High Glucose-Mediated Tyrosine Nitration of PI3-Kinase: A Molecular Switch of Survival and Apoptosis in Endothelial Cells

Senescent endothelial cells: a potential target for diabetic retinopathy

Diabetic retinopathy (DR) is a diabetic complication that results in visual impairment and relevant retinal diseases. Current therapeutic strategies on DR primarily focus on antiangiogenic therapies, which particularly target vascular endothelial growth factor and its related signaling transduction. However, these therapies still have limitations due to the intricate pathogenesis of DR. Emerging studies have shown that premature senescence of endothelial cells (ECs) in a hyperglycemic environment is involved in the disease process of DR and plays multiple roles at different stages. Moreover, these surprising discoveries have driven the development of senotherapeutics and strategies targeting senescent endothelial cells (SECs), which present challenging but promising prospects in DR treatment. In this review, we focus on the inducers and mechanisms of EC senescence in the pathogenesis of DR and summarize the current research advances in the development of senotherapeutics and strategies that target SECs for DR treatment. Herein, we highlight the role played by key factors at different stages of EC senescence, which will be critical for facilitating the development of future innovative treatment strategies that target the different stages of senescence in DR.

Ferroptosis: new insight into the mechanisms of diabetic nephropathy and retinopathy

Diabetic nephropathy (DN) and diabetic retinopathy (DR) are the most serious and common diabetes-associated complications. DN and DR are all highly prevalent and dangerous global diseases, but the underlying mechanism remains to be elucidated. Ferroptosis, a relatively recently described type of cell death, has been confirmed to be involved in the occurrence and development of various diabetic complications. The disturbance of cellular iron metabolism directly triggers ferroptosis, and abnormal iron metabolism is closely related to diabetes. However, the molecular mechanism underlying the role of ferroptosis in DN and DR is still unclear, and needs further study. In this review article, we summarize and evaluate the mechanism of ferroptosis and its role and progress in DN and DR, it provides new ideas for the diagnosis and treatment of DN and DR.

Gastrodin protects endothelial cells against high glucose-induced injury through up-regulation of PPARβ and alleviation of nitrative stress

In diabetes mellitus (DM), high glucose can result in endothelial cell injury, and then lead to diabetic vascular complications. Gastrodin, as the mainly components of Chinese traditional herb Tianma (Gastrodia elata Bl.), has been widely used for cardiovascular diseases. However, the known of the effect of gastrodin on endothelial cell injury is still limited. In this study, we aimed to investigate the effect and possible mechanism of gastrodin on high glucose-injured human umbilical vein endothelial cells (HUVEC). High glucose (30 mmol/L) treatment caused HUVEC injury. After gastrodin (0.1, 1, 10 μmol/L) treatment, compared with the high glucose group, the cell proliferation ability increased in a dose-dependent manner. Meanwhile, gastrodin (10 μmol/L) up-regulated the mRNA and protein expressions of PPARβ and eNOS, decreased the expressions of iNOS, also reduced the protein expression of 3-nitrotyrosine, and lowed the level of ONOO^-, increased NO content. Both the PPARβ antagonist GSK0660 (1 μmol/L) and the eNOS inhibitor L-NAME (10 μmol/L) were able to block the above effects of gastrodin. In conclusion, gastrodin protectes vascular endothelial cells from high glucose injury, which may be, at least partly, mediated by up-regulating the expression of PPARβ and negatively regulating nitrative stress.

Nitration of cAMP-Response Element Binding Protein Participates in Myocardial Infarction-Induced Myocardial Fibrosis via Accelerating Transcription of Col1a2 and Cxcl12

Aims: Myocardial fibrosis after myocardial infarction (MI) leads to heart failure. Nitration of protein can alter its function. cAMP-response element binding protein (CREB) is a key transcription factor involved in fibrosis. However, little is known about the role of nitrated CREB in MI-induced myocardial fibrosis. Meanwhile, downstream genes of transcription factor CREB in myocardial fibrosis have not been identified. This study aims to verify the hypothesis that nitrated CREB promotes MI-induced myocardial fibrosis via regulating the transcription of Col1a2 and Cxcl12. Results: Our study showed that (1) the level of nitrative stress was elevated and nitrated CREB was higher in the myocardium after MI. Tyr182, 307, and 336 were the nitration sites of CREB; (2) with the administration of peroxynitrite (ONOO^-) scavengers, CREB phosphorylation, nuclear translocation, and binding activity to TORC2 (transducers of regulated CREB-2) were attenuated; (3) the expressions of extracellular matrix (ECM) proteins were upregulated and downregulated in accordance with the expression alteration of CREB both in vitro and in vivo; (4) CREB accelerated transcription of Col1a2 and Cxcl12 after MI directly. With the administration of ONOO^- scavengers, ECM protein expressions were attenuated; meanwhile, the messenger RNA (mRNA) levels of Col1a2 and Cxcl12 were alleviated as well. Innovation and Conclusion: Nitration of transcription factor CREB participates in MI-induced myocardial fibrosis through enhancing its phosphorylation, nuclear translocation, and binding activity to TORCs, among which CREB transcripts Col1a2 and Cxcl12 directly. These data indicated that nitrated CREB might be a potential therapeutic target against MI-induced myocardial fibrosis.

lncRNA ZFAS1 Positively Facilitates Endothelial Ferroptosis via miR-7-5p/ACSL4 Axis in Diabetic Retinopathy

Accumulating evidence has suggested the significant role of long noncoding RNAs (lncRNA) in regulating ferroptosis, while its regulatory mechanism in diabetic retinopathy (DR) remains unelucidated. In this work, we first demonstrated that lncRNA zinc finger antisense 1 (ZFAS1) is upregulated in high glucose-cultured human retinal endothelial cells (hRECs) and ZFAS1 inhibition attenuated high glucose- (HG-) induced ferroptosis, which was evidenced by cell viability, total iron and ferrous iron levels, reactive oxygen species (ROS) level, and Glutathione Peroxidase 4 (GP_X4) expression detection. Mechanistically, we validated that ZFAS1 may act as a competing endogenous RNA by competitively binding with microRNA-7-5p (miR-7-5p) and modulating the expression of its downstream molecule acyl-CoA synthetase long-chain family member 4 (ACSL4), which is now identified as a classic driver gene of ferroptosis process. In conclusion, our results demonstrate that HG-induced ZFAS1 elevation activates ferroptosis in hRECs and the ZFAS1/miR-7-5p/ACSL4 axis may serve as a therapeutic target for endothelial dysfunction in DR.

TPTEP1 suppresses high glucose-induced dysfunction in retinal vascular endothelial cells by interacting with STAT3 and targeting VEGFA

AIMS

Diabetic retinopathy (DR) is a vascular complication of diabetes mellitus that causes visual impairment and blindness. Long noncoding RNAs (lncRNAs) have been revealed to be involved in biological processes of several diseases including DR. We designed this study to investigate the specific role of TPTEP1 in DR.

METHODS

First, we mimicked diabetic conditions with high glucose (HG) stimulation of human retinal vascular endothelial cells (HRVECs) and measured TPTEP1 expression in HG-stimulated HRVECs using RT-qPCR analysis. Then, CCK-8, Transwell, and Matrigel tube formation assays as well as western blot analysis were performed to reveal the biological functions of TPTEP1 in HG-stimulated HRVECs. Subsequently, bioinformatics analysis, RNA pull down, luciferase reporter and ChIP assays as well as western blot analysis evaluated the relationship of TPTEP1, signal transducer and activator of transcription 3 (STAT3) and vascular endothelial growth factor A (VEGFA) in HG-stimulated HRVECs. Finally, to verify the regulation of the TPTEP1/STAT3/VEGFA axis in HG-stimulated HRVECs, rescue experiments were carried out in HG-stimulated HRVECs.

