DKK3 promotes renal fibrosis by increasing MFF-mediated mitochondrial dysfunction in Wnt/ß-catenin pathway-dependent manner.

BACKGROUND: Chronic kidney disease (CKD) lacks effective treatments and renal fibrosis (RF) is one of CKD's outcomes. Dickkopf 3 (DKK3) has been identified as an agonist in CKD. However, the underlying mechanisms of DKK3 in CKD are not fully understood. METHODS: H2O2-treated HK-2 cells and ureteric obstruction (UUO) mice were used as RF models. Biomarkers, Masson staining, PAS staining, and TUNEL were used to assess kidney function and apoptosis. Oxidative stress and mitochondria function were also evaluated. CCK-8 and flow cytometry were utilized to assess cell viability and apoptosis. Western blotting, IHC, and qRT-PCR were performed to detect molecular expression levels. Immunofluorescence was applied to determine the subcellular localization. Dual luciferase assay, MeRIP, RIP, and ChIP were used to validate the m6A level and the molecule interaction. RESULTS: DKK3 was upregulated in UUO mouse kidney tissue and H2O2-treated HK-2 cells. Knockdown of DKK3 inhibited oxidative stress, maintained mitochondrial homeostasis, and alleviated kidney damage and RF in UUO mice. Furthermore, DKK3 silencing suppressed HK-2 cell apoptosis, oxidative stress, and mitochondria fission. Mechanistically, DKK3 upregulation was related to the high m6A level regulated by METTL3. DKK3 activated TCF4/ß-catenin and enhanced MFF transcriptional expression by binding to its promoter. Overexpression of MFF reversed in the inhibitory effect of DKK3 knockdown on cell damage. CONCLUSION: Upregulation of DKK3 caused by m6A modification activated the Wnt/ß-catenin pathway to increase MFF transcriptional expression, leading to mitochondrial dysfunction and oxidative stress, thereby promoting RF progression.

Wnt/ß-catenin Pathway Aggravates Renal Fibrosis by Activating PUM2 Transcription to Repress YME1L-mediated Mitochondrial Homeostasis.

Chronic kidney disease (CKD) affects more than 10% of people worldwide and is a leading cause of death. However, the pathogenesis of CKD remains elusive. The oxidative stress and mitochondrial membrane potential were detected using Enzyme-linked immunosorbent assay and JC-1 assay. Co-immunoprecipitation, dual-luciferase assay, chromatin IP, RNA IP and RNA pull-down were used to validate the interactions among genes. Exploiting a H2O2-induced fibrosis model in vitro, PUM2 expression was upregulated in Human kidney 2 cell (HK-2) cells, along with reduced cell viability, enhanced oxidative stress, impaired mitochondrial potential, and upregulated expressions of fibrosis-associated proteins. While PUM2 knockdown reversed the H2O2-induced injury in HK-2 cells. Mechanically, Wnt/ß-catenin pathway activated PUM2 transcription via TCF4. It was further identified that Wnt/ß-catenin pathway inhibited YME1L expression through PUM2-mediated destabilizing of its mRNA. PUM2 aggravated H2O2-induced oxidative stress, mitochondrial dysfunction, and renal fibrosis in HK-2 cell via suppressing YME1L expression. Our study revealed that Wnt/ß-catenin aggravated renal fibrosis by activating PUM2 transcription to repress YME1L-mediated mitochondrial homeostasis, providing novel insights and potential therapeutic targets for the treatment of kidney fibrosis.

Identification and characterization of two immune-related subtypes in human chronic kidney disease.

BACKGROUND: Immune response plays a vital role in the initiation and development of chronic kidney disease (CKD). Detailed mechanisms and specific immune-related biomarkers of CKD need further clarification. We aimed to identify and characterize immune-related infiltrates that are implicated in the CKD development using a bioinformatics method. METHODS: The expression profiles of GSE66494 dataset were acquired from the Gene Expression Omnibus (GEO) database. Patients with CKD were divided into low- vs. high-immune subtypes based on their immune score. Based on such analysis, we identified differentially expressed genes (DEGs) of low- and high-immune subtypes. The weight gene co-expression network analysis (WGCNA) was used to identify immune-associated modules between two subtypes. The gene set enriched (GSEA) and variation (GSVA) analyses were correlated with their functional types using the molecular complex detection (MCODE) method. Finally, the immune infiltration landscape between subtypes was revealed using the xCell algorithm. RESULTS: The total number of 131 differentially expressed immune-related genes (DEIRGs) were identified between low- vs. high-immune subtypes. Out of them GSEA/GSVA results identified and enriched immune- and inflammation-related pathways. In particular, GSVA results indicated that immune-related pathways were activated in high-immune subgroups. The core DEIRG genes that were identified to be involved in CKD development included: the protein tyrosine phosphatase receptor type C (PTPRC; also known as CD45) regulating cell growth and differentiation, an early activation marker (CD69), co-receptor for T cell receptor (CD8A), and T cell co-stimulatory signal (CD28). These core DEIRD genes were further verified by the GSE96804 dataset. We also found a higher proportion of immune cells infiltrating the high-immune subgroup. Furthermore, the four core genes were positively correlated with most immune cell types. CONCLUSION: Among 131 DEIRG genes, four genes (PTPRC, CD69, CD8A, and CD28) were identified as potential biomarkers associated with the immune cell infiltration in CKD patients, which may provide a novel insight for immunotherapy for CKD.

DKK3 promotes oxidative stress injury and fibrosis in HK-2 cells by activating NOX4 via ß-catenin/TCF4 signaling.

Oxidative stress and fibrosis may accelerate the progression of chronic kidney disease (CKD). DKK3 is related to regulating renal fibrosis and CKD. However, the molecular mechanism of DKK3 in regulating oxidative stress and fibrosis during CKD development has not been clarified, which deserves to be investigated. Human proximal tubule epithelial cells (HK-2 cells) were treated with H2O2 to establish a cell model of renal fibrosis. The mRNA and protein expressions were analyzed using qRT-PCR and western blot, respectively. Cell viability and apoptosis were evaluated using MTT assay and flow cytometry, respectively. ROS production was estimated using DCFH-DA. The interactions among TCF4, ß-catenin and NOX4 were validated using luciferase activity assay, ChIP and Co-IP. Herein, our results revealed that DKK3 was highly expressed in HK-2 cells treated with H2O2. DKK3 depletion increased H2O2-treated HK-2 cell viability and reduced cell apoptosis, oxidative stress, and fibrosis. Mechanically, DKK3 promoted formation of the ß-catenin/TCF4 complex, and activated NOX4 transcription. Upregulation of NOX4 or TCF4 weakened the inhibitory effect of DKK3 knockdown on oxidative stress and fibrosis in H2O2-stimulated HK-2 cells. All our results suggested that DKK3 accelerated oxidative stress and fibrosis through promoting ß-catenin/TCF4 complex-mediated activation of NOX4 transcription, which could lead to novel molecules and therapeutic targets for CKD.

Silencing of Central (Pro)renin Receptor Ameliorates Salt-Induced Renal Injury in Chronic Kidney Disease.

Aims: A high-salt diet can aggravate oxidative stress, and renal fibrosis via the brain and renal renin-angiotensin system (RAS) axis in chronic kidney disease (CKD) rats. (Pro)renin receptor (PRR) plays a role in regulating RAS and oxidative stress locally. However, whether central PRR regulates salt-induced renal injury in CKD remains undefined. Here, we hypothesized that the reduction of central PRR expression could ameliorate central lesions and thereby ameliorate renal injury in high-salt-load CKD rats. Results: We investigated RAS, sympathetic nerve activity, oxidative stress, inflammation, and tissue injury in subfornical organs and kidneys in high-salt-load 5/6 nephrectomy CKD rats after the silencing of central PRR expression by intracerebroventricular lentivirus-RNAi. We found that the sympathetic nerve activity was reduced, and the levels of inflammation and oxidative stress were decreased in both brain and kidney. Renal injury and fibrosis were ameliorated. To explore the mechanism by which central inhibition of PRR expression ameliorates kidney damage, we blocked central MAPK/ERK1/2 and PI3K/Akt signaling pathways as well as angiotensin converting enzyme 1-angiotensin II-angiotensin type 1 receptors (ACE1-Ang II-AT1R) axis. Salt-induced overexpression of renal RAS, inflammation, oxidative stress, and fibrosis in CKD rats were prevented by central blockade of the pathways. Innovation: This study provides new insights into the mechanisms underlying salt-induced kidney damage. Targeting central PRR or PRR-mediated signaling pathway may be a novel strategy for the treatment of CKD. Conclusions: These results suggested that the silencing of central PRR expression ameliorates salt-induced renal injury in CKD through Ang II-dependent and -independent pathways.

