Most chronic kidney injuries inevitably progress to irreversible renal fibrosis. Tubular epithelial-to-mesenchymal transition (EMT) is recognized to play pivotal roles in the process of renal fibrosis. However, a comprehensive understanding of the pathogenesis of renal scar formation and progression remains an urgent task for renal researchers. The endogenously produced microRNAs (miRNAs), proved to play important roles in gene regulation, probably regulate most genes involved in EMT. In this study, we applied microarray analysis to investigate the expression profiles of miRNA in murine interstitial fibrotic kidneys induced by unilateral ureteral obstruction (UUO). It was found that miR-200a and miR-141, two members of the miR-200 family, were downregulated at the early phase of UUO. In TGF-β1-induced tubular EMT in vitro, it was also found that the members of the miR-200 family were downregulated in a Smad signaling-dependent manner. It was demonstrated that the miR-200 family was responsible for protecting tubular epithelial cells from mesenchymal transition by target suppression of zinc finger E-box-binding homeobox (ZEB) 1 and ZEB2, which are E-cadherin transcriptional repressors. The results suggest that downregulation of the miR-200 family initiates the dedifferentiation of renal tubules and progression of renal fibrosis, which might provide important targets for novel therapeutic strategies.

Tubular atrophy resulting from epithelial cell loss is one of the characteristic features in the development of chronic renal interstitial fibrosis. Although the trigger(s) and mechanism for tubular cell loss remain undefined, the hyperactive transforming growth factor (TGF)-␤1 signaling has long been suspected to play an active role. Here we demonstrate that although TGF-␤1 did not induce cell death per se, it dramatically potentiated renal tubular cell apoptosis initiated by other death cues in vitro. Pre-incubation of human kidney epithelial cells (HKC) with TGF-␤1 markedly promoted staurosporine-induced cell death in a time-and dose-dependent manner. TGF-␤1 dramatically accelerated the cleavage and activation of pro-caspase-9, but not procaspase-8, in HKC cells. This event was followed by an accelerated activation of pro-caspase-3. To elucidate the mechanism underlying TGF-␤1 promotion of tubular cell death, we investigated the signaling pathways activated by TGF-␤1. Both Smad-2 and p38 mitogenactivated protein (MAP) kinase were rapidly activated by TGF-␤1, as demonstrated by the early induction of phosphorylated Smad-2 and p38 MAP kinase, respectively. We found that overexpression of inhibitory Smad-7 completely abolished Smad-2 phosphorylation and activation induced by TGF-␤1 but did not inhibit TGF-␤1-induced apoptosis. However, suppression of p38 MAP kinase with chemical inhibitor SC68376 not only abolished p38 MAP kinase phosphorylation but also obliterated apoptosis induced by TGF-␤1. These results suggest that hyperactive TGF-␤1 signaling potentiates renal tubular epithelial cell apoptosis by a Smadindependent, p38 MAP kinase-dependent mechanism.

Activation and expansion of interstitial fibroblasts and myofibroblasts play an essential role in the evolution of renal fibrosis. After obstructive injury, mice lacking tissue-type plasminogen activator (tPA) have fewer myofibroblasts and less interstitial fibrosis than wild-type controls. This suggests that tPA controls the size of the fibroblast/myofibroblast population in vivo, and this study sought to determine the underlying mechanism. In vitro, tPA inhibited staurosporine or H 2 O 2 -induced caspase-3 activation, prevented cellular DNA fragmentation, and suppressed the release of cytochrome C from mitochondria into the cytosol in a rat interstitial fibroblast cell line (NRK-49F). tPA also protected TGF-␤1-activated myofibroblasts from apoptosis. This antiapoptotic effect of tPA was independent of its protease activity but required its membrane receptor, the LDL receptor-related protein 1 (LRP-1). Deletion or knockdown of LRP-1 abolished tPA-mediated cell survival, whereas re-introduction of an LRP-1 minigene in a mouse LRP-1-deficient fibroblast cell line (PEA-13) restored the cytoprotective ability of tPA. tPA triggered a cascade of survival signaling involving extracellular signal-regulated kinase 1/2 (Erk1/2), p90RSK, and phosphorylation of Bad. Blockade of Erk1/2 activation abrogated the antiapoptotic effect of tPA, whereas expression of constitutively active MEK1 promoted cell survival similar to tPA. In vivo, compared with wild-type controls, apoptosis of interstitial myofibroblasts was increased in tPA Ϫ/Ϫ mice after obstructive injury, and myofibroblasts were completely depleted 4 wk after relief of the obstruction. Together, these findings illustrate that tPA is a survival factor that prevents apoptosis of renal interstitial fibroblasts and myofibroblasts through an LRP-1-, Erk1/2-, p90RSK-, and Bad-dependent mechanism.

. Mice lacking the matrix metalloproteinase-9 gene reduce renal interstitial fibrosis in obstructive nephropathy.

