Mechanisms of ß-adrenergic receptors agonists in mediating pro and anti-apoptotic pathways in hyperglycemic Müller cells.

BACKGROUND: The current study aimed to investigate the stimulatory effect of beta-adrenergic receptors (ß-ARs) on brain derived neurotropic factor (BDNF) and cAMP response element binding protein (CREB). METHODS: Human Müller cells were cultured in low and high glucose conditions. Cells were treated with xamoterol (selective agonist for ß1-AR), salmeterol (selective agonist for ß2-AR), isoproterenol (ß-ARs agonist) and propranolol (ß-ARs antagonist), at 20 µM concentration for 24 h. Western Blotting assay was performed for the gene expression analysis. DNA damage was evaluated by TUNEL assay. DCFH-DA assay was used to check the level of reactive oxygen species (ROS). Cytochrome C release was measured by ELISA. RESULTS: Xamoterol, salmeterol and isoproterenol showed no effect on Caspase-8 but it reduced the apoptosis and increased the expression of BDNF in Müller cells. A significant change in the expression of caspase-3 was observed in cells treated with xamoterol and salmeterol as compared to isoproterenol. Xamoterol, salmeterol and isoproterenol significantly decreased the reactive oxygen species (ROS) when treated for 24 hours. Glucose-induced cytochrome c release was disrupted in Müller cells. CONCLUSION: ß-ARs, stimulated by agonist play a protective role in hyperglycemic Müller cells, with the suppression of glucose-induced caspase-3 and cytochrome c release. B-Ars may directly mediate the gene expression of BDNF.

Beta Adrenergic Receptors Stimulation Attenuates Phosphorylation of NF-κB and IκBα in Hyperglycemic Endothelial Cells.

BACKGROUND/AIMS: NF-κB induces transcription of a number of genes, associated with inflammation and apoptosis. In this study, we have investigated the effect of ß-adrenergic receptor stimulation on NF-κB and IκBα in HUVECs. METHODS: Human umbilical vein endothelial cells (HUVECs) were cultured in high and low glucose concentrations. All HUVECs were treated with different concentrations of isoproterenol and propranolol for different time periods. The analytical procedures consisted of Western Blot, ELISA, DCFH-DA and TUNEL assays. RESULTS: Isoproterenol (agonist of a beta-adrenergic receptor) significantly reduced phosphorylation at Ser-536 of NF-κB; and Ser-32 and Ser-36 of IκBα in hyperglycemic HUVECs. Isoproterenol also significantly reduced apoptosis and ROS generation. No effect of IκBα was observed on Tyr-42 phosphorylation. The effect of isoproterenol was reversed by the antagonist propranolol. We also checked if NF-κB inhibitor MG132 causes any change at the level of apoptosis. However, we observed an almost similar effect. CONCLUSION: Given data demonstrates that beta-adrenergic receptors stimulation has a protective effect on HUVECs that might be occuring via NF-κß and IκBα pathway.

Molecular mechanisms of diabetic retinopathy, general preventive strategies, and novel therapeutic targets.

The growing number of people with diabetes worldwide suggests that diabetic retinopathy (DR) and diabetic macular edema (DME) will continue to be sight threatening factors. The pathogenesis of diabetic retinopathy is a widespread cause of visual impairment in the world and a range of hyperglycemia-linked pathways have been implicated in the initiation and progression of this condition. Despite understanding the polyol pathway flux, activation of protein kinase C (KPC) isoforms, increased hexosamine pathway flux, and increased advanced glycation end-product (AGE) formation, pathogenic mechanisms underlying diabetes induced vision loss are not fully understood. The purpose of this paper is to review molecular mechanisms that regulate cell survival and apoptosis of retinal cells and discuss new and exciting therapeutic targets with comparison to the old and inefficient preventive strategies. This review highlights the recent advancements in understanding hyperglycemia-induced biochemical and molecular alterations, systemic metabolic factors, and aberrant activation of signaling cascades that ultimately lead to activation of a number of transcription factors causing functional and structural damage to retinal cells. It also reviews the established interventions and emerging molecular targets to avert diabetic retinopathy and its associated risk factors.

Differential expression and role of hyperglycemia induced oxidative stress in epigenetic regulation of ß1, ß2 and ß3-adrenergic receptors in retinal endothelial cells.

BACKGROUND: Aberrant epigenetic profiles are concomitant with a spectrum of developmental defects and diseases. Role of methylation is an increasingly accepted factor in the pathophysiology of diabetes and its associated complications. This study aims to examine the correlation between oxidative stress and methylation of ß1, ß2 and ß3-adrenergic receptors and to analyze the differential variability in the expression of these genes under hyperglycemic conditions. METHODS: Human retinal endothelial cells were cultured in CSC complete medium in normal (5 mM) or high (25 mM) glucose to mimic a diabetic condition. Reverse transcription PCR and Western Blotting were performed to examine the expression of ß1, ß2 and ß3-adrenergic receptors. For detections, immunocytochemistry was used. Bisulfite sequencing method was used for promoter methylation analysis. Apoptosis was determined by the terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay. Dichlorodihydrofluorescein diacetate (DCFH-DA) assay was used to measure reactive oxygen species (ROS) production in the cells. RESULTS: ß1 and ß3-adrenergic receptors were expressed in retinal endothelial cells while ß2-adrenergic receptor was not detectable both at protein and mRNA levels. Hyperglycemia had no significant effect on ß1 and ß2-adrenergic receptors methylation and expression however ß3-adrenergic receptors showed a significantly higher expression (p < 0.05) and methylation (p < 0.01) in high and low glucose concentration respectively. Apoptosis and oxidative stress were inversely correlated with ß3-adrenergic receptors methylation with no significant effect on ß1 and ß2-adrenergic receptors. ß2-adrenergic receptor was hypermethylated with halted expression. CONCLUSION: Our study demonstrates that ß1 and ß3-adrenergic receptors expressed in human retinal endothelial cells. Oxidative stress and apoptosis are inversely proportional to the extent of promoter methylation, suggesting that methylation loss might be due to oxidative stress-induced DNA damage.