Genomics and Proteomics for Pathogensis and Pathophysiology of IgA Nephropathy

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This project was aimed to clarify pathogenesis and pathophysiology of human IgA nephropathy by genomics and proteomics. First, human glomerulus cDNA library was prepared and approximately 6,000 clones were sequenced. The glomerular genes have been banked and annotated to make a glomerular gene database. By cDNA microarray technique unique genes up-or down-regulated in human kidney tissues from patients with IgA nephropathy were searched. We paid an attention on one gene since it had not been characterized yet and was significantly and uniquely up-regulated in human IgA nephropathy kidney tissues. The gene was presumed to encord a membrane protein with a single membrane spanning domain and mucin-like domain. By immunohistochemistry using an antibody against a presumed peptide, the protein was localized at basolateral membrane of proximal tubules in normal human kidney tissues. To understand a physiologic function of this molecule, other molecules which might bind with this protein was searched by a yeast two-hybrid system. One of hybridized molecules was a receptor for a growth hormone expressed at the same site in human kidney tissues. An interaction between these molecules was examined in culture using cells highly expressed with these genes. We found that this new molecule interfered or attenuated signal transduction after binding of he growth factor to the receptor when interacted at the cytoplasmic domain. By proteomics using 2D gel electrophoresis and MALDI-TOF mass spectrometer (MS) or LC MS/MS approximately 500 spots out of 1500 spots were identified in normal human glomerulus samples. Database of the spots with annotation of each molecule was prepared to open through the internet. Proteomic analysis of IgA nephropathy samples by 2D gel electrophoresis and MS was difficult because of imitation of sample amounts.