The PI3K/Akt signaling pathway mediates the high glucose-induced expression of extracellular matrix molecules in human retinal pigment epithelial cells

Crosstalk between MiRNAs/lncRNAs and PI3K/AKT signaling pathway in diabetes mellitus: Mechanistic and therapeutic perspectives

Diabetes as a fastest growing diseases worldwide is characterized by elevated blood glucose levels. There's an enormous financial burden associated with this endocrine disorder, with unequal access to health care between developed and developing countries. PI3Ks (phosphoinositide 3-kinases) have been demonstrated to be crucial for glucose homeostasis, and malfunctioning of these molecules can contribute to an increase in glucose serum levels, the main pathophysiological feature of diabetes. Additionally, recent evidence suggests that miRNAs and lncRNAs are reciprocally interacting with this signaling pathway. It is therefore evident that abnormal regulation of miRNAs/lncRNAs in the lncRNAs/miRNAs/PI3K/AKT axis is related to clinicopathological characteristics and plays a crucial role in the regulation of biological processes. It has therefore been attempted in this review to describe the interaction between PI3K/AKT signaling pathway and various miRNAs/lncRNAs and their importance in DM biology. We also presented the clinical applications of PI3K/AKT-related ncRNAs/herbal medicine in patients with DM.

Hepatocyte growth factor promotes retinal pigment epithelium cell activity through MET/AKT signaling pathway

AIM

To explore the effects of hepatocyte growth factor (HGF) on retinal pigment epithelium (RPE) cell behaviors.

METHODS

The human adult retinal pigment epithelial cell line-19 (ARPE-19) were treated by HGF or mesenchymal-epithelial transition factor (MET) inhibitor SU11274 in vitro. Cell viability was detected by a Cell Counting Kit-8 assay. Cell proliferation and motility was detected by a bromodeoxyuridine incorporation assay and a wound healing assay, respectively. The expression levels of MET, phosphorylated MET, protein kinase B (AKT), and phosphorylated AKT proteins were determined by Western blot assay. The MET and phosphorylated MET proteins were also determined by immunofluorescence assay.

RESULTS

HGF increased ARPE-19 cells' viability, proliferation and migration, and induced an increase of phosphorylated MET and phosphorylated AKT proteins. SU11274 significantly reduced cell viability, proliferation, and migration and decreased the expression of MET and AKT proteins. SU11274 suppressed HGF-induced increase of viability, proliferation, and migration in ARPE-19 cells. Additionally, SU11274 also blocked HGF-induced phosphorylation of MET and AKT proteins.

CONCLUSION

HGF enhances cellular viability, proliferation, and migration in RPE cells through the MET/AKT signaling pathway, whereas this enhancement is suppressed by the MET inhibitor SU11274. HGF-induced MET/AKT signaling might be a vital contributor of RPE cells survival.

The significance of glutaredoxins for diabetes mellitus and its complications

Diabetes mellitus is a non-communicable metabolic disease hallmarked by chronic hyperglycemia caused by beta-cell failure. Diabetic complications affect the vasculature and result in macro- and microangiopathies, which account for a significantly increased morbidity and mortality. The rising incidence and prevalence of diabetes is a major global health burden. There are no feasible strategies for beta-cell preservation available in daily clinical practice. Therefore, patients rely on antidiabetic drugs or the application of exogenous insulin. Glutaredoxins (Grxs) are ubiquitously expressed and highly conserved members of the thioredoxin family of proteins. They have specific functions in redox-mediated signal transduction, iron homeostasis and biosynthesis of iron-sulfur (FeS) proteins, and the regulation of cell proliferation, survival, and function. The involvement of Grxs in chronic diseases has been a topic of research for several decades, suggesting them as therapeutic targets. Little is known about their role in diabetes and its complications. Therefore, this review summarizes the available literature on the significance of Grxs in diabetes and its complications. In conclusion, Grxs are differentially expressed in the endocrine pancreas and in tissues affected by diabetic complications, such as the heart, the kidneys, the eye, and the vasculature. They are involved in several pathways essential for insulin signaling, metabolic inflammation, glucose and fatty acid uptake and processing, cell survival, and iron and mitochondrial metabolism. Most studies describe significant changes in glutaredoxin expression and/or activity in response to the diabetic metabolism. In general, mitigated levels of Grxs are associated with oxidative distress, cell damage, and even cell death. The induced overexpression is considered a potential part of the cellular stress-response, counteracting oxidative distress and exerting beneficial impact on cell function such as insulin secretion, cytokine expression, and enzyme activity.

