Mechanical stretch induces podocyte hypertrophy in vitro.
BACKGROUND
Increased intraglomerular pressure is a final pathway toward glomerulosclerosis in systemic hypertension, diabetes, and focal segmental glomerulosclerosis (FSGS). Increased intraglomerular pressure causes stress-tension, or stretch, on resident glomerular cells. However, the effects of stretch on podocyte growth, and the mechanisms that underlie this, have not been elucidated.


METHODS
To test the hypothesis that stretch alters podocyte growth, cultured mouse podocytes were exposed to cyclic mechanical stretch created by vacuum; control cells were grown under similar conditions, but not exposed to stretch. Proliferation (cell cycle phases) and hypertrophy (forward light scatter) were measured in stretched and control podocytes by flow cytometry. The role of the cyclin-dependent kinase (CDK) inhibitors, p21 and p27, was examined by stretching podocytes isolated from p21 and p27 knockout (-/-) mice, and the role of specific signaling pathways was assessed by Western blot analysis and blocking studies.


RESULTS
Our results showed that stretch reduced cell cycle progression in wild-type and single p27-/- podocytes and induced hypertrophy in these cells in all phases of the cell cycle at 24, 48, and 72 hours. In contrast, stretch did not induce hypertrophy in single p21-/- and double p21/p27-/- podocytes. Stretch-induced hypertrophy required cell cycle entry, and was prevented by specifically blocking extracellular signal-regulated kinase 1/2 (Erk1/2) or Akt. Although stretch increased p38 activation, inhibition of this pathway had no effect on hypertrophy.


CONCLUSIONS
Mechanical stretch induces hypertrophy in podocytes in vitro in all phases of the cell cycle. This effect is cell cycle dependent, and requires p21, Erk1/2, and Akt. Stretch may play a role in podocyte injury when intraglomerular pressure is increased.
Petermann
Arndt T
AT
Department of Medicine, Division of Nephrology, University of Washington School of Medicine, Seattle, Washington 98195, USA.
Pippin
Jeffrey
J
Durvasula
Raghu
R
Pichler
Raimund
R
Hiromura
Keiju
K
Monkawa
Toshi
T
Couser
William G
WG
Shankland
Stuart J
SJ
D000818:Animals; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000235:genetics / Q000502:physiology; D049108:Cell Enlargement; D002478:Cells, Cultured; D003470:Culture Media; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D066298:In Vitro Techniques; D007678:Kidney Glomerulus / Q000166:cytology* / Q000502:physiology; D020935:MAP Kinase Signaling System; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008934:Mitogens; D008954:Models, Biological; D013314:Stress, Mechanical; D025521:Tumor Suppressor Proteins / Q000172:deficiency / Q000235:genetics
C493957:Cdkn1a protein, mouse; C493961:Cdkn1b protein, mouse; D018797:Cell Cycle Proteins; D003470:Culture Media; D050759:Cyclin-Dependent Kinase Inhibitor p21; D008934:Mitogens; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27