MAGI-1 Interacts with Nephrin to Maintain Slit Diaphragm Structure through Enhanced Rap1 Activation in Podocytes

MAGI-1 is a multidomain cytosolic scaffolding protein that in the kidney is specifically located at the podocyte slit diaphragm, a specialized junction that is universally injured in proteinuric diseases. There it interacts with several essential molecules, including nephrin and neph1, which are required for slit diaphragm formation and as an intracellular signaling hub. Here, we show that diminished MAGI-1 expression in cultured podocytes reduced nephrin and neph1 membrane localization and weakened tight junction integrity. Global magi1 knock-out mice, however, demonstrated normal glomerular histology and function into adulthood. We hypothesized that a second mild but complementary genetic insult might induce glomerular disease susceptibility in these mice. To identify such a gene, we utilized the developing fly eye to test for functional complementation between MAGI and its binding partners. In this way, we identified diminished expression of fly Hibris (nephrin) or Roughest (neph1) as dramatically exacerbating the effects of MAGI depletion. Indeed, when these combinations were studied in mice, the addition of nephrin, but not neph1, heterozygosity to homozygous deletion of MAGI-1 resulted in spontaneous glomerulosclerosis. In cultured podocytes, MAGI-1 depletion reduced intercellular contact-induced Rap1 activation, a pathway critical for proper podocyte function. Similarly, magi1 knock-out mice showed diminished glomerular Rap1 activation, an effect dramatically enhanced by concomitant nephrin haploinsufficiency. Finally, combined overexpression of MAGI-1 and nephrin increased Rap1 activation, but not when substituting a mutant MAGI-1 that cannot bind nephrin. We conclude that the interaction between nephrin and MAGI-1 regulates Rap1 activation in podocytes to maintain long term slit diaphragm structure.     

支链氨基酸在运动中的作用研究进展

支链氨基酸(BCAAs)由亮氨酸、异亮氨酸和缬氨酸组成,是人体重要的必需氨基酸,参与人体多种生理活动。本文在大量查阅相关文献的基础上,就支链氨基酸在运动中的作用进行述评。支链氨基酸在运动中能够为机体提供能量,通过参与糖代谢过程而维持糖原含量;可调节蛋白质的代谢过程,抑制蛋白质降解并促进合成代谢;抑制自由基和乳酸的产生并加快其廓清速率,保护细胞膜与线粒体的生物功能,减缓抑制性神经递质的生成与集聚。在对抗运动性疲劳、提高运动能力和削弱延迟性肌肉酸痛方面有巨大影响。但关于长期补充支链氨基酸的毒副作用、不良效应等问题,仍有待进一步研究与探索。     

时钟基因BMAL1在运动性骨骼肌损伤恢复中的作用*

目的: 探讨时钟基因BMAL1在运动性骨骼肌损伤恢复中的作用。方法: 208只8周龄SD大鼠随机分为对照组(C组,n=104)和运动组(E组,n=104)。E组于跑台进行90 min下坡跑,运动后于0 h, 6 h,12 h,18 h, 24 h, 30 h, 36 h, 42 h, 48 h, 54 h, 60 h, 66 h, 72 h各取C组、E组8只大鼠腓肠肌,通过实时荧光定量PCR实验检测骨骼肌核心时钟基因BMAL1表达量,应用余弦分析软件circacompare (R package)获取拟合余弦曲线参数,分析其节律性振荡的变化趋势;透射电镜观察骨骼肌肌纤维超微结构变化;免疫印迹法(Western blot)检测骨骼肌BMAL1、DESMIN表达;免疫荧光观测BMAL1与DESMIN的定位及含量变化。结果: C组BMAL1 mRNA在72 h内呈现3个完整近日节律周期;E组BMAL1 mRNA在 0 h～24 h近日节律消失。与C组比较,E组在运动后0 h、6 h、12 h、18 h,BMAL1 mRNA含量显著升高(P＜0.05),在运动后0 h、12 hBMAL1蛋白表达显著升高(P＜0.05)、24 h至72 h恢复至无明显差异(P＞0.05);在运动后0 h、12 h,DESMIN蛋白表达降低(P＜0.05),24 h开始逐渐升高,48 h显著升高(P＜0.01),至72 h恢复至无明显差异(P＞0.05)。E组BMAL1与DESMIN在运动后0 h、12 h、24 h发生共定位,0 h～24 h共定位呈现先降低后升高的趋势,24 h的荧光强度达到最高值。结论: 运动后时钟基因BMAL1可能与调控骨架蛋白DESMIN的协同作用增强,从而与促进肌纤维结构恢复有关。     

Protein concentration in urine of normal owl monkeys.

