IMMUNOCYTOCHEMICAL DEMONSTRATION OF A LIPID DROPLET-SPECIFIC CAPSULE IN CULTURED LEYDIG-CELLS OF THE GOLDEN-HAMSTERS

In this report, we provide direct evidence for the presence of a lipid droplet-associated capsule in hamster steroidogenic Leydig cells by u sing a monoclonal antibody A2. Leydig cells are characterized by conta ining many lipid droplets and having 3 beta-hydroxysteroid dehydrogena se activity. Immunofluorescence staining with this antibody demonstrat ed a rim or capsule surrounding the lipid droplets in Leydig cells, a pattern not seen with anti-vimentin antibody. Immunogold labelling con firmed ultrastructurally that antibody binding was distributed on the lipid droplet surface. In order to investigate the possible function o f the capsule, we examined the morphological changes induced in the ca psule following stimulation with LH or dibutyryl cAMP; the fluorescent intensity of the capsule was seen to gradually decrease, accompanied by a decrease in number and size of lipid droplets, and the response t o both reagents was time- and concentration-dependent. We thus conclud e that hormonal stimulation resulting in the detachment of certain cap sular proteins from the surface of lipid droplets is mediated via the cAMP signaling pathway and may allow cholesterol ester hydrolytic enzy me direct access to its substrate in the lipid droplet. (C) 1996 Wiley -Liss, Inc.