Mechanistic insights into the alterations and regulation of the AKT signaling pathway in diabetic retinopathy

In the early stages of diabetic retinopathy (DR), diabetes-related hyperglycemia directly inhibits the AKT signaling pathway by increasing oxidative stress or inhibiting growth factor expression, which leads to retinal cell apoptosis, nerve proliferation and fundus microvascular disease. However, due to compensatory vascular hyperplasia in the late stage of DR, the vascular endothelial growth factor (VEGF)/phosphatidylinositol 3 kinase (PI3K)/AKT cascade is activated, resulting in opposite levels of AKT regulation compared with the early stage. Studies have shown that many factors, including insulin, insulin-like growth factor-1 (IGF-1), VEGF and others, can regulate the AKT pathway. Disruption of the insulin pathway decreases AKT activation. IGF-1 downregulation decreases the activation of AKT in DR, which abrogates the neuroprotective effect, upregulates VEGF expression and thus induces neovascularization. Although inhibiting VEGF is the main treatment for neovascularization in DR, excessive inhibition may lead to apoptosis in inner retinal neurons. AKT pathway substrates, including mammalian target of rapamycin (mTOR), forkhead box O (FOXO), glycogen synthase kinase-3 (GSK-3)/nuclear factor erythroid 2-related factor 2 (Nrf2), and nuclear factor kappa-B (NF-κB), are a research focus. mTOR inhibitors can delay or prevent retinal microangiopathy, whereas low mTOR activity can decrease retinal protein synthesis. Inactivated AKT fails to inhibit FOXO and thus causes apoptosis. The GSK-3/Nrf2 cascade regulates oxidation and inflammation in DR. NF-κB is activated in diabetic retinas and is involved in inflammation and apoptosis. Many pathways or vital activities, such as the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) and mitogen-activated protein kinase (MAPK) signaling pathways, interact with the AKT pathway to influence DR development. Numerous regulatory methods can simultaneously impact the AKT pathway and other pathways, and it is essential to consider both the connections and interactions between these pathways. In this review, we summarize changes in the AKT signaling pathway in DR and targeted drugs based on these potential sites.

Aberrant Akt2 signaling in the RPE may contribute to retinal fibrosis process in diabetic retinopathy

Diabetic Retinopathy (DR) is a complication of diabetes that causes blindness in adults. Retinal fibrosis is closely associated with developing proliferative diabetic retinopathy (PDR). Clinical studies have shown that fibrotic membranes exhibit uncontrolled growth in PDR and contribute to retinal detachment from RPE cells, ultimately leading to vision loss. While anti-VEGF agents and invasive laser treatments are the primary treatments for PDR, retinal fibrosis has received minimal attention as a potential target for therapeutic intervention. Therefore, to investigate the potential role of Akt2 in the diabetes-induced retinal fibrosis process, we generated RPE-specific Akt2 conditional knockout (cKO) mice and induced diabetes in these mice and Akt2^fl/fl control mice by intraperitoneal injection of streptozotocin. After an 8-month duration of diabetes (10 months of age), the mice were euthanized and expression of tight junction proteins, epithelial-mesenchymal transition (EMT), and fibrosis markers were examined in the RPE. Diabetes induction in the floxed control mice decreased levels of the RPE tight junction protein ZO-1 and adherens junction proteins occludin and E-cadherin; these decreases were rescued in Akt2 cKO diabetic mice. Loss of Akt2 also inhibited diabetes-induced elevation of RNA and protein levels of the EMT markers Snail/Slug and Twist1 in the RPE as compared to Akt2^fl/fl diabetic mice. We also found that in Akt2 cKO mice diabetes-induced increase of fibrosis markers, including collagen IV, Connective tissue growth factor (CTGF), fibronectin, and alpha-SMA was attenuated. Furthermore, we observed that high glucose-induced alterations in EMT and fibrosis markers in wild-type (WT) RPE explants were rescued in the presence of PI3K and ERK inhibitors, indicating diabetes-induced retinal fibrosis may be mediated via the PI3K/Akt2/ERK signaling, which could provide a novel target for DR therapy.

Rhein Inhibits Proliferation, Extracellular Matrix Deposition, and Inflammation in Mesangial Cells via ROS/Akt Signaling Pathway

It has been reported that rhein, a Chinese herbal compound, has a potent anti-inflammatory effect on various diseases. However, it remains elusive whether rhein has a protective effect on chronic kidney disease (CKD) and what its underlying mechanism may be. In the present study, we evaluated whether rhein could prevent lipopolysaccharide (LPS)-induced proliferation, expression of extracellular matrix (ECM) proteins, and inflammation in rat mesangial cells (MCs), and whether these effects were mediated by reactive oxygen species (ROS) and Akt signaling. We also investigated the protective effect of rhein on renal function in a rat CKD model. Results showed that rhein significantly suppressed LPS-initiated proliferation in MCs in a cell counting kit-8 (CCK8) assay. Meanwhile, rhein significantly inhibited LPS-induced expression of ECM proteins and inflammation, as indicated by the decreased expression of fibronectin, α smooth muscle actin (α-SMA), tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), interleukin 6 (IL-6), and interferon γ (IFN-γ). Of note, rhein significantly enhanced LPS-induced production of reactive oxygen species (ROS) and inhibited LPS-induced Akt phosphorylation. Furthermore, the inhibitory effect of rhein on Akt phosphorylation was inhibited by H2O2 scavenger catalase. Importantly, the protective effect of rhein was almost totally lost in the presence of phosphatidylinositol 3-kinase (PI3K) protagonist insulin-like growth factor 1 (IGF-1). Finally, rhein significantly decreased 24 h urinary protein, serum creatinine (SCr), and blood urea nitrogen (BUN) in CKD rats. Collectively, these results suggested that rhein improved CKD through inhibition of proliferation, ECM synthesis, and inflammation via ROS/Akt signaling in MCs.

