Novel insight into cGAS-STING pathway in ischemic stroke: from pre- to post-disease

Abstract

Ischemic stroke, a primary cause of disability and the second leading cause of mortality, has emerged as an urgent public health issue. Growing evidence suggests that the Cyclic GMP-AMP synthase (cGAS)- Stimulator of interferon genes (STING) pathway, a component of innate immunity, is closely associated with microglia activation, neuroinflammation, and regulated cell death in ischemic stroke. However, the mechanisms underlying this pathway remain inadequately understood. This article comprehensively reviews the existing literature on the cGAS-STING pathway and its multifaceted relationship with ischemic stroke. Initially, it examines how various risk factors and pre-disease mechanisms such as metabolic dysfunction and senescence (e.g., hypertension, hyperglycemia, hyperlipidemia) affect the cGAS-STING pathway in relation to ischemic stroke. Subsequently, we explore in depth the potential pathophysiological relationship between this pathway and oxidative stress, endoplasmic reticulum stress, neuroinflammation as well as regulated cell death including ferroptosis and PANoptosis following cerebral ischemia injury. Finally, it suggests that intervention targeting the cGAS-STING pathway may serve as promising therapeutic strategies for addressing neuroinflammation associated with ischemic stroke. Taken together, this review concludes that targeting the microglia cGAS-STING pathway may shed light on the exploration of new therapeutic strategies against ischemic stroke.

Keywords: cGAS-STING pathway; intervention target; ischemic stroke; microglia; neuroinflammation.

Figure 1

Depiction of the cGAS-STING pathway. Various dsDNA molecules derived from viruses, bacteria, deceased cells, or cellular organelles such as the nucleus and mitochondria, bind to and activate the corresponding sites of the dsDNA sensor cGAS. Subsequently, cGAS catalyzes the synthesis of 2′3′-cGAMP, which binds to the ER adaptor STING. Upon activation, STING translocates from the ER to the Golgi apparatus, where it activates the kinases TBK1 and IKK. These kinases phosphorylate IRF3 and NF-κB, respectively. IRF3 and NF-κB then transcribe pro-inflammatory cytokines in the nucleus, which are subsequently released to activate responsive receptors and initiate an inflammatory cascade response, such as the IFNR-mediated JAK-STAT signal pathway. Ultimately, it regulates the ISRE, thereby promoting the expression of ISGs.

Figure 2

Senescence and atherosclerosis affect vascular endothelial function through cGAS-STING pathway. In Senescence cells, mitochondrial dysfunction, reduced nuDNA stability, and impaired DNA damage repair mechanisms lead to intracellular DNA accumulation, subsequently activating the cGAS-STING pathway. This not only results in the reduction of iNOS and NO, affecting vasodilation, but also promotes SASP production, impacting endothelial cell function. Atherosclerotic plaques lead to endothelial cell damage, elevated Ca²⁺ levels inhibit the suppressive role of STIM1 on the cGAS-STING pathway and also promote AMPK-mediated activation of the cGAS-STING pathway. Furthermore, mtDNA resulting from mitochondrial damage also activates the cGAS-STING pathway.

Figure 3

The connection between cGAS-STING pathway and oxidative stress. Ischemic stroke induces elevated expression of P16 and P53 in neurons within the ischemic region, subsequently modulating the cell cycle through the regulation of Rb and E2f1, leading to DNA damage. On another front, mitochondrial damage also results in increased cytoplasmic mtDNA levels. Furthermore, ROS enhances the resistance of DNA to degradation by nucleases, including DNase II and TREX1, leading to the accumulation of DNA in the cytoplasm. Subsequently, activated STING upregulates NOCA4 expression, leading to ferritinophagy and a surge in ROS production via the Fenton reaction. However, ROS can impede the phosphorylation of STING Cys147, thereby hindering the downstream formation of the protein complex involved in innate immune signaling by inhibiting the transfer of STING from the ER to the Golgi apparatus.

Figure 4

The connection between cGAS–STING pathway and ferroptosis. The cGAS-STING pathway is subject to physiological negative regulation by ferroptosis in multiple respects, while its excessive activation is implicated in the initiation of ferroptosis. STING promotes the upregulation of NCOA4, subsequently inhibiting Ferritin, leading to an elevation in the LIP. This results in lipid peroxidation of the cellular membrane’s PUFA, thereby inducing ferroptos0069s. Additionally, STING promotes the activation of FADS2, which enhances PUFA levels, thereby providing a substrate for lipid peroxidation. However, PUFA can impede STING activation. The infiltration of peripheral CD8+ T cells modulates the function of system Xc- through IFN-γ signaling. This leads to a depletion of glutathione, indirectly inhibiting GPX4 activity, subsequently attenuating GPX4’s promotive effect on downstream STING.

Figure 5

The connection between cGAS-STING pathway and PANoptosis. ZBP1, a sensor protein for PANoptosis, can be induced by the IFN-1 downstream of the cGAS-STING pathway. Importantly, the cGAS-STING pathway not only directly regulates PANoptosis through IFN-1, but also modulates pyroptosis, apoptosis, and necroptosis respectively to regulate PANoptosis. While the cGAS-STING pathway downstream of pro-inflammatory cytokines can promote pyroptosis, it can also regulate Caspase protein-induced apoptosis. Moreover, cGAS-STING mediates necroptosis by interacting with PERK and promoting downstream RIPK phosphorylation.

Figure 6

The HMGB1-NETs-cGAS-STING pathway serves as a mediator for hemorrhagic transformation: A Hypothesis. In ischemic stroke, ischemic neurons release HMGB1, enhancing cGAS’s affinity for the NETs scaffold, which in turn activates the microglial cGAS-STING pathway and induces pro-inflammatory cytokine production. t-PA treatment for ischemic stroke further promotes neutrophil degranulation and NET formation, exacerbating the activation of the microglial cGAS-STING pathway. The released pro-inflammatory cytokines, in conjunction with t-PA, compromise the BBB, increasing its permeability, leading to brain hemorrhage. Furthermore, as neutrophils migrate to the ischemic region and the continuous formation of NETs ensues, this process intensifies, resulting in HT during t-PA treatment for ischemic stroke.