Edited by Xiao-Fan Wang M2 macrophage polarization is known to underlie kidney fibrosis. We previously reported that most of the members of the Wnt family of signaling proteins are induced in fibrotic kidneys. Dysregulation of the signaling protein Wnt5a is associated with fibrosis, but little is known about the role of Wnt5a in regulating M2 macrophage activation that results in kidney fibrosis. Here, using murine Raw 264.7 cells and bone marrow-derived macrophages, we found that Wnt5a enhanced transforming growth factor ␤1 (TGF␤1)-induced macrophage M2 polarization as well as expression of the transcriptional regulators Yes-associated protein (Yap)/transcriptional coactivator with PDZ-binding motif (Taz). Verteporfin blockade of Yap/Taz inhibited both Wnt5a-and TGF␤1-induced macrophage M2 polarization. In mouse models of kidney fibrosis, shRNA-mediated knockdown of Wnt5a expression diminished kidney fibrosis, macrophage Yap/Taz expression, and M2 polarization. Moreover, genetic ablation of Taz in macrophages attenuated kidney fibrosis and macrophage M2 polarization in mice. Collectively, these results indicate that Wnt5a promotes kidney fibrosis by stimulating Yap/Taz-mediated macrophage M2 polarization.

These observations suggest that vitamin D analogue possesses renoprotective activity through suppression of the matrix-producing myofibroblast activation. This action of vitamin D is mediated, at least in part, by up-regulating antifibrotic HGF gene expression in renal interstitial fibroblasts.

Urate is produced as the major end product of purine metabolism. In the last decade, the incidence of hyperuricemia increased markedly, and similar trends in the epidemiology of metabolic syndrome have been observed. Hyperuricemia is associated with renal disease, and recent studies have reported that mild hyperuricemia results in hypertension, intrarenal vascular disease, and renal injury. This has led to the hypothesis that uric acid may contribute to renal fibrosis and progressive renal disease. Our purpose was to investigate the relationship between uric acid and renal tubular injury. We applied the method of intraperitoneal injection of uric acid to generate the hyperuricemic mouse model. Compared with the saline injection group, the expression of lysyl oxidase (LOX) and fibronectin in kidneys was increased significantly in hyperuricemic groups. In vitro, uric acid significantly induced NRK-52E cells to express the ECM marker fibronectin, as well as LOX, which plays a pivotal role in ECM maturation, in a time- and dose-dependent manner. Upregulation of the urate transporter URAT1, which is located in the apical membrane of proximal tubules, sensitized the uric acid-induced fibronectin and LOX induction, while both knocking down URAT1 expression in tubular epithelial cells by RNA interference and inhibiting URAT1 function pharmacologically attenuated LOX and fibronectin expression. Furthermore, knockdown of LOX expression by a small interfering RNA strategy led to a decrease in fibronectin abundance induced by uric acid treatment. In addition, evidence of a uric acid-induced activation of the NF-kappaB signaling cascade was observed. Our findings highlight a need for carefully reevaluating our previous view on the pathological roles of hyperuricemia in the kidney and nephropathy induced by uric acid in clinical practice.

IntroductionWhether continuous venovenous hemofiltration (CVVHF) is superior to extended daily hemofiltration (EDHF) for the treatment of septic AKI is unknown. We compared the effect of CVVHF (greater than 72 hours) with EDHF (8 to 12 hours daily) on renal recovery and mortality in patients with severe sepsis or septic shock and concurrent acute kidney injury (AKI).MethodsA retrospective analysis of 145 septic AKI patients who underwent renal replacement therapy (RRT) between July 2009 and May 2013 was performed. These patients were treated by CVVHF or EDHF with the same polyacrylonitrile membrane and bicarbonate-based buffer. The primary outcomes measured were occurrence of renal recovery and all-cause mortality by 60 days.ResultsSixty-five and eighty patients were treated with CVVHF and EDHF, respectively. Patients in the CVVHF group had significantly higher recovery of renal function (50.77% of CVVHF group versus 32.50% in the EDHF group, P = 0.026). Median time to renal recovery was 17.26 days for CVVHF patients and 25.46 days for EDHF patients (P = 0.039). Sixty-day all-cause mortality was similar between CVVHF and EDHF groups (44.62%, and 46.25%, respectively; P = 0.844). 55.38% of patients on CVVHF and 28.75% on EDHF developed hypophosphatemia (P = 0.001). The other adverse events related to RRT did not differ between groups. On multivariate analysis, including physiologically clinical relevant variables, CVVHF therapy was significantly associated with recovery of renal function (HR 3.74; 95% CI 1.82 to 7.68; P < 0.001), but not with mortality (HR 0.69; 95% CI 0.34 to 1.41; P = 0.312).ConclusionsPatients undergoing CVVHF therapy had significantly improved renal recovery independent of clinically relevant variables. The patients with septic AKI had similar 60-day all-cause mortality rates, regardless of type of RRT.