Insulin is a potent survival factor in mesangial cells: role of the PI3-kinase/Akt pathway.
BACKGROUND
Elucidating the mechanisms of apoptosis is important for understanding the molecular mechanisms underlying glomerular disease. The phosphatidylinositol 3 kinase (PI3-kinase)/Akt pathway is essential for survival signaling in non-renal cells. However, little is known about the anti-apoptotic effect of insulin and the role of the PI3-kinase/Akt pathway in mesangial cells (MC) apoptosis.


METHODS
Apoptosis was induced in wild type, p27Kip1 (p27) -/- and p21Cip1/Waf1 (p21) -/- mouse MC by survival factor withdrawal, actinomycin D, ultraviolet (UV)-B irradiation and cycloheximide in the presence or absence of insulin (1 micromol/L) or insulin-like growth factor-I (IGF-I; 100 ng/mL). The activation and levels of Akt, extracellular signal regulated kinase (ERK) and specific cell cycle proteins were determined by Western blot analysis.


RESULTS
Insulin and IGF-I inhibited wild-type MC apoptosis induced by survival factor withdrawal, actinomycin D, ultraviolet-B irradiation and cycloheximide and in p27 -/- MC when apoptosis was induced by survival factor withdrawal. Akt was activated by insulin and IGF-I during apoptosis. Blocking PI3-kinase with LY294002 reduced Akt activation and abrogated the anti-apoptotic effect of insulin. ERK was activated during apoptosis and blocking ERK activation with U0126 or PD98059 partially rescued MC from apoptosis. Moreover, insulin also suppressed ERK activation during apoptosis. Our results also showed that the CDK-inhibitor p21 was increased by insulin and that p21 up-regulation was PI3-kinase/Akt pathway dependent. Furthermore, p21 -/- MC apoptosis induced by survival factor withdrawal was not rescued by insulin in contrast to the wild-type and p27 -/- MC. These data suggest that p21 may have a critical role in the anti-apoptotic effect of insulin.


CONCLUSIONS
Insulin is a potent survival factor for MC in response to a number of different apoptotic triggers, and this effect is mediated through the PI3-kinase/Akt pathway. Moreover, ERK and p21 may be involved in anti-apoptotic effect of insulin in MC.
Hiromura
Keiju
K
Division of Nephrology, Department of Medicine, University of Washington School of Medicine, Seattle, Washington, USA. hiromura@med.gunma-u.ac.jp
Monkawa
Toshiaki
T
Petermann
Arndt T
AT
Durvasula
Raghu V
RV
Shankland
Stuart J
SJ
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D018797:Cell Cycle Proteins / Q000235:genetics / Q000502:physiology; D002470:Cell Survival / Q000502:physiology; D002478:Cells, Cultured; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D016213:Cyclins / Q000235:genetics / Q000502:physiology; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000378:metabolism; D005920:Glomerular Mesangium / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D007328:Insulin / Q000494:pharmacology / Q000502:physiology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout / Q000235:genetics; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000502:physiology
D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D016213:Cyclins; D004791:Enzyme Inhibitors; D007328:Insulin; D007334:Insulin-Like Growth Factor I; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D025521:Tumor Suppressor Proteins; C493957:Cdkn1a protein, mouse; C493961:Cdkn1b protein, mouse