The role of HIF-1α in the TGF-β2-mediated epithelial-to-mesenchymal transition of human lens epithelial cells

Unexpected and Synergistical Effects of All-Trans Retinoic Acid and TGF-β2 on Biological Aspects of 2D and 3D Cultured ARPE19 Cells

Objectives: To study the effects of all-trans retinoic acid (ATRA) on TGF-β2-induced effects of human retinal pigment epithelium cells under normoxia and hypoxia conditions. Methods: Two-dimensionally (2D) and three-dimensionally (3D) cultured ARPE19 cells were subjected to cellular functional analyses by transepithelial electrical resistance (TEER) and an extracellular flux assay (2D), measurement of levels of reactive oxygen species (ROS), gene expression analyses of COL1, αSMA, Zo-1, HIF1α, and PGC1α (2D), and physical property analyses (3D). Results: Under a normoxia condition, treatment with 100 nM ATRA substantially decreased barrier function regardless of the presence of 5 ng/mL TGF-β2 in 2D ARPE19 monolayer cells. Under a hypoxia condition, treatment with ATRA conversely increased barrier function, but the effect was masked by a marked increase in effects induced by TGF-β2. Although ATRA alone did not affect cellular metabolism and ROS levels in 2D ARPE cells, treatment with ATRA under a hypoxia condition did not affect ROS levels but shifted cellular metabolism from mitochondrial respiration to glycolysis. The changes of cellular metabolism and ROS levels were more pronounced with treatment of both ATRA and TGF-β2 independently of oxygen conditions. Changes in mRNA expressions of some of the above genes suggested the involvement of synergistical regulation of cellular functions by TGF-β2 and hypoxia. In 3D ARPE spheroids, the size was decreased and the stiffness was increased by either treatment with TGF-β2 or ATRA, but these changes were unexpectedly modulated by both ATRA and TGF-β2 treatment regardless of oxygen conditions. Conclusions: The findings reported herein indicate that TGF-β2 and hypoxia synergistically and differentially induce effects in 2D and 3D cultured ARPE19 cells and that their cellular properties are significantly altered by the presence of ATRA.

Pharmacological regulation of HIF-1α, RGC death, and glaucoma

Hypoxia can regulate oxygen-sensitive pathways that could be neuroprotective to compensate for the detrimental effects of low oxygen. However, prolonged hypoxia can activate neurodegenerative pathways. HIF-1α is upregulated/stabilized in hypoxic conditions, promoting alteration of gene expression, and ultimately leading to cell-death. Therefore, regulation of HIF-1α expression pharmacologically is a vital approach to mitigate cell death. In this review, we provide information showing the role of HIF-1α and its associated pathways in ocular retinopathies. We also discuss the beneficial roles of HIF-1α inhibitor, KC7F2, in ocular pathologies. Finally, we provided our own data demonstrating RGC neuroprotection by KC7F2 in glaucomatous animals.

HIF-1 inhibition reverses opacity in a rat model of galactose-induced cataract

Cataract is an eye disease, in which the lens becomes opaque, causing vision loss and blindness. The detailed mechanism of cataract development has not been characterized, and effective drug therapies remain unavailable. Here, we investigated the effects of Hypoxia-inducible factor 1 (HIF-1) inhibitors using an ex vivo model, in which rat lenses were cultured in galactose-containing medium to induce opacity formation. We found that treatment with the HIF-1 inhibitors 2-Methoxyestradiol (2ME2), YC-1, and Bavachinin decreased lens opacity. Microarray analysis on 2ME2-treated samples, in which opacity was decreased, identified genes upregulated by galactose and downregulated by inhibitor treatment. Subsequent STRING analysis on genes that showed expression change by RT-qPCR identified two clusters. First cluster related to the cytoskeleton and epithelial-mesenchymal transition (EMT). Second cluster related to the oxidative stress, and apoptosis. ACTA2, a known marker for EMT, and TXNIP, a suppressor of cell proliferation and activator of apoptosis, were present in each cluster. Thus, suppression of EMT and apoptosis, as well as activation of cell proliferation, appear to underlie the decrease in lens opacity.