Renal and cerebral RAS interaction contributes to diabetic kidney disease.

The diabetes mellitus has posed a grave threat on human health, and is bound to result in renal trauma by uncertain mechanisms. Increasing evidences indicated that the activation of the renin-angiotensin system plays a pivotal role during the progression of diabetic kidney disease. In streptozotocin (STZ)-induced type 1 diabetic rat model, the losartan (a selective angiotensin II type 1 (AT1) receptor antagonist) and tempol (4-Hydroxy-TEMPO, reactive oxygen species scavenger) were administrated through intracerebroventricular injection or intragastric gavage. Intracerebroventricular administration of clonidine or renal denervation was carried out to block sympathetic nerve traffic. Compared with non-diabetic rats, the reno-cerebral axis was over-activated, including activity of renin-angiotensin system (RAS), oxidative stress, and sympathetic activity in diabetic rats. Central blockade of RAS inhibited the central oxidative stress and sympathetic activity, which led to decrease of intrarenal RAS activity and oxidative stress. Meanwhile, central administration of tempol reduced brain RAS, thus downregulated renal RAS activity and oxidative stress. Importantly, oral administration by intragastric gavage of high dose of losartan and tempol achieved the same effect. The results suggested that there is a cross-talk between renal and cerebral RAS/reactive oxygen species, contributing to the progression of diabetic kidney disease. The subfornical organ, paraventricular nucleus, and supraoptic nucleus in the forebrain also play a key role in development and progression of renal trauma through reno-cerebral reflex axis.

A stimuli-responsive drug release nanoplatform for kidney-specific anti-fibrosis treatment.

The renoprotective effects of hypoxia inducible-factor (HIF) activators have been demonstrated by improving renal hypoxia in chronic kidney disease. Cobalt chloride is one of the most widely used HIF activators in biomedicine; however, poor kidney targeting and undesirable side effects greatly limit its clinical applications. Here, we report a novel stimuli-responsive drug release nanoplatform in which glutathione (GSH)-modified Au nanoparticles (GLAuNPs) and Co2+ self-assemble into nanoassemblies (GLAuNPs-Co) through coordination interactions between empty orbitals of Co2+ and lone pairs of GSH. The GLAuNPs, when used as a drug carrier, demonstrated high drug loading capacity and pH-triggered drug release after assembling with Co2+. The acidic environment of lysosomes in renal fibrosis tissues could disassemble GLAuNPs-Co and release Co2+. Moreover, encapsulation of the Co2+ ions in the GLAuNPs greatly lowered the cytotoxicity of Co2+ in kidney tubule cells. Tissue fluorescence imaging showed that GLAuNPs-Co specifically accumulated in the kidneys, especially in the renal proximal tubules. After GLAuNPs-Co was intraperitoneally injected into ureter-obstructed mice, significant attenuation of interstitial fibrosis was exhibited. The beneficial effects can be mainly ascribed to miR-29c expression restored by HIF-α activation. These findings revealed that GLAuNPs-Co have pH-responsive drug release and renal targeting capabilities; thus, they are a promising drug delivery platform for treating kidney disease.

Targeted Ablation of Distal Cerebrospinal Fluid-Contacting Nucleus Alleviates Renal Fibrosis in Chronic Kidney Disease.

