Human retinal endothelial cells express functional interleukin-6 receptor

Abstract

Background Interleukin (IL)-6 is an inflammatory cytokine present in the eye during non-infectious uveitis, where it contributes to the progression of inflammation. There are two major IL-6 signaling pathways: classic signaling and trans-signaling. Classic signaling requires cellular expression of the IL-6 receptor (IL-6R), which exists in membrane-bound (mIL-6R) and soluble (sIL-6R) forms. Prevailing dogma is that vascular endothelial cells do not produce IL-6R, relying on trans-signaling during inflammation. However, the literature is inconsistent, including with respect to human retinal endothelial cells. Findings We examined IL-6R transcript and protein expression in multiple primary human retinal endothelial cell isolates, and assessed the effect of IL-6 on the transcellular electrical resistance of monolayers. Using reverse transcription-polymerase chain reaction, IL-6R, mIL-6R and sIL-6R transcripts were amplified in 6 primary human retinal endothelial isolates. Flow cytometry on 5 primary human retinal endothelial cell isolates under non-permeabilizing conditions and following permeabilization demonstrated intracellular stores of IL-6R and the presence of mIL-6R. When measured in real-time, transcellular electrical resistance of an expanded human retinal endothelial cell isolate, also shown to express IL-6R, decreased significantly on treatment with recombinant IL-6 in comparison to non-treated cells across 5 independent experiments. Conclusions Our findings indicate that human retinal endothelial cells produce IL-6R transcript and functional IL-6R protein. The potential for classic signaling in human retinal endothelial cells has implications for the development of therapeutics targeted against IL-6-mediated pathology in non-infectious uveitis.

In-vitro safety assessment of meropenem on human retinal pigment epithelium (RPE)

“…Both IL-1b and IL-6, which are being investigated here, have been implicated in the development of retinal vasculitis caused by other, more common factors. The use of their antagonists has proven successful in the treatment of retinal vasculitis [ 37 , 38 ]. However, it is worth noting that the levels of cytokines observed in in-vitro experiments may differ from those observed in in-vivo examinations, and resultant clinical consequences could not be easily anticipated [ 34 ].…”

Relationship between vitreous interleukin-6 levels and vitreous particles findings on widefield optical coherence tomography in posterior uveitis

“…Other reports have examined where IL-6 is produced, such as the retinal pigment epithelium (RPE), Muller cells or retinal endothelial cells [37][38][39]. IL-6 has been reported to produce vascular endothelial growth factor (VEGF) [40][41][42][43].…”

Inflammatory cytokines as mediators of retinal endothelial barrier dysfunction in non‐infectious uveitis

“…Therefore, it has been suggested that during inflammatory states, sIL‐6R is generated by proteolysis or alternative splicing from mIL‐6R expressed by infiltrating leukocytes, enabling IL‐6 to activate the retinal endothelium through the IL‐6/sIL‐6R/gp130 complex 122,128 . In recent work, we used flow cytometry to demonstrate the presence of mIL‐6 on multiple primary human retinal endothelial cell isolates and demonstrated this protein to be functional in experiments tracking electrical impedance of IL‐6‐treated retinal endothelial cell monolayers 129 …”

“…Elevated intraocular levels of IL‐6 have been reported in cases of posterior uveitis, and IL‐6 blockade has been particularly effective in treating retinal vascular leakage and macular oedema in uveitis 131–135 . However, there has been an ongoing debate on the effect of IL‐6 on retinal endothelial permeability, with several authors describing decreased barrier impedance in the presence of the cytokine, 48,120,129 and others reporting no effect 46,121 . Some investigators have suggested that endothelial permeability is mediated only by trans‐signalling, since co‐administration of sIL‐6R and IL‐6 was necessary to elicit hyperpermeability 122,123 .…”

“…Some investigators have suggested that endothelial permeability is mediated only by trans‐signalling, since co‐administration of sIL‐6R and IL‐6 was necessary to elicit hyperpermeability 122,123 . There also remains some controversy regarding expression of the IL‐6R by the retinal endothelium 121,122,125,126,129 …”