Glycolysis Aids in Human Lens Epithelial Cells' Adaptation to Hypoxia

Hypoxic environments are known to trigger pathological damage in multiple cellular subtypes. Interestingly, the lens is a naturally hypoxic tissue, with glycolysis serving as its main source of energy. Hypoxia is essential for maintaining the long-term transparency of the lens in addition to avoiding nuclear cataracts. Herein, we explore the complex mechanisms by which lens epithelial cells adapt to hypoxic conditions while maintaining their normal growth and metabolic activity. Our data show that the glycolysis pathway is significantly upregulated during human lens epithelial (HLE) cells exposure to hypoxia. The inhibition of glycolysis under hypoxic conditions incited endoplasmic reticulum (ER) stress and reactive oxygen species (ROS) production in HLE cells, leading to cellular apoptosis. After ATP was replenished, the damage to the cells was not completely recovered, and ER stress, ROS production, and cell apoptosis still occurred. These results suggest that glycolysis not only performs energy metabolism in the process of HLE cells adapting to hypoxia, but also helps them continuously resist cell apoptosis caused by ER stress and ROS production. Furthermore, our proteomic atlas provides possible rescue mechanisms for cellular damage caused by hypoxia.

GINS4 suppresses ferroptosis by antagonizing p53 acetylation with Snail

Ferroptosis is an iron-dependent oxidative, nonapoptotic form of regulated cell death caused by the destruction of redox homeostasis. Recent studies have uncovered complex cellular networks that regulate ferroptosis. GINS4 is a promoter of eukaryotic G1/S-cell cycle as a regulator of initiation and elongation of DNA replication, but little is known about its impact on ferroptosis. Here, we found that GINS4 was involved in the regulation of ferroptosis in lung adenocarcinoma (LUAD). CRISPR/Cas9-mediated GINS4 KO facilitated ferroptosis. Interestingly, depletion of GINS4 could effectively induce G1, G1/S, S, and G2/M cells to ferroptosis, especially for G2/M cells. Mechanistically, GINS4 suppressed p53 stability through activating Snail that antagonized the acetylation of p53, and p53 lysine residue 351 (K351 for human p53) was the key site for GINS4-suppressed p53-mediated ferroptosis. Together, our data demonstrate that GINS4 is a potential oncogene in LUAD that functions to destabilize p53 and then inhibits ferroptosis, providing a potential therapeutic target for LUAD.

Role of HIF-1α in pathogenic mechanisms of keloids

BACKGROUDS AND OBJECTIVE

Keloids are defined as overrepairing products that develop after skin lesions. Keloids are characterized by the proliferation of fibroblasts and the overaccumulation of extracellular matrix components (mainly collagen), leading to a locally hypoxic microenvironment. Hence, this article was aimed to review hypoxia in pathogenesis of keloids.

METHODS

We reviewed and summarized the relevant published studies.

RESULTS

Hypoxia results in the accumulation of hypoxia-inducible factor 1α (HIF-1α) in keloids, contributing to overactivation of the fibrotic signaling pathway, epithelial-mesenchymal transition, and changes in metabolism, eventually leading to aggravated fibrosis, infiltrative growth, and radiotherapy resistance.

CONCLUSION

It is, therefore, essential to understand the role of HIF-1α in the pathogenic mechanisms of keloids in order to develop new therapeutic approaches.

Hypoxia Differently Affects TGF-β2-Induced Epithelial Mesenchymal Transitions in the 2D and 3D Culture of the Human Retinal Pigment Epithelium Cells

The hypoxia associated with the transforming growth factor-β2 (TGF-β2)-induced epithelial mesenchymal transition (EMT) of human retinal pigment epithelium (HRPE) cells is well recognized as the essential underlying mechanism responsible for the development of proliferative retinal diseases. In vitro, three-dimensional (3D) models associated with spontaneous O₂ gradients can be used to recapitulate the pathological levels of hypoxia to study the effect of hypoxia on the TGF-β2-induced EMT of HRPE cells in detail, we used two-dimensional-(2D) and 3D-cultured HRPE cells. TGF-β2 and hypoxia significantly and synergistically increased the barrier function of the 2D HRPE monolayers, as evidenced by TEER measurements, the downsizing and stiffening of the 3D HRPE spheroids and the mRNA expression of most of the ECM proteins. A real-time metabolic analysis indicated that TGF-β2 caused a decrease in the maximal capacity of mitochondrial oxidative phosphorylation in the 2D HRPE cells, whereas, in the case of 3D HRPE spheroids, TGF-β2 increased proton leakage. The findings reported herein indicate that the TGF-β2-induced EMT of both the 2D and 3D cultured HRPE cells were greatly modified by hypoxia, but during these EMT processes, the metabolic plasticity was different between 2D and 3D HRPE cells, suggesting that the mechanisms responsible for the EMT of the HRPE cells may be variable during their spatial spreading.

