Assessment of podocyte injury using two novel glomerular markers

The glomerular filtration barrier is an efficient filtration system, which ensures proper function of the kidney by avoiding proteinuria. At the same time, this barrier is also the most vulnerable component of the kidney. The podocyte, a terminal differentiated cell, is the key player in maintaining integrity. Most of the kidney diseases initiate from injuries of the podocytes, which lead to effacement with slit diaphragm disruption, followed ultimately by cell detachment and loss. Such a lesion can only be detected by electron microscopy. The goal of the present work was to identify early marker(s) of podocyte injury, which are uniquely expressed in these cells and are very sensitive to stress or any other type of insults. With such marker at hand, early evaluation of podocyte injury and disease progression to the entire nephron can be explored. By applying gene expression profile analysis on laser capture microdissected glomeruli two novel podocytes markers, Semaphorin-3G (Sema3G) and Cystatin C (CYTC) could be identified. Their specific expression in podocytes was further confirmed by the use of in situ hybridization and immunohistochemistry on kidney tissue sections. In a next step, modulation of Sema3G and CYTC was further assessed in models of podocyte injury (functional injury, immune-deposition related injury and drug-induced toxicity models). Sema3G is a very sensitive marker to podocyte injury, which was down regulated in all animal model tested except functional injury model. In the opposite, CYTC was upregulated only in the drug-induced toxicity model. By combining the in situ localization of these newly characterized markers with the well validated kidney injury molecule -1 (KIM-1), it was possible to follow the sequence of events from early podocyte injury to entire nephron damage. Hence, this represents a valuable tool for exploring the pathogenesis of glomerulopathy.