Mesenchymal marker expression is elevated in Müller cells exposed to high glucose and in animal models of diabetic retinopathy

Müller cells trophism and pathology as the next therapeutic targets for retinal diseases

Müller cells are a crucial retinal cell type involved in multiple regulatory processes and functions that are essential for retinal health and functionality. Acting as structural and functional support for retinal neurons and photoreceptors, Müller cells produce growth factors, regulate ion and fluid homeostasis, and facilitate neuronal signaling. They play a pivotal role in retinal morphogenesis and cell differentiation, significantly contributing to macular development. Due to their radial morphology and unique cytoskeletal organization, Müller cells act as optical fibers, efficiently channeling photons directly to the photoreceptors. In response to retinal damage, Müller cells undergo specific gene expression and functional changes that serve as a first line of defense for neurons, but can also lead to unwarranted cell dysfunction, contributing to cell death and neurodegeneration. In some species, Müller cells can reactivate their developmental program, promoting retinal regeneration and plasticity-a remarkable ability that holds promising therapeutic potential if harnessed in mammals. The crucial and multifaceted roles of Müller cells-that we propose to collectively call "Müller cells trophism"-highlight the necessity of maintaining their functionality. Dysfunction of Müller cells, termed "Müller cells pathology," has been associated with a plethora of retinal diseases, including age-related macular degeneration, diabetic retinopathy, vitreomacular disorders, macular telangiectasia, and inherited retinal dystrophies. In this review, we outline how even subtle disruptions in Müller cells trophism can drive the pathological cascade of Müller cells pathology, emphasizing the need for targeted therapies to preserve retinal health and prevent disease progression.

Thyroid Hormone Signaling in Retinal Development and Function: Implications for Diabetic Retinopathy and Age-Related Macular Degeneration

Thyroid Hormones (THs) play a central role in the development, cell growth, differentiation, and metabolic homeostasis of neurosensory systems, including the retina. The coordinated activity of various components of TH signaling, such as TH receptors (THRs) and the TH processing enzymes deiodinases 2 and 3 (DIO2, DIO3), is required for proper retinal maturation and function of the adult photoreceptors, Müller glial cells, and pigmented epithelial cells. Alterations of TH homeostasis, as observed both in frank or subclinical thyroid disorders, have been associated with sight-threatening diseases leading to irreversible vision loss i.e., diabetic retinopathy (DR), and age-related macular degeneration (AMD). Although observational studies do not allow causal inference, emerging data from preclinical models suggest a possible correlation between TH signaling imbalance and the development of retina disease. In this review, we analyze the most important features of TH signaling relevant to retinal development and function and its possible implication in DR and AMD etiology. A better understanding of TH pathways in these pathological settings might help identify novel targets and therapeutic strategies for the prevention and management of retinal disease.

N-cadherin cleavage: A critical function that induces diabetic retinopathy fibrosis via regulation of β-catenin translocation

Retinal fibrosis is a severe pathological change in the late stage of diabetic retinopathy and is also the leading cause of blindness. We have previously revealed that N-cadherin was significantly increased in type 1 and type 2 diabetic mice retinas and the fibrovascular membranes from proliferative diabetic retinopathy (PDR) patients. However, whether N-cadherin directly induces retinal fibrosis in DR and the related mechanism is unknown. Here, we investigated the pathogenic role of N-cadherin in mediating retinal fibrosis and further explored the relevant therapeutic targets. We found that the level of N-cadherin was significantly increased in PDR patients and STZ-induced diabetic mice and positively correlated with the fibrotic molecules Connective Tissue Growth Factor (CTGF) and fibronectin (FN). Moreover, intravitreal injection of N-cadherin adenovirus significantly increased the expression of FN and CTGF in normal mice retinas. Mechanistically, overexpression of N-cadherin promotes N-cadherin cleavage, and N-cadherin cleavage can further induce translocation of non-p-β-catenin in the nucleus and upregulation of fibrotic molecules. Furthermore, we found a novel N-cadherin cleavage inhibitor, pigment epithelial-derived factor (PEDF), which ameliorated the N-cadherin cleavage and subsequent retinal fibrosis in diabetic mice. Thus, our findings provide novel evidence that elevated N-cadherin level not only acts as a classic EMT maker but also plays a causative role in diabetic retinal fibrosis, and targeting N-cadherin cleavage may provide a strategy to inhibit retinal fibrosis in DR patients.

The G-Protein-Coupled Formyl Peptide Receptor 2 Promotes Endothelial-Mesenchymal Transition in Diabetic Retinopathy

INTRODUCTION

In proliferative diabetic retinopathy (PDR), retinal neovascularization is the essential pathogenic process that is linked to endothelial-to-mesenchymal transition (EndoMT) induced by high glucose (HG). This pathophysiological process may be regulated by a G-protein-coupled chemoattractant receptor FPR2 (mouse Fpr2), involved in inflammatory cell migration and proliferation. In the current study, we investigated the role of Fpr2 in regulating EndoMT and the underlying mechanisms during diabetic retinopathy progression.

METHODS

FPR2 agonist or inhibitor was added to human microvascular endothelial cells (HMECs) exposed to normal glucose or HG. Morphologic, phenotypic, and functional changes of HMECs as well as the formation of microvasculature related to EndoMT were assessed. EndoMT biomarkers were detected in the retinal tissues of diabetic mice and fibrovascular epiretinal membranes (FVMs) from patients with PDR.

