Targeting the IL-36R Axis: IL-36Ra suppressed retinal neovascularization and leakage by regulating vascular homeostasis and inflammatory pathways

Retinal neovascularization (RNV) represents a major cause of severe visual impairment and is driven by the interplay between pathological angiogenesis, vascular instability, and inflammation. Although anti-vascular endothelial growth factor (VEGF) therapy remains the mainstay of treatment, incomplete response and persistent vascular dysfunction highlight the need for alternative therapeutic strategies. Interleukin-36 receptor antagonist (IL-36Ra), an endogenous antagonist of IL-36 signaling, has emerged as a potential regulator of inflammatory and vascular homeostasis, however, its role in hypoxia-induced RNV remains unclear. The expression of IL-36, IL-36 receptor (IL-36R), and IL-36Ra was assessed by immunofluorescence, qRT-PCR and western blot. Recombinant IL-36Ra (rIL-36Ra) was administered intravitreally to evaluate its effects on RNV, acellular capillary formation, vascular leakage, and non-perfusion. Vascular barrier integrity was examined by analyzing tight junction (TJ) proteins, matrix metalloproteinases (MMP2, MMP9) activity, and tissue inhibitors of metalloproteinases (TIMP1, TIMP2, TIMP3) expression. In vitro, human vascular endothelial cells (HRMVECs) were treated with rIL-36 with or without rIL-36Ra to assess invasion, tube formation, migration, and proliferation, together with pericyte recruitment. Mechanistic studies further examined vascular-stabilizing, pro-angiogenic, and inflammatory signaling pathways. Hypoxia disrupted the IL-36 signaling balance, characterized by increased IL-36/IL-36R expression and reduced IL-36Ra. Intravitreal rIL-36Ra significantly attenuated RNV, acellular capillary formation, vascular leakage and non-perfusion areas. IL-36Ra restored vascular barrier integrity by upregulating ZO-1, ZO-2 and occludin, suppressing MMP2, MMP9 activity, and enhancing TIMP1, TIMP2, TIMP3 expression. In vitro, rIL-36Ra reversed IL-36-induced endothelial invasion, tube formation, migration, and proliferation while promoting pericyte recruitment. Mechanistically, IL-36Ra shifted the vascular microenvironment toward stabilization by activating the platelet-derived growth factor receptor-β (PDGFR-β)/Angiopoietin1 (Ang1)/phosphorylated (p)-Tie2 signaling and inhibiting vascular endothelial growth factor receptor 2 (VEGFR2)/Ang2 signaling. Meanwhile, IL-36Ra attenuated inflammatory factor release through inhibition of the MyD88/MAPK/NF-κB pathway. These findings identified dysregulated IL-36 signaling as an important contributor to hypoxia-induced RNV. IL-36Ra exerted multimodal vascular protection by restoring endothelial barrier integrity, promoting pericyte-associated vascular stabilization, and suppressing angiogenic and inflammatory signaling. Targeting the IL-36/IL-36R axis may therefore provide a promising therapeutic strategy for RNV diseases beyond VEGF intervention. Retinal neovascularization (RNV) occurs when abnormal blood vessels grow in the retina, often in response to insufficient oxygen. These abnormal vessels are fragile, prone to leakage, and associated with inflammation, which can ultimately lead to severe vision loss. Although current treatments mainly target VEGF, a key driver of blood vessel growth, they do not fully correct all of the processes responsible for retinal vascular damage. In this study, we investigated IL-36Ra, a naturally occurring protein that blocks IL-36 signaling. We found that low-oxygen conditions increased IL-36 and its receptor in the retina while reducing the protective protein IL-36Ra, suggesting that an imbalance in this signaling system may contribute to retinal vascular injury. When recombinant IL-36Ra was injected into the eye, abnormal retinal blood vessel growth was reduced. IL-36Ra also decreased vascular leakage, reduced areas with insufficient blood flow, and limited the formation of damaged, cell-free capillaries. Importantly, IL-36Ra strengthened the proteins that maintain the barrier between vascular endothelial cells and regulated enzymes involved in the breakdown of the vascular extracellular environment. Further experiments showed that IL-36Ra enhanced molecular signals associated with vascular stability while suppressing signals that promote abnormal angiogenesis. It also reduced inflammatory signaling through the MyD88/MAPK/NF-κB pathway. Together, our findings suggest that IL-36Ra protects the retina through several complementary mechanisms: suppressing abnormal blood vessel growth, reducing inflammation, strengthening the vascular barrier, and promoting blood vessel stabilization. Targeting IL-36 signaling may therefore provide a new therapeutic approach for retinal neovascular diseases that complements existing anti-VEGF treatments.