The potential function of distal cerebrospinal fluid-contacting nucleus (dCSF-CNs) in chronic kidney disease (CKD) development is poorly understood. We hypothesized that dCSF-CNs might affect the renin-angiotensin system (RAS) in kidney injury progression, with dCSF-CNs ablation potentially alleviating local RAS and renal fibrosis in rats after five-sixths nephrectomy (5/6Nx). Part of rats were randomly administered artificial cerebrospinal fluid (aCSF) intracerebroventricularly (icv), followed by 5/6Nx or sham operation; and other part of rats were administered Cholera toxin B subunit conjugated with saporin (CB-SAP) for dCSF-CNs lesion before 5/6Nx. The effect of CB-SAP on dCSF-CNs ablation was confirmed by double immunofluorescence staining. RAS component, NOX2 and c-fos levels in the subfornical organ (SFO), hypothalamic paraventricular nucleus (PVN) and hippocampus, as well as tyrosine hydroxylase (TH) and c-fos positive cells in rostral ventrolateral medulla (RVLM) were assessed. Next, the levels of RAS components (angiotensinogen [AGT], angiotensin-converting enzyme [ACE], Ang II type 1 receptor [AT1R], angiotensin-converting enzyme 2 [ACE2], and Mas receptor), NADPH oxidases (NOX2 and catalase), inflammatory cytokines (monocyte chemotactic protein 1 [MCP-1] and IL-6), and fibrotic factors (fibronectin and collagen I) were assessed. Less CB-labeled neurons were found in dCSF-CNs of CB-SAP-treated rats compared with 5/6Nx animals. Meanwhile, CB-SAP downregulated AGT, Ang II, AT1R, NOX2, catalase, MCP-1, IL-6, fibronectin, and collagen I, and upregulated ACE2 and Mas receptor, compared with CKD rats. More TH and c-fos positive cells were found in RVLM of 5/6Nx rats but the number decreased after dCSF-CNs ablation. Targeted dCSF-CNs ablation could alleviate renal inflammation and fibrosis in chronic kidney injury by inhibiting cerebral and renal RAS/NADPH oxidase.

PTEN, Insulin Resistance and Cancer.

BACKGROUND: The tumor suppressor PTEN serves as a negative regulator of PI3K/PTEN/Akt signaling pathway that regulates cellular functions such as cell growth, differentiation, proliferation and migration. The PI3K/PTEN/Akt signaling cascades might also have effect on glucose uptake via translocation of GLUT-4. Insulin controls energy storage and the whole body glucose homeostasis. Its binding to insulin receptor on the surface of diverse cells allows glucose entry into cells, and activates a variety of cellular actions. Insulin resistance is a common metabolic feature and established risk factor of many diseases. Its fundamental principle is inability of insulin to exert its normal metabolic effects, and nutrient imbalance and abnormal lipid accumulation in skeletal muscle, liver and adipose tissues. METHODS: We review the literature on the structure and function of PTEN and its involvement in insulin resistance and tumor regulation, and summarized the detailed scientific achievements on this topic. RESULTS: Suppressing PTEN expression plays a role in pro- or anti-inflammatory state during insulin resistance associated with obesity. Selective disruption of PTEN in pancreatic α-cells demonstrates that a lack of PTEN reduces circulating glucagon levels and protects against hyperglycemia and insulin resistance in high-fat diet-fed mice. Loss-of-function PTEN mutations in adipose tissue results in systemic glucose tolerance and insulin sensitivity improvement because of ascended recruitment of the GLUT-4 towards the membrane. Targeting tissuespecific PTEN deletion improves insulin sensitivity and protects from systemic insulin resistance. PTEN, as an important tumor suppressor gene, is frequently deleted or mutated in a variety of human tumors. Inactivation of PTEN by loss-of-function mutations leads to deregulated hyperproliferation of cells, leading to oncogenic transformation. CONCLUSION: Considering PTEN's important role in insulin resistance and tumor regulation, targeting the PTEN gene and/or protein will likely provide an efficient strategy for therapeutic intervention in cancer and metabolic diseases like type 2 diabetes mellitus, obesity, and cardiovascular dysfunction.

