title: Mechanisms through which bradykinin promotes glomerular injury in diabetes.
abstract: In diabetes, mesangial cell proliferation and extracellular matrix expansion are critical components in the development of glomerulosclerosis. We reported that diabetes alters the activity of the kallikrein-kinin system and that these alterations contribute to the development of diabetic nephropathy. The present study examined the influence of streptozotocin-induced diabetes on the renal expression of bradykinin (BK) B2 receptors (B2KR), connective tissue growth factor (CTGF), transforming growth factor-beta (TGF-beta), and TGF-beta type II receptor (TGF-betaRII) and assessed the signaling mechanisms through which B2KR activation may promote glomerular injury. Eight weeks after the induction of diabetes, renal mRNA levels of B2KR, CTGF, and TGF-beta as well as protein levels of CTGF and TGF-betaRII were measured in control (C), diabetic (D), and insulin-treated diabetic (D+I) rats. Renal B2KR and TGF-beta mRNA levels expressed relative to beta-actin mRNA levels and CTGF and TGF-betaRII protein levels were significantly increased in D and D+I rats compared with C rats (P < 0.03, n = 5). To assess the contribution of B2KR activation on modulating the expression of CTGF, TGF-betaRII, and collagen I, mesangial cells (MC) were treated with BK (10(-8) M) for 24 h and CTGF and TGF-betaRII protein levels were measured by Western blots and collagen I mRNA levels were measured by RT-PCR. A two- to threefold increase in CTGF and TGF-betaRII protein levels was observed in response to BK stimulation (P < 0.001, n = 6). In addition, a marked increase in collagen I mRNA levels was observed in response to BK stimulation. Treatment of MC with BK (10(-8) M) for 5 min significantly increased the tyrosine phosphorylation of p60src kinase and of p42/p44 MAPK (P < 0.05, n = 4). Inhibition of src kinase by PP1 (10 microM) inhibited the increase in p42/p44 MAPK activation in response to BK. Finally, to determine whether BK stimulates CTGF, TGF-betaRII, and collagen I expression via activation of MAPK pathways, MC were pretreated with an inhibitor of p42/p44 MAPK (PD-98059) for 45 min, followed by BK (10(-8) M) stimulation for 24 h. Selective inhibition of p42/p44 MAPK significantly inhibited the BK-induced increase in CTGF, TGF-betaRII, and collagen I levels. These findings are the first to demonstrate that BK regulates the expression of CTGF, TGF-betaRII, and collagen I in MC and provide a mechanistic pathway through which B2KR activation may contribute to the development of diabetic nephropathy.
authors.affiliation: Dept. of Medicine, Division of Endocrinology-Diabetes-Medical Genetics, Medical Univ. of South Carolina, 114 Doughty St., PO Box 250776, Charleston, SC 29425, USA.
authors.forename: Yan
authors.initials: Y
authors.lastname: Tan
authors.forename: Bing
authors.initials: B
authors.lastname: Wang
authors.forename: Joo-Seob
authors.initials: JS
authors.lastname: Keum
authors.forename: Ayad A
authors.initials: AA
authors.lastname: Jaffa
mesh_terms: D000818:Animals; D015153:Blotting, Western; D001920:Bradykinin / Q000096:biosynthesis / Q000494:pharmacology / Q000502:physiology*; D002478:Cells, Cultured; D024042:Collagen Type I / Q000096:biosynthesis; D024043:Collagen Type II / Q000096:biosynthesis; D055513:Connective Tissue Growth Factor; D018076:DNA, Complementary / Q000096:biosynthesis / Q000235:genetics; D003921:Diabetes Mellitus, Experimental / Q000473:pathology; D003928:Diabetic Nephropathies / Q000378:metabolism / Q000473:pathology*; D005920:Glomerular Mesangium / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D017874:Immediate-Early Proteins / Q000096:biosynthesis; D036341:Intercellular Signaling Peptides and Proteins / Q000096:biosynthesis; D007678:Kidney Glomerulus / Q000378:metabolism / Q000473:pathology*; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000096:biosynthesis; D015688:Oncogene Protein pp60(v-src) / Q000378:metabolism; D012313:RNA / Q000096:biosynthesis / Q000302:isolation & purification; D051381:Rats; D017207:Rats, Sprague-Dawley; D043782:Receptor, Bradykinin B2 / Q000096:biosynthesis; D018125:Receptors, Transforming Growth Factor beta / Q000096:biosynthesis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology; D015854:Up-Regulation / Q000502:physiology
chemical_list: C526316:CCN2 protein, rat; D024042:Collagen Type I; D024043:Collagen Type II; D018076:DNA, Complementary; D017874:Immediate-Early Proteins; D036341:Intercellular Signaling Peptides and Proteins; D043782:Receptor, Bradykinin B2; D018125:Receptors, Transforming Growth Factor beta; D055513:Connective Tissue Growth Factor; D012313:RNA; D015688:Oncogene Protein pp60(v-src); D020928:Mitogen-Activated Protein Kinases; D001920:Bradykinin