6Cultured human podocytes Actin filaments FIG. 6. Human podocytes in culture. A: image obtained by light microscopy shows small buds of foot processes beginning to form (white arrows). B: actin filaments stained by phalloidin.Foot process buds: white arrows
9Albumin Sieving Coefficient Properties of the Glomerular Barrier and Mechanisms of ProteinuriaTABLE 1.Reported sieving coefficients for albumin in studies with "controlled" tubular modificationSpeciesAlbumin Sieving CoefficientTechniqueReference Nos.RatIn vivo + lysine310Tissue uptake17918Micropuncture317Humans, FanconiUrine proteomics2080.0015cIPK123, 213, 214, 301, 302Mouse0.00231340.0029190.0080IPK no tubular cell inhibitor2280.0087Fixed kidney530.0450IPK after tubular cell inhibitor2250.0800TABLE 1. Reported sieving coefficients for albumin in studies with "controlled" tubular modification
10Properties of the Glomerular Barrier and Mechanisms of Proteinuria TABLE 2.Sieving coefficients for various proteins in selected studiesType of ProteinSE RadiusSieving CoefficientChargeReferencesNeutral or slightly cationic proteins nAlbumin35.50.03302280.026019 Kappa-dimer28.40.1490179 nHRP32.00.07003480.1100302 nMyoglobin19.60.7700 cMyoglobin17.50.74002 IgG54.00.002318 LDH-546.00.0056176Anionic proteins Albumin0.0021–230.00152140.00060.0007 Ovalbumin27.40.0770–13301 Orosomucoid40.50.0036–24 aHRP0.0690–60.0450–110.01702240.0100–14 aMyoglobin0.5100 LDH-10.0011–19
166=effacement, foot process 1= subepithelial, MN2=subepithelial humps,post-infectiours GN3=Subendothelial4=Mesangial5=GMB-Ab complexe.g., Goodpasture’s6=effacement, foot processAnatomy of a normal glomerular capillary is shown on the left. Note the fenestrated endothelium (EN), glomerular basement membrane (GBM), and the epithelium with its foot processes (EP). The mesangium is composed of mesangial cells (MC) surrounded by extracellular matrix (MM) in direct contact with the endothelium. Ultrafiltration occurs across the glomerular wall and through channels in the mesangial matrix into the urinary space (US). Typical localization of immune deposits and other pathologic changes is depicted on the right. (1) Uniform subepithelial deposits as in membranous nephropathy. (2) Large, irregular subepithelial deposits or "humps" seen in acute postinfectious glomerulonephritis. (3) Subendothelial deposits as in diffuse proliferative lupus glomerulonephritis. (4) Mesangial deposits characteristic of immunoglobulin A nephropathy. (5) Antibody binding to the glomerular basement membrane (as in Goodpasture's syndrome) does not produce visible deposits, but a smooth linear pattern is seen on immunofluorescence. (6) Effacement of the epithelial foot processes is common in all forms of glomerular injury with proteinuria. (Redrawn, with permission, from Luke RG et al. Nephrology and hypertension. In: Medical Knowledge Self-Assessment Program IX. American College of Physicians, 1992.)
17NORMAL GBM. LEFT - a single glomerulus NORMAL GBM. LEFT - a single glomerulus. There are one million of these in each kidney. RIGHT - a close up of the GBM (G) around part of one tiny blood vessel in a glomerulus (red circle in left hand diagram)
18Diagram of a blood vessel with a normal GBM in a glomerulus (compare with the diagram above) A blood vessel with a thin GBMThin Glomerular Membrane Disease
19Lipid Accumulation Patients 1&2, In tubular Epithelial cells. Figure 1 Lipid accumulation in human kidney samples visualized by Oil Red O stainingKidney surgical specimens were obtained from patients undergoing radical nephrectomy for renal cell carcinoma. Normal kidney cortex samples were dissected by an experienced pathologist, away from the tumor. The samples were frozen, sectioned, and stained with hematoxylin and Oil Red O to visualize the distribution of lipids within renal structures. Left panels are representative images from three different patients (original color images are shown here in gray scale). For each image, a computer-based color deconvolution algorithm was used to separately visualize Oil Red O staining in the red channel (right panels). In these examples, lipid deposits are localized mostly within tubular epithelial cells in patients 1 and 2, but are not detectable in patient 3.
20Overwhelms beta-oxidation High Alb filtrationLuminal or apical side(a) Under normal conditions, fatty acids enter the proximal tubule cell from the basolateral side as well as from the apical (luminal) side, carried on albumin. Albumin is degraded in lysosomes, but transcytosis has also been proposed. Depending on cellular energy needs, intracellular fatty acids are directed to mitochondrial b-oxidation or to triglyceride stores. (b) Several conditions can theoretically lead to increased fatty acid intake into the proximal tubule cell, including high albumin filtration, high fatty acid to albumin molar ratio, and circulating lipid disturbances. These conditions, alone or in combination, may cause increased intracellular concentration of fatty acids, exceeding the b-oxidative capacity of mitochondria. This leads to intracellular accumulation of triglycerides and to the generation of lipid metabolites with potential toxic effect.Entry of free non-esterified fatty acids into proximal tubule cellsand the role of albumin as ‘Trojan horse’
21Competes with glutamine Fatty acids may affect proximal tubule ammonium production by mitochondrial substrate competitionAmmonium (NH4+) is produced in the proximal tubule by the metabolism of glutamine to α-ketoglutarate, which then continues in the Krebs cycle. The products of fatty acid β-oxidation also enter the Krebs cycle. Increased intracellular concentration of fatty acids may compete with glutamine as mitochondrial substrate, decreasing its utilization and reducing ammonium production.