Salt-induced phosphoproteomic changes in the hypothalamic paraventricular nucleus in rats with chronic renal failure.

Hypothalamic paraventricular nucleus (PVN) is a cardiovascular regulating center within the brain, which plays a critical role in high salt-induced progression of chronic renal failure (CRF). However, the phosphoproteomic changes in the PVN caused by CRF remain unclear. This study aimed to perform large-scale phosphoproteomic analysis of PVN induced by CRF and high salt intake. In this study, eight weeks post 5/6 nephrectomy (CRF model) or sham operation, Sprague-Dawley rats were fed a high-salt (4%) or normal-salt (0.4%) diet for 3weeks. TiO2 enrichment, iTRAQ labeling, and liquid chromatography tandem mass spectrometry were applied for phosphoproteomic profiling of PVN. A total of 3723 unique phosphopeptides corresponding to 1530 phosphoproteins were identified. Compared with sham group, 133 upregulated and 141 downregulated phosphopeptides were identified in CRF group during normal-salt feeding. However, with a high-salt diet, 160 phosphopeptides were upregulated and 142 downregulated in the CRF group. Gene Ontology analysis revealed that these phosphoproteins were involved in binding, catalytic, transporter, and other molecular functions. Search Tool for the Retrieval of Interacting Genes protein-protein analysis showed direct or indirect functional links among 25 differentially expressed phosphoproteins in CRF rats compared with sham group. However, 24 differentially phosphorylated proteins induced by high salt intake were functionally linked in CRF animals. The altered phosphorylation levels of dynamin 1, TPPP and Erk1/2 were validated. Phosphoproteomic changes of PVN triggered by CRF and high salt-load have been investigated. It will provide new insight into pathogenetic mechanisms of development of chronic kidney disease and salt sensitivity.

Increased Apoptosis in the Paraventricular Nucleus Mediated by AT1R/Ras/ERK1/2 Signaling Results in Sympathetic Hyperactivity and Renovascular Hypertension in Rats after Kidney Injury.

Background: The central nervous system plays a vital role in the development of hypertension, but the molecular regulatory mechanisms are not fully understood. This study aimed to explore signaling in the paraventricular nucleus (PVN) which might contribute to renal hypertension. Methods: Renal hypertension model was established by five-sixth nephrectomy operation (5/6Nx) in male Sprague Dawley rats. Ten weeks afterwards, they were random assigned to no treatment, or intracerebroventricular injection (ICV) with artificial cerebrospinal fluid, losartan [angiotensin II receptor type 1 (AT1R) antagonist], farnesylthiosalicylic acid (Ras inhibitor), PD98059 (MEK inhibitor), or SB203580 (p38 inhibitor) and Z-DEVD-FMK (caspase-3 inhibitor). Before and after treatment, physiological and biochemical indices were measured. Immunohistochemistry, western blot and RT-PCR were applied to quantify key components of renin-angiotensin system, apoptosis-related proteins, Ras-GTP, and MAPKs in the PVN samples. TUNEL assay was used to measure the situ apoptosis in PVN. Results: The 5/6Nx rats showed significantly elevated systolic blood pressure, urinary protein excretion, serum creatinine, and plasma norepinephrine (p < 0.05) compared to sham rats. The expression of angiotensinogen, Ang II, AT1R, p-ERK1/2, or apoptosis-promoting protein Bax were 1.08-, 2.10-, 0.74-, 0.82-, 0.83-fold higher in the PVN of 5/6Nx rats, than that of sham rats, as indicated by immunohistochemistry. Western blot confirmed the increased levels of AT1R, p-ERK1/2 and Bax; meanwhile, Ras-GTP and p-p38 were also found higher in the PVN of 5/6Nx rats, as well as the apoptosis marker cleaved caspase-3 and TUNEL staining. In 5/6Nx rats, ICV infusion of AT1R antagonist, Ras inhibitor, MEK inhibitor or caspase-3 inhibitor could lower systolic blood pressure (20.8-, 20.8-, 18.9-, 14.3%-fold) together with plasma norepinephrine (53.9-, 57.8-,63.3-, 52.3%-fold). Western blot revealed that blocking the signaling of AT1R, Ras, or MEK/ERK1/2 would significantly reduce PVN apoptosis as indicated by changes of apoptosis-related proteins (p < 0.05). AT1R inhibition would cause reduction in Ras-GTP and p-ERK1/2, but not vice versa; such intervention with corresponding inhibitors also suggested the unidirectional regulation of Ras to ERK1/2. Conclusion: These findings demonstrated that the activation of renin-angiotensin system in PVN could induce apoptosis through Ras/ERK1/2 pathway, which then led to increased sympathetic nerve activity and renal hypertension in 5/6Nx rats.

