Cellular structures involved in albumin interaction with preadipocytes in various stages of adipogenesis, in vitro.
Albumin is the major carrier of long chain free fatty acids, that are known to be heavily utilized by fat cells. To investigate the cellular structures involved in the interaction of albumin with preadipocytes, precursor fat cells isolated from rat epididymal fat pads were cultured in Dulbecco's modified Eagle's medium supplemented with 5% fetal calf serum and antibiotics. Cell differentiation was induced by 1.7 nM insulin added to the culture medium. The ensuing cells in various stages of differentiation were incubated with albumin, alone or bearing oleic acid, adsorbed to 5 nm gold particles (Alb-Au or Alb-OA-Au) for 10 min at 37 degrees C. As control, polyethyleneglycol-gold and IgG-gold complexes were used in same conditions. After extensive washing, the cell monolayer was fixed in 2.5% glutaraldehyde, and processed for electron microscopy. Examination of thin sections and morphometric analysis showed that: a) in the process of adipogenesis induced in vitro four cell types were simultaneously present: fibroblast-like cells (F), early adipocytes (EA), adipocytes (A) and aged adipocytes (AA); b) upon incubation with Alb-Au, the probe labelled preferentially coated pits and coated vesicles and only some uncoated vesicles; in time the tracer was found in endosomes, occasionally, multivesicular bodies and lysosome-like structures. The binding and uptake was dependent on the stage of cell differentiation, being less pronounced in fibroblast-like cells and increased in later stages (A and AA); c) Alb-OA-Au labelled the same structural features like the Alb-Au (i.e. coated pits and vesicles); however, the binding to the cell membrane was fourfold higher than that of Alb-Au in F and EA stages and was maintained at the same level in A and AA stages; d) control probes were taken up only by adipocytes and aged adipocytes, cells that express a strong phagocytic function for all tracers used. These results indicated that albumin bound to gold and especially albumin-bearing fatty acids-gold, bind preferentially to coated pits and vesicles of preadipocytes. Further internalization of albumin-gold particles seems to be non-specific, since both the probes and the controls adsorbed to gold were delivered to the same endosomal-lysosomal compartment.
Institute of Cellular Biology and Pathology, Bucharest, Rumania.
M
M
Raicu
D017667:Adipocytes / Q000166:cytology* / Q000378:metabolism* / Q000648:ultrastructure; D000418:Albumins / Q000032:analysis / Q000378:metabolism*; D000818:Animals; D002454:Cell Differentiation; D002478:Cells, Cultured; D016922:Cellular Senescence; D066298:In Vitro Techniques; D002479:Inclusion Bodies / Q000502:physiology*; D007425:Intracellular Membranes / Q000378:metabolism / Q000648:ultrastructure; D008297:Male; D008854:Microscopy, Electron; D051381:Rats; D017208:Rats, Wistar; D013234:Stem Cells / Q000166:cytology* / Q000378:metabolism* / Q000648:ultrastructure
D000418:Albumins