Albumin-induced epithelial-mesenchymal transition and ER stress are regulated through a common ROS-c-Src kinase-mTOR pathway: effect of imatinib mesylate

The protective effect of imatinib against pancreatic β-cell apoptosis induced by dexamethasone via increased GSTP1 expression and reduced oxidative stress

Glucocorticoids (GCs) are known to stimulate pancreatic beta (β)-cell apoptosis via several mechanisms, including oxidative stress. Our previous study suggested an increase in dexamethasone-induced pancreatic β-cell apoptosis via a reduction of glutathione S-transferase P1 (GSTP1), which is an antioxidant enzyme. Imatinib, which is a tyrosine kinase inhibitor, also exerts antioxidant effect. This study aims to test our hypothesis that imatinib would prevent pancreatic β-cell apoptosis induced by dexamethasone via increased GSTP1 expression and reduced oxidative stress. Our results revealed that dexamethasone significantly increased apoptosis in INS-1 cells when compared to the control, and that imatinib significantly decreased INS-1 cell apoptosis induced by dexamethasone. Moreover, dexamethasone significantly increased superoxide production in INS-1 cells when compared to the control; however, imatinib, when combined with dexamethasone, significantly reduced superoxide production in INS-1 cells. Dexamethasone significantly decreased GSTP1, p-ERK1/2, and BCL2 protein expression, but significantly increased p-JNK, p-p38, and BAX protein expression in INS-1 cells-all compared to control. Importantly, imatinib significantly ameliorated the effect of dexamethasone on the expression of GSTP1, p-ERK1/2, p-JNK, p-p38 MAPK, BAX, and BCL2. Furthermore-6-(7-nitro-2,1,3-benzoxadiazol-4-ylthio) hexanol (NBDHEX), which is a GSTP1 inhibitor, neutralized the protective effect of imatinib against pancreatic β-cell apoptosis induced by dexamethasone. In conclusion, imatinib decreases pancreatic β-cell apoptosis induced by dexamethasone via increased GSTP1 expression and reduced oxidative stress.

An EMT-Related Gene Signature to Predict the Prognosis of Triple-Negative Breast Cancer

INTRODUCTION

Epithelial-mesenchymal transition (EMT) is an important biological process in tumor invasion and metastasis, and thus a potential indicator of the progression and drug resistance of breast cancer. This study comprehensively analyzed EMT-related genes in triple-negative breast cancer (TNBC) to develop an EMT-related prognostic gene signature.

METHODS

With the application of The Cancer Genome Atlas (TCGA) database, Molecular Taxonomy of Breast Cancer International Consortium (METABRIC), and the Genotype-Tissue Expression (GTEx) database, we identified EMT-related signature genes (EMGs) by Cox univariate regression and LASSO regression analysis. Risk scores were calculated and used to divide patients with TNBC into high-risk group and low-risk groups by the median value. Kaplan-Meier (K-M) and receiver operating characteristic (ROC) curve analyses were applied for model validation. Independent prognostic predictors were used to develop nomograms. Then, we assessed the risk model in terms of the immune microenvironment, genetic alteration and DNA methylation effects on prognosis, the probability of response to immunotherapy and chemotherapy, and small molecule drugs predicted by The Connectivity Map (Cmap) database.

RESULTS

Thirteen EMT-related genes with independent prognostic value were identified and used to stratify the patients with TNBC into high- and low-risk groups. The survival analysis revealed that patients in the high-risk group had significantly poorer overall survival than patients in the low-risk group. Populations of immune cells, including CD4 memory resting T cells, CD4 memory activated T cells, and activated dendritic cells, significantly differed between the high- and low-risk groups. Moreover, some therapeutic drugs to which the high-risk group might show sensitivity were identified.

CONCLUSIONS

Our research identified the significant impact of EMGs on prognosis in TNBC, providing new strategies for personalizing TNBC treatment and improving clinical outcomes.

Diosmetin-7-O-β-D-glucopyranoside suppresses endothelial-mesenchymal transformation through endoplasmic reticulum stress in cardiac fibrosis

Diosmetin-7-O-β-D-glucopyranoside (Diosmetin-7-O-glucoside) is a natural flavonoid glycoside known to have a therapeutic application for cardiovascular diseases. Cardiac fibrosis is the main pathological change in the end stage of cardiovascular diseases. Endothelial-mesenchymal transformation (EndMT) induced by endoplasmic reticulum stress (ER stress) via Src pathways is involved in the process of cardiac fibrosis. However, it is unclear whether and how diosmetin-7-O-glucoside regulates EndMT and ER stress to treat cardiac fibrosis. In this study, molecular docking results showed that diosmetin-7-O-glucoside bound well to ER stress and Src pathway markers. Diosmetin-7-O-glucoside suppressed cardiac fibrosis induced by isoprenaline (ISO) and reduced the levels of EndMT, ER stress in mice heart. Primary cardiac microvascular endothelial cells (CMECs) were induced by transforming growth factor-β1 (TGF-β1) to perform EndMT. Diosmetin-7-O-glucoside could effectively regulate EndMT and diminish the accumulation of collagen I and collagen III. We also showed that the tube formation in CMECs was restored, and the capacity of migration was partially inhibited. Diosmetin-7-O-glucoside also ameliorated ER stress through the three unfolded protein response branches, as evidenced by organelle structure in transmission electron microscopy images and the expression of protein biomarkers like the glucose-regulated protein 78 (GRP78) and C/EBP homologous protein (CHOP). Further analysis showed that diosmetin-7-O-glucoside could suppress the expression level of Src phosphorylation, then block EndMT with the maintenance of endothelial appearance and endothelial marker expression. These results suggested that the diosmetin-7-O-glucoside can regulate EndMT through ER stress, at least in part via Src-dependent pathways.

Routes of Albumin Overload Toxicity in Renal Tubular Epithelial Cells

Besides being a marker of kidney disease severity, albuminuria exerts a toxic effect on renal proximal tubular epithelial cells (RPTECs). We evaluated whether an unfolded protein response (UPR) or DNA damage response (DDR) is elicited in RPTECs exposed to high albumin concentration. The deleterious outcomes of the above pathways, apoptosis, senescence, or epithelial-to-mesenchymal transition (EMT) were evaluated. Albumin caused reactive oxygen species (ROS) overproduction and protein modification, and a UPR assessed the level of crucial molecules involved in this pathway. ROS also induced a DDR evaluated by critical molecules involved in this pathway. Apoptosis ensued through the extrinsic pathway. Senescence also occurred, and the RPTECs acquired a senescence-associated secretory phenotype since they overproduced IL-1β and TGF-β1. The latter may contribute to the observed EMT. Agents against endoplasmic reticulum stress (ERS) only partially alleviated the above changes, while the inhibition of ROS upregulation prevented both UPR and DDR and all the subsequent harmful effects. Briefly, albumin overload causes cellular apoptosis, senescence, and EMT in RPTECs by triggering UPR and DDR. Promising anti-ERS factors are beneficial but cannot eliminate the albumin-induced deleterious effects because DDR also occurs. Factors that suppress ROS overproduction may be more effective since they could halt UPR and DDR.

In Humanized Sickle Cell Mice, Imatinib Protects Against Sickle Cell-Related Injury

Drug repurposing is a valuable strategy for rare diseases. Sickle cell disease (SCD) is a rare hereditary hemolytic anemia accompanied by acute and chronic painful episodes, most often in the context of vaso-occlusive crisis (VOC). Although progress in the knowledge of pathophysiology of SCD have allowed the development of new therapeutic options, a large fraction of patients still exhibits unmet therapeutic needs, with persistence of VOCs and chronic disease progression. Here, we show that imatinib, an oral tyrosine kinase inhibitor developed for the treatment of chronic myelogenous leukemia, acts as multimodal therapy targeting signal transduction pathways involved in the pathogenesis of both anemia and inflammatory vasculopathy of humanized murine model for SCD. In addition, imatinib inhibits the platelet-derived growth factor-B-dependent pathway, interfering with the profibrotic response to hypoxia/reperfusion injury, used to mimic acute VOCs. Our data indicate that imatinib might be considered as possible new therapeutic tool for chronic treatment of SCD.

Pan-Src kinase inhibitor treatment attenuates diabetic kidney injury via inhibition of Fyn kinase-mediated endoplasmic reticulum stress

Src family kinases (SFKs) have been implicated in the pathogenesis of kidney fibrosis. However, the specific mechanism by which SFKs contribute to the progression of diabetic kidney disease (DKD) remains unclear. Our preliminary transcriptome analysis suggested that SFK expression was increased in diabetic kidneys and that the expression of Fyn (a member of the SFKs), along with genes related to unfolded protein responses from the endoplasmic reticulum (ER) stress signaling pathway, was upregulated in the tubules of human diabetic kidneys. Thus, we examined whether SFK-induced ER stress is associated with DKD progression. Mouse proximal tubular (mProx24) cells were transfected with Fyn or Lyn siRNA and exposed to high glucose and palmitate (HG-Pal). Streptozotocin-induced diabetic rats were treated with KF-1607, a novel pan-Src kinase inhibitor (SKI) with low toxicity. The effect of KF-1607 was compared to that of losartan, a standard treatment for patients with DKD. Among the SFK family members, the Fyn and Lyn kinases were upregulated under diabetic stress. HG-Pal induced p70S6 kinase and JNK/CHOP signaling and promoted tubular injury. Fyn knockdown but not Lyn knockdown inhibited this detrimental signaling pathway. In addition, diabetic rats treated with KF-1607 showed improved kidney function and decreased ER stress, inflammation, and fibrosis compared with those treated with losartan. Collectively, these findings indicate that Fyn kinase is a specific member of the SFKs implicated in ER stress activation leading to proximal tubular injury in the diabetic milieu and that pan-SKI treatment attenuates kidney injury in diabetic rats. These data highlight Fyn kinase as a viable target for the development of therapeutic agents for DKD.

Insights into a signaling pathway that promotes diabetic kidney disease could lead to new therapies that protect against this major cause of kidney failure. Past studies have suggested that the various Src family kinase (SFK) signaling proteins play a part in the cell death and scar tissue formation associated with diabetic kidney disease. Hunjoo Ha of Ewha Womans University, Seoul, South Korea, and colleagues have now focused on one particular SFK, Fyn, as a direct driver of the kidney damage seen in mouse models of diabetes. Genetic interventions that selectively inhibit Fyn suppressed this damage, as did treatment with an oral drug that broadly inactivates SFKs. This experimental drug proved as effective as controlling inflammation and oxidative damage in the kidney as an already clinically approved treatment, confirming the significance of SFK signaling in this condition.

Src Family Kinases: A Potential Therapeutic Target for Acute Kidney Injury

Src family kinases (SFKs) are non-receptor tyrosine kinases and play a key role in regulating signal transduction. The mechanism of SFKs in various tumors has been widely studied, and there are more and more studies on its role in the kidney. Acute kidney injury (AKI) is a disease with complex pathogenesis, including oxidative stress (OS), inflammation, endoplasmic reticulum (ER) stress, autophagy, and apoptosis. In addition, fibrosis has a significant impact on the progression of AKI to developing chronic kidney disease (CKD). The mortality rate of this disease is very high, and there is no effective treatment drug at present. In recent years, some studies have found that SFKs, especially Src, Fyn, and Lyn, are involved in the pathogenesis of AKI. In this paper, the structure, function, and role of SFKs in AKI are discussed. SFKs play a crucial role in the occurrence and development of AKI, making them promising molecular targets for the treatment of AKI.

Unraveling the Molecular Nexus between GPCRs, ERS, and EMT

G protein-coupled receptors (GPCRs) represent a large family of transmembrane proteins that transduce an external stimulus into a variety of cellular responses. They play a critical role in various pathological conditions in humans, including cancer, by regulating a number of key processes involved in tumor formation and progression. The epithelial-mesenchymal transition (EMT) is a fundamental process in promoting cancer cell invasion and tumor dissemination leading to metastasis, an often intractable state of the disease. Uncontrolled proliferation and persistent metabolism of cancer cells also induce oxidative stress, hypoxia, and depletion of growth factors and nutrients. These disturbances lead to the accumulation of misfolded proteins in the endoplasmic reticulum (ER) and induce a cellular condition called ER stress (ERS) which is counteracted by activation of the unfolded protein response (UPR). Many GPCRs modulate ERS and UPR signaling via ERS sensors, IRE1α, PERK, and ATF6, to support cancer cell survival and inhibit cell death. By regulating downstream signaling pathways such as NF-κB, MAPK/ERK, PI3K/AKT, TGF-β, and Wnt/β-catenin, GPCRs also upregulate mesenchymal transcription factors including Snail, ZEB, and Twist superfamilies which regulate cell polarity, cytoskeleton remodeling, migration, and invasion. Likewise, ERS-induced UPR upregulates gene transcription and expression of proteins related to EMT enhancing tumor aggressiveness. Though GPCRs are attractive therapeutic targets in cancer biology, much less is known about their roles in regulating ERS and EMT. Here, we will discuss the interplay in GPCR-ERS linked to the EMT process of cancer cells, with a particular focus on oncogenes and molecular signaling pathways.

mTOR Signaling in Kidney Diseases

The mammalian target of rapamycin (mTOR), a serine/threonine protein kinase, is crucial in regulating cell growth, metabolism, proliferation, and survival. Under physiologic conditions, mTOR signaling maintains podocyte and tubular cell homeostasis. In AKI, activation of mTOR signaling in tubular cells and interstitial fibroblasts promotes renal regeneration and repair. However, constitutive activation of mTOR signaling in kidneys results in the initiation and progression of glomerular hypertrophy, interstitial fibrosis, polycystic kidney disease, and renal cell carcinoma. Here, we summarize the recent studies about mTOR signaling in renal physiology and injury, and discuss the possibility of its use as a therapeutic target for kidney diseases.

A novel PPARɣ ligand, PPZ023, overcomes radioresistance via ER stress and cell death in human non-small-cell lung cancer cells

Peroxisome proliferator-activated receptor gamma (PPARɣ) agonists exert powerful anticancer effects by suppressing tumor growth. In this study, we developed PPZ023 (1-(2-(ethylthio)benzyl)-4-(2-methoxyphenyl)piperazine), a novel PPAR ligand candidate, and investigated the underlying signaling pathways in both non-small-cell lung cancer (NSCLC) and radio-resistant NSCLC cells. To identify whether PPZ023 has anticancer effects in NSCLC and radioresistant NSCLC cells, we performed WST-1, LDH, Western blot, and caspase-3 and -9 activity assays. Furthermore, we isolated exosomes from PPZ023-treated NSCLC cells and studied cell death signaling. PPZ023 reduces cell viability and increases LDH cytotoxicity and caspase-3 activity in NSCLC cells. PPZ023 induces cell death by generating reactive oxygen species (ROS) and triggering mitochondrial cytochrome c release. PPZ023 treatment causes cell death via the PERK–eIF2α–CHOP axis in both NSCLC cell lysates and exosomes, and PERK and CHOP knockdown significantly blocks ER stress-mediated apoptosis by reducing cleaved caspase-3. Interestingly, diphenyleneiodonium (DPI, a Nox inhibitor) inhibits PPZ023-induced cell death via ER stress, and PPARɣ knockdown inhibits PPZ023-induced ROS, ER stress, and cell death. Moreover, PPZ023, in combination with radiation, causes synergic cell death via exosomal ER stress in radioresistant NSCLC cells, indicating that PPZ023/radiation overcomes radioresistance. Taken together, our results suggest that PPZ023 is a powerful anticancer reagent for overcoming radioresistance.

A novel small molecule drug candidate known as PPZ023 could be a powerful anti-cancer agent due to its ability to overcome the resistance of tumors to radiation therapy. Sung Hee Hong and colleagues at the Korea Institute of Radiological and Medical Sciences in Seoul, South Korea, investigated the effects of the molecule on lung cancer cells, including cells that that had acquired resistance to radiotherapy. PPZ023 induces the death of cancer cells by binding to a protein in a known signaling pathway, which generates damaging chemicals known as reactive oxygen species. The researchers identified additional molecular details of the anti-cancer activity. They found the radiotherapy resistance of cancer cells is reversed when PPZ023 promotes cell death via a pathway interfering with the folding of newly formed proteins in a cell structure called the endoplasmic reticulum.

Establishment of renal proximal tubule cell lines derived from the kidney of p53 knockout mice

The human cell line HK-2 is most commonly used as a model of renal proximal tubular epithelial cells (PTECs) for various studies despite the absence or low expression of transporters characteristic of parental PTECs. In an effort to develop reliable PTEC models, several human cell lines have been newly established over the last decade. In contrast, reliable mouse PTEC models are still unavailable. In this study, we established immortalized renal cortex tubule cell lines derived from p53 knockout mice and evaluated various PTEC characteristics toward the development of reliable mouse PTEC models. Here, we focus on MuRTE61, one of 13 newly established clonal cell lines. Albumin uptake in MuRTE61 cells was verified by incubation with fluorescent dye-labeled albumin. RT-PCR confirmed the expression of efflux transporter genes characteristic of PTECs in the MuRTE61 cells. MuRTE61 cells exhibited high sensitivity to treatment with cisplatin, a nephrotoxic agent, accompanied by upregulated expression of the uptake transporter Slc22a2 gene. Furthermore, MuRTE61 cells consistently formed spheroids with a lumen and apicobasal polarity in three-dimensional Matrigel cultures. Apical brush border microvilli were also observed in the spheroids by transmission electron microscopy. These data validate that MuRTE61 can be characterized as a reliable mouse PTEC line. In future, detailed analysis of reliable mouse and human PTEC lines will provide an accurate extrapolation of results of experiments using mice and humans, and may help resolve apparent inconsistencies between mouse and human nephrotoxicity.

Febuxostat inhibits TGF‑β1‑induced epithelial‑mesenchymal transition via downregulation of USAG‑1 expression in Madin‑Darby canine kidney cells in vitro

Our previous study demonstrated that febuxostat, a xanthine oxidase inhibitor, can alleviate kidney dysfunction and ameliorate renal tubulointerstitial fibrosis in a rat unilateral ureteral obstruction (UUO) model; however, the underlying mechanisms remain unknown. Increasing evidence has revealed that epithelial-mesenchymal transition (EMT) is one of the key mechanisms mediating the progression of renal tubulointerstitial fibrosis in chronic kidney disease (CKD). Uterine sensitization-associated gene-1 (USAG-1), a kidney-specific bone morphogenetic protein antagonist, is involved in the development of numerous types of CKDs. The present study aimed to investigate the role of febuxostat in the process of EMT in Madin-Darby canine kidney (MDCK) cells in vitro. Western blotting, reverse transcription-semiquantitative polymerase chain reaction analysis and immunofluorescence staining were used to evaluate the expression levels of bone morphogenetic protein 7, USAG-1, α-smooth muscle actin (α-SMA) and E-cadherin, respectively. The results demonstrated that the expression of USAG-1 and α-SMA increased, and that of E-cadherin decreased significantly in MDCK cells following treatment with transforming growth factor-β1 (TGF-β1). The application of small interfering RNA-USAG-1 potently inhibited TGF-β1-induced EMT. Subsequently, the effects of febuxostat on TGF-β1-induced EMT was investigated. The results demonstrated that febuxostat downregulated the expression of USAG-1, and reversed TGF-β1-induced EMT in MDCK cells. Furthermore, pretreatment with febuxostat significantly restored the decreased expression levels of phosphorylated Smad1/5/8 induced by TGF-β1 in MDCK cells. The results of the present study suggested that USAG-1 may be involved in the EMT process of MDCK cells induced by TGF-β1, and febuxostat inhibited EMT by activating the Smad1/5/8 signaling pathway via downregulating the expression of USAG-1 in MDCK cells.

Novel β-phenylacrylic acid derivatives exert anti-cancer activity by inducing Src-mediated apoptosis in wild-type KRAS colon cancer

Many stress conditions including chemotherapy treatment is known to activate Src and under certain condition Src can induce the apoptotic signal via c-Jun N-terminal kinase (JNK) activation. Here we report that the newly synthesized β-phenylacrylic acid derivatives, MHY791 and MHY1036 (MHYs), bind to epidermal growth factor receptor (EGFR) tyrosine kinase domains and function as EGFR inhibitors, having anti-cancer activities selectively in wild-type KRAS colon cancer. Mechanistically, MHYs-induced Src/JNK activation which enhanced their pro-apoptotic effects and therefore inhibition of Src by the chemical inhibitor PP2 or Src siRNA abolished the response. In addition, MHYs generated reactive oxygen species and increased ER stress, and pretreatment with antioxidant-inhibited MHY-induced ER stress, Src activation, and apoptosis. Furthermore, the irreversible EGFR inhibitor PD168393 also activated Src while the reversible EGFR inhibitor gefitinib showed the opposite effect, indicating that MHYs are the irreversible EGFR inhibitor. Collectively, Src can play a key role in apoptosis induced by the novel EGFR inhibitor MHYs, suggesting that activation of Src might prove effective in treating EGFR/wild-type KRAS colon cancer.

Regulation of transforming growth factor β-mediated epithelial-mesenchymal transition of lens epithelial cells by c-Src kinase under high glucose conditions

Recent studies have reported that high glucose (HG) conditions may contribute to the acceleration of renal cell apoptosis and renal fibrosis by inducing epithelial-mesenchymal transition (EMT) of tubular epithelial cells, in which c-Src kinase and transforming growth factor (TGF)-β are key modulators. In the present study, the roles of c-Src kinase and TGF-β in EMT of lens epithelial cells (LECs) under HG conditions were investigated. Results indicated human lens epithelial B3 (HLE-B3) cells under HG conditions exhibited significantly increased protein expression levels of phosphorylated c-Src (p-Src⁴¹⁸) (P<0.05) and secreted a significantly increased amount of TGF-β compared with HLE-B3 cells under normal glucose conditions (P<0.05). Notably the c-Src inhibitor PP1 and the activin receptor-like kinase 5 (ALK5) inhibitor SB431542 suppressed EMT of HLE-B3 cells. Results indicated that PP1 significantly inhibited the activities of c-Src and ALK5 and the secretion of TGF-β, whereas SB431542 only significantly downregulated the protein expression levels and secretion of TGF-β (P<0.05). Following c-Src knockdown, the protein expression levels of p-Src⁴¹⁸, ALK5 and TGF-β were significantly decreased, the secretion of TGF-β was significantly suppressed (both P<0.05) and EMT was decreased in HLE-B3 cells. These results suggest that c-Src and TGF-β may promote EMT of LECs under HG conditions, with c-Src as the upstream regulatory molecule. Thus, the signal axis of c-Src/TGF-β in EMT of LECs may be a potential novel therapeutic target for the prevention of diabetic subcapsular cataract.

Hypoxia inducible factor-1α mediates the profibrotic effect of albumin in renal tubular cells

Proteinuria is closely associated with the progression of chronic kidney diseases (CKD) by producing renal tubulointerstitial fibrosis. Over-activation of hypoxia inducible factor (HIF)-1α has been implicated in the progression of CKD. The present study tested the hypothesis that HIF-1α mediates albumin-induced profibrotic effect in cultured renal proximal tubular cells. Incubation of the cells with albumin (40 μg/ml) for 72 hrs significantly increased the protein levels of HIF-1α, tissue inhibitor of metalloproteinase (TIMP)-1 and collagen-I, which were blocked by HIF-1α shRNA. Albumin also stimulated an epithelial-mesenchymal transition (EMT) as indicated by the decrease in epithelial marker E-cadherin, and the increase in mesenchymal markers α-smooth muscle actin and fibroblast-specific protein 1. HIF-1α shRNA blocked albumin-induced changes in these EMT markers as well. Furthermore, albumin reduced the level of hydroxylated HIF-1α, indicating an inhibition of the activity of prolyl-hydroxylases, enzymes promoting the degradation of HIF-1α. An anti-oxidant ascorbate reversed albumin-induced inhibition of prolyl-hydroxylase activity. Overexpression of prolyl-hydroxylase 2 (PHD2) transgene, a predominant isoform of PHDs in renal tubules, to reduce HIF-1α level significantly attenuated albumin-induced increases in TIMP-1 and collagen-I levels. These results suggest that albumin-induced oxidative stress inhibits PHD activity to accumulate HIF-1α, which mediates albumin-induced profibrotic effects in renal tubular cells.

TGF‑β signaling: A complex role in tumorigenesis (Review)

Tumor progression can be affected by various cellular components of tumor cells and/or by tumor microenvironmental factors. The tumor microenvironment comprises a variety of nonmalignant stromal cells and inflammatory cytokines, which are pivotal in tumor promotion and progression. The transforming growth factor‑β (TGF‑β) ligands (TGF‑β1, 2 and 3) are secreted inflammatory cytokines, which are known to be involved in various aspects of tumor development through two transmembrane serine‑threonine kinase receptors, TGFβR1 and TGFβR2. TGF‑β promotes or inhibits tumorigenesis depending on the concurrent gene mutations and tissue microenvironment present through the small mothers against decapentaplegic (Smad) and non‑Smad pathways. This review aims to provide a comprehensive overview of the role of the TGF‑β pathway in tumor initiation and progression.

The Role of Endoplasmic Reticulum Stress in Diabetic Nephropathy

PURPOSE OF REVIEW

Diabetic nephropathy (DN) has become the leading cause of end-stage renal disease (ESRD) worldwide. Accumulating evidence suggests that endoplasmic reticulum (ER) stress plays a major role in the development and progression of DN. Recent findings suggested that many attributes of DN, such as hyperglycemia, proteinuria, and increased advanced glycation end products and free fatty acids, can all trigger unfolded protein response (UPR) in kidney cells. Herein, we review the current knowledge on the role of ER stress in the setting of kidney injury with a specific emphasis on DN.

RECENT FINDINGS

As maladaptive ER stress response caused by excessively prolonged UPR will eventually cause cell death and increase kidney injury, several ER stress inhibitors have been shown to improve DN in animal models, albeit blocking both adaptive and maladaptive UPR. More recently, reticulon-1A (RTN1A), an ER-associated protein, was shown to be increased in both human and mouse diabetic kidneys. Its expression correlates with the progression of DN, and its polymorphisms are associated with kidney disease in people with diabetes. Increased RTN1A expression heightened the ER stress response and renal cell apoptosis, and conversely reduced RTN1A in renal cells decreased apoptosis and ameliorated kidney injury and DN progression, suggesting that RTN1A may be a novel target to specifically restrain the maladaptive UPR. These findings suggest that ER stress response in renal cells is a key driver of progression of DN and that the inhibition of the unchecked ER stress response in DN, such as by inhibition of RTN1A function, may be a promising therapeutic approach against DN.

Malignant Pleural Effusion and ascites Induce Epithelial-Mesenchymal Transition and Cancer Stem-like Cell Properties via the Vascular Endothelial Growth Factor (VEGF)/Phosphatidylinositol 3-Kinase (PI3K)/Akt/Mechanistic Target of Rapamycin (mTOR) Pathway

Malignant pleural effusion (PE) and ascites, common clinical manifestations in advanced cancer patients, are associated with a poor prognosis. However, the biological characteristics of malignant PE and ascites are not clarified. Here we report that malignant PE and ascites can induce a frequent epithelial-mesenchymal transition program and endow tumor cells with stem cell properties with high efficiency, which promotes tumor growth, chemoresistance, and immune evasion. We determine that this epithelial-mesenchymal transition process is mainly dependent on VEGF, one initiator of the PI3K/Akt/mechanistic target of rapamycin (mTOR) pathway. From the clinical observation, we define a therapeutic option with VEGF antibody for malignant PE and ascites. Taken together, our findings clarify a novel biological characteristic of malignant PE and ascites in cancer progression and provide a promising and available strategy for cancer patients with recurrent/refractory malignant PE and ascites.

Effect of Immunosuppressive Therapy on Proteinogram in Rats

BACKGROUND It has been observed that the use of immunosuppressive drugs in patients after transplantation of vascularized organs may be associated with changes in the concentration of certain fractions of plasma proteins. The concentration of these proteins was correlated with an increased risk of occurrence of stage 3 chronic kidney disease (CKD). This article examines the effect of the most commonly used immunosuppressive drugs on the concentration of plasma proteins in Wistar rats. MATERIAL AND METHODS The study involved 36 rats grouped according to the immunosuppressive regimen used (tacrolimus, mycophenolate mofetil, cyclosporine A, rapamycin, and prednisone). The rats in all study groups were treated with a 3-drug protocol for 6 months. The treatment dose was adjusted based on available data in the literature. No drugs were administered to the control group. The rats were sacrificed and blood samples collected to determine the concentration of plasma proteins using electrophoresis technique. RESULTS Statistically significant differences were observed between protein concentrations within the studied groups. The differences related to the proteins with masses of 195 kDa, 170 kDa, 103 kDa, and 58 kDa. CONCLUSIONS (1) Immunosuppressive drugs caused changes in the proteinogram of plasma proteins. (2) The strongest effect on rat plasma proteins was exerted by a regimen based on rapamycin. Intermediate, weak, and weakest effects were observed in regimens based on cyclosporine A, tacrolimus, and mycophenolate mofetil, respectively.

Knockdown of RTN1A attenuates ER stress and kidney injury in albumin overload-induced nephropathy

Our previous studies have suggested a critical role of reticulon (RTN)1A in mediating endoplasmic reticulum (ER) stress in kidney cells of animal models and humans with kidney diseases. A large body of evidence suggests that proteinuria itself can cause tubular cell injury leading to the progression of kidney disease. In the present study, we determined whether RTN1A mediates proteinuria-induced tubular cell injury through increased ER stress. We found that incubation of HK2 cells with human serum albumin induced the expression of RTN1A and ER stress markers, whereas knockdown of RTN1A expression attenuated human serum albumin-induced ER stress and tubular cell apoptosis in vitro. In vivo, we found that tubular cell-specific RTN1 knockdown resulted in a significant attenuation of tubular cell ER stress, apoptosis, and renal fibrosis in a model of albumin overload nephropathy. Based on these findings, we conclude that RTN1A is a key mediator for proteinuria-induced tubular cell toxicity and renal fibrosis.

Up-regulation of the kinin B2 receptor pathway modulates the TGF-β/Smad signaling cascade to reduce renal fibrosis induced by albumin

The presence of high protein levels in the glomerular filtrate plays an important role in renal fibrosis, a disorder that justifies the use of animal models of experimental proteinuria. Such models have proved useful as tools in the study of the pathogenesis of chronic, progressive renal disease. Since bradykinin and the kinin B2 receptor (B2R) belong to a renoprotective system with mechanisms still unclarified, we investigated its anti-fibrotic role in the in vivo rat model of overload proteinuria. Upon up-regulating the kinin system by a high potassium diet we observed reduction of tubulointerstitial fibrosis, decreased renal expression of α-smooth muscle actin (α-SMA) and vimentin, reduced Smad3 phosphorylation and increase of Smad7. These cellular and molecular effects were reversed by HOE-140, a specific B2R antagonist. In vitro experiments, performed on a cell line of proximal tubular epithelial cells, showed that high concentrations of albumin induced expression of mesenchymal biomarkers, in concomitance with increases in TGF-β1 mRNA and its functionally active peptide, TGF-β1. Stimulation of the tubule cells by bradykinin inhibited the albumin-induced changes, namely α-SMA and vimentin were reduced, and cytokeratin recovered together with increase in Smad7 levels and decrease in type II TGF-β1 receptor, TGF-β1 mRNA and its active fragment. The protective changes produced by bradykinin in vitro were blocked by HOE-140. The development of stable bradykinin analogues and/or up-regulation of the B2R signaling pathway may prove value in the management of chronic renal fibrosis in progressive proteinuric renal diseases.

Activation of AMP-activated protein kinase prevents TGF-β1-induced epithelial-mesenchymal transition and myofibroblast activation

Transforming growth factor (TGF)-β contributes to tubulointerstitial fibrosis. We investigated the mechanism by which TGF-β exerts its profibrotic effects and specifically the role of AMP-activated protein kinase (AMPK) in kidney tubular epithelial cells and interstitial fibroblasts. In proximal tubular epithelial cells, TGF-β1 treatment causes a decrease in AMPK phosphorylation and activation together with increased fibronectin and α-smooth muscle actin expression and decreased in E-cadherin. TGF-β1 causes similar changes in interstitial fibroblasts. Activation of AMPK with 5-aminoimidazole-4-carboxamide 1-β-d-ribofuranoside, metformin, or overexpression of constitutively active AMPK markedly attenuated TGF-β1 functions. Conversely, inhibition of AMPK with adenine 9-β-d-arabinofuranoside or siRNA-mediated knockdown of AMPK (official name PRKAA1) mimicked the effect of TGF-β1 and enhanced basal and TGF-β1-induced phenotypic changes. Importantly, we found that tuberin contributed to the protective effects of AMPK and that TGF-β1 promoted cell injury by blocking AMPK-mediated tuberin phosphorylation and activation. In the kidney cortex of TGF-β transgenic mice, the significant decrease in AMPK phosphorylation and tuberin phosphorylation on its AMPK-dependent activating site was associated with an increase in mesenchymal markers and a decrease in E-cadherin. Collectively, the data indicate that TGF-β exerts its profibrotic action in vitro and in vivo via inactivation of AMPK. AMPK and tuberin activation prevent tubulointerstitial injury induced by TGF-β. Activators of AMPK provide potential therapeutic strategy to prevent kidney fibrosis and progressive kidney disease.

Stem cell conditioned culture media attenuated albumin-induced epithelial-mesenchymal transition in renal tubular cells

Background

Proteinuria-induced epithelial-mesenchymal transition (EMT) plays an important role in progressive renal tubulointerstitial fibrosis in chronic renal disease. Stem cell therapy has been used for different diseases. Stem cell conditioned culture media (SCM) exhibits similar beneficial effects as stem cell therapy. The present study tested the hypothesis that SCM inhibits albumin-induced EMT in cultured renal tubular cells.

Methods

Rat renal tubular cells were treated with/without albumin (20 μmg/ml) plus SCM or control cell media (CCM). EMT markers and inflammatory factors were measured by Western blot and fluorescent images.

Results

Albumin induced EMT as shown by significant decreases in levels of epithelial marker E-cadherin, increases in mesenchymal markers fibroblast-specific protein 1 and α-smooth muscle actin, and elevations in collagen I. SCM inhibited all these changes. Meanwhile, albumin induced NF-κB translocation from cytosol into nucleus and that SCM blocked the nuclear translocation of NF-κB. Albumin also increased the levels of pro-inflammatory factor monocyte chemoattractant protein-1 (MCP)-1 by nearly 30 fold compared with control. SCM almost abolished albumin-induced increase of MCP-1.

Conclusion

These results suggest that SCM attenuated albumin-induced EMT in renal tubular cells via inhibiting activation of inflammatory factors, which may serve as a new therapeutic approach for chronic kidney diseases.

Albumin overload down-regulates integrin-β1 through reactive oxygen species-endoplasmic reticulum stress pathway in podocytes

Proteinuria is a major hallmark of glomerular nephropathy and endoplasmic reticulum (ER) stress plays an important role in glomerular nephropathy. The protein levels of integrin-β1 in podocytes are found to be negative correlation with amount of proteinuria. This study investigated whether urinary protein, particularly albumin, induced ER stress that consequently reduced integrin-β1 expression. All experiments were performed using primary cultured rat podocyte. Protein and mRNA expression were measured by western blotting and semiquantified reverse transcriptase polymerase chain reaction. Albumin uptake was found at 1 h after albumin addition. Albumin reduced precursor and mature forms of integrin-β1, but did not change mRNA levels of integrin-β1. Albumin induced reactive oxygen species (ROS) generation and ER stress. Antioxidant (N-acetylcysteine) suppressed albumin-induced ER stress and decrements in precursor and mature forms of integrin-β1. Then, ER stress inhibitors (4-phenylbutyrate and salubrinal) also inhibited albumin-induced decrements in precursor and mature forms of integrin-β1. The potent ER stress inducers (thapsigargin and tunicamycin) directly decreased precursor and mature forms of integrin-β1 and led appearance of unglycosylated core protein of integrin-β1. Our results show that in proteinuric disease, albumin decreases precursor and mature forms of integrin-β1 through ROS-ER stress pathway in podocytes.

Stress in the kidney is the road to pERdition: is endoplasmic reticulum stress a pathogenic mediator of diabetic nephropathy?

The endoplasmic reticulum (ER) is an organelle that primarily functions to synthesise new proteins and degrade old proteins. Owing to the continual and variable nature of protein turnover, protein synthesis is inherently an error-prone process and is therefore tightly regulated. Fortunately, if this balance between synthesis and degradation is perturbed, an intrinsic response, the unfolded protein response (UPR) is activated to restore ER homoeostasis through the action of inositol-requiring protein 1, activating transcription factor 6 and PKR-like ER kinase transmembrane sensors. However, if the UPR is oversaturated and misfolded proteins accumulate, the ER can shift into a cytotoxic response, a physiological phenomenon known as ER stress. The mechanistic pathways of the UPR have been extensively explored; however, the role of this process in such a synthetic organ as the kidney requires further clarification. This review will focus on these aspects and will discuss the role of ER stress in specific resident kidney cells and how this may be integral in the pathogenesis and progression of diabetic nephropathy (DN). Given that diabetes is a perturbed state of protein turnover in most tissues, it is important to understand if ER stress is a secondary or tertiary response to other changes within the diabetic milieu or if it is an independent accelerator of kidney disease. Modulators of ER stress could provide a valuable tool for the treatment of DN and are under active investigation in other contexts.

Potential role of Akt signaling in chronic kidney disease

Renal fibrosis, particularly tubulointerstitial fibrosis, is the common final outcome of almost all chronic kidney diseases. However, the mechanisms involved in the development of renal fibrosis are poorly understood. The Akt (also known as protein kinase B, PKB) family is serine/threonine protein kinases that play critical roles in regulating growth, proliferation, survival, metabolism and other cellular activities. Cytokines, high-glucose medium, transforming growth factor-β1 or advanced glycation end-products activate Akt in different renal cells. Increased Akt activation has been found in experimental tubulointerstitial fibrosis. In addition, Akt activation is also an important node in diverse signaling cascades involved in kidney damage. These data give evidence for a role for Akt in renal fibrosis, but no reviews are available on the role of Akt in the process. Thus, our aim is to review the role of Akt activation and signaling in renal fibrosis.

Mis-regulation of mammalian target of rapamycin (mTOR) complexes induced by albuminuria in proximal tubules

High albumin concentrations in the proximal tubule of the kidney causes tubulointerstitial injury, but how this process occurs is not completely known. To address the signal transduction pathways mis-regulated in renal injury, we studied the modulation of mammalian target of rapamycin (mTOR) complexes by physiologic and pathophysiologic albumin concentrations in proximal tubule cells. Physiologic albumin concentrations activated the PI3K/mTORC2/PKB/mTORC1/S6 kinase (S6K) pathway, but pathophysiologically high albumin concentrations overactivated mTORC1 and inhibited mTORC2 activity. This control process involved the activation of ERK1/2, which promoted the inhibition of TSC2 and activation of S6K. Furthermore, S6K was crucial to promoting the over activation of mTORC1 and inhibition of mTORC2. Megalin expression at the luminal membrane is reduced by high concentrations of albumin. In addition, knockdown of megalin mimicked all the effects of pathophysiologic albumin concentrations, which disrupt normal signal transduction pathways and lead to an overactivation of mTORC1 and inhibition of mTORC2. These data provide new perspectives for understanding the molecular mechanisms behind the effects of albumin on the progression of renal disease.

Mesenchymal stem cells modulate albumin-induced renal tubular inflammation and fibrosis

Bone marrow-derived mesenchymal stem cells (BM-MSCs) have recently shown promise as a therapeutic tool in various types of chronic kidney disease (CKD) models. However, the mechanism of action is incompletely understood. As renal prognosis in CKD is largely determined by the degree of renal tubular injury that correlates with residual proteinuria, we hypothesized that BM-MSCs may exert modulatory effects on renal tubular inflammation and epithelial-to-mesenchymal transition (EMT) under a protein-overloaded milieu. Using a co-culture model of human proximal tubular epithelial cells (PTECs) and BM-MSCs, we showed that concomitant stimulation of BM-MSCs by albumin excess was a prerequisite for them to attenuate albumin-induced IL-6, IL-8, TNF-α, CCL-2, CCL-5 overexpression in PTECs, which was partly mediated via deactivation of tubular NF-κB signaling. In addition, albumin induced tubular EMT, as shown by E-cadherin loss and α-SMA, FN and collagen IV overexpression, was also prevented by BM-MSC co-culture. Albumin-overloaded BM-MSCs per se retained their tri-lineage differentiation capacity and overexpressed hepatocyte growth factor (HGF) and TNFα-stimulating gene (TSG)-6 via P38 and NF-κB signaling. Albumin-induced tubular CCL-2, CCL-5 and TNF-α overexpression were suppressed by recombinant HGF treatment, while the upregulation of α-SMA, FN and collagen IV was attenuated by recombinant TSG-6. Neutralizing HGF and TSG-6 abolished the anti-inflammatory and anti-EMT effects of BM-MSC co-culture in albumin-induced PTECs, respectively. In vivo, albumin-overloaded mice treated with mouse BM-MSCs had markedly reduced BUN, tubular CCL-2 and CCL-5 expression, α-SMA and collagen IV accumulation independent of changes in proteinuria. These data suggest anti-inflammatory and anti-fibrotic roles of BM-MSCs on renal tubular cells under a protein overloaded condition, probably mediated via the paracrine action of HGF and TSG-6.

Antiangiogenic therapy using sunitinib combined with rapamycin retards tumor growth but promotes metastasis

BACKGROUND: This study investigated the synergistic effect of sunitinib and rapamycin on tumor growth and metastasis in murine breast cancer model. METHODS: The synergistic antitumor effect of sunitinib and rapamycin on tumor growth and metastasis was investigated. Myeloid-derived suppressor cells (MDSCs) in spleens and lungs were assessed. Tumor hypoxia, vessel density and micrometastasis were evaluated. Versican, indoleamine 2,3-dioxygenase (IDO), arginase 1, interleukin-6 (IL-6), IL-10, and transforming growth factor β (TGF-β) in the lungs and tumors were examined. IL-6 and TGF-β in the blood were evaluated. RESULTS: Synergism between sunitinib and rapamycin on tumor growth was observed. Sunitinib plus rapamycin reduced splenomegaly, MDSCs in spleens and lungs, and microvessel density in tumor microenvironment, while exacerbated hypoxia and promoted cancer lung metastasis. Sunitinib plus rapamycin markedly induced versican, IDO, arginase 1, IL-6, and TGF-β expression in the lungs, whereas it reduced IDO and IL-10 expression in the primary tumor tissues. IL-6 levels in the circulation were increased after rapamycin and combination therapies. CONCLUSIONS: The combination of sunitinib plus rapamycin reduced the tumor growth but promoted tumor metastasis. This study warrants that further mTOR inhibition treatment should be closely watched in clinical setting, especially combined with antiangiogenic therapy.

Epithelial-mesenchymal transition induces endoplasmic-reticulum-stress response in human colorectal tumor cells

Tumor cells are stressed by unfavorable environmental conditions like hypoxia or starvation. Driven by the resulting cellular stress tumor cells undergo epithelial-mesenchymal transition. Additionally, cellular stress is accompanied by endoplasmic reticulum-stress which induces an unfolded protein response. It is unknown if epithelial-mesenchymal transition and endoplasmic reticulum-stress are occurring as independent parallel events or if an interrelationship exists between both of them. Here, we show that in colorectal cancer cells endoplasmic reticulum-stress depends on the induction of ZEB-1, which is a main factor of epithelial-mesenchymal transition. In the absence of ZEB-1 colorectal cancer cells cannot mount endoplasmic reticulum-stress as a reaction on cellular stress situations like hypoxia or starvation. Thus, our data suggest that there is a hierarchy in the development of cellular stress which starts with the presence of environmental stress that induces epithelial-mesenchymal transition which allows finally endoplasmic reticulum-stress. This finding highlights the central role of epithelial-mesenchymal transition during the process of tumorigenesis as epithelial-mesenchymal transition is also associated with chemoresistance and cancer stemness. Consequently, endoplasmic reticulum-stress might be a well suited target for chemotherapy of colorectal cancers.

Modulation of albumin-induced endoplasmic reticulum stress in renal proximal tubule cells by upregulation of mapk phosphatase-1

High amounts of albumin in urine cause tubulointerstitial damage that leads to a rapid deterioration of the renal function. Albumin exerts its injurious effects on renal cells through a process named endoplasmic reticulum (ER) stress due to the accumulation of unfolded proteins in the ER lumen. In addition, albumin promotes phosphorylation and consequent activation of MAPKs such as ERK1/2. Since ERK1/2 activation promoted by albumin is a transient event, the aims of the present work were to identify the phosphatase involved in their dephosphorylation in albumin-exposed cells and to analyze the putative regulation of this phosphatase by albumin. We also sought to determine the role played by the phospho/dephosphorylation of ERK1/2 in the cellular response to albumin-induced ER stress. MAP kinase phosphatase-1, MKP-1, is a nuclear enzyme involved in rapid MAPK dephosphorylation. Here we present evidence supporting the notion that this phosphatase is responsible for ERK1/2 dephosphorylation after albumin exposure in OK cells. Moreover, we demonstrate that exposure of OK cells to albumin transiently increases MKP-1 protein levels. The increase was evident after 15 min of exposure, peaked at 1 h (6-fold) and declined thereafter. In cells overexpressing flag-MKP-1, albumin caused the accumulation of this chimera, promoting MKP-1 stabilization by a posttranslational mechanism. Albumin also promoted a transient increase in MKP-1 mRNA levels (3-fold at 1 h) through the activation of gene transcription. In addition, we also show that albumin increased mRNA levels of GRP78, a key marker of ER stress, through an ERK-dependent pathway. In line with this finding, our studies demonstrate that flag-MKP-1 overexpression blunted albumin-induced GRP78 upregulation. Thus, our work demonstrates that albumin overload not only triggers MAPK activation but also tightly upregulates MKP-1 expression, which might modulate ER stress response to albumin overload.

Pathological in situ reprogramming of somatic cells by the unfolded protein response

In response to tissue injuries, terminally differentiated cells are reprogrammed to undergo dedifferentiation to gain mitogenic and metabolic properties. The dedifferentiated cells acquire an immature phenotype, proliferate actively, produce abundant extracellular matrix, and recruit circulating leukocytes via secretion of chemokines, contributing to tissue repair and/or fibrosis. However, this remodeling process is self-limiting, and in the later phase, the activated, dedifferentiated cells are reprogrammed to redifferentiate into a mature, quiescent phenotype. Currently, molecular mechanisms underlying this bidirectional pathological reprogramming remain elusive. It is known that the unfolded protein response (UPR) is induced at local tissues under pathological situations and affects cellular fate-survival or death. It is also known that the UPR is involved in cell differentiation and organogenesis during embryonic development. In this review, we describe a hypothesis for regulatory roles of the UPR in the pathological reprogramming of somatic cells (ie, cellular dedifferentiation and redifferentiation at the sites of injury).

Ras and rheb signaling in survival and cell death

One of the most obvious hallmarks of cancer is uncontrolled proliferation of cells partly due to independence of growth factor supply. A major component of mitogenic signaling is Ras, a small GTPase. It was the first identified human protooncogene and is known since more than three decades to promote cellular proliferation and growth. Ras was shown to support growth factor-independent survival during development and to protect from chemical or mechanical lesion-induced neuronal degeneration in postmitotic neurons. In contrast, for specific patho-physiological cases and cellular systems it has been shown that Ras may also promote cell death. Proteins from the Ras association family (Rassf, especially Rassf1 and Rassf5) are tumor suppressors that are activated by Ras-GTP, triggering apoptosis via e.g., activation of mammalian sterile 20-like (MST1) kinase. In contrast to Ras, their expression is suppressed in many types of tumours, which makes Rassf proteins an exciting model for understanding the divergent effects of Ras activity. It seems likely that the outcome of Ras signaling depends on the balance between the activation of its various downstream effectors, thus determining cellular fate towards either proliferation or apoptosis. Ras homologue enriched in brain (Rheb) is a protein from the Ras superfamily that is also known to promote proliferation, growth, and regeneration through the mammalian target of rapamycin (mTor) pathway. However, recent evidences indicate that the Rheb-mTor pathway may switch its function from a pro-growth into a cell death pathway, depending on the cellular situation. In contrast to Ras signaling, for Rheb, the cellular context is likely to modulate the whole Rheb-mTor pathway towards cellular death or survival, respectively.

Endoplasmic reticulum stress and C/EBP homologous protein-induced Bax translocation are involved in angiotensin II-induced apoptosis in cultured neonatal rat cardiomyocytes

The aim of this study was to identify the roles and potential mechanisms of endoplasmic reticulum stress (ER stress), proapoptotic transcription factor C/EBP homologous protein (CHOP) and Bax in angiotensin II (Ang II)-induced cardiomyocyte apoptosis. Cultured neonatal rat cardiomyocytes were incubated with Ang II or antisense CHOP oligonucleotide which was used to inhibit CHOP expression. Expressions of ER chaperone immunoglobulin heavy chain-binding protein (BiP), CHOP and cytochrome c were examined by Western blotting. Mitochondrial membrane potential (MMP) was detected by a spectrofluorimeter. Apoptosis was analyzed with flow cytometry. Bax translocation was determined by double-labeling of immunofluorescence and Western blotting. Our results showed that Ang II-induced cardiomyocyte apoptosis was associated with the upregulations of BiP and CHOP, Bax translocation, MMP deplorization and cytochrome c release. These above effects were suppressed by antisense CHOP oligonucleotide. Furthermore, BiP and CHOP expressions, reactive oxygen species (ROS) production and cardiomyocyte apoptosis, which were upregulated by Ang II, were depressed by the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor apocynin. From our results, ROS, ER stress and CHOP-mediated Bax translocation may be involved in Ang II-induced cardiomyocyte apoptosis.

Endoplasmic reticulum stress signaling is involved in mitomycin C (MMC)-induced apoptosis in human fibroblasts via PERK pathway

Endoplasmic reticulum (ER) stress-mediated cell apoptosis has been implicated in various cell types, including fibroblasts. Previous studies have shown that mitomycin C (MMC)-induced apoptosis occurs in fibroblasts, but the effects of MMC on ER stress-mediated apoptosis in fibroblasts have not been examined. Here, MMC-induced apoptosis in human primary fibroblasts was investigated by exposing cells to a single dose of MMC for 5 minutes. Significant inhibition of cell proliferation and increased apoptosis were observed using a cell viability assay, Annexin V/propidium iodide double staining, cell cycle analysis, and TUNEL (terminal deoxynucleotidyl transferase dUTP nick-end labeling) staining. Upregulation of proapoptotic factors, including cleaved caspase-3 and poly ADP-ribose polymerase (PARP), was detected by Western blotting. MMC-induced apoptosis was correlated with elevation of 78-kDa glucose-regulated protein (GRP78) and C/EBP homologous protein (CHOP), which are hallmarks of ER stress. Three unfolded protein response (UPR) sensors (inositol-requiring enzyme 1, IRE1; activating transcription factor 6, ATF6; and PKR-like ER kinase, PERK) and their downstream signaling pathways were also activated. Knockdown of CHOP attenuated MMC-induced apoptosis by increasing the ratio of BCL-2/BAX and decreasing BIM expression, suggesting that ER stress is involved in MMC-induced fibroblast apoptosis. Interestingly, knockdown of PERK significantly decreased ER stress-mediated apoptosis by reducing the expression of CHOP, BIM and cleaved caspase-3. Reactive oxygen species (ROS) scavenging also decreased the expression of GRP78, phospho-PERK, CHOP, and BIM. These results demonstrate that MMC-induced apoptosis is triggered by ROS generation and PERK activation.

Suppression of XBP1S mediates high glucose-induced oxidative stress and extracellular matrix synthesis in renal mesangial cell and kidney of diabetic rats

Recent evidences suggest that endoplasmic reticulum (ER) stress was involved in multi pathological conditions, including diabetic nephropathy (DN). X-box binding protein 1(XBP1), as a key mediator of ER stress, has been proved having the capability of preventing oxidative stress. In this study, we investigated the effects of spliced XBP1 (XBP1S), the dominant active form of XBP1, on high glucose (HG)-induced reactive oxygen species (ROS) production and extracellular matrix (ECM) synthesis in cultured renal mesangial cells (MCs) and renal cortex of STZ-induced diabetic rats. Real time PCR and Western blot were used to evaluate the mRNA and protein levels respectively. Transfection of recombinant adenovirus vector carrying XBP1S gene (Ad-XBP1S) was used to upregulate XBP1S expression. XBP1S siRNA was used to knockdown XBP1S expression. ROS level was detected by dihydroethidium (DHE) fluorescent probe assay. The results showed that HG treatment significantly reduced XBP1S protein and mRNA level in the cultured MCs while no obvious change was observed in unspliced XBP1 (XBP1U). In the mean time, the ROS production, collagen IV and fibronectin expressions were increased. Diphenylene-chloride iodonium (DPI), a NADPH oxidase inhibtor, prevented HG-induced increases in ROS as well as collagen IV and fibronectin expressions. Transfection of Ad-XBP1S reversed HG-induced ROS production and ECM expressions. Knockdown intrinsic XBP1S expression induced increases in ROS production and ECM expressions. Supplementation of supreoxide reversed the inhibitory effect of Ad-XBP1S transfection on ECM synthesis. P47phox was increased in HG-treated MCs. Ad-XBP1S transfection reversed HG-induced p47phox increase while XBP1S knockdown upregulated p47phox expression. In the renal cortex of diabetic rats, the expression of XBP1S was reduced while p47phox, collagen IV and fibronectin expression were elevated. These results suggested that XBP1S pathway of ER stress was involved in HG-induced oxidative stress and ECM synthesis. A downstream target of XBP1S in regulating ROS formation might be NADPH oxidase.

AMP-activated protein kinase inhibits TGF-β-, angiotensin II-, aldosterone-, high glucose-, and albumin-induced epithelial-mesenchymal transition

The epithelial-mesenchymal transition (EMT) is a novel mechanism that promotes renal fibrosis. Transforming growth factor-β (TGF-β), angiotensin II, aldosterone, high glucose, and urinary albumin are well-known causes of EMT and renal fibrosis. We examined whether and how activation of AMP-activated protein kinase (AMPK) suppressed EMT induced by the above agents in tubular epithelial cells. All experiments were performed using HK-2 cells. Protein expression was measured by Western blot analysis. Intracellular reactive oxygen species (ROS) were analyzed by flow cytometry. Exposure of tubular cells to TGF-β (10 ng/ml), angiotensin II (1 μM), aldosterone (100 nM), high glucose (30 mM), and albumin (5 mg/ml) for 5 days induced EMT, as shown by upregulation of α-smooth muscle actin and downregulation of E-cadherin. ROS and NADPH oxidase 4 (Nox4) expression were increased, and antioxidants such as tiron and N-acetylcysteine inhibited EMT induction. Metformin (the best known clinical activator of AMPK) suppressed EMT induction through inhibition of ROS via induction of heme oxygenase-1 and endogenous antioxidant thioredoxin. An AMPK inhibitor (compound C) and AMPK small interfering RNA blocked the effect of metformin, and another AMPK activator [5-aminoimidazole-4-carboxamide-1β riboside (AICAR)] exerted the same effects as metformin. In conclusion, AMPK activation might be beneficial in attenuating the tubulointerstitial fibrosis induced by TGF-β, angiotensin II, aldosterone, high glucose, and urinary albumin.

Long- and short-term treatment with imatinib attenuates the development of chronic kidney disease in experimental anti-glomerular basement membrane nephritis

BACKGROUND

Imatinib is a selective tyrosine kinase inhibitor that can block platelet-derived growth factor (PDGF) receptor activity. Imatinib is also known as an anti-inflammatory agent. We examined the therapeutic effects of long- or short-term imatinib treatment in Wistar-Kyoto (WKY) rats with established anti-glomerular basement membrane (GBM) nephritis.

METHODS

Nephrotoxic serum (NTS) nephritis was induced in WKY rats on day 0. Groups of animals were given either imatinib or vehicle daily by intraperitoneal injection, from day 7 to day 49 in the long-term treatment study, and from day 7 to 13 in the short-term treatment study; all rats were sacrificed at day 50.

RESULTS

In long-term treatment, imatinib showed marked renoprotective effects; imatinib suppressed proteinuria, improved renal function, attenuated the development of glomerulosclerosis and tubulointerstitial injury and reduced the expression levels of collagen type I and transforming growth factor-beta (TGF-β) in renal cortex. The key finding of the present study was that short-term treatment with imatinib also significantly attenuated the development of renal injury until day 50, although the degree of renoprotection was slightly inferior to that of long-term treatment.

CONCLUSIONS

These results suggest that administration of imatinib is a promising strategy for limiting the progression of glomerulonephritis (GN) to end-stage renal failure. In particular, a short period of treatment at an early stage of GN is more beneficial in terms of cost-effectiveness and reduction of adverse effects in comparison to a continuous and long period of treatment.

Endoplasmic reticulum stress mediates aristolochic acid I-induced apoptosis in human renal proximal tubular epithelial cells

Aristolochic acid (AA), derived from the Aristolochia species, has been associated with aristolochic acid nephropathy (AAN), which has emerged as a worldwide disease. Aristolochic acid I (AAI) is the main ingredient of AA, and the underlying mechanisms for AAI-induced nephrotoxicity are still unclear. In this study, we investigated whether endoplasmic reticulum (ER) stress was involved in AAI-induced nephrotoxicity. The results showed that treatment of HK-2 cells (a human proximal tubular epithelial cell line) with AAI caused an increase in eukaryotic initiation factor-2α (eIF2α) phosphorylation, X-box binding protein 1 (XBP1) mRNA splicing and the expression of glucose-regulated protein (GRP) 78 and CAAT/enhancer-binding protein-homologous protein (CHOP). These events represent typical markers of the ER stress-related signaling pathway. Pretreatment with 4-phenylbutyrate (4-PBA) or salubrinal (Sal) significantly inhibited AAI-induced apoptosis, indicating the role of ER stress in AAI-induced apoptosis. In addition, AAI-induced cell death followed an increase of reactive oxygen species (ROS) formation in HK-2 cells. Pretreatment with N-acetyl cysteine (NAC) or glutathione (GSH) significantly inhibited AAI-induced ER stress proteins and cell death, suggesting that ROS mediate AAI-induced ER stress. Taken together, these results suggest that the ER stress response is involved in apoptosis induced by AAI in HK-2 cells, thus offering a new insight into the nephrotoxicity of AAI.