The abnormal expressions of tristetraprolin and the VEGF family in uraemic rats with peritoneal dialysis

Differential Expression of Anti-Inflammatory RNA Binding Proteins in Lupus Nephritis

Lupus nephritis (LN) is a type of immunological complex glomerulonephritis characterized by chronic renal inflammation which is exacerbated by infiltrating leukocytes and fueled by a variety of pro-inflammatory cytokines. A profound understanding of the pathogenesis of LN is necessary to identify the optimal molecular targets. The role of RNA-binding proteins (RBPs) in post-transcriptional gene regulation in the immune system is being explored in greater depth to better understand how this regulation is implicated in inflammatory and autoimmune diseases. Tristetraprolin (TTP), Roquin-1/2, and Regnase-1 are 3 RBPs that play a critical role in the regulation of pro-inflammatory mediators by gating the degradation and/or translational silencing of target mRNAs. In this study, we proposed to focus on the differential expression of these RBPs in immune cells and renal biopsies from LN patients, as well as their regulatory impact on a specific target. Herein, we highlight a novel target of anti-inflammatory treatment by revealing the mechanisms underlying RBP expression and the interaction between RBPs and their target RNAs.

Activation of the MKK3-p38-MK2-ZFP36 Axis by Coronavirus Infection Restricts the Upregulation of AU-Rich Element-Containing Transcripts in Proinflammatory Responses

Coronavirus infections induce the expression of multiple proinflammatory cytokines and chemokines. We have previously shown that in cells infected with gammacoronavirus infectious bronchitis virus (IBV), interleukin 6 (IL-6), and IL-8 were drastically upregulated, and the MAP kinase p38 and the integrated stress response pathways were implicated in this process. In this study, we report that coronavirus infection activates a negative regulatory loop that restricts the upregulation of a number of proinflammatory genes. As revealed by the initial transcriptomic and subsequent validation analyses, the anti-inflammatory adenine-uridine (AU)-rich element (ARE)-binding protein, zinc finger protein 36 (ZFP36), and its related family members were upregulated in cells infected with IBV and three other coronaviruses, alphacoronaviruses porcine epidemic diarrhea virus (PEDV), human coronavirus 229E (HCoV-229E), and betacoronavirus HCoV-OC43, respectively. Characterization of the functional roles of ZFP36 during IBV infection demonstrated that ZFP36 promoted the degradation of transcripts coding for IL-6, IL-8, dual-specificity phosphatase 1 (DUSP1), prostaglandin-endoperoxide synthase 2 (PTGS2) and TNF-α-induced protein 3 (TNFAIP3), through binding to AREs in these transcripts. Consistently, knockdown and inhibition of JNK and p38 kinase activities reduced the expression of ZFP36, as well as the expression of IL-6 and IL-8. On the contrary, overexpression of mitogen-activated protein kinase kinase 3 (MKK3) and MAPKAP kinase-2 (MK2), the upstream and downstream kinases of p38, respectively, increased the expression of ZFP36 and decreased the expression of IL-8. Taken together, this study reveals an important regulatory role of the MKK3-p38-MK2-ZFP36 axis in coronavirus infection-induced proinflammatory response. IMPORTANCE Excessive and uncontrolled induction and release of proinflammatory cytokines and chemokines, the so-called cytokine release syndrome (CRS), would cause life-threatening complications and multiple organ failure in severe coronavirus infections, including severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS) and COVID-19. This study reveals that coronavirus infection also induces the expression of ZFP36, an anti-inflammatory ARE-binding protein, promoting the degradation of ARE-containing transcripts coding for IL-6 and IL-8 as well as a number of other proteins related to inflammatory response. Furthermore, the p38 MAP kinase, its upstream kinase MKK3 and downstream kinase MK2 were shown to play a regulatory role in upregulation of ZFP36 during coronavirus infection cycles. This MKK3-p38-MK2-ZFP36 axis would constitute a potential therapeutic target for severe coronavirus infections.