Crocin as a vision supplement

Crocin is a natural ingredient of saffron (Crocus sativus L.) flower that has shown potential for application as a supplement in eye health and preserving vision. Crocin has been examined for its potential to treat various eye diseases such as glaucoma, macular dystrophies, diabetic retinopathy, and age-related macular degeneration. This review briefly discusses the role of crocin in different eye diseases. The underlying pathophysiological pathways involved in the effect of crocin on ophthalmic diseases are also reviewed. Preclinical evidence shows the cytoprotective, antioxidative, anti-inflammatory, and blood-flow enhancing effects of crocin in retinal tissue. Crocin also affects the retinal pathologies by activating PI3K/Akt and inhibiting NF-κB signalling pathways. Clinical evidence suggests that crocin improves outcomes in patients with retinal degenerations, retinal dystrophies, and glaucoma. Overall, crocin can be suggested as a potential vision supplement in healthy populations and patients with eye diseases. However, more clinical studies with larger sample sizes and longer follow-up durations are needed to confirm the current evidence.

Distinct Mechanisms of Human Retinal Endothelial Barrier Modulation In Vitro by Mediators of Diabetes and Uveitis

Ocular diseases such as diabetic retinopathy (DR) and uveitis are associated with injury to the blood–retinal barrier (BRB). Whereas high glucose (HG) and advanced glycation end products (AGE) contribute to DR, bacterial infections causing uveitis are triggered by endotoxins such as lipopolysaccharide (LPS). It is unclear how HG, AGE, and LPS affect human retinal endothelial cell (HREC) junctions. Moreover, tumor necrosis factor-α (TNFα) is elevated in both DR and ocular infections. In the current study, we determined the direct effects of HG, AGE, TNFα, and LPS on the expression and intracellular distribution of claudin-5, VE-cadherin, and β-catenin in HRECs and how these mediators affect Akt and P38 MAP kinase that have been implicated in ocular pathologies. In our results, whereas HG, AGE, and TNFα activated both Akt and P38 MAPK, LPS treatment suppressed Akt but increased P38 MAPK phosphorylation. Furthermore, while treatment with AGE and HG increased cell-junction protein expression in HRECs, LPS elicited a paradoxical effect. By contrast, when HG treatment increased HREC-barrier resistance, AGE and LPS stimulation compromised it, and TNFα had no effect. Together, our results demonstrated the differential effects of the mediators of diabetes and infection on HREC-barrier modulation leading to BRB injury.

Starvation to Glucose Reprograms Development of Neurovascular Unit in Embryonic Retinal Cells

Perinatal exposure to starvation is a risk factor for development of severe retinopathy in adult patients with diabetes. However, the underlying mechanisms are not completely understood. In the present study, we shed light on molecular consequences of exposure to short-time glucose starvation on the transcriptome profile of mouse embryonic retinal cells. We found a profound downregulation of genes regulating development of retinal neurons, which was accompanied by reduced expression of genes encoding for glycolytic enzymes and glutamatergic signaling. At the same time, glial and vascular markers were upregulated, mimicking the diabetes-associated increase of angiogenesis—a hallmark of pathogenic features in diabetic retinopathy. Energy deprivation as a consequence of starvation to glucose seems to be compensated by upregulation of genes involved in fatty acid elongation. Results from the present study demonstrate that short-term glucose deprivation during early fetal life differentially alters expression of metabolism- and function-related genes and could have detrimental and lasting effects on gene expression in the retinal neurons, glial cells, and vascular elements and thus potentially disrupting gene regulatory networks essential for the formation of the retinal neurovascular unit. Abnormal developmental programming during retinogenesis may serve as a trigger of reactive gliosis, accelerated neurodegeneration, and increased vascularization, which may promote development of severe retinopathy in patients with diabetes later in life.

Transcriptome-based insights into gene networks controlling myopia prevention

Myopia (short-sightedness), usually caused by excessive elongation of the eye during development, has reached epidemic proportions worldwide. In animal systems including the chicken model, several treatments have been shown to inhibit ocular elongation and experimental myopia. Although diverse in their apparent mechanism of action, each one leads to a reduction in the rate of ocular growth. We hypothesize that a defined set of retinal molecular changes may underlie growth inhibition, irrespective of the treatment agent used. Accordingly, across five well-established but diverse methods of inhibiting myopia, significant overlap is seen in the retinal transcriptome profile (transcript levels and alternative splicing events) in chicks when analyzed by RNA-seq. Within the two major pathway networks enriched during growth inhibition, that of cell signaling and circadian entrainment, transcription factors form the largest functional grouping. Importantly, a large percentage of those genes forming the defined retinal response are downstream targets of the transcription factor EGR1 which itself shows a universal response to all five growth-inhibitory treatments. This supports EGR1's previously implicated role in ocular growth regulation. Finally, by contrasting our data with human linkage and GWAS studies on refractive error, we confirm the applicability of our study to the human condition. Together, these findings suggest that a universal set of transcriptome changes, which sit within a well-defined retinal network that cannot be bypassed, is fundamental to growth regulation, thus paving a way for designing novel targets for myopia therapies.

