The interdependence of EGF-R and SGK-1 in fibronectin expression in primary kidney cortical fibroblast cells

Vaccarin suppresses diabetic nephropathy through inhibiting the EGFR/ERK1/2 signaling pathway

Diabetic nephropathy (DN) is recognized as one of the primary causes of chronic kidney disease and end-stage renal disease. Vaccarin (VAC) confers favorable effects on cardiovascular and metabolic diseases, including type 2 diabetes mellitus (T2DM). Nonetheless, the potential role and mechanism of VAC in the etiology of DN have yet to be completely elucidated. In this study, a classical mouse model of T2DM is experimentally induced via a high-fat diet (HFD)/streptozocin (STZ) regimen. Renal histological changes are assessed via H&E staining. Masson staining and immunohistochemistry (IHC) are employed to assess renal fibrosis. RT-PCR is utilized to quantify the mRNA levels of renal fibrosis, oxidative stress and inflammation markers. The levels of malondialdehyde (MDA) and reactive oxygen species (ROS), as well as the content of glutathione peroxidase (GSH-Px), are measured. The protein expressions of collagen I, TGF-β1, α-SMA, E-cadherin, Nrf2, catalase, SOD3, SOD2, SOD1, p-ERK, p-EGFR (Y845), p-EGFR (Y1173), p-NFκB P65, t-ERK, t-EGFR and t-NFκB P65 are detected by western blot analysis. Our results reveal that VAC has a beneficial effect on DN mice by improving renal function and mitigating histological damage. This is achieved through its inhibition of renal fibrosis, inflammatory cytokine overproduction, and ROS generation. Moreover, VAC treatment effectively suppresses the process of epithelial-mesenchymal transition (EMT), a crucial characteristic of renal fibrosis, in high glucose (HG)-induced HK-2 cells. Network pharmacology analysis and molecular docking identify epidermal growth factor receptor (EGFR) as a potential target for VAC. Amino acid site mutations reveal that Lys-879, Ile-918, and Ala-920 of EGFR may mediate the direct binding of VAC to EGFR. In support of these findings, VAC reduces the phosphorylation levels of both EGFR and its downstream mediator, extracellular signal-regulated kinase 1/2 (ERK1/2), in diabetic kidneys and HG-treated HK-2 cells. Notably, blocking either EGFR or ERK1/2 yields renal benefits similar to those observed with VAC treatment. Therefore, this study reveals that VAC attenuates renal damage via inactivation of the EGFR/ERK1/2 signaling axis in T2DM patients.

Roflumilast alleviates adenine-induced chronic kidney disease by regulating inflammatory biomarkers

The present investigation was carried out to explore the role of roflumilast, a PDE4 inhibitor, as a potential treatment option for chronic kidney disease. Forty-six male Wistar rats were divided into five groups: Control, Disease control (50 mg/kg Adenine p.o.), Adenine + Roflumilast (0.5, 1 and 1.5 mg/kg, p.o.). Various urinary and serum biomarkers, antioxidant status, histopathology, and protein expression of inflammatory markers were measured to investigate the effects of roflumilast on kidney functions. Adenine was found to elevate the levels of serum creatinine, urea, uric acid, sodium, potassium, chloride, magnesium, and phosphorus and reduce the level of serum calcium. Further, adenine significantly increased the serum TGF-β levels and reduced the anti-oxidant indices. Significant elevation was observed in protein expression of IL-1β, TNF-α, MCP-1, ICAM-1, and Fibronectin. Histopathologically, adenine caused thickening of the glomerular basement membrane, inflammatory cells infiltration, atrophy, and glomeruli deterioration. However, Roflumilast administration (1 mg/kg) remarkably decrease serum creatinine, urea, uric acid, sodium, potassium, chloride, magnesium, phosphorus by 61%, 40%, 44%, 41%, 49%, 58%, 59% and 42% respectively, and increase in calcium by 158%. Moreover, Roflumilast (1 mg/kg) significantly reduced serum TGF-β levels by 50% and elevated anti-oxidant indices by 257%, 112%, and 60%, respectively. The protein expression was significantly reduced by 5.5-fold, 7-fold, 5.7-fold, 6.2-fold, and 5.1-fold individually. Roflumilast noticeably improved the structure of glomeruli, tubules, and cellular functioning. The study confirmed that Roflumilast has the potential to ameliorate renal injury by reducing and regulating inflammatory responses.

