Binding and Uptake of Albumin By The Glomerular Podocyte.

Glomerular podocytes are critical regulators of glomerular permeability via the slit diaphragm and may play a role in cleaning the glomerular filter. Whether podocytes are able to bind and endocytose proteins has not been previously clarified and quantified. The aims of this thesis are to study protein endocytosis in conditionally immortalised mouse and human podocytes using FITC-albumin by direct quantitative assay, fluorescence and electron microscopy, and to determine whether pharmacological or biological agents may alter this postulated function. Mouse and human podocytes displayed specific one-site binding and avid endocytosis for FITC-albumin. Accumulation of endocytosed albumin could be demonstrated visually within intracellular vesicles. This function is likely to be highly significant in health and disease. The mimicking of proteinuric conditions in vitro gave variable results. Protein endocytosis by podocytes may represent a useful, measurable phenotypic characteristic against which potentially injurious or beneficial interventions can be assessed. Podocyte FITC-albumin endocytosis was sensitive to pre-treatment with the pharmacological agent’s simvastatin and ciglitazone which may be considered as reno-protective. Microparticles (MPs) are vesicular structures formed by cell membrane blebbing upon cell activation or apoptosis. They are present at low levels in the circulation and become elevated in disease. Pre-treatment with monocyte and endothelial MPs had no effect on podocyte endocytosis of protein. However, MPs were shown to induce podocyte secretion of MCP-1, IL-6, and VEGF. Potentially the increased secretion of these mediators in vivo may have a significant affect on generating renal inflammation and increasing glomerular permeability to proteins. MPs may provide a link between systemic inflammation, endothelial activation, podocyte dysfunction and proteinuria. The findings presented in this thesis add to our understanding of podocyte function and dysfunction. They identify and quantify for the first time a pharmacologically sensitive protein endocytosis function of the podocyte. In addition these findings introduce MPs as novel biological agents with a potential role in kidney inflammation and the progression of renal disease.