Nagai Kojiro, Matsubara Takeshi, Mima Akira, Sumi Eriko, Kanamori Hiroshi, Iehara Noriyuki, Fukatsu Atsushi, Yanagita Motoko, Nakano Toru, Ishimoto Yoshikazu, Kita Toru, Doi Toshio, Arai Hidenori
Department of Geriatric Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan.
Kidney Int. 2005 Aug;68(2):552-61. doi: 10.1111/j.1523-1755.2005.00433.x.
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.
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.
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.
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.
我们已经报道过Gas6参与糖尿病肾病中观察到的肾小球肥大。然而，肾小球肥大所涉及的分子机制仍然未知，尤其是在体内。
在体内，通过链脲佐菌素（STZ）诱导大鼠和小鼠患糖尿病，并检测肾小球中Akt/mTOR通路的激活情况。在体外，通过[³H]亮氨酸掺入和测量细胞面积来评估系膜肥大。
注射STZ 12周后，当观察到系膜和肾小球肥大时，大鼠肾小球裂解物中的Akt、p70 S6激酶和4E-BP-1被诱导并磷酸化。然后我们通过用华法林治疗STZ诱导的大鼠来研究Gas6的作用，发现华法林治疗可抑制这些分子的磷酸化以及肥大。接下来我们检测高糖刺激是否能诱导系膜细胞中Gas6/Axl的表达。与5.6 mmol/L葡萄糖刺激相比，用25 mmol/L葡萄糖刺激细胞可增加Gas6/Axl的表达和系膜细胞大小。这种肥大效应在Gas6基因敲除小鼠来源的系膜细胞中消失。我们还发现LY294002和雷帕霉素可阻断Gas6诱导的Akt/mTOR通路激活和系膜肥大。此外，在STZ处理的Gas6基因敲除小鼠中发现的磷酸化Akt阳性或4E-BP-1阳性区域比STZ处理的野生型小鼠少。
我们的研究表明，Akt/mTOR通路是Gas6介导的系膜和肾小球肥大中的关键信号级联反应，并揭示了Gas6/Axl和Akt/mTOR通路在糖尿病肾病发展中的关键作用。