Nicotine-mediated OTUD3 downregulation inhibits VEGF-C mRNA decay to promote lymphatic metastasis of human esophageal cancer

Nicotine addiction and the occurrence of lymph node spread are two major significant factors associated with esophageal cancer's poor prognosis; however, nicotine's role in inducing lymphatic metastasis of esophageal cancer remains unclear. Here we show that OTU domain-containing protein 3 (OTUD3) is downregulated by nicotine and correlates with poor prognosis in heavy-smoking esophageal cancer patients. OTUD3 directly interacts with ZFP36 ring finger protein (ZFP36) and stabilizes it by inhibiting FBXW7-mediated K48-linked polyubiquitination. ZFP36 binds with the VEGF-C 3-'UTR and recruits the RNA degrading complex to induce its rapid mRNA decay. Downregulation of OTUD3 and ZFP36 is essential for nicotine-induced VEGF-C production and lymphatic metastasis in esophageal cancer. This study establishes that the OTUD3/ZFP36/VEGF-C axis plays a vital role in nicotine addiction-induced lymphatic metastasis, suggesting that OTUD3 may serve as a prognostic marker, and induction of the VEGF-C mRNA decay might be a potential therapeutic strategy against human esophageal cancer.

Tetramethylpyrazine Ameliorates Peritoneal Angiogenesis by Regulating VEGF/Hippo/YAP Signaling

Angiogenesis of human peritoneal vascular endothelial cells (HPVECs), linked to vascular endothelial growth factor (VEGF)/VEGF receptor 2 (VEGFR2) signaling, is a complication of peritoneal fibrosis (PF). Hippo/YAP signaling interacts with VEGF/VEGFR2 signaling, but the effect on peritoneal angiogenesis and PF has not been studied. We tested VEGF/Hippo/YAP inhibition by tetramethylpyrazine (TMP) in PF mice and HPVECs. This treatment ameliorated peritoneal dialysis (PD)–induced angiogenesis and PF. In mice, PF was associated with upregulation of VEGF, and TMP ameliorated submesothelial fibrosis, perivascular bleeding, and Collagen I abundance. In HPVECs, angiogenesis occurred due to human peritoneal mesothelial cells (HPMCs)–conditioned medium, and TMP alleviated HPVECs migration, tube formation, and YAP nuclear translocation. YAP knockdown PF mouse and HPVEC models were established to further confirm our finding. YAP deletion attenuated the PD-induced or VEGF-induced increase in angiogenesis and PF. The amount of CYR61 and CTGF was significantly less in the YAP knockdown group. To study the possibility that TMP could benefit angiogenesis, we measured the HPVECs migration and tube formation and found that both were sharply increased in YAP overexpression; TMP treatment partly abolished these increases. As well, the amount of VEGFR localized in the trans-Golgi network was lower by double immunofluorescence; VEGFR and its downstream signaling pathways including p-ERK, p-P38, and p-Akt were more in HPVECs with YAP overexpression. Overall, TMP treatment ameliorated angiogenesis, PF, and peritoneum injury. These changes were accompanied by inhibition of VEGF/Hippo/YAP.

Vascular endothelial growth factor-mediated peritoneal neoangiogenesis in peritoneal dialysis

