Thrombospondin-1 mediates distal tubule hypertrophy induced by glycated albumin.
Diabetic nephropathy is characterized by early hypertrophy in both glomerular and tubuloepithelial elements. However, no studies to date have established a direct causal link between hyperglycaemia and renal hypertrophy. Our previous studies have found that high glucose does not induce cellular hypertrophy or expression of TGF-beta1 (transforming growth factor-beta1) in distal renal tubule cells [Yang, Guh, Yang, Lai, Tsai, Hung, Chang and Chuang (1998) J. Am. Soc. Nephrol. 9, 182-193]. In the present study, we used AGEs (advanced glycation end-products) to mimic long-term hyperglycaemia. Similar to glucose, AGEs did not induce TGF-beta1 mRNA in distal renal tubule cells [MDCK (Madin-Darby canine kidney) cells]; however, TGF-beta1 bioactivity was increased significantly. This result indicated post-translational regulation. Since TSP-1 (thrombospondin-1) has been demonstrated to activate latent TGF-beta1 in a variety of systems, the following experiments were performed. We found that AGEs dose-dependently increased both intracellular and extracellular levels of TSP-1. Purified TSP-1, like AGEs, increased the cellular protein content. Furthermore, anti-TSP-1 neutralizing antibodies attenuated the AGE-induced increase in TGF-beta1 bioactivity and hypertrophy. Thus TSP-1 might mediate AGE-induced distal renal tubule hypertrophy. In addition, we observed several putative transcription factor binding sites in the TSP-1 promoter, including those for AP-1 (activator protein-1), CREB (cAMP response element binding protein), NF-kappaB (nuclear factor-kappaB), SRF (serum response factor) and HSF (heat-shock factor), by sequence mapping. We used an enhancer assay to screen possible transcription factors involved. We showed that AP-1 and CREB were specifically induced by AGEs; furthermore, TFD (transcription factor decoy) for AP-1 could attenuate the AGE-induced increases in TSP-1 levels and cellular hypertrophy. Thus regulation of TSP-1 might be critical for hyperglycaemic distal tubule hypertrophy. Furthermore, TSP-1 TFD might be a potential approach to ameliorate diabetic renal hypertrophy.
Yang
Yu-Lin
YL
Graduate Institute of Biological Science and Biotechnology, Chung Hwa College of Medical Technology, Tainan, Taiwan. yulinhelpme@sinamail.com
Chuang
Lea-Yea
LY
Guh
Jinn-Yuh
JY
Liu
Shu-Fen
SF
Hung
Min-Yuan
MY
Liao
Tung-Nan
TN
Huang
Yu-Lun
YL
D000818:Animals; D001665:Binding Sites; D002460:Cell Line / Q000378:metabolism; D048429:Cell Size; D003928:Diabetic Nephropathies / Q000378:metabolism / Q000473:pathology*; D004285:Dogs; D004742:Enhancer Elements, Genetic / Q000235:genetics; D005786:Gene Expression Regulation / Q000187:drug effects; D017127:Glycation End Products, Advanced / Q000494:pharmacology*; D006801:Humans; D006984:Hypertrophy; D007668:Kidney; D007686:Kidney Tubules, Distal / Q000473:pathology*; D008168:Lung; D008907:Mink; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000096:biosynthesis; D012709:Serum Albumin / Q000494:pharmacology*; D013873:Thionucleotides / Q000235:genetics; D019700:Thrombospondin 1 / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism / Q000494:pharmacology; D016212:Transforming Growth Factor beta / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D053773:Transforming Growth Factor beta1; D000093423:Glycated Serum Albumin
D017127:Glycation End Products, Advanced; D012333:RNA, Messenger; D012709:Serum Albumin; C508960:TGFB1 protein, human; D013873:Thionucleotides; D019700:Thrombospondin 1; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D000093423:Glycated Serum Albumin