Statin-sensitive endocytosis of albumin by glomerular podocytes.
Glomerular podocytes are critical regulators of glomerular permeability via the slit diaphragm and may play a role in cleaning the glomerular filter. Whether podocytes are able to endocytose proteins is uncertain. We studied protein endocytosis in conditionally immortalized mouse and human podocytes using FITC-albumin by direct quantitative assay and by fluorescence microscopy and electron microscopy in mouse podocytes. Furthermore, in vivo uptake was studied in human, rat, and mouse podocytes. Both mouse and human podocytes displayed specific one-site binding for FITC-albumin with K(d) of 0.91 or 0.44 mg/ml and B(max) of 3.15 or 0.81 microg/mg cell protein, respectively. In addition, they showed avid endocytosis of FITC-albumin with K(m) of 9.48 or 4.5 mg/ml and V(max) of 474.3 or 97.4 microg.mg cell protein(-1).h(-1), respectively. Immunoglobulin and transferrin were inefficient competitors of this process, indicating some specificity for albumin. Accumulation of endocytosed albumin could be demonstrated in intracellular vesicles by fluorescence confocal microscopy and electron microscopy. Endocytosis was sensitive to pretreatment with simvastatin. In vivo accumulation of albumin was found in all three species but was most pronounced in the rat. We conclude that podocytes are able to endocytose protein in a statin-sensitive manner. This function is likely to be highly significant in health and disease. In addition, protein endocytosis by podocytes may represent a useful, measurable phenotypic characteristic against which potentially injurious or beneficial interventions can be assessed.
Eyre
Jeanette
J
Dept. of Infection, Immunity, and Inflammation, University of Leicester, Leicester LE5 4PW, UK.
Ioannou
Kyriakos
K
Grubb
Blair D
BD
Saleem
Moin A
MA
Mathieson
Peter W
PW
Brunskill
Nigel J
NJ
Christensen
Erik I
EI
Topham
Peter S
PS
D000818:Animals; D004705:Endocytosis / Q000187:drug effects* / Q000528:radiation effects*; D016650:Fluorescein-5-isothiocyanate / Q000031:analogs & derivatives / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D046529:Microscopy, Electron, Transmission; D050199:Podocytes / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012709:Serum Albumin / Q000378:metabolism*; D019821:Simvastatin / Q000494:pharmacology*
C518288:FITC-albumin; D012709:Serum Albumin; D019821:Simvastatin; D016650:Fluorescein-5-isothiocyanate