Exploring RIP1 Inhibition as Treatment for Glaucoma-Related Retinal Ganglion Cell Death

Glaucoma is a leading cause of irreversible blindness, yet the molecular mechanisms underlying its progression remain only partially understood. A recent industry study by Roche and Genentech scientists sheds light on the role of receptor-interacting protein kinase 1 (RIP1) in mice with retinal pathologies. RIP1 is a critical mediator of multiple signaling pathways that promote inflammatory responses and cell death. Their findings reveal that RIP1 is a promising target for therapeutic intervention, because RIP1-mediated necroptosis is a key contributor to glaucoma pathogenesis. By inhibiting RIP1, they demonstrated significant neuroprotection, reduced inflammation, and preserved visual function in glaucoma models. These results suggest that RIP1 inhibitors could offer a novel strategy for slowing disease progression and preventing vision loss.

Necroptosis in Neurodegenerative Diseases

Glaucoma is characterized by progressive retinal ganglion cell (RGC) degeneration. While the exact mechanisms remain unclear, increasing evidence suggests that neuroinflammation plays a significant role in disease progression. Elevated levels of pro-inflammatory cytokines, such as Tumor Necrosis Factor (TNF), have been detected in the aqueous humor of glaucoma patients, indicating immune system involvement in disease progression.

RGC death in glaucoma can occur via two distinct mechanisms: apoptosis, a caspase-dependent programmed cell death pathway, and necroptosis, a regulated, caspase-independent form of inflammatory cell death. Unlike apoptosis, necroptosis leads to membrane rupture and inflammatory signaling. A key mediator of necroptosis is Receptor-Interacting Protein Kinase 1 (RIP1): RIP1 interacts with RIP3 to phosphorylate Mixed Lineage Kinase Domain-Like Protein (MLKL), ultimately disrupting cell membranes and triggering inflammation. This pathway is largely dependent on TNF and has been implicated in neurodegenerative diseases, including glaucoma.

RIP1 Kinase-Dead Mice in Glaucoma Models

To investigate RIP1’s role in RGC degeneration, the researchers used two established mouse models of glaucoma: First, the optic nerve crush model induces RGC loss through mechanical injury of the optic nerve and primarily triggers apoptosis. Second, the ischemia-reperfusion injury (IRI) model mimics retinal ischemic damage through the blockage of retinal blood supply and results in heightened inflammation and necroptotic RGC death.

To assess the contribution of necroptosis, they generated a RIP1 kinase-dead (RIP1-KD) mouse line. This loss-of-function mutation prevents RIP1 from activating necroptotic signaling. Additionally, they created RIP3-knockout (RIP3-KO) and MLKL-knockout (MLKL-KO) mice to further dissect the pathway.

When compared to wild-type (WT) mice, RIP1-KD mice exhibited significantly higher RGC survival and preserved function in both nerve crush and IRI glaucoma models. RIP3-KO and MLKL-KO mice showed only moderate RGC protection, with significant effects limited to the IRI model, suggesting that RIP1 has additional roles and is involved in further pathways beyond RIP3/MLKL activation. Visual function, assessed via Striatech’s OptoDrum, was better preserved in RIP1-KD mice than in WT mice. However, RIP3-KO and MLKL-KO mice showed no significant improvement in visual acuity. Microglial infiltration was significantly reduced in RIP1-KD mice, indicating a decrease in neuroinflammation. RIP3-KO and MLKL-KO mice exhibited only partial reductions in microglial activation. These findings suggest that RIP1 plays a central role in RGC degeneration, and its inhibition offers neuroprotection beyond simply blocking necroptosis.

Optineurin Mutation Sensitizes RGCs to RIP1-Mediated Necroptosis

Optineurin (OPTN) is a multifunctional protein involved in autophagy, intracellular trafficking, immune regulation, and neuroprotection. Mutations in OPTN, such as E50K, have been linked to severe glaucoma cases, often leading to accelerated RGC loss. Interestingly, OPTN also interacts with TBK1, a known RIP1 inhibitor, raising the question of whether OPTN mutations influence necroptosis.

To test this, the researchers generated OPTN-WT, OPTN-KO, and OPTN-E50K cell lines and exposed them to necroptotic stimuli. OPTN-KO and OPTN-E50K cells showed increased susceptibility to necroptosis, with higher RIP1, RIP3, and MLKL activity, as indicated by heightened phosphorylation levels. This implies that the OPTN-E50K mutation sensitizes RGCs to RIP1-mediated inflammatory cell death, potentially worsening glaucoma progression.

Pharmaceutical Inhibition of RIP1 Reduces RGC Death

Further supporting RIP1 as a therapeutic target, the researchers examined transgenic mice expressing OPTN-WT and OPTN-E50K in their retinas. They found that OPTN-E50K retinas exhibited higher RIP1 phosphorylation, increased TNF-α expression, and greater microglial infiltration. RGC bodies in OPTN-E50K mice appeared shrunken, which is a hallmark of cell death. To prove that these symptoms were RIP1 dependent, the mice were subjected to treatment with a RIP1 inhibitor. After administration, there was a significant reduction in RGC degeneration, supporting the notion that pharmacological targeting of RIP1 may mitigate RGC loss in glaucoma, particularly in patients with OPTN mutations.

Glaucoma Patients Exhibit Increased Necroptosis Markers

To translate these findings to human disease, the researchers analyzed post-mortem glaucoma patient retinas. They observed elevated levels of TNF-α, RIP3, and cleaved caspase-3, indicating both apoptotic and necroptotic cell death. Increased immune activation was evident, with higher levels of neutrophils and leukocytes in the inner retinal layers. These findings reinforce that neuroinflammation and necroptosis play crucial roles in glaucoma pathogenesis.

Clinical potential of RIP1 inhibition

This study provides strong evidence that RIP1 inhibition protects RGCs by reducing necroptosis, preserving retinal function, and mitigating neuroinflammation. RIP1 inhibition increases RGC survival and preserves visual function in glaucoma models. OPTN mutations, particularly E50K, sensitize RGCs to RIP1-mediated necroptosis. Pharmacological inhibition of RIP1 reduces neuroinflammation and RGC loss, making it a potential therapeutic avenue for glaucoma treatment. Given that RIP1-mediated necroptosis is implicated in other neurodegenerative diseases, such as age-related macular degeneration (AMD) and amyotrophic lateral sclerosis (ALS), targeting this pathway could have broad clinical applications. Future research could explore RIP1 inhibitors in human trials to assess their efficacy in preventing vision loss in glaucoma patients.

Blog author: Emilia Kawecka, Technical University of Munich, Student Assistant at Striatech

Original article:
Kim, B.K., Goncharov, T., Archaimbault, S.A. et al. RIP1 inhibition protects retinal ganglion cells in glaucoma models of ocular injury. Cell Death Differ 32, 353–368 (2025).
https://doi.org/10.1038/s41418-024-01390-7