The type-I interferon (IFN) system represents the first line of defense against viral pathogens. Recognition of the virus initiates complex signaling pathways that result in the transcriptional induction of IFNs, which are then secreted. Secreted IFNs stimulate nearby cells and result in the production of numerous proinflammatory cytokines and antiviral factors. Of particular note, IFN-induced tetratricopeptide repeat (IFIT) proteins have been thoroughly studied because of their antiviral activity against different viral pathogens. Although classically studied as an antiviral protein, IFIT expression has recently been investigated in the context of nonviral pathologies, such as cancer and sepsis. In oral squamous cell carcinoma (OSCC), IFIT1 and IFIT3 promote metastasis, while IFIT2 exhibits the opposite effect. The role of IFIT proteins during bacterial/fungal sepsis is still under investigation, with studies showing conflicting roles for IFIT2 in disease severity. In the setting of viral sepsis, IFIT proteins play a key role in clearing viral infection. As a result, many viral pathogens, such as SARS-CoV-2, employ mechanisms to inhibit the type-I IFN system and promote viral replication. In cancers that are characterized by upregulated IFIT proteins, medications that decrease IFIT expression may reduce metastasis and improve survival rates. Likewise, in cases of viral sepsis, therapeutics that increase IFIT expression may improve viral clearance and reduce the risk of septic shock. By understanding the effect of IFIT proteins in different pathologies, novel therapeutics can be developed to halt disease progression.

Sepsis is among the most dangerous known diseases, resulting from the dysregulation of the innate immune system in a process that is characterized largely by proinflammatory cytokines. It manifests as an excessive immune response to a pathogen and often leads to life-threatening complications such as shock and multiple-organ failure.

Many disease processes result from disruption of physiologic cell signaling pathways. Cancer often develops from the loss of cell cycle regulation, while inflammatory disease results from dysregulated immune activity. Likewise, many microbial infections avoid immune clearance by interfering with cellular antimicrobial pathways. Retinoic Acid (RA) is a dynamic compound, derived from vitamin A, that can regulate various signaling pathways. RA induced cell signaling has proven beneficial against different diseases, such as Acute Promyelocytic Leukemia (APL) and psoriasis. Against APL, RA induces cellular differentiation in cancer cells to restore proper function. In psoriasis, RA downregulates inflammatory pathways, such as NF-κB. RA’s anti-inflammatory properties have also been examined in the context of sepsis, where recent animal studies have shown positive benefits. Along with regulating inflammation, RA exhibits indirect antimicrobial properties. Unlike conventional antimicrobials which target pathogens directly, RA functions as a host-directed therapy (HDT), promoting cell antimicrobial defenses. Recent studies examining RA have shown that it can improve macrophage clearance of microbial pathogens and stimulate the antiviral type-I interferon (IFN) response. RA’s effectiveness has been demonstrated against clinically relevant pathogens, such as Mycobacterium tuberculosis, Aspergillus fumigatus, and Measles virus. In this review, the therapeutic potential of RA to treat various diseases by regulating cell signaling pathways will be explored.

The ongoing COVID-19 pandemic has revealed the shortfalls in our understanding of how to treat coronavirus infections. With almost 7 million case fatalities of COVID-19 globally, the catalog of FDA-approved antiviral therapeutics is limited compared to other medications, such as antibiotics. All-trans retinoic acid (RA), or activated vitamin A, has been studied as a potential therapeutic against coronavirus infection because of its antiviral properties. Due to its impact on different signaling pathways, RA’s mechanism of action during coronavirus infection has not been thoroughly described. To determine RA’s mechanism of action, we examined its effect against a mouse coronavirus, mouse hepatitis virus strain A59 (MHV). We demonstrated that RA significantly decreased viral titers in infected mouse L929 fibroblasts and RAW 264.7 macrophages. The reduced viral titers were associated with a corresponding decrease in MHV nucleocapsid protein expression. Using interferon regulatory factor 3 (IRF3) knockout RAW 264.7 cells, we demonstrated that RA-induced suppression of MHV required IRF3 activity. RNA-seq analysis of wildtype and IRF3 knockout RAW cells showed that RA upregulated calcium/calmodulin (CaM) signaling proteins, such as CaM kinase kinase 1 (CaMKK1). When treated with a CaMKK inhibitor, RA was unable to upregulate IRF activation during MHV infection. In conclusion, our results demonstrate that RA-induced protection against coronavirus infection depends on IRF3 and CaMKK.

Previously characterized as a purely immune mediated disease, sepsis is now recognized as a dysregulated multisystem response against a pathogen. Recognition of the infectious agent by pathogen recognition receptors (PRRs) can initiate activation of the NF-?B signaling pathway and promote the secretion of proinflammatory cytokines.

Translation: The University of Toledo Journal of Medical Sciences is the online journal launched by the University of Toledo. Manuscripts will be considered on the understanding that they report original work and are not under consideration for publication by any other journal. The journal publishes original articles reporting experimental results of basic or clinical research, case reports, and reviews. The journal uses a single blind peer review system and each manuscript, based on the results presented in its original submission, will be evaluated by two student reviewers and one faculty reviewer. This process will provide an opportunity for medical students, graduate students, residents, fellows and faculty to publish research observation in a timely manner.