Podocyte expression of the CDK-inhibitor p57 during development and disease.
BACKGROUND
The mature podocyte is a terminally differentiated cell with a limited proliferative capacity. The precise cell cycle proteins necessary for establishing podocyte quiescence during development or permitting podocyte cell cycle re-entry in disease states have not been fully defined. Accordingly, we studied the role of the cyclin dependent kinase (CDK)-inhibitor p57Kip2 (p57) in modulating these processes.


METHODS
The expression of p57 protein in relation to markers of DNA synthesis was examined in developing mouse kidneys, and in the passive Heymann nephritis (PHN) and anti-glomerular antibody models of glomerular disease by immunohistochemistry. The role of p57 in glomerulogenesis was explored by examining renal tissue from embryonic p57-/- mice, and the expression of p21, p27 and p57 protein and mRNA was examined in podocytes in vitro.


RESULTS
The de novo expression of p57 during glomerulogenesis coincides with the cessation of podocyte proliferation, and the establishment of a mature phenotype, and p57 is expressed exclusively in podocytes in mature glomeruli. However, p57 knockout mice have normal glomerular podocyte development. In addition, mRNA but not protein levels of p57 increased upon differentiation of podocytes in vitro. There was a marked decrease in p57 expression in both animal models of podocyte injury. This was diffuse in PHN, whereas in the murine model, loss of expression of p57 occurred predominantly in proliferating podocytes, expressing proliferating cell nuclear antigen (PCNA).


CONCLUSIONS
Despite the de novo expression of p57 protein coinciding with the cessation of primitive podocyte proliferation during glomerulogenesis, embryonic p57-/- mice glomeruli were histologically normal. Cultured podocytes did not require changes in p57 protein levels to undergo differentiation. These data suggest that p57 alone is not required for podocyte differentiation, and that other cell cycle regulators may play a role. Furthermore, although injury to mature podocytes in experimental glomerular disease is associated with a decrease in p57, the levels of all three members of the Cip/Kip family of CDK inhibitors appear to determine the capability of podocytes to proliferate.
Hiromura
K
K
Department of Medicine, Division of Nephrology, University of Washington School of Medicine, Seattle, Washington 98195, USA. stuartjs@u.washington.edu
Haseley
L A
LA
Zhang
P
P
Monkawa
T
T
Durvasula
R
R
Petermann
A T
AT
Alpers
C E
CE
Mundel
P
P
Shankland
S J
SJ
D000818:Animals; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D002454:Cell Differentiation / Q000502:physiology; D002478:Cells, Cultured; D016922:Cellular Senescence; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis; D004622:Embryo, Mammalian / Q000378:metabolism; D005314:Embryonic and Fetal Development / Q000502:physiology; D005921:Glomerulonephritis / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D006358:Hot Temperature; D007668:Kidney / Q000196:embryology* / Q000378:metabolism* / Q000473:pathology; D007678:Kidney Glomerulus / Q000196:embryology; D051379:Mice; D018345:Mice, Knockout / Q000235:genetics; D014018:Tissue Distribution; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology
C493961:Cdkn1b protein, mouse; D018797:Cell Cycle Proteins; D016213:Cyclins; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004247:DNA; D018844:Cyclin-Dependent Kinases