Dissecting Efficacy and Metabolic Characteristic Mechanism of Taxifolin on Renal Fibrosis by Multivariate Approach and Ultra-Performance Liquid Chromatography Coupled With Mass Spectrometry-Based Metabolomics Strategy

Taxifolin (TFN) is an important natural compound with antifibrotic activity; however, its pharmacological mechanism is not clear. In this study, our aim is to gain insight into the effects of TFN and its potential mechanisms in unilateral ureteral obstruction (UUO) animal model using metabolomics approach to identify the metabolic biomarkers and perturbed pathways. Serum metabolomics analysis by UPLC-Q-TOF/MS was carried out to discover the changes in the metabolic profile. It showed that TFN has a significant protective effect on UUO-induced renal fibrosis and a total of 32 potential biomarkers were identified and related to RF progression. Of note, 27 biomarkers were regulated by TFN treatment, which participate in eight metabolic pathways, including phenylalanine, tyrosine and tryptophan biosynthesis, and phenylalanine metabolism. It also showed that metabolomics was a promising strategy to better dissect metabolic characteristics and pharmacological mechanisms of natural compounds by multivariate approach and ultra-performance liquid chromatography coupled with mass spectrometry.

Modulation of myelin formation by combined high affinity with extracellular matrix structure of electrospun silk fibroin nanoscaffolds

Remyelination is a major therapeutic goal in peripheral nerve regeneration, serving to restore function of demyelinated axons and provide neuroprotection. In order to apply myelin biogenesis strategies to peripheral nerve defects, the tissue engineered substitutes might be amenable to the promotion of this repair process. Electrospun nanofibers are considered as promising scaffolds for tissue engineering due to extracellular matrix mimicking factor and enhanced electrostatic interaction resulting in a controllable 3 D nanofibrous membrane. In order to explore the role of electrospun silk fibroin (SF) membrane in myelination, co-culture of dorsal root ganglion (DRG) neurons and Schwann cells (SCs) in vitro was established and observed. Scanning electron microscopy was used to observe DRG adhesion to the membranes, the electrospinning SF membrane is more favorable to the adhesion of DRG. The immunofluorescence staining of MAG and NF showed considerable amount of myelin were formed, and the myelin was tightly wrapped around the axons of the neurons, which was confirmed under the scanning electron microscope observation. Real-time quantitative PCR technique was used to determine the gene expression level of DRG neurons cultured at different time points. The results showed that the mRNA levels of N-cadherin, laminin, fibronectin were higher than those in the control group. Our results showed that the electrospun SF nanofibers can provide topographical and chemical cues that mimic (to a certain extent) the extracellular matrix.

Erhuang Formula ameliorates renal damage in adenine-induced chronic renal failure rats via inhibiting inflammatory and fibrotic responses

AIMS

The present study aimed to evaluate the protective effects of Erhuang Formula (EHF) and explore its pharmacological mechanisms on adenine-induced chronic renal failure (CRF).

MATERIALS AND METHODS

The compounds in EHF were analyzed by HPLC/MS. Adenine-induced CRF rats were administrated by EHF. The effects were evaluated by renal function examination and histology staining. Immunostaining of some proteins related cell adhesion was performedin renal tissues, including E-cadherin, β-catenin, fibronectin and laminin. The qRT-PCR was carried out determination of gene expression related inflammation and fibrosis including NF-κB, TNF-α, TGF-β1, α-SMA and osteopontin (OPN).

RESULTS

Ten compounds in EHF were identified including liquiritigenin, farnesene, vaccarin, pachymic acid, cycloastragenol, astilbin, 3,5,6,7,8,3',4'-heptemthoxyflavone, physcion, emodin and curzerene. Abnormal renal function and histology had significant improvements by EHF treatment. The protein expression of β-catenin, fibronectin and laminin were significantly increased and the protein expression of E-cadherin significantly decreased in CRF groups. However, these protein expressions were restored to normal levels in EHF group. Furthermore, low expression of PPARγ and high expression of NF-κB, TNF-α, TGF-β1, α-SMA and OPN were substantially restored by EHF treatment in a dose-dependent manner.

CONCLUSIONS

EHF ameliorated renal damage in adenine-induced CRF rats, and the mechanisms might involve in the inhibition of inflammatory and fibrotic responses and the regulation of PPARγ, NF-κB and TGF-β signaling pathways.

