永井 良三

A novel murine model of aging (kl/kl mice) has been developed by in vivo mutagenesis. We analyzed endothelial function in this strain. Ring preparations of the thoracic aorta were obtained from 6- to 9-week old wild-type (+/+) and heterozygous (kl/+) klotho mice. The aortas of kl/+ mice showed an exaggerated contractile response to norepinephrine and attenuated vasodilator responses to acetylcholine and lecithinized superoxide dismutase (SOD) compared to +/+ mice. The response to sodium nitroprusside was unaltered in kl/+ mice. The contraction in response to norepinephrine was augmented by treatment with N(G)-nitro-L-arginine methyl ester (L-NAME, 10(-5) M) to a greater extent in +/+ mice than in kl/+ mice. Treatment with L-NAME abolished the vasodilator responses to both acetylcholine and lecithinized SOD. NO metabolites (NO2- and NO3-) and cGMP concentrations in the urine were significantly reduced in kl/+ mice compared to +/+ mice. However, the urinary excretion of 6-keto-prostaglandin F1alpha was unaltered. There was little immunostaining for NO synthase and vascular endothelial growth factor (VEGF) in the aorta of kl/+ mice. No immunostaining for NO synthase was noted in the aorta of kl/kl mice. The expression of the klotho gene product may have a role in the regulation of VEGF expression and is tightly linked to endothelial release of NO.

BACKGROUND/AIMS: We previously showed that the mesangial expression of nonmuscle-type myosin heavy chain, SMemb, was related to glomerular sclerosis. Although angiotensin II (AII) is known to promote the glomerular accumulation of extracellular matrix and sclerosis, the effect of AII on the mesangial expression of SMemb is unknown. Thus, we investigated the effect of AII on the mesangial expression of SMemb and synthesis of fibronectin. METHODS: We continuously administered AII to Sprague-Dawley rats with subcutaneous osmotic minipumps for 14 days. Control animals received normal saline instead. The effects of oral administration of an AII type 1 (AT1) receptor antagonist, candesartan cilexetil, and a vasodilator, hydralazine, were also examined. RESULTS: Semiquantitative immunohistochemical evaluation and Western blot analysis showed that AII significantly enhanced glomerular expression of SMemb (0.87 +/- 0.33 vs. 0.40 +/- 0.19 for immunohistochemical grading, p < 0.05; 2.55 +/- 0.88 vs. 1.16 +/- 0.75 for Western blot analysis, p < 0.05). Glomerular fibronectin was also increased in AII-administered rats (301.7 +/- 206.8 ng/5 microg protein vs. 95.8 +/- 81.3 ng/5 microg protein, p < 0.05). Candesartan cilexetil attenuated these effects. On the other hand, hydralazine did not change the glomerular expression of SMemb enhanced by AII administration. CONCLUSION: All induced a phenotypic alteration in mesangial cells, enhanced the mesangial expression of SMemb and stimulated the fibronectin synthesis. These results suggest that the mesangial expression of SMemb is related to glomerular matrix accumulation and that AII mediates both mesangial processes via AT1 receptors.