MYPT1/PP1-Mediated EZH2 Dephosphorylation at S21 Promotes Epithelial-Mesenchymal Transition in Fibrosis through Control of Multiple Families of Genes

The methyltransferase EZH2 plays an important role in regulating chromatin conformation and gene transcription. Phosphorylation of EZH2 at S21 by AKT kinase suppresses its function. However, protein phosphatases responsible for the dephosphorylation of EZH2-S21 remain elusive. Here, it is demonstrated that EZH2 is highly expressed in the ocular lens, and AKT-EZH2 axis is important in TGFβ-induced epithelial-mesenchymal transition (EMT). More importantly, it is identified that MYPT1/PP1 dephosphorylates EZH2-S21 and thus modulates its functions. MYPT1 knockout accelerates EMT, but expression of the EZH2-S21A mutant suppresses EMT through control of multiple families of genes. Furthermore, the phosphorylation status and gene expression modulation of EZH2 are implicated in control of anterior subcapsular cataracts (ASC) in human and mouse eyes. Together, the results identify the specific phosphatase for EZH2-S21 and reveal EZH2 dephosphorylation control of several families of genes implicated in lens EMT and ASC pathogenesis. These results provide important novel information in EZH2 function and regulation.

Cataract inhibitors: Present needs and future challenges

Cataracts result from opacification of the ocular lens and represent the leading cause of blindness worldwide. After surgical removal of the diseased lens material and implantation of an artificial intraocular lens, up to 50% of cataract patients develop a secondary lens defect called posterior capsular opacification (PCO). While vision can be restored in PCO patients by a laser-mediated capsulotomy, novel therapies involving inhibition of aldose reductase are now being developed to prevent PCO development and complications of laser capsulotomy. A question we wished to address was whether cataract surgeons believe there is an unmet need for a preventative PCO therapy, whether they would prescribe such a therapy were it available, and to assess their perceptions regarding the benefits of and obstacles to adopting novel PCO therapies in the place of laser capsulotomy. We gathered perspectives from adult, pediatric, and veterinary cataract surgeons using an online questionnaire. From 161 surgeon responses, we found that the majority of adult, pediatric, and veterinary cataract surgeons (78% n = 35, 88% n = 37, and 96% n = 71 respectively) believed there is an unmet need for preventative PCO therapy, with more than 95% expressing interest in incorporating such therapy into surgical protocols. Perceived benefits included optimizing visual outcomes, avoiding the need for additional procedures, eliminating complications related to neodymium:yttrium-aluminum-garnet laser, preserving the posterior capsule particularly in patients receiving multifocal intraocular lens implants, providing a viable solution for PCO in animals, and using it in developing countries that lack access to neodymium:yttrium-aluminum-garnet lasers. Perceived obstacles included potential lack of reimbursement by insurance companies, and the need for strong efficacy and safety profiles. Among adult surgeons, 70% (n = 31) indicated that preventative PCO therapy could add value to premium intraocular lens packages. Our studies revealed that cataract surgeons overwhelmingly support the development of preventative PCO therapy, and that clinical trials will play a critical role to test the safety and efficacy of specific therapeutic agents.

Metformin attenuates the epithelial-mesenchymal transition of lens epithelial cells through the AMPK/TGF-β/Smad2/3 signalling pathway

