Abstract
Purpose :
Development of novel anti-angiogenic therapies distinct from VEGF is critical for the identification of new treatments for blindness-inducing age-related macular degeneration. Leukemia inhibitory factor (LIF), a member of the IL-6 cytokine family, has recently been identified as a potent endothelial cell (EC) mitogen in vitro and in vivo. Surprisingly, although the same results were seen in vitro for oncostatin M (OSM), another member of the IL-6 family, intravitreal (iv) injection of this cytokine decreased vascular density and inhibited laser-induced CNV in vivo. We hypothesize that LIF and OSM act through distinct mechanisms to exert their mitogenic potential on ECs.
Methods :
Bovine choroidal, aortic, and retinal ECs were treated with various concentrations of LIF and OSM and key signaling mechanisms were tested by western blot and RT-qPCR. siRNA was used to knock-down the main receptors for LIF and OSM. Retinas from mice subjected to LIF and OSM iv injections were flat mounted, and neovascularization and inflammatory cell infiltration were assessed by confocal microscopy.
Results :
OSM promoted proliferation of choroidal and retinal ECs through the JAK-STAT3 pathway. Conversely, OSM inhibited bovine aortic EC growth also via activation of JAK-STAT3 pathway. Interestingly, OSM, but not LIF, was able to upregulate IL-6 mRNA in choroidal and retinal ECs, as opposed to aortic ECs. Moreover, the mitogenic potential of OSM was mediated by different receptors in choroidal and aortic ECs. In vivo, as opposed to LIF, OSM inhibited neovascularization at low concentrations and was associated with an increase macrophage infiltration into the retina. However, high concentrations of OSM were able to stimulate retinal angiogenesis and were associated with reduced macrophage infiltration.
Conclusions :
OSM exerts opposing responses in various EC subtypes via activation of the same signaling pathway. Additionally, OSM signals through different receptors, suggesting that different EC types have unique gene expression patterns, which determines their differential responses to the same stimulus. Moreover, our in vivo data points towards a role for OSM in the recruitment of inflammatory cells such as macrophages to the retina in a concentration-dependent manner. Overall, these data demonstrate that LIF and OSM act through distinct mechanisms in ECs.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.