Na/Ca交換体(NCX)は,心筋細胞内からのCa2+汲み出しに中心的役割を果たす膜上タンパクであるが,その機能異常がどのような影響を生体に及ぼすのかは判っていない.今回我々は,NCXノックアウトヘテロ接合体(NCX KO)マウスと正常な同胞(WT)を用いてNCX機能異常に関する検討を行った.単離心室筋細胞を電気刺激し,細胞内Ca2+濃度([Ca2+]i)変化を観察した(fluo-3,室温).誘発された[Ca2+]iトランジェントの振幅はNCX KOで有意に大きく,続いてcaffeine(20mM)処理をして測定した筋小胞体(SR)内Ca2+量は,NCX KOで著明に増加していた.ノーザンブロットによるL型Ca2+チャネルの発現レベルに差がないことから,電気刺激時の[Ca+]i振幅の上昇はSR内Ca2+量の増加によるCa2+依存性Ca+放出の増強によるためと考えられた.これらの結果から,NCX KOマウス心室筋細胞はCa2+-overloadに陥りやすいと考えられた.横行大動脈部分に縮窄を形成し心肥大を誘発したところ,NCX KO心においてより顕著な肥大が観察された.心内圧測定の結果から,心内圧上昇がNCX KOマウスにおいてより大きかったことがその原因と推察された.血行動態上の拡張期dip&plateauパターンやドップラーエコー上の左室拡張早期流入血流減速時間(DCT)の短縮といった拡張不全所見を認めるなど,NCX KOにて心肥大が著明であることを示唆する生理学的所見も得られた.一方, WTではすでに収縮不全(EF低下)を呈しSR CaATPase(SERCA)の発現の低下も伴っていることから,心不全へ移行しているものと思われた.総括すると,NCX機能の低下は,圧負荷に対する肥大反応は加速するものの心不全への移行に関しては抑制的に作用すると考えられる.不全心ではNCXの発現および機能が上昇しているとされているが,このことからも心不全の進行にNCX機能変化が大きく関与する可能性が示唆された.

Peroxisome proliferator-activated receptor (PPAR) gamma is a ligand-activated transcription factor and a member of the nuclear hormone receptor superfamily that is thought to be the master regulator of fat storage; however, the relationship between PPARgamma and insulin sensitivity is highly controversial. We show here that supraphysiological activation of PPARgamma by PPARgamma agonist thiazolidinediones (TZD) markedly increases triglyceride (TG) content of white adipose tissue (WAT), thereby decreasing TG content of liver and muscle, leading to amelioration of insulin resistance at the expense of obesity. Moderate reduction of PPARgamma activity by heterozygous PPARgamma deficiency decreases TG content of WAT, skeletal muscle, and liver due to increased leptin expression and increase in fatty acid combustion and decrease in lipogenesis, thereby ameliorating high fat diet-induced obesity and insulin resistance. Moreover, although heterozygous PPARgamma deficiency and TZD have opposite effects on total WAT mass, heterozygous PPARgamma deficiency decreases lipogenesis in WAT, whereas TZD stimulate adipocyte differentiation and apoptosis, thereby both preventing adipocyte hypertrophy, which is associated with alleviation of insulin resistance presumably due to decreases in free fatty acids, and tumor necrosis factor alpha, and up-regulation of adiponectin, at least in part. We conclude that, although by different mechanisms, both heterozygous PPARgamma deficiency and PPARgamma agonist improve insulin resistance, which is associated with decreased TG content of muscle/liver and prevention of adipocyte hypertrophy.

BACKGROUND: It remains unclear how hemodynamic overload induces cardiac hypertrophy. Recently, activation of calcium-dependent phosphatase, calcineurin, has been elucidated to induce cardiac hypertrophy. In the present study, we examined the role of calcineurin in load-induced cardiac hypertrophy by using Dahl salt-sensitive (DS) rats, which develop both pressure and volume overload when fed a high salt diet. METHODS AND RESULTS: In the DS rat heart, the activity of calcineurin was increased and cardiac hypertrophy was induced by high salt diet. Treatment of DS rats with the calcineurin inhibitor FK506 (0.1 or 0.01 mg/kg every second day) from the age of 6 weeks to 12 weeks inhibited the activation of calcineurin in the heart in a dose-dependent manner and attenuated the development of load-induced cardiac hypertrophy and fibrosis without change of hemodynamic parameters. Additionally, treatment with 0.1 mg/kg every second day but not with 0.01 mg/kg every second day of FK506 from the age of 12 weeks to 16 weeks induced regression of cardiac hypertrophy in DS rats. Load-induced reprogramming of gene expression was also suppressed by the FK506 treatment. CONCLUSIONS: These results suggest that calcineurin is involved in the development of cardiac hypertrophy in rats with salt-sensitive hypertension and that inhibition of calcineurin could induce regression of cardiac hypertrophy.