Ion channels as a therapeutic target for renal fibrosis

Renal ion channel transport and electrolyte disturbances play an important role in the process of functional impairment and fibrosis in the kidney. It is well known that there are limited effective drugs for the treatment of renal fibrosis, and since a large number of ion channels are involved in the renal fibrosis process, understanding the mechanisms of ion channel transport and the complex network of signaling cascades between them is essential to identify potential therapeutic approaches to slow down renal fibrosis. This review summarizes the current work of ion channels in renal fibrosis. We pay close attention to the effect of cystic fibrosis transmembrane conductance regulator (CFTR), transmembrane Member 16A (TMEM16A) and other Cl− channel mediated signaling pathways and ion concentrations on fibrosis, as well as the various complex mechanisms for the action of Ca2+ handling channels including Ca2+-release-activated Ca2+ channel (CRAC), purinergic receptor, and transient receptor potential (TRP) channels. Furthermore, we also focus on the contribution of Na+ transport such as epithelial sodium channel (ENaC), Na+, K+-ATPase, Na+-H+ exchangers, and K+ channels like Ca2+-activated K+ channels, voltage-dependent K+ channel, ATP-sensitive K+ channels on renal fibrosis. Proposed potential therapeutic approaches through further dissection of these mechanisms may provide new therapeutic opportunities to reduce the burden of chronic kidney disease.

Three-dimensional building morphology impacts on PM2.5 distribution in urban landscape settings in Zhejiang, China

Three-dimensional (3D) urban landscape patterns and building morphology are crucial for urban planning and essential for urban landscape functions. In this study, fixed and mobile monitoring sites were used to determine the spatial distribution of PM_2.5 concentrations in Hangzhou. Six 3D metrics were selected to analyze the response of PM_2.5 pollution to landscape patterns and building morphology, while their two-dimensional (2D) counterparts' metrics were also analyzed to contrast the differences. A variance partitioning analysis (VPA) was performed to measure the combined and relative contribution of 3D and 2D metrics to the changes in PM_2.5 concentrations. The results showed that: (1) on the 3D scale, forming a building pattern with a combination of different building heights can eliminate the accumulation of PM_2.5; (2) on the 2D scale, fragmentation and decentralization of landscapes and building patches alleviate PM_2.5 pollution; and (3) 3D building morphology indicators have the highest explanatory power (40.94%) for the changes of PM_2.5 concentrations. It turns out that the explanatory power of 3D metrics for PM_2.5 concentrations changes is much greater than that of 2D metrics. In addition, when compared to building morphology indicators from a single dimension, the combination of 2D and 3D metrics is better able to reflect urban PM_2.5 pollution. The results of this study expand our understanding of how PM_2.5 pollution responds to 2D and 3D metrics and provide useful information for urban planning.

circPlekha7 suppresses renal fibrosis via targeting miR-493-3p/KLF4

Aims: The authors aim to investigate the function of circPlekha7 in renal fibrosis. Methods: Human renal tissues from chronic kidney disease patients, kidney cell line and primary cultured renal tubular epithelial cells were used. TGF-β1-treated human kidney 2 cells/tubular epithelial cells and a unilateral ureteral obstruction mouse model were employed to study renal fibrosis. Results: circPlekha7 was diminished in renal tissues from chronic kidney disease patients and TGF-β1-treated human kidney 2 cells and tubular epithelial cells, while miR-493-3p was upregulated. Overexpression of circPlekha7 or knockdown of miR-493-3p suppressed TGF-β1 induced enhancements on epithelial to mesenchymal transition and fibrogenesis, as well as attenuated renal fibrosis and injury in mice subjected to unilateral ureteral obstruction. circPlekha7 bound with miR-493-3p, which directly targeted KLF4. Conclusion: circPlekha7 inhibits epithelial to mesenchymal transition of renal tubular epithelial cells and fibrosis via targeting miR-493-3p to de-repress KLF4/mitofusin2 expression.

