AJP - Renal Physiology, Vol 252, Issue 4 627-F634, Copyright © 1987 by American Physiological Society
Endocytosis by cultured mesangial cells and associated changes in prostaglandin E2 synthesis
P. C. Singhal, G. H. Ding, S. DeCandido, N. Franki, R. M. Hays and D. Schlondorff
The mechanism of macromolecule uptake by cultured mesangial cells was
studied by use of transmission electron microscopy. In parallel, we
investigated the effect of macromolecular uptake on prostaglandin E2 (PGE2)
formation. Cultured rat mesangial cells were studied in their third
passage. As model molecules, we used colloidal gold particles (10 nm
diameter) coated either with polyethylene glycol (PEG) or fresh serum
(SCG). Mesangial cells were incubated from 1 to 60 min and up to 12 h with
either PEG or SCG particles. Endocytosis of SCG significantly exceeded that
of PEG particles. The mechanism involved binding to coated pits, followed
by formation of coated vesicles (endosomes), and eventually delivery of
particles to lysosomes. Pretreatment with cytochalasin B virtually
prevented endocytosis of SCG particles, indicating active participation of
the cytoskeleton. Determination of PGE2 production in parallel showed that
SCG significantly stimulated PGE2 synthesis within minutes, whereas
PEG-coated gold had no effect. When gold particles were coated with
decomplemented serum instead of fresh serum, the stimulation of PGE2 was
partially, but not completely, prevented, indicating that complement may be
one, but not the only ligand responsible for enhanced PGE2 production.
Stimulation of PGE2 synthesis by SCG was not dependent on actual
endocytosis, as it was not altered by cytochalasin B pretreatment. Thus,
surface ligand-receptor interaction may be sufficient to trigger PGE2
synthesis. The interaction between mesangial endocytosis and PGE2
production may be important for glomerular pathophysiology.
