Targeting Interleukin-6 cis-trans balance in Müller cell dysfunction

Project Summary Diabetic retinopathy (DR) is a sight-threatening neurovasculopathy and the leading cause of blindness in adults. The number of DR patients is growing, but therapeutic approaches are limited, and many patients develop DR despite treatment with anti-VEGF therapies. Increasing evidence suggests that Interleukin-6 (IL-6) plays a prominent role in DR pathogenesis. IL-6, a pleiotropic cytokine, functions through multiple signaling modalities, including “cis-signaling” through a membrane-bound IL-6 receptor and “trans-signaling” through a soluble IL-6 receptor. Studies suggest that the pro-inflammatory actions of IL-6 are mediated by trans-signaling, whereas many regenerative activities of IL-6 are mediated by cis-signaling. We have observed that selective inhibition of IL-6 trans-signaling with the drug sgp130Fc restored normal expression of VEGFA and VEGFB within the inner nuclear layer (INL) of the retina. Müller glial cells (MGCs), a specialized glial cell type critical for retinal homeostasis, are the major source of VEGF production in the mature retina, and, while VEGFA is implicated in both blood-retinal barrier (BRB) breakdown and increased oxidative stress, VEGFB is thought to be protective. Our preliminary studies support the idea that IL-6 cis- and trans-signaling differentially modulate VEGFA and VEGFB expression in MGCs, and that some of the effects of IL-6 on oxidative stress and endothelial (EC) barrier function may be mediated by VEGF signaling. These observations led us to hypothesize that: (i) IL-6 cis- and trans-signaling differentially modulate MGC-derived VEGF expression; and (ii) disruption of the “IL-6 cis-trans balance” contributes to the retinal pathology seen in diabetic retinopathy. We will test this hypothesis with the following Specific Aims: Aim 1 will test the hypothesis that disruption of the IL-6 cis-trans balance in MGCs alters VEGFA and VEGFB expression, leading to MGC oxidative stress and inner BRB breakdown. In this aim, we will: (i) identify the intracellular signaling mechanisms that lead to the differential effects of IL-6 cis- and trans-signaling in MGCs and determine how these intersect with VEGF signaling. (ii) Determine the role of VEGFA and VEGFB in oxidative stress induced by IL-6 trans-signaling, and how IL-6 modulates the VEGF-oxidative stress positive feedback loop in MGCs. (iii) Determine whether IL-6 cis- and trans-signaling affect the MGC-EC interactions that maintain the inner blood-retinal barrier and if any of these effects modulated by VEGF signaling. Aim 2 will test the hypothesis that disruption of the IL-6 cis-trans balance in diabetic mice contributes to VEGF dysregulation and MGC dysfunction. Experiments in this Aim will answer: (i) Do IL-6 cis- and trans-signaling affect MGC-driven VEGF signaling, oxidative damage, and breakdown of the inner blood-retinal barrier in the diabetic mouse retina? (ii) Does treatment with sgp130Fc restore the IL-6 cis-trans balance in vivo, and does this treatment affect the efficacy of anti-VEGF therapy to prevent structural and functional changes in the diabetic retina? Results from these studies have the potential to provide a new therapeutic approach to mitigate the retinal neurovascular pathology associated with diabetes by restoring the IL-6 cis-trans balance in the retina.