Targeting NIK-mediated Microglial Polarization: A Novel Therapeutic Strategy for Diabetic Retinopathy

Background Diabetic retinopathy (DR) is a sight-threatening microvascular complication characterized by blood-retina barrier (BRB) disruption. While inflammation is central to early DR, the role of the non-canonical NF-κB pathway remains poorly understood. Methods We established a murine DR model and performed RNA-seq. Retinal microglial activation and the expression of NF-κB-inducing kinase (NIK) were assessed via immunohistochemistry and Western blot. In vitro, we employed AGEs-treated HMC3 microglia and a co-culture system with human retinal microvascular endothelial cells (hRMECs) under NIK knockdown or pharmacological inhibition (using the NIK inhibitor B022). Molecular mechanisms were delineated using ChIP-qPCR and pathway analysis. Results RNA-seq revealed significant enrichment of non-canonical NF-κB signaling in DR. NIK was significantly upregulated in DR retinas, specifically in microglia. NIK knockdown in vitro attenuated microglial activation, suppressed pro-inflammatory M1 markers (iNOS, TNF-α, IL-1β, IL-6), and promoted anti-inflammatory M2 markers (Arg-1, IL-10). Mechanistically, NIK drives microglial polarization via the non-canonical NF-κB pathway (IKKα/p52), with p52 directly binding to promoters of M1/M2 genes. In co-culture, NIK knockdown or B022 treatment rescued hRMECs from AGEs-activated microglia-induced dysfunction, improving viability, reducing apoptosis, and restoring barrier integrity. Intravitreal administration of B022 in DR mice mitigated retinal vascular leakage, reduced apoptosis, and rebalanced M1/M2 polarization. Conclusions Our study identifies NIK as a master regulator of microglial polarization in DR via non-canonical NF-κB signaling. By disrupting BRB integrity, NIK-driven neuroinflammation is a critical pathogenic mechanism. The NIK inhibitor B022 demonstrates strong therapeutic potential, positioning NIK as a novel molecular target for treating diabetic retinopathy.