Drug-Screening Strategies for Inhibition of Virus-Induced Neuronal Cell Death

Retinoic acid-induced differentiation and oxidative stress inhibitors increase resistance of human neuroblastoma cells to La Crosse virus-induced cell death

La Crosse Virus (LACV) encephalitis patients are at risk for long-term deficits in cognitive function due to neuronal apoptosis following virus infection. However, the specific etiology underlying neuronal damage remains elusive. In this study, we examined how differentiation and mitotic inhibition of neuroblastoma cells influence their susceptibility to LACV infection and cell death. Treatment of SH-SY5Y cells with retinoic acid induced a neuronal cell phenotype which was similarly susceptible to LACV infection as untreated cells but had significantly delayed virus-induced cell death. Protein and RNA transcript analysis showed that retinoic acid-treated cells had decreased oxidative stress responses to LACV infection compared to untreated cells. Modulation of oxidative stress in untreated cells with specific compounds also delayed cell death, without substantially impacting virus production. Thus, the oxidative stress response of neurons to virus infection may be a key component of neuronal susceptibility to virus-induced cell death.

IMPORTANCE

Encephalitic viruses like La Crosse Virus (LACV) infect and kill neurons. Disease onset and progression is rapid meaning the time frame to treat patients before significant and long-lasting damage occurs is limited. Examining how neurons, the primary cells infected by LACV in the brain, resist virus-induced cell death can provide avenues for determining which pathways to target for effective treatments. In the current study, we studied how changing neuroblastoma growth and metabolism with retinoic acid treatment impacted their susceptibility to LACV-induced cell death. We utilized this information to test compounds for preventing death in these cells.

Developing peptide-based fusion inhibitors as an antiviral strategy utilizing coronin 1 as a template

Enveloped viruses enter the host cells by endocytosis and subsequently fuse with the endosomal membranes, or fuse with the plasma membrane at the cell surface. The crucial stage of viral infection, regardless of the route taken to enter the host cell, is membrane fusion. The present work aims to develop a peptide-based fusion inhibitor that prevents membrane fusion by modifying the properties of the participating membranes, without targeting a protein. This would allow us to develop a fusion inhibitor that might work against a larger spectrum of enveloped viruses as it does not target any specific viral fusion protein. With this goal in mind, we have designed a novel peptide by modifying a native sequence derived from coronin 1, a phagosomal protein, that helps to avoid lysosomal degradation of mycobacterium-loaded phagosomes. The designed peptide, mTG-23, inhibits ∼30-40% fusion between small unilamellar vesicles containing varying amounts of cholesterol by modulating the biophysical properties of the participating bilayers. As a proof of principle, we have further demonstrated that the mTG-23 inhibits Influenza A virus infection in A549 and MDCK cells (with ∼EC50 of 20.45 μM and 21.55 μM, respectively), where viral envelope and endosomal membrane fusion is a crucial step. Through a gamut of biophysical and biochemical methods, we surmise that mTG-23 inhibits viral infection by inhibiting viral envelope and endosomal membrane fusion. We envisage that the proposed antiviral strategy can be extended to other viruses that employ a similar modus operandi, providing a novel pan-antiviral approach.

Effective inhibition of HCoV-OC43 and SARS-CoV-2 by phytochemicals in vitro and in vivo

OBJECTIVE

Several coronaviruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and human coronavirus OC43 (HCoV-OC43), can cause respiratory infections in humans. To address the need for reliable anti-coronavirus therapeutics, we screened 16 active phytochemicals selected from medicinal plants used in traditional applications for respiratory-related illnesses.

METHODS

An initial screen was completed using HCoV-OC43 to identify compounds that inhibit virus-induced cytopathic effect (CPE) and cell death inhibition. Then the top hits were validated in vitro against both HCoV-OC43 and SARS-CoV-2 by determining virus titer in cell supernatant and virus-induced cell death. Finally, the most active phytochemical was validated in vivo in the SARS-CoV-2-infected B6.Cg-Tg(K18-ACE2)2Prlmn/J mouse model.

