Podocyturia: What is in a name?

Abstract

The podocyte is a highly differentiated cell located in the outer space of the glomerular basement membrane that deals with many different functions. This phylogenetically preserved cell that is responsible for the virtually absence of proteins in the urine lacks of the capacity to divide under normal conditions. When podocytes receive molecular insults, which normally occur during stress conditions as glomerulonephritis, hyperfiltration or metabolic disturbances, they adapt to the new situation by contracting their actin fibers. This adaptive behavior puts at risk the quality of the plasmatic filtration due to the denudation of the glomerular basement membrane, the potential mesangial inflammation and the appearance of proteinuria; podocytes run the risk of detachment from the basement membrane due to a decrease in the adherence to the surrounding matrix after contraction, a process called foot processes effacement. Podocytes change their shape and under constant mechanical stress they finally detach, rendering the glomerular basement membrane unprotected unless other contiguous podocytes are capable of covering the surface. However, these still anchored podocytes are generally also under the same stress situation and follow the same pathway. Podocyturia refers to the presence of these differentiated cells in the urinary sediment. Noteworthy, the podocytes that are encountered in the urine are viable despite the glomerular hostile environment and the urinary acidity. Podocyturia can precede proteinuria and can aggravate it. Therefore, in diseases that can threaten the glomerular normal environment, the presence and the quantification of urinary podocytes can be of remarkable relevance, as it can herald or accompany the appearance of proteinuria, and could offer another view to the interpretation and clinical approach and outcome of proteinuria. However, its identification needs a wide-spread training among biochemists and technicians, as well as commercially available kits.

Keywords: Glomerular basement membrane; nephron; podocyte; podocyturia; proteinuria.