Lipid droplets and steroidogenic cells

Abstract

Lipid droplets (LDs) in steroidogenic tissues have a cholesteryl ester (CE) core surrounded by a phospholipid monolayer that is coated with associated proteins. Compared with other tissues, they tend to be smaller in size and more numerous in numbers. These LDs are enriched with PLIN1c, PLIN2 and PLIN3. Both CIDE A and B are found in mouse ovary. Free cholesterol (FC) released upon hormone stimulation from LDs is the preferred source of cholesterol substrate for steroidogenesis, and HSL is the major neutral cholesterol esterase mediating the conversion of CEs to FC. Through the interaction of HSL with vimentin and StAR, FC is translocated to mitochondria for steroid hormone production. Proteomic analyses of LDs isolated from loaded primary ovarian granulosa cells, mouse MLTC-1 Leydig tumor cells and mouse testes revealed LD associated proteins that are actively involved in modulating lipid homeostasis along with a number of steroidogenic enzymes. Microscopy analysis confirmed the localization of many of these proteins to LDs. These studies broaden the role of LDs to include being a platform for functional steroidogenic enzyme activity or as a port for transferring steroidogenic enzymes and/or steroid intermediates, in addition to being a storage depot for CEs.

Dephosphorylation of MAP2D enhances its binding to vimentin in preovulatory ovarian granulosa cells

“…A dynamic vimentin cytoskeleton is thought to play a unique role in steroidogenic cells by modulating the accessibility of cholesterolester-containing lipid droplets to mitochondria (reviewed in Hall and Almahbobi, 1997;Shen et al, 2016). Lipid droplets from adrenal cells and adipocytes are surrounded by a vimentin-enriched phospholipid monolayer (Almahbobi et al, 1992;Brasaemle et al, 2004;Franke et al, 1987;Lieber and Evans, 1996).…”

“…However, vimentin filaments are believed to play a unique role (reviewed in Hall and Almahbobi, 1997;Shen et al, 2016). Lipid droplets in steroidogenic cells are composed of a cholesterol ester core surrounded by a phospholipid monolayer that contains a large number of proteins, including vimentin and hormone sensitive lipase (reviewed in Shen et al, 2016).…”

“…However, vimentin filaments are believed to play a unique role (reviewed in Hall and Almahbobi, 1997;Shen et al, 2016). Lipid droplets in steroidogenic cells are composed of a cholesterol ester core surrounded by a phospholipid monolayer that contains a large number of proteins, including vimentin and hormone sensitive lipase (reviewed in Shen et al, 2016). Vimentin has been shown to interact with both hormone-sensitive lipase and steroidogenic acute regulatory protein in adipocytes and adrenal cells, respectively (Shen et al, 2010(Shen et al, , 2003.…”

Lipid droplet functions beyond energy storage

“…The LD core can accumulate the precursors of molecules important for intercellular communication, such as steroid hormones and FA signals [70, 71]. In specialized endocrine cells of the gonads and adrenals, cholesteryl esters stored in LDs provide an important source of cholesterol for the mitochondrial biosynthesis of several different steroid hormones [72].…”

“…In specialized endocrine cells of the gonads and adrenals, cholesteryl esters stored in LDs provide an important source of cholesterol for the mitochondrial biosynthesis of several different steroid hormones [72]. Proteomic analyses of LDs from several types of steroid-producing cells indicate that they copurify with some steroidogenic enzymes [71, 73]. This has led to the idea that, in addition to cholesterol storage, LDs may also function as a site for steroidogenic enzymes and/or the transfer of steroid intermediates [71, 73].…”