Effects of Ranibizumab and Aflibercept on Human Müller Cells and Photoreceptors under Stress Conditions

Trolox aids coenzyme Q10 in neuroprotection against NMDA induced damage via upregulation of VEGF in rat model of glutamate excitotoxicity

Glutamate induced damage to retinal ganglion cells (RGCs) requires tight physiological regulation of the N-methyl-D-aspartate (NMDA) receptors. Previously, studies have demonstrated the neuroprotective abilities of antioxidants like coenzyme Q10 (CoQ10) and vitamin E analogs like α-tocopherol against neuropathies resulting from NMDA insult, but have failed to shed light on the effect of CoQ10 and trolox, a hydrophilic analog of vitamin E, on glaucomatous neurodegeneration. In the current study, we wanted to investigate whether the combined effect of trolox with CoQ10 could alleviate NMDA-induced death of retinal cells while also trying to elucidate the underlying mechanism in relation to the yet unexplained role of vascular endothelial growth factor (VEGF) in NMDA-mediated excitotoxicity. After successful NMDA-induced degeneration, we followed it up with the treatment of combination of Trolox and CoQ10. The structural damage by NMDA was repaired significantly and retina retained structural integrity comparable to levels of control in the treatment group of Trolox and CoQ10. Detection of ROS generation after NMDA insult showed that together, Trolox and CoQ10 could significantly bring down the high levels of free radicals while also rescuing mitochondrial membrane potential (MMP). A significant increase in NMDA receptor Grin2A by CoQ10 alone as well as by CoQ10 and trolox was accompanied by a lowered Grin2B receptor expression, suggesting neuroprotective action of Trolox and CoQ10. Subsequently, lowered VEGFR1 and VEGFR2 receptor expression by NMDA treatment also recovered when subjected to combined treatment of Trolox and CoQ10. Western blot analyses also indicated the same whereby Trolox and CoQ10 could increase the diminished levels of phosphorylated VEGFR2. Immunofluorescence studies also indicated a positive correlation between recovered VEGFR2 and NMDAR2A levels and diminished levels of NMDAR2D, confirming the results obtained by RT-PCR analysis. This is the first report in our knowledge that demonstrates the efficacy of trolox in combination with CoQ10 highlighting the importance of maintaining VEGF levels that are lowered in ocular diseases due to NMDA-related toxicities.

Kdm6a deficiency in microglia/macrophages epigenetically silences Lcn2 expression and reduces photoreceptor dysfunction in diabetic retinopathy

Diabetic retinopathy (DR) is one of the leading causes of severe visual impairment worldwide. However, the role of adaptive immune inflammation driven by microglia/macrophages in DR is not yet well elucidated. Kdm6a is a histone demethylase that removes the trimethyl groups of histones H3K27 and plays important biological roles in activating target genes. To elucidate the role of Kdm6a in microglia/macrophages in diabetic retinas, we established diabetic animal models with conditional knockout mice to investigate the impacts of Kdm6a deficiency. The RNA-seq analysis, mass spectrum examination, immunohistochemistry and detection of enzyme activities were used to elucidate the effect of Kdm6a deletion on gene transcription in microglia/macrophages. The expression of Kdm6a was increased in the retinas of diabetic mice compared to the control group. Loss of Kdm6a in microglia/macrophages ameliorated the diabetes-induced retinal thickness decrease, inflammation, and visual impairment. Kdm6a in microglia/macrophages regulated Lcn2 expression in a demethylase activity-dependent manner and inhibited glycolysis progression in photoreceptor cells through Lcn2. These results suggest that Kdm6a in microglia/macrophages aggravated diabetic retinopathy by promoting the expression of Lcn2 and impairing glycolysis progression in photoreceptor cells.

Selective knockdown of hexokinase 2 in rods leads to age-related photoreceptor degeneration and retinal metabolic remodeling

Photoreceptors, the primary site of phototransduction in the retina, require energy and metabolites to constantly renew their outer segments. They preferentially consume most glucose through aerobic glycolysis despite possessing abundant mitochondria and enzymes for oxidative phosphorylation (OXPHOS). Exactly how photoreceptors balance aerobic glycolysis and mitochondrial OXPHOS to regulate their survival is still unclear. We crossed rhodopsin-Cre mice with hexokinase 2 (HK2)-floxed mice to study the effect of knocking down HK2, the first rate-limiting enzyme in glycolysis, on retinal health and metabolic remodeling. Immunohistochemistry and Western blots were performed to study changes in photoreceptor-specific proteins and key enzymes in glycolysis and the tricarboxylic acid (TCA) cycle. Changes in retinal structure and function were studied by optical coherence tomography and electroretinography. Mass spectrometry was performed to profile changes in ¹³C-glucose-derived metabolites in glycolysis and the TCA cycle. We found that knocking down HK2 in rods led to age-related photoreceptor degeneration, evidenced by reduced expression of photoreceptor-specific proteins, age-related reductions of the outer nuclear layer, photoreceptor inner and outer segments and impaired electroretinographic responses. Loss of HK2 in rods led to upregulation of HK1, phosphorylation of pyruvate kinase muscle isozyme 2, mitochondrial stress proteins and enzymes in the TCA cycle. Mass spectrometry found that the deletion of HK2 in rods resulted in accumulation of ¹³C-glucose along with decreased pyruvate and increased metabolites in the TCA cycle. Our data suggest that HK2-mediated aerobic glycolysis is indispensable for the maintenance of photoreceptor structure and function and that long-term inhibition of glycolysis leads to photoreceptor degeneration.

Quercetin Mitigates Inflammatory Responses Induced by Vascular Endothelial Growth Factor in Mouse Retinal Photoreceptor Cells through Suppression of Nuclear Factor Kappa B

Retinal vascular endothelial growth factor (VEGF) increased by neovascularization is well known as a pathogenic factor in ocular neovascular diseases. However, it is still unclear how retinal neurons are damaged by VEGF. The aims of this study are to demonstrate the inflammatory protein expression regulated by VEGF using mouse photoreceptor-derived cells and the protective effect of quercetin against VEGF-induced inflammatory response. Expression and phosphorylation of protein and expression of mRNA were detected by immunoblot and reverse transcriptase polymerase chain reaction. VEGF-induced degradation of limiting membrane and translocation of nuclear factor kappa B (NF-κB) were analyzed by immunocytochemistry. VEGF treatment activated angiogenic signaling pathway in photoreceptor cells. In addition, adhesion molecules and matrix metalloproteinases were increased in VEGF-treated photoreceptor cells. All these events were reversed by quercetin. Zona occludins-1 and β-catenin decreased by VEGF were recovered by quercetin. NF-κB signaling pathway regulated by VEGF through phosphorylations of mitogen-activated protein kinases (MAPK) and protein kinase B (Akt) was suppressed by quercetin. These results suggest that quercetin suppressed VEGF-induced excessive inflammatory response in retinal photoreceptor cells by inactivation of NF-κB signals through inhibition of MAPKs and Akt. These data may provide a basic information for development of pharmaceuticals or nutraceuticals for treatment of retinal diseases caused by excessive VEGF.