Mechanisms of action of prolonged VEGF exposure on the blood-retinal barrier: Implications for the treatment of diabetic macular edema

• Applicants: Dr. Martin Busch; Dr. Heidrun Deißler; Professor Dr. Matus Rehak; Professor Dr. Andreas Stahl
• Subject Area: Ophthalmology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 532772298

Diseases of high socio-economic relevance such as diabetic macular edema are associated with increased leves of vascular endothelial growth factor A (VEGFA) in the vitreous. Therapy with intravitreally injected VEGF-binding proteins is often successful, but the cause of a so-called therapy failure, which is observed in a substantial number of patients, remains unclear. Moreover intravitreal therapy must be repeated regularly, often monthly, therefore the burden on the patient, practitioner, and health care system, as well as the cumulative risks of repeated intravitreal injections, are substantial. By better understanding how elevated intravitreal VEGFA levels lead to macular edema, improved therapeutic approaches can be developed that target the cause rather than later stages of the disease. VEGFA is known to increase the permeability of retinal endothelial cells which are part of the inner blood-retinal barrier. We have shown that such an impairment of the barrier is strongly associated with decreased expression of the tight-junction protein claudin-1. Moreover, our studies have revealed that this dysfunction can be reversed only transiently by specific inhibition of VEGFA-induced signal transduction – an observation that is consistent with the clinical picture of only temporary effects of VEGF antagonists. We also observed that VEGFA alters the expression profile of specific microRNAs in retinal endothelial cells, which may help to explain the mechanism by which the growth factor modulates the inner blood-retinal barrier. Now we want to explore in more detail how long-term exposure with VEGFA results in elevated permeability of retinal endothelial cells in order to identify new and potentially more causal targets for therapy. To this end, we investigate which protein kinases remain activated, which proteins are involved in the degradation of the tight junction protein claudin-1, how the expression of various microRNAs is altered in retinal endothelial cells by long-term exposure to VEGFA and whether barrier impairment can be modulated by miRNA silencing. In this regard, the planned experimental approach mimics the therapy of preexisting macular edema caused by prolonged exposure to VEGFA. Thus, this approach better reflects the clinical reality, in which therapy for macular edema usually starts only after it has existed for some time. Methodologically, an organ-on-chip model is used, which reproduces very well the in vivo situation of retinal endothelial cells under shear stress. An immortalized cell line of retinal endothelial cells as well as primary human retinal endothelial cells, also co-cultured with retinal pericytes are used to ensure a good transferability of the results to clinical practice.

• DFG Programme: Research Grants