Dickkopf-3: Current Knowledge in Kidney Diseases

Dickkopf-related protein 3 (DKK3) is a secreted glycoprotein that has been implicated in the pathogenesis of a variety of diseases. Recent evidence suggests that urinary DKK3 may serve as a potential biomarker for monitoring kidney disease progression and assessing the effects of interventions. We review the biological role of DKK3 as an agonist in chronic kidney disease (CKD) and autosomal dominant polycystic kidney disease (ADPKD) and as an antagonist in idiopathic membranous nephropathy (IMN). In addition, we present the clinical applications of DKK3 in acute kidney disease and tubulointerstitial fibrosis, suggesting that urine DKK3 may be a potential biomarker for acute kidney disease and CKD. Further research into the mechanism of DKK3 and its use as a diagnostic tool, alone or in combination with other biomarkers, could prove clinically useful for better understanding the pathology of kidney diseases and improving early detection and treatment.

Overexpression of UBE2C correlates with poor prognosis in gastric cancer patients

OBJECTIVE

The ubiquitin-conjugating enzyme E2C (UBE2C) has been known as a crucial factor upregulated in various tumors. The functions of UBE2C is mainly involved in the pathway protein ubiquitination. This study investigates the expression of UBE2C in gastric cancers and its correlation with overall survival rate.

MATERIALS AND METHODS

Real-time PCR (RT-PCR) and Western blotting were performed to determine the expression of UBE2C in gastric cancer samples and adjacent normal tissues. Immunohistochemical staining was used to assess the expression of UBE2C in 216 paraffin-embedded gastric cancer tissues.

RESULTS

The mRNA and relevant protein levels of UBE2C in gastric cancer tissues are significantly greater than those in the adjacent normal tissues. Also, the expression of UBE2C is found to correlate with lymphatic metastasis, serosa invasion, TNM (Malignant Tumors) staging and Lauren's classification (p<0.05). The univariate analysis shows that the overexpression of UBE2C associates with poor prognosis (p=0.001). The multivariate analysis demonstrates that expression of UBE2C, lymphatic metastasis, and TNM staging are independent prognostic indicators.

CONCLUSIONS

This study shows that overexpression of UBE2C contributes to the development of gastric cancer, and UBE2C has the potential to be exploited as a therapeutic target.

Inhibition of HDAC6 activity in kidney diseases: a new perspective

Histone deacetylase 6 (HDAC6), a cytoplasmic enzyme that plays important roles in many biological processes, is one isoform of a family of HDAC enzymes that catalyse the removal of functional acetyl groups from proteins. HDAC6 stands out from the other members of this family because it almost exclusively deacetylates cytoplasmic proteins and exerts deacetylation-independent effects, which has led to the successful development of relatively isoform-specific inhibitors of its enzymatic action. Numerous studies have recently demonstrated that HDAC6 expression and activity are increased in kidney disease, such as autosomal dominant polycystic kidney disease (ADPKD), renal fibrosis, and acute kidney injury (AKI), among others. Moreover, HDAC6 inhibitors have been investigated for use in treating these diseases. In fact, HDAC6 inhibitors effectively limit the progression of kidney diseases, suggesting that targeting HDAC6 may provide a novel treatment approach. However, the primary challenge in developing HDAC6-targeted therapies is understanding how the renoprotective effect of NDAC6 inhibitors can be selectively harnessed. Here, we discuss the unique function of HDAC6 and recapitulate the alluring potential of its inhibitors in kidney diseases.

The Role of Y-Box Binding Protein 1 in Kidney Injury: Friend or Foe?

Y-box-binding protein 1 (YB-1) is a multifunctional protein involved in various cellular processes via the transcriptional and translational regulation of target gene expression. YB-1 promotes acute or chronic kidney injury through multiple molecular pathways; however, accumulating evidence suggests that significantly increased YB-1 levels are of great importance in renoprotection. In addition, YB-1 may contribute to obesity-related kidney disease by promoting adipogenesis. Thus, the role of YB-1 in kidney injury is complicated, and no comprehensive review is currently available. In this review, we summarise recent progress in our understanding of the function of YB-1 in kidney injury and provide an overview of the dual role of YB-1 in kidney disease. Moreover, we propose that YB-1 is a potential therapeutic target to restrict kidney disease.

Overexpression of UBE2C correlates with poor prognosis in gastric cancer patients

OBJECTIVE

The ubiquitin-conjugating enzyme E2C (UBE2C) has been known as a crucial factor upregulated in various tumors. The functions of UBE2C is mainly involved in the pathway protein ubiquitination. This study investigates the expression of UBE2C in gastric cancers and its correlation with overall survival rate.

