Transcriptional profiling of the kidney glomerulus

Abstract

The kidney glomerulus plays a crucial role in ultraltration of the blood through the glomerular capillary wall. Glomerulus injury may occur in many systemic and primary kidney diseases or as secondary eects to drugs and infections. It has been shown that many known glomerular specic/enriched genes play crucial roles in the maintenance of glomerular ltration function and in the pathogenesis of the known glomerular diseases of known etiology. With functional genomics and bioinformatics approaches, the identication of additional glomerular specic/enriched gene transcripts will provide a better understanding of the glomerular physiology and function, as well as the mechanisms of glomerular diseases where causes and pathogenic processes are still poorly understood.

To achieve the goal of identifying glomerular genes, we, firstly, performed comparative analysis of mouse glomerular EST libraries and whole kidney EST libraries. In this study, we found 497 glomerular enriched genes. These glomerular enriched genes were validated by dierent approaches. In situ hybridization conrmed the cellular location of six new glomerular markers. Apart from the mouse kidney EST library comparisons, we integrated the results of glomerular enriched genes from four additional expression-proling platforms, and made a comprehensive catalogue of glomerular genes. Based on this, a protein-protein interaction network in glomerulus (GlomNet) was constructed. To further understanding the gene expression prole of human glomerulus, we performed transcriptional proling of human kidney glomeruli which were obtained from renal needle biopsies taken from live renal transplant donors. By comparison with our mouse transcriptional proling data, we observed a surprisingly large dierence between the most glomerulus-specc genes in humans and mice, respectively. Furthermore, the common glomerular enriched genes between human and mouse were classied into six dierent clusters according to their expression specicity in human and mouse glomeruli.

To gain insight into glomerular transcriptional changes that accompany pathological processes leading to proteinuria, we analyzed gene expression proles following glomerular injury in the mouse lipopolysaccharide (LPS)-induced proteinuria model. LPS triggered the specic gene expression pattern changes in the glomerulus and regulated several dierent pathways. We observed that podocyte number decreased signicantly in the model. Moreover, the genes encoded collagen 1, 2 and laminin 2 chains which are expressed in the embryonic kidney glomerulus increased their expression in LPS-treated mice, suggesting remodeling of the glomerular basement membrane, caused by activation or dedierentiation of glomerular cells.

In summary, the new glomerular gene transcripts identied in this thesis provide the foundation for targeted analysis of individual genes and pathways, and the GlomNet provides a preliminary systematic view of the relationships and interactions between dierent components in the glomerulus. The methodology of human glomerular transcription proling can be applied for the identication of diagnostic and prognostic markers for renal diseases. The transcriptional prole changes accompanying LPS-induced proteinuria may provide clues about mechanisms involved in proteinuria. The information from this study contributes new insights for the glomerular function, physiology and the disease mechanisms.