Inhibition of cGAS-STING pathway alleviates neuroinflammation-induced retinal ganglion cell death after ischemia/reperfusion injury

Inactivation of cGAS signaling pathway mediated by TDP-43 deficiency protects microglia from hypoxia/reoxygenation induced injury

BACKGROUND

Microglia are damaged during cerebral ischemia-reperfusion (I/R). This study was performed to investigate the regulatory effect of tAR DNA-binding protein-43 (TDP-43) on microglia after cerebral I/R in vitro and in vivo.

METHOD

The hypoxia/reoxygenation (H/R) treated microglia and rats with middle cerebral artery occlusion surgery were constructed respectively. The TDP-43 expression in brain tissues and microglia of each group was evaluated by qPCR and western blotting methods. Cell viability and cell apoptosis were combined to evaluate the degree of cell injury. As for animal experiments, neurological score and infarct volume were obtained to evaluate neurological injury.

RESULTS

The levels of TDP-43 in the brain tissues of I/R group were higher than that in sham group. Both TDP-43 and Iba1, a typical microglia marker, were expressed in the brain tissues. TDP-43 was also elevated in microglia with H/R treatment. Inhibition of TDP-43 significantly down-regulated neurological deficit scores of rats after I/R surgery, and weakened the H/R treatment induced injury by promoting cell viability, inhibiting cell apoptosis, down-regulating IL-6 and iNOS levels, and up-regulating Arg-1 and IL-10 levels. Inactivation of cGAS pathway mediated by TDP-43 knockdown protects microglia from H/R treatment induced injury.

CONCLUSION

The highly expressed TDP-43 level is associated with cerebral I/R, and inhibition of TDP-43 protects microglia from H/R induced injury through cGAS pathway in vitro and in vivo.

Therapeutic intervention in neuroinflammation for neovascular ocular diseases through targeting the cGAS-STING-necroptosis pathway

The microglia-mediated neuroinflammation have been shown to play a crucial role in the ocular pathological angiogenesis process, but specific immunotherapies for neovascular ocular diseases are still lacking. This study proposed that targeting GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) might be a novel immunotherapy for these angiogenesis diseases. We found a significant upregulation of CGAS and STING genes in the RNA-seq data derived from retinal tissues of the patients with proliferative diabetic retinopathy. In experimental models of ocular angiogenesis including laser-induced choroidal neovascularization (CNV) and oxygen-induced retinopathy (OIR), the cGAS-STING pathway was activated as angiogenesis progressed. Either genetic deletion or pharmacological inhibition of STING resulted in a remarkable suppression of neovascularization in both models. Furthermore, cGAS-STING signaling was specifically activated in myeloid cells, triggering the subsequent RIP1-RIP3-MLKL pathway activation and leading to necroptosis-mediated inflammation. Notably, targeted inhibition of the cGAS-STING pathway with C-176 or SN-011 could significantly suppress pathological angiogenesis in CNV and OIR. Additionally, the combination of C-176 or SN-011 with anti-VEGF therapy led to least angiogenesis, markedly enhancing the anti-angiogenic effectiveness. Together, our findings provide compelling evidence for the importance of the cGAS-STING-necroptosis axis in pathological angiogenesis, highlighting its potential as a promising immunotherapeutic target for treating neovascular ocular diseases.

Targeting cGAS-STING signaling protects retinal ganglion cells from DNA damage-induced cell loss and promotes visual recovery in glaucoma

BACKGROUND

Glaucoma is an optic neurodegenerative disease. Retinal ganglion cells (RGCs) are the fundamental neurons in the trabecular meshwork, and their loss is the main pathological reason for glaucoma. The present study was to investigate mechanisms that regulate RGCs survival.

METHODS

A mouse model of glaucoma was established by injecting hypertonic saline into the limbal veins. RGCs apoptosis was detected by using flow cytometry. Protein expressions in RGCs in response to DNA damage inducer cisplatin treatment were detected by immunofluorescence and western blot. The expressions of inflammatory cytokines were determined using ELISA and real-time PCR.

RESULTS

In the hypertonic saline-injected mice, we found visual function was impaired followed by the increased expression of γH2AX and activation of cGAS-STING signaling. We found that DNA damage inducer cisplatin treatment incurred significant DNA damage, cell apoptosis, and inflammatory response. Mechanistically, cisplatin treatment triggered activation of the cGAS-STING signaling by disrupting mitochondrial function. Suppression of cGAS-STING ameliorated inflammation and protected visual function in glaucoma mice.

CONCLUSIONS

The data demonstrated that cGAS-STING signaling is activated in the damaged retinal ganglion cells, which is associated with increased inflammatory responses, DNA damage, and mitochondrial dysfunction. Targeting the cGAS-STING signaling pathway represents a potential way to alleviate glaucoma-related visual function.

Cytosolic DNA initiates a vicious circle of aging-related endothelial inflammation and mitochondrial dysfunction via STING: the inhibitory effect of Cilostazol

Endothelial senescence, aging-related inflammation, and mitochondrial dysfunction are prominent features of vascular aging and contribute to the development of aging-associated vascular disease. Accumulating evidence indicates that DNA damage occurs in aging vascular cells, especially in endothelial cells (ECs). However, the mechanism of EC senescence has not been completely elucidated, and so far, there is no specific drug in the clinic to treat EC senescence and vascular aging. Here we show that various aging stimuli induce nuclear DNA and mitochondrial damage in ECs, thus facilitating the release of cytoplasmic free DNA (cfDNA), which activates the DNA-sensing adapter protein STING. STING activation led to a senescence-associated secretory phenotype (SASP), thereby releasing pro-aging cytokines and cfDNA to further exacerbate mitochondrial damage and EC senescence, thus forming a vicious circle, all of which can be suppressed by STING knockdown or inhibition. Using next-generation RNA sequencing, we demonstrate that STING activation stimulates, whereas STING inhibition disrupts pathways associated with cell senescence and SASP. In vivo studies unravel that endothelial-specific Sting deficiency alleviates aging-related endothelial inflammation and mitochondrial dysfunction and prevents the development of atherosclerosis in mice. By screening FDA-approved vasoprotective drugs, we identified Cilostazol as a new STING inhibitor that attenuates aging-related endothelial inflammation both in vitro and in vivo. We demonstrated that Cilostazol significantly inhibited STING translocation from the ER to the Golgi apparatus during STING activation by targeting S162 and S243 residues of STING. These results disclose the deleterious effects of a cfDNA-STING-SASP-cfDNA vicious circle on EC senescence and atherogenesis and suggest that the STING pathway is a promising therapeutic target for vascular aging-related diseases. A proposed model illustrates the central role of STING in mediating a vicious circle of cfDNA-STING-SASP-cfDNA to aggravate age-related endothelial inflammation and mitochondrial damage.

AIBP: A New Safeguard against Glaucomatous Neuroinflammation

Glaucoma is a group of ocular diseases that cause irreversible blindness. It is characterized by multifactorial degeneration of the optic nerve axons and retinal ganglion cells (RGCs), resulting in the loss of vision. Major components of glaucoma pathogenesis include glia-driven neuroinflammation and impairment of mitochondrial dynamics and bioenergetics, leading to retinal neurodegeneration. In this review article, we summarize current evidence for the emerging role of apolipoprotein A-I binding protein (AIBP) as an important anti-inflammatory and neuroprotective factor in the retina. Due to its association with toll-like receptor 4 (TLR4), extracellular AIBP selectively removes excess cholesterol from the plasma membrane of inflammatory and activated cells. This results in the reduced expression of TLR4-associated, cholesterol-rich lipid rafts and the inhibition of downstream inflammatory signaling. Intracellular AIBP is localized to mitochondria and modulates mitophagy through the ubiquitination of mitofusins 1 and 2. Importantly, elevated intraocular pressure induces AIBP deficiency in mouse models and in human glaucomatous retina. AIBP deficiency leads to the activation of TLR4 in Müller glia, triggering mitochondrial dysfunction in both RGCs and Müller glia, and compromising visual function in a mouse model. Conversely, restoring AIBP expression in the retina reduces neuroinflammation, prevents RGCs death, and protects visual function. These results provide new insight into the mechanism of AIBP function in the retina and suggest a therapeutic potential for restoring retinal AIBP expression in the treatment of glaucoma.