MATERIALS AND METHODS

Real-time PCR (RT-PCR) and Western blotting were performed to determine the expression of UBE2C in gastric cancer samples and adjacent normal tissues. Immunohistochemical staining was used to assess the expression of UBE2C in 216 paraffin-embedded gastric cancer tissues.

RESULTS

The mRNA and relevant protein levels of UBE2C in gastric cancer tissues are significantly greater than those in the adjacent normal tissues. Also, the expression of UBE2C is found to correlate with lymphatic metastasis, serosa invasion, TNM (Malignant Tumors) staging and Lauren's classification (p<0.05). The univariate analysis shows that the overexpression of UBE2C associates with poor prognosis (p=0.001). The multivariate analysis demonstrates that expression of UBE2C, lymphatic metastasis, and TNM staging are independent prognostic indicators.

CONCLUSIONS

This study shows that overexpression of UBE2C contributes to the development of gastric cancer, and UBE2C has the potential to be exploited as a therapeutic target.

α-klotho and anemia in patients with chronic kidney disease patients: A new perspective

Normocytic normochromic anemia is a common complication of chronic kidney disease (CKD) and is associated with numerous adverse consequences. Certain symptoms previously attributed to CKD are now known to be a consequence of anemia. Anemia contributes to an increased cardiac output, and the development of left ventricular hypertrophy, angina and congestive heart failure, leading to high morbidity and mortality in patients with CKD. The multifunctional α-klotho (KL) protein, which is predominantly expressed in the kidneys, is associated with the occurrence of anemia in patients with CKD. The present review presents current evidence on the potential role of α-KL in renal anemia. Low expression of α-KL appears to improve anemia in patients with CKD, and has been hypothesized to be a compensatory mechanism to attenuate the effects of anemia in patients with CKD. Further understanding of the role of α-KL in renal anemia may offer novel insights into the treatment of patients with CKD complicated with anemia.

Effects of caloric restriction on peroxisome proliferator-activated receptors and positive transcription elongation factor b expression in obese rats

OBJECTIVE

To investigate the effect of caloric restriction (CR) on expressions of peroxisome proliferators-activated receptors (PPARs) and positive transcription elongation factor b (P-TEFb) (including cyclin-dependent kinase 9 (CDK9) and cyclin T1) protein in visceral adipose tissue of obese rats.

MATERIALS AND METHODS

Obese rats were induced by high-fat diet for 8 weeks. Then they were divided into three groups: Model (n=5), 50% Calorie Restricted (50% CR, n=5), Intermittent Fasting (IF) (eight cycles of 3-d fasting and 3-d refeeding, n=6) for 8 weeks. Biochemical parameters were measured. Protein and mRNA expression of Cdk9, cyclin T1 and PPARs were qualified in visceral adipose tissue.

RESULTS

A significant decline in fasting plasma glucose (FPG), homeostatic model assessment of insulin resistance (HOMA-IR), body weight, and visceral fat weight was observed in 50% CR group. The IF group exhibited a significant decrease in FPG, HOMA-IR, visceral fat weight. Both 50% CR and IF down-regulated mRNA and protein expression of PPARγ and Cdk9, cyclin T1 and up-regulated mRNA and protein expression of PPARβ.

CONCLUSIONS

These results suggest that the effects of 50% CR and IF on HOMA-IR, body weight, visceral fat weight, P-TEFb and PPARγ expression may be related to their protective potential on obesity.

The NLPR3 inflammasome and obesity-related kidney disease

Over the past decade, the prevalence of obesity has increased, accompanied by a parallel increase in the prevalence of chronic kidney disease (CKD). Mounting evidence suggests that high body mass index (BMI) and obesity are important risk factors for CKD, but little is known about the mechanisms of obesity‐related kidney disease (ORKD). The NLRP3 inflammasome is a polyprotein complex that plays a crucial role in the inflammatory process, and numerous recent studies suggest that the NLRP3 inflammasome is involved in ORKD development and may serve as a key modulator of ORKD. Moreover, inhibiting activation of the NLRP3 inflammasome has been shown to attenuate ORKD. In this review, we summarize recent progress in understanding the link between the NLRP3 inflammasome and ORKD and discuss targeting the NLRP3 inflammasome as a novel therapeutic approach for ORKD.

