Toll-like receptor (TLR)-2/4 expression in retinal ganglion cells in a high-glucose environment and its implications

Abstract

ABSTRACT. Diabetic retinopathy (DR), a major complication of diabetes mellitus, is the leading cause of adult blindness. The Toll-like receptor (TLR) family is believed to be involved in the pathogenesis and progression of DR. Here, we investigated the expression profiles of TLR-2 and TLR-4 in retinal ganglion cells (RGCs), in an attempt to elucidate the role of these molecules in the etiology of DR. In vitro cultured RGCs were divided into control and high-glucose groups. The mRNA and protein levels of TLR-2, TLR-4, and nuclear factor (NF)-κB were detected by real-time PCR and western blotting. RGCs were further transfected with specific siRNA targeting TLR2/TLR4; the proliferation of transfected RGCs and their tumor necrosis factor (TNF)-α and interleukin (IL)-8 secretory capacity were analyzed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and enzyme-linked immunosorbent assays (ELISA), respectively. In a high-glucose environment, TLR-2/4 expression was significantly upregulated in RGCs (while their viability decreased); additionally, NF-κB expression and secretion of TNF-α and IL-8 were significantly increased. Co-silencing of the TLR-2 and TLR-4 genes inhibited NF-κB expression and TNF-α/IL-8 secretion, while increasing the survival rate of RGCs. Therefore, a high-glucose environment can potentiate the expression of TLR-2 and TLR-4 in RGCs, activate the downstream signaling pathway, and increase the secretion of pro-inflammatory factors, thereby aggravating DR.

Toll-like receptors activation, signaling, and targeting: an overview

“…The expression of TLR-2 was upregulated in obese/T2DM patients and was associated with inflammatory response as assessed by increased serum levels of IL-18 (Mohamed et al, 2016). A high-glucose level could also induce TLR-2 and TLR-4 expression in retinal ganglion cells via increase in the secretion of pro-inflammatory factors in diabetic retinopathy (Zhao et al, 2016).…”

The Role of Microglia in Diabetic Retinopathy: Inflammation, Microvasculature Defects and Neurodegeneration

“…The activation of microglia is determined by extracellular signals, including neuronal damage, chronic neurodegeneration, dying cells, extracellular liposaccharides and nucleic acids, which are recognized by a broad range of receptors [ 82 , 96 ], such as toll-like receptors (TLR) and receptors of advanced glycation end products. These enable microglia to detect pathogens via signaling of the pro-inflammatory nuclear transcription factor NFκB [ 97 ]. Translocation of NFκB is followed by production of cytokines and other inflammatory mediators.…”

“…Decreasing oxidation stress, e.g., via VP10/39 would be a promising therapeutic for DR [ 130 ]. The activation of NFκB leads to further production of cytokines and other inflammatory mediators [ 97 ]. NFκB was increased in activated microglia after hypoxia induction and was required for retinal angiogenesis [ 65 ].…”

Diabetic microangiopathy: Pathogenetic insights and novel therapeutic approaches

“…In addition, TLR-2 and -4 signaling pathways appear to be the main triggers of these inflammatory responses. Recent in vitro studies have shown that high concentrations of glucose significantly increase TLR-2 and TLR-4 mRNA and protein expression in human microvascular ECs, as well as the activation of NF-κB p65, the expression of inflammatory markers such as interleukin (IL)-8, IL-1β, TNF-α, MCP-1, and vascular cell adhesion molecule (VCAM)-1 and intercellular adhesion molecule (ICAM)-1 [64,65]. All these events were reversed by TLR-4 or TLR-2 inhibition, or dual inhibition of these pathways by TLR4/2 inhibitory peptide.…”