICAM-1, vWF, increased production of PGI2, and was associated with the formation of low number of LDs. However in the presence of atglistatin, the inhibitor of triacyclglycerols hydrolysis, the number of LDs significantly increased. In contrast, in endothelium stimulated by human TNF-α (hTNF-α) or FasL, apart from endothelial inflammation, displayed also apoptosis as evidenced by high annexin expression and significant LDs formation. Raman imaging confirmed that LDs were localized in endothelium and revealed significant heterogeneity in biochemical composition of endothelial LDs that dependent on endothelial stimuli. Repertoire of LDs included LDs rich in highly unsaturated lipids, assigned to the inflammation, as well as LDs featured by more saturated lipids linked to apoptosis, where Raman signals indicating content of cholesterol and phospholipids were higher for endothelial apoptosis in comparison to endothelial inflammation. The heterogeneity in chemical composition of LDs suggested more complex pathophysiological role of endothelial LDs then previously appreciated.