RESULTS

TPTEP1 presented a significant downregulation in HG-stimulated HRVECs. Additionally, TPTEP1 overexpression reduced viability, migration, and angiogenesis in HG-stimulated HRVECs. Moreover, TPTEP1 suppressed phosphorylation and nuclear translocation of STAT3, and thereby downregulated VEGFA mRNA and protein levels. Furthermore, TPTEP1 overexpression-mediated suppression of HG-induced dysfunction in HRVECs was countervailed by STAT3 upregulation or VEGFA upregulation.

CONCLUSIONS

TPTEP1 alleviated HG-induced dysfunction in HRVECs via interacting with STAT3 and targeting VEGFA.

Isoquercitrin protects HUVECs against high glucose‑induced apoptosis through regulating p53 proteasomal degradation

High glucose (HG)-induced endothelial apoptosis serves an important role in the vascular dysfunction associated with diabetes mellitus (DM). It has been reported that isoquercitrin (IQC), a flavonoid glucoside, possesses an anti-DM effect, but the mechanism requires further investigation. The present study investigated the effect of IQC against HG-induced apoptosis in human umbilical vein endothelial cells (HUVECs) and explored its molecular mechanism. HUVECs were treated with 5 or 30 mM glucose for 48 h. Endothelial cell viability was monitored using the Cell Counting Kit-8 assay. Mitochondrial membrane potential was detected by JC-1 staining. Apoptosis was observed by TUNEL staining and flow cytometry. Western blotting was used for the analysis of apoptosis-associated proteins Bax, Bcl-2, cleaved (C)-caspase3, total-caspase3, p53 and phosphorylated p53. Reverse transcription-quantitative PCR was used to analyze the mRNA expression levels of Bax, Bcl-2 and p53. Immunofluorescence staining was utilized to detect the expression levels and distribution of p53 and ubiquitin specific peptidase 10 (USP10) in HUVECs. The results revealed that IQC significantly attenuated HG-induced endothelial apoptosis, as shown by decreased apoptotic cells observed by TUNEL, JC-1 staining and flow cytometry. Moreover, under HG stress, IQC treatment markedly inhibited the increased expression levels of the pro-apoptotic proteins p53, Bax and C-caspase3, and increased the expression levels of the anti-apoptotic protein Bcl-2 in HUVECs. However, the anti-apoptotic effect of IQC against HG was partially blunted by increasing p53 protein levels in vitro. IQC influenced the mRNA expression levels of Bax and Bcl-2 in response to HG, but it did not affect the transcription of p53. Notably, IQC inhibited the HG-induced phosphorylation of p53 at Ser15 and the nuclear transport of USP10, destabilizing p53 and increasing the proteasomal degradation of the p53 protein. The current findings revealed that IQC exerted a protective effect against the HG-induced apoptosis of endothelial cells by regulating the proteasomal degradation of the p53 protein, suggesting that IQC may be used as a novel therapeutic compound to ameliorate DM-induced vascular complications.

Nitration-induced ubiquitination and degradation control quality of ERK1

The mitogen-activated protein kinase ERK1/2 (ERKs, extracellular-regulated protein kinases) plays important roles in a wide spectrum of cellular processes and have been implicated in many disease states. The spatiotemporal regulation of ERK activity has been extensively studied. However, scarce information has been available regarding the quality control of the kinases to scavenge malfunctioning ERKs. Using site-specific mutagenesis and mass spectrometry, we found that the disruption of the conserved H-bond between Y210 and E237 of ERK1 through point mutation at or naturally occurring nitration on Y210 initiates a quality control program dependent on chaperon systems and CHIP (C-terminal of Hsp70-interacting protein)-mediated ubiquitination and degradation. The H-bond is also important for the quality control of ERK2, but through a distinct mechanism. These findings clearly demonstrate how malfunctioning ERKs are eliminated when cells are in certain stress conditions or unhealthy states, and could represent a general mechanism for scavenging malfunctioning kinases in stress conditions.