No abstract

To advance our understanding of development, function and diseases in the kidney glomerulus, we have established and large-scale sequenced cDNA libraries from mouse glomeruli at different stages of development, resulting in a catalogue of 6053 different genes. The glomerular cDNA clones were arrayed and hybridized against a series of labeled targets from isolated glomeruli, non-glomerular kidney tissue, FACS-sorted podocytes and brain capillaries, which identified over 300 glomerular cell-enriched transcripts, some of which were further sublocalized to podocytes, mesangial cells and juxtaglomerular cells by in situ hybridization. For the earliest podocyte marker identified, Foxc2, knockout mice were used to analyze the role of this protein during glomerular development. We show that Foxc2 controls the expression of a distinct set of podocyte genes involved in podocyte differentiation and glomerular basement membrane maturation. The primary podocyte defects also cause abnormal differentiation and organization of the glomerular vascular cells. We surmise that studies on the other novel glomerulus-enriched transcripts identified in this study will provide new insight into glomerular development and pathomechanisms of disease.

The most common NPHS1 gene mutations, Fin-major and Fin-minor, both lead to an absence of nephrin and podocyte slit diaphragms, as well as a clinically severe form of NPHS1, the Finnish type of congenital nephrotic syndrome.

Disturbances in many different molecular pathways and interactions can lead to the same clinical end points of proteinuria and end-stage renal disease. Proteinuria is often accompanied by a cytopathological change in the glomerulus that is referred to as effacement (retraction) of the podocyte foot processes. The molecular mechanisms that lead to proteinuria and podocyte effacement are poorly understood; therefore, targeted therapies are lacking. During the past 5 years, however, a large body of data has emerged in this field. The discovery of podocyte gene defects that underlie some hereditary proteinuric syndromes has changed our understanding of the relative contributions of components of the glomerular filter. Furthermore, pathogenic pathways activated in podocytes during proteinuria have been identified. Together, these findings pinpoint the podocyte as the most obvious candidate for therapeutic intervention. In the near future, the use of large-scale expression profiling platforms, transgenic mouse lines, and other in vivo gene delivery methods will further expand our understanding of the pathology of the glomerular filtration barrier, and perhaps reveal novel target molecules for the therapy of proteinuric kidney diseases.