Japanese Encephalitis Virus Infection Causes an Imbalance in the Activation of Mitochondrial Fusion/Fission Genes and Triggers the Activation of NOX2-mediated Oxidative Stress and Neuronal Cell Death

The fate of neuronal synapse homeostasis in aging, infection, and inflammation

Neuroplasticity is the brain's ability to reorganize and modify its neuronal connections in response to environmental stimuli, experiences, learning, and disease processes. This encompasses a variety of mechanisms, including changes in synaptic strength and connectivity, the formation of new synapses, alterations in neuronal structure and function, and the generation of new neurons. Proper functioning of synapses, which facilitate neuron-to-neuron communication, is crucial for brain activity. Neuronal synapse homeostasis, which involves regulating and maintaining synaptic strength and function in the central nervous system (CNS), is vital for this process. Disruptions in synaptic balance, due to factors like inflammation, aging, or infection, can lead to impaired brain function. This review highlights the main aspects and mechanisms underlying synaptic homeostasis, particularly in the context of aging, infection, and inflammation.

Flaviviruses manipulate mitochondrial processes to evade the innate immune response

Mitochondria are essential eukaryotic organelles that regulate a range of cellular processes, from metabolism to calcium homeostasis and programmed cell death. They serve as essential platforms for antiviral signaling proteins during the innate immune response to viral infections. Mitochondria are dynamic structures, undergoing frequent fusion and fission processes that regulate various aspects of mitochondrial biology, including innate immunity. Pathogens have evolved sophisticated mechanisms to manipulate mitochondrial morphology and function to facilitate their replication. In this review, we examine the emerging literature on how flaviviruses modulate mitochondrial processes.

Japanese encephalitis virus infection causes reactive oxygen species-mediated skeletal muscle damage

Skeletal muscle wasting is a clinically proven pathology associated with Japanese encephalitis virus (JEV) infection; however, underlying factors that govern skeletal muscle damage are yet to be explored. The current study aims to investigate the pathobiology of skeletal muscle damage using a mouse model of JEV infection. Our study reveals a significant increment in viral copy number in skeletal muscle post-JEV infection, which is associated with enhanced skeletal muscle cell death. Molecular and biochemical analysis confirms NOX2-dependent generation of reactive oxygen species, leading to autophagy flux inhibition and cell apoptosis. Along with this, an alteration in mitochondrial dynamics (change in fusion and fission process) and a decrease in the total number of mitochondria copies were found during JEV disease progression. The study represents the initial evidence of skeletal muscle damage caused by JEV and provides insights into potential avenues for therapeutic advancement.

Intracellular Iron Accumulation Induces Inflammatory and Oxidative Status of the Host After Japanese Encephalitis Viral Infection

The factors mitigating the microglia/macrophage activation and inflammatory damage in Japanese encephalitis (JE) virus infected CNS are still being ascertained. We aim to characterize the changes in iron transporter and iron storage proteins along with inflammatory and oxidative stress-mediated signaling during the JE viral infection. Cortical tissue samples from mice with JE viral infection were processed for biochemical, histological, and molecular analysis. Iron storage protein, i.e., ferritin, was found significantly increased post-JE viral infection, and iron accumulation was noted in cortical tissue. Key proinflammatory associated markers, such as TNF-α, IL-6, and its regulator TLR4, were found to be increased, while SOCS1 (anti-inflammatory regulator) transcription decreased with increased levels of oxidative stress markers NOX2-mediated NF-ΚB/p65 and protein carbonyl. Furthermore, it is noted that hepcidin level increased and ferroportin level decreased, and iron transporter gene expression got imbalanced after JE viral infection. This observation was further confirmed by deferoxamine (DFO) treatment to JE viral infection mice model, where the decline in hepcidin transcription level and iron load in cortical tissue of JE viral infected animals was noted. However, no change was found in the ferroportin level compared to JE viral infected animals. Together, these findings suggest that iron overload and hepcidin-ferroportin regulation are involved in JE viral infection disease pathologies and associated with the inflammatory and oxidative status of the host during infection.

Involvement of NOX2-derived ROS in human hepatoma HepG2 cell death induced by Entamoeba histolytica

Entamoeba histolytica is an enteric tissue-invasive protozoan parasite causing amoebic colitis and liver abscesses in humans. Amoebic contact with host cells activates intracellular signaling pathways that lead to host cell death via generation of caspase-3, calpain, Ca2+ elevation, and reactive oxygen species (ROS). We previously reported that various NADPH oxidases (NOXs) are responsible for ROS-dependent death of various host cells induced by amoeba. In the present study, we investigated the specific NOX isoform involved in ROS-dependent death of hepatocytes induced by amoebas. Co-incubation of hepatoma HepG2 cells with live amoebic trophozoites resulted in remarkably increased DNA fragmentation compared to cells incubated with medium alone. HepG2 cells that adhered to amoebic trophozoites showed strong dichlorodihydrofluorescein diacetate (DCF-DA) fluorescence, suggesting intracellular ROS accumulation within host cells stimulated by amoebic trophozoites. Pretreatment of HepG2 cells with the general NOX inhibitor DPI or NOX2-specific inhibitor GSK 2795039 reduced Entamoeba-induced ROS generation. Similarly, Entamoeba-induced LDH release from HepG2 cells was effectively inhibited by pretreatment with DPI or GSK 2795039. In NOX2-silenced HepG2 cells, Entamoeba-induced LDH release was also significantly inhibited compared with controls. Taken together, the results support an important role of NOX2-derived ROS in hepatocyte death induced by E. histolytica.

Alteration in mitochondrial dynamics promotes the proinflammatory response of microglia and is involved in cerebellar dysfunction of young and aged mice following LPS exposure

Cerebellar dysfunction is implicated in impaired motor coordination and balance, thus disturbing the dynamics of sensorimotor integration. Neuroinflammation and aging could be prominent contributors to cerebellar aberration. Additionally, changes in mitochondrial dynamics may precede microglia activation in several chronic neurodegenerative diseases; however, the underlying mechanism remains largely unknown.Here using LPS (1 mg/kg i.p. for four consecutive days) stimulation in both young (3 months old) and aged (12 months old) mice, followed by molecular analysis on the 21st day, we have explored the correlation between aging and mitochondrial dynamic alteration in the backdrop of chronic neuroinflammation. Following LPS stimulation, we observed microglia activation and subsequent elevation in proinflammatory cytokines (M1; TNF-α, IFN-γ) with NLRP3 activationand a concomitant reduction in the expression of anti-inflammatory markers (M2; YM1, TGF-β1) in the cerebellar tissue of aged mice compared with the young LPS and aged controls. Remarkably, senescence (p21, p27, p53) and epigenetic (HDAC2) markers were found upregulated in the cerebellum tissue of the aged LPS group, suggesting their crucial role in LPS-induced cerebellar deficit. Further, we demonstrated alteration in the antagonistic forces of mitochondrial fusion and fission with increased expression of the mitochondrial fission-related gene [FIS1] and decreased fusion-related genes [MFN1 and MFN2]. We noted increased mtDNA copy number, microglia activation, and inflammatory response of IL1β and IFN-γ post-chronic neuroinflammation in aged LPS group. Our results suggest that the crosstalk between mitochondrial dynamics and altered microglial activation paradigm in chronic neuroinflammatory conditions may be the key to understanding the cerebellar molecular mechanism.