The excretion of urinary protein was evaluated in 62 owl monkeys using timed urine collections. The ratio of urine protein to urine creatinine concentrations (Up/c) was determined for each monkey. Linear regression analysis was used to calculate the correlation between that ratio and urine protein (mg/dl) and 24-hour urinary protein loss (mg/kg). The coefficient of determination for Up/c to urine protein and 24-hour urinary protein loss was significant (P less than or equal to 0.0001). Determination of the Up/c in a urine specimen was found to be an acceptable diagnostic technique for detection and quantitative estimation of proteinuria.     

谷氨酰胺对大鼠运动性疲劳的改善作用及其机制

目的: 探讨谷氨酰胺(Gln)对大鼠运动性疲劳、骨骼肌氧化应激和肝脏细胞凋亡的改善作用。方法: 将8周龄SPF级雄性SD大鼠20只, 体重180～220 g,适应性喂养1周后随机分为对照组和谷氨酰胺干预组,每组10只。谷氨酰胺干预组采用每天1.0 g/kg/d谷氨酰胺灌胃(约2 ml),对照组以等体积生理盐水灌胃(约2 ml),持续7 d。随后进行力竭实验,禁食不禁水12 h后处死大鼠,检测血清及骨骼肌谷胱甘肽(GSH)和丙二醛(MDA)水平及超氧化物歧化酶(SOD)活力,检测血清乳酸(LD)水平及肌酸激酶(CK)和乳酸脱氢酶(LDH)活力;荧光实时定量PCR检测肝组织Bcl-2和Bax 基因表达水平。结果: 与对照组相比,谷氨酰胺干预组大鼠力竭时间显著延长(P＜0.05),血清CK、LDH及LD水平显著降低(P＜0.05),血清与骨骼肌中GSH和SOD水平显著提高(P＜0.05),MDA水平明显降低(P＜0.05);肝组织Bax 基因表达水平显著降低(P＜0.05),Bcl-2 基因表达水平明显显著增高(P＜ 0.05)。结论: 谷氨酰胺有缓解大鼠运动性疲劳的作用,其机制可能与降低骨骼肌氧化应激程度和延缓肝脏细胞凋亡率有关。     

Increase of Soluble Casein during Storage of Sterilized Concentrated Skim Milk

We previously demonstrated that a methionine-threonine-supplemented low (8.5%) casein diet (8.5CMT) reduced symptoms such as proteinuria in nephritic rats without severe protein malnutrition. In this study, we examined whether or not L-arginine supplementation to 8.5CMT would exacerbate proteinuria and other symptoms in nephritic rats. Male Wistar rats with glomerulonephritis induced by a single intravenous injection of nephrotoxic serum were fed either a 20% casein diet (control), 8.5% casein diet, 8.5CMT, or L-arginine-supplemented 8.5CMT (8.5CMTA) for 16 days. The 8.5CMTA, as compared with the 8.5CMT, aggravated proteinuria and glomerulonephritis. Administration of L-N^G-nitroarginine methyl ester, an inhibitor of nitric oxide synthase, to 8.5CMTA-fed nephritic rats by drinking water for 14 days canceled the adverse effect of L-arginine on proteinuria and histopathological damage in glomeruli. These results suggest that the supplementation of L-arginine makes exacerbation via nitric oxide production in glomerulonephritis.     

MTOR regulates autophagic flux in the glomerulus

Sirolimus (rapamycin), an inhibitor of the mechanistic target of rapamycin (MTOR), was originally proposed as an immunosuppressant to prevent rejection of solid organ transplants. There were expectations that MTOR inhibitors would replace nephrotoxic calcineurin inhibitors (CNIs). Despite its potential advantages, evidence that sirolimus causes de novo or worsening proteinuria is unequivocal. Given the well-recognized proteinuric effect of MTOR inhibitors, we were interested in understanding its role in maintaining the glomerular filtration barrier. To investigate this in vivo, we developed a mouse model with a podocyte selective deletion of the Mtor gene (Mtor pod-KO).     

Structures of LRP2 reveal a molecular machine for endocytosis

1. Download : Download high-res image (296KB)
2. Download : Download full-size image