Abstract
Purpose :
Interleukin-6 (IL-6), a pleiotropic cytokine involved in chronic inflammatory diseases such as diabetic retinopathy, mediates its cellular effects via two distinct signaling pathways, IL-6 classical and IL-6 trans-signaling. IL-6 classical signaling has been associated with neuroprotective effects, whereas, IL-6 trans-signaling has been associated with angiogenesis, one of the detrimental events in diabetic retinopathy. However, the effects of IL-6 trans-signaling on the retinal vasculature have not been tested in the context of diabetic retinopathy, and therefore, were the aim of this study.
Methods :
Primary human retinal endothelial cells (HREC) were isolated from retinas of non-diabetic donors. HRECs were treated with normal (7.8mM) and high (25mM) glucose for 12-96 hours in the presence or absence of recombinant IL-6/sIL-6R (10-50ng/mL) or VEGF-A (10ng/mL). Release of inflammatory and pro-angiogenic cytokines was assessed using multiplex magnetic bead assays. Viability was determined using trypan blue exclusion. The ability of HRECs to form tubular networks was assessed using matrigel.
Results :
Treatment of HRECs with IL-6/sIL-6R (10ng/mL) under normal glucose conditions promoted the release of pro-inflammatory cytokines, such as IL-1b(214.5±84.6pg/mL/mg protein; normal: 99.1±18.6pg/mL/mg protein), TNF-a(25±3.34pg/mL/mg protein; normal: 12.85±5.89pg/mL/mg protein), IL-6 (2600±1572pg/mL/mg protein; normal: 1333±152.8pg/mL/mg protein), and IFN-γ (1753±647.3pg/mL/mg protein; normal: 772.8±275.6pg/mL/mg protein) [p<0.05, n=3]. In addition, IL-6/sIL-6R (10ng/mL) increased cell death from 13.0±2.7% to 25.3±9.4% [p<0.05, n=8]. Higher concentrations of IL-6/sIL-6R (50ng/mL) caused VEGF-A release (2359.7±523.3pg/mL/mg protein; normal: 503.6±163.1pg/mL/mg protein; p<0.05, n=5). Indicating its pro-angiogenic capability, IL-6/sIL-6R (10ng/mL) led to increased tubular network branching. Interestingly, increasing glucose levels did not seem to influence the effects of IL-6/sIL-6R on HREC functions.
Conclusions :
Our results demonstrate that IL-6 trans-signaling majorly affects functional behavior of human retinal endothelial cells. Therefore, targeting the IL-6 trans-signaling pathway will open the way for the development of new therapies to prevent vascular dysfunction in diabetic retinopathy while still maintaining neuroprotective effects of IL-6 itself.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.