Avian influenza H5N1: an update on molecular pathogenesis

Chloroquine: Autophagy inhibitor, antimalarial, bitter taste receptor agonist in fight against COVID-19, a reality check?

The recent SARS-CoV-2 pandemic poses one of the greatest challenges to modern medicine. Therefore, identification of new therapeutic strategies seems essential either based on novel vaccines or drugs or simply repurposing existing drugs. Notably, due to their known safety profile, repurposing of existing drugs is the fastest and highly efficient approach to bring a therapeutic to a clinic for any new indication. One such drug that has been used extensively for decades is chloroquine (CQ, with its derivatives) either for malaria, lupus and rheumatoid arthritis. Accumulating body of evidence from experimental pharmacology suggests that CQ and related analogues also activate certain pathways that can potentially be exploited for therapeutic gain. For example, in the airways, this has opened an attractive avenue for developing novel bitter taste ligands as a new class of bronchodilators for asthma. While CQ and its derivatives have been proposed as a therapy in COVID-19, it remains to be seen whether it really work in the clinic? To this end, our perspective aims to provide a timely yet brief insights on the existing literature on CQ and the controversies surrounding its use in COVID-19. Further, we also highlight some of cell-based mechanism(s) that CQ and its derivatives affect in mediating variety of physiological responses in the cell. We believe, data emanating from the clinical studies and continual understanding of the fundamental mechanisms may potentially help in designing effective therapeutic strategies that meets both efficacy and safety criteria for COVID-19.

Autophagy is involved in the acute lung injury induced by H9N2 influenza virus

Influenza A virus usually leads to economic loss to breeding farms and pose a serious threat to human health. Virus infecting tissues directly and influenza virus-induced excessive production of inflammatory factors play the key role in pathogenesis of the disease, but the mechanism is not well clarified. Here, the role of autophagy was investigated in H9N2 influenza virus-triggered inflammation. The results showed that autophagy was induced by H9N2 virus in A549 cells and in mice. Inhibiting autophagy by an autophagy inhibitor (3-methyladenine, 3-MA) or knockdown of Atg5(autophagy-related gene) by Atg5 siRNA significantly suppressed H9N2 virus replication, H9N2 virus-triggered inflammatory cytokines and chemokines, including IL-1β, TNF-α, IL-8, and CCL5 in vitro and in vivo, and suppressed H9N2 virus-triggered acute lung injury as indicated as accumulative mortality of mice, inflammatory cellular infiltrate and interstitial edema, thickening of the alveolar walls in mice lung tissues, increased inflammatory cytokines and chemokines, increased W/D ratio in mice. Moreover, autophagy mediated inflammatory responses through Akt-mTOR, NF-κB and MAPKs signaling pathways. Our data showed that autophagy was essential in H9N2 influenza virus-triggered inflammatory responses, and autophagy could be target to treat influenza virus-caused lung inflammation.

High-precision extraction and concentration detection of airborne disease microorganisms based on microfluidic chip

Accurate monitoring of the content of specific disease micro-organisms in the air is one of the key technologies for early warning of airborne diseases. Based on the principle of aerosol particle motion in the microenvironment, this paper proposes a microfluidic chip method for accurately extracting diseased micro-organisms directly from the gas stream. The chip consists of a two-stage coupling of parallel double-sheath flow focusing and radial sheath flow acceleration. Considering the case of extracting mold spores (near spherical shape, average particle size 6  μ m) and strawberry gray mold spores (near spherical shape, average particle size 10  μ m) from the mixture (concentration of the mixture is about 3.4 × 10 8 /ml), the performance of the chip was evaluated using two indicators: extraction rate and purity. The results showed that the extraction rates of mold spores and gray mildew spores were 89% and 76% and the purges were 98% and 87%, respectively, achieving high-purity and accurate extraction of fungal spores and greatly improving the detection accuracy. It could be used as the development basis of microbial sensor for the early rapid detection of crop fungal diseases.

Neuraminidase of Influenza A Virus Binds Lysosome-Associated Membrane Proteins Directly and Induces Lysosome Rupture

As a recycling center, lysosomes are filled with numerous acid hydrolase enzymes that break down waste materials and invading pathogens. Recently, lysosomal cell death has been defined as "lysosomal membrane permeabilization and the consequent leakage of lysosome contents into cytosol." Here, we show that the neuraminidase (NA) of H5N1 influenza A virus markedly deglycosylates and degrades lysosome-associated membrane proteins (LAMPs; the most abundant membrane proteins of lysosome), which induces lysosomal rupture, and finally leads to cell death of alveolar epithelial carcinoma A549 cells and human tracheal epithelial cells. The NA inhibitors peramivir and zanamivir could effectively block the deglycosylation of LAMPs, inhibit the virus cell entry, and prevent cell death induced by the H5N1 influenza virus. The NA of seasonal H1N1 virus, however, does not share these characteristics. Our findings not only reveal a novel role of NA in the early stage of the H5N1 influenza virus life cycle but also elucidate the molecular mechanism of lysosomal rupture crucial for influenza virus induced cell death.

IMPORTANCE

The integrity of lysosomes is vital for maintaining cell homeostasis, cellular defense and clearance of invading pathogens. This study shows that the H5N1 influenza virus could induce lysosomal rupture through deglycosylating lysosome-associated membrane proteins (LAMPs) mediated by the neuraminidase activity of NA protein. NA inhibitors such as peramivir and zanamivir could inhibit the deglycosylation of LAMPs and protect lysosomes, which also further interferes with the H5N1 influenza virus infection at early stage of life cycle. This work is significant because it presents new concepts for NA's function, as well as for influenza inhibitors' mechanism of action, and could partially explain the high mortality and high viral load after H5N1 virus infection in human beings and why NA inhibitors have more potent therapeutic effects for lethal avian influenza virus infections at early stage.