Peritoneal dialysis (PD) is an important renal replacement therapy for patients with end-stage renal diseases, which is limited by peritoneal neoangiogenesis leading to ultrafiltration failure (UFF). Vascular endothelial growth factor (VEGF) and its receptors are key angiogenic factors involved in almost every step of peritoneal neoangiogenesis. Impaired mesothelial cells are the major sources of VEGF in the peritoneum. The expression of VEGF will be up-regulated in specific pathological conditions in PD patients, such as with non-biocompatible peritoneal dialysate, uremia and inflammation, and so on. Other working cells (i.e. vascular endothelial cells, macrophages and adipocytes) can also stimulate the secretion of VEGF. Meanwhile, hypoxia and activation of complement system further aggravate peritoneal injury and contribute to neoangiogenesis. There are several signalling pathways participating in VEGF-mediated peritoneal neoangiogenesis including tumour growth factor-β, Wnt/β-catenin, Notch and interleukin-6/signal transducer and activator of transcription 3. Moreover, VEGF is highly expressed in dialysate effluent of long-term PD patients and is associated with peritoneal transport function, which supports its role in the alteration of peritoneal structure and function. In this review, we systematically summarize the angiogenic effect of VEGF and evaluate it as a potential target for the prevention of peritoneal neoangiogenesis and UFF. Preservation of the peritoneal membrane using targeted therapy of VEGF-mediated peritoneal neoangiogenesis may increase the longevity of the PD modality for those who require life-long dialysis.

miR-15a-5p suppresses inflammation and fibrosis of peritoneal mesothelial cells induced by peritoneal dialysis via targeting VEGFA

Long-term peritoneal dialysis (PD) often ends up with ultrafiltration failure (UFF) which is partially caused by persistent inflammation and fibrosis of peritoneal tissues. However, the mechanism is still unclear. In the current study, the peritoneum from UFF patients demonstrated inflammation and fibrosis which were positively related to the expression of vascular endothelial growth factor A (VEGFA). The in vitro model using human peritoneal mesothelial cells (HPMCs) stimulated by high glucose or advanced glycation end (AGE) product showed consistent changes of inflammation, fibrosis, and VEGFA. What's more, we showed that VEGFA was an instigator of inflammation and fibrosis. Several microRNAs (miRNAs) have been reported to regulate expression of VEGFA elsewhere. Five of them were selected to test the expression in the peritoneum of patients with PD. Results suggested that miR-15a-5p was the most significantly downregulated one. Also, in high glucose or AGE product-stimulated HPMCs, miR-15a-5p decreased. When miRNA mimic was used to restore the expression of miR-15a-5p, high glucose-induced VEGFA was repressed. The predicted binding site between these two molecules was confirmed by the dual-luciferase assay. Restoration of miR-15a-5p restrained inflammation and fibrosis of HPMCs. TGF-β1/Smad2 was shown to be the downstream signaling pathway and their activity was regulated by miR-15a-5p/VEGFA. In conclusion, our current study demonstrates that miR-15a-5p acts as a regulator of VEGFA mRNA and the following inflammation and fibrosis in peritoneal mesothelial cells. The miR-15a-5p/VEGFA pathway may be a potential target for preventing ultrafiltration failure in patients with PD.

Effects of RNA interference-mediated gene silencing of VEGF on the ultrafiltration failure in a rat model of peritoneal dialysis

We investigated the effects of RNAi-mediated gene silencing of vascular endothelial growth factor (VEGF) on ultrafiltration failure (UFF) in rats with peritoneal dialysis (PD). Sprague–Dawley (SD) male rats were classified into normal, sham operation, and uremic model groups. Uremic rats were subcategorized into uremia, PD2, VEGF shRNA-2, vector-2, PD2 + Endostar, PD4, VEGF shRNA-4, Vector-4, and PD4 + Endostar groups. Peritoneal Equilibration Test (PET) was conducted to assess ultrafiltration volume (UFV) and mass transfer of glucose (MTG). mRNA and protein expressions of VEGF were detected using quantitative real-time PCR (qRT-PCR) and Western blotting. Immunohistochemistry was performed to detect microvessel density (MVD). Compared with the normal group, decreased UFV and increased MTG were observed in rest of the groups. Compared with the uremia group, UFV decreased, while MTG, expression of VEGFs, and number of new blood capillaries increased in the PD2, Vector-2, PD4, and Vector-4 groups. The PD4 and Vector-4 groups exhibited lower UFV and higher MTG than the PD2 group. In the VEGF shRNA-2, PD2 + Endostar, VEGF shRNA-4, and in PD4 + Endostar group increased UFV, reduced MTG and expression of VEGF, and decreased number of new blood capillaries were detected. Compared with the PD4 group, in the VEGF shRNA-4 and PD4 + Endostar groups, UFV increased, MTG and expression of VEGF decreased, and number of new blood capillaries reduced. VEGF expression was negatively correlated with UFV, but positively correlated with MTG. The results obtained in the study revealed that down-regulation of VEGF by RNAi could be a novel target approach for the treatment of UFF.