Targeted inhibition of endoplasmic reticulum stress: New hope for renal fibrosis (Review)

Chronic kidney disease (CKD) has a very high mortality rate and remains a global health challenge. Inhibiting renal fibrosis is one of the most promising therapeutic strategies for CKD. Recent studies have indicated that endoplasmic reticulum stress (ERS) serves an active role in the development of acute and chronic kidney disease, especially with regards to renal fibrosis. In the current review, the authors summarize the latest understanding of the role of ERS during the onset of renal fibrosis. ERS promotes renal fibrosis through multiple signaling pathways, such as transforming growth factor-β, epithelial-mesenchymal transition and oxidative stress. In addition, ERS also causes podocyte damage, leading to increased proteinuria and the development of renal fibrosis in rat models. In conclusion, targeted inhibition of ERS may become a promising therapeutic strategy for renal fibrosis.

Matrix Metalloproteinases-7 and Kidney Fibrosis

Matrix metalloproteinase-7 (MMP-7) is a secreted zinc- and calcium-dependent endopeptidase that degrades a broad range of extracellular matrix substrates and additional substrates. MMP-7 playsa crucial role in a diverse array of cellular processes and appears to be a key regulator of fibrosis in several diseases, including pulmonary fibrosis, liver fibrosis, and cystic fibrosis. In particular, the relationship between MMP-7 and kidney fibrosis has attracted significant attention in recent years. Growing evidence indicates that MMP-7 plays an important role in the pathogenesis of kidney fibrosis. Here, we summarize the recent progress in the understanding of the role of MMP-7 in kidney fibrosis. In particular, we discuss how MMP-7 contributes to kidney fibrotic lesions via the following three pathways: epithelial-mesenchymal transition (EMT), transforming growth factor-beta (TGF-β) signaling, and extracellular matrix (ECM) deposition. Further dissection of the crosstalk among and regulation of these pathways will help clinicians and researchers develop effective therapeutic approaches for treating chronic kidney disease.

The Role of Krüppel-like Factor 4 in Renal Fibrosis

Chronic kidney disease (CKD) caused by renal fibrosis is an important public health concern. It is therefore necessary to understand the molecular pathogenesis of renal fibrosis in order to develop novel therapeutic strategies. KLF4 is the most extensively studied factor among the various members of the Krüppel-like factor (KLF) family of zinc finger-containing transcription factors. Many studies have demonstrated that KLF4 inhibits the activation of myofibroblasts and exerts an inhibitory effect on fibrosis. However, other studies have indicated that KLF4 may promote renal fibrosis. These controversial results suggest that KLF4 may be crucially involved in the development of renal fibrosis, although the underlying mechanism(s) remain unclear. Here, we summarize the recent progress made in understanding the role of KLF4 in renal fibrosis. Together, these findings suggest that KLF4 may participate in the development of renal fibrosis, but that its inhibition of fibrosis is greater than its promotion of the condition, which suggests that KLF4 may serve as a novel therapeutic target for renal fibrosis.

Disruption of Type-I IFN pathway ameliorates preservation damage in mouse orthotopic liver transplantation via HO-1 dependent mechanism

Ischemia/reperfusion injury (IRI) remains unresolved problem in clinical organ transplantation. We analyzed the role of Type-I interferon (IFN) pathway in a clinically relevant murine model of extended hepatic cold preservation followed by orthotopic liver transplantation (OLT). Livers from Type-I IFN receptor (IFNAR) knockout (KO) or wild-type (WT) mice (C57/BL6) were harvested, preserved at 4°C in UW solution for 20 h and transplanted to groups of syngeneic IFNAR KO or WT recipients. Liver graft but not recipient IFNAR deficiency was required to consistently ameliorate IRI in OLTs. Indeed, disruption of Type-I IFN signaling decreased serum alanine aminotransferase (sALT) levels (p < 0.001), diminished Suzuki's score of histological OLT damage (p < 0.01) and improved 14-day survival (from 42%[5/12] in WT to 92%[11/12] in IFNAR KO; p < 0.05). Unlike in WT group, IFNAR deficiency attenuated OLT expression of TNF-α, IL-1β, IL-6, MCP-1, CXCL-10, ICAM-1; diminished infiltration by macrophages/PMNs; and enhanced expression of antioxidant HO-1/Nrf2. The frequency of TUNEL+ apoptotic cells and caspase-3 activity/expression selectively decreased in IFNAR KO group. Small interfering (si)RNA-directed targeting of HO-1 restored cardinal features of liver IRI in otherwise resistant IFNAR-deficient OLTs. Thus, intact Type-I IFN signaling is required for hepatic IRI, whereas HO-1 is needed for cytoprotection against innate immunity-dominated organ preservation damage in IFNAR-deficient liver transplants.

