Critical Analysis Of The Article On Zika Virus
In the article, author discuss Zika Virus, a mosquito-borne flavivirus can cause severe neurological disorders. In human, Author argue neuronal death induced by Zika virus infection can be treated by NMDA receptor blockade. and Zika virus can cause adult neuron death by glutamate excitotoxicity. By experimental research author also proves IFN-α/βR confers resistance to Zika Virus infection in mice. Author states Zika virus can cause adult neuron death by excitotoxicity. If neuron was infected by Zika virus, oxidative stress can be triggered causing abnormal depolarization and over the release of glutamate from presynaptic membrane of the infected neuron. According to several studies, glutamate is playing an important role in neuron function and affect adult neurogenesis. However Glutamatergic overstimulation leads to excitotoxicity by over stimulating ionotropic glutamate (NMDARs) receptors, this will lead to neuronal calcium overload and eventually cause neurodegeneration. When healthy neighbouring neurons received, glutamate signal they will also die because of neuron excitotoxicity of Zika virus. To support the argument that Zika virus uses excitotoxicity as a mechanism to induce cell death, authors conduct the experiment by comparing neuronal cells and primary cultures of glial cell, both was taken from the brain of immunocompetent mice and infect both with Zika virus, they found that after 72 hours of infection. Zika virus can cause neuronal cell death by replicating. . They also found the amount of virus in neurons is two to three times greater than the amount in glial cells, this indicates neuronal cells is more accessible for ZIKV virus.
Another experimental evidence provided by author is Dizocilpine can effectively prevent neuronal cell death at 100M, this is because Dizocilpine is a NMDAR antagonist, it can stop the flowing of Ca ion by blocking the ion channel on the receptor. Furthermore, Agmatine can stop neuronal cell death in all dose, Agmatine has multiple function in treating CNS disorder such as modulate glutamate NMDARs pathway and relieve oxidative stress. This indicate NMDAR plays an important role in Zika virus neuronal degeneration process, by blocking the ion channel can effetely stop the excitotoxicity caused by Zika virus. To answer the second question, we find Interferon-α/β (IFN-α/β) receptor depleted mice are susceptible to be infected by Zika virus because interferon system is a vital component in fighting viral infections in mammalian cells. Toll-like receptors that present in the endosomal compartments and cell membranes would detect the genetic material secreted by the invading RNA viruses, whereas materials in the viral replication would be detected by the cytoplasmic sensors. This would lead to the activation of transcription factors, which results in the production of IFN. It is suggested that IFN-α/β receptor binds to a range of endogenous cytokines (IFN), which leads to the activation of downstream signalling pathways and hence stimulates the immune defence of human bodies.
Zika virus is a type of flavi virus and contains an RNA genome. Therefore, the genetic material of Zika virus would be detected by the sensors of the IFN system, which results in the inhibition of the viral replication. In IFN-α/β receptor depleted mice, type I interferons cannot bind to its receptors and the following immune response will not be triggered. Furthermore, adaptive immune response and humoral immunity can also impacted by type I interferon, it is the essential protective factor in type I IFN abundant mice. Thus, the activation of the IFN system can stimulate adaptive immune cells such as B cells and T cells, which produce more potent damages to the virus. B cells can produce specific antibodies to attack the ZIKV virus and could also help with priming T cells. Virus-specific antibodies are more effective and produce a better effect in killing the virus. Mice that lack of IFN-α/β receptors has less ability to trigger adaptive immune response and hence is more likely to be infected by Zika virus. In this study, in order to find the dead cell caused by Zika virus, scientist use different dye to separate live cell and dead cell by using ethidium homodimer-1 and calcein acetoxymethyl ester. , this is because each dye has unique characteristic. in live cell we use calcein acetoxymethyl ester because it is a non-fluorescent, and it can go in and out freely to the plasma membrane of live cells because it has no charge on it.
Once calcein acetoxymethyl ester gets inside the cell, calcein acetoxymethyl ester will be converted to a fluorescent form by removing the lipophilic blocking groups by nonspecific esterases in the cytoplasm, this will provide the stained live cell with intense uniform green fluorescence, because calcein acetoxymethyl ester is polynomic dye it can be well stained and retained on the live cell. On the other hand, dead cell or dying cell can be isolated by ethidium homodimer assay, this is because ethidium homodimer-1 can bind with DNA within the cell, it can be detected by using UV light microscope. When cell is alive EthD-1 is not able to penetrate through the intact plasma membrane on the surface. However, when cell died or dying plasma membrane of the cell becomes disrupted, ethidium homodimer may enter those cells and bind to DNA within those cells. Because live cells don't have a compromised membrane, the ethidium homodimer can't enter, that's why ethidium homodimer only works on died or dying cell.