MiRNA-29c regulates the expression of inflammatory cytokines in diabetic nephropathy by targeting tristetraprolin

Diabetic nephropathy is one of the most prevalent chronic complications of Diabetes mellitus, but its pathogenesis remains elusive. This study was designed to determine the role of tristetraprolin (TTP), inflammatory cytokines and microRNAs (miRNAs) in DN. The blood and urine samples were obtained from 32 patients with DN, 33 patients with type 2 DM, and 35 normal healthy subjects as controls. Renal tissue samples were also obtained from 10 DN patients and 10 normal controls. The miRNA microarray analyses were performed in pooled plasma and urine sediment samples of eight DN patients and eight age- and sex-matched health control subjects and three paired renal tissues from patients with DN and normal controls. Conditionally immortalized mouse podocytes (MPC5) were used a cell model. The expressions of TTP and cytokines in patient samples and cultured cells were determined by qRT-PCR and Western blotting or ELISA. Our results indicated that miRNA-29c directly targeted TTP and promoted inflammatory response under hyperglycemic conditions. Overexpression of miRNA-29c in podocytes resulted in an increase in inflammatory cytokines and inhibition of miRNA-29c by using its inhibitor reduced the inflammatory cytokines in podocytes. Finally, miRNA-29c promoted the progression of DN by targeting TTP, providing a target for a therapeutic intervention of DN.

IL-6 promotes epithelial-to-mesenchymal transition of human peritoneal mesothelial cells possibly through the JAK2/STAT3 signaling pathway

Long-term peritoneal dialysis (PD) therapy results in functional and structural alteration of the peritoneal membrane, including epithelial-to-mesenchymal transition (EMT). Interleukin 6 (IL-6) is a local pleiotropic cytokine, hypothesized to play an important role in EMT. This study was designed to investigate the role of IL-6 in EMT and peritoneal membrane dysfunction in long-term PD patients by assessing the level of IL-6 in dialysate and exploring the relationship between IL-6, the related signaling pathway JAK2/STAT3, and EMT, using in vitro cellular and molecular techniques. Plasma and dialysate levels of IL-6 were significantly higher in PD ultrafiltration failure patients compared with patients without ultrafiltration failure and were negatively correlated with measures of PD adequacy. In vitro IL-6 treatment changed human peritoneal mesothelial cell phenotype from a typical cobblestone-like to a fibroblast-like appearance and increased cell viability. IL-6 treatment increased α-smooth muscle actin and vascular endothelial growth factor expression but decreased E-cadherin expression. IL-6 treatment activated the JAK/STAT signaling pathway. However, the JAK2/STAT3 inhibitor WP1066 prevented IL-6-induced activation of the JAK2/STAT3 pathway and EMT. We conclude that IL-6 promotes the EMT process, possibly by activating the JAK2/STAT3 signaling pathway. IL-6 may serve as a novel therapeutic target for preventing EMT, and preservation of the peritoneal membrane may arise from these studies.

