Cytosolic Receptor Melanoma Differentiation-Associated Protein 5 Mediates Preconditioning-Induced Neuroprotection Against Cerebral Ischemic Injury

A STING agonist preconditions against ischaemic stroke via an adaptive antiviral Type 1 interferon response

Converging lines of inquiry have highlighted the importance of the Type I Antiviral Response not only in defending against viruses but also in preconditioning the brain against ischaemic stroke. Despite this understanding, treatments that foster brain resilience by driving antiviral interferon responses have yet to be developed for human use. Studies from our lab showed that tilorone, the first human antiviral immunomodulatory agent to be developed, robustly preconditioned against stroke in mice and rats. Tilorone is a DNA intercalator; therefore, we hypothesized that it stabilizes cytosolic DNA (released from the mitochondria or the nucleus), thereby activating cGAS (Cyclic GMP-AMP Synthase), a homeostatic DNA sensor, and its downstream pathway. This pathway involves STING (Stimulator of Interferon Genes), TBK1 (Tank Binding Kinase 1), and IRF-3 (Interferon Regulatory Protein-3) and culminates in a protective Type I Interferon Response. We tested this hypothesis by examining the ability of structurally diverse small molecule agonists of STING to protect against oxygen/glucose deprivation in vitro in mouse cortical cultures and in vivo against transient ischaemia in mice. The STING agonists significantly reduced cell death both in vitro and in vivo but failed to do so in STING knockout mice. As expected, STING agonist-induced protection was associated with the induction of interferon related genes and the effects could be abrogated in vitro by a TBK1 inhibitor. Taken together, these findings in mice identify STING as a therapeutic target for preconditioning the brain against ischaemic stroke in vitro and in vivo. Moreover, they suggest that clinically approved STING agonists such as Ganciclovir or α-Mangostin are candidate drugs that could be tested in humans as a prophylactic treatment to alleviate brain injury associated with ischemic stroke.

Pre- and post-conditioning with poly I:C exerts neuroprotective effect against cerebral ischemia injury in animal models: A systematic review and meta-analysis

BACKGROUND

Toll-like receptor (TLR) agonist polyinosinic-polycytidylic acid (poly I:C) exerts neuroprotective effects against cerebral ischemia (CI), but concrete evidence supporting its exact mechanism of action is unclear.

METHODS

We evaluated the neuroprotective role of poly I:C by assessing CI indicators such as brain infarct volume (BIV), neurological deficit score (N.S.), and signaling pathway proteins. Moreover, we performed a narrative review to illustrate the mechanism of action of TLRs and their role in CI. Our search identified 164 articles and 10 met the inclusion criterion.

RESULTS

Poly I:C reduces BIV and N.S. (p = 0.00 and p = 0.03). Interestingly, both pre- and post-conditioning decrease BIV (preC p = 0.04 and postC p = 0.00) and N.S. (preC p = 0.03 and postC p = 0.00). Furthermore, poly I:C upregulates TLR3 [SMD = 0.64; CIs (0.56, 0.72); p = 0.00], downregulates nuclear factor-κB (NF-κB) [SMD = -1.78; CIs (-2.67, -0.88); p = 0.0)], and tumor necrosis factor alpha (TNF-α) [SMD = -16.83; CIs (-22.63, -11.02); p = 0.00].

CONCLUSION

We showed that poly I:C is neuroprotective and acts via the TLR3/NF-κB/TNF-α pathway. Our review indicated that suppressing TLR 2/4 may illicit neuroprotection against CI. Further research on simultaneous activation of TLR3 with poly I:C and suppression of TLR 2/4 might open new vistas for the development of therapeutics against CI.

Structural insights into the distinctive RNA recognition and therapeutic potentials of RIG-I-like receptors

RNA viruses, including the coronavirus, develop a unique strategy to evade the host immune response by interrupting the normal function of cytosolic retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs). RLRs rapidly detect atypical nucleic acids, thereby triggering the antiviral innate immune signaling cascade and subsequently activates the interferons transcription and induction of other proinflammatory cytokines and chemokines. Nonetheless, these receptors are manipulated by viral proteins to subvert the host immune system and sustain the infectivity and replication potential of the virus. RIG-I senses the single-stranded, double-stranded, and short double-stranded RNAs and recognizes the key signature, a 5'-triphosphate moiety, at the blunt end of the viral RNA. Meanwhile, the melanoma differentiation-associated gene 5 (MDA5) is triggered by longer double stranded RNAs, messenger RNAs lacking 2'-O-methylation in their 5'-cap, and RNA aggregates. Therefore, structural insights into the nucleic-acid-sensing and downstream signaling mechanisms of these receptors hold great promise for developing effective antiviral therapeutic interventions. This review highlights the critical roles played by RLRs in viral infections as well as their ligand recognition mechanisms. In addition, we highlight the crosstalk between the toll-like receptors and RLRs and provide a comprehensive overview of RLR-associated diseases as well as the therapeutic potential of RLRs for the development of antiviral-drugs. Moreover, we believe that these RLR-based antivirals will serve as a step toward countering the recent coronavirus disease 2019 pandemic.

