The cover image shows metabolism of cholesteryl ester (CE) and role of hormone-sensitive lipase (HSL) in steroidogenesis. The hydrolysis of cholesteryl esters stored in lipid droplets is an important source of cholesterol for optimum steroid biosynthesis. HSL is a multifunctional enzyme that is responsible for neutral cholesteryl ester hydrolase activity. E600 blocks the release of cholesterol from lipid droplets (LD) and thus affects StAR expression and steroid synthesis. Circulating lipoproteins (HDL or LDL) bind to scavenger receptor class B, type 1 (SR-B1) and release cholesteryl esters into the cells. Free cholesterol (FC) for steroid production is mostly obtained in rodents via HDL-mediated cholesteryl ester internalization and followed by cleavage by HSL. However, receptor-mediated uptake of lipoprotein-derived cholesteryl esters is processed via the LDL receptor in the human systems. De novo synthesis of cholesterol from acetyl-co-enzyme A (AC-CoA) provides also FC for steroid synthesis. The StAR protein regulates steroidogenesis by controlling the transport of cholesterol from the outer to the inner mitochondrial membrane, the site of the cytochrome P450scc enzyme. Conversion of cholesterol is the first enzymatic step in steroid hormone biosynthesis. LD, lipid droplets; AL, acid lipase; NP-C1 and C2, Niemann-Pick C1 and C2; Ly, lysosome; HR, HMG-co-enzyme A reductase. HDL, high density lipoprotein; LDL, low density lipoprotein. (See P.R. Manna et al., 321-333)
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