NOD2 promotes endothelial-to-mesenchymal transition of glomerular endothelial cells via MEK/ERK signaling pathway in diabetic nephropathy

Endothelial-to-mesenchymal transition (EndMT) of glomerular vascular endothelial cells (GEnCs) is now considered to play a critical role in diabetic nephropathy (DN). NOD2 is newly discovered to be closely related to DN renal injury. However, the relationship between NOD2 and EndMT of GEnCs has never been reported. In the present study, we found that NOD2 over-expression was positively correlated with the severity of DN injury in human renal biopsy samples. Immunohistochemical staining of DN renal slices showed gradual absence of endothelial character and gain of mesenchymal character, both of which were associated with NOD2 over-expression. In high glucose stimulated GEnCs, NOD2 was increased. What's more, over-expression and activation of NOD2 could both promote EndMT of GEnCs. On the other hand, silencing of NOD2 markedly attenuated EndMT induced by high glucose. Mechanically, we further found that MEK/ERK signaling pathway was involved in NOD2-regulated EndMT. Collectively, our results indicate that NOD2 has a regulatory role in EndMT via activation of MEK/ERK in high glucose-treated GEnCs. Targeting this pathway is a promising strategy for intervention of DN endothelial dysfunction.

Protective effect of mycophenolate mofetil on residual renal function in peritoneal dialysis patients: An open label feasibility study

AIM

This study aims to evaluate the safety of mycophenolate mofetil (MMF) and its effect on residual renal function (RRF) during peritoneal dialysis (PD).

METHODS

This is a prospective, randomized study comprising 60 PD patients. The patients were assigned either to the MMF group (MMF dosage: 1.0-1.5 g/day in two divided doses for 6 months, followed by a dose of 0.5-0.75 g/day for another 6 months) or to the control group. The patients close monitoring for 1 year. Variables related to residual renal function, including urine volume, measured glomerular filtration rate (GFR), and renal Kt/V, were measured at four time points.

RESULTS

There were no significant changes in urinary protein excretion in either group (P > 0.05). The MMF group showed a significantly higher urine volume than the control group (955.38 ± 243.54 vs 786.15 ± 279.62 mL/day, P = 0.024). The renal kt/V was also significantly higher in the MMF group (0.59 ± 0.11 in MMF vs 0.50 ± 0.19 in control group, P = 0.032). There was significant difference in the renal measured GFR between the two groups at 6, 9 and 12 months (MMF vs control at 6 months, 6.14 ± 0.66 vs 5.58 ± 0.65 mL/min per 1.73m² , P = 0.003; at 9 months, 5.68 ± 0.80 vs 4.78 ± 0.75, P < 0.001; at 12 months, 5.44 ± 0.91 vs 4.43 ± 0.93, P < 0.001). MMF was well tolerated without any serious complications.

CONCLUSION

The use of MMF in PD patients tends to better preserve RRF.

Tristetraprolin exerts tumor suppressive functions on the tumorigenesis of glioma by targeting IL-13

The RNA-binding protein tristetraprolin (TTP) is an adenine/uridine (AU)-rich elements (AREs)-binding protein that can induce the decay of AREs containing mRNAs. In this study, we demonstrated that TTP is significantly down-regulated in human glioma tissue samples and cell lines. It is also associated with diminished survival in glioma patients. Gain- and loss-of-function studies demonstrated that TTP inhibited the growth, migration and invasion of glioma cells through regulation of interleukin (IL)-13. Furthermore, mechanistic investigations showed that TTP attenuated activation of PI3K/Akt/mTOR pathway by IL-13, and the ectopic expression of IL-13 markedly abrogated the anti-invasive effect of TTP. Additionally, TTP were found inversely correlated with IL-13 in glioma specimens. In conclusion, our results suggested that the low expression of TTP is significantly associated with the growth and metastasis of human glioma cells by targeting IL-13, while TTP may be a potential therapeutic target for glioma treatment.