Sotrastaurin, a protein kinase C inhibitor, ameliorates ischemia and reperfusion injury in rat orthotopic liver transplantation

Sotraustaurin (STN), a small molecule, targeted protein kinase C (PKC) inhibitor that prevents T-lymphocyte activation via a calcineurin-independent pathway, is currently being tested in Phase II renal and liver transplantation clinical trials. We have documented the key role of activated T cells in the inflammation cascade leading to liver ischemia/reperfusion injury (IRI). This study explores putative cytoprotective functions of STN in a clinically relevant rat model of hepatic cold ischemia followed by orthotopic liver transplantation (OLT). Livers from Sprague-Dawley rats were stored for 30 h at 4°C in UW solution, and then transplanted to syngeneic recipients. STN treatment of liver donors/recipients or recipients only prolonged OLT survival to >90% (vs. 40% in controls), decreased hepatocellular damage and improved histological features of IRI. STN treatment decreased activation of T cells, and diminished macrophage/neutrophil accumulation in OLTs. These beneficial effects were accompanied by diminished apoptosis, NF-κB/ERK signaling, depressed proapoptotic cleaved caspase-3, yet upregulated antiapoptotic Bcl-2/Bcl-xl and hepatic cell proliferation. In vitro, STN decreased PKCθ/IκBα activation and IL-2/IFN-γ production in ConA-stimulated spleen T cells, and diminished TNF-α/IL-1β in macrophage-T cell cocultures. This study documents positive effects of STN on liver IRI in OLT rat model that may translate as an additional benefit of STN in clinical liver transplantation.

Interaction between the intermediary electron acceptor (pheophytin) and a possible plastoquinone-iron complex in photosystem II reaction centers

Photoreduction of the intermediary electron acceptor, pheophytin (Pheo), in photosystem II reaction centers of spinach chloroplasts or subchloroplast particles (TSF-II and TSF-IIa) at 220 K and redox potential E(h) = -450 mV produces an EPR doublet centered at g = 2.00 with a splitting of 52 G at 7 K in addition to a narrow signal attributed to Pheo([unk]) (g = 2.0033, DeltaH approximately 13 G). The doublet is eliminated after extraction of lyophilized TSF-II with hexane containing 0.13-0.16% methanol but is restored by reconstitution with plastoquinone A (alone or with beta-carotene) although not with vitamin K(1). TSF-II and TSF-IIa are found to contain approximately 2 nonheme Fe atoms per reaction center. Incubation with 0.55 M LiClO(4) plus 2.5 mM o-phenanthroline (but not with 0.55 M LiClO(4) alone) decreases this value to approximately 0.6 and completely eliminates the EPR doublet, but photoreduction of Pheo is not significantly affected. Partial restoration of the doublet (about 25%) was achieved by subsequent incubation with 0.2 mM Fe(2+), but not with either Mn(2+) or Mg(2+). The Fe removal results in the development of a photoinduced EPR signal (g = 2.0044 +/- 0.0003, DeltaH = 9.2 +/- 0.5 G) at E(h) = 50 mV, which is not observed after extraction with 0.16% methanol in hexane. It is ascribed to plastosemiquinone no longer coupled to Fe in photosystem II reaction centers. The results show that a complex of plastoquinone and Fe can act as the stable "primary" electron acceptor in photosystem II reaction centers and that the interaction of its singly reduced form with the reduced intermediary acceptor, Pheo([unk]), is responsible for the EPR doublet.