Posterior capsule opacification (PCO) is a common ocular fibrosis disease related to the epithelial-mesenchymal transition (EMT) of human lens epithelial cells (HLECs). However, safe and effective drugs that prevent or treat PCO are lacking. Metformin (Mtf) has been used to treat fibrosis-related diseases affecting many organs and tissues, but its effect on ocular fibrosis-related diseases is unclear. We investigated whether Mtf can inhibit EMT and fibrosis in HLECs to prevent and treat PCO and elucidated the potential molecular mechanism. Here, we established an HLEC model of TGF-β-induced EMT and found that 400 μM Mtf inhibited vertical and lateral migration and EMT-related gene and protein expression in HLECs. Smad2/3 are downstream molecules of TGF-β that enter the nucleus to regulate EMT-related gene expression during the occurrence and development of PCO. We revealed that Mtf suppressed TGF-β-induced Smad2/3 phosphorylation and nuclear translocation. Mtf induces AMP-activated protein kinase (AMPK) phosphorylation. In this study, we found that Mtf induced the activation of AMPK phosphorylation in HLECs. To further explore the mechanism of Mtf, we pretreated HLECs with Compound C (an AMPK inhibitor) to repeat the above experiments and found that Compound C abolished the inhibitory effect of Mtf on HLEC EMT and the TGF-β/Smad2/3 signalling pathway. Thus, Mtf targets AMPK phosphorylation to inhibit the TGF-β/Smad2/3 signalling pathway and prevent HLEC EMT. Notably, we first illustrated the AMPK/TGF-β/Smad2/3 signalling pathway in HLECs, which may provide a new therapeutic strategy for PCO.

Mitochondrial calcium uniporter promotes cell proliferation and migration in esophageal cancer

Increasing evidence has suggested that mitochondrial calcium uniporter (MCU) is involved in various types of cancer. However, its functions remain unclear in esophageal cancer. The aim of the present study was to explore its abnormal expression and clinical implications in esophageal cancer. A total of 110 patients with esophageal cancer were enrolled in the study. Western blotting was performed to examine the protein expression levels of MCU in 8 pairs of esophageal cancer and adjacent normal tissues. Using immunochemistry, a total of 110 esophageal cancer specimens were analyzed to identify the association between MCU expression and clinicopathological features of patients with esophageal cancer. Furthermore, immunofluorescence of MCU was performed. Pearson's correlation analysis was performed between MCU and hypoxia inducible factor (HIF)-1α/VEGF/E-cadherin/Vimentin expression based on western blotting. After KYSE-150 and TE-1 cells were treated with the MCU agonist Spermine and a small interfering RNA against MCU (si-MCU), a series of functional assays were performed, including Cell Counting Kit-8, colony formation and Transwell assays. The results revealed that, compared with in adjacent normal tissues, MCU was highly expressed in esophageal cancer tissues. MCU expression was significantly associated with depth of invasion, lymph node metastasis, TNM stage and distant metastasis. Moreover, MCU was significantly correlated with HIF-1α/VEGF/E-cadherin/Vimentin in esophageal cancer tissues. MCU overexpression promoted VEGF, MMP2, Vimentin and N-cadherin expression, while it inhibited E-cadherin expression in KYSE-150 and TE-1 cells, and opposite results were observed after transfection with si-MCU. Furthermore, MCU overexpression accelerated the proliferation and migration of KYSE-150 and TE-1 cells. Thus, the current findings suggested that high MCU expression may participate in cell proliferation, migration and epithelial-mesenchymal transition in esophageal cancer.

Posterior Capsule Opacification: A Review of Experimental Studies

Posterior capsule opacification (PCO) is the most common complication of cataract surgery. It causes a gradual deterioration of visual acuity, which would otherwise improve after a successful procedure. Despite recent advances in ophthalmology, this complication has not been eradicated, and the incidence of PCO can be as high as 10%. This article reviews the literature concerning the pathomechanism of PCO and examines the biochemical pathways involved in its formation and methods to prevent this complication. We also review the reported tests performed in cell cultures under laboratory conditions and in experimental animal models and in ex vivo human lens capsules. Finally, we describe research involving human eyes in the clinical setting and pharmacological methods that may reduce the frequency of PCO. Due to the multifactorial etiology of PCO, in vitro studies make it possible to assess the factors contributing to its complications and search for new therapeutic targets. Not all pathways involved in cell proliferation, migration, and contraction of the lens capsule are reproducible in laboratory conditions; moreover, PCO in humans and laboratory animals may be additionally stimulated by various degrees of postoperative reactions depending on the course of surgery. Therefore, further studies are necessary.