Protective Effects of Bu-Shen-Huo-Xue Formula against 5/6 Nephrectomy-Induced Chronic Renal Failure in Rats

Chronic renal failure (CRF) is a serious disease related to increasing incidence and prevalence as well as decline in quality of life. Bu-Shen-Huo-Xue formula (BSHX), one of traditional herbal formulations, has been clinically employed to treat CRF for decades, but the mechanisms involved have not been investigated. In the present study, we investigated the effects of BSHX on some closely related parameters in 5/6 nephrectomy CRF rats. Rats with CRF were divided into five groups, namely, one control group, one enalapril group, and three BSHX treatment groups (0.25, 0.5, and 1 g/kg·d). The rats subjected to sham operation were used as a normal control. After eight weeks of treatment, BSHX significantly decreased the levels of Scr and BUN, downregulated the mRNA expression levels of TGF-β₁, CTGF, NF-κB, TNF-α, and OPN, upregulated the mRNA expression of PPARγ, and reduced in situ expression of fibronectin and laminins. Histological findings also showed significant amelioration of the damaged renal tissue. BSHX protects 5/6 nephrectomy rats against chronic renal failure probably via regulating the expression of TNF-α, NF-κB, TGF-β₁, CTGF, PPARγ, OPN, fibronectin, and laminins and is useful for therapy of CRF.

Tribbles homolog 3 attenuates mammalian target of rapamycin complex-2 signaling and inflammation in the diabetic kidney

The endoplasmic reticulum (ER) stress response is activated in the diabetic kidney and functions to reduce ER protein accumulation and improve cellular function. We previously showed that tribbles homolog 3 (TRB3), an ER stress-associated protein, is upregulated in the diabetic kidney. Here, we investigated whether absence of TRB3 alters outcomes in diabetic nephropathy. Type 1 diabetes was induced in TRB3 wild-type and knockout ((-/-)) mice by low-dose streptozotocin, and the mice were followed for 12 weeks. Diabetic TRB3(-/-) mice developed higher levels of albuminuria and increased expression of inflammatory cytokine and chemokine mRNA in renal cortices relative to wild-type littermates, despite similar hyperglycemia. Diabetic TRB3(-/-) mice also expressed higher levels of ER stress-associated molecules in both the renal cortices and glomeruli. This change was associated with higher renal cortical phosphorylation of AKT at serine 473 (Ser(473)), which is the AKT site phosphorylated by mammalian target of rapamycin complex-2 (mTORC2). We show in renal tubular cells that TRB3 binds to mTOR and the rapamycin-insensitive companion of mTOR (Rictor), a protein specific to mTORC2. Finally, we demonstrate in murine tubular cells that TRB3 can inhibit secretion of IL-6. Thus, TRB3 reduces albuminuria and inflammatory gene expression in diabetic kidney disease by a mechanism that may involve inhibition of the mTORC2/AKT pathway and may prove to be a novel therapeutic target.

Sustained activation of EGFR triggers renal fibrogenesis after acute kidney injury

Severe acute kidney injury (AKI) is frequently accompanied by maladaptive repair and renal fibrogenesis; however, the molecular mechanisms that mediate these acute and chronic consequences of AKI remain poorly understood. In this study, we examined the role of epidermal growth factor receptor (EGFR) in these processes using waved-2 (Wa-2) mice, which have reduced EGFR activity, and their wild-type (WT) littermates after renal ischemia. Renal EGFR phosphorylation was induced within 2 days after ischemia, increased over time, and remained elevated at 28 days in WT mice, but this was diminished in Wa-2 mice. At the early stage of postischemia (2 days), Wa-2 mice developed more severe acute renal tubular damage with less reparative responses as indicated by enhanced tubular cell apoptosis, and reduced dedifferentiation and proliferation as compared to WT animals. At the late stage of postischemia (28 days), Wa-2 mice exhibited a less severe renal interstitial fibrosis as shown by reduced activation/proliferation of renal myofibroblasts and decreased deposition of extracellular matrix proteins. EGFR activation also contributed to cell cycle arrest at the G2/M phase, a cellular event associated with production of profibrogenetic factors, in the injured kidney. Collectively, these results indicate that severe AKI results in sustained activation of EGFR, which is required for reparative response of renal tubular cells initially, but eventually leads to fibrogenesis.

Mammalian tribbles homologs at the crossroads of endoplasmic reticulum stress and Mammalian target of rapamycin pathways

In 2000, investigators discovered Tribbles, a Drosophila protein that coordinates morphogenesis by inhibiting mitosis. Further work has delineated Xenopus (Xtrb2), Nematode (Nipi-3), and mammalian homologs of Drosophila tribbles, which include TRB1, TRB2, and TRB3. The sequences of tribbles homologs are highly conserved, and despite their protein kinase structure, to date they have not been shown to have kinase activity. TRB family members play a role in the differentiation of macrophages, lymphocytes, muscle cells, adipocytes, and osteoblasts. TRB isoforms also coordinate a number of critical cellular processes including glucose and lipid metabolism, inflammation, cellular stress, survival, apoptosis, and tumorigenesis. TRB family members modulate multiple complex signaling networks including mitogen activated protein kinase cascades, protein kinase B/AKT signaling, mammalian target of rapamycin, and inflammatory pathways. The following review will discuss metazoan homologs of Drosophila tribbles, their structure, expression patterns, and functions. In particular, we will focus on TRB3 function in the kidney in podocytes. This review will also discuss the key signaling pathways with which tribbles proteins interact and provide a rationale for developing novel therapeutics that exploit these interactions to provide better treatment options for both acute and chronic kidney disease.