Double-Stranded RNA Immunomodulators in Prostate Cancer

Relatively simple, synthetic, double-stranded RNAs can be powerful viral pathogen-associated molecular pattern (PAMP) mimics, inducing a panoply of antiviral and antitumor responses that act at multiple stages of host defense. Their mechanisms of action and uses are beginning to be understood, alone, in combination with other therapeutics, or as novel PAMP-adjuvants providing the critical danger signal that has been missing from most cancer and other modern vaccines. Dose, timing, route of administration combinations, and other clinical variables can have a critical impact on immunogenicity. This article reviews advances in the use of polyinosinic-polycytidylic acid and derivatives, in particular poly-ICLC.

COVID-19: Oxidative Preconditioning as a Potential Therapeutic Approach

This Article summarizes the likely benefits of central nervous system oxidative preconditioning in the reduction of COVID-19 based on its putative pathogenesis. The current COVID-19 outbreak caused a pandemic with millions of infected patients and death cases worldwide. The clinical features of severe acute respiratory syndrome coronavirus (SARS-CoV) was initially linked with respiratory disorders, but recent studies have reported alterations of neurological and cerebrovascular functions in COVID-19 patients. The main viral infection features are related to cell death, inflammation, and cytokine generation, which can be associated with the dysregulation of redox systems or oxidative stress. However, until now, there is no available and effective therapeutic approach. Thus, it is necessary to search for care and adequate protection against the disease, especially for susceptible and vulnerable groups. Preconditioning, a well-known antioxidative stress and anti-inflammatory approach, is protective against many neurological age-related disorders. COVID-19 severity and morbidity have been observed in elderly patients. The aim of the present study is to elucidate the possible protective role of oxidative preconditioning in aged patients at high risk of developing severe COVID-19 complications.

The role of microglia in ischemic preconditioning

Ischemic preconditioning (IPC) is an experimental phenomenon in which a brief ischemic stimulus confers protection against a subsequent prolonged ischemic event. Initially thought to be due to mechanistic changes in neurons, our understanding of IPC has evolved to encompass a global reprogramming of the Central Nervous System (CNS) after transient ischemia/reperfusion that requires innate immune signaling pathways including Toll-like receptors (TLRs) and Type I interferons. Microglia are the CNS resident neuroimmune cells that express these key innate immune receptors. Studies suggest that microglia are required for IPC-mediated neuronal and axonal protection. Multiple paradigms targeting TLRs have converged on a distinctive Type I interferon response in microglia that is critical for preconditioning-mediated protection against ischemia. These pathways can be targeted through administration of TLR agonists, cytokines including interferon-β, and pharmaceutical agents that induce preconditioning through cross-tolerance mechanisms. Transcriptomic analyses and single cell RNA studies point to specific gene expression signatures in microglia that functionally shift these mutable cells to an immunomodulatory or protective phenotype. Although there are technological challenges and gaps in knowledge to overcome, the targeting of specific molecular signaling pathways in microglia is a promising direction for development of novel and effective pharmacotherapies for stroke. Studies on preconditioning in animal models, including nonhuman primates, show promise as prophylactic preconditioning treatments for selected at risk patient populations. In addition, our growing understanding of the mechanisms of IPC-mediated protection is identifying novel cellular and molecular targets for therapeutic interventions that could apply broadly to both acute stroke and chronic vascular cognitive impairment patients.

The efficacy of poly-ICLC against Ebola-Zaire virus (EBOV) infection in mice and cynomolgus monkeys

The potential protection of poly-ICLC (Hiltonol^®) a double stranded RNA (dsRNA) against EBOV infection was assessed with prophylactic and therapeutic administration to wild type and TLR3-negative mice, and in non-human primates (NHPs) by measuring EBOL serum titers, survival extension, and serum liver and kidney function markers. Various doses of aqueous and liposomal poly-ICLC monotherapy provided robust protection in otherwise lethal murine EBOV challenge models, when treatment is started on the day 0 or one day after virus challenge. There was no advantage of liposomal vs. the aqueous poly-ICLC form. Protection appeared to be independent of TLR-3. NHPs treated with poly-ICLC and challenged with EBOV survived longer but eventually succumbed to Ebola infection. Nevertheless, the liver and kidney serum markers were markedly reduced in the infected and treated NHPs. In the two longest surviving poly-ICLC- treated NHPs, the day 10 serum EBOV titer was reduced 2.1 and 30 fold respectively.

Potential Medications or Compounds Acting on Toll-like Receptors in Cerebral Ischemia

Background:

Toll-like receptors play an integral role in the process of inflammatory response after ischemic in-jury. The therapeutic potential acting on TLRs is worth of evaluations. The aim of this review was to introduce readers some potential medications or compounds which could alleviate the ischemic damage via TLRs.

Methods:

Research articles online on TLRs were reviewed. Categorizations were listed according to the follows, methods acting on TLRs directly, modulations of MyD88 or TRIF signaling pathway, and the ischemic tolerance induced by the pre-conditioning or postconditioning with TLR ligands or minor cerebral ischemia via acting on TLRs.

Results:

There are only a few studies concerning on direct effects. Anti-TLR4 or anti-TLR2 therapies may serve as promis-ing strategies in acute events. Approaches targeting on inhibiting NF-κB signaling pathway and enhancing interferon regu-latory factor dependent signaling have attracted great interests. Not only drugs but compounds extracted from traditional Chinese medicine have been used to identify their neuroprotective effects against cerebral ischemia. In addition, many re-searchers have reported the positive therapeutic effects of preconditioning with agonists of TLR2, 3, 4, 7 and 9. Several trails have also explored the potential of postconditioning, which provide a new idea in ischemic treatments. Considering all the evidence above, many drugs and new compounds may have great potential to reduce ischemic insults.

Conclusion:

This review will focus on promising therapies which exerting neuroprotective effects against ischemic injury by acting on TLRs.

The interferon response as a common final pathway for many preconditioning stimuli: unexpected crosstalk between hypoxic adaptation and antiviral defense

Despite major advances in understanding how the brain goes awry in disease, identification of therapeutics for neuroprotection in stroke remains an unsolved challenge. A promising strategy to delineate endogenous mechanisms of neuroprotection is to understand adaptive homeostatic transcription induced by sublethal ischemia. Homeostatic adaptation is defined as the body's restorative responses to stress. Activating adaptive homeostatic pathways can lead to transcription of a panoply of genes involved in cell survival and repair, can suppress pro-death signaling, and can stimulate metabolic changes congruent with survival. All of these mechanisms have been shown to be operative in protection induced by sublethal stress. In this context, central mediators of cellular adaptation to hypoxic and viral stress have been implicated in preconditioning. Here we present data that suggest an unexpected convergence in the pathways triggering adaptation to hypoxia and viral infection leading to preconditioning neuroprotection in the CNS.

PolyICLC Exerts Pro- and Anti-HIV Effects on the DC-T Cell Milieu In Vitro and In Vivo

Myeloid dendritic cells (mDCs) contribute to both HIV pathogenesis and elicitation of antiviral immunity. Understanding how mDC responses to stimuli shape HIV infection outcomes will inform HIV prevention and treatment strategies. The long double-stranded RNA (dsRNA) viral mimic, polyinosinic polycytidylic acid (polyIC, PIC) potently stimulates DCs to focus Th1 responses, triggers direct antiviral activity in vitro, and boosts anti-HIV responses in vivo. Stabilized polyICLC (PICLC) is being developed for vaccine adjuvant applications in humans, making it critical to understand how mDC sensing of PICLC influences HIV infection. Using the monocyte-derived DC (moDC) model, we sought to describe how PICLC (vs. other dsRNAs) impacts HIV infection within DCs and DC-T cell mixtures. We extended this work to in vivo macaque rectal transmission studies by administering PICLC with or before rectal SIVmac239 (SIVwt) or SIVmac239ΔNef (SIVΔNef) challenge. Like PIC, PICLC activated DCs and T cells, increased expression of α4β7 and CD169, and induced type I IFN responses in vitro. The type of dsRNA and timing of dsRNA exposure differentially impacted in vitro DC-driven HIV infection. Rectal PICLC treatment similarly induced DC and T cell activation and pro- and anti-HIV factors locally and systemically. Importantly, this did not enhance SIV transmission in vivo. Instead, SIV acquisition was marginally reduced after a single high dose challenge. Interestingly, in the PICLC-treated, SIVΔNef-infected animals, SIVΔNef viremia was higher, in line with the importance of DC and T cell activation in SIVΔNef replication. In the right combination anti-HIV strategy, PICLC has the potential to limit HIV infection and boost HIV immunity.