Gas6 induces Akt/mTOR-mediated mesangial hypertrophy in diabetic nephropathy.
BACKGROUND
We have already reported Gas6 is involved in glomerular hypertrophy observed in diabetic nephropathy. However, the molecular mechanisms involved in glomerular hypertrophy are still unknown, especially in vivo.


METHODS
In vivo, diabetes was induced in rats and mice by streptozotocin (STZ) and the activation of the Akt/mTOR pathway in glomeruli was examined. In vitro, mesangial hypertrophy was assessed by [(3)H]leucine incorporation and measuring cell areas.


RESULTS
Akt, p70 S6 kinase, and 4E-BP-1 were induced and phosphorylated in rat glomerular lysates after 12 weeks of STZ injection when mesangial and glomerular hypertrophy was observed. We then examined the role of Gas6 by treating STZ-rats with warfarin, and found that warfarin treatment inhibited the phosphorylation of these molecules as well as the hypertrophy. We next examined whether high glucose stimulation can induce the expression of Gas6/Axl in mesangial cells. Stimulation of the cells with 25 mmol/L of glucose increased the expression of Gas6/Axl and mesangial cell size compared with that with 5.6 mmol/L of glucose. This hypertrophic effect was abolished in mesangial cells derived from Gas6 knockout mice. We also found that LY294002 and rapamycin blocked Gas6-induced activation of the Akt/mTOR pathway and mesangial hypertrophy. Furthermore, less phosphorylated Akt-positive or 4E-BP-1-positive areas were found in STZ-treated Gas6 knockout mice than in STZ-treated wild-type mice.


CONCLUSIONS
Our study indicates that the Akt/mTOR pathway is a key signaling cascade in Gas6-mediated mesangial and glomerular hypertrophy and revealed a crucial role of Gas6/Axl and the Akt/mTOR pathway in the development of diabetic nephropathy.
Nagai
Kojiro
K
Department of Geriatric Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan.
Matsubara
Takeshi
T
Mima
Akira
A
Sumi
Eriko
E
Kanamori
Hiroshi
H
Iehara
Noriyuki
N
Fukatsu
Atsushi
A
Yanagita
Motoko
M
Nakano
Toru
T
Ishimoto
Yoshikazu
Y
Kita
Toru
T
Doi
Toshio
T
Arai
Hidenori
H
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D002070:Butadienes / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D050760:Cyclin-Dependent Kinase Inhibitor p27; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D003928:Diabetic Nephropathies / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D039642:Eukaryotic Initiation Factors; D005260:Female; D005920:Glomerular Mesangium / Q000378:metabolism / Q000473:pathology*; D005947:Glucose / Q000494:pharmacology; D006984:Hypertrophy; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009025:Morpholines / Q000494:pharmacology; D009570:Nitriles / Q000494:pharmacology; D010750:Phosphoproteins / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017207:Rats, Sprague-Dawley; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D000099255:Growth Arrest-Specific Protein 6
D048868:Adaptor Proteins, Signal Transducing; D000903:Antibiotics, Antineoplastic; D002070:Butadienes; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D002867:Chromones; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004791:Enzyme Inhibitors; D039642:Eukaryotic Initiation Factors; D005947:Glucose; D036341:Intercellular Signaling Peptides and Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009025:Morpholines; D009570:Nitriles; D010750:Phosphoproteins; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; D025521:Tumor Suppressor Proteins; D000099255:Growth Arrest-Specific Protein 6; C493961:Cdkn1b protein, mouse; C493962:Cdkn1b protein, rat; C499527:Eif4ebp1 protein, mouse; C499526:Eif4ebp1 protein, rat; C113580:U 0126; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C546843:mTOR protein, mouse; C546845:mTOR protein, rat; C494920:Akt1 protein, rat