Circular RNAs (circRNAs) represent single-stranded RNA species that contain covalently closed 3′ and 5′ ends that provide them more stability than linear RNA, which has free ends. Emerging evidence indicates that circRNAs perform essential functions in many DNA viruses, including coronaviruses, Epstein–Barr viruses, cytomegalovirus, and Kaposi sarcoma viruses. Recent studies have confirmed that circRNAs are present in viruses, including DNA and RNA viruses, and play various important functions such as evading host immune response, disease pathogenesis, protein translation, miRNA sponges, regulating cell proliferation, and virus replication. Studies have confirmed that circRNAs can be biological signatures or pathological markers for autoimmune diseases, neurological diseases, and cancers. However, our understanding of circRNAs in DNA and RNA viruses is still limited, and functional evaluation of viral and host circRNAs is essential to completely understand their biological functions. In the present review, we describe the metabolism and cellular roles of circRNA, including its roles in various diseases and viral and cellular circRNA functions. Circular RNAs are found to interact with RNA, proteins, and DNA, and thus can modulate cellular processes, including translation, transcription, splicing, and other functions. Circular RNAs interfere with various signaling pathways and take part in vital functions in various biological, physiological, cellular, and pathophysiological processes. We also summarize recent evidence demonstrating cellular and viral circRNA’s roles in DNA and RNA viruses in this growing field of research.

Viral vectors have emerged as powerful tools for delivering and expressing foreign genes, playing a pivotal role in gene therapy. Among these vectors, cytomegalovirus (CMV) stands out as a promising viral vector due to its distinctive attributes including large packaging capacity, ability to achieve superinfection, broad host range, capacity to induce CD8+ T cell responses, lack of integration into the host genome, and other qualities that make it an appealing vector candidate. Engineered attenuated CMV strains such as Towne and AD169 that have a ~15 kb genomic DNA deletion caused by virus passage guarantee human safety. CMV’s large genome enables the efficient incorporation of substantial foreign genes as demonstrated by CMV vector-based therapies for SIV, tuberculosis, cancer, malaria, aging, COVID-19, and more. CMV is capable of reinfecting hosts regardless of prior infection or immunity, making it highly suitable for multiple vector administrations. In addition to its broad cellular tropism and sustained high-level gene expression, CMV triggers robust, virus-specific CD8⁺ T cell responses, offering a significant advantage as a vaccine vector. To date, successful development and testing of murine CMV (MCMV) and rhesus CMV (RhCMV) vectors in animal models have demonstrated the efficacy of CMV-based vectors. These investigations have explored the potential of CMV vectors for vaccines against HIV, cancer, tuberculosis, malaria, and other infectious pathogens, as well as for other gene therapy applications. Moreover, the generation of single-cycle replication CMV vectors, produced by deleting essential genes, ensures robust safety in an immunocompromised population. The results of these studies emphasize CMV’s effectiveness as a gene delivery vehicle and shed light on the future applications of a CMV vector. While challenges such as production complexities and storage limitations need to be addressed, ongoing efforts to bridge the gap between animal models and human translation continue to fuel the optimism surrounding CMV-based vectors. This review will outline the properties of CMV vectors and discuss their future applications as well as possible limitations.

