Toxic effects of extracellular histones and their neutralization by vitreous in retinal detachment

Abstract

Histones are DNA-binding proteins and are involved in chromatin remodeling and regulation of gene expression. Histones can be released after tissue injuries, and the extracellular histones cause cellular damage and organ dysfunction. Regardless of their clinical significance, the role and relevance of histones in ocular diseases are unknown. We studied the role of histones in eyes with retinal detachment (RD). Vitreous samples were collected during vitrectomy, and the concentration of histone H3 was measured by enzyme-linked immunosorbent assay. The location of the histones and related molecules was examined in a rat RD model. The release of histones and their effects on rat retinal progenitor cells R28 and ARPE-19 were evaluated in vitro. In addition, the protective role of the vitreous body against histones was tested. The intravitreal concentration of histones was higher in eyes with RD (mean, 30.9±9.8 ng/ml) than in control eyes (below the limit of detection, Po0.05). In the rat RD model, histone H3 was observed on the outer side of the detached retina and was associated with photoreceptor death. Histone H3 was released from cultured R28 by oxidative stress. Histones at a concentration 10 mg/ml induced the production of interleukin-8 in ARPE-19 cells (2.5-fold increase, Po0.05) that was mediated through the ERK1/2-and p38 MAPK-dependent pathways and Toll-like receptor 4. Histones were toxic to cells at concentrations of Z20 mg/ml. Vitreous body or hyaluronan decreased toxicity of histones by inhibiting diffusion of histones. These results indicate that histones are released from retinas with RD and may modulate the subretinal microenvironment by functioning as damage-associated molecular pattern molecules, thereby inducing proinflammatory cytokines or cell toxicity. In addition, the important role of the vitreous body and hyaluronan in protecting the retina from these toxic effects is suggested.

Profiles of Inflammatory Cytokines in the Vitreous Fluid from Patients with Rhegmatogenous Retinal Detachment and Their Correlations with Clinical Features

“…Moreover, the amount of detached area and the duration of the RRD may also be related to the severity of the RRD that ultimately leads to the photoreceptor cell death and the development of fibrous proliferation through the upregulated cytokines. The photoreceptor cell death induces the release of intracellular molecules such as histones and high-mobility group box 1 proteins that are known to upregulate the expression of intravitreal IL-8 [9] and MCP-1 [10], respectively. Therefore, the increase of these intravitreal cytokine levels could indicate the level of presumed photoreceptor damage and could potentially have an important impact on the clinical field, as it is important to be able to preoperatively estimate the level of inflammation in the vitreous space in RRD patients.…”

Extracellular histones, cell-free DNA, or nucleosomes: differences in immunostimulation

“…Similarly, several ELISAs have been developed that quantify specific histone subtypes. 11, 18, 81, 83, 91 These assays often make use of polyclonal antibodies raised against histones and it is therefore unlikely that the antibodies used in these assays will solely detect free histones. Alternatively, ELISAs have been developed that specifically detect nucleosomes.…”

Biology, role and therapeutic potential of circulating histones in acute inflammatory disorders

“…These effects were reduced in TLR2/4 knock‐out mice and more pronounced following LPS priming, which increased TLR2/4 mRNA transcription. Low doses of histone H3 (10 μg/mL) have been shown to induce release of IL‐6 and IL‐8 in ARPE‐19 cells, as well as lead to the phosphorylation of ERKs, p38 MAPK and JNK and inhibition of these kinases all resulted in reduced cytokine release 32. Higher doses (50 μg/mL), however, led to cell death in a manner that could not be inhibited using signalling kinase inhibitors.…”

“…Low doses of histone H3 (10 μg/mL) have been shown to induce release of IL-6 and IL-8 in ARPE-19 cells, as well as lead to the phosphorylation of ERKs, p38 MAPK and JNK and inhibition of these kinases all resulted in reduced cytokine release. 32 Higher doses (50 μg/mL), however, led to cell death in a manner that could not be inhibited using signalling kinase inhibitors. Histones also exacerbate ischaemia/reperfusion injury by a TLR9/MyD88-dependent mechanism and enhance extracellular DNA-mediated activation of TLR9 in immune cells.…”