Albumin induces cellular fibrosis by upregulating transforming growth factor-beta ligand and its receptors in renal distal tubule cells.
Albuminuria is indicative of nephropathy. However, little literature has focused on the role of albumin in renal distal tubule fibrosis. We used a well-defined distal tubule cell, Madin-Darby Canine Kidney (MDCK). Proliferation and cytotoxicity were examined. The conditioned supernatant was collected and subjected to ELISA assay for detection of fibronectin and TGF-beta1. Reverse transcription-PCR and Western blot assay were performed to evaluate the expression of mRNA and protein of two types of TGF-beta receptors (TbetaR). Flow cytometry assay and phosphotyrosine (pY)-specific antibodies were used to assay the phosphorylation status of TbetaR. We showed that albumin dose dependently (0, 0.1, 1, or 10 mg/ml) inhibited cellular growth in MDCK cells without inducing cellular cytotoxicity. In addition, albumin significantly upregulated the secretion of both fibronectin and TGF-beta1 at dose over 1 mg/ml. Moreover, 24 h pretreatment of albumin significantly enhanced exogenous TGF-beta1-induced secretion of fibronectin. These observations were reminiscent of the implications of TbetaR since TbetaR appears to correlate with the susceptibility of cellular fibrosis. We found that albumin significantly increased protein levels of type I TbetaR (TbetaRI) instead of type II receptors (TbetaRII). In addition, phosphorylation level of TbetaRII of both pY259 and pY424 was significantly enhanced instead of pY336. The novel observation indicates that extreme dose of albumin upregulates TGF-beta autocrine loop by upregulating TGF-beta1, TbetaRI, and the receptor kinase activity of TbetaRII by inducing tyrosine phosphorylation on key amino residue of TbetaRII in renal distal tubule cells. These combinational effects might contribute to the pathogenesis of renal fibrosis.
Liu
Hung-Chang
HC
Graduate Institute of Biological Science and Technology, Chung Hwa College of Medical Technology, Tainan, Taiwan.
Liao
Tung-Nan
TN
Lee
Tao-Chen
TC
Chuang
Lea-Yea
LY
Guh
Jinn-Yuh
JY
Liu
Shu-Fen
SF
Hu
Min-Shou
MS
Yang
Ya-Lin
YL
Lin
Shyh-Horng
SH
Hung
Min-Yuan
MY
Huang
Jau-Shyang
JS
Hung
Tsung-Jen
TJ
Chen
Chun-Da
CD
Chiang
Tai-An
TA
Chan
Jun-Yu
JY
Chen
Sen-Yi
SY
Yang
Yu-Lin
YL
D000418:Albumins / Q000494:pharmacology*; D000818:Animals; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D048429:Cell Size / Q000187:drug effects; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005353:Fibronectins / Q000378:metabolism; D005355:Fibrosis / Q000139:chemically induced*; D007686:Kidney Tubules, Distal / Q000187:drug effects / Q000378:metabolism*; D008024:Ligands; D010766:Phosphorylation; D011485:Protein Binding; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism; D015854:Up-Regulation
D000418:Albumins; D005353:Fibronectins; D008024:Ligands; D018125:Receptors, Transforming Growth Factor beta; D016212:Transforming Growth Factor beta; D014443:Tyrosine