RESULTS

HG upregulated FPR2 in HMECs, which triggered morphological changes, and the cells acquired mesenchymal phenotype, with enhanced cell migration, viability, and angiogenic process shown by tube formation and aortic ring sprouting. Inhibition of FPR2 attenuated HG-induced EndoMT and endothelial cell migration to form vessel-like tube structures. RNA sequence and protein analysis further revealed that inhibition of FPR2 decreased the expression of genes associated with EndoMT. ERK1/2 and P38 signaling pathway was activated in HMECs, promoting neovascularization in HG-induced EndoMT of HMECs. In vivo, increased expression of mesenchymal markers was detected in the retina of diabetic mice and FVMs from patients with PDR. FPR2 deficiency was associated with diminished EndoMT-related phenotypic changes in the retina of diabetic mice.

CONCLUSIONS

FPR2 is actively involved in the progression of EndoMT that may contribute to the pathogenesis of PDR. Thus, FPR2 may be a potential therapeutic target for PDR.

Blockade of the TGF-β pathway by galunisertib inhibits the glial-mesenchymal transition in Müller glial cells

Aging increases the risks for developing fibrocontractile membranes on the retina, which causes significant macular distortion, as in the idiopathic epiretinal membrane (iERM). Retinal Müller glial cells are components of these membranes and may play a key role in the iERM pathogenesis. The transforming growth factor-β (TGF-β) induces Müller cell transdifferentiation into myofibroblast, reducing glial cell markers (glutamine synthetase, GS, and glial fibrillary acidic protein, GFAP) and increasing α-smooth muscle actin (α-SMA). Our aim was to investigate the effect of the TGF-β inhibitor galunisertib (LY2157299) on the glial-mesenchymal transition and contraction of Müller cells. MIO-M1 human Müller cells were treated with TGF-β1 (10 ng/mL), galunisertib (5, 10 and 20 μM) and TGF-β1+galunisertib for 24h and 48h. Galunisertib cytotoxicity was analyzed by MTT and trypan blue, and TGF-β1 blockade by phospho-SMAD3 immunofluorescence. Caspase-3 (cell death indicator), GS, GFAP and α-SMA expression was examined by immunofluorescence, Western blotting, and qPCR analysis. Cell contractility was determined by collagen gel contraction assay with Müller cells incorporated. Galunisertib did not show cytotoxicity at the concentrations evaluated and maintained the Müller cells phenotype, ensuring the GS expression. Galunisertib inhibited the TGF-β1 pathway by decreasing phospho-SMAD3 immunoreactivity, attenuated the α-SMA expression, and prevented the contraction of Müller cells in collagen gel. Although more studies are needed, in vitro assays suggest that galunisertib may be a potential candidate to attenuate the formation of fibrocontractile membranes and prevent retinal detachment and consequent loss of vision.

Biochemical mechanism underlying the pathogenesis of diabetic retinopathy and other diabetic complications in humans: the methanol-formaldehyde-formic acid hypothesis

Hyperglycemia in diabetic patients is associated with abnormally-elevated cellular glucose levels. It is hypothesized that increased cellular glucose will lead to increased formation of endogenous methanol and/or formaldehyde, both of which are then metabolically converted to formic acid. These one-carbon metabolites are known to be present naturally in humans, and their levels are increased under diabetic conditions. Mechanistically, while formaldehyde is a cross-linking agent capable of causing extensive cytotoxicity, formic acid is an inhibitor of mitochondrial cytochrome oxidase, capable of inducing histotoxic hypoxia, ATP deficiency and cytotoxicity. Chronic increase in the production and accumulation of these toxic one-carbon metabolites in diabetic patients can drive the pathogenesis of ocular as well as other diabetic complications. This hypothesis is supported by a large body of experimental and clinical observations scattered in the literature. For instance, methanol is known to have organ- and species-selective toxicities, including the characteristic ocular lesions commonly seen in humans and non-human primates, but not in rodents. Similarly, some of the diabetic complications (such as ocular lesions) also have a characteristic species-selective pattern, closely resembling methanol intoxication. Moreover, while alcohol consumption or combined use of folic acid plus vitamin B is beneficial for mitigating acute methanol toxicity in humans, their use also improves the outcomes of diabetic complications. In addition, there is also a large body of evidence from biochemical and cellular studies. Together, there is considerable experimental support for the proposed hypothesis that increased metabolic formation of toxic one-carbon metabolites in diabetic patients contributes importantly to the development of various clinical complications.

O-GlcNAcylation of MORC2 at threonine 556 by OGT couples TGF-β signaling to breast cancer progression

MORC family CW-type zinc finger 2 (MORC2) is a newly identified chromatin-remodeling enzyme involved in DNA damage response and gene transcription, and its dysregulation has been linked with Charcot-Marie-Tooth disease, neurodevelopmental disorder, and cancer. Despite its functional importance, how MORC2 is regulated remains enigmatic. Here, we report that MORC2 is O-GlcNAcylated by O-GlcNAc transferase (OGT) at threonine 556. Mutation of this site or pharmacological inhibition of OGT impairs MORC2-mediated breast cancer cell migration and invasion in vitro and lung colonization in vivo. Moreover, transforming growth factor-β1 (TGF-β1) induces MORC2 O-GlcNAcylation through enhancing the stability of glutamine-fructose-6-phosphate aminotransferase (GFAT), the rate-limiting enzyme for producing the sugar donor for OGT. O-GlcNAcylated MORC2 is required for transcriptional activation of TGF-β1 target genes connective tissue growth factor (CTGF) and snail family transcriptional repressor 1 (SNAIL). In support of these observations, knockdown of GFAT, SNAIL or CTGF compromises TGF-β1-induced, MORC2 O-GlcNAcylation-mediated breast cancer cell migration and invasion. Clinically, high expression of OGT, MORC2, SNAIL, and CTGF in breast tumors is associated with poor patient prognosis. Collectively, these findings uncover a previously unrecognized mechanistic role for MORC2 O-GlcNAcylation in breast cancer progression and provide evidence for targeting MORC2-dependent breast cancer through blocking its O-GlcNAcylation.

Characteristics of Whale Müller Glia in Primary and Immortalized Cultures

Müller cells are the principal glial cells in the retina and they assume many of the functions carried out by astrocytes, oligodendrocytes and ependymal cells in other regions of the central nervous system. Müller cells express growth factors, neurotransmitter transporters and antioxidant agents that could fulfill important roles in preventing excitotoxic damage to retinal neurons. Vertebrate Müller cells are well-defined cells, characterized by a common set of features throughout the phylum. Nevertheless, several major differences have been observed among the Müller cells in distinct vertebrates, such as neurogenesis, the capacity to reprogram fish Müller glia to neurons. Here, the Müller glia of the largest adult mammal in the world, the whale, have been analyzed, and given the difficulties in obtaining cetacean cells for study, these whale glia were analyzed both in primary cultures and as immortalized whale Müller cells. After isolating the retina from the eye of a beached sei whale (Balaenoptera borealis), primary Müller cell cultures were established and once the cultures reached confluence, half of the cultures were immortalized with the simian virus 40 (SV40) large T-antigen commonly used to immortalize human cell lines. The primary cell cultures were grown until cells reached senescence. Expression of the principal molecular markers of Müller cells (GFAP, Vimentin and Glutamine synthetase) was studied in both primary and immortalized cells at each culture passage. Proliferation kinetics of the cells were analyzed by time-lapse microscopy: the time between divisions, the time that cells take to divide, and the proportion of dividing cells in the same field. The karyotypes of the primary and immortalized whale Müller cells were also characterized. Our results shown that W21M proliferate more rapidly and they have a stable karyotype. W21M cells display a heterogeneous cell morphology, less motility and a distinctive expression of some typical molecular markers of Müller cells, with an increase in dedifferentiation markers like α-SMA and β-III tubulin, while they preserve their GS expression depending on the culture passage. Here we also discuss the possible influence of the animal's age and size on these cells, and on their senescence.

Proteomic profiling and correlations with clinical features reveal biomarkers indicative of diabetic retinopathy with diabetic kidney disease

Diabetic retinopathy (DR) and diabetic kidney disease (DKD) are complications of diabetes and place serious health and economic burdens on society. However, the identification and characterization of early biomarkers for DKD, especially for nonproliferative DR (NPDR) patients with DKD, are still needed. This study aimed to demonstrate the plasma proteomic profiles of NPDR+DKD and NPDR patients and identify potential biomarkers for early diagnosis of DKD. Fifteen plasma samples from the NPDR group and nine from the NPDR+DKD group were analyzed by LC-MS/MS to identify the differentially expressed proteins between the two groups. Functional enrichment, protein-protein interaction and clinical feature correlation analyses revealed the target protein candidates, which were verified using ELISA and receiver operating characteristic (ROC) analysis. In total, 410 proteins were detected in plasma; 15 were significantly upregulated and 7 were downregulated in the NPDR+DKD group. Bioinformatics analysis suggested that DKD is closely related to cell adhesion and immunity pathways. β-2-Microglobulin (B2M) and vimentin (VIM) were upregulated in NPDR+DKD, enriched as hub proteins and strongly correlated with clinical features. ELISA showed that B2M (p<0.001) and VIM (p<0.0001) were significantly upregulated in NPDR+DKD compared with NPDR. In ROC analysis, B2M and VIM could distinguish DKD from NPDR with area under the curve values of 0.9000 (p < 0.0001) and 0.9950. Our proteomic study revealed alterations in the proteomic profile and identified VIM and B2M as early biomarkers of DKD, laying the foundation for the prevention, diagnosis and treatment of DKD.

MiR-195 inhibits the ubiquitination and degradation of YY1 by Smurf2, and induces EMT and cell permeability of retinal pigment epithelial cells

The dysregulated microRNAs (miRNAs) are involved in diabetic retinopathy progression. Epithelial mesenchymal transition (EMT) and cell permeability are important events in diabetic retinopathy. However, the function and mechanism of miR-195 in EMT and cell permeability in diabetic retinopathy remain largely unclear. Diabetic retinopathy models were established using streptozotocin (STZ)-induced diabetic mice and high glucose (HG)-stimulated ARPE-19 cells. Retina injury was investigated by hematoxylin-eosin (HE) staining. EMT and cell permeability were analyzed by western blotting, immunofluorescence, wound healing, and FITC-dextran assays. MiR-195 expression was detected via qRT-PCR. YY1, VEGFA, Snail1, and Smurf2 levels were detected via western blotting. The interaction relationship was analyzed via ChIP, Co-IP, or dual-luciferase reporter assay. The retina injury, EMT, and cell permeability were induced in STZ-induced diabetic mice. HG induced EMT and cell permeability in ARPE-19 cells. MiR-195, YY1, VEGFA, and Snail1 levels were enhanced, but Smurf2 abundance was reduced in STZ-induced diabetic mice and HG-stimulated ARPE-19 cells. VEGFA knockdown decreased Snail1 expression and attenuated HG-induced EMT and cell permeability. YY1 silence reduced VEGFA and Snail1 expression, and mitigated HG-induced EMT and cell permeability. YY1 could bind with VEGFA and Snail1, and it was degraded via Smurf2-mediated ubiquitination. MiR-195 knockdown upregulated Smurf2 to decrease YY1 expression and inhibited HG-induced EMT and cell permeability. MiR-195 targeted Smurf2, increased expression of YY1, VEGFA, and Snail1, and promoted HG-induced EMT and cell permeability. MiR-195 promotes EMT and cell permeability of HG-stimulated ARPE-19 cells by increasing VEGFA/Snail1 via inhibiting the Smurf2-mediated ubiquitination of YY1.

HspB4/αA-Crystallin Modulates Neuroinflammation in the Retina via the Stress-Specific Inflammatory Pathways

PURPOSE

We have previously demonstrated that HspB4/αA-crystallin, a molecular chaperone, plays an important intrinsic neuroprotective role during diabetes, by its phosphorylation on residue 148. We also reported that HspB4/αA-crystallin is highly expressed by glial cells. There is a growing interest in the potential causative role of low-grade inflammation in diabetic retinopathy pathophysiology and retinal Müller glial cells' (MGCs') participation in the inflammatory response. MGCs indeed play a central role in retinal homeostasis via secreting various cytokines and other mediators. Hence, this study was carried out to delineate and understand the regulatory function of HspB4/αA-crystallin in the inflammatory response associated with metabolic stresses.

METHODS

Primary MGCs were isolated from knockout HspB4/αA-crystallin mice. These primary cells were then transfected with plasmids encoding either wild-type (WT), phosphomimetic (T148D), or non-phosphorylatable mutants (T148A) of HspB4/αA-crystallin. The cells were exposed to multiple metabolic stresses including serum starvation (SS) or high glucose with TNF-alpha (HG + T) before being further evaluated for the expression of inflammatory markers by qPCR. The total protein expression along with subcellular localization of NF-kB and the NLRP3 component was assessed by Western blot.

RESULTS

Elevated levels of IL-6, IL-1β, MCP-1, and IL-18 in SS were significantly diminished in MGCs overexpressing WT and further in T148D as compared to EV. The HG + T-induced increase in these inflammatory markers was also dampened by WT and even more significantly by T148D overexpression, whereas T148A was ineffective in either stress. Further analysis revealed that overexpression of WT or the T148D, also led to a significant reduction of Nlrp3, Asc, and caspase-1 transcript expression in serum-deprived MGCs and nearly abolished the NF-kB induction in HG + T diabetes-like stress. This mechanistic effect was further evaluated at the protein level and confirmed the stress-dependent regulation of NLRP3 and NF-kB by αA-crystallin.

CONCLUSIONS

The data gathered in this study demonstrate the central regulatory role of HspB4/αA-crystallin and its modulation by phosphorylation on T148 in retinal MGCs. For the first time, this study demonstrates that HspB4/αA-crystallin can dampen the stress-induced expression of pro-inflammatory cytokines through the modulation of multiple key inflammatory pathways, therefore, suggesting its potential as a therapeutic target for the modulation of chronic neuroinflammation.

Involvement of Müller Glial Autoinduction of TGF-β in Diabetic Fibrovascular Proliferation Via Glial-Mesenchymal Transition

Purpose

Müller glial–mesenchymal transition (GMT) is reported as the fibrogenic mechanism promoted by TGF-β–SNAIL axis in Müller cells transdifferentiated into myofibroblasts. Here we show the multifaceted involvement of TGF-β in diabetic fibrovascular proliferation via Müller GMT and VEGF-A production.

Methods

Surgically excised fibrovascular tissues from the eyes of patients with proliferative diabetic retinopathy were processed for immunofluorescence analyses of TGF-β downstream molecules. Human Müller glial cells were used to evaluate changes in gene and protein expression with real-time quantitative PCR and ELISA, respectively. Immunoblot analyses were performed to detect TGF-β signal activation.

Results

Müller glial cells in patient fibrovascular tissues were immunopositive for GMT-related molecular markers, including SNAIL and smooth muscle protein 22, together with colocalization of VEGF-A and TGF-β receptors. In vitro administration of TGF-β1/2 upregulated TGFB1 and TGFB2, both of which were suppressed by inhibitors for nuclear factor-κB, glycogen synthase kinase-3, and p38 mitogen-activated protein kinase. Of the various profibrotic cytokines, TGF-β1/2 application exclusively induced Müller glial VEGFA mRNA expression, which was decreased by pretreatment with small interfering RNA for SMAD2 and inhibitors for p38 mitogen-activated protein kinase and phosphatidylinositol 3-kinase. Supporting these findings, TGF-β1/2 stimulation to Müller cells increased the phosphorylation of these intracellular signaling molecules, all of which were also activated in Müller glial cells in patient fibrovascular tissues.

Conclusions

This study underscored the significance of Müller glial autoinduction of TGF-β as a pathogenic cue to facilitate diabetic fibrovascular proliferation via TGF-β–driven GMT and VEGF-A–driven angiogenesis.

Diabetes Induced Alterations in Murine Vitreous Proteome Are Mitigated by IL-6 Trans-Signaling Inhibition

Purpose

Diabetic retinopathy (DR) is a microvascular complication caused by prolonged hyperglycemia and characterized by leaky retinal vasculature and ischemia-induced angiogenesis. Vitreous humor is a gel-like biofluid in the posterior segment of the eye between the lens and the retina. Disease-related changes are observed in the biochemical constituents of the vitreous, including proteins and macromolecules. Recently, we found that IL-6 trans-signaling plays a significant role in the vascular leakage and retinal pathology associated with DR. Therefore, in this study, comprehensive proteomic profiling of the murine vitreous was performed to identify diabetes-induced alterations and to determine effects of IL-6 trans-signaling inhibition on these changes.

Methods

Vitreous samples from mice were collected by evisceration, and proteomic analyses were performed using liquid chromatography–tandem mass spectrometry (LC-MS/MS).

Results

A total of 154 proteins were identified with high confidence in control mice and were considered to be characteristic of healthy murine vitreous fluid. The levels of 72 vitreous proteins were significantly altered in diabetic mice, including several members of heat shock proteins, 14-3-3 proteins, and tubulins. Alterations in 52 out of 72 proteins in diabetic mice were mitigated by IL-6 trans-signaling inhibition.

Conclusions

Proteomic analysis of murine vitreous fluid performed in this study provides important information about the changes caused by diabetes in the ocular microenvironment. These diabetes-induced alterations in the murine vitreous proteome were mitigated by IL-6 trans-signaling inhibition. These findings further support that IL-6 trans-signaling may be an important therapeutic target for the treatment of DR.

Plasma Rich in Growth Factors (PRGF) Increases the Number of Retinal Müller Glia in Culture but Not the Survival of Retinal Neurons

Plasma rich in growth factors (PRGF) is a subtype of platelet-rich plasma (PRP) that stimulates tissue regeneration and may promote neuronal survival. It has been employed in ophthalmology to achieve tissue repair in some retinal pathologies, although how PRGF acts in the retina is still poorly understood. As a part of the central nervous system, the retina has limited capacity for repair capacity following damage, and retinal insult can provoke the death of retinal ganglion cells (RGCs), potentially producing irreversible blindness. RGCs are in close contact with glial cells, such as Müller cells, that help maintain homeostasis in the retina. In this study, the aim was to determine whether PRGF can protect RGCs and whether it increases the number of Müller cells. Therefore, PRGF were tested on primary cell cultures of porcine RGCs and Müller cells, as well as on co-cultures of these two cell types. Moreover, the inflammatory component of PRGF was analyzed and the cytokines in the different PRGFs were quantified. In addition, we set out to determine if blocking the inflammatory components of PRGF alters its effect on the cells in culture. The presence of PRGF compromises RGC survival in pure cultures and in co-culture with Müller cells, but this effect was reversed by heat-inactivation of the PRGF. The detrimental effect of PRGF on RGCs could be in part due to the presence of cytokines and specifically, to the presence of pro-inflammatory cytokines that compromise their survival. However, other factors are likely to be present in the PRGF that have a deleterious effect on the RGCs since the exposure to antibodies against these cytokines were insufficient to protect RGCs. Moreover, PRGF promotes Müller cell survival. In conclusion, PRGF hinders the survival of RGCs in the presence or absence of Müller cells, yet it promotes Müller cell survival that could be the reason of retina healing observed in the in vivo treatments, with some cytokines possibly implicated. Although PRGF could stimulate tissue regeneration, further studies should be performed to evaluate the effect of PRGF on neurons and the implication of its potential inflammatory role in such processes.

Hawthorn polyphenols reduce high glucose-induced inflammation and apoptosis in ARPE-19 cells by regulating miR-34a/SIRT1 to reduce acetylation

Diabetic retinopathy is a major complication in patients with diabetes. Herein, we investigate how hawthorn polyphenol extract (HPE) affects high glucose-induced oxidation, inflammation, and apoptosis in ARPE-19 cells. HPLC-MS/MS was used to determine HPE content and composition. Reactive oxygen species (ROS) production was assessed using fluorescence microscopy, while glucose-induced gene and protein expressions were analyzed using real-time PCR and western blotting in cells transfected with miR-34a mimics. We found that treating cells with 10 μg/ml of HPE, 30 μM procyanidin B2, chlorogenic acid, epicatechin, or resveratrol (positive control) significantly reduced ROS production and decreased apoptosis and inflammation-related factors (p < .01). Moreover, the expression level of SIRT1 was increased, while that of acetylated NF-κB p65 and p53 proteins was decreased. These data suggest that HPE can inhibit oxidative damage, inflammation, and apoptosis through the AMPK/SIRT1/NF-κB pathway, and decrease miR-34a/SIRT1/p53 pathway activation in ARPE-19 cells, thereby demonstrating a potential use as a food additive to mitigate hyperglycemia-induced retinal damage. PRACTICAL APPLICATIONS: Hawthorn polyphenol extract (HPE) significantly reduced ROS levels, apoptosis, and the expression of inflammation-related factors in ARPE-19 cells. HPE also inhibited the AMPK/SIRT1/NF-κB and miR-34a/SIRT1/p53 pathways, which are involved in hyperglycemia-induced inflammation and apoptosis of ARPE-19 cells by regulating acetylation. Thus, HPE, as a potential food additive, may mitigate hyperglycemia-induced retinal damage.

Elevated pigment epithelium-derived factor induces diabetic erectile dysfunction via interruption of the Akt/Hsp90β/eNOS complex

AIMS/HYPOTHESIS

Diabetes mellitus erectile dysfunction (DMED) is a common complication of diabetes. The level of pigment epithelium-derived factor (PEDF) is significantly upregulated in the serum of individuals with obesity and diabetes. However, whether elevated PEDF levels contribute to DMED remains unknown. This study aimed to investigate the pathogenic role of PEDF and its related mechanism in DMED.

METHODS

We enrolled 65 men, of whom 20 were nondiabetic control participants, 21 participants with diabetes but without erectile dysfunction, and 24 with DMED. The International Index of Erectile Function (IIEF-5) questionnaire was administered to evaluate erectile function. Plasma PEDF in diabetic participants and streptozotocin (STZ)-induced diabetic animals was detected by ELISA. Erectile function was evaluated by measuring the intracavernous pressure (ICP) and the ICP/mean arterial pressure (MAP) ratio in STZ-induced diabetic rats treated with PEDF-neutralising antibody (PEDF-Ab), db/db mice treated with PEDF-Ab, and Pedf knockout mice with STZ-induced diabetes. The overexpression of PEDF was implemented by intraperitoneal injection of recombinant PEDF and intracavernous injection of PEDF-expressing adenovirus. A mechanistic study was performed by immunofluorescence staining, bimolecular fluorescence complementation (BiFC), immunoprecipitation and western blotting.

RESULTS

We found that the plasma level of PEDF was significantly higher in participants with DMED compared with diabetic counterparts without erectile dysfunction and nondiabetic controls. Interestingly, PEDF levels were negatively correlated with plasma nitrite/nitrate levels and erectile function in DMED patients and STZ-induced diabetic rats. Furthermore, overexpression of PEDF significantly suppressed ICP and endothelial nitric oxide synthase (eNOS) phosphorylation in control rats. In contrast, the PEDF-Ab and Pedf knockout ameliorated ICP and eNOS phosphorylation in diabetic rats and mice. Mechanistically, PEDF promoted the membrane translocation of Hsp90β and directly bound to the amino acid residues 341-724 of Hsp90β on the endothelial cell surface, subsequently blocking intracellular Hsp90β/Akt/eNOS complex formation and downregulating eNOS phosphorylation.

CONCLUSIONS/INTERPRETATION

These results indicate that elevated PEDF levels contribute to impaired erectile function by suppressing Hsp90β-mediated eNOS phosphorylation and that PEDF may represent a novel therapeutic target for diabetic erectile dysfunction. Graphical abstract.

Liraglutide Up-regulation Thioredoxin Attenuated Müller Cells Apoptosis in High Glucose by Regulating Oxidative Stress and Endoplasmic Reticulum Stress

Purpose: Diabetic retinopathy (DR) has become one of the most important complications of diabetes which is the leading cause of vision impairment and blindness all over the world. Increasing evidence shows that reactive gliosis are basic pathological features of early DR. The study was aimed to explore the protective effect and mechanism of Liraglutide (LIRA) which has similar properties to Glucagon-like peptide-1 (GLP-1) on Müller cell damage induced by diabetes. Materials and methods: In vitro, the Müller cell was cultured in high glucose (HG) to establish the model of diabetic retinopathy. The apoptosis was detected using flow cytometry. Western blot and immunofluorescence were used to detect the expression of related proteins. DCFH-DA probe was used to detect the ROS generation. Results: The data showed that the apoptosis and the expression of GFAP were increased significantly with HG treatment. However, the apoptosis percentage and the expression of GFAP were decreased after LIRA treatment. Moreover, the expression of p-Erk/Nrf2/Trx-signaling pathway proteins was also up-regulated and the generation of ROS was decreased after LIRA treatment which was inhibited after treatment with U0126 (Erk inhibitor). Besides, endoplasmic reticulum stress (ER stress) related proteins were up-regulated after Trx down-regulation by transfection with sh-RNA. Conclusions: LIRA could protect Müller cells from HG-induced damage via activating p-Erk pathway through increasing Trx expression which attenuated oxidative stress and ER stress. Trx could play a key role in the process.

Diabetes-Induced Inflammation and Vascular Alterations in the Goto-Kakizaki Rat Retina

PURPOSE

Diabetic retinopathy is characterized by multiple microcirculatory dysfunctions and angiogenesis resulting from hyperglycemia, oxidative stress, and inflammation. In this study, the retina and retinal pigmented epithelium of non-insulin-dependent diabetic Goto-Kakizaki (GK) rats were examined to detect microvascular alterations, gliosis, macrophage infiltration, lipid deposits, and fibrosis. Emphasis was given to the distribution of kinin B1 receptor (B1R) and vascular endothelial growth factor (VEGF), two major factors in inflammation and angiogenesis.

MATERIALS AND METHODS

30-week-old male GK rats and age-matched Wistar rats were used. The retinal vascular bed was examined using ADPase staining. The level of lipid accumulation was graded using triglyceride staining with Oil red O. Macrophage and retinal microglia activation, as well as other markers, were revealed by immunohistochemistry and studied with confocal laser scanning microscopy.

RESULTS

Abundant lipid deposits were observed in the Bruch's membrane of GK rats. Immunohistochemistry and quantitative analysis showed significantly higher B1R, VEGF, Iba1 (microglia), CD11 (macrophages), fibronectin, and collagen I labeling in the diabetic retina. B1R immunolabeling was detected in the vascular layers of the GK retina. A strong VEGF staining within different retinal cell processes was detected and a pattern of GFAP staining suggested strong Müller cells/astrocytes reactivity. Microgliosis was apparent in the GK retina. A greater tortuosity of the retinal microvessels (an index of endothelial dysfunction) and their increased number were also observed in GK retinas.

CONCLUSIONS

Data suggest retinal vascular bed alterations in spontaneous type 2 diabetic retinas at 30 weeks. Lipid and collagen accumulation in the retina and choroid, in addition to retinal upregulation of VEGF and B1R, microgliosis, and Müller cell reactivity, may contribute to vascular alterations and inflammatory processes.

LncRNA HULC Polymorphism Is Associated With Recurrent Spontaneous Abortion Susceptibility in the Southern Chinese Population

Previous studies have revealed that genetic variation in genes that regulate cell migration might be associated with susceptibility to recurrent spontaneous abortion. HULC regulates the migration of a variety of cells, and genetic polymorphisms of HULC are associated with susceptibility to a variety of diseases, but their association with susceptibility to recurrent spontaneous abortion has not been reported. This study included 610 cases of recurrent spontaneous abortion and 817 normal controls, and the polymorphisms of the four SNPs were genotyped using the TaqMan method. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to assess the associations between selected SNPs and susceptibility to recurrent spontaneous abortion. Our results showed that three SNPs were significantly associated with a reduced risk of recurrent spontaneous abortion: rs1041279 (GG vs. GC/CC: adjusted OR = 0.745, 95% CI = 0.559–0.993, P = 0.0445), rs7770772 (GC/CC vs. GG: adjusted OR = 0.757, 95% CI = 0.606–0.946, P = 0.0143), and rs17144343 (AA/GA vs GG adjusted OR = 0.526, 95% CI = 0.366–0.755, P = 0.0005). Individuals with one to four genotypes showed a reduced risk of recurrent spontaneous abortion (adjusted OR = 0.749, 95% CI = 0.598–0.939, P = 0.0123). This cumulative effect on protection increased with increases in the observed number of genotypes (adjusted OR = 0.727, 95% CI = 0.625–0.846, ptrend < 0.0001). Our study suggests that HULC might be a biomarker for risk for recurrent spontaneous abortion, but larger sample studies are needed to verify this result.

Notoginsenoside R1 Ameliorates Diabetic Retinopathy through PINK1-Dependent Activation of Mitophagy

: Accumulating evidence has indicated that inflammation, oxidative stress, apoptosis, and autophagy in retinal Müller cells are involved in diabetic retinopathy (DR). Notoginsenoside R1 (NGR1), a novel saponin extracted from Panax notoginseng, posesses pharmacological properties, including treating diabetic encephalopathy and improving microcirculatory disorders. Nevertheless, its beneficial effects on DR and the potential mechanism remain to be elucidated. In this study, we found retinal vascular degeneration, reduced retinal thickness, and impaired retinal function in db/db mice were all dramatically attenuated by oral treatment with NGR1 (30 mg/kg) for 12 weeks. NGR1 pretreatment also significantly inhibited apoptosis, markedly suppressed the VEGF expression, markedly increased PEDF expression and markedly inhibited oxidative stress and inflammation in rat retinal Müller cells (rMC-1) subjected to high glucose (HG) and in the retinas of db/db mice. Furthermore, NGR1 pre-treatment upregulated the level of PINK1 and Parkin, increased the LC3-II/LC3-I ratio, and downregulated the level of p62/SQSTM1 in rMC-1 cells induced by HG and in the retinas of db/db mice. Moreover, NGR1 administration enhanced the co-localization of GFP-LC3 puncta and MitoTracker in rMC-1 cells. Importantly, knockdown of PINK1 abolished the protective effects of NGR1. In conclusion, these phenomena suggested that NGR1 prevented DR via PINK1-dependent enhancement of mitophagy.

TGF-β-SNAIL axis induces Müller glial-mesenchymal transition in the pathogenesis of idiopathic epiretinal membrane

The epithelial-mesenchymal transition (EMT) is a key process in fibrogenic diseases where transdifferentiated myofibroblasts produce excessive amounts of extracellular matrix, resulting in organ dysfunction. Idiopathic epiretinal membrane (iERM) is a vision-threatening disorder characterized by fibrocellular proliferation and contraction on the central retina. Müller glial cells, which regulate retinal physiology and structure, are the major cellular components in the iERM tissue; however, the pathological role of this cell type remains incompletely understood. Here we revealed the involvement of Müller glial-mesenchymal transition (GMT), as an alternative to EMT, in the pathogenesis of iERM lacking epithelial contribution in nature. Of various pro-fibrotic cytokines, transforming growth factor (TGF)-β1 stimulation to human Müller glial cells exclusively increased mRNA and protein levels of several EMT-related molecular markers, together with the transcription factor SNAIL but not SLUG or TWIST. TGF-β1-stimulated Müller cells also exhibited EMT-related cell motility, while reducing the expression of glutamine synthetase (GS), a Müller glial marker. Notably, all of these TGF-β-induced EMT features were reversed by SNAI1 knockdown in Müller cells. iERM patient specimens demonstrated co-immunolocalization of SNAIL with TGF-β1, GS, and smooth muscle protein 22. Our data implicated a critical role of the TGF-β-SNAIL axis in Müller GMT to promote iERM formation.

The role of placental growth factor (PlGF) and its receptor system in retinal vascular diseases

Placental growth factor (PlGF) is a member of the vascular endothelial growth factor (VEGF) family. Upon binding to VEGF- and neuropilin-receptor sub-types, PlGF modulates a range of neural, glial and vascular cell responses that are distinct from VEGF-A. As PlGF expression is selectively associated with pathological angiogenesis and inflammation, its blockade does not affect the healthy vasculature. PlGF actions have been extensively described in tumor biology but more recently there has been accumulating preclinical evidence that indicates that this growth factor could have an important role in retinal diseases. High levels of PlGF have been found in aqueous humor, vitreous and/or retina of patients exhibiting retinopathies, especially those with diabetic retinopathy (DR) and neovascular age-related macular degeneration (nvAMD). Expression of this growth factor seems to correlate closely with many of the key pathogenic features of early and late retinopathy in preclinical models. For example, studies using genetic modification and/or pharmacological treatment to block PlGF in the laser-induced choroidal neovascularization (CNV) model, oxygen-induced retinopathy model, as well as various murine diabetic models, have shown that PlGF deletion or inhibition can reduce neovascularization, retinal leakage, inflammation and gliosis, without affecting vascular development or inducing neuronal degeneration. Moreover, an inhibitory effect of PlGF blockade on retinal scarring in the mouse CNV model has also been recently demonstrated and was found to be unique for PlGF inhibition, as compared to various VEGF inhibition strategies. Together, these preclinical results suggest that anti-PlGF therapy might have advantages over anti-VEGF treatment, and that it may have clinical applications as a standalone treatment or in combination with anti-VEGF. Additional clinical studies are clearly needed to further elucidate the role of PlGF and its potential as a therapeutic target in ocular diseases.

Aloin Inhibits Müller Cells Swelling in a Rat Model of Thioacetamide-Induced Hepatic Retinopathy

Swelling of retinal Müller cells is implicated in retinal edema and neuronal degeneration. Müller cell swelling is observed in patients with liver failure and is referred to as hepatic retinopathy. In the present study, we evaluated the effects of aloin, an anthraquinone-C-glycoside present in various Aloe species, on Müller cell dysfunction in a rat model of thioacetamide (TAA)-induced hepatic retinopathy. Experimental hepatic retinopathy was induced by three injections of TAA (200 mg/kg/day, intraperitoneal injection) for 3 days in rats. After the last injection of TAA, aloin (50 and 100 mg/kg) was orally gavaged for 5 days. The effects of aloin on the liver injury, serum ammonia levels, Müller cell swelling, glial fibrillary acidic protein (GFAP) expression, and gene expression of Kir4.1 and aquaporin-4 were examined. TAA-injected rats exhibited liver failure and hyperammonemia. In the TAA-injected rats, Müller cell bodies were highly enlarged, and GFAP, an indicator of retinal stress, was highly expressed in the retinas, indicating a predominant Müller cell gliosis. However, administration of aloin suppressed liver injury as well as Müller cell swelling through the normalization of Kir4.1 and aquaporin-4 channels, which play a key role in potassium and water transport in Müller cells. These results indicate that aloin may be helpful to protect retinal injury associated with liver failure.

A journey into the retina: Müller glia commanding survival and death

Müller glial cells (MGCs) are known to participate actively in retinal development and to contribute to homoeostasis through many intracellular mechanisms. As there are no homologous cells in other neuronal tissues, it is certain that retinal health depends on MGCs. These macroglial cells are located at the centre of the columnar subunit and have a great ability to interact with neurons, astrocytes, microglia and endothelial cells in order to modulate different events. Several investigations have focused their attention on the role of MGCs in diabetic retinopathy, a progressive pathology where several insults coexist. As expected, data suggest that MGCs display different responses according to the severity of the stimulus, and therefore trigger distinct events throughout the course of the disease. Here, we describe physiological functions of MGCs and their participation in inflammation, gliosis, synthesis and secretion of trophic and antioxidant factors in the diabetic retina. We invite the reader to consider the protective/deleterious role of MGCs in the early and late stages of the disease. In the light of the results, we open up the discussion around and ask the question: Is it possible that the modulation of a single cell type could improve or even re-establish retinal function after an injury?

Rg1 inhibits high glucose-induced mesenchymal activation and fibrosis via regulating miR-2113/RP11-982M15.8/Zeb1 pathway

Recent study has showed that Ginsenoside Rg1, the mian active compound of Panax ginseng, could ameliorate oxidative stress and myocardial apoptosis in diabetes mellitus. However, the roles and mechanisms of Rg1 in proliferative diabetic retinopathy (PDR) are still unclear. In the present study, we aimed to investigate the effects of Rg1 on mesenchymal activation of high-glucose (HG) cultured müller cells. High glucose conditions up-regulate MMP-2, MMP-9 and down-regulate TIMP-2, and promote mesenchymal activation in Müller cells. And Rg1 inhibits the HG-induced mesenchymal activation and HG-increased MMP-2 and MMP-9 and HG-decreased TIMP-2 in Müller cells. HG up-regulates Zeb1 and lncRNA RP11-982M15.8, and down-regulates miR-2113, and Rg1 inhibits these effects of HG. Both inhibition of miR-2113 and over-expression of RP11-982M15.8 significantly restored the HG induced mesenchymal activasion. Taken together, our findings suggested that Rg1 inhibited HG-induced mesenchymal activation and fibrosis via regulating miR-2113/RP11-982M15.8/Zeb1 pathway.

Müller cells and diabetic retinopathy

Müller cells are one of the primary glial cell types found in the retina and play a significant role in maintaining retinal function and health. Since Müller cells are the only cell type to span the entire width of the retina and have contact to almost every cell type in the retina they are uniquely positioned to perform a wide variety of functions necessary to maintaining retinal homeostasis. In the healthy retina, Müller cells recycle neurotransmitters, prevent glutamate toxicity, redistribute ions by spatial buffering, participate in the retinoid cycle, and regulate nutrient supplies by multiple mechanisms. Any disturbance to the retinal environment is going to influence proper Müller cell function and well being which in turn will affect the entire retina. This is evident in a disease like diabetic retinopathy where Müller cells contribute to neuronal dysfunction, the production of pro-angiogenic factors leading to neovascularization, the set up of a chronic inflammatory retinal environment, and eventual cell death. In this review, we highlight the importance of Müller cells in maintaining a healthy and functioning retina and discuss various pathological events of diabetic retinopathy in which Müller cells seem to play a crucial role. The beneficial and detrimental effects of cytokine and growth factor production by Müller cells on the microvasculature and retinal neuronal tissue will be outlined. Understanding Müller cell functions within the retina and restoring such function in diabetic retinopathy should become a cornerstone for developing effective therapies to treat diabetic retinopathy.