The glomerular basement membrane (GBM) is a specialized extracellular matrix and a crucial component of the kidney's glomerular filtration barrier (GFB) between the vasculature and the urinary space. The GBM is initially co-synthesized by, and lies between, the podocytes and the glomerular endothelial cells, and it is bound by mesangial cells at the base of each capillary loop. The GBM's major components are laminin-521 (alpha5beta2gamma1), type IV collagen (the alpha3/4/5 network), nidogens-1 and -2, and the heparin sulfate proteoglycan agrin. Of these 9 components, mutations that affect 4 of them cause human kidney disease: mutations that affect the collagen IV chains cause Alport syndrome (hereditary glomerulonephritis), and those that affect laminin beta2 (LAMB2) cause Pierson syndrome/congenital nephrotic syndrome. The well-defined nature of the glomerular defects and the existence of well- characterized mouse models make these diseases especially attractive for targeted therapy. Several groups have already explored the potential for cell-based therapies aimed at replacing the missing collagen IV network in Alport mice. Although the positive effects of bone marrow and other cell transplants or infusions on progression of kidney disease seem promising, the reported effects of these procedures on the GBM's collagen IV network have been disparate and controversial. Here we propose experiments aimed at directly testing the feasibility of altering the GBM after it has matured in mouse models of Alport syndrome and Pierson syndrome/congenital nephrotic syndrome, with the goal of replacing the abnormal networks present in the mutants with the networks normally present in healthy mature glomeruli. We will use newly generated podocyte-specific reverse tetracycline transactivator transgenic mice and existing collagen IV and laminin mutant and transgenic mice to attempt to induce network restoration after GBM maturation. The results of these feasibility studies will have implications not only for treating human kidney disease, but also for our basic understanding of basement membrane biology, GBM plasticity, and cell/matrix interactions!
The glomerular basement membrane (GBM) is an important component of the glomerular filtration barrier that prevents the leakage of plasma proteins into the urine. Some patients with kidney disease have abnormal GBM composition. The overall goal of this proposal is to use a mouse model system to investigate whether an abnormal GBM composition can be normalized in patients and whether this will improve and/or prolong kidney function.
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