nephrin and Edema

APOL1, a secreted high-density lipoprotein, is expressed in different human tissues. Genetic variants of APOL1 are described to be associated with the development of end stage renal diseases in African Americans. In human kidney, APOL1 is mainly expressed in podocytes that are responsible for proper blood filtration. Since mice do not express ApoL1, the zebrafish is an ideal model to study the role of ApoL1. Injection of morpholinos against zApoL1 into zebrafish eggs and larvae, respectively, induces severe edema indicating a leakage of the filtration barrier. This was demonstrated in zApoL1 knockdown larvae by intravascular injection of fluorescently-labeled 10- and 500-kDa dextrans and by clearance of the vitamin D-binding protein from the circulation. Immunohistochemistry and RT-PCR revealed the reduction of nephrin, a podocyte-specific protein essential for blood filtration. Coinjection of human nephrin mRNA rescued the zApoL1 knockdown induced phenotype. Reduced APOL1 and nephrin levels were also found in biopsies of patients suffering from end stage renal diseases. Our results demonstrate that zApoL1 is essential for proper blood filtration in the zebrafish glomerulus and that zApoL1 affects the expression of nephrin.

Topics: Animals; Apolipoproteins; Edema; Endothelium; Gene Expression Regulation; Glomerular Filtration Barrier; Larva; Membrane Proteins; Organ Specificity; Pericardium; Podocytes; Zebrafish; Zebrafish Proteins

Congenital nephrotic syndrome of the Finnish type is a serious renal disease belonging to the Finnish disease heritage. It appears as substantial proteinuria, hypoproteinemia and edema in a newborn. Kidney transplantation is the only effective treatment. The cause of the disease is a mutation in the gene encoding the nephrin protein. Nephrin is produced by the epithelial cell (podocyte) of the glomerulus. It is expressed in the slit membrane connecting the pedicles of the podocyte. This finding has revolutionized the concept of glomerular filtration and set off active research on the pathogenetic mechanisms of proteinuria.

Topics: Edema; Finland; Genotype; Glomerular Filtration Rate; Humans; Hypoproteinemia; Infant, Newborn; Kidney Transplantation; Membrane Proteins; Mutation; Nephrotic Syndrome; Proteinuria

Edema in nephrotic syndrome results from renal retention of sodium and alteration of the permeability properties of capillaries. Nephrotic syndrome induced by puromycin aminonucleoside (PAN) in rats reproduces the biological and clinical signs of the human disease, and has been widely used to identify the cellular mechanisms of sodium retention. Unfortunately, mice do not develop nephrotic syndrome in response to PAN, and we still lack a good mouse model of the disease in which the genetic tools necessary for further characterizing the pathophysiological pathway could be used. Mouse resistance to PAN has been attributed to a defect in glomerular adenosine deaminase (ADA), which metabolizes PAN. We therefore attempted to develop a mouse line sensitive to PAN through induction of normal adenosine metabolism in their podocytes.. A mouse line expressing functional ADA under the control of the podocyte-specific podocin promoter was generated by transgenesis. The effect of PAN on urinary excretion of sodium and proteins was compared in rats and in mice over-expressing ADA and in littermates.. We confirmed that expression of ADA mRNAs was much lower in wild type mouse than in rat glomerulus. Transgenic mice expressed ADA specifically in the glomerulus, and their ADA activity was of the same order of magnitude as in rats. Nonetheless, ADA transgenic mice remained insensitive to PAN treatment in terms of both proteinuria and sodium retention.. Along with previous results, this study shows that adenosine deaminase is necessary but not sufficient to confer PAN sensitivity to podocytes. ADA transgenic mice could be used as a background strain for further transgenesis.

Topics: Adenosine Deaminase; Animals; Drug Resistance; Edema; Enzyme Induction; Genes, Synthetic; Intracellular Signaling Peptides and Proteins; Kidney Glomerulus; Membrane Proteins; Mice; Mice, Transgenic; Natriuresis; Nephrotic Syndrome; Podocytes; Promoter Regions, Genetic; Proteinuria; Puromycin Aminonucleoside; Rats; Recombinant Fusion Proteins; RNA, Messenger; Species Specificity

Topics: Actins; Albuminuria; Capillaries; Child; Edema; Humans; Hyperlipidemias; Incidence; Intracellular Signaling Peptides and Proteins; Kidney Glomerulus; Membrane Proteins; Nephrotic Syndrome; Phenotype; Proteinuria; Renal Circulation; RNA, Transfer, Leu

A mouse model for congenital nephrotic syndrome (NPHS1) was generated by inactivating the nephrin gene (Nphs1) in embryonic stem cells by homologous recombination. The targeting construct contained the Escherichia coli lacZ gene as a reporter for the Nphs1 promoter. Mice homozygous for inactivated Nphs1 were born at an expected frequency of 25%. Although seemingly normal at birth, they immediately developed massive proteinuria and edema and died within 24 h. The kidneys of null mice exhibited enlarged Bowman's spaces, dilated tubuli, effacement of podocyte foot processes and absence of the slit diaphragm, essentially as found in human NPHS1 patients. In addition to expression in glomerular podocytes, the reporter gene was expressed in the brain and pancreas of (+/-) and (-/-) mice. In the brain, expression was localized to the ventricular zone of the fourth ventricle, the developing spinal cord, cerebellum, hippocampus and olfactory bulb. In the cerebellum, the expression was seen in radial glial cells. Neither anatomical nor morphological abnormalities were observed in the brains of null mice.

Topics: Alleles; Animals; Animals, Newborn; beta-Galactosidase; Blotting, Western; Brain; Edema; Electrophoresis, Polyacrylamide Gel; Gene Targeting; Genes, Reporter; Genotype; Homozygote; Immunohistochemistry; Kidney; Membrane Proteins; Mice; Microscopy, Electron; Models, Genetic; Organ Size; Pancreas; Promoter Regions, Genetic; Protein Biosynthesis; Proteins; Proteinuria; Time Factors