Differential effects of albumin on cytokine gene expression in proximal tubular epithelial cells
Sir,
Protein-induced activation of proximal tubular epithelial cells (PTECs) plays a central role in mediating interstitial macrophage accumulation in chronic glomerular diseases [1]. In vitro, short-term exposure of cultured PTECs to nephrotic-range concentrations of native or modified (glycated or lipidated) plasma proteins (albumin, IgG and complement) induces the gene expression of chemoattractants (such as RANTES, MCP-1, endothelin and fibronectin) and alters the spatial arrangement of adhesion molecules [1]. This study was undertaken to investigate whether albumin has differential effects on the gene expression of cytokines with classical macrophage activating [interleukin-1ß (IL-1ß), tumour necrosis factor-
(TNF-
), IL-6 and IL-12 p40], deactivating (IL-4 and IL-10) or immunomodulatory transforming growth factor-ß (TGF-ß1) properties.
Confluent primary cultured rat PTECs were exposed to vehicle, lipopolysaccharide (5 µg/ml, LPS, Escherichia coli, serotype 026:B6, Sigma-Aldrich, Australia) or endotoxin-free delipidated bovine serum albumin (dBSA, 15 mg/ml, Sigma-Adrich, Australia) for 8 h [2,3]. Isolation of total cellular RNA and mRNA expression was assessed by semi-quantitative reverse transcriptionpolymerase chain reaction (RTPCR) as described previously [2,3].
In unstimulated PTECs, weak constitutive expression of all cytokines was detected, except for IL-1ß and IL-4 (Figure 1). Exposure to LPS induced IL-1ß, IL-6, IL-10, IL-12 p40 and TNF-
. In contrast, dBSA increased IL-1ß, TNF-
and IL-6, but did not induce IL-10 or IL-12 p40. For both LPS and dBSA, there was a trend for an increase in TGF-ß1 mRNA, and IL-4 remained undetectable.

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Fig. 1. Cytokine mRNA expression in proximal tubular epithelial cells exposed to vehicle (control, C), delipidated bovine serum albumin (dBSA 15 mg/ml) and lipopolysaccharide (LPS, 5 µg/ml), as assessed by semi-quantiative RTPCR [2,3]. The PCR product was separated on a 1.6% agarose gel containing ethidium bromide (0.5 µg/ml) and photographed under ultraviolet illumination. Cytokine gene expression was the ratio of the volume density of the cytokine to that of the housekeeping gene, glyceraldehyde-3-phosphate dehydrogenase, as determined by densitometry of the negatives. Note that IL-4 mRNA was undetectable in unstimulated or stimulated PTECs and the data are not shown in the figure. Data are expressed as mean±SEM (n = 6 per group). *P<0.05 compared with C.
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These results demonstrate that albumin is proinflammatory and selectively induced the transcription of cytokines with classical macrophage-activating properties in PTECs. The mechanism by which albumin mediates these proinflammatory effects requires evaluation of the signal transducing pathways, and it remains to be determined whether other plasma proteins share these effects. In contrast to human PTECs [4], TGF-ß1 mRNA was not significantly induced in rat PTECs by albumin, and this might be due to differences in the duration of albumin exposure (24 h in [4]) and/or possibly species-specific variations.
Gopala K. Rangan,
Yiping Wang,
Yuet-Ching Tay and
David C.H. Harris
Centre for Transplant and
Renal Research
Westmead Millennium Institute
The University of Sydney
at Westmead Hospital
Westmead
Sydney
Australia 2145
Email: g.rangan{at}wmi.usyd.edu.au
Acknowledgments
This study was supported by the Australian Kidney Foundation (G.K.R.) and project grant 970721 from the National Health Medical Research Council of Australia (D.C.H.).
Conflict of interest statement. None declared.
References
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- Wang Y, Chen J, Chen L, Tay YC, Rangan GK, Harris DC. Induction of monocyte chemoattractant protein-1 in proximal tubule cells by urinary protein. J Am Soc Nephrol 1997; 8: 15371545[Abstract]
- Rangan GK, Wang Y, Tay YC, Harris DC. Inhibition of NF-
B with antioxidants is correlated with reduced cytokine transcription in PTC. Am J Physiol 1997; 277: F779F789
- Yard BA, Chorianopoulos E, Herr D, van der Woude FJ. Regulation of endothelin and transforming growth factor-ß1 production in cultured proximal tubular cells by albumin and heparan sulphate glycosaminoglycans. Nephrol Dial Transplant 2001; 16: 17691775[Abstract/Free Full Text]