The coronavirus disease 2019 (COVID-19) pandemic has disproportionately affected individuals with pre-existing medical conditions, such as neurocognitive disorders. Premorbid neurocognitive conditions compounded by COVID-19 can escalate into COVID-associated neurological complications, leading to severe illness or even death. As COVID-19 continues to persist and vaccines lose efficacy against emerging variants, individuals with neurocognitive disorders often experience prolonged symptoms that are further exacerbated by repeated breakthrough infections of highly diversified viral variants due to emergence of new viral mutations. Despite the significance of neurocognitive disorders as risk factors for COVID-19-related mortality and long COVID, the underlying causes remain largely unknown. In this study, we report a link between ORF3a expression and COVID-associated neuroinflammation and neurocytotoxicity in postmortem brain tissues from COVID-19 patients. These findings were further verified through neural cell-based in vitro and in vivo animal studies introducing ORF3a either alone or in the context of viral infection. As a membrane-associated protein, ORF3a induces upregulation of Sur1-regulated ion channels, resulting in intracellular Ca ²⁺ influx, apoptosis, and necrosis through both NF-kB-dependent and independent proinflammatory responses in astrocytes. These findings reveal a novel clinical and mechanistic link between ORF3a and Sur1-regulated ion channels, which are highly responsive to neuroinflammatory conditions causing neurodegeneration. Additionally, we have identified a Food and Drug Administration-approved drug, glibenclamide, and a natural antiviral compound glycyrrhizin that effectively mitigates the neuropathological effects of ORF3a, underscoring the therapeutic potential and clinical significance of these findings. IMPORTANCE: Coronavirus disease 2019 (COVID-19) disproportionately affects individuals with pre-existing neurocognitive conditions primarily due to COVID-19-associated neuroinflammation and neurotoxicity (CNN), which can progress to COVID-associated neurological disorders (CANDs), leading to severe illness and mortality. Despite CNN’s significant contribution to CANDs and related morbidity and mortality, its underlying causes remain poorly understood. Our study identifies ORF3a as a key driver of CNN, establishing a direct clinical and functional link between ORF3a and CNN linking to CANDs. Mechanistically, ORF3a disrupts ion homeostasis in astrocytes by promoting Ca² ⁺ influx through Sur1-regulated ion channels, contributing to CNN. Notably, the Food and Drug Administration-approved drug glibenclamide, a Sur1-specific inhibitor, and the natural compound glycyrrhizin effectively mitigate ORF3a-induced neuropathology, highlighting ORF3a as a promising therapeutic target. These findings present a potential strategy to eliminate CNN and prevent CANDs.

Endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) represent fundamental cellular adaptive mechanisms that maintain protein homeostasis and metabolic balance. Many RNA viruses, particularly flaviviruses such as dengue virus (DENV), Zika virus (ZIKV), West Nile virus (WNV), yellow fever virus (YFV), and Japanese encephalitis virus (JEV), extensively remodel the ER to establish replication compartments and assemble progeny virions. This massive reorganization disrupts ER homeostasis, leading to UPR activation. Emerging evidence reveals that flaviviruses not only trigger but also manipulate the three UPR branches—PERK, IRE1, and ATF6—to optimize viral translation, replication, and egress. In parallel, flavivirus infection profoundly alters host lipid metabolism and promotes dynamic changes in lipid droplets (LDs), key organelles that mediate lipid storage and serve as scaffolds for viral replication and assembly. The UPR intimately connects to LD biogenesis through transcriptional and translational programs mediated by XBP1, ATF4, and ATF6, thereby coupling ER stress responses to lipid remodeling and energy homeostasis. This intricate crosstalk between UPR and LDs creates a metabolic and structural niche favorable for viral replication but detrimental to host cell integrity. This review provides a comprehensive analysis of the molecular mechanisms by which flaviviruses exploit ER stress and the UPR to reprogram lipid metabolism and LD dynamics. We highlight the dual role of UPR signaling in promoting adaptive lipid synthesis and initiating cell death under prolonged stress, discuss recent insights into ER–LD interactions during flavivirus infection, and explore therapeutic opportunities targeting UPR–lipid metabolic pathways as broad-spectrum antiviral strategies. Understanding this interconnected network will advance our knowledge of viral pathogenesis and identify new avenues for host-directed antiviral intervention.

5′-Adenosine monophosphate-activated protein kinase (AMPK) is the principal cellular energy sensor that coordinates metabolic adaptation by balancing anabolic and catabolic pathways in response to energic stress. Beyond its canonical role in maintaining energy homeostasis, AMPK has emerged as a central regulator of host–pathogen interactions by integrating lipid metabolism, autophagy, mitochondrial dynamics, oxidative stress, and innate immune signaling. Flaviviruses, including dengue virus, Zika virus, West Nile virus, Japanese encephalitis virus, and yellow fever virus, extensively remodel host metabolism to establish productive infection. As a master regulator of cellular metabolism, AMPK can either restrict or facilitate flavivirus replication in a context-dependent manner by regulating lipid droplet biogenesis, fatty acid synthesis and beta-oxidation, autophagy, mitochondrial homeostasis, and interferon-mediated antiviral responses. Conversely, flaviviruses actively manipulate AMPK signaling and its downstream metabolic networks to promote endoplasmic reticulum remodeling, replication organelle biogenesis, energy production, and immune evasion. In this review, we summarize recent advances in understanding the multifaceted roles of AMPK during flavivirus infection, with an emphasis on its regulation of metabolic reprogramming, organelle remodeling, and antiviral immunity. We further discuss the therapeutic potential of pharmacologically targeting AMPK and its downstream pathways as a host-directed strategy for broad-spectrum antiviral intervention against flaviviruses.