Binding of lipid droplets and mitochondria to intermediate filaments in rat Leydig cells

We have examined the distribution of lipid droplets and mitochondria in relation to the cytoskeletons of Leydig cells in primary culture by using light and electron microscopy on living, intact and detergent-extracted cells. After mild extraction with Triton X-100 lipid droplets and mitochondria retained their original distribution within the cell. Double immunofluorescent microscopy showed that both structures co-localise with intermediate filaments. Transmission electron microscopy of intact (unextracted) and mildly extracted Leydig cells showed that intermediate filaments are closely associated with mitochondria and lipid droplets. By examination of stereo pairs, intermediate filaments were shown to establish direct contact with mitochondria and lipid droplets. The association of droplets and mitochondria with intermediate filaments suggests possible mechanisms by which the transport of cholesterol takes place from droplets to mitochondria where this substrate enters the steroidogenic pathway.