RESULTS

The phytochemicals lycorine (LYC), capsaicin, rottlerin (RTL), piperine and chebulinic acid (CHU) inhibited HCoV-OC43-induced cytopathic effect and reduced viral titres by up to 4 log. LYC, RTL and CHU also suppressed virus replication and cell death following SARS-CoV-2 infection. In vivo, RTL significantly reduced SARS-CoV-2-induced mortality by ∼40% in human angiotensin-converting enzyme 2 (ACE2)-expressing K18 mice.

CONCLUSION

Collectively, these studies indicate that RTL and other phytochemicals have therapeutic potential to reduce SARS-CoV-2 and HCoV-OC43 infections.

Neurotoxic properties of the Zika virus envelope protein

Prenatal Zika virus (ZIKV) infection is a serious global concern as it can lead to brain injury and many serious birth defects, collectively known as congenital Zika syndrome. Brain injury likely results from viral mediated toxicity in neural progenitor cells. Additionally, postnatal ZIKV infections have been linked to neurological complications, yet the mechanisms driving these manifestations are not well understood. Existing data suggest that the ZIKV envelope protein can persist in the central nervous system for extended periods of time, but it is unknown if this protein can independently contribute to neuronal toxicity. Here we find that the ZIKV envelope protein is neurotoxic, leading to overexpression of poly adenosine diphosphate -ribose polymerase 1, which can induce parthanatos. Together, these data suggest that neuronal toxicity resulting from the envelope protein may contribute to the pathogenesis of post-natal ZIKV-related neurologic complications.

Therapeutic targeting of organelles for inhibition of Zika virus replication in neurons

Zika virus (ZIKV) is an arbovirus belonging to the family Flaviviridae. Since 2015, ZIKV infection has emerged as a leading cause of virus-induced placental insufficiency, microcephaly and other neuronal complications. Currently, no therapeutics have been approved to treat ZIKV infection. In this study, we examined how targeted inhibition of cellular organelles or trafficking processes affected ZIKV infection and replication in neural progenitor cells. We found that blocking endocytosis, Golgi function or structural filaments like actin or microtubules had moderate effects on virus replication. However, inducing endoplasmic reticulum (ER) stress by treatment with Thapsigargin substantially inhibited virus production, suggesting the ER might be a candidate cellular target. Further analysis showed that sarcoplasmic/endoplasmic reticulum Ca2+-ATPases (SERCA) was important for ZIKV inhibition. Collectively, these studies indicate that targeting the SERCA-dependent ER stress pathway may be useful to develop antivirals to inhibit ZIKV replication.

Rottlerin plays an antiviral role at early and late steps of Zika virus infection

Infection of Zika virus (ZIKV) may cause microcephaly and other neurological disorders, while no vaccines and drugs are available. Our study revealed that rottlerin confers a broad antiviral activity against several enveloped viruses, including ZIKV, vesicular stomatitis virus, and herpes simplex virus, but not against two naked viruses (enterovirus 71 and encephalomyocarditis virus). Rottlerin does not have a direct virucidal effect on the virions, and its antiviral effect is independent of its regulation on PKCδ or ATP. Both pretreatment and post-treatment of rottlerin effectively reduce the viral replication of ZIKV. The pretreatment of rottlerin disturbs the endocytosis of enveloped viruses, while the post-treatment of rottlerin acts at a late stage through disturbing the maturation of ZIKV. Importantly, administration of rottlerin in neonatal mice significantly decreased the ZIKV replication in vivo, and alleviated the neurological symptoms caused by ZIKV. Our work suggests that rottlerin exerts an antiviral activity at two distinct steps of viral infection, and can be potentially developed as a prophylactic and therapeutic agent.

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Rottlerin confers an antiviral activity against several enveloped viruses including Zika virus.

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Rottlerin interferes with the endocytosis and maturation step of Zika virus.

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Rottlerin inhibits the ZIKV replication in vivo, and alleviates the neurological symptoms caused by Zika virus.