Enterovirus 71 induces apoptosis by directly modulating the conformational activation of pro-apoptotic protein Bax

Functions of Viroporins in the Viral Life Cycle and Their Regulation of Host Cell Responses

Viroporins are virally encoded transmembrane proteins that are essential for viral pathogenicity and can participate in various stages of the viral life cycle, thereby promoting viral proliferation. Viroporins have multifaceted effects on host cell biological functions, including altering cell membrane permeability, triggering inflammasome formation, inducing apoptosis and autophagy, and evading immune responses, thereby ensuring that the virus completes its life cycle. Viroporins are also virulence factors, and their complete or partial deletion often reduces virion release and reduces viral pathogenicity, highlighting the important role of these proteins in the viral life cycle. Thus, viroporins represent a common drug-protein target for inhibiting drugs and the development of antiviral therapies. This article reviews current studies on the functions of viroporins in the viral life cycle and their regulation of host cell responses, with the aim of improving the understanding of this growing family of viral proteins.

Gasdermin E is required for induction of pyroptosis and severe disease during enterovirus 71 infection

Pyroptosis is an inflammatory form of programmed cell death that is executed by the gasdermin (GSDM)-N domain of GSDM family proteins, which form pores in the plasma membrane. Although pyroptosis acts as a host defense against invasive pathogen infection, its role in the pathogenesis of enterovirus 71 (EV71) infection is unclear. In the current study, we found that EV71 infection induces cleavage of GSDM E (GSDME) by using western blotting analysis, an essential step in the switch from caspase-3-mediated apoptosis to pyroptosis. We show that this cleavage is independent of the 3C and 2A proteases of EV71. However, caspase-3 activation is essential for this cleavage, as GSDME could not be cleaved in caspase-3-KO cells upon EV71 infection. Further analyses showed that EV71 infection induced pyroptosis in WT cells but not in caspase-3/GSDME double-KO cells. Importantly, GSDME is required to induce severe disease during EV71 infection, as GSDME deficiency in mice was shown to alleviate pathological symptoms. In conclusion, our results reveal that GSDME is important for the pathogenesis of EV71 via mediating initiation of pyroptosis.

The Effect of NeuroAid (MLC901) on Cholestasis-Induced Spatial Memory Impairment with Respect to the Expression of BAX, BCL-2, BAD, PGC-1α and TFAM Genes in the Hippocampus of Male Wistar Rats

Cholestasis is a bile flow reduction that is induced following Bile Duct Ligation (BDL). Cholestasis impairs memory and induces apoptosis. Apoptosis consists of two pathways: intrinsic and extrinsic. The intrinsic pathway is modulated by BCL-2 (B cell lymphoma-2) family proteins. BCL-2 (a pro-survival BCL-2 protein) has anti-apoptotic effect, while BAD (BCL-2-associated death) and BAX (BCL-2-associated X), the other members of BCL-2 family have pro-apoptotic effect. Furthermore, TFAM (mitochondrial transcriptional factor A) is involved in transcription and maintenance of mitochondrial DNA and PGC-1α (peroxisome proliferator-activated receptor γ coactivator-1α) is a master regulator of mitochondrial biogenesis. On the other hand, NeuroAid is a Traditional Chinese Medicine with neuroprotective and anti-apoptosis effects. In this study, we evaluated the effect of cholestasis on spatial memory and expression of BCL-2, BAD, BAX, TFAM, and PGC-1α in the hippocampus of rats. Additionally, we assessed the effect of NeuroAid on cholestasis-induced cognitive and genetic alterations. Cholestasis was induced by BDL surgery and NeuroAid was injected intraperitoneal at the dose of 0.4 mg/kg. Furthermore, spatial memory was evaluated using Morris Water Maze (MWM) apparatus. The results showed cholestasis impaired spatial memory, increased the expression of BAD and BAX, decreased the expression of TFAM and PGC-1α, and did not alter the expression of BCL-2. Also, NeuroAid decreased the expression of BAD and BAX and increased the expression of TFAM, PGC-1α, and BCL-2. In conclusion, cholestasis impaired spatial memory and increased the expression of pro-apoptotic genes. Also, cholestasis decreased the expression of TFAM and PGC-1α. Interestingly, NeuroAid restored the effects of cholestasis.

