Klotho is a novel therapeutic target in peritoneal fibrosis via Wnt signaling inhibition.

BACKGROUND: Long-term exposure to bioincompatible peritoneal dialysate causes the loss of mesothelial cells and accumulation of matrix proteins, leading to an increase in the thickness of the submesothelial layer, thereby limiting the long-term effectiveness of peritoneal dialysis (PD). However, the detailed molecular mechanisms underlying the process of peritoneal fibrosis have not been clearly elucidated. Wnt/ß-catenin signaling pathway activation has been suggested to play a pivotal role in the development of organ fibrosis. Moreover, Klotho protein can regulate Wnt/ß-catenin signaling. We examined the role of Klotho protein in reducing peritoneal fibrosis by inhibiting Wnt/ß-catenin signaling. METHODS: The ß-catenin-activated transgenic (BAT) driving expression of nuclear ß-galactosidase reporter transgenic (BAT-LacZ) mice, the alpha-Klotho gene under control of human elongation factor 1 alpha promoter [Klotho transgenic (KLTG) and C57BL/6 background] and C57BL/6 mice [wild-type (WT)] were used. The mice received daily intraperitoneal (i.p.) injections of 4.25% glucose with lactate (PD solution) or saline as a control for 4 weeks. Other mice received daily i.p. injections of the same volume of saline (normal control). RESULTS: After exposure to PD, Wnt signal activation was observed on the peritoneal mesothelial cells in WT-PD mice. The peritoneal fibrosis was also accelerated in WT-PD mice. The protein expression of ß-catenin and Wnt-inducible genes were also remarkably increased in WT-PD mice. On the other hand, KLTG-PD mice attenuated activation of Wnt/ß-catenin signaling after exposure to PD and ameliorated the progression of peritoneal fibrosis. CONCLUSIONS: Overexpression of Klotho protein protects the peritoneal membrane through attenuation of the Wnt/ß-catenin signaling pathway. The availability of recombinant Klotho protein would provide a novel potential therapeutic target in peritoneal fibrosis.

Angiostatin production increases in response to decreased nitric oxide in aging rat kidney.

The development of interstitial fibrosis occurs with aging. Impaired angiogenesis, associated with progressive loss of the renal microvasculature, is thought to be a cause of age-related nephropathy. However, the mechanism of capillary loss in aging kidney has not been fully elucidated. Angiostatin is a kringle-containing fragment of plasminogen and is a potent inhibitor of angiogenesis in vivo. Whether angiostatin generation is increased in the aging kidney has not been investigated. We examined 4, 10, 16, and 24-month-old Sprague-Dawley rats for angiostatin production and found that angiostatin generation was increased in aged rats. The protein expression and the activity of cathepsin D-the enzyme for angiostatin production--were increased in aged rats. In the aging kidney, nitric oxide (NO) availability is decreased. To investigate the role of NO in angiostatin production, human umbilical vein endothelial cells were treated with L-NG-nitroarginine methyl ester (L-NAME). L-NAME-treated cells showed increased cathepsin D activity and angiostatin production. For in vivo experiments, 16- to 18-month-old rats were treated with L-NAME or molsidomine for 3 months. Angiostatin production was increased in L-NAME-treated kidney, accompanied by increased cathepsin D activity. In contrast, angiostatin production was decreased in molsidomine-treated kidney, accompanied by decreased cathepsin D activity. In conclusion, angiostatin generation by cathepsin D was increased in the aging rat kidney. Decreased NO production activated cathepsin D activity. Increased angiostatin production may be related to capillary loss and interstitial damage in the aging rat kidney.

Selective estrogen receptor modulation attenuates proteinuria-induced renal tubular damage by modulating mitochondrial oxidative status.

Proteinuria is an independent risk factor for progressive renal diseases because it initiates or aggravates tubulointerstitial injury. Clinically, females are less susceptible to progression of chronic kidney disease; however, the mechanisms underlying the renoprotective effect of estrogen receptor stimulation have yet to be clarified. Recently, inflammasome-dependent inflammatory responses were shown to be triggered by free fatty acids, and mitochondria-derived reactive oxygen species were shown to be required for this response. Albumin-bound free fatty acids trigger inflammasome activation through mitochondrial reactive oxygen species production in human proximal tubule epithelial cells in vitro, an effect inhibited by raloxifene. Female ICR-derived glomerulonephritic mice (mice with hereditary nephritic syndrome) were ovariectomized and treated with raloxifene, a selective estrogen receptor modulator. Ovariectomized mice showed activation of tubular inflammasomes and elevated levels of inflammasome-dependent cytokines. Raloxifene attenuated these changes ameliorating tubulointerstitial damage, reduced production of reactive oxygen species, averted morphological changes, and improved respiratory function in mitochondria. The expression of genes that encode rate-limiting enzymes in the mitochondrial ß-oxidation pathway was reduced by ovariectomy but enhanced by raloxifene. Thus, inflammasomes may be a novel and promising therapeutic target for proteinuria-induced renal injury.

Endothelial dysfunction promotes the transition from compensatory renal hypertrophy to kidney injury after unilateral nephrectomy in mice.

Loss of functional nephrons associated with chronic kidney disease induces glomerular hyperfiltration and compensatory renal hypertrophy. We hypothesized that the endothelial nitric oxide synthase (eNOS) [soluble guanylate cyclase (sGC)] protein kinase G (PKG) pathway plays an important role in compensatory renal hypertrophy after unilateral nephrectomy. Analysis of mice subjected to unilateral nephrectomy showed increases in kidney weight-to-body weight and total protein-to-DNA ratios in wild-type but not eNOS knockout (eNOSKO) mice. Serum creatinine and blood urea nitrogen increased after nephrectomy in eNOSKO but not in wild-type mice. Furthermore, Bay 41-2272, an sGC stimulator, induced compensatory renal hypertrophy in eNOSKO mice and rescued renal function. The NO donor S-nitrosoglutathione (GSNO) and Bay 41-2272 stimulated PKG activity and induced phosphorylation of Akt protein in human proximal tubular cells. GSNO also induced phosphorylation of eukaryotic initiation factor 4E-binding protein and ribosomal protein S6. Our results highlight the importance of the eNOS-NO-PKG pathway in compensatory renal hypertrophy and suggest that reduced eNOS-NO bioavailability due to endothelial dysfunction is the underlying mechanism of failure of compensatory hypertrophy and acceleration of progressive renal dysfunction.

Tacrolimus induces glomerular injury via endothelial dysfunction caused by reactive oxygen species and inflammatory change.

BACKGROUND/AIMS: The immunosuppressive drug tacrolimus (FK506) is used clinically to reduce the rejection rate in patients with kidney transplantation; however, the resultant nephrotoxicity remains a serious problem. In the present study we attempted to elucidate the mechanisms of glomerular injury induced by FK506 and the renoprotective effects of the angiotensin II receptor blocker telmisartan. METHODS: Seven-week-old male Wistar rats were divided into three groups: vehicle group, FK506 group, and FK506 + telmisartan group. After 8 weeks, we assessed kidney function and renal morphological changes including oxidative stress. We also assessed the effect of FK506 in human glomerular endothelial cells (hGECs) with regard to reactive oxygen species (ROS). RESULTS: FK506 induced ROS production via activation of NAD(P)H oxidase in the glomeruli. Expression of ICAM mRNA was increased in glomeruli from the FK506 group. These effects resulted in macrophage infiltration into the glomeruli. FK506 directly promoted NAD(P)H oxidase activity and accelerated production of ROS in hGECs. Conversely, cotreatment with telmisartan inhibited both NAD(P)H oxidase activity and production of ROS. CONCLUSION: These findings suggest that glomerular injury resulting from FK506 is caused by oxidative stress mediated by activation of NAD(P)H oxidase and that telmisartan exerts a renoprotective effect via antioxidative activity.

Overexpression of klotho protein modulates uninephrectomy-induced compensatory renal hypertrophy by suppressing IGF-I signals.

The klotho gene is highly expressed in the distal convoluted tubule of the kidney, while its encoded protein has many physiological and pathophysiological renal roles. We investigated the effect of klotho protein on physiological compensatory renal hypertrophy after nephrectomy in klotho transgenic (KLTG) mice. Renal hypertrophy was suppressed in KLTG mice compared with wild-type mice, and this was associated with suppression of insulin growth factor-1 (IGF-1) signaling by klotho protein. In vitro, IGF-1 signaling was suppressed in human proximal tubular cells transfected with the klotho plasmid. Our data suggest that klotho modulates compensatory renal hypertrophy after nephrectomy via suppression of the IGF-1 signaling pathway, indicating a novel physiological role for klotho protein in the kidney.

Role of Na+, K+-ATPase alpha1 subunit in the intracellular accumulation of cisplatin.

The present study was undertaken to identify what regulates intracellular cisplatin (CDDP) accumulation and what changes in membrane fraction of CDDDP-resistant cell line. The CDDP-resistant rat hepatoma cell line, H4-II-E/CDDP, shows a significant decrease in intracellular platinum accumulation compared with parental H4-II-E cells, although there was no difference in the efflux of CDDP between these two cell lines. In this study, we examined the contribution of functional change in active transport to the CDDP resistance of H4-II-E/CDDP cells. Compared with the resistant cells, platinum accumulation in the parental cells was clearly decreased by low temperature or ATP depletion. In addition, the Na+, K+-ATPase inhibitor ouabain and the K+ channel inhibitor tetraethylammonium decreased platinum accumulation in parental cells but did not change the accumulation in resistant cells. Amphotericin B, an antifungal agent, increased the intracellular platinum accumulation in resistant cells to the same level as in parent cells. Western blot analysis demonstrated that the Na+, K+-ATPase alpha1 subunit was reduced in resistant cells compared with the parental cells, although there was no difference in the expression of the beta1 subunit between the two cell lines. Furthermore, the Na+, K+-ATPase alpha1 subunit of H4-II-E was decreased following a 24-h exposure to CDDP. These results suggest that Na+, K+-ATPase-dependent active transport of CDDP does not occur in resistant cells, and, furthermore, our findings provide the first evidence that the Na+, K+-ATPase alpha1 subunit plays an important role in the transport of CDDP.

Posttraumatic symptoms in Japanese bereaved family members with special regard to suicide and homicide cases.

The authors investigated posttraumatic stress disorder (PTSD) symptoms in Japanese bereaved family members using a questionnaire. Participants were bereaved as a result of suicide and homicide (n = 51 and 49, respectively), with natural death (n = 56) as a control; and their relationships to the deceased were parent-child (n = 79), conjugal (n = 42), and others (n = 35). With regard to the 3 main PTSD-related criteria, (a) re-experiencing symptoms were not dependent on the manner of death or the relationship to the deceased; (b) avoidance behaviors were more highly related to homicide than natural death for relatives other than parent-child and conjugal relationships; and (c) hyperarousal and maladaptation symptoms were more serious for conjugal loss. These findings suggest that avoidance behaviors in homicidal cases are more closely associated with a distant family relationship, whereas conjugal loss is traumatic, irrespective of the manner of death, often causing hyperarousal and maladaptation symptoms.