The HIF-1α/p53/miRNA-34a/Klotho axis in retinal pigment epithelial cells promotes subretinal fibrosis and exacerbates choroidal neovascularization

Wet age‐related macular degeneration (wAMD), characterized by choroidal neovascularization (CNV), is a leading cause of irreversible vision loss among elderly people in developed nations. Subretinal fibrosis, mediated by epithelial‐mesenchymal transition (EMT) of retinal pigment epithelium (RPE) cells, leads to unsuccessful anti‐vascular endothelial growth factor (VEGF) agent treatments in CNV patients. Under hypoxic conditions, hypoxia‐inducible factor‐1α (HIF‐1α) increases the stability and activation of p53, which activates microRNA‐34a (miRNA‐34a) transcription to promote fibrosis. Additionally, Klotho is a target gene of miRNA‐34a that inhibits fibrosis. This study aimed to explore the role of the HIF‐1α/p53/miRNA‐34a/Klotho axis in subretinal fibrosis and CNV. Hypoxia‐induced HIF‐1α promoted p53 stability, phosphorylation and nuclear translocation in ARPE‐19 cells (a human RPE cell line). HIF‐1α‐dependent p53 activation up‐regulated miRNA‐34a expression in ARPE‐19 cells following hypoxia. Moreover, hypoxia‐induced p53‐dependent miRNA‐34a inhibited the expression of Klotho in ARPE‐19 cells. Additionally, the HIF‐1α/p53/miRNA‐34a/Klotho axis facilitated hypoxia‐induced EMT in ARPE‐19 cells. In vivo, blockade of the HIF‐1α/p53/miRNA‐34a/Klotho axis alleviated the formation of mouse laser‐induced CNV and subretinal fibrosis. In short, the HIF‐1α/p53/miRNA‐34a/Klotho axis in RPE cells promoted subretinal fibrosis, thus aggravating the formation of CNV.

The Expression and Role of Hypoxia-induced Factor-1α in Human Tenon's Capsule Fibroblasts under Hypoxia

PURPOSE

To determine the expression of hypoxia-induced factor-1α (HIF-1α) and its downstream factors in human Tenon's capsule fibroblasts (HTFs) and changes in HTFs biological functions, we explored the role of HIF-1α in HTFs under hypoxia to provide a basis for studying the regulation of HIF-1α in wound healing after glaucoma surgery.

MATERIALS AND METHODS

we established HTFs hypoxia model in vitro, meanwhile the HIF-1α agonist VH298 or inhibitor KC7F2 was added to HTFs, and the normoxia group was used as a control. Western blot, immunofluorescence and ELISA were used to detect the expression of HIF-1α, vascular endothelial growth factor (VEGF), transforming growth factor-β (TGF-β), Smads and collagen I. The proliferation of HTFs was quantified by cell counting kit-8, and cell migration was tested by healing scratch test.

RESULTS

HIF-1α protein expression increased under hypoxia, peaked from 4-24 h, and then decreased. The secretion of VEGF and TGF-β increased with prolonged hypoxia time. VH298 and KC7F2 upregulated and downregulated the levels of VEGF and TGF-β, respectively, suggesting that HIF-1α upregulates and downregulates the levels of VEGF and TGF-β in HTFs under hypoxia, respectively. HIF-1α upregulated the proliferation, migration and collagen synthesis of HTFs under hypoxia.

CONCLUSIONS

Regulating HIF-1α and its downstream factors effectively regulated HTFs proliferation, migration and collagen synthesis. HIF-1α is a promising regulator in the study of wound healing after glaucoma surgery.

Gestational Exposure to Cigarette Smoke Suppresses the Gasotransmitter H2S Biogenesis and the Effects Are Transmitted Transgenerationally

Rationale: Gestational cigarette smoke (CS) impairs lung angiogenesis and alveolarization, promoting transgenerational development of asthma and bronchopulmonary dysplasia (BPD). Hydrogen sulfide (H2S), a proangiogenic, pro-alveolarization, and anti-asthmatic gasotransmitter is synthesized by cystathionine-γ-lyase (CSE), cystathionine-β-synthase (CBS), and 3-mercaptopyruvate sulfur transferase (3MST). Objective: Determine if gestational CS exposure affected the expression of H2S synthesizing enzymes in the mouse lung and human placenta. Methods: Mice were exposed throughout gestational period to secondhand CS (SS) at approximating the dose of CS received by a pregnant woman sitting in a smoking bar for 3 h/days during pregnancy. Lungs from 7-days old control and SS-exposed pups and human placenta from mothers who were either non-smokers or smokers during pregnancy were analyzed for expression of the enzymes. Measurements: Mouse lungs and human placentas were examined for the expression of CSE, CBS, and 3MST by immunohistochemical staining, qRT-PCR and/or Western blot (WB) analyses. Results: Compared to controls, mouse lung exposed gestationally to SS had significantly lower levels of CSE, CBS, and 3MST. Moreover, the SS-induced suppression of CSE and CBS in F1 lungs was transmitted to the F2 generation without significant change in the magnitude of the suppression. These changes were associated with impaired epithelial-mesenchymal transition (EMT)-a process required for normal lung angiogenesis and alveolarization. Additionally, the placentas from mothers who smoked during pregnancy, expressed significantly lower levels of CSE, CBS, and 3MST, and the effects were partially moderated by quitting smoking during the first trimester. Conclusions: Lung H2S synthesizing enzymes are downregulated by gestational CS and the effects are transmitted to F2 progeny. Smoking during pregnancy decreases H2S synthesizing enzymes is human placentas, which may correlate with the increased risk of asthma/BPD in children.

The effects of c-Src kinase on EMT signaling pathway in human lens epithelial cells associated with lens diseases

Background

The signaling pathway of epithelial to mesenchymal transition (EMT) is regulated by c-Src kinase in many cells. The purpose of this study was to investigate the effects of c-Src kinase on EMT of human lens epithelial cells in vivo stimulated by different factors.

Methods

Human lens epithelial cells, HLE-B3, were exposed to either an inflammatory factor, specifically IL-1α, IL-6, TNF-α or IL-1β, at 10 ng/mL or high glucose (35.5 mM) for 30 mins. Activity of c-Src kinase was evaluated by the expression of p-Src⁴¹⁸ with western blot assay. To investigate the effects of activation of c-Src on EMT, HLE-B3 cells were transfected with pCDNA3.1-Src^Y530F to upregulate activity of c-Src kinase, and pSlience4.1-ShSrc to knock it down. The expressions of c-Src kinase and molecular markers of EMT such as E-cadherin, ZO-1, α-SMA, and Vimentin were examined at 48 h by RT-PCR and western blot. At 48 h and 72 h of transfection, cell proliferation was detected by MTT, and cell mobility and migration were determined by scratch and transwell assays.

Results

Activity of c-Src kinase, which causes the expression of p-Src⁴¹⁸, was upregulated by different inflammatory factors and high glucose in HLE-B3 cells. When HLE-B3 cells were transfected with pCDNA3.1-Src^Y530F, the expression of c-Src kinase was upregulated on both mRNA and protein levels, and activity of c-Src kinase, expression of p-Src⁴¹⁸ increased. The expressions of both E-cadherin and ZO-1 were suppressed, while the expressions of vimentin and α-SMA were elevated on both mRNA and protein levels at the same time. Cell proliferation, mobility and migration increased along with activation of c-Src kinase. Conversely, when HLE-B3 cells were transfected with pSlience4.1-ShSrc, both c-Src kinase and p-Src⁴¹⁸ expressions were knocked down. The expressions of E-cadherin and ZO-1 increased, but the expressions of Vimentin and α-SMA decreased; meanwhile, cell proliferation, mobility and migration reduced.

Conclusions

The c-Src kinase in lens epithelial cells is easily activated by external stimuli, resulting in the induction of cell proliferation, mobility, migration and EMT.

Effects of Post-translational Modifications on Membrane Localization and Signaling of Prostanoid GPCR-G Protein Complexes and the Role of Hypoxia

G protein-coupled receptors (GPCRs) play a pivotal role in the adaptive responses to cellular stresses such as hypoxia. In addition to influencing cellular gene expression profiles, hypoxic microenvironments can perturb membrane protein localization, altering GPCR effector scaffolding and altering downstream signaling. Studies using proteomics approaches have revealed significant regulation of GPCR and G proteins by their state of post-translational modification. The aim of this review is to examine the effects of post-translational modifications on membrane localization and signaling of GPCR-G protein complexes, with an emphasis on vascular prostanoid receptors, and to highlight what is known about the effect of cellular hypoxia on these mechanisms. Understanding post-translational modifications of protein targets will help to define GPCR targets in treatment of disease, and to inform research into mechanisms of hypoxic cellular responses.