Effects of Treadmill Exercise on the Expression Level of BAX, BAD, BCL-2, BCL-XL, TFAM, and PGC-1α in the Hippocampus of Thimerosal-Treated Rats

Thimerosal (THIM) induces neurotoxic changes including neuronal death and releases apoptosis inducing factors from mitochondria to cytosol. THIM alters the expression level of factors involved in apoptosis. On the other hand, the anti-apoptotic effects of exercise have been reported. In this study, we aimed to discover the effect of three protocols of treadmill exercise on the expression level of mitochondrial transcription factor A (TFAM), peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), BCL-2-associated death (BAD), BCL-2-associated X (BAX), BCL-XL, and BCL-2 (a pro-survival BCL-2 protein) in the hippocampus of control and THIM-exposed rats. Male Wistar rats were used in this research. Real-time PCR was applied to assess genes expression. The results showed that THIM increased the expression of pro-apoptotic factors (BAD and BAX), decreased the expression of anti-apoptotic factors (BCL-2 and BCL-XL), and decreased the expression of factors involved in mitochondrial biogenesis (TFAM and PGC-1α). Treadmill exercise protocols reversed the effect of THIM on all genes. In addition, treadmill exercise protocols decreased the expression of BAD and BAX, increased the expression of BCL-2, and increased the expression of TFAM and PGC-1α in control rats. In conclusion, THIM induced a pro-apoptotic effect and disturbed mitochondrial biogenesis and stability, whereas treadmill exercise reversed these effects.

Inhibition of Enterovirus A71 by a Novel 2-Phenyl-Benzimidazole Derivative

Enterovirus A71 (EV-A71) infection has emerged as a significant public health concern at the global level. Epidemic events of EV-A71 have been reported worldwide, and this succession of outbreaks has heightened concern that EV-A71 may become a public health threat. In recent years, widespread A71 enterovirus also occurred in European countries. EV-A71 infection causes hand-foot-mouth disease (HFMD), herpangina, and fever. However, it can sometimes induce a variety of neurological complications, including encephalitis, aseptic meningitis, pulmonary edema, and acute flaccid paralysis. We identified new benzimidazole derivatives and described theirin vitrocytotoxicity and broad-spectrum anti-enterovirus activity. Among them, derivative 2b resulted in interesting activity against EV-A71, and therefore it was selected for further investigations. Compound 2b proved to be able to protect cell monolayers from EV-A71-induced cytopathogenicity, with an EC₅₀ of 3 µM. Moreover, Vero-76 cells resulted in being significantly protected from necrosis and apoptosis when treated with 2b at 20 and 80 µM. Compound 2b reduced viral adsorption to Vero-76 cells, and when evaluated in a time-of-addition assay, the derivative had the highest effect when added during the infection period. Moreover, derivative 2b reduced viral penetration into host cells. Besides, 2b did not affect intestinal monolayers permeability, showing no toxic effects. A detailed insight into the efficacy of compound 2b against EV-A71 showed a dose-dependent reduction in the viral titer, also at low concentrations. Mechanism of action investigations suggested that our derivative can inhibit viral endocytosis by reducing viral attachment to and penetration into host cells. Pharmacokinetic and toxicity predictions validated compound 2b as a good candidate for furtherin vivoassays.

Production and characterization of a neutralizing antibody against botulinum neurotoxin A

As a category A toxic, the botulinum toxin(BoNT) is responsible for human botulism with an estimated lethal dose of 1 ng/kg which greatly increases the potential risk of use as bioweapons. Therefore, the development of anti-BoNT antibodies is urgent. In this paper, the H_C domain of BoNT/A was purified and immunized with Balb/c mice. Monoclonal antibodies were screened against BoNT/A from 55 stable positive hybridoma cell lines, and one with the strongest neutralizing activity, designated as ML06, was subcloned, sequenced, and classified as IgG1(κ) subclass. The mouse protection assays showed that ML06 can neutralize the toxin of BoNT/A effectively both in vitro and in vivo, in a dose-dependent manner. The therapeutic assays showed that only 20% of mice injected with 4 LD₅₀ BoNT/A can survive another injection of ML06 after 4 h. The prophylaxis assays showed the residual ML06 from mice injected with ML06 two weeks ago can protect mice against 4 LD₅₀ BoNT/A challenge completely. Collectively, our results indicated that ML06 served as a good candidate for further development of immune therapeutics for BoNT/A.

