Lipid‐depleted white adipose cells: An electron microscope study

Abstract

This report presents an electron microscope study of white adipose cells depleted of their lipid inclusion by prolonged low food intake. The tissue was fixed in phosphate-buffered 1% osmium tetroxide, embedded in Vestopal W, and sections were stained with lead hydroxide. Such cells differ in shape and size from signet-ring cells. They are ovoid, diminished in size, and the cell surface has become indented in all planes of the cell. The intercellular space is expanded with concentrations of collagen fibers in close association with the cell surface. These changes are presumed to be mechanical events associated with loss of lipid from the cell. Subcellular changes include the appearance of a n extremely large number of pinocytotic vesicles and cytoplasmic vesicles similar in appearance, membrane-bound dense bodies, five-layered membranous structures, vesiculated bodies, and areas of flocculent material. Mitochondria and nuclei appear to be similar to their counterparts in signet-ring cells. Observations are discussed with relation to ultrastructural changes reported in other studies in which adipose cells were depleted of fat by acute starvation or experimental deprivation of insulin. It is suggested that intracellular structural changes are probably associated with adaptive alterations in the metabolism of the cell.

Morphological changes of the adipose cell plasma membrane during lipolysis.

“…As far as the number of membrane invaginations per square micrometer of adipocyte plasma membrane is concerned, our data correlate well with previous conventional microscope analysis (13,14,16,19,22,23). However, when the FIGUr, E 4 Freeze-fracture replica showing the A face (inner leaflet) of the membrane, the cross-fractured cytoplasm (Cy), and the central lipid droplet of a control adipose cell.…”

“…The changes in the morphology of the adipocyte induced by lipolysis are also well documented (13,14,16,19,22,23): they consist mainly of a decrease of the central lipid droplet accompanied by a folding of the plasma membrane which is thrown into numerous processes (Fig. 3); the latter become progressively more prominent and complex with the duration of lipolysis, whether through fasting or through acute diabetes.…”

“…Previous studies of the changes induced by lipolysis in the morphology of the white adipose cell have shown an increase in the number of microvesicular invaginations (so-called "pinocytosis") of the plasma membrane during lipolysis (13,14,16,19,22,23). However, these data remained essentially qualitative since they were based on the examination of conventional thin sections which were not assessed by a morphometric approach.…”

“…These two determinations show that the number per square micrometer (local concentration) of both structural features progressively increases with the duration of diabetes and fasting, while that at the same time their number per entire cell (total content) remains unchanged. These data thus show: (a) a reorganization of the adipose cell plasma membrane during lipolysis; and (b) that this reorganization can be detected only by determining the concentration and the total content of the structural features of the membrane involved.Previous studies of the changes induced by lipolysis in the morphology of the white adipose cell have shown an increase in the number of microvesicular invaginations (so-called "pinocytosis") of the plasma membrane during lipolysis (13,14,16,19,22,23). However, these data remained essentially qualitative since they were based on the examination of conventional thin sections which were not assessed by a morphometric approach.…”

Rapid transformation of white adipocytes into fat-oxidizing machines

“…4B). The apparent increase in mitochondria cannot be explained entirely by the reduction in cytoplasmic volume resulting from lipid depletion, because starvation-induced volume reduction of adipocytes is not associated with a comparable abundance of mitochondria (20). Moreover, the mitochondria in starvation are pleomorphic and have a less electron-dense matrix (20).…”