For their study, Jarad and colleagues in the labs of Jeffrey Miner, Ph.D., associate professor of medicine and cell biology and physiology, worked with mice lacking the gene for laminin beta 2, a protein that is part of the GBM. Two years ago, scientists linked a human mutation in the gene for laminin beta 2 to an inherited disorder that causes kidney disease and abnormalities in the eye and the neuromuscular system.
Scientists gave the mice ferritin, a protein often used as an imaging agent because it is easily detected by electron microscopes. They then used an electron microscope to take pictures of ferritin in the kidney and found it slipped more readily through the GBM in the genetically modified mice than it did in normal mice.
How comparable is ferritin to the blood proteins nephrologists are concerned about?
"Ferritin is actually much bigger than most blood proteins," Miner notes, "but other scientists have previously shown that, like blood proteins, ferritin is normally retained by the kidney."
Miner suspects--but cannot yet prove--that the problems in the slit diaphragm detected by the Finnish team may slow the ability of water to pass through the diaphragm and into the urine without affecting the passage of blood proteins. This could increase the concentration of protein passed into the urine without increasing the actual quantity of protein passed.
"It may be that the GBM is what determines the absolute amount of protein that's able to cross over into the urine, and the slit diaphragm and related structures determine its concentration," he explains. "It's a very complicated combination of fluid dynamics and physiology that we're s
Contact: Michael C. Purdy
Washington University School of Medicine