Melatonin Attenuates High Glucose-Induced Changes in Beta Amyloid Precursor Protein Processing in Human Neuroblastoma Cells

Diabetes mellitus (DM), one of metabolic diseases, has been suggested as a risk factor for Alzheimer's disease (AD). However, how the metabolic pathway activates amyloid precursor protein (APP) processing enzymes then contributes to the increase of amyloid-beta (Aβ) production, is not clearly understood. In the present study, we aimed to examine the protective effect of melatonin against hyperglycemia-induced alterations in the amyloidogenic pathway. High concentration of glucose was used to induce hyperglycemia in human neuroblastoma SH-SY5Y cells. We found that 30 mM glucose affected the expression of insulin receptors and glucose transporters, which indicated the disruption of glucose sensing. High glucose induced the activation of the phosphorylated protein kinase B (pAkt)/GSK-3β signaling pathway and a significant increase in the expression of β-site beta APP cleaving enzyme (BACE1), presenilin1 (PS1) and Aβ42. Pretreatment with melatonin significantly reversed these parameters. We also showed that these effects are similar to those effects in the presence of the GSK-3β blocker, N-(4-methoxybenyl)-N'-(5-nitro-1,3-thiazol-2-yl) urea (ARA) in glucose-treated hyperglycemic cells. These suggested that melatonin exerted an inhibitory effect on the activation of APP-cleaving enzymes via the GSK-3β signaling pathway. Pretreatment with luzindole, a melatonin receptor MT1 antagonist, significantly prevented the effect of melatonin on the glucose-induced increase level of APP processing enzymes. This suggested that melatonin attenuated the toxic effect on hyperglycemia involving the amyloidogenic pathway partially mediated via melatonin receptor. Taken together the present results suggested that melatonin has a beneficial role in preventing Aβ generation in a cellular model of hyperglycemia-induced DM.

Momordica charantia silver nanoparticles modulate S/JAK/STAT and P13K/Akt/PTEN signalling pathways in the kidney of streptozotocin-induced diabetic rats

Objectives

Diabetes nephropathy (DN) is one of the complications of diabetes mellitus (DM) marked by gradual progressive loss of renal function. SOCS/JAK/STAT and PI3K/Akt/PTEN signalling pathways are among the chain of interactions implicated in the onset, progression and pathology of DN. Momordica charantia (bitter melon) is often used in folk medicine as therapy for DM due to its hypoglycemic properties. This study was designed to evaluate M. charantia silver nanoparticles' therapeutic effect on DN-induced by streptozotocin (STZ) in Wistar rats.

Methods

The M. charantia nanoparticles used was synthesized using the filtrate from the plant methanolic extract added to 1 mM concentration of aqueous silver nitrate. DM was induced in Wistar rats by intraperitoneal injection of STZ (65 mg/kg). The animals' treatment groups were divided into; Diabetic control (65 mg/kg STZ), Control, and groups treated with silver nitrate (10 mg/kg), M. charantia nanoparticles (50 mg/kg), metformin (100 mg/kg), and plant extract (100 mg/kg). Treatment was terminated after 11 days. RT-PCR determined renal mRNA expression of Akt, PI3k, PTEN, TGF-β, JAK2, STAT3, STAT5, SOCS3, SOCS4 and glucokinase (GCK). Consequently, characterized compounds from M. charantia identified from literatures were docked with PI3K, JAK2 and TGF-β and STAT3 to retrieve potential hits.

Results

Oral administration of M. charantia nanoparticles (50 mg/kg) to STZ-induced diabetic untreated rats significantly ((p < 0.05) down-regulated the mRNA expression of Akt, PI3k, TGF-β, JAK2, STAT3 and upregulated the mRNA expression of PTEN, SOCS3 and SOCS4, thus establishing the role of M. charantia nanoparticles in alleviating DN in diabetic rats. Additionally, there was a significant up-regulation of glucose metabolizing gene (glucokinase) upon administering M. charantia nanoparticles. Molecular docking results showed 12 compounds from bitter melon with docking score ranging from -6.114 kcal/mol to -8.221 kcal/mol that are likely to exert anti-diabetic properties.

Conclusion

Observation drawn from this study suggests that M. charantia nanoparticles ameliorate DN through regulation of SOCS/JAK/STAT and PI3K/Akt/PTEN signalling pathways.

β-elemene down-regulates HIF-lα, VEGF and iNOS in human retinal pigment epithelial cells under high glucose conditions

AIM

To investigate the effects and mechanism of β-elemene on the expressions of hypoxia-inducible factor-1α (HIF-lα), vascular endothelial growth factor (VEGF) and inducible nitric oxide synthase (iNOS) in human retinal pigment epithelial (RPE) cells under high glucose conditions.

METHODS

ARPE-19 cell line was cultured under eight conditions: 1) low glucose (LG; 5.5 mmol/L); 2) high glucose (HG; 33 mmol/L); 3) high glucose with 20 µg/mL β-elemene (HG+20E); 4) high glucose with 40 µg/mL β-elemene (HG+40E); 5) high glucose with SB203590 [HG+SB203590, p38-mitogen-activated protein kinase (p38-MAPK) pathway inhibitor]; 6) high glucose with LY294002 [HG+LY294002, phosphoinositide 3-kinase/protein kinase B (PI3K/Akt) pathway inhibitor]; 7) high glucose with 40 µg/mL β-elemene and SB203590 (HG+40E+SB203590); and 8) high glucose with 40 µg/mL β-elemene and LY294002 (HG+40E+LY294002). Cells were treated in conditions 1-4 for 24 and 48h, while for 48h in conditions 5-8. Then mRNA and protein levels of HIF-1α, VEGF and iNOS in cells were measured by real-time polymerase chain reaction (qPCR), immunofluorescence and Western blotting, respectively. Furthermore, protein levels of total p38-MAPK, phosphorylated p38-MAPK (p38-MAPK-P), total Akt and phosphorylated Akt (Akt-P) in cells of conditions 2 and 4 which treated for 48h were measured by Western blotting.

RESULTS

The mRNA levels and protein levels of HIF-1α, VEGF and iNOS in cells were significantly reduced in conditions 3-8 when compared with those in condition 2 (P<0.05). These reductions were more obvious in conditions treated for 48h than in conditions treated for 24h. The protein levels of p38-MAPK-P and Akt-P in cells of condition 4 were significantly lower than in condition 2 (P<0.01).

CONCLUSION

β-elemene down-regulates HIF-1α, VEGF and iNOS in ARPE-19 cells under a high glucose condition. The inhibitory effect of β-elemene is more significant when its concentration and treatment time are increased, as well as it is combined with SB203590 or LY294002 treatment. P38-MAPK and PI3K/Akt signaling pathways may play a role in this inhibitory effect.

Phosphoinositides in Retinal Function and Disease

Phosphatidylinositol and its phosphorylated derivatives, the phosphoinositides, play many important roles in all eukaryotic cells. These include modulation of physical properties of membranes, activation or inhibition of membrane-associated proteins, recruitment of peripheral membrane proteins that act as effectors, and control of membrane trafficking. They also serve as precursors for important second messengers, inositol (1,4,5) trisphosphate and diacylglycerol. Animal models and human diseases involving defects in phosphoinositide regulatory pathways have revealed their importance for function in the mammalian retina and retinal pigmented epithelium. New technologies for localizing, measuring and genetically manipulating them are revealing new information about their importance for the function and health of the vertebrate retina.

Identification of novel differentially expressed genes in retinas of STZ-induced long-term diabetic rats through RNA sequencing

BACKGROUND

The aim of this research was to investigate the retinal transcriptome changes in long-term streptozotocin (STZ)-induced rats' retinas using RNA sequencing (RNA-seq), to explore the molecular mechanisms of diabetic retinopathy (DR), and to identify novel targets for the treatment of DR by comparing the gene expression profile we obtained.

METHODS

In this study, 6 healthy male SD rats were randomly divided into wild-type (WT) group and streptozotocin (STZ)-induced group, 3 rats each group. After 6 months, 3 normal retina samples and 3 DM retina samples (2 retinas from the same rat were considered as 1 sample) were tested and differentially expressed genes (DEGs) were measured by RNA-seq technology. Then, we did Gene Ontology (GO) enrichment analysis and KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analysis and validated the results of RNA-seq through qRT-PCR.

RESULTS

A total of 118 DEGs were identified, of which 72 were up-regulated and 46 were down-regulated. The enriched GO terms showed that 3 most significant enrichment terms were binding (molecular function), cell part (cellular component), and biological regulation (biological process). The results of the KEGG pathway analysis revealed a significant enrichment in cell adhesion molecules, PI3K-Akt signaling pathway, and allograft rejection, etc. CONCLUSION: Our research has identified specific DEGs and also speculated their potential functions, which will provide novel targets to explore the molecular mechanisms of DR.

Tangeretin Inhibition of High-Glucose-Induced IL-1β, IL-6, TGF-β1, and VEGF Expression in Human RPE Cells

Tangeretin, a natural compound extracted from citrus plants, has been reported to have antiproliferative, antidiabetic, anti-invasive, and antioxidant properties. However, the role of tangeretin in diabetic retinopathy (DR) is unknown. In the present study, we investigated whether tangeretin had any effect on the expression of interleukin 1 beta (IL-1β), interleukin 6 (IL-6), transforming growth factor beta 1 (TGF-β1), and vascular endothelial growth factor (VEGF) in human retinal pigment epithelial (RPE) cells under high-glucose (HG) conditions. Our results illustrated that HG levels induced IL-1β, IL-6, TGF-β1, and VEGF expression and that tangeretin significantly reduced HG-induced IL-1β, IL-6, TGF-β1, and VEGF expression in human RPE cells. Moreover, tangeretin efficiently inhibited the activation of the protein kinase B (Akt) signalling pathway in HG-stimulated RPE cells. Therefore, tangeretin may serve a role in the treatment of DR.

Gremlin in the Vitreous of Patients with Proliferative Diabetic Retinopathy and the Downregulation of Gremlin in Retinal Pigment Epithelial Cells

Diabetic retinopathy (DR) is one of the most common causes of blindness globally. Proliferative DR (PDR), an advanced stage of DR, is characterized by the formation of fibrotic membranes at the vitreoretinal interface. The proliferation, migration, and secretion of extracellular matrix molecules in retinal pigment epithelial (RPE) cells contribute to the formation of fibrotic membranes in PDR. Gremlin has been reported to be upregulated in response to elevated glucose levels in the retina of diabetic rat and bovine pericytes. However, the role of gremlin in PDR remains unclear. In the present study, the vitreous concentrations of gremlin were significantly higher in the PDR (67.79 ± 33.96) group than in the control (45.31 ± 12.31) group, and high glucose levels induced the expression of gremlin in RPE cells. The elevated expression of extracellular matrix molecules, such as fibronectin and collagen IV, was significantly reduced by gremlin siRNA in human RPE cells under high-glucose conditions. Thus, gremlin may play a vital role in the development of PDR.

Compromised Barrier Function in Human Induced Pluripotent Stem-Cell-Derived Retinal Pigment Epithelial Cells from Type 2 Diabetic Patients

In diabetic patients, high blood glucose induces alterations in retinal function and can lead to visual impairment due to diabetic retinopathy. In immortalized retinal pigment epithelial (RPE) cultures, high glucose concentrations are shown to lead to impairment in epithelial barrier properties. For the first time, the induced pluripotent stem-cell-derived retinal pigment epithelium (hiPSC-RPE) cell lines derived from type 2 diabetics and healthy control patients were utilized to assess the effects of glucose concentration on the cellular functionality. We show that both type 2 diabetic and healthy control hiPSC-RPE lines differentiate and mature well, both in high and normal glucose concentrations, express RPE specific genes, secrete pigment epithelium derived factor, and form a polarized cell layer. Here, type 2 diabetic hiPSC-RPE cells had a decreased barrier function compared to controls. Added insulin increased the epithelial cell layer tightness in normal glucose concentrations, and the effect was more evident in type 2 diabetics than in healthy control hiPSC-RPE cells. In addition, the preliminary functionality assessments showed that type 2 diabetic hiPSC-RPE cells had attenuated autophagy detected via ubiquitin-binding protein p62/Sequestosome-1 (p62/SQSTM1) accumulation, and lowered pro- matrix metalloproteinase 2 (proMMP2) as well as increased pro-MMP9 secretion. These results suggest that the cellular ability to tolerate stress is possibly decreased in type 2 diabetic RPE cells.

All‑trans‑retinoic acid modulates TGF‑β‑induced apoptosis, proliferation, migration and extracellular matrix synthesis of conjunctival fibroblasts by inhibiting PI3K/AKT signaling

Conjunctival fiber generation is implicated in a wide spectrum of ocular diseases. Conjunctival wound healing is characterized by inflammation followed by re‑epithelialization, synthesis of new extracellular matrix (ECM), wound contraction and subconjunctival scar formation. The primary cause for the failure of glaucoma filtration surgery results from the excessive scarring of the filtering bleb. All‑trans‑retinoic acid (ATRA), a derivative of vitamin A, is a potent regulator of ECM synthesis, growth and differentiation. Following a previous study, which revealed that ATRA could inhibit transforming growth factor‑β‑induced human conjunctival fibroblast (HConF)‑mediated collagen gel contraction, the present study aimed to investigate the effects of ATRA on HConF migration, apoptosis, proliferation and ECM synthesis. To achieve this, the present study used Transwell migration, wound healing and Cell Counting Kit‑8 assays, flow cytometry and western blot analysis. In addition, the present study aimed to elucidate the mechanism of ATRA in mediating resistance to conjunctival scar formation. ATRA treatment resulted in an increased level of HConF apoptosis, reduced proliferation and migration, decreased collagen I and fibronectin expression, and decreased phosphorylation of PI3K and AKT. Thus, the present study showed a role for ATRA in inhibiting HConF migration, proliferation and ECM synthesis, and in promoting HConF apoptosis through the inhibition of the PI3K/AKT signaling pathway.

Macula Densa SGLT1-NOS1-Tubuloglomerular Feedback Pathway, a New Mechanism for Glomerular Hyperfiltration during Hyperglycemia

BACKGROUND

Glomerular hyperfiltration is common in early diabetes and is considered a risk factor for later diabetic nephropathy. We propose that sodium-glucose cotransporter 1 (SGLT1) senses increases in luminal glucose at the macula densa, enhancing generation of neuronal nitric oxide synthase 1 (NOS1)-dependent nitric oxide (NO) in the macula densa and blunting the tubuloglomerular feedback (TGF) response, thereby promoting the rise in GFR.

METHODS

We used microperfusion, micropuncture, and renal clearance of FITC-inulin to examine the effects of tubular glucose on NO generation at the macula densa, TGF, and GFR in wild-type and macula densa-specific NOS1 knockout mice.

RESULTS

Acute intravenous injection of glucose induced hyperglycemia and glucosuria with increased GFR in mice. We found that tubular glucose blunts the TGF response in vivo and in vitro and stimulates NO generation at the macula densa. We also showed that SGLT1 is expressed at the macula densa; in the presence of tubular glucose, SGLT1 inhibits TGF and NO generation, but this action is blocked when the SGLT1 inhibitor KGA-2727 is present. In addition, we demonstrated that glucose increases NOS1 expression and NOS1 phosphorylation at Ser1417 in mouse renal cortex and cultured human kidney tissue. In macula densa-specific NOS1 knockout mice, glucose had no effect on NO generation, TGF, and GFR.

CONCLUSIONS

We identified a novel mechanism of acute hyperglycemia-induced hyperfiltration wherein increases in luminal glucose at the macula densa upregulate the expression and activity of NOS1 via SGLT1, blunting the TGF response and promoting glomerular hyperfiltration.

Matrix metalloproteinase 9 inhibits the motility of highly aggressive HSC-3 oral squamous cell carcinoma cells

Pro-tumorigenic activities of matrix metalloproteinase (MMP) 9 have been linked to many cancers, but recently the tumour-suppressing role of MMP9 has also been elucidated. The multifaceted evidence on this subject prompted us to examine the role of MMP9 in the behaviour of oral tongue squamous cell carcinoma (OTSCC) cells. We used gelatinase-specific inhibitor, CTT2, and short hairpin (sh) RNA gene silencing to study the effects of MMP9 on proliferation, motility and invasion of an aggressive OTSCC cell line, HSC-3. We found that the migration and invasion of HSC-3 cells were increased by CTT2 and shRNA silencing of MMP9. Proliferation, in turn, was decreased by MMP9 inhibition. Furthermore, arresten-overexpressing HSC-3 cells expressed increased levels of MMP9, but exhibited decreased motility compared with controls. Interestingly, these cells restored their migratory capabilities by CTT2 inhibition of MMP9. Hence, although higher MMP9 expression could give rise to an increased tumour growth in vivo due to increased proliferation, in some circumstances, it may participate in yet unidentified molecular mechanisms that reduce the cell movement in OTSCC.

LRP1 is required for novobiocin-mediated fibronectin turnover

Fibronectin (FN) plays a major role in the stability and organization of the extracellular matrix (ECM). We have previously demonstrated that FN interacts directly with Hsp90, as well as showing that the Hsp90 inhibitor novobiocin results in FN turnover via a receptor mediated process. However, the receptor involved has not been previously identified. LRP1 is a ubiquitous receptor responsible for the internalisation of numerous ligands that binds both Hsp90 and FN, and therefore we investigated whether LRP1 was involved in novobiocin-mediated FN turnover. FN, LRP1 and Hsp90 could be isolated in a common complex, and inhibition of Hsp90 by novobiocin increased the colocalisation of FN and LRP1. Novobiocin induced an increase (at low concentrations) followed by a loss of FN that was primarily derived from extracellular matrix-associated FN and led to a concomitant increase in intracellular FN. The effect of novobiocin was specific to LRP1-expressing cells and could be recapitulated by an LRP1 blocking antibody and the allosteric C-terminal Hsp90 inhibitor SM253, but not the N-terminal inhibitor geldanamycin. Together these data suggest that LRP1 is required for FN turnover in response to Hsp90 inhibition by novobiocin, which may have unintended physiological consequences in contexts where C-terminal Hsp90 inhibition is to be used therapeutically.

Identification of the functional pathways altered by placental cell exposure to high glucose: lessons from the transcript and metabolite interactome

The specific consequences of hyperglycaemia on placental metabolism and function are incompletely understood but likely contribute to poor pregnancy outcomes associated with diabetes mellitus (DM). This study aimed to identify the functional biochemical pathways perturbed by placental exposure to high glucose levels through integrative analysis of the trophoblast transcriptome and metabolome. The human trophoblast cell line, BeWo, was cultured in 5 or 25 mM glucose, as a model of the placenta in DM. Transcriptomic analysis using microarrays, demonstrated 5632 differentially expressed gene transcripts (≥± 1.3 fold change (FC)) following exposure to high glucose. These genes were used to generate interactome models of transcript response using BioGRID (non-inferred network: 2500 nodes (genes) and 10541 protein-protein interactions). Ultra performance-liquid chromatography-mass spectrometry (MS) and gas chromatography-MS analysis of intracellular extracts and culture medium were used to assess the response of metabolite profiles to high glucose concentration. The interactions of altered genes and metabolites were assessed using the MetScape interactome database, resulting in an integrated model of systemic transcriptome (2969 genes) and metabolome (41 metabolites) response within placental cells exposed to high glucose. The functional pathways which demonstrated significant change in response to high glucose included fatty acid β-oxidation, phospholipid metabolism and phosphatidylinositol phosphate signalling.

Effects of High Glucose on the Expression of LAMA1 and Biological Behavior of Choroid Retinal Endothelial Cells

Hyperglycemia is one of the main causes of proliferative diabetic retinopathy (PDR) characterized by thickening of the vascular basement membrane. Laminin alpha 1 (LAMA1) is a primary component of laminin, a major protein constituent of the basement membrane. In this study, we investigated the role of LAMA1 in the development of PDR. Retinal choroidal vascular endothelial cells (RF/6A line) were exposed to glucose at different concentrations (5 mM, 15 mM, 25 mM, and 35 mM) and analyzed for cell growth, migration, proliferation, and adhesion. LAMA1 expression was examined 24 and 48 h following glucose treatment using Western blotting, RT-PCR, and immunofluorescence. The results showed that the proliferation, migration, and adhesion of RF/6A cells were increased by high glucose, whereas LAMA1 expression was slightly higher at 15 mM but decreased at 25 mM and 35 mM glucose compared to control. Thus, the changes in the biological behavior of high glucose-exposed retinal vascular endothelial cells correspond to variations in LAMA1 expression, indicating a possibility for LAMA1 involvement in PDR development. Our findings suggest that LAMA1 may play a role in PDR and, thus, may serve as a potential target for DR diagnosis and/or treatment.

NPPB modulates apoptosis, proliferation, migration and extracellular matrix synthesis of conjunctival fibroblasts by inhibiting PI3K/AKT signaling

When treating glaucoma, excessive scar tissue reactions reduce the postoperative survival rate of the filtering bleb. Accumulating evidence has demonstrated that the proliferation, migration and extracellular matrix (ECM) synthesis of fibroblasts are important molecular mechanisms underlying scar formation. Recent evidence has demonstrated that chloride channels play an important role in controlling cell proliferation, apoptosis, migration and the cell cycle process in several cell types, but the effects of chloride channels on conjunctival fibroblasts have not be studied. The aim of the present study was to investigate the effects of the chloride channel blocker 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) on cell proliferation, apoptosis, migration, cell cycle progression and ECM synthesis in human conjunctival fibroblasts (HConFs), and to further investigate the mechanism of resistance to scar formation following glaucoma filtration surgery. HConFs were exposed to NPPB or lubiprostone. Cell proliferation and viability was evaluated using the Cell Counting Kit-8. Cell migration was measured using Transwell migration and scratch‑wound assays. Flow cytometry was used to study apoptosis and cell cycle progression. Quantitative polymerase chain reaction and western blot analyses were performed to determine mRNA and protein expression levels, respectively. Following NPPB treatment, HConFs exhibited reduced proliferation and migration, along with increased apoptosis. NPPB also inhibited cell cycle progression by arresting cells in the G0̸G1 phase and reducing collagen I and fibronectin expression, as well as the phosphorylation of phosphoinositide 3-kinase (PI3K) and protein kinase B (AKT). However, lubiprostone treatment exerted the opposite effects on HConFs. Therefore, NPPB treatment inhibited proliferation, migration, cell cycle progression and synthesis of the ECM, while promoting apoptosis in HConFs, by inhibiting the PI3K̸AKT signaling pathway.

The CLC-2 Chloride Channel Modulates ECM Synthesis, Differentiation, and Migration of Human Conjunctival Fibroblasts via the PI3K/Akt Signaling Pathway

Recent evidence suggests that chloride channels are critical for cell proliferation, migration, and differentiation. We examined the effects of transforming growth factor (TGF)-β1 on chloride channel expression and associations with human conjunctival fibroblast (HConF) biology. To investigate the potential role of chloride channel (CLC)-2 in migration, transition to myofibroblasts and extracellular matrix (ECM) synthesis of HconF, a small interfering RNA (siRNA) approach was applied. TGF-β1-induced migration and transition of fibroblasts to myofibroblasts characterized by α-smooth muscle actin (α-SMA) expression, supported by increased endogenous expression of CLC-2 protein and mRNA transcripts. ECM (collagen I and fibronectin) synthesis in HConF was enhanced by TGF-β1. CLC-2 siRNA treatment reduced TGF-β1-induced cell migration, transition of fibroblasts to myofibroblasts, and ECM synthesis of HConF. CLC-2 siRNA treatment in the presence of TGF-β1 inhibited phosphorylation of PI3K and Akt in HConF. These findings demonstrate that CLC-2 chloride channels are important for TGF-β1-induced migration, differentiation, and ECM synthesis via PI3K/Akt signaling in HConF.