Fatty acids carried on albumin modulate proximal tubular cell fibronectin production: a role for protein kinase C.
BACKGROUND
Proteinuric renal disease is associated with accumulation of tubulointerstitial matrix proteins. Human proximal tubular cells (PTCs) produce fibronectin in response to serum proteins but not albumin alone. It has been suggested that renal toxicity of filtered albumin depends on its lipid moiety. We therefore investigated the functional consequences of different fatty acids (FAs) carried on human albumin after exposure to human PTCs in culture.


METHODS
Confluent human PTCs were exposed to recombinant human serum albumin (rHSA) or palmitate (P)-, stearate (S)-, oleate (O)-, and linoleate (L)-complexed rHSA. In all experimental conditions, test media contained 1 mg/ml rHSA alone or carrying 100 mmol FAs. Mitogenic response was assessed by [(3)H]thymidine incorporation. Cell culture supernatants were assayed for fibronectin. Protein kinase C (PKC) activity was assessed in cell lysates.


RESULTS
Apical exposure to rHSA alone or the O-rHSA complex stimulated a significant increase in [(3)H]thymidine incorporation, whereas the L-rHSA complex was markedly inhibitory to human PTC growth. The L-rHSA complex was associated with severe cytotoxicity as assessed by lactate dehydrogenase release. Among all conditions, O-rHSA was the only test media that significantly increased fibronectin levels over control conditions (150.1+/-10.6% over control, P<0.05, n=3). Pre-treatment of PTCs with PKC inhibitors before O-rHSA exposure resulted in a dose-dependent decrease in fibronectin secretion. O-rHSA activated PKC significantly compared with controls.


CONCLUSIONS
We conclude that rHSA has a mitogenic effect on human PTCs, but fibronectin secretion was only induced by O-complexed rHSA and the O-rHSA effect was mediated via PKC activation. Involvement of PKC signal transduction pathway may be a novel therapeutic target for ameliorating proteinuria-induced tubular injury.
Arici
Mustafa
M
Department of Nephrology, Leicester General Hospital, Gwendolen Road, Leicester, UK.
Brown
Jeremy
J
Williams
Matthew
M
Harris
Kevin P G
KP
Walls
John
J
Brunskill
Nigel J
NJ
D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005227:Fatty Acids / Q000378:metabolism* / Q000494:pharmacology; D005353:Fibronectins / Q000378:metabolism*; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism*; D019301:Oleic Acid / Q000378:metabolism / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism / Q000494:pharmacology; D012709:Serum Albumin / Q000378:metabolism* / Q000494:pharmacology
D004791:Enzyme Inhibitors; D005227:Fatty Acids; D005353:Fibronectins; D011994:Recombinant Proteins; D012709:Serum Albumin; D019301:Oleic Acid; D011493:Protein Kinase C