Genetic or pharmacologic blockade of EGFR inhibits renal fibrosis

Although enhanced activation of the EGF receptor (EGFR) associates with the development and progression of renal fibrosis, the mechanisms linking these observations are not completely understood. Here, after unilateral ureteral obstruction (UUO), wild-type mice exhibited sustained EGFR phosphorylation in the kidney and developed renal fibrosis that was more severe than the renal fibrosis observed in waved-2 mice, which have reduced EGFR tyrosine kinase activity. Waved-2 mice also showed fewer renal tubular cells arrested at G2/M, reduced expression of α-smooth muscle actin (α-SMA), downregulation of multiple genes encoding profibrogenic cytokines, including TGF-β1, and dephosphorylation of Smad3, STAT3, and ERK1/2. Administration of the specific EGFR inhibitor gefitinib recapitulated this phenotype in wild-type mice after UUO. Furthermore, inactivation of either EGFR or STAT3 reduced UUO-induced expression of lipocalin-2, a molecule associated with the pathogenesis of CKD. In cultured renal interstitial fibroblasts, inhibition of EGFR also abrogated TGF-β1- or serum-induced phosphorylation of EGFR, STAT3, ERK1/2, and Smad3 as well as expression of α-SMA and extracelluar matrix proteins. Taken together, these data suggest that EGFR may mediate renal fibrogenesis by promoting transition of renal epithelial cells to a profibrotic phenotype, increased production of inflammatory factors, and activation of renal interstitial fibroblasts. Inhibition of EGFR may have therapeutic potential for fibrotic kidney disease.

Tyrosine kinase inhibitor, genistein, reduces renal inflammation and injury in streptozotocin-induced diabetic mice

Tyrosine kinase inhibition is known to reduce diabetes-induced end-organ damage but the mechanisms remain elusive. We hypothesized that inhibition of tyrosine kinase reduces renal inflammation and injury in streptozotocin-induced diabetes. Male C57BL/6 mice were given daily injections of streptozotocin (45 mg/kg/day, i.p. for 5 days); control animals received the vehicle (citrate buffer). Thereafter, streptozotocin-treated mice were treated with genistein (10 mg/kg, i.p three times a week for 10 weeks, n=8-10/group) or the vehicle (5% DMSO). The streptozotocin-treated mice displayed significant elevation in blood glucose level and decrease in plasma insulin level compared to their vehicle-treated controls. Treatment with genistein reduced blood glucose level (~15%; p<0.05) without a significant effect on plasma insulin level; however, blood glucose remained significantly higher than the control group. The development of diabetes was associated with significant increases in total protein, albumin, nephrin and collagen excretions compared to their controls. In addition, the diabetic mice displayed increased urinary MCP-1 excretion in association with increased renal ICAM-1 expression and apoptotic cells. Furthermore, renal gp91 expression levels and urinary Thio-Barbituric Acid Reactive Substances (TBARs) excretion, indices of oxidative stress, were also elevated in diabetic mice. These changes were associated with increased renal phospho-tyrosine expression and renal phospho-ERK/ERK ratio. Importantly, treatment with genistein reduced all these parameters towards control values. Collectively, the results suggest that the reno-protective effect of genistein likely relates to reduced renal inflammation, oxidative stress and apoptosis in diabetic mice.

Serum- and glucocorticoid-regulated kinase 1 is upregulated following unilateral ureteral obstruction causing epithelial-mesenchymal transition

Obstructive nephropathy leads to chronic kidney disease, characterized by a progressive epithelial-to-mesenchymal cell transition (EMT)-driven interstitial fibrosis. To identify the mechanisms causing EMT, we used the mouse model of unilateral ureteral obstruction and found a rapid and significant increase in serum- and glucocorticoid-regulated kinase-1 (SGK1) expression in the kidneys with an obstructed ureter. Knockout of SGK1 significantly suppressed obstruction-induced EMT, kidney fibrosis, increased glycogen synthase kinase-3β activity, and decreased accumulation of the transcriptional repressor Snail. This caused a reduced expression of the mesenchymal marker α-smooth muscle actin, and collagen deposition in this model. In cultured kidney epithelial cells, mechanical stretch or treatment with transforming growth factor-β not only stimulated the transcription of SGK1, but also stimulated EMT in an SGK1-dependent manner. Activated SGK1 stimulated Snail accumulation and downregulation of the epithelial marker E-cadherin. Hence, our study shows that SGK1 is involved in mediating fibrosis associated with obstructive nephropathy.