Angiotensin-converting enzyme 2 protects from lethal avian influenza A H5N1 infections

The potential for avian influenza H5N1 outbreaks has increased in recent years. Thus, it is paramount to develop novel strategies to alleviate death rates. Here we show that avian influenza A H5N1-infected patients exhibit markedly increased serum levels of angiotensin II. High serum levels of angiotensin II appear to be linked to the severity and lethality of infection, at least in some patients. In experimental mouse models, infection with highly pathogenic avian influenza A H5N1 virus results in downregulation of angiotensin-converting enzyme 2 (ACE2) expression in the lung and increased serum angiotensin II levels. Genetic inactivation of ACE2 causes severe lung injury in H5N1-challenged mice, confirming a role of ACE2 in H5N1-induced lung pathologies. Administration of recombinant human ACE2 ameliorates avian influenza H5N1 virus-induced lung injury in mice. Our data link H5N1 virus-induced acute lung failure to ACE2 and provide a potential treatment strategy to address future flu pandemics.

Role of Fat-Soluble Vitamins A and D in the Pathogenesis of Influenza: A New Perspective

Reduced exposure to solar radiation, leading to a deficiency of vitamin D and hence impaired innate immunity, has been suggested as a trigger for influenza viral replication and as an explanation of seasonal influenza. Although this hypothesis accounts for many unexplained facts about the epidemiology of influenza, gaps remain in understanding the pathogenesis and manifestations of the disease. Several observations suggest a role for vitamin A compounds (retinoids) in the disease. This paper presents a new model of the etiopathogenesis of influenza, suggesting that host resistance and susceptibility depend importantly on the ratio of vitamin D to vitamin A activity. Retinoid concentrations within normal physiological limits appear to inhibit influenza pathogenesis whereas higher background concentrations (i.e., very low vitamin D : A ratios) increase the risk of severe complications of the disease. There is also evidence that influenza-induced or preexisting liver disease, diabetes, and obesity worsen the severity of infection, possibly via liver dysfunction and alterations in retinoid metabolism. The model could be tested by determining the presence of retinoids in the secretions of patients with influenza and by studies of retinoid profiles in patients and controls. Potential strategies for prevention and treatment are discussed.

An overview of the highly pathogenic H5N1 influenza virus

Since the first human case of H5N1 avian influenza virus infection was reported in 1997, this highly pathogenic virus has infected hundreds of people around the world and resulted in many deaths. The ability of H5N1 to cross species boundaries, and the presence of polymorphisms that enhance virulence, present challenges to developing clear strategies to prevent the pandemic spread of this highly pathogenic avian influenza (HPAI) virus. This review summarizes the current understanding of, and recent research on, the avian influenza H5N1 virus, including transmission, virulence, pathogenesis, clinical characteristics, treatment and prevention.

Altered lymphocyte counts in a pediatric patient with H5N1 infection

Flow cytometry was used to analyze the changes in lymphocyte subsets in the youngest child with avian influenza in China. During the early stage, the absolute CD3 count was 62.9% (lower limit of normal), the CD8 count was 32.5% (slightly higher than normal), and the CD4 count was 28.6% (lower than normal). The CD4/CD8 ratio was also decreased (0.88). The natural killer (CD3CD1656) cell count was 4.9% (lower than normal). During the convalescent stage, the CD4 count and the CD4/CD8 ratio returned to normal. The CD3CD1656 count increased from its value at the early stage of the disease.

Inhibition of autophagy ameliorates acute lung injury caused by avian influenza A H5N1 infection

The threat of a new influenza pandemic has existed since 1997, when the highly pathogenic H5N1 strain of avian influenza A virus infected humans in Hong Kong and spread across Asia, where it continued to infect poultry and people. The human mortality rate of H5N1 infection is about 60%, whereas that of seasonal H1N1 infection is less than 0.1%. The high mortality rate associated with H5N1 infection is predominantly a result of respiratory failure caused by acute lung injury; however, how viral infection contributes to this disease pathology is unclear. Here, we used electron microscopy to show the accumulation of autophagosomes in H5N1-infected lungs from a human cadaver and mice, as well as in infected A549 human epithelial lung cells. We also showed that H5N1, but not seasonal H1N1, induced autophagic cell death in alveolar epithelial cells through a pathway involving the kinase Akt, the tumor suppressor protein TSC2, and the mammalian target of rapamycin. Additionally, we suggest that the hemagglutinin protein of H5N1 may be responsible for stimulating autophagy. When applied prophylactically, reagents that blocked virus-induced autophagic signaling substantially increased the survival rate of mice and substantially ameliorated the acute lung injury and mortality caused by H5N1 infection. We conclude that the autophagic cell death of alveolar epithelial cells likely plays a crucial role in the high mortality rate of H5N1 infection, and we suggest that autophagy-blocking agents might be useful as prophylactics and therapeutics against infection of humans by the H5N1 virus.

Specific sites of N-linked glycosylation on the hemagglutinin of H1N1 subtype influenza A virus determine sensitivity to inhibitors of the innate immune system and virulence in mice

Oligosaccharides on the hemagglutinin (HA) and neuraminidase of influenza A virus (IAV) are a target for recognition by lectins of the innate immune system, including soluble surfactant protein-D and the macrophage mannose receptor on airway macrophages. Glycans attached to the head of H1 subtype of IAV differ markedