High-glucose-induced CARM1 expression regulates apoptosis of human retinal pigment epithelial cells via histone 3 arginine 17 dimethylation: Role in diabetic retinopathy

The emerging role of CARM1 in cancer

Coactivator-associated arginine methyltransferase 1 (CARM1), pivotal for catalyzing arginine methylation of histone and non-histone proteins, plays a crucial role in developing various cancers. CARM1 was initially recognized as a transcriptional coregulator by orchestrating chromatin remodeling, transcription regulation, mRNA splicing and stability. This diverse functionality contributes to the recruitment of transcription factors that foster malignancies. Going beyond its established involvement in transcriptional control, CARM1-mediated methylation influences a spectrum of biological processes, including the cell cycle, metabolism, autophagy, redox homeostasis, and inflammation. By manipulating these physiological functions, CARM1 becomes essential in critical processes such as tumorigenesis, metastasis, and therapeutic resistance. Consequently, it emerges as a viable target for therapeutic intervention and a possible biomarker for medication response in specific cancer types. This review provides a comprehensive exploration of the various physiological functions of CARM1 in the context of cancer. Furthermore, we discuss potential CARM1-targeting pharmaceutical interventions for cancer therapy.

Protein Arginine Methyltransferases: Emerging Targets in Cardiovascular and Metabolic Disease

Cardiovascular diseases (CVDs) and metabolic disorders stand as formidable challenges that significantly impact the clinical outcomes and living quality for afflicted individuals. An intricate comprehension of the underlying mechanisms is paramount for the development of efficacious therapeutic strategies. Protein arginine methyltransferases (PRMTs), a class of enzymes responsible for the precise regulation of protein methylation, have ascended to pivotal roles and emerged as crucial regulators within the intrinsic pathophysiology of these diseases. Herein, we review recent advancements in research elucidating on the multifaceted involvements of PRMTs in cardiovascular system and metabolic diseases, contributing significantly to deepen our understanding of the pathogenesis and progression of these maladies. In addition, this review provides a comprehensive analysis to unveil the distinctive roles of PRMTs across diverse cell types implicated in cardiovascular and metabolic disorders, which holds great potential to reveal novel therapeutic interventions targeting PRMTs, thus presenting promising perspectives to effectively address the substantial global burden imposed by CVDs and metabolic disorders.

Dysregulation of arginine methylation in tumorigenesis

Protein methylation, similar to DNA methylation, primarily involves post-translational modification (PTM) targeting residues of nitrogen-containing side-chains and other residues. Protein arginine methylation, occurred on arginine residue, is mainly mediated by protein arginine methyltransferases (PRMTs), which are ubiquitously present in a multitude of organisms and are intricately involved in the regulation of numerous biological processes. Specifically, PRMTs are pivotal in the process of gene transcription regulation, and protein function modulation. Abnormal arginine methylation, particularly in histones, can induce dysregulation of gene expression, thereby leading to the development of cancer. The recent advancements in modification mediated by PRMTs and cancer research have had a profound impact on our understanding of the abnormal modification involved in carcinogenesis and progression. This review will provide a defined overview of these recent progression, with the aim of augmenting our knowledge on the role of PRMTs in progression and their potential application in cancer therapy.

PRMT4 interacts with NCOA4 to inhibit ferritinophagy in cisplatin-induced acute kidney injury

Cisplatin-induced acute kidney injury (AKI) is commonly seen in the clinical practice, and ferroptosis, a type of non-apoptotic cell death, plays a pivotal role in it. Previous studies suggested that protein arginine methyltransferase 4 (PRMT4) was incorporated in various bioprocesses, but its role in renal injuries has not been investigated. Our present study showed that PRMT4 was highly expressed in renal proximal tubular cells, and it was downregulated in cisplatin-induced AKI. Besides, genetic disruption of PRMT4 exacerbated, while its overexpression attenuated, cisplatin-induced redox injuries in renal proximal epithelia. Mechanistically, our work showed that PRMT4 interacted with NCOA4 to inhibit ferritinophagy, a type of selective autophagy favoring lipid peroxidation to accelerate ferroptosis. Taken together, our study demonstrated that PRMT4 interacted with NCOA4 to attenuate ferroptosis in cisplatin-induced AKI, suggesting that PRMT4 might present as a new therapeutic target for cisplatin-related nephropathy.

Coactivator-associated arginine methyltransferase 1: A versatile player in cell differentiation and development

Protein arginine methylation is a common post-translational modification involved in the regulation of various cellular functions. Coactivator-associated arginine methyltransferase 1 (CARM1) is a protein arginine methyltransferase that asymmetrically dimethylates histone H3 and non-histone proteins to regulate gene transcription. CARM1 has been found to play important roles in cell differentiation and development, cell cycle progression, autophagy, metabolism, pre-mRNA splicing and transportation, and DNA replication. In this review, we describe the molecular characteristics of CARM1 and summarize its roles in the regulation of cell differentiation and development in mammals.

Protein arginine N-methyltransferase 4 (PRMT4) contributes to lymphopenia in experimental sepsis

BACKGROUND

One hallmark of sepsis is the reduced number of lymphocytes, termed lymphopenia, that occurs from decreased lymphocyte proliferation or increased cell death contributing to immune suppression. Histone modification enzymes regulate immunity by their epigenetic and non-epigenetic functions; however, the role of these enzymes in lymphopenia remains elusive.

METHODS

We used molecular biological approaches to investigate the high expression and function of a chromatin modulator protein arginine N-methyltransferase 4 (PRMT4)/coactivator-associated arginine methyltransferase 1 in human samples from septic patients and cellular and animal septic models.

RESULTS

We identified that PRMT4 is elevated systemically in septic patients and experimental sepsis. Gram-negative bacteria and their derived endotoxin lipopolysaccharide (LPS) increased PRMT4 in B and T lymphocytes and THP-1 monocytes. Single-cell RNA sequencing results indicate an increase of PRMT4 gene expression in activated T lymphocytes. Augmented PRMT4 is crucial for inducing lymphocyte apoptosis but not monocyte THP-1 cells. Ectopic expression of PRMT4 protein caused substantial lymphocyte death via caspase 3-mediated cell death signalling, and knockout of PRMT4 abolished LPS-mediated lymphocyte death. PRMT4 inhibition with a small molecule compound attenuated lymphocyte death in complementary models of sepsis.

CONCLUSIONS

These findings demonstrate a previously uncharacterised role of a key chromatin modulator in lymphocyte survival that may shed light on devising therapeutic modalities to lessen the severity of septic immunosuppression.

Novel Biotherapeutics Targeting Biomolecular and Cellular Approaches in Diabetic Wound Healing

Wound healing responses play a major role in chronic inflammation, which affects millions of people around the world. One of the daunting tasks of creating a wound-healing drug is finding equilibrium in the inflammatory cascade. In this study, the molecular and cellular mechanisms to regulate wound healing are explained, and recent research is addressed that demonstrates the molecular and cellular events during diabetic wound healing. Moreover, a range of factors or agents that facilitate wound healing have also been investigated as possible targets for successful treatment. It also summarises the various advances in research findings that have revealed promising molecular targets in the fields of therapy and diagnosis of cellular physiology and pathology of wound healing, such as neuropeptides, substance P, T cell immune response cDNA 7, miRNA, and treprostinil growth factors such as fibroblast growth factor, including thymosin beta 4, and immunomodulators as major therapeutic targets.

Epigenetics and Degenerative Retinal Diseases: Prospects for New Therapeutic Approaches

ABSTRACT

There is growing evidence that retinal degenerative diseases are accompanied by epigenetic changes in both deoxyribonucleic acid methylation and histone modification. Even in the monogenic disease retinitis pigmentosa, there is a cascade of changes in gene expression that correlate with epigenetic changes, suggesting that many of the symptoms, and degenerative changes, may be a result of epigenetic changes downstream from the genetic mutation. This is supported by data from studies of diabetic retinopathy and macular degeneration, 2 diseases where it has been difficult to define a single causative change. Initial studies with modifiers of deoxyribonucleic acid methylation suggest that they can provide therapeutic benefit. A number of drugs are available to inhibit specific epigenetic histone modifier enzymes, and these offer the possibility of new therapeutic approaches to retinal disease. Systemic treatment with inhibitors of histone demethylases and histone deacetylases have arrested rod degeneration in rodent models of retinitis pigmentosa. Some evidence has suggested that similar treatments may provide benefits for patients with diabetic retinopathy. Because differentiation of retinal stem cells is regulated in part by epigenetic mechanisms, it may also be possible to direct stem cell differentiation pathways through the use of selective epigenetic modifiers. This is predicted to provide a valuable avenue to accelerate the introduction of regenerative approaches to retinal disease. Epigenetic modifiers are poised to become a powerful new approach to treat retinal degenerative diseases.

CDKN2AIP-induced cell senescence and apoptosis of testicular seminoma are associated with CARM1 and eIF4β

Testicular seminoma is a relatively rare tumor which is mostly detected in male population aged from 15 to 35 years old. Although several molecular biomarkers have been identified to be associated with testicular seminoma pathogenesis, the exact mechanism for testicular seminoma progression remains largely unknown. CDKN2A interacting protein (CDKN2AIP) has previously been identified as a tumor suppressor in multiple malignant diseases. In this study, we aimed to further explore its role in testicular seminoma as well as the underlying molecular mechanisms. Retrospective testicular seminoma clinical samples, normal tissues, NTERA-2 cell line, and mouse xenograft models were used in this study. RT-qPCR, western blot analysis, immunofluorescence microscopy, Co-IP and IP-MS experiments were performed to detect the expression of CDKN2AIP and its interaction with CARM1 and eIF4β. SA-β-gal staining assay and H3K9me3 activity experiments were used to subsequently evaluate the cell senescence and apoptosis. Mouse xenograft animal model was used for in vivo study. The results showed that CDKN2AIP is highly expressed in normal testis samples, and is significantly suppressed in testicular seminoma clinical samples and cell line model. Up-regulation of CDKN2AIP is significantly associated with the inhibition of testicular seminoma tumor growth and the increase of cell senescence and apoptosis. CDKN2AIP exhibits anti-tumor activity by interacting with CARM1 and eIF4β. CDKN2AIP induces testicular seminoma cell senescence by suppressing CARM1 expression and eIF4β phosphorylation. The CDKN2AIP-CARM1 and CDKN2AIP-eIF4β interactions, which induce tumor cell senescence and apoptosis, may be the potential druggable molecular pathways in testicular seminoma tumor pathogenesis and progression.

MiR-192 attenuates high glucose-induced pyroptosis in retinal pigment epithelial cells via inflammasome modulation

Diabetic retinopathy is one of the most characteristic complications of diabetes mellitus, and pyroptosis plays acrucial role in the onset and development of diabetic retinopathy. Although microRNA-192 (miR-192) has been demonstrated to be involved in diabetic retinopathy progression, to the best of our knowledge, its potential and mechanism in cell pyroptosis in diabetic retinopathy have not been studied. The present study demonstrated that high glucose (HG) contributes to the pyroptosis of retinal pigment epithelial (RPE) cells in a dose-dependent manner. The results revealed that miR-192 was weakly expressed in HG-induced RPE cells. Furthermore, overexpression of miR-192 abrogated the role of HG in RPE cell pyroptosis. Based on the bioinformatics analysis, a dual-luciferase reporter assay, and an RNA pull-down assay, FTO α-ketoglutarate-dependent dioxygenase (FTO) was demonstrated to be a direct target of miR-192. Additionally, upregulation of FTO abolished the effects of miR-192 on RPE cells treated with HG. Nucleotide-binding domain leucine-rich repeat family protein 3 (NLRP3) inflammasome activation is vital for cell pyroptosis, and FTO functions as a pivotal modulator in the N⁶-methyladenosine modifications of various genes. Mechanistically, FTO enhanced NLRP3 expression by facilitating demethylation of NLRP3. In conclusion, the present results demonstrate that miR-192 represses RPE cell pyroptosis triggered by HG via regulation of the FTO/NLRP3 signaling pathway.

Long non‑coding RNA MALAT1 is involved in retinal pigment epithelial cell damage caused by high glucose treatment

The present study aimed to explore the role of long non‑coding RNA metastasis associated lung adenocarcinoma transcript 1 (lncRNA MALAT1) in high glucose (HG)‑induced ARPE‑19 cell damage. ARPE‑19 cells were cultured and treated with HG (25 mmol/l glucose). MALAT1 expression was silenced following transfection of small interfering RNA. Cell apoptosis was measured using flow cytometry. The cellular levels of reactive oxygen species (ROS), malondialdehyde and superoxide dismutase activity were all measured to examine oxidative stress. Gene expression levels of MALAT1 were determined by reverse transcription‑quantitative (RT‑q)PCR, while expression of tumor necrosis factor (TNF)‑α, monocyte chemotactic protein 1 (MCP‑1), intercellular cell adhesion molecule 1 (ICAM‑1) and vascular endothelial growth factor (VEGF) was detected using RT‑qPCR and western blotting. MALAT1 expression was markedly increased in ARPE‑19 cells treated with HG. HG treatment caused increased apoptosis and elevated ROS‑induced stress in ARPE‑19 cells and these effects could be partly attenuated by MALAT1 knockdown. Increased gene expression levels of TNF‑α, MCP‑1, ICAM‑1 and VEGF induced by HG were also alleviated by MALAT1 inhibition. Therefore, lncRNA MALAT1 is the key factor in ARPE‑19 cell damage caused by HG and may be a promising therapeutic target for clinical DR therapy. However, further studies are still required to reveal the detailed mechanisms underlying lncRNA MALAT1 function.

Circular RNA circZNF532 facilitates angiogenesis and inflammation in diabetic retinopathy via regulating miR-1243/CARM1 axis

BACKGROUND

Diabetic retinopathy (DR) is a serious complication of diabetes. Numerous reports have validated that circular RNAs (circRNAs) participate in DR progression. This study aimed to elucidate the role and potential mechanism of circRNA zinc finger protein 532 (circZNF532) in DR.

METHODS

The levels of circZNF532, miR-1243, and coactivator associated arginine methyltransferase 1 (CARM1) in DR patients and human retinal microvascular endothelial cells (hRMECs) were determined by quantitative real-time PCR and western blot. Colony formation assay, transwell assay, tube formation assay and enzyme-linked immunosorbent assay were used to assess the biological function of hRMECs. The binding relationship between miR-1243 and circZNF532/CARM1 was verified by dual-luciferase reporter and RNA immunoprecipitation assays.

RESULTS

circZNF532 and CARM1 levels were increased, while miR-1243 level was reduced in DR patients and high glucose (HG)-stimulated hRMECs. In terms of mechanism, miR-1243 competitively bound to circZNF532 and CARM1. Down-regulation of circZNF532 restrained HG-induced hRMECs proliferation, migration, invasion, angiogenesis and inflammation via regulating miR-1243. In addition, miR-1243 inhibited HG-triggered hRMECs progression via targeting CARM1.

CONCLUSION

circZNF532 facilitated HG-induced angiogenesis and inflammation in hRMECs via modulating the miR-1243/CARM1 pathway, suggesting that circZNF532 might be a potential biomarker for DR treatment.

Circ-ADAM9 Promotes High Glucose-Induced Retinal Pigment Epithelial Cell Injury in DR via Regulating miR-338-3p/CARM1 Axis

Background. Circular RNAs (circRNAs) have been reported to be involved in the regulation of retinal pigment epithelial (RPE) cell injury and are closely related to the development of diabetic retinopathy (DR). More research is needed to confirm the role and mechanism of circ-ADAM9 in DR progression. Methods. High glucose (HG)-induced RPE cells (ARPE-19) were used to mimic the hyperglycemia condition. The expression of circ-ADAM9, microRNA (miR)-338-3p, and coactivator-associated arginine methyltransferase 1 (CARM1) was measured using quantitative real-time PCR. Cell proliferation and apoptosis were determined using MTT assay, EdU assay, and flow cytometry. The protein expression of apoptosis markers and CARM1 was examined by the western blot analysis. Also, MDA level and SOD activity were determined to assess cell oxidative stress. In addition, the interaction between miR-338-3p and circ-ADAM9 or CARM1 was confirmed by dual-luciferase reporter assay and RIP assay. Results. The expression of circ-ADAM9 was upregulated in DR patients and HG-induced ARPE-19 cells. Silenced circ-ADAM9 could promote proliferation and inhibit inflammation, apoptosis, and oxidative stress in HG-induced ARPE9 cells. In terms of mechanism, circ-ADAM9 could sponge miR-338-3p to upregulate CARM1. The inhibitory effect of circ-ADAM9 knockdown on HG-induced ARPE9 cell injury could be reversed by an miR-338-3p inhibitor. As a target of miR-338-3p, CARM1 knockdown could alleviate HG-induced ARPE9 cells’ injury, and its overexpression also could reverse the negatively regulation of miR-338-3p on HG-induced ARPE9 cell injury. Conclusion. Circ-ADAM9 contributed to HG-induced ARPE9 cell injury by regulating miR-338-3p/CARM1 axis, which provided effective targets for DR treatment.

Endotoxin stabilizes protein arginine methyltransferase 4 (PRMT4) protein triggering death of lung epithelia

Lung epithelial cell death is a prominent feature of acute lung injury and acute respiratory distress syndrome (ALI/ARDS), which results from severe pulmonary infection leading to respiratory failure. Multiple mechanisms are believed to contribute to the death of epithelia; however, limited data propose a role for epigenetic modifiers. In this study, we report that a chromatin modulator protein arginine N-methyltransferase 4/coactivator-associated arginine methyltransferase 1 (PRMT4/CARM1) is elevated in human lung tissues with pneumonia and in experimental lung injury models. Here PRMT4 is normally targeted for its degradation by an E3 ubiquitin ligase, SCF^FBXO9, that interacts with PRMT4 via a phosphodegron to ubiquitinate the chromatin modulator at K228 leading to its proteasomal degradation. Bacterial-derived endotoxin reduced levels of SCF^FBXO9 thus increasing PRMT4 cellular concentrations linked to epithelial cell death. Elevated PRMT4 protein caused substantial epithelial cell death via caspase 3-mediated cell death signaling, and depletion of PRMT4 abolished LPS-mediated epithelial cell death both in cellular and murine injury models. These findings implicate a unique molecular interaction between SCF^FBXO9 and PRMT4 and its regulation by endotoxin that impacts the life span of lung epithelia, which may play a key role in the pathobiology of tissue injury observed during critical respiratory illness.

Exendin-4 inhibits high glucose-induced oxidative stress in retinal pigment epithelial cells by modulating the expression and activation of p66Shc

PURPOSE

Activation of p⁶⁶Sch, an adaptor protein, is associated with oxidative stress and apoptosis and has been implicated in the pathogenesis of diabetes-induced retinal pigment epithelial cell damage and diabetic retinopathy. Exendin-4 is a glucagon-like protein that protects against diabetic retinopathy, but the mechanism of action is not well understood. This study aimed to investigate whether Exendin-4 could protect against high glucose-induced oxidative stress and apoptosis in the adult human retinal pigment epithelial-19 cell line by modulating levels and activation of p⁶⁶Shc and to study the underlying mechanisms.

MATERIALS AND METHODS

Adult human retinal pigment epithelial-19 cells were cultured under low (5 µM) or high glucose (100 µM) conditions in the presence or absence of Exendin-4 and with or without pre-incubation with Exendin-9-39, a glucagon-like peptide-1 receptor antagonist.

RESULTS

In a dose-dependent manner, Exendin-4 inhibited high glucose-induced cell death and decreased levels of reactive oxygen species, lactate dehydrogenase release, and single single-stranded DNA. At the most effective concentration (100 µM), Exendin-4 reduced mitochondrial levels of phospho-p⁶⁶Shc (Ser³⁶), cytoplasmic levels of cleaved caspase-3 and cytochrome-c, and NADPH oxidase levels in high glucose-treated cells. It also increased levels of glutathione and magnesium superoxide dismutase and protein levels of magnesium superoxide dismutase but downregulated total protein levels of protein kinase-β and p⁶⁶Shc and inhibited c-Jun N-terminal kinase phosphorylation in both low- and high glucose-treated cells. All these Exendin-4 effects, however, were inhibited by Exendin-9-39.

CONCLUSIONS

Exendin-4 protects against high glucose-induced adult human retinal pigment epithelial-19 cell damage by increasing antioxidants, downregulating NADPH, and inhibiting mitochondria-mediated apoptosis, effects that are associated with the inhibition of c-Jun N-terminal kinase and downregulation of protein kinase-β and p⁶⁶Shc.

PRMT4 drives post-ischemic angiogenesis via YB1/VEGF signaling

Angiogenesis is an integral process in many ischemic disorders, and vascular endothelial growth factor (VEGF) plays an important role in it. Protein arginine methyltransferase 4 (PRMT4), a member of the type I PRMT family, is involved in various biological activities, but its role in endothelial cell (EC) remains elusive. Here, we aimed to investigate the role of PRMT4 in ischemic angiogenesis and explore the possible underlying mechanism. We found that PRMT4 was upregulated in ischemic muscles, and VEGF treatment potentiated its expression in ECs. In vitro, adenovirus-mediated PRMT4 overexpression promoted, while its gene disruption inhibited, EC proliferation, migration, and tube formation. In an in vivo hindlimb ischemia model, forced expression of PRMT4 in ECs showed accelerated blood flow recovery and increased capillary density, whereas its knockdown exhibited the opposite effect. Mechanistically, PRMT4 activated the transcription of VEGF via the interaction with Y-box binding protein-1 (YB1), leading to accelerated angiogenesis. Interestingly, the loss of YB1 partially abolished PRMT4-mediated angiogenesis in vitro. Collectively, our data revealed that PRMT4 promoted angiogenesis through interacting with YB1 and the consequential VEGF upregulation, suggesting that PRMT4 may present as a potential therapeutic target in ischemic angiogenesis. KEY MESSAGES: •PRMT4 is induced by VEGF and upregulated in a hindlimb ischemia model. •PRMT4 promotes angiogenesis both in vitro and in vivo. •PRMT4 regulates VEGF expression through interacting with YB1. •YB1 knockdown retards PRMT4-mediated angiogenic effects in vitro.

Blocking the Spinal Fbxo3/CARM1/K+ Channel Epigenetic Silencing Pathway as a Strategy for Neuropathic Pain Relief

Many epigenetic regulators are involved in pain-associated spinal plasticity. Coactivator-associated arginine methyltransferase 1 (CARM1), an epigenetic regulator of histone arginine methylation, is a highly interesting target in neuroplasticity. However, its potential contribution to spinal plasticity-associated neuropathic pain development remains poorly explored. Here, we report that nerve injury decreased the expression of spinal CARM1 and induced allodynia. Moreover, decreasing spinal CARM1 expression by Fbxo3-mediated CARM1 ubiquitination promoted H3R17me2 decrement at the K+ channel promoter, thereby causing K+ channel epigenetic silencing and the development of neuropathic pain. Remarkably, in naïve rats, decreasing spinal CARM1 using CARM1 siRNA or a CARM1 inhibitor resulted in similar epigenetic signaling and allodynia. Furthermore, intrathecal administration of BC-1215 (a novel Fbxo3 inhibitor) prevented CARM1 ubiquitination to block K+ channel gene silencing and ameliorate allodynia after nerve injury. Collectively, the results reveal that this newly identified spinal Fbxo3-CARM1-K+ channel gene functional axis promotes neuropathic pain. These findings provide essential insights that will aid in the development of more efficient and specific therapies against neuropathic pain.

Activation of Insulin-Like Growth Factor-2 Ameliorates Retinal Cell Damage and Exerts Protection in in vitro Model of Diabetic Retinopathy

BACKGROUND

The major event in the development of diabetes-related blindness and vision impairment is the onset of retinal cell damage. Overall awareness of insulin-like growth factor-2 (IGF2) mechanisms emphasizes its protective behavior in retinal cells that help to provide new information about the development of treatment for retinal complications.

OBJECTIVES

This study analyzes the effect of in vitro changes associated with the cell survival and rescue mechanism in IGF2 inhibition and activation using chromeceptin and IGF2 peptides in ARPE-19 cells cultured in high glucose conditions.

METHOD

Cell death was induced using high glucose (15 mmol/L), IGF2 inhibition was done using chromeceptin (1 µM) (Sigma Aldrich, Saint Louis, MO, USA), and IGF2 activation was done using IGF2 peptide (10 ng/mL). The cells were analyzed for changes in cell proliferation, apoptosis markers, antioxidant molecules, and alteration of cytokines.

RESULTS

The study demonstrated that cells lacking IGF2 exhibited a significant increase in reactive oxygen levels with apoptosis patterns. Also, gene expression analysis by qRT-PCR demonstrated a significant increase in Yes-associated protein 1, CDK2, TNF-α, and BIRC5 genes in cells under high glucose stress and IGF inhibition compared to control. Further, the cytokine analysis also revealed that cells devoid of IGF2 activated an increase in cytokines such as IL-8, CX43, ICAM-1, IL-17, CCL3, and MCP-1 and decreased paraoxonase compared to normal control cells. On the other hand, ARPE-19 cells grown in high glucose shows that IGF2 increases the survival genes with reduced levels of inflammatory cytokines.

CONCLUSION

The finding of the investigation, therefore, shows that the use of IGF2 activators may prevent the progression of ocular dysfunction in the control of diabetes-related complications.

Genetic evidence for partial redundancy between the arginine methyltransferases CARM1 and PRMT6

CARM1 is a protein arginine methyltransferase (PRMT) that acts as a coactivator in a number of transcriptional programs. CARM1 orchestrates this coactivator activity in part by depositing the H3R17me2a histone mark in the vicinity of gene promoters that it regulates. However, the gross levels of H3R17me2a in CARM1 KO mice did not significantly decrease, indicating that other PRMT(s) may compensate for this loss. We thus performed a screen of type I PRMTs, which revealed that PRMT6 can also deposit the H3R17me2a mark in vitro CARM1 knockout mice are perinatally lethal and display a reduced fetal size, whereas PRMT6 null mice are viable, which permits the generation of double knockouts. Embryos that are null for both CARM1 and PRMT6 are noticeably smaller than CARM1 null embryos, providing in vivo evidence of redundancy. Mouse embryonic fibroblasts (MEFs) from the double knockout embryos display an absence of the H3R17me2a mark during mitosis and increased signs of DNA damage. Moreover, using the combination of CARM1 and PRMT6 inhibitors suppresses the cell proliferation of WT MEFs, suggesting a synergistic effect between CARM1 and PRMT6 inhibitions. These studies provide direct evidence that PRMT6 also deposits the H3R17me2a mark and acts redundantly with CARM1.

MicroRNA-203a-3p regulates CoCl2-induced apoptosis in human retinal pigment epithelial cells by targeting suppressor of cytokine signaling 3

PURPOSE

The apoptosis of human retinal pigment epithelial cells (RPEs) plays a critical role in the pathogenesis of diabetic retinopathy (DR), but the molecular mechanisms remain unclear. In this study, we explored the function of miR-203a-3p in CoCl₂-induced RPEs apoptosis.

METHODS

The cellular localization of miR-203a-3p was assessed by in situ hybridization. Luciferase reporter assays were performed to validate that suppressor of cytokine signaling 3(SOCS3) as a direct target of miR-203a-3p. Effects of miR-203a-3p manipulation on RPEs apoptosis were evaluated using TdT-mediated dUTP Nick-End Labeling (TUNEL) and Flow Cytometry. Expression levels of miR-203a-3p was analyzed by RT-PCR, the expression of target proteins was detected by western blot.

RESULTS

miR-203a-3p was found to be located in the RPE layer of the retinas from normal and diabetic rats and SOCS3 was a direct target of miR-203a-3p. miR-203a-3p mimics resulted in improved CoCl₂-induced apoptosis of RPEs, overexpression of SOCS3 or c-Jun N-terminal kinase (JNK) inhibitor SP600125 reversed the pro-apoptotic effect of miR-203a-3p, to a certain extent.

CONCLUSIONS

Our data implied a crucial role of miR-203a-3p as a novel regulator of CoCl₂-induced RPEs apoptosis through SOCS3. Deregulation of miR-203a-3p/SOCS3/JNK/c-Jun cascade thus may serve as an important contributor to RPEs apoptosis in DR.

CARM1 promotes non-small cell lung cancer progression through upregulating CCNE2 expression

The underlying molecular mechanisms of tumorigenesis and progression of non-small cell lung cancer (NSCLC) are not yet fully elucidated. In the present study, invitro functional dissections suggest that siRNA-mediated silencing of CCNE2 profoundly attenuated the proliferative and colony-formative abilities of NSCLC PC9 and HCC827 cells, while forced overexpression of CCNE2 significantly strengthened the proliferative and colony-formative capabilities of these cells. Intriguingly, by ChIP and luciferase reporter gene assays, we observed that CARM1 is recruited to the promoter regions of CCNE2 gene and acts as a transcriptional activator. Mechanically, the asymmetric di-methylation of H3R17me2a and H3R26me2a, as the catalytic substrates of CARM1, were highly enriched at the core promoter regions of CCNE2 gene, thereby activating the expression of CCNE2. In vitro and in vivo rescue experiments demonstrated that restoration of CCNE2 expression significantly abolished the CARM1 shRNA-mediated inhibition of cell proliferation, indicating that the oncogenic function of CARM1, at least partially, depended on the activation of CCNE2. Inhibition of CARM1 enzymatic activity could significantly repress CCNE2 expression in NSCLC cells. In addition, the expression of CARM1 was significantly elevated and positively correlated with CCNE2 levels in 20 cases of NSCLC patients. Both CARM1 and CCNE2 are highly associated with shorter 10-year overall survival of at a large cohort of 461 cases of NSCLC patients from the Kaplan-Meier plotter database. To summarize, these findings provide compelling evidence that CARM1 could promote NSCLC progression via activation of CCNE2, paving the way for future therapeutic strategies in NSCLC.

Long Noncoding RNA MEG3 Inhibits Apoptosis of Retinal Pigment Epithelium Cells Induced by High Glucose via the miR-93/Nrf2 Axis

Diabetic retinopathy (DR) is the leading cause of visual impairment in developed nations. Though plasma microRNA-93 (miR-93) is associated with the risk of DR, the function and regulatory mechanism of miR-93 during DR remains unclear. Blood samples were collected from 12 DR patients and 12 healthy controls. Primary human retinal pigment epithelium (RPE) cells and ARPE-19 cells were cultured in 5 mmol/L or 33 mmol/L d-glucose medium. Long noncoding (lnc) RNA MEG3 and miR-93 expression was detected by real-time quantitative PCR. The effect of MEG3 and miR-93 on high glucose (HG)-induced apoptosis was detected by MTT and flow cytometry. IL-6 and tumor necrosis factor-α levels were detected by enzyme-linked immunosorbent assay. The relationships among MEG3, miR-93, and Nrf2 (also known as NFE2L2) were explored via dual-luciferase reporter assay. lncRNA MEG3 and Nrf2 were decreased and miR-93 was increased in blood samples of DR patients and HG-treated human RPE and ARPE-19 cells. Overexpression of miR-93 inhibited cell proliferation and promoted apoptosis, whereas overexpression of Nrf2 or MEG3 promoted proliferation and suppressed apoptosis and inflammation. In addition, MEG3 targeted miR-93 and down-regulated miR-93. Moreover, miR-93 directly targeted Nrf2 and negatively regulated Nrf2. This study suggests that lncRNA MEG3 depresses HG-induced apoptosis and inflammation of RPE via miR-93/Nrf2 axis, providing a novel perspective on the genesis and development of DR.

Protein Arginine Methyltransferase 4 Regulates Adipose Tissue Lipolysis in Type 1 Diabetic Mice

PURPOSE

Hypertriglyceridemia is considered to be driven by increased lipolysis in type 1 diabetes mellitus (T1DM). However, information regarding the transcriptional circuitry that governs lipolysis remains incomplete in T1DM. Protein arginine methyltransferase 4 (PRMT4), a transcriptional coactivation factor, promotes autophagy and may play an important role in lipolysis. We wonder whether activated lipolysis in T1DM is regulated by PRMT4.

MATERIALS AND METHODS

Recombinant adeno-associated virus was adopted to overexpress PRMT4 in adipose tissue of mice. Streptozotocin (150 mg/kg) was injected intraperitoneally into mice to induce T1DM. Plasma insulin, triglycerides, free fatty acids (FFAs) levels were determined using commercial assay kits. Differentiated adipocytes were applied to verify the regulation of PRMT4 on lipolysis.

RESULTS

Elevated serum triglycerides and FFAs were observed in PRMT4-overexpressed T1DM mice. We also observed that PRMT4 over-expression induced the decrease of fat pads weights and adipocyte sizes. Moreover, expression levels of lipolysis-related molecules, including ATGL, HSL, and MAGL, and HSL phosphorylation levels were increased in PRMT4-overexpressed mice when compared to those of control mice. In vitro, PRMT4 promoted FFAs release and activated HSL phosphorylation, whereas PRMT4 knockdown inhibited these processes.

CONCLUSION

PRMT4 promotes lipolysis and increases serum triglyceride in T1DM.

PRMT4 overexpression aggravates cardiac remodeling following myocardial infarction by promoting cardiomyocyte apoptosis

Myocardial infarction due to coronary artery occlusion leads to adverse cardiac remodeling and heart failure. Apoptotic loss of cardiomyocytes near the ischemia area enlarges infarct area and promotes cardiac remodeling. Protein arginine methyltransferase 4 (PRMT4), a type I protein arginine methyltransferase, is involved in many cellular processes. Here we aimed to investigate the role of PRMT4 in cardiomyocyte apoptosis and myocardial infarction. We found that PRMT4 expression was markedly increased in ischemic heart and hypoxic cardiomyocytes. In vivo, cardiac-specific overexpression of PRMT4 in mice resulted in decreased survival rate, reduced left ventricular function, and aggravated cardiac remodeling following myocardial infarction. Mechanistically, PRMT4 overexpression promoted hypoxia-induced cardiomyocytes apoptosis, while its inhibition abolished these effects. Taken together, our work suggested an essential role of PRMT4 in myocardial infarction and cardiomyocyte apoptosis.

Cisplatin-induced ototoxicity involves interaction of PRMT3 and cannabinoid system

This study investigated whether protein arginine methyltransferase (PRMT) and the cannabinoid system are involved in cisplatin-induced ototoxicity. Cisplatin increased cytosine-cytosine-adenosine-adenosine-thymidine-enhancer-binding protein homologous protein expression. This effect is indicative of an increase in endoplasmic reticulum (ER) stress, and apoptosis signaling including cleavage of caspase-3, caspase-9, poly-adenosine diphosphate-ribose polymerase, and phospho-p53, as well as expression of PRMT3, PRMT4 and fatty acid amide hydrolase (FAAH)1 in House Ear Institute-Organ of Corti 1 (HEI-OC1) cells. In addition, overexpression of PRMT3 or PRMT4 increased the expression of FAAH1 expression, apoptosis, and ER stress signaling in HEI-OC1 cells, whereas PRMT3 or PRMT4 knockdown had the opposite effect. Furthermore, overexpression of FAAH1 increased apoptosis and ER stress, but expression of the PRMTs was unchanged. In addition, a cannabinoid 1 receptor agonist and FAAH inhibitor attenuated apoptosis and ER stress, while cisplatin increased the binding of PRMT3 with FAAH1. In the in vivo experiments, cisplatin was injected intraperitoneally at 6 mg/kg/day into C57BL/6 mice, and 7 days later, this study confirmed that PRMT3 and PRMT4 were upregulated in the organ of Corti of the mice. These results indicate that cisplatin-induced ototoxicity was correlated with PRMT3, PRMT4 and the cannabinoid system, and PRMT3 binding with FAAH1 was increased by cisplatin in HEI-OC1 cells. Therefore, this study suggests that PRMT3 mediates cisplatin-induced ototoxicity via interaction with FAAH1 in vitro and in vivo.

Downregulation of lncRNA BANCR participates in the development of retinopathy among diabetic patients

The long non-coding (lnc)RNA B-Raf proto-oncogene, serine/threonine kinase-activated non-protein coding RNA (BANCR) is a well-characterized oncogene, while its potential functions in other diseases remain elusive. In the present study, the possible association of BANCR with diabetic retinopathy was investigated. A total of 244 patients with diabetes were followed up every 6 months for 8 years to record the occurrence of retinopathy. A total of 38 patients developed diabetic retinopathy. During the follow-up, the plasma levels of lncRNA BANCR decreased in those patients with diabetic retinopathy but not in those with other complications or without any complications. The plasma levels of lncRNA BANCR at 12 months prior to the diagnosis of diabetic retinopathy are able to sufficiently distinguish diabetic retinopathy patients from healthy controls and diabetic patients without any obvious complications. In vitro, high-glucose treatment failed to affect the expression of lncRNA BANCR in the human retinal pigment epithelial cell line ARPE-19. However, lncRNA BANCR overexpression inhibited the apoptosis of ARPE-19 cells under high-glucose conditions. Therefore, it is indicated that lncRNA BANCR participates in the development of retinopathy in diabetic patients through its regulatory role in cell apoptosis, and may serve as a novel prognostic indicator and therapeutic target.

MiR-455-5p ameliorates HG-induced apoptosis, oxidative stress and inflammatory via targeting SOCS3 in retinal pigment epithelial cells

Diabetic retinopathy (DR) remains the leading cause of blindness in adults with diabetes mellitus. Numerous microRNAs (miRNAs) have been identified to modulate the pathogenesis of DR. The main purpose of this study was to evaluate the potential roles of miR-455-5p in high glucose (HG)-treated retinal pigment epithelial (RPE) cells and underlying mechanisms. Our present investigation discovered that the expression of miR-455-5p was apparently downregulated in ARPE-19 cells stimulated with HG. In addition, forced expression of miR-455-5p markedly enhanced cell viability and restrained HG-induced apoptosis accompanied by decreased BCL2-associated X protein (Bax)/B-cell leukemia/lymphoma 2 (Bcl-2) ratio and expression of apoptotic marker cleaved caspase-3 during HG challenged. Subsequently, augmentation of miR-455-5p remarkably alleviated HG-triggered oxidative stress injury as reflected by decreased the production of intracellular reactive oxygen species (ROS) and malondialdehyde (MDA) content as well as NADPH oxidase 4 expression, concomitant with enhanced the activities of superoxide dismutase, catalase, and GPX stimulated with HG. Furthermore, enforced expression of miR-455-5p effectively ameliorated HG-stimulated inflammatory response as exemplified by repressing the secretion of inflammatory cytokines interleukin 1β (IL-1β), IL-6, and tumour necrosis factor-α in ARPE-19 cells challenged by HG. Most importantly, we successfully identified suppressor of cytokine signaling 3 (SOCS3) as a direct target gene of miR-455-5p, and miR-455-5p negatively regulated the expression of SOCS3. Mechanistically, restoration of SOCS3 abrogated the beneficial effects of miR-455-5p on apoptosis, accumulation of ROS, and inflammatory factors production in response to HG. Taken together, these findings demonstrated that miR-455-5p relieved HG-induced damage through repressing apoptosis, oxidant stress, and inflammatory response by targeting SOCS3. The study gives evidence that miR-455-5p may serve as a new potential therapeutic agent for DR treatment.

The co-activator-associated arginine methyltransferase 1 (CARM1) gene is overexpressed in type 2 diabetes

PURPOSE

We examined the expression of a panel of epigenetic enzymes catalyzing histone tails post-transcriptional modifications, together with effectors of metabolic and inflammatory alterations, in type 2 diabetes.

METHODS

Cross-sectional, case-control study of 21 people with type 2 diabetes and 21 matched controls. Total RNA was extracted from white cells and reverse transcribed. PCR primer assays for 84 key genes encoding enzymes known to modify genomic DNA and histones were performed. Western blot was performed on lysates using primary antibodies for abnormally expressed enzymes. Hormones and cytokines were measured by multiplex kits. A Bayesian network was built to investigate the relationships between epigenetic, cytokine, and endocrine variables.

RESULTS

Co-activator-associated aRginine Methyltransferase 1 (CARM1) expression showed a five-fold higher median value, matched by higher protein levels, among patients who also had increased GIP, IL-4, IL-7, IL-13, IL-17, FGF basic, G-CSF, IFN-γ, and TNFα and decreased IP-10. In a Bayesian network approach, CARM1 expression showed a conditional dependence on diabetes, but was independent of all other variables nor appeared to influence any.

CONCLUSIONS

Increased CARM1 expression in type 2 diabetes suggests that epigenetic mechanisms are altered in human diabetes. The impact of lifestyle and pharmacological treatment on regulation of this enzyme should be further investigated.

Targeting epigenetic mechanisms in diabetic wound healing

Impaired wound healing is a major secondary complication of type 2 diabetes that often results in limb loss and disability. Normal tissue repair progresses through discrete phases including hemostasis, inflammation, proliferation, and remodeling. In diabetes, normal progression through these phases is impaired resulting in a sustained inflammatory state and dysfunctional epithelialization in the wound. Due to their plasticity, macrophages play a critical role in the transition from the inflammation phase to the proliferation phase. Diabetes disrupts macrophage function by impairing monocyte recruitment to the wound, reducing phagocytosis, and prohibiting the transition of inflammatory macrophages to an anti-inflammatory state. Diabetes also impedes keratinocyte and fibroblast function during the later phases resulting in impaired epithelialization of the wound. Several recent studies suggest that altered epigenetic regulation of both immune and structural cells in wounds may influence cell phenotypes and healing, particularly in pathologic states, such as diabetes. Specifically, it has been shown that macrophage plasticity during wound repair is partly regulated epigenetically and that diabetes alters this epigenetic regulation and contributes to a sustained inflammatory state. Epigenetic regulation is also known to regulate keratinocyte and fibroblast function during wound repair. In this review, we provide an introduction to the epigenetic mechanisms that regulate tissue repair and highlight recent findings that demonstrate, how epigenetic events are altered during the course of diabetic wound healing.

High-glucose induces retinal pigment epithelium mitochondrial pathways of apoptosis and inhibits mitophagy by regulating ROS/PINK1/Parkin signal pathway

Diabetic retinopathy (DR) seriously endangers human beings' health, uncovering the underlying mechanism might help to cure DR. In this study, we found that the effects of glucose on retinal pigment epithelium (RPE) varies in a dose dependent manner, high-glucose (50mM) promotes reactive oxygen species (ROS) generation and cell apoptosis, inhibits cell mitophagy as well as proliferative abilities, while low-glucose (15mM) induces ROS production and cell mitophagy, but has little impacts on cell apoptosis and proliferation. Of note, the toxic effects of high-glucose (50mM) on RPE are alleviated by ROS scavengers and aggravated by autophagy inhibitor 3-methyladenine (3-MA) or mitophagy inhibitor cyclosporin A (CsA). High-glucose (50mM) induced ROS generation is merely eliminated by ROS scavengers instead of mitophagy or autophagy inhibitor. We also proved that high-glucose (50mM) inhibits cell proliferation and promotes cell apoptosis by regulating ROS mediated inhibition of mitophagy. In addition, mitophagy associated proteins PINK1 and Parkin are downregulated by high-glucose (50mM) or hydrogen peroxide treatments, which are reversed by ROS scavengers. Of note, Knock-down of PINK1 decreases phospharylated Parkin instead of total Parkin levels in RPE. Intriguingly, high-glucose's inhibiting effects on cell mitophagy as well as proliferation and its promoting effects on cell apoptosis are reversed by either PINK1 or Parkin overexpression. Therefore, we concluded that high-glucose promotes RPE apoptosis and inhibits cell proliferation as well as mitophagy by regulating ROS mediated inactivation of ROS/PINK1/Parkin signal pathway.

Curcumin inhibits high glucose‑induced inflammatory injury in human retinal pigment epithelial cells through the ROS‑PI3K/AKT/mTOR signaling pathway

Diabetic retinopathy (DR) is a retinal disease caused by metabolic disorders of glucose tolerance that can lead to irreversible blindness if not adequately treated. Retinal pigment epithelial cell (RPEC) dysfunction contributes to the pathogenesis of DR. In the present study the anti‑inflammatory effect of curcumin (CUR) was investigated in RPECs damaged by high glucose levels. RPEC treated with 30 mmol/l glucose was regarded as high glucose group, and cells treated with 24.4 mmol/l mannitol was set as equivalent osmolarity group. Cell Counting Kit‑8 assay was used to measure RPEC viability, the expression of phosphorylated (p)‑AKT and p‑mammalian target of rapamycin (mTOR) were assessed by western blot, and secretion of tumor necrosis factor (TNF)‑α, interleukin (IL)‑6 and IL‑1β in the culture medium was measured by ELISA. Intracellular reactive oxygen species (ROS) levels were measured by laser scanning confocal microscope. The present data indicated that, compared with mannitol treatment, high glucose treatment reduced RPEC viability, increased TNF‑α, IL‑6 and IL‑1β secretion, increased ROS formation and promoted phosphorylation of AKT and mTOR. The antioxidant N‑acetylcysteine, the phosphoinositide 3‑kinase (PI3K)/AKT inhibitor LY294002 and the mTOR inhibitor rapamycin ameliorated the effects of high glucose. In addition, pretreatment with 10 µmol/l CUR reduced secretion levels of TNF‑α, IL‑6 and IL‑1β, ROS formation and phosphorylation of AKT and mTOR. In conclusion, CUR inhibited high glucose‑induced inflammatory injury in RPECs by interfering with the ROS/PI3K/AKT/mTOR signaling pathway. The present study may reveal the molecular mechanism of CUR inhibition effects to high glucose‑induced inflammatory injury in RPEC.

Epigenetic control of gene regulation during development and disease: A view from the retina

Complex biological processes, such as organogenesis and homeostasis, are stringently regulated by genetic programs that are fine-tuned by epigenetic factors to establish cell fates and/or to respond to the microenvironment. Gene regulatory networks that guide cell differentiation and function are modulated and stabilized by modifications to DNA, RNA and proteins. In this review, we focus on two key epigenetic changes - DNA methylation and histone modifications - and discuss their contribution to retinal development, aging and disease, especially in the context of age-related macular degeneration (AMD) and diabetic retinopathy. We highlight less-studied roles of DNA methylation and provide the RNA expression profiles of epigenetic enzymes in human and mouse retina in comparison to other tissues. We also review computational tools and emergent technologies to profile, analyze and integrate epigenetic information. We suggest implementation of editing tools and single-cell technologies to trace and perturb the epigenome for delineating its role in transcriptional regulation. Finally, we present our thoughts on exciting avenues for exploring epigenome in retinal metabolism, disease modeling, and regeneration.

Integrated bioinformatic changes and analysis of retina with time in diabetic rats

Diabetic retinopathy (DR) is the most common chronic complication of diabetes. It can cause impaired vision and even blindness. However, the pathological mechanism of DR is still unknown. In the present study, we use bioinformatic analysis to reveal the pathological changes of early DR in a streptozotocin (STZ) induced diabetes rat model. The dataset GSE28831 was downloaded from the Gene Expression Omnibus (GEO) database. To clarify the pathological mechanism of early DR, genes which were up-regulated (UP group) or down-regulated (DOWN group) over time were identified. One hundred eighty six genes in the UP group and 85 genes in the DOWN group were defined. There were in total 28 Gene ontology (GO) terms with a P value lower than 0.05 in UP group, including astrocyte development, neutrophil chemotaxis, neutrophil aggregation, mesenchymal cell proliferation and so on. In the DOWN group, there were totally 14 GO terms with a P value lower than 0.05, including visual perception, lens development in camera-type eye, camera-type eye development, bicellular tight junction and so on. Signaling pathways were analyzed with all genes in the UP and DOWN groups, and leukocyte transendothelial migration and tight junction were selected. Protein–protein interaction (PPI) network was constructed and six hub genes Diras3, Actn1, Tssk6, Cnot6l, Tek and Fgf4 were selected with connection degree ≥5. S100a8, S100a9 and Tek may be potential targets for DR diagnosis and treatment. This study provides the basis for the diagnosis and treatment of DR in the future.

Ocular lesions in leptin receptor-deficient medaka (Oryzias latipes)

Ocular lesions in leptin receptor-deficient medaka were examined histopathologically at 10, 28, and 37 weeks post hatching. Leptin receptor-deficient medaka at 28 and 37 weeks old showed hyperglycemia and hypoinsulinemia. Histopathologically, vacuolation, swelling, fragmentation, and liquefaction of the lens fibers and dilatation of the retinal central veins, retinal capillaries, iridal veins and capillaries, and choroidal veins were observed in leptin receptor-deficient medaka at 28 and 37 weeks old. Thinning of the total retina, pigment epithelial layer, layer of rods and cones, outer granular layer, outer plexiform layer, inner granular layer, and inner plexiform layer was observed in leptin receptor-deficient medaka at 28 and 37 weeks compared with in control medaka. These histopathological characteristics in leptin receptor-deficient medaka are similar to characteristics in ocular lesions of rodent models for type II diabetes mellitus, making leptin receptor-deficient medaka a useful model of diabetic cataract and retinopathy.

Dual contribution of TRPV4 antagonism in the regulatory effect of vasoinhibins on blood-retinal barrier permeability: diabetic milieu makes a difference

Breakdown of the blood-retinal barrier (BRB), as occurs in diabetic retinopathy and other chronic retinal diseases, results in vasogenic edema and neural tissue damage, causing vision loss. Vasoinhibins are N-terminal fragments of prolactin that prevent BRB breakdown during diabetes. They modulate the expression of some transient receptor potential (TRP) family members, yet their role in regulating the TRP vanilloid subtype 4 (TRPV4) remains unknown. TRPV4 is a calcium-permeable channel involved in barrier permeability, which blockade has been shown to prevent and resolve pulmonary edema. We found TRPV4 expression in the endothelium and retinal pigment epithelium (RPE) components of the BRB, and that TRPV4-selective antagonists (RN-1734 and GSK2193874) resolve BRB breakdown in diabetic rats. Using human RPE (ARPE-19) cell monolayers and endothelial cell systems, we further observed that (i) GSK2193874 does not seem to contribute to the regulation of BRB and RPE permeability by vasoinhibins under diabetic or hyperglycemic-mimicking conditions, but that (ii) vasoinhibins can block TRPV4 to maintain BRB and endothelial permeability. Our results provide important insights into the pathogenesis of diabetic retinopathy that will further guide us toward rationally-guided new therapies: synergistic combination of selective TRPV4 blockers and vasoinhibins can be proposed to mitigate diabetes-evoked BRB breakdown.

Oxidative stress destabilizes protein arginine methyltransferase 4 via glycogen synthase kinase 3β to impede lung epithelial cell migration

Oxidative stress impacts normal cellular function leading to the pathogenesis of various diseases including pulmonary illnesses. Protein arginine methyltransferase 4 (PRMT4) is critical for normal lung alveolar epithelial cell development; however, the regulation of PRMT4 within such pulmonary diseases has yet to be elucidated. Using biochemical approaches, we uncovered that peroxide (H₂O₂) treatment decreases PRMT4 protein stability in murine lung epithelial (MLE12) cells to impede cell migration. Protein kinase glycogen synthase kinase 3β (GSK-3β) interacts with PRMT4 and catalyzes PRMT4 T132 phosphorylation that protects PRMT4 from ubiquitin proteasomal degradation. H₂O₂ downregulates GSK-3β to reduce PRMT4 at protein level. PRMT4 promotes cell migration and H₂O₂ degrades PRMT4 to inhibit lung epithelial cell migration. These observations demonstrate that oxidative stress destabilizes PRMT4 via GSK-3β signaling to impede lung epithelial cell migration that may hinder the lung repair and regeneration process.

Effects of diabetic retinopathy on the barrier functions of the retinal pigment epithelium

Diabetic retinopathy is a debilitating microvascular complication of diabetes mellitus. A rich literature describes the breakdown of retinal endothelial cells and the inner blood-retinal barrier, but the effects of diabetes on the retinal pigment epithelium (RPE) has received much less attention. RPE lies between the choroid and neurosensory retina to form the outer blood-retinal barrier. RPE's specialized and dynamic barrier functions are crucial for maintaining retinal health. RPE barrier functions include a collection of interrelated structures and activities that regulate the transepithelial movement of solutes, including: diffusion through the paracellular spaces, facilitated diffusion through the cells, active transport, receptor-mediated and bulk phase transcytosis, and metabolic processing of solutes in transit. In the later stages of diabetic retinopathy, the tight junctions that regulate the paracellular space begin to disassemble, but there are earlier effects on the other aspects of RPE barrier function, particularly active transport and metabolic processing. With advanced understanding of RPE-specific barrier functions, and more in vivo-like culture models, the time is ripe for revisiting experiments in the literature to resolve controversies and extend our understanding of how diabetes affects the outer blood-retinal barrier.

Oxidative Stress-Related Mechanisms and Antioxidant Therapy in Diabetic Retinopathy

Diabetic retinopathy (DR) is one of the most common microvascular complications of diabetes and is the leading cause of blindness in young adults. Oxidative stress has been implicated as a critical cause of DR. Metabolic abnormalities induced by high-glucose levels are involved in the development of DR and appear to be influenced by oxidative stress. The imbalance between reactive oxygen species (ROS) production and the antioxidant defense system activates several oxidative stress-related mechanisms that promote the pathogenesis of DR. The damage caused by oxidative stress persists for a considerable time, even after the blood glucose concentration has returned to a normal level. Animal experiments have proved that the use of antioxidants is a beneficial therapeutic strategy for the treatment of DR, but more data are required from clinical trials. The aims of this review are to highlight the improvements to our understanding of the oxidative stress-related mechanisms underlying the development of DR and provide a summary of the main antioxidant therapy strategies used to treat the disease.

High glucose promotes the migration of retinal pigment epithelial cells through increased oxidative stress and PEDF expression

Defects in the outer blood-retinal barrier have significant impact on the pathogenesis of diabetic retinopathy and macular edema. However, the detailed mechanisms involved remain largely unknown. This is, in part, attributed to the lack of suitable animal and cell culture models, including those of mouse origin. We recently reported a method for the culture of retinal pigment epithelial (RPE) cells from wild-type and transgenic mice. The RPE cells are responsible for maintaining the integrity of the outer blood-retinal barrier whose dysfunction during diabetes has a significant impact on vision. Here we determined the impact of high glucose on the function of RPE cells. We showed that high glucose conditions resulted in enhanced migration and increased the level of oxidative stress in RPE cells, but minimally impacted their rate of proliferation and apoptosis. High glucose also minimally affected the cell-matrix and cell-cell interactions of RPE cells. However, the expression of integrins and extracellular matrix proteins including pigment epithelium-derived factor (PEDF) were altered under high glucose conditions. Incubation of RPE cells with the antioxidant N-acetylcysteine under high glucose conditions restored normal migration and PEDF expression. These cells also exhibited increased nuclear localization of the antioxidant transcription factor Nrf2 and ZO-1, reduced levels of β-catenin and phagocytic activity, and minimal effect on production of vascular endothelial growth factor, inflammatory cytokines, and Akt, MAPK, and Src signaling pathways. Thus high glucose conditions promote RPE cell migration through increased oxidative stress and expression of PEDF without a significant effect on the rate of proliferation and apoptosis.

MicroRNA-29 regulates high-glucose-induced apoptosis in human retinal pigment epithelial cells through PTEN

Hyperglycemia or high-glucose (HG)-induced apoptosis in human retinal pigment epithelial (RPE) cells is a characteristic process in diabetic retinopathy. In our study, we examined whether microRNA-29 (miR-29) may regulate HG-induced RPE cell apoptosis. Human RPE cell line, ARPE-19 cells, was treated with various high concentration of glucose in vitro. HG-induced RPE cell apoptosis was examined by terminal deoxynucleotide transferase-mediated dUTP nick end labeling (TUNEL) assay and miR-29 gene expression by quantitative RT-PCR (qRT-PCR). miR-29 was then downregulated in RPE cells, and its effect on HG-induced apoptosis was examined by TUNEL assay and western blot assay on caspase-7 protein. Association of miR-29 on its downstream target, PTEN, in HG-induced RPE cell apoptosis was evaluated by dual-luciferase assay and qRT-PCR. PTEN was silenced in RPE cells. The effects of PTEN downregulation on miR-29-mediated HG-induced RPE cell apoptosis were also examined by TUNEL and western blot assays. HG induced significant apoptosis in RPE cells in a dose-dependent manner. miR-29 was upregulated by HG in RPE cells. miR-29 downregulation protected HG-induced apoptosis and reduced the production of caspase-7 protein in RPE cells. PTEN was shown to be directly downregulated by HG and then upregulated by miR-29 downregulation in RPE cells. Small interfering RNA (siRNA)-mediated PTEN downregulation reversed the protective effect of miR-29 downregulation on HG-induced RPE cell apoptosis. This study demonstrates that miR-29, through inverse association of PTEN, plays an important role in the process of HG-induced apoptosis in RPE cells.

PRMT1 and PRMT4 Regulate Oxidative Stress-Induced Retinal Pigment Epithelial Cell Damage in SIRT1-Dependent and SIRT1-Independent Manners

Oxidative stress-induced retinal pigment epithelial (RPE) cell damage is involved in the progression of diabetic retinopathy. Arginine methylation catalyzed by protein arginine methyltransferases (PRMTs) has emerged as an important histone modification involved in diverse diseases. Sirtuin (SIRT1) is a protein deacetylase implicated in the onset of metabolic diseases. Therefore, we examined the roles of type I PRMTs and their relationship with SIRT1 in human RPE cells under H2O2-induced oxidative stress. H2O2 treatment increased PRMT1 and PRMT4 expression but decreased SIRT1 expression. Similar to H2O2 treatment, PRMT1 or PRMT4 overexpression increased RPE cell damage. Moreover, the H2O2-induced RPE cell damage was attenuated by PRMT1 or PRMT4 knockdown and SIRT1 overexpression. In this study, we revealed that SIRT1 expression was regulated by PRMT1 but not by PRMT4. Finally, we found that PRMT1 and PRMT4 expression is increased in the RPE layer of streptozotocin-treated rats. Taken together, we demonstrated that oxidative stress induces apoptosis both via PRMT1 in a SIRT1-dependent manner and via PRMT4 in a SIRT1-independent manner. The inhibition of the expression of type I PRMTs, especially PRMT1 and PRMT4, and increased SIRT1 could be therapeutic approaches for diabetic retinopathy.

The progress in understanding and treatment of diabetic retinopathy

Diabetic retinopathy is the most frequently occurring complication of diabetes mellitus and remains a leading cause of vision loss globally. Its aetiology and pathology have been extensively studied for half a century, yet there are disappointingly few therapeutic options. Although some new treatments have been introduced for diabetic macular oedema (DMO) (e.g. intravitreal vascular endothelial growth factor inhibitors ('anti-VEGFs') and new steroids), up to 50% of patients fail to respond. Furthermore, for people with proliferative diabetic retinopathy (PDR), laser photocoagulation remains a mainstay therapy, even though it is an inherently destructive procedure. This review summarises the clinical features of diabetic retinopathy and its risk factors. It describes details of retinal pathology and how advances in our understanding of pathogenesis have led to identification of new therapeutic targets. We emphasise that although there have been significant advances, there is still a pressing need for a better understanding basic mechanisms enable development of reliable and robust means to identify patients at highest risk, and to intervene effectively before vision loss occurs.