BNIP3 deletion ameliorated enterovirus 71 infection-induced hand, foot and mouth disease via inhibiting apoptosis, autophagy, and inflammation in mice

Bcl2/adenovirus E1B protein-interacting protein 3 (BNIP3) plays a key role in cellular response to stress by regulating apoptosis and selective autophagy. The present study aimed to determine the effects of BNIP3 on enterovirus (EV) 71 infection-induced hand, foot and mouth disease (HFMD), and the apoptosis, autophagy and inflammatory in mice and SH-SY5Y human neuroblastoma cell line. Neonatal BALB/c mice were injected with EV 71 strain to induce the HFMD. Western blotting and ELISA were used to measure the protein expression and cytokine levels. The BNIP3 mRNA and protein levels in the brain were increased in EV 71-infected mice. By contrast, the BNIP3-knockout (KO) mice with EV 71 infection had higher health score and survival rate. BNIP3 deletion reversed the increase of cleaved-caspase 3, cleaved-caspase 8, Bax, LC3 II and LC3 II/LC3 I levels, and the decrease of Bcl2 and Bcl2/Bax and LC3 I levels in the brain of mice with EV 71 infection. The EV 71 infection-induced increase of tumor necrosis factor (TNF)-α, monocyte chemotactic protein (MCP)-1, interleukin (IL)-1β, IL-6, interferon (IFN)-α and IFN-γ levels were inhibited in BNIP3-KO mice. BNIP3 knockdown with small interfering RNA (siRNA) inhibited the EV 71 infection-induced the increases of apoptosis, autophagy and inflammatory factors in SH-SY5Y cells. BNIP3 overexpression further facilitated the EV 71 infection-induced increase of these inflammatory factors in SH-SY5Y cells. These results demonstrated that BNIP3 deletion ameliorated EV 71 infection-induced HFMD via inhibiting apoptosis, autophagy and inflammation in mice. BNIP3 may be a therapeutic target for HFMD.

Regulation of Apoptosis by Enteroviruses

Enterovirus infection can cause a variety of diseases and severely impair the health of humans, animals, poultry, and other organisms. To resist viral infection, host organisms clear infected cells and viruses via apoptosis. However, throughout their long-term competition with host cells, enteroviruses have evolved a series of mechanisms to regulate the balance of apoptosis in order to replicate and proliferate. In the early stage of infection, enteroviruses mainly inhibit apoptosis by regulating the PI3K/Akt pathway and the autophagy pathway and by impairing cell sensors, thereby delaying viral replication. In the late stage of infection, enteroviruses mainly regulate apoptotic pathways and the host translation process via various viral proteins, ultimately inducing apoptosis. This paper discusses the means by which these two phenomena are balanced in enteroviruses to produce virus-favoring conditions – in a temporal sequence or through competition with each other. This information is important for further elucidation of the relevant mechanisms of acute infection by enteroviruses and other members of the picornavirus family.

The involvement of regulated cell death forms in modulating the bacterial and viral pathogenesis

Apoptosis, necroptosis and pyroptosis represent three distinct types of regulated cell death forms, which play significant roles in response to viral and bacterial infections. Whereas apoptosis is characterized by cell shrinkage, nuclear condensation, bleb formation and retained membrane integrity, necroptosis and pyroptosis exhibit osmotic imbalance driven cytoplasmic swelling and early membrane damage. These three cell death forms exert distinct immune stimulatory potential. The caspase driven apoptotic cell demise is considered in many circumstances as anti-inflammatory, whereas the two lytic cell death modalities can efficiently trigger immune response by releasing damage associated molecular patterns to the extracellular space. The relevance of these cell death modalities in infections can be best demonstrated by the presence of viral proteins that directly interfere with cell death pathways. Conversely, some pathogens hijack the cell death signaling routes to initiate a targeted attack against the immune cells of the host, and extracellular bacteria can benefit from the destruction of intact extracellular barriers upon cell death induction. The complexity and the crosstalk between these cell death modalities reflect a continuous evolutionary race between pathogens and host. This chapter discusses the current advances in the research of cell death signaling with regard to viral and bacterial infections and describes the network of the cell death initiating molecular mechanisms that selectively recognize pathogen associated molecular patterns.

Effect of cholestasis and NeuroAid treatment on the expression of Bax, Bcl-2, Pgc-1α and Tfam genes involved in apoptosis and mitochondrial biogenesis in the striatum of male rats

Cholestasis means impaired bile synthesis or secretion. In fact, it is a bile flow reduction following Bile Duct Ligation (BDL). Cholestasis has a main role in necrosis and apoptosis. Apoptosis is a form of programmed cell death that has intrinsic and extrinsic pathways. The intrinsic pathway is mediated by Bcl-2 (B cell lymphoma-2) proteins which integrate death and survival signals. Bcl-2 has anti-apoptotic and Bax has pro-apoptotic effects. Also, striatum is one of the brain regions that has high expressions of Bcl-2 proteins. Moreover, Tfam and Pgc-1α are involved in mitochondrial biogenesis. On the other hand, NeuroAid, is a drug that has neuroprotective and anti-apoptosis effects. In this study, using quantitative PCR, we measured the expression of all these genes in the striatum of male rats following BDL and NeuroAid administration. Results showed, BDL increased the expression of Bax and Tfam and decreased the expression of Bcl-2. NeuroAid restored the effect of BDL on the expression of Bax, while did not alter the effect of BDL on Bcl-2. In addition, it increased the expression of Tfam that was previously elevated by BDL and raised the expression of Tfam in normal rats. Both BDL and NeuroAid, had no effect on Pgc-1α. In conclusion, cholestasis increased the expression of Bax and decreased the expression of Bcl-2, and this effect may have related to enhanced susceptibility of mitochondrial pathways following oxidative stress. Tfam expression was increased following cholestasis and this effect may have related to cellular compensatory mechanisms against high accumulation of free radicals or mitochondrial biogenesis failure. Furthermore, NeuroAid may play a role against apoptosis and can be used to increase mitochondrial biogenesis.

Apoptosis and Autophagy in Picornavirus Infection

Cell death is a fundamental process in maintaining cellular homeostasis, which can be either accidental or programed. Programed cell death depends on the specific signaling pathways, resulting in either lytic or non-lytic morphology. It exists in two primary forms: apoptosis and autophagic cell death. Apoptosis is a non-lytic and selective cell death program, which is executed by caspases in response to non-self or external stimuli. In contrast, autophagy is crucial for maintaining cellular homeostasis via the degradation and recycling of cellular components. These two mechanisms also function in the defense against pathogen attack. However, picornaviruses have evolved to utilize diverse strategies and target critical components to regulate the apoptotic and autophagic processes for optimal replication and the release from the host cell. Although an increasing number of investigations have shown that the apoptosis and autophagy are altered in picornavirus infection, the mechanism by which viruses take advantage of these two processes remains unknown. In this review, we discuss the mechanisms of picornavirus executes cellular apoptosis and autophagy at the molecular level and the relationship between these interactions and viral pathogenesis.

Hesperetin post-treatment prevents rat cardiomyocytes from hypoxia/reoxygenation injury in vitro via activating PI3K/Akt signaling pathway

Hesperidin (HES), a citrus fruit extract, has beneficial effects on various ischemia/reperfusion (I/R) models. Here, we investigated the possible positive effect of hesperetin (HPT), an active metabolite of HES, and identified the potential molecular mechanisms involved in cardiomyocytes H/R-induced injury. To construct the cardiomyocyte model of hypoxia/reoxygenation (H/R) injury, cultured neonatal rat cardiomyocytes were subjected to 3h of hypoxia followed by 3h of reoxygenation. Cell viability and apoptosis were detected. The levels of Apoptosis-related proteins and PI3K/Akt proteins were detected by western blot. Our results showed that HPT post-treatment significantly inhibited apoptosis by elevating the expression of Bcl-2, decreasing the expression of Bax and cleaved caspase-3, and diminished the apoptotic cardiomyocytes ratio. Mechanism studies demonstrated that HPT post-treatment up-regulated the expression levels of p-PI3K, and p-Akt. Co-treatment of the cardiomyocytes with the PI3K/Akt-specific inhibitor LY294002 blocked the HPT-induced cardioprotective effects. Taken together, these data suggested that HPT post-treatment prevented cardiomyocytes from H/R injury in vitro most likely through the activation of PI3K/Akt signaling pathway.