Mechanical forces and TGFbeta1 reduce podocyte adhesion through alpha3beta1 integrin downregulation.
BACKGROUND
Podocyturia is a marker of diabetic nephr- opathy, a possible determinant of its progression and a powerful risk factor for cardiovascular disease. A reduction in podocyte adhesion to the glomerular basement membrane (GBM) via downregulation of alpha3beta1 integrin expression, the main podocyte anchoring dimer to the GBM, may represent one of the mechanisms of podocyturia in glomerular disease. This study investigated the role of mechanical forces and transforming growth factor beta1 (TGFbeta1) in podocyte adhesion and integrin expression.


METHODS
Conditionally immortalized murine podocytes were exposed to mechanical stretch and/or TGFbeta1 for 48 h. Podocyte adhesion, apoptosis and alpha3beta1 integrin expression were assessed.


RESULTS
Stretch and TGFbeta1 significantly reduced podocyte adhesion and alpha3beta1 integrin expression, events paralleled by increased apoptosis. Blockade of beta1 integrin, with a specific antibody, demonstrated a reduced podocyte adhesion indicating that beta1 integrin downregulation was required for the loss of podocyte adhesion. This was linked to an increase in podocyte apoptosis. The role of apoptosis in podocyte adhesion was further investigated using caspase-3 inhibitors. Podocyte apoptosis inhibition did not affect stretch- and TGFbeta1-mediated integrin downregulation and the loss of podocyte adhesion, suggesting that alpha3beta1 integrin downregulation is sufficient to alter cell adhesion. Although stretch significantly increased podocyte TGFbeta type I, II and III receptors but not podocyte TGFbeta1 secretion, the combination of stretch and TGFbeta1 did not show any additive or synergistic effects on podocyte adhesion and alpha3beta1 integrin expression.


CONCLUSIONS
These results suggest that downregulation of alpha3beta1 integrin expression, by mechanical forces or TGFbeta1, is per se sufficient to reduce podocyte adhesion. Apoptosis may represent a parallel important determinant of the podocyte loss from the GBM.
King's College London, UK.
Cecile
C
Dessapt
Marc Olivier
MO
Baradez
Anthea
A
Hayward
Alessandra
A
Dei Cas
Stephen M
SM
Thomas
Giancarlo
G
Viberti
Luigi
L
Gnudi
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D002448:Cell Adhesion / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D015536:Down-Regulation / Q000187:drug effects; D005109:Extracellular Matrix / Q000502:physiology; D050533:Glomerular Basement Membrane / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D006031:Glycosylation; D039201:Integrin alpha3beta1 / Q000737:chemistry / Q000502:physiology*; D007674:Kidney Diseases / Q000209:etiology / Q000473:pathology / Q000503:physiopathology; D051379:Mice; D050199:Podocytes / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D018125:Receptors, Transforming Growth Factor beta / Q000145:classification / Q000502:physiology; D013314:Stress, Mechanical; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology*
D039201:Integrin alpha3beta1; D018125:Receptors, Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1