[Advanced oxidation protein products induce epithelial-to-mesenchymal transition in cultured human proximal tubular epithelial cells via oxidative stress].

OBJECTIVE: To investigate the effects of advanced oxidation protein products (AOPP) on epithelial-to-mesenchymal transition (EMT) in cultured human proximal tubular epithelial cells (HK-2) and explore the mechanism. METHODS: HK-2 cells treated with 50, 100, 200, and 400 µg/ml AOPP or 50 µg/m bovine serum albumin (BSA) for 24 h, or with 200 µg/ml AOPP for 0.5, 1, 3, 6, 12, and 24 h were examined for the protein expression of α-SMA and E-cadherin. In cells pretreated with diphenyleneiodonium (DPI) or cytoplasmic superoxide dismutase (C-SOD), the effects of 50 µg/ml BSA and 200 µg/ml AOPP were assessed on the expressions of α-SMA and E-cadherin, malondialdehyde (MDA) level, superoxide dismutase (SOD) activity, catalase (CAT) activity, and glutathione peroxidase (GSH-px) activity. RESULTS: AOPP treatment up-regulated α-SMA expression and down-regulated E-cadherin expression in a dose- and time-dependent fashion. AOPP exposure of the cells resulted in increased MDA level and lowered activities of SOD, CAT and GSH-PX. DPI and C-SOD partially attenuated the effects of AOPP on α-SMA, E-cadherin, MDA, SOD, CAT and GSH-px. CONCLUSION: AOPP can induce EMT in cultured HK-2 cells via oxidative stress, and this effect can be attenuated by inhibiting the activation of NADPH oxidase and using antioxidants to delay the progression of renal interstitial fibrosis.

[Correlation between TMEM39A gene polymorphism and systemic lupus erythematosus in Chinese Han patients].

OBJECTIVE: To investigate the association between single nucleotide polymorphisms (SNPs) of the transmembrane protein 39A (TMEM39A) at the loci 1880G/A, 2442T/G, and 2456A/T and systemic lupus erythematosus (SLE) in Chinese Han patients. METHODS: TMEM39A gene polymorphisms at 3 loci (1880G/A, 2442T/G, 2456 A/T) were analyzed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in 110 Chinese Han patients with SLE and 80 normal control subjects, and the allele and genotype frequencies were compared by Chi-square test between the two groups. RESULTS: Both the genotype frequencies (AA, GA and GG) and allele frequencies (A and G) at 1880G/A differed significantly between SLE cases and the normal controls (P=0.002 and P=0.044, respectively). The two groups also showed significant differences in the genotype frequencies (GG, TG and TT) (P=0.001) and allele frequencies (G and T) (P=0.041) at 2442T/G. No significant differences were found in the genotype frequencies (TT, AT and AA) or allele frequencies (T and A) at 2456A/T between the two groups (P>0.05). The allele and genotype frequencies of the 3 SNPs showed no significant differences between lupus nephritis (LN) patients and non-LN patients. CONCLUSION: The TMEM39A polymorphisms at 1880G/A and 2442T/G, but not at 2456 A/T gene, may be associated with the susceptibility to SLE in Chinese Han population. The genotype or allele frequencies of the 3 SNPs have no effect on the incidence of lupus nephritis.