Advanced glycation end-products activate extracellular signal-regulated kinase via the oxidative stress-EGF receptor pathway in renal fibroblasts

Advanced glycation end-products (AGEs), epidermal growth factor receptor (EGFR), reactive oxygen species (ROS), and extracellular signal-regulated kinases (ERK) are implicated in diabetic nephropathy (DN). Therefore, we asked if AGEs-induced ERK protein phosphorylation and mitogenesis are dependent on the receptor for AGEs (RAGE)-ROS-EGFR pathway in normal rat kidney interstitial fibroblast (NRK-49F) cells. We found that AGEs (100 microg/ml) activated EGFR and ERK1/2, which was attenuated by RAGE short-hairpin RNA (shRNA). AGEs also increased RAGE protein and intracellular ROS levels while RAGE shRNA and N-acetylcysteine (NAC) attenuated AGEs-induced intracellular ROS. Hydrogen peroxide (5-25 microM) increased RAGE protein level while activating both EGFR and ERK1/2. Low-dose hydrogen peroxide (5 microM) increased whereas high-dose hydrogen peroxide (100 microM) decreased mitogenesis at 3 days. AGEs-activated EGFR and ERK1/2 were attenuated by an anti-oxidant (NAC) and an EGFR inhibitor (Iressa). Moreover, AGEs-induced mitogenesis was attenuated by RAGE shRNA, NAC, Iressa, and an ERK1/2 inhibitor (PD98059). In conclusion, it was found that AGEs-induced mitogenesis is dependent on the RAGE-ROS-EGFR-ERK1/2 pathway whereas AGEs-activated ERK1/2 is dependent on the RAGE-ROS-EGFR pathway in NRK-49F cells.

Targeting SGK1 in diabetes

Compelling evidence is accumulating indicating a pathophysiological role of the serum-and-glucocorticoid-inducible-kinase-1 (SGK1) in the development and complications of diabetes. SGK1 is ubiquitously expressed with exquisitely high transcriptional volatility. Stimulators of SGK1 expression include hyperglycemia, cell shrinkage, ischemia, glucocorticoids and mineralocorticoids. SGK1 is activated by insulin and growth factors via PI3K, 3-phosphoinositide dependent kinase PDK1 and mTOR. SGK1 activates ion channels (including ENaC, TRPV5, ROMK, KCNE1/KCNQ1 and CLCKa/Barttin), carriers (including NCC, NKCC, NHE3, SGLT1 and EAAT3), and the Na(+)/K(+)-ATPase. It regulates the activity of several enzymes (e.g., glycogen-synthase-kinase-3, ubiquitin-ligase Nedd4-2, phosphomannose-mutase-2), and transcription factors (e.g., forkhead-transcription-factor FOXO3a, beta-catenin and NF-kappaB). A common SGK1 gene variant ( approximately 3 - 5% prevalence in Caucasians, approximately 10% in Africans) is associated with increased blood pressure, obesity and type 2 diabetes. In patients suffering from type 2 diabetes, SGK1 presumably contributes to fluid retention and hypertension, enhanced coagulation and increased deposition of matrix proteins leading to tissue fibrosis such as diabetic nephropathy. Accordingly, targeting SGK1 may favourably influence occurrence and course of type 2 diabetes.

High glucose promotes the CTGF expression in human mesangial cells via serum and glucocorticoid-induced kinase 1 pathway

The role of serum and glucocorticoid-induced kinase 1 (SGK1) pathway in the connective tissue growth factor (CTGF) expression was investigated in cultured human mesangial cells (HMCs) under high glucose. By using RT-PCR and Western blot, the effect of SGK1 on the CTGF expression in HMCs under high glucose was examined. Overexpression of active SGK1 in HMCs transfected with pIRES2-EGFP-S422D hSGK1 (SD) could increase the expression of phosphorylated SGK1 and CTGF as compared with HMCs groups transfected with pIRES2-EGFP (FP) under high glucose or normal glucose. Overexpression of inactive SGK1 in HMCs transfected with pIRES2-EGFP-K127N hSGK1 (KN) could decrease phosphorylated SGK1 and CTGF expression as compared with HMCs groups transfected with FP under high glucose. In conclusion, these results suggest that high glucose-induced CTGF expression is mediated through the active SGK1 in HMCs.