Redox titration of fluorescence yield of photosystem II

The variable fluorescence yield of photosystem II is dependent on the redox state of the fluorescence quencher molecule or the primary electron acceptor of the system. We have carried out redox titrations of fluorescence yield of a photochemically active photosystem-II reaction-center particle and have measured the redox potential of the photosystem-II primary acceptor.During reductive titrations using dithionite as the reductant, only a single quenching transition was observed. For instance, at pH 7.0, the midpoint potential of the fluorescence transition is -325 mV, and those at a pH between 6.0 and 7.5 are consistent with a pH dependence of about 60 mV/pH unit. At a given pH, the midpoint potential of the transition closely corresponds to that of the most negative transition previously measured in unfractionated chloroplasts (both by chemical reductive titration). Oxidative titrations using ferricyanide as the oxidant yielded hysteresis in the titration curves.Similar changes in fluorescence yield were observed in redox titrations by electrochemical reduction or oxidation. Electrochemical reductive and oxidative titrations yielded reversible transitions, contrary to the hysteresis observed during chemical oxidative titration. From coulometric-titration data, we have estimated that most likely one electron is involved in the redox transition of the fluorescence-quencher or primary-electron-acceptor molecule of photosystem II. These findings are consistent with the current proposal that a membrane-bound plastoquinone functions as the primary acceptor of photosystem II.

Spectral and kinetic evidence for two early electron acceptors in photosystem I

Triton-fractionated photosystem-I particles poised at -625 mV, where the two bound iron-sulfur proteins are reduced, have been studied by optical and electron paramagnetic resonance spectroscopies from 293 to 5 K. At 5-9 K, these particles exhibit two decay components with lifetimes of 1.3 and 130 msec in the laser pulse-induced absorption and electron paramagnetic resonance signal changes. Spectral properties of the 130-msec decay component reflect the charge separation between P-700 and some iron-sulfur center having a broad optical absorbance in the 400- to 550-nm region and a previously reported electron paramagnetic resonance signal with g = 1.78, 1.88, and 2.08. Spectral properties of the 1-msec decay component indicate photoinduced charge separation between P-700 and a chlorophyll a dimer having absorption bands at 420, 450, and 700 nm. It is assumed that these two acceptors participate in the electron transfer from P-700(*) to the bound iron-sulfur proteins.

Oxidation-reduction potentials of bound iron-sulfur proteins of photosystem I

Digitonin - fractionated photosystem - I subchloroplasts were titrated potentiometrically between -450 and -610 mV at pH 10. Examination of the titrated subchloroplasts by low-temperature (13 degrees K) electron paramagnetic resonance spectroscopy revealed resonances centered at values of 2.05, 1.94, 1.92, 1.89, and 1.86 on the g-factor scale. The peak heights depended on the potentials at which the chloroplasts were poised. The resonances of at least three iron-sulfur centers can be recognized: one with lines at g = 2.05 and 1.94; one with lines at g = 2.05, 1.92, and 1.89; and one for which only a line at g = 1.86 has been resolved. The midpoint potentials of the iron-sulfur species fall into two distinctly separate regions: the titration profile of the g = 1.94 signal, the first segment of the g = 2.05 plot, and the rise phase of the g = 1.86 signal had a value of -530 +/- 5 mV; the upper segment of the g = 2.05 plot, the decrease phase of the g = 1.86 signal, and the g = 1.89 profile had a midpoint potential estimated to be [unk] -580 mV. The oxidation-reduction reaction of each of the bound iron-sulfur species, as represented by the changes of the electron paramagnetic resonance spectra, was reversible and apparently involved a two-electron change.Titration at pH 9 could only be carried to -560 mV, and essentially only the first half of the titration behavior as found at pH 10 was seen. At any given potential more positive than -560 mV, the part of the iron-sulfur protein that was not reduced electrochemically could be reduced photochemically, but only to the maximum extent reduced electrochemically at -560 mV. Whereas, chloroplasts illuminated at room temperature and then frozen while still being illuminated developed a signal similar to that produced by electrochemical reduction at -610 mV, illumination at 77 degrees K did not bring about photoreduction beyond that accomplished electrochemically at about -560 mV.Dithionite alone in the dark and under anaerobic conditions brought about a partial reduction to the extent of the first electrochemical reduction step. Dithionite plus illumination at room temperature or dithionite plus methyl viologen in the dark produced the maximum signal. Electron paramagnetic resonance spectra due to either light or electrochemically reduced iron-sulfur proteins showed no detectable decay for at least 3 days when samples were stored in the dark at 77 degrees K.