HIV-1 Tat reduces nephrin in human podocytes: a potential mechanism for enhanced glomerular permeability in HIV-associated nephropathy.
OBJECTIVE
To determine whether HIV-1 Tat may directly alter glomerular permeability in HIV-associated nephropathy (HIVAN).


METHODS
Heavy proteinuria is a hallmark of HIVAN. The slit diaphragm is the ultimate glomerular filtration barrier critical for maintaining the efficiency of the ultrafiltration unit of the kidney. In this study, we evaluated the direct effect of Tat protein on the permeability of isolated glomeruli and on the expression of nephrin, the main slit diaphragm component, by human cultured podocytes.


METHODS
Permeability was studied by measuring the permeability to albumin in isolated rat glomeruli. We also evaluated the expression of nephrin in human cultured podocytes by using immunofluorescence and Western blot.


RESULTS
We found that Tat increased albumin permeability in isolated glomeruli, and rapidly induced the redistribution and loss of nephrin in cultured podocytes. Pretreatment of glomeruli and podocytes with blocking antibodies showed that Tat reduced nephrin expression by engaging vascular endothelial growth factor receptors types 2 and 3 and the integrin alphavbeta3. Pre-incubation of podocytes with two platelet-activating factor (PAF) receptor antagonists prevented the loss and redistribution of nephrin induced by Tat, suggesting that PAF is an intracellular mediator of Tat action. Tat induced a rapid PAF synthesis by podocytes. When podocytes transfected to overexpress PAF-acetylhydrolase, the main catabolic enzyme of PAF, were stimulated with Tat, the redistribution and loss of nephrin was abrogated.


CONCLUSIONS
The present results define a mechanism by which Tat may reduce nephrin expression in podocytes, thus increasing glomerular permeability. This provides new insights in the understanding of HIVAN pathogenesis.
Doublier
Sophie
S
Department of Internal Medicine and Center of Experimental Research and Medical Sciences (CERMS), University of Turin, Turin, Italy.
Zennaro
Cristina
C
Spatola
Tiziana
T
Lupia
Enrico
E
Bottelli
Antonella
A
Deregibus
Maria Chiara
MC
Carraro
Michele
M
Conaldi
Pier Giulio
PG
Camussi
Giovanni
G
D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase / Q000096:biosynthesis / Q000235:genetics; D016263:AIDS-Associated Nephropathy / Q000503:physiopathology*; D000818:Animals; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000187:drug effects; D015696:Gene Products, tat / Q000494:pharmacology* / Q000502:physiology; D015497:HIV-1; D006801:Humans; D007678:Kidney Glomerulus / Q000187:drug effects* / Q000378:metabolism / Q000503:physiopathology; D008565:Membrane Proteins / Q000378:metabolism*; D010539:Permeability / Q000187:drug effects; D050199:Podocytes / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000494:pharmacology; D012709:Serum Albumin / Q000493:pharmacokinetics; D046509:Tissue Culture Techniques; D014162:Transfection; D054322:tat Gene Products, Human Immunodeficiency Virus
D015696:Gene Products, tat; D008565:Membrane Proteins; D011994:Recombinant Proteins; D012709:Serum Albumin; C113267:nephrin; D054322:tat Gene Products, Human Immunodeficiency Virus; D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase