Differential regulation of Snail by hypoxia and hyperglycemia in human proximal tubule cells

Roles of Post-Translational Modifications of Transcription Factors Involved in Breast Cancer Hypoxia

BC is the most commonly diagnosed cancer and the second leading cause of cancer death among women worldwide. Cellular stress is a condition that leads to disrupted homeostasis by extrinsic and intrinsic factors. Among other stressors, hypoxia is a driving force for breast cancer (BC) progression and a general hallmark of solid tumors. Thus, intratumoral hypoxia is an important determinant of invasion, metastasis, treatment failure, prognosis, and patient mortality. Acquisition of the epithelial-mesenchymal transition (EMT) phenotype is also a consequence of tumor hypoxia. The cellular response to hypoxia is mainly regulated by the hypoxia signaling pathway, governed by hypoxia-inducible factors (HIFs), mainly HIF1α. HIFs are a family of transcription factors (TFs), which induce the expression of target genes involved in cell survival and proliferation, metabolic reprogramming, angiogenesis, resisting apoptosis, invasion, and metastasis. HIF1α cooperates with a large number of other TFs. In this review, we focused on the crosstalk and cooperation between HIF1α and other TFs involved in the cellular response to hypoxia in BC. We identified a cluster of TFs, proposed as the HIF1α-TF interactome, that orchestrates the transcription of target genes involved in hypoxia, due to their post-translational modifications (PTMs), including phosphorylation/dephosphorylation, ubiquitination/deubiquitination, SUMOylation, hydroxylation, acetylation, S-nitrosylation, and palmitoylation. PTMs of these HIF1α-related TFs drive their stability and activity, degradation and turnover, and the bidirectional translocation between the cytoplasm or plasma membrane and nucleus of BC cells, as well as the transcription/activation of proteins encoded by oncogenes or inactivation of tumor suppressor target genes. Consequently, PTMs of TFs in the HIF1α interactome are crucial regulatory mechanisms that drive the cellular response to oxygen deprivation in BC cells.

A comprehensive lifestyle index and its associations with DNA methylation and type 2 diabetes among Ghanaian adults: the rodam study

BACKGROUND

A series of modifiable lifestyle factors, such as diet quality, physical activity, alcohol intake, and smoking, may drive the rising burden of type 2 diabetes (T2DM) among sub-Saharan Africans globally. It is unclear whether epigenetic changes play a mediatory role in the associations between these lifestyle factors and T2DM. We assessed the associations between a comprehensive lifestyle index, DNA methylation and T2DM among Ghanaian adults.

METHODS

We used whole-blood Illumina 450 k DNA methylation data from 713 Ghanaians from the Research on Obesity and Diabetes among African Migrants (RODAM) study. We constructed a comprehensive lifestyle index based on established cut-offs for diet quality, physical activity, alcohol intake, and smoking status. In the T2DM-free discovery cohort (n = 457), linear models were fitted to identify differentially methylated positions (DMPs) and differentially methylated regions (DMRs) associated with the lifestyle index after adjustment for age, sex, body mass index (BMI), and technical covariates. Associations between the identified DMPs and the primary outcome (T2DM), as well as secondary outcomes (fasting blood glucose (FBG) and HbA1c), were determined via logistic and linear regression models, respectively.

RESULTS

In the present study population (mean age: 52 ± 10 years; male: 42.6%), the comprehensive lifestyle index showed a significant association with one DMP annotated to an intergenic region on chromosome 7 (false discovery rate (FDR) = 0.024). Others were annotated to ADCY7, SMARCE1, AHRR, LOXL2, and PTBP1 genes. One DMR was identified and annotated to the GFPT2 gene (familywise error rate (FWER) from bumphunter bootstrap = 0.036). None of the DMPs showed significant associations with T2DM; directions of effect were positive for the DMP in the AHRR and inverse for all the other DMPs. Higher methylation of the ADCY7 DMP was associated with higher FBG (p = 0.024); LOXL2 DMP was associated with lower FBG (p = 0.023) and HbA1c (p = 0.049); and PTBP1 DMP was associated with lower HbA1c (p = 0.002).

CONCLUSIONS

In this explorative epigenome-wide association study among Ghanaians, we identified one DMP and DMR associated with a comprehensive lifestyle index not previously associated with individual lifestyle factors. Based on our findings, we infer that lifestyle factors in combination, affect DNA methylation, thereby influencing the risk of T2DM among Ghanaian adults living in different contexts.

Altered Expression of EMT-Related Factors Snail, Wnt4, and Notch2 in the Short-Term Streptozotocin-Induced Diabetic Rat Kidneys

Background: The aim of this study was to determine the expression of epithelial to mesenchymal transition (EMT)-related transcription factors Snail, Wnt4, and Notch2 with key roles in renal fibrosis, in different renal areas of diabetic rats: glomeruli (G), proximal and distal convoluted tubules (PCT; DCT). Methods: Male Sprague Dawley rats were instilled with 55 mg/kg streptozotocin (diabetes mellitus type I model, DM group) or citrate buffer (control group). Kidney samples were collected 2 weeks and 2 months after DM induction and processed for immunohistochemistry. Results: Diabetic animals showed higher Wnt4 kidney expression both 2 weeks and 2 months post-DM induction, while Snail expression significantly increased only 2 weeks after DM initiation (p < 0.0001). We determined significantly higher expression of examined EMT-related genes in different kidney regions in diabetic animals compared with controls. The most substantial differences were observed in tubular epithelial cells in the period of 2 weeks after induction, with higher Snail and Wnt4 expression in PCT and increased Snail and Notch2 expression in DCT of diabetic animals (p < 0.0001; p < 0.001). Conclusion: The obtained results point to the EMT-related factors Snail, Wnt4, and Notch2 as a potential contributor to diabetic nephropathy development and progression. Changes in their expression, especially in PCT and DCT, could serve as diagnostic biomarkers for the early stages of DM and might be a promising novel therapeutic target in this condition.

SENP1 protects cisplatin-induced AKI by attenuating apoptosis through regulation of HIF-1α

BACKGROUND

Acute kidney injury is a clinical syndrome with both high morbidity and mortality. However, the underlying molecular mechanism of AKI is still largely unknown. The role of SENP1 in AKI is unclear, while one of its substrates, HIF-1α possesses nephroprotective effect in AKI. Herein, this study aimed to reveal the role of SENP1/HIF-1α axis in AKI by using both cell and animal models.

METHODS

We investigated the effects of AKI on SENP1 expression using clinical samples, and cisplatin-induced AKI model based on mice or HK-2 cells. The influence of SENP1 knockdown or over-expression on cisplatin-induced AKI was studied in vitro and in vivo. Following the exploration of the change in HIF-1α expression brought by AKI, the synergistic effects of SENP1 knockdown and HIF-1α over-expression on AKI were examined.

RESULTS

The results showed the up-regulation of SENP1 in clinical specimens, as well as cell and animal models. The knockdown or over-expression of SENP1 in HK-2 cells could promote or inhibit AKI through regulating cell apoptosis, respectively. Moreover, SENP1^+/- mice suffered from much more serious AKI compared with mice in wild type group. Furthermore, we found that HIF-1α over-expression could attenuate the promoted cell apoptosis as well as AKI induced by SENP1 knockdown.

CONCLUSIONS

we showed that SENP1 provided protection for kidney in AKI via regulating cell apoptosis and through the regulation of HIF-1α. This study could benefit for the understanding of the pathogenesis of AKI and provide potential therapeutic target for AKI treatment.

A novel role of snail in regulating tuberin/AMPK pathways to promote renal fibrosis in the new mouse model of type II diabetes

Epithelial-mesenchymal transition (EMT) plays an important role in tissue fibrosis following chronic exposure to hyperglycemia. This study investigates the role of chronic diabetes in regulating tuberin/snail/AMPK to enhance EMT and increase renal fibrosis. A new mouse model of db/db/TSC2 ^+/- was generated by backcrossing db/db mice and TSC2 ^+/- mice. Wild type (WT), db/db, TSC2 ^+/- and dbdb/TSC2 ^+/- mice were sacrificed at ages 6 and 8 months old. Tuberin protein level was significantly decreased in kidneys from diabetic compared to WT mice at both ages. In addition, tuberin and E-cadherin protein levels were significantly decreased in dbdb/TSC2 ^+/- compared to TSC2 ^+/- and db/db mice. In contrast, p-PS6K, NFkB, snail, vimentin, fibronectin, and α-SMA protein levels were significantly increased in dbdb/TSC2 ^+/- compared to db/db and TSC2 ^+/- mice at ages 6 and 8 months. Both downregulation of AMPK by DN-AMPK and downregulation of tuberin by siRNA resulted in increased NFkB, snail, and fibronectin protein expression and decreased E-cadherin protein expression in mouse primary renal proximal tubular cells. Interestingly, downregulation of snail by siRNA increased tuberin expression via feedback through activation of AMPK and reversed the expression of epithelial proteins such as E-cadherin as well as mesenchymal proteins such as fibronectin, NF-KB, vimentin, and α-SMA in mouse primary renal proximal tubular cells isolated from kidneys of four mice genotypes. The data show that chronic diabetes significantly decreases tuberin expression and that provides strong evidence that tuberin is a major key protein involved in regulating EMT. These data also demonstrated a novel role for snail in regulating of AMPK/tuberin to enhance EMT and renal cell fibrosis in diabetes.

Functions of the SNAI family in chondrocyte-to-osteocyte development

Different cellular mechanisms contribute to osteocyte development. And while critical roles for members of the zinc finger protein SNAI family (SNAIs) have been discussed in cancer-related models, there are few reviews summarizing their importance for chondrocyte-to-osteocyte development. To help fill this gap, we review the roles of SNAIs in the development of mature osteocytes from chondrocytes, including the regulation of chondro- and osteogenesis through different signaling pathways and in programmed cell death. We also discuss how epigenetic factors-including DNA methylation, histone methylation and acetylation, and noncoding RNAs-contribute differently to both chondrocyte and osteocyte development. To better grasp the important roles of SNAIs in bone development, we also review genotype-phenotype correlations in different animal models. We end with comments about the possible importance of the SNAI family in cartilage/bone development and the potential applications for therapeutic goals.

Tubular Numb promotes renal interstitial fibrosis via modulating HIF-1α protein stability

Tubulointerstitial fibrosis is the ultimate common pathway of all manners of chronic kidney disease. We previously demonstrated that specific deletion of Numb in proximal tubular cells (PTCs) prevented G2/M arrest and attenuated renal fibrosis. However, how Numb modulates cell cycle arrest remains unclear. Here, we showed that Numb overexpression significantly increased the protein level of hypoxia-inducible factor-1α (HIF-1α). Numb overexpression-induced G2/M arrest was blocked by silencing endogenous HIF-1α, subsequently downregulated the expression of cyclin G1 which is an atypical cyclin to promote G2/M arrest of PTCs. Further analysis revealed that Numb-augmented HIF-1α protein was blocked by simultaneously overexpressing MDM2. Moreover, silencing Numb decreased TGF-β1-induceded HIF-1α protein expression. While endogenous MDM2 was knocked down this reduction was reversed, indicating that Numb stabilized HIF-1α protein via interfering MDM2-mediated HIF-1α protein degradation. Interestingly, HIF-1α overexpression significantly upregulated the expression of Numb and silencing endogenous HIF-1α blocked CoCl₂ or TGF-β1-induced Numb expression. Chromatin immunoprecipitation (ChIP) assays demonstrated that HIF-1α binded to the promoter region of Numb. This binding was significantly increased by TGF-β1. Collectively, these data indicate that Numb and HIF-1α cooperates to promote G2/M arrest of PTCs, and thus aggravates tubulointerstitial fibrosis. Numb might be a potential target for the therapy of tubulointerstitial fibrosis.

Hypoxia in chronic kidney disease: towards a paradigm shift?

Chronic kidney disease (CKD) is defined as an alteration of kidney structure and/or function lasting for >3 months [1]. CKD affects 10% of the general adult population and is responsible for large healthcare costs [2]. Since the end of the last century, the role of hypoxia in CKD progression has controversially been discussed. To date, there is evidence of the presence of hypoxia in late-stage renal disease, but we lack time-course evidence, stage correlation and also spatial co-localization with fibrotic lesions to ensure its causative role. The classical view of hypoxia in CKD progression is that it is caused by peritubular capillary alterations, renal anaemia and increased oxygen consumption regardless of the primary injury. In this classical view, hypoxia is assumed to further induce pro-fibrotic and pro-inflammatory responses, as well as oxidative stress, leading to CKD worsening as part of a vicious circle. However, recent investigations tend to question this paradigm, and both the presence of hypoxia and its role in CKD progression are still not clearly demonstrated. Hypoxia-inducible factor (HIF) is the main transcriptional regulator of the hypoxia response. Genetic HIF modulation leads to variable effects on CKD progression in different murine models. In contrast, pharmacological modulation of the HIF pathway [i.e. by HIF hydroxylase inhibitors (HIs)] appears to be generally protective against fibrosis progression experimentally. We here review the existing literature on the role of hypoxia, the HIF pathway and HIF HIs in CKD progression and summarize the evidence that supports or rejects the hypoxia hypothesis, respectively.

Recent advances in understanding the role of hypoxia-inducible factor 1α in renal fibrosis

Renal fibrosis is the most common pathological manifestation of chronic kidney disease (CKD), and with numerous influencing factors, its pathogenesis is complex. Epithelial-mesenchymal transition (EMT) is known to promote the progression of renal fibrosis via alterations in the secreted proteome. Moreover, blocking or even reversing EMT can effectively reduce the degree of fibrosis. As such, targeting the key molecules responsible for promoting EMT may be an effective strategy for inhibiting renal fibrosis. Research in recent years has demonstrated that hypoxia-inducible factor 1α (HIF-1α) acts to promote renal fibrosis through regulation of EMT. However, the relationship between HIF-1α and EMT remains incompletely understood. In the present review, the underlying mechanism of the interaction between HIF-1α and EMT is explored to provide novel insight into the pathogenesis of renal fibrosis and new ideas for early targeted intervention.

Mechanism and Consequences of The Impaired Hif-1α Response to Hypoxia in Human Proximal Tubular HK-2 Cells Exposed to High Glucose

Renal hypoxia and loss of proximal tubular cells (PTC) are relevant in diabetic nephropathy. Hypoxia inhibits hypoxia-inducible factor-1α (HIF-1α) degradation, which leads to cellular adaptive responses through HIF-1-dependent activation of gene hypoxia-responsive elements (HRE). However, the diabetic microenvironment represses the HIF-1/HRE response in PTC. Here we studied the mechanism and consequences of impaired HIF-1α regulation in human proximal tubular HK-2 cells incubated in hyperglycemia. Inhibition at different levels of the canonical pathway of HIF-1α degradation did not activate the HIF-1/HRE response under hyperglycemia, except when proteasome was inhibited. Further studies suggested that hyperglycemia disrupts the interaction of HIF-1α with Hsp90, a known cause of proteasomal degradation of HIF-1α. Impaired HIF-1α regulation in cells exposed to hyperglycemic, hypoxic diabetic-like milieu led to diminished production of vascular endothelial growth factor-A and inhibition of cell migration (responses respectively involved in tubular protection and repair). These effects, as well as impaired HIF-1α regulation, were reproduced in normoglycemia in HK-2 cells incubated with microparticles released by HK-2 cells exposed to diabetic-like milieu. In summary, these results highlight the role of proteasome-dependent mechanisms of HIF-1α degradation on diabetes-induced HK-2 cells dysfunction and suggest that cell-derived microparticles may mediate negative effects of the diabetic milieu on PTC.

[Dexmedetomidine hydrochloride up-regulates expression of hypoxia inducible factor-1α to alleviate renal ischemiareperfusion injury in diabetic rats]

OBJECTIVE

To verify whether dexmedetomidine hydrochloride (Dex) alleviates renal ischemia-reperfusion (IR) injury in diabetic rats by increasing the expression of hypoxia inducible factor-1α (HIF-1α).

METHODS

A rat model of type 2 diabetes mellitus was established by high-fat diet and streptozotocin injection. The rats were subjected to daily intragastric administration of 0.05 mg/kg digoxin for 7 consecutive days and intraperitoneal injection of Dex 2 h before renal IR injury induced by ligation of the bilateral renal arteries for 60 min followed by reperfusion for 120 min. After reperfusion, blood samples were taken for detection of serum creatinine (Scr) and urea nitrogen (BUN) levels. Western blotting was used to detect the expression of HIF-1α, cleaved caspase-3, Bcl-2, and Bax in the renal tissues; the expression of the HIF-1α, p-eNOS, and eNOS were detected using ELISA. The percentage of apoptotic glomerular cells was assessed using TUNEL assay.

RESULTS

The levels of Scr, BUN, HIF-1α, p-eNOS, and eNOS and the percentage of apoptotic cells in both normal and diabetic rats increased significantly after renal IR injury (P &lt; 0.05). The expressions of Scr, BUN, p-eNOS, and eNOS decreased while HIF-1α expression increased significantly in Dex-treated rats with renal IR injury (P &lt; 0.05). Compared with the non-diabetic rats, the diabetic rats showed more obvious increase in the expressions of Scr, BUN, p-eNOS, and eNOS following renal IR injury. In the diabetic rats with renal IR injury, Dex treatment prior to the injury significantly lowered the expressions of Scr, BUN, p-eNOS, eNOS, cleaved caspase-3, and Bax, decreased the percentage of apoptotic cells, and increased the levels of HIF-1a and Bcl-2 (P &lt; 0.05). Digoxin treatment significantly antagonized the effects of Dex in the diabetic rats with renal IR injury by increasing the expressions of cleaved caspase-3 and Bax, promoting glomerular cell apoptosis, and decreasing renal expressions of HIF-1 and Bcl-2 (P &lt; 0.05).

CONCLUSIONS

Dex alleviates renal IR injury in diabetic rats probably by inhibiting renal expression of HIF-1α and glomerular cell apoptosis.

Lysyl oxidase-like 2 inhibition ameliorates glomerulosclerosis and albuminuria in diabetic nephropathy

Diabetic nephropathy is characterised by the excessive amount of extracellular matrix in glomeruli and tubulointerstitial space. Lysyl oxidase-like 2 (LOXL2) is elevated in renal fibrosis and known to play key roles in ECM stabilisation by facilitating collagen cross-links, epithelial to mesenchymal transition and myofibroblast activation. Thus, targeting LOXL2 may prove to be a useful strategy to prevent diabetic nephropathy. We explored the renoprotective effect of a selective small molecule LOXL2 inhibitor (PXS-S2B) in a streptozotocin-induced diabetes model. Diabetic mice were treated with PXS-S2B for 24 weeks and outcomes compared with untreated diabetic mice and with telmisartan treated animals as comparator of current standard of care. Diabetic mice had albuminuria, higher glomerulosclerosis scores, upregulation of fibrosis markers and increased renal cortical LOXL2 expression. Treatment with PXS-S2B reduced albuminuria and ameliorated glomerulosclerosis. This was associated with reduced expression of glomerular fibronectin and tubulointerstitial collagen I. The renoprotective effects of both PXS-S2B and telmisartan were more marked in the glomerular compartment than in the tubulointerstitial space. The study reveals that LOXL2 inhibition was beneficial in preserving glomerular structure and function. Thus, LOXL2 may be a potential therapeutic target in diabetic nephropathy.

Snail and kidney fibrosis

Snail family zinc finger 1 (SNAI1) is a transcription factor expressed during renal embryogenesis, and re-expressed in various settings of acute kidney injury (AKI). Subjected to tight regulation, SNAI1 controls major biological processes responsible for renal fibrogenesis, including mesenchymal reprogramming of tubular epithelial cells, shutdown of fatty acid metabolism, cell cycle arrest and inflammation of the microenvironment surrounding tubular epithelial cells. The present review describes in detail the interactions of SNAI1 with AKI-associated signalling pathways. We also discuss how this central factor has been iteratively (and promisingly) targeted in a number of animal models in order to prevent or slow down renal fibrogenesis.

Acetylation of hMOF Modulates H4K16ac to Regulate DNA Repair Genes in Response to Oxidative Stress

Oxidative stress is considered to be a key risk state for a variety of human diseases. In response to oxidative stress, the regulation of transcriptional expression of DNA repair genes would be important to DNA repair and genomic stability. However, the overall pattern of transcriptional expression of DNA repair genes and the underlying molecular response mechanism to oxidative stress remain unclear. Here, by employing colorectal cancer cell lines following exposure to hydrogen peroxide, we generated expression profiles of DNA repair genes via RNA-seq and identified gene subsets that are induced or repressed following oxidative stress exposure. RRBS-seq analyses further indicated that transcriptional regulation of most of the DNA repair genes that were induced or repressed is independent of their DNA methylation status. Our analyses also indicate that hydrogen peroxide induces deacetylase SIRT1 which decreases chromatin affinity and the activity of histone acetyltransferase hMOF toward H4K16ac and results in decreased transcriptional expression of DNA repair genes. Taken together, our findings provide a potential mechanism by which oxidative stress suppresses DNA repair genes which is independent of the DNA methylation status of their promoters.

Lysyl oxidase‑like 2 is expressed in kidney tissue and is associated with the progression of tubulointerstitial fibrosis

Tubulointerstitial fibrosis is a common end point of chronic kidney diseases, and preventing its progression is key to avoiding renal failure. Transforming growth factor-β (TGF-β) and associated molecules promote tubulointerstitial fibrosis; however, effective therapies targeting these molecules have yet to be developed. Lysyl oxidase-like 2 (LOXL2), which is involved in invasive growth and metastasis of malignant neoplasms, has recently been reported to serve a key role in hepatic and pulmonary fibrosis. However, little is currently known regarding LOXL2 expression in the kidney and its involvement in tubulointerstitial fibrosis. The present study evaluated LOXL2 expression in human and mouse kidney tissues, as well as in cultured renal cells. LOXL2 protein expression was detected in glomerular capillary loops and tubular epithelial cells in human and mouse kidneys. Glomerular LOXL2 was localized to the cytoplasm of podocytes, as determined by double immunofluorescence microscopy using a podocyte marker (synaptopodin). This result was supported by western blot analysis, which demonstrated that LOXL2 protein expression is present in cultured human podocytes and HK-2 human proximal tubular cells. In addition, the mRNA and protein expression levels of LOXL2 were higher in a mouse model of tubulointerstitial fibrosis compared with in control mice. In addition, immunohistochemistry results demonstrated that LOXL2 is present in the fibrous interstitium and infiltrating mononuclear cells in a mouse model of tubulointerstitial fibrosis. The present study demonstrated that LOXL2 is expressed in compartments of renal tissue, where it appears to contribute to the progression of tubulointerstitial fibrosis.

Effect of berberine on the renal tubular epithelial-to-mesenchymal transition by inhibition of the Notch/snail pathway in diabetic nephropathy model KKAy mice

Renal tubular epithelial-to-mesenchymal transition (EMT) and renal tubular interstitial fibrosis are the main pathological changes of diabetic nephropathy (DN), which is a common cause of end-stage renal disease. Previous studies have suggested that berberine (BBR) has antifibrotic effects in the kidney and can reduce apoptosis and inhibit the EMT of podocytes in DN. However, the effect of BBR on the renal tubular EMT in DN and its mechanisms of action are unknown. This study was performed to explore the effects of BBR on the renal tubular EMT and the molecular mechanisms of BBR in DN model KKAy mice and on the high glucose (HG)-induced EMT in mouse renal tubular epithelial cells. Our results showed that, relative to the model mice, the mice in the treatment group had an improved general state and reduced blood glucose and 24-h urinary protein levels. Degradation of renal function was ameliorated by BBR. We also observed the protective effects of BBR on renal structural changes, including normalization of an index of renal interstitial fibrosis and kidney weight/body weight. Moreover, BBR suppressed the activation of the Notch/snail pathway and upregulated the α-SMA and E-cadherin levels in DN model KKAy mice. BBR was further found to prevent HG-induced EMT events and to inhibit the HG-induced expression of Notch pathway members and snail1 in mouse renal tubular epithelial cells. Our findings indicate that BBR has a therapeutic effect on DN, including its inhibition of the renal tubular EMT and renal interstitial fibrosis. Furthermore, the BBR-mediated EMT inhibition occurs through Notch/snail pathway regulation.

Lysyl Oxidase and the Tumor Microenvironment

The lysyl oxidase (LOX) family of oxidases contains a group of extracellular copper-dependent enzymes that catalyze the cross-linking of collagen and elastin by oxidation, thus maintaining the rigidity and structural stability of the extracellular matrix (ECM). Aberrant expression or activation of LOX alters the cellular microenvironment, leading to many diseases, including atherosclerosis, tissue fibrosis, and cancer. Recently, a number of studies have shown that LOX is overexpressed in most cancers and that it is involved in the regulation of tumor progression and metastasis. In contrast, a few reports have also indicated the tumor-suppressing role of LOX. In this short review, we discuss recent research on the correlations between LOX and cancer. Further, the role of LOX in tumor microenvironment remodeling, tumorigenesis, and metastasis and the underlying mechanisms have also been elucidated.

Decreased Satellite Cell Number and Function in Humans and Mice With Type 1 Diabetes Is the Result of Altered Notch Signaling

Type 1 diabetes (T1D) negatively influences skeletal muscle health; however, its effect on muscle satellite cells (SCs) remains largely unknown. SCs from samples from rodents (Akita) and human subjects with T1D were examined to discern differences in SC density and functionality compared with samples from their respective control subjects. Examination of the Notch pathway was undertaken to investigate its role in changes to SC functionality. Compared with controls, Akita mice demonstrated increased muscle damage after eccentric exercise along with a decline in SC density and myogenic capacity. Quantification of components of the Notch signaling pathway revealed a persistent activation of Notch signaling in Akita SCs, which could be reversed with the Notch inhibitor DAPT. Similar to Akita samples, skeletal muscle from human subjects with T1D displayed a significant reduction in SC content, and the Notch ligand, DLL1, was significantly increased compared with control subjects, supporting the dysregulated Notch pathway observed in Akita muscles. These data indicate that persistent activation in Notch signaling impairs SC functionality in the T1D muscle, resulting in a decline in SC content. Given the vital role played by the SC in muscle growth and maintenance, these findings suggest that impairments in SC capacities play a primary role in the skeletal muscle myopathy that characterizes T1D.

SMYD3 stimulates EZR and LOXL2 transcription to enhance proliferation, migration, and invasion in esophageal squamous cell carcinoma

Epigenetic alterations, including DNA methylation and histone modifications, are involved in the regulation of cancer initiation and progression. SET and MYND domain-containing protein 3 (SMYD3), a methyltransferase, plays an important role in transcriptional regulation during human cancer progression. However, SMYD3 expression and its function in esophageal squamous cell carcinoma (ESCC) remain unknown. In this study, SMYD3 expression was studied by immunohistochemistry in a tumor tissue microarray from 131 cases of ESCC patients. Statistical analysis showed that overall survival of patients with high SMYD3 expressing in primary tumors was significantly lower than that of patients with low SMYD3-expressing tumors (P = .008, log-rank test). Increased expression of SMYD3 was found to be associated with lymph node metastasis in ESCC (P = .036) and was an independent prognostic factor for poor overall survival (P = .025). RNAi-mediated knockdown of SMYD3 suppressed ESCC cell proliferation, migration, and invasion in vitro and inhibited local tumor invasion in vivo. SMYD3 regulated transcription of EZR and LOXL2 by directly binding to the sequences of the promoter regions of these target genes, as demonstrated by a chromatin immunoprecipitation assay. Immunohistochemical staining of ESCC tissues also confirmed that protein levels of EZR and LOXL2 positively correlated with SMYD3 expression, and the Spearman correlation coefficients (rs) were 0.78 (n = 81; P < .01) and 0.637 (n = 103; P < .01), respectively. These results indicate that SMYD3 enhances tumorigenicity in ESCC through enhancing transcription of genes involved in proliferation, migration, and invasion.

Hes1: a key role in stemness, metastasis and multidrug resistance

Hes1 is one mammalian counterpart of the Hairy and Enhancer of split proteins that play a critical role in many physiological processes including cellular differentiation, cell cycle arrest, apoptosis and self-renewal ability. Recent studies have shown that Hes1 functions in the maintenance of cancer stem cells (CSCs), metastasis and antagonizing drug-induced apoptosis. Pathways that are involved in the up-regulation of Hes1 level canonically or non-canonically, such as the Hedgehog, Wnt and hypoxia pathways are frequently aberrant in cancer cells. Here, we summarize the recent data supporting the idea that Hes1 may have an important function in the maintenance of cancer stem cells self-renewal, cancer metastasis, and epithelial-mesenchymal transition (EMT) process induction, as well as chemotherapy resistance, and conclude with the possible mechanisms by which Hes1 functions have their effect, as well as their crosstalk with other carcinogenic signaling pathways.

Effect of Tongxinluo on Nephrin Expression via Inhibition of Notch1/Snail Pathway in Diabetic Rats

Podocyte injury is an important mechanism of diabetic nephropathy (DN). Accumulating evidence suggests that nephrin expression is decreased in podocyte in DN. Moreover, it has been demonstrated that tongxinluo (TXL) can ameliorate renal structure disruption and dysfunction in DN. However, the effect of TXL on podocyte injury in DN and its molecular mechanism is unclear. In order to explore the effect of TXL on podocyte injury and its molecular mechanism in DN, our in vivo and in vitro studies were performed. Our results showed that TXL increased nephrin expression in diabetic rats and in high glucose cultured podocyte. Meanwhile, TXL decreased ICN1 (the intracellular domain of notch), HES1, and snail expression in podocyte in vivo and in vitro. More importantly, we found that TXL protected podocyte from injury in DN. The results demonstrated that TXL inhibited the activation of notch1/snail pathway and increased nephrin expression, which may be a mechanism of protecting effect on podocyte injury in DN.

Human antigen R mediated post-transcriptional regulation of epithelial-mesenchymal transition related genes in diabetic nephropathy

BACKGROUND

Human antigen R (HuR) is a ubiquitously expressed RNA-binding protein that modulates gene expression at the post-transcriptional level. While cytoplasmic HuR expression was identified as a marker in epithelial-mesenchymal transition (EMT) process of several types of cancer, its role in diabetic nephropathy (DN) remains unclear.

METHODS

Renal biopsies from Type 2 diabetic patients and STZ-induced DN rats were stained for HuR and EMT markers. Redistribution of HuR was detected by immunostaining and western blot in high glucose stimulated cells. RNAi was used to supress HuR expression. The binding affinity for EMT-related genes was evaluated by immunoprecipitation.

RESULTS

Cytoplasmic HuR expression was elevated in human and rat DN specimens along with EMT changes compared to normal controls. HuR shuttling between nucleus and cytoplasm facilitated epithelial to mesenchymal transition in renal epithelial cells. The suppression of HuR partially inhibited EMT of high glucose stimulated HK-2 cells. Furthermore, HuR bound to 3'-UTRs of critical cytokines or transcription factors mRNA involved in EMT process.

CONCLUSION

Acquired phenotypic traits of EMT were partially through the enhanced HuR-binding proteins and its post-transcriptional regulation role in DN.

γ-Secretase inhibition promotes fibrotic effects of albumin in proximal tubular epithelial cells

BACKGROUND AND PURPOSE

Albuminuria is an important biomarker of renal dysfunction and is a major mediator of renal damage and fibrosis during kidney disease. The mechanisms underlying albumin-induced renal fibrosis remain unclear. There has been significant interest in γ-secretase activity in tubular epithelial cells in recent times; however, its potential role in albumin-induced fibrosis has not been investigated.

EXPERIMENTAL APPROACH

The primary aim of this study was to examine the role of γ-secretase in albumin-induced fibrotic effects in proximal tubular cells. The effects of increasing albumin concentrations on fibrosis indicators and mediators in the human HK-2 cell line were examined in the presence and absence of a γ-secretase inhibitor, compound E.

KEY RESULTS

Treatment with albumin resulted in a number of pro-fibrotic effects, including up-regulation of fibronectin, TGF-β1 and the EGF-R. Interestingly, similar effects were observed in response to treatment with the γ-secretase inhibitor, compound E. Co-treatment of cells with albumin and an EGF-R inhibitor, AG-1478, resulted in significant inhibition of the observed pro-fibrotic effects, suggesting a major role for the EGF-R in albumin-induced fibrotic events. Albumin-induced effects on the EGF-R appeared to be mediated through inhibition of γ-secretase activity and were dependent on ERK-MAPK signalling.

CONCLUSIONS AND IMPLICATIONS

These results provide novel insights into the mechanisms of albumin-induced fibrotic effects in tubular epithelial cells, suggesting important roles for the γ-secretase and the EGF-R. These results suggest that the proposed use of γ-secretase inhibitors as anti-fibrotic agents requires further investigation.

The therapeutic potential of targeting the epithelial-mesenchymal transition in cancer

INTRODUCTION

The process of epithelial-to-mesenchymal transition (EMT) has long been advocated as a process during tumor progression and the acquisition of metastatic potential of human cancers. EMT has also been linked with resistance to cancer therapies.

AREAS COVERED

Basic research has provided evidence connecting EMT to increased invasion, angiogenesis and metastasis of cancer cells. A number of signaling pathways such as notch, wnt, hedgehog and PI3K-AKT, and various other individual factors therein, have been intricately connected to the onset of EMT. Here, we provide latest updates on the evidences that further highlight an association between various signaling pathways and EMT, with a focus on therapeutic targets that may have the potential to reverse EMT.

EXPERT OPINION

Our understanding of EMT and its underlying causes is rapidly evolving and a number of putative targets have been identified. It is crucial, now than ever before, to design novel translational and clinical studies for the benefit of advanced stage cancer patients with metastatic disease.

Silencing of hypoxia-inducible factor-1α gene attenuates chronic ischemic renal injury in two-kidney, one-clip rats

Overactivation of hypoxia-inducible factor (HIF)-1α is implicated as a pathogenic factor in chronic kidney diseases (CKD). However, controversy exists regarding the roles of HIF-1α in CKD. Additionally, although hypoxia and HIF-1α activation are observed in various CKD and HIF-1α has been shown to stimulate fibrogenic factors, there is no direct evidence whether HIF-1α is an injurious or protective factor in chronic renal hypoxic injury. The present study determined whether knocking down the HIF-1α gene can attenuate or exaggerate kidney damage using a chronic renal ischemic model. Chronic renal ischemia was induced by unilaterally clamping the left renal artery for 3 wk in Sprague-Dawley rats. HIF-1α short hairpin (sh) RNA or control vectors were transfected into the left kidneys. Experimental groups were sham+control vector, clip+control vector, and clip+HIF-1α shRNA. Enalapril was used to normalize blood pressure 1 wk after clamping the renal artery. HIF-1α protein levels were remarkably increased in clipped kidneys, and this increase was blocked by shRNA. Morphological examination showed that HIF-1α shRNA significantly attenuated injury in clipped kidneys: glomerular injury indices were 0.71 ± 0.04, 2.50 ± 0.12, and 1.34 ± 0.11, and the percentage of globally damaged glomeruli was 0.02, 34.3 ± 5.0, and 6.3 ± 1.6 in sham, clip, and clip+shRNA groups, respectively. The protein levels of collagen and α-smooth muscle actin also dramatically increased in clipped kidneys, but this effect was blocked by HIF-1α shRNA. In conclusion, long-term overactivation of HIF-1α is a pathogenic factor in chronic renal injury associated with ischemia/hypoxia.

Notch Signaling Molecules Activate TGF- β in Rat Mesangial Cells under High Glucose Conditions

The involvement of the Notch signaling pathway in the cellular differentiation of the mammalian kidney is established. Recently, the dysregulation of Notch signaling molecules has been identified in acute and chronic renal injuries, fibrosis models, and diabetic kidney biopsies. The canonical Notch ligand , Jagged1, is upregulated in a transforming growth factor-beta- (TGF- β -) dependent manner during chronic kidney disease. TGF- β , a central mediator of renal fibrosis, also is a major contributor to the development of diabetic nephropathy. To explore the roles and possible mechanisms of Notch signaling molecules in the pathogenesis of diabetic nephropathy, we exposed cultured rat mesangial cells to a γ -secretase inhibitor (DAPT) or high glucose and measured the expression of Notch signaling molecules and the fibrosis index. Notch pathway-related molecules, TGF- β , and fibronectin increased with exposure to high glucose and decreased with DAPT treatment. Our results suggest that the Notch signaling pathway may precipitate diabetic nephropathy via TGF- β activation.

Luteolin reduces the invasive potential of malignant melanoma cells by targeting β3 integrin and the epithelial-mesenchymal transition

AIM

To investigate whether luteolin, a highly prevalent flavonoid, reverses the effects of epithelial-mesenchymal transition (EMT) in vitro and in vivo and to determine the mechanisms underlying this reversal.

METHODS

Murine malignant melanoma B16F10 cells were exposed to 1% O(2) for 24 h. Cellular mobility and adhesion were assessed using Boyden chamber transwell assay and cell adhesion assay, respectively. EMT-related proteins, such as E-cadherin and N-cadherin, were examined using Western blotting. Female C57BL/6 mice (6 to 8 weeks old) were injected with B16F10 cells (1×10(6) cells in 0.2 mL per mouse) via the lateral tail vein. The mice were treated with luteolin (10 or 20 mg/kg, ip) daily for 23 d. On the 23rd day after tumor injection, the mice were sacrificed, and the lungs were collected, and metastatic foci in the lung surfaces were photographed. Tissue sections were analyzed with immunohistochemistry and HE staining.

RESULTS

Hypoxia changed the morphology of B16F10 cells in vitro from the cobblestone-like to mesenchymal-like strips, which was accompanied by increased cellular adhesion and invasion. Luteolin (5-50 μmol/L) suppressed the hypoxia-induced changes in the cells in a dose-dependent manner. Hypoxia significantly decreased the expression of E-cadherin while increased the expression of N-cadherin in the cells (indicating the occurrence of EMT-like transformation), which was reversed by luteolin (5 μmol/L). In B16F10 cells, luteolin up-regulated E-cadherin at least partly via inhibiting the β3 integrin/FAK signal pathway. In experimental metastasis model mice, treatment with luteolin (10 or 20 mg/kg) reduced metastatic colonization in the lungs by 50%. Furthermore, the treatment increased the expression of E-cadherin while reduced the expression of vimentin and β3 integrin in the tumor tissues.

CONCLUSION

Luteolin inhibits the hypoxia-induced EMT in malignant melanoma cells both in vitro and in vivo via the regulation of β3 integrin, suggesting that luteolin may be applied as a potential anticancer chemopreventative and chemotherapeutic agent.

High glucose induced differential expression of lysyl oxidase and its isoform in ARPE-19 cells

PURPOSE

Lysyl oxidase (LOX) stabilizes the extracellular matrix (ECM) by cross-linking collagen and elastin molecules. In proliferative diabetic retinopathy (PDR), there is ECM remodeling with neovascularization and basement membrane changes. While protease activities are well reported, the role of LOX in the pathogenesis of diabetic retinopathy is less studied. This study was done to see the effect of high glucose on the activity and expression of LOX and its isoforms in ARPE-19 cells.

MATERIALS AND METHODS

ARPE-19 cells were exposed to high glucose up to 48 h, and LOX activity was determined by N-acetyl-3,7-dihydroxyphenoxazine assay. The mRNA expression of LOX and its isoforms was done by real-time PCR and the protein expression by ELISA. Immunohistochemistry for LOX was done in epiretinal membrane from PDR.

RESULTS

With an increase in glucose concentration LOX activity and protein was reduced significantly at 30 mM glucose at 48 h. mRNA expression of LOX, LOXL1, and LOXL2 varied with time and concentration of glucose. Vascular endothelial growth factor (VEGF) increased the LOX activity as well as the mRNA expression. Pigment epithelium-derived factor (PEDF) downregulated the mRNA expression of LOX, LOXL1, and LOXL2. The matrix metalloprotease (MMP) activity increased significantly with the increase in glucose concentration. The diabetic neovascular membrane showed increased immunostaining of LOX.

CONCLUSIONS

This study suggests that although the LOX activity, which is composite of all the isoforms, was reduced under high glucose conditions, there was a differential mRNA expression with increased LOX and LOXL1 and decreased LOXL2 expression.

Hyperglycemia causes renal cell damage via CCN2-induced activation of the TrkA receptor: implications for diabetic nephropathy

CCN2, a secreted profibrotic protein, is highly expressed in diabetic nephropathy (DN) and implicated in its pathogenesis; however, the actions of CCN2 in DN remain elusive. We previously demonstrated that CCN2 triggers signaling via tropomyosin receptor kinase A (TrkA). Trace expression of TrkA is found in normal kidneys, but its expression is elevated in several nephropathies; yet its role in DN is unexplored. In this study we show de novo expression of TrkA in human and murine DN. We go on to study the molecular mechanisms leading to TrkA activation and show that it involves hypoxia, as demonstrated by ischemia-reperfusion injury and in vitro experiments mimicking hypoxia, implicating hypoxia as a common pathway leading to disease. We also expose renal cells to hyperglycemia, which led to TrkA phosphorylation in mesangial cells, tubular epithelial cells, and podocytes but not in glomerular endothelial cells and renal fibroblasts. In addition, we report that hyperglycemia caused an induction of phosphorylated extracellular signal-related kinase 1/2 and Snail1 that was abrogated by silencing of TrkA or CCN2 using small interfering RNA. In conclusion, we provide novel evidence that TrkA is activated in diabetic kidneys and suggest that anti-TrkA therapy may prove beneficial in DN.

SnoN as a key regulator of the high glucose-induced epithelial-mesenchymal transition in cells of the proximal tubule

BACKGROUND/AIMS

Ski-related protein N (SnoN) suppression is essential to transforming growth factor-β1 induction and the epithelial-mesenchymal transition (EMT) in several cancer cells. The role of SnoN in diabetic nephropathy is unknown. We aimed to determine the role of SnoN in the EMT of proximal tubule cells (PTCs) maintained under high glucose conditions.

METHODS

Immunohistochemistry, immunocytochemistry, Western blotting, small interfering RNA gene silencing, viral transduction and RT-PCR were used to assess changes in SnoN, E-cadherin, cytokeratin-18, α-smooth muscle actin and fibronectin expression using an in vivo streptozotocin-induced rat diabetic nephropathy model, and PTCs exposed to high glucose (25 mmol/l).

RESULTS

High glucose induced EMT in vitro and in vivo. Exposure of PTCs to a high concentration of glucose suppressed SnoN expression in a time-dependent manner compared with normal glucose and high osmolarity-treated groups. SnoN gene silencing under high glucose conditions appears to enhance the transition of PTC phenotype. Conversely, ectopic expression of exogenous SnoN after transfection conferred tubular epithelial cell resistance to high glucose-induced EMT.

CONCLUSION

SnoN plays a negative role in high glucose-induced EMT in PTCs. The effect of SnoN downregulation in vivo and in vitro suggests that SnoN may be a potential therapeutic target.

The role of IL-7 in renal proximal tubule epithelial cells fibrosis

BACKGROUND

Hyperglycemia is the most important risk factor in the progression of renal fibrosis in diabetic kidney. Based on previous studies, interleukin-7 (IL-7) may exert antifibrotic activities in pulmonary fibrosis model. However, the role of IL-7 in the pathogenesis of renal tubulointerstitial fibrosis remains unclear. Thus, we hereby elucidate the effects of IL-7 in cultured renal proximal tubular epithelial cells (designated as HK-2) treated under hyperglycemic condition.

METHODS

Cells were cultured in high glucose (27.5mM) for 2 days. Different concentration of IL-7 (10, 50, 100 or 200ng/ml) was added in the last 24h of culture. ELISA was used to evaluate the secreted protein such as fibronectin and TGF-β(1). Western blot was used to examine the EMT marker (including α-smooth muscle actin (α-SMA) and E-cadherin), signal transducer (including Smad Smad2/3 and Smad7) and EMT initiator (e.g. Snail). Immunofluorescence staining was used to assay the in situ expression of proteins (e.g. fibronectin and Snail).

RESULTS

We found that IL-7 significantly attenuated high glucose-inhibited cellular growth and high glucose-induced fibrosis. More importantly, high glucose-induced up-regulation of fibronectin, TGF-β, TGF-β RII and pSmad2/3 was markedly inhibited by IL-7. On the contrary, high glucose-induced down-regulation of Smad7 was significantly reversed by IL-7 instead. IL-7 markedly inhibited high glucose-induced increase in α-SMA and Snail and decrease in E-cadherin.

CONCLUSION

We demonstrate that IL-7 has the potential to inhibit high glucose-induced renal proximal tubular fibrosis partly by modulating Smads and EMT pathway.