New Insights into the Effects of Chronic Kidney Failure and Dialysate Exposure on the Peritoneum

♦ INTRODUCTION: Chronic uremia and the exposure to dialysis solutions during peritoneal dialysis (PD) induce peritoneal alterations. Using a long-term peritoneal exposure model, we compared the effects of chronic kidney failure (CKD) itself and exposure to either a 'conventional' or a 'biocompatible' dialysis solution on peritoneal morphology and function. ♦ METHODS: Wistar rats (Harlan, Zeist, the Netherlands) were grouped into: normal kidney function (NKF), CKD induced by 70% nephrectomy, CKD receiving daily peritoneal infusions with 3.86% glucose Dianeal (CKDD), or Physioneal (both solutions from Baxter Healthcare, Castlebar, Ireland) (CKDP). At 16 weeks, a peritoneal function test was performed, and histology, ultrastructure, and hydroxyproline content of peritoneal tissue were assessed. ♦ RESULTS: Comparing CKD with NKF, peritoneal transport rates were higher, mesothelial cells (MC) displayed increased number of microvilli, blood and lymph vasculature expanded, vascular basal lamina appeared thicker, with limited areas of duplication, and fibrosis had developed. All alterations, except lymphangiogenesis, were enhanced by exposure to both dialysis fluids. Distinct MC alterations were observed in CKDD and CKDP, the latter displaying prominent basolateral protrusions. In addition, CKDP was associated with a trend towards less fibrosis compared to CKDD. ♦ CONCLUSIONS: Chronic kidney failure itself induced peritoneal alterations, which were in part augmented by exposure to glucose-based dialysis solutions. Overall, the conventional and biocompatible solutions had similar long-term effects on the peritoneum. Importantly, the latter may attenuate the development of fibrosis.

Supplementation with high-dose trans-resveratrol improves ultrafiltration in peritoneal dialysis patients: a prospective, randomized, double-blind study

BACKGROUND

Ultrafiltration (UF) failure mostly contributes to technical failure in peritoneal dialysis (PD) patients, and one of its responsible factors is peritoneal angiogenesis. Resveratrol has been proposed to have an angiogenesis-ameliorating effect on tumor patients. We hypothesize trans-resveratrol has beneficial effects on angiogenesis-related markers in PD patients.

METHODS

In this prospective, randomized, and double-blind trial, 72 patients were randomly assigned to 12-week treatment of low-dose or high-dose (150 or 450 mg/d) trans-resveratrol or a placebo. Visits were scheduled at 0, 4, 8, and 12 weeks after treatment. Clinical indices including 24-hour UF volume, UF rate, 24-hour urine volume, residual renal function, and dialysis adequacy (kt/v) were measured. Angiogenesis markers including vascular endothelial growth factor (VEGF), fetal liver kinase-1 (Flk-1), angiopoietin-2 (Ang-2), tyrosine kinase 2 (Tie-2), and thrombospondin-1 (Tsp-1) in peritoneal effluent were also assessed by enzyme-linked immunosorbent assay.

RESULTS

Finally, 64 out of 72 patients were analyzed, 18 in the high-dose group, 22 in the low-dose group, and 24 in the placebo group. Over the 12-week period, patients in the high-dose group [mean change from baseline (95% CI): 171.4 (141.3-201.5) (mL), p = 0.003 (Net UF); 11.3(10.5-12.1) (mL/h), p = 0.02 (UF rate)] or the low-dose group [mean change from baseline (95% CI: 98.1 (49.5-146.7) (mL), p = 0.007 (Net UF); 6.5 (4.4-8.6) (mL/h), p = 0.04 (UF rate)] versus the placebo group had a significantly greater improvement in mean net UF volume and UF rate. The appearance rates of VEGF, Flk-1, and Ang-2 were more significantly reduced (appearance rates of Tie-2 and Tsp-1 increased) in the high-dose group versus the placebo group, but not in the low-dose group.

CONCLUSION

Supplementation with trans-resveratrol is beneficial to improve ultrafiltration in PD patients, and high-dose supplementation may improve ultrafiltration by ameliorating angiogenesis induced by conventional lactate-buffered PD solutions.