Programmed Cell Death-Dependent Host Defense in Ocular Herpes Simplex Virus Infection

Herpes simplex keratitis: A brief clinical overview

The aim of our minireview is to provide a brief overview of the diagnosis, clinical aspects, treatment options, management, and current literature available regarding herpes simplex keratitis (HSK). This type of corneal viral infection is caused by the herpes simplex virus (HSV), which can affect several tissues, including the cornea. One significant aspect of HSK is its potential to cause recurrent episodes of inflammation and damage to the cornea. After the initial infection, the HSV can establish a latent infection in the trigeminal ganglion, a nerve cluster near the eye. The virus may remain dormant for extended periods. Periodic reactivation of the virus can occur, leading to recurrent episodes of HSK. Factors triggering reactivation include stress, illness, immunosuppression, or trauma. Recurrent episodes can manifest in different clinical patterns, ranging from mild epithelial involvement to more severe stromal or endothelial disease. The severity and frequency of recurrences vary among individuals. Severe cases of HSK, especially those involving the stroma and leading to scarring, can result in vision impairment or even blindness in extreme cases. The cornea's clarity is crucial for good vision, and scarring can compromise this, potentially leading to visual impairment. The management of HSK involves not only treating acute episodes but also implementing long-term strategies to prevent recurrences and attempt repairs of corneal nerve endings via neurotization. Antiviral medications, such as oral Acyclovir or topical Ganciclovir, may be prescribed for prophylaxis. The immune response to the virus can contribute to corneal damage. Inflammation, caused by the body's attempt to control the infection, may inadvertently harm the corneal tissues. Clinicians should be informed about triggers and advised on measures to minimize the risk of reactivation. In summary, the recurrent nature of HSK underscores the importance of both acute and long-term management strategies to preserve corneal health and maintain optimal visual function.

Baicalin inhibits influenza A (H1N1)-induced pyroptosis of lung alveolar epithelial cells via caspase-3/GSDME pathway

Baicalin (7-d-glucuronic acid-5, 6-dihydroxyflavone) derived from the root of Scutellaria baicalensis used as Traditional Chinese Medicine (TCM) has been revealed to exert potential antiviral activity via various pathways, while the molecular mechanisms have not been fully understood. Pyroptosis, an inflammatory form of programmed cell death (PCD), is reported to play a crucial role in host cell fate during viral infection. In this study, transcriptome analysis of mice lung tissue reveals that baicalin reverses the alterations of the mRNA levels of PCD-associated genes upon H1N1 challenge, with a concomitant decrease in the population of H1N1-induced propidium iodide (PI)⁺ and Annexin Ⅴ⁺ cells. Intriguingly, we find that baicalin contributes to the survival of infected lung alveolar epithelial cells partly through its inhibition of H1N1-induced cell pyroptosis, which is manifested by reduced bubble-like protrusion cells and lactate dehydrogenase (LDH) release. Moreover, the antipyroptosis effect of baicalin in response to H1N1 infection is found to be mediated by its repression on caspase-3/Gasdermin E (GSDME) pathway. Cleaved caspase-3 and N-terminal fragment of GSDME (GSDME-N) are detected in H1N1-infected cell lines and mice lung tissues, which are markedly reversed by baicalin treatment. Furthermore, inhibition of caspase-3/GSDME pathway by caspase-3 inhibitor or siRNA exerts an antipyroptosis effect equal to that of baicalin treatment in infected A549 and BEAS-2B cells, indicating a pivotal role of caspase-3 in the antiviral activities of baicalin. Conclusively, for the first time, we demonstrate that baicalin could effectively suppress H1N1-induced pyroptosis of lung alveolar epithelial cells via caspase-3/GSDME pathway both in vitro and in vivo.

Neutrophil Extracellular Traps and Their Possible Implications in Ocular Herpes Infection

Neutrophil extracellular traps (NETs) are net-like structures released from neutrophils. NETs predominantly contain cell-free deoxyribonucleic acid (DNA) decorated with histones and neutrophil granule proteins. Numerous extrinsic and intrinsic stimuli can induce the formation of NETs such as pathogens, cytokines, immune complexes, microcrystals, antibodies, and other physiological stimuli. The mechanism of NETosis induction can either be ROS-dependent or independent based on the catalase producing activity of the pathogen. NADPH is the source of ROS production, which in turn depends on the upregulation of Ca2+ production in the cytoplasm. ROS-independent induction of NETosis is regulated through toll-like receptors (TLRs). Besides capturing and eliminating pathogens, NETs also aggravate the inflammatory response and thus act as a double-edged sword. Currently, there are growing reports of NETosis induction during bacterial and fungal ocular infections leading to different pathologies, but there is no direct report suggesting its role during herpes simplex virus (HSV) infection. There are innumerable independent reports showing that the major effectors of NETosis are also directly affected by HSV infection, and thus, there is a strong possibility that HSV interacts with these facilitators that can either result in virally mediated modulation of NETosis or NETosis-mediated suppression of ocular HSV infection. This review focuses on the mechanism of NETs formation during different ocular pathologies, with its prime focus on highlighting their potential implications during HSV ocular infections and acting as prospective targets for the treatment of ocular diseases.

Approaches to Evaluating Necroptosis in Virus-Infected Cells

The immune system functions to protect the host from pathogens. To counter host defense mechanisms, pathogens have developed unique strategies to evade detection or restrict host immune responses. Programmed cell death is a major contributor to the multiple host responses that help to eliminate infected cells for obligate intracellular pathogens like viruses. Initiation of programmed cell death pathways during the early stages of viral infections is critical for organismal survival as it restricts the virus from replicating and serves to drive antiviral inflammation immune recruitment through the release of damage-associated molecular patterns (DAMPs) from the dying cell. Necroptosis has been implicated as a critical programmed cell death pathway in a diverse set of diseases and pathological conditions including acute viral infections. This cell death pathway occurs when certain host sensors are triggered leading to the downstream induction of mixed-lineage kinase domain-like protein (MLKL). MLKL induction leads to cytoplasmic membrane disruption and subsequent cellular destruction with the release of DAMPs. As the role of this cell death pathway in human disease becomes apparent, methods identifying necroptosis patterns and outcomes will need to be further developed. Here, we discuss advances in our understanding of how viruses counteract necroptosis, methods to quantify the pathway, its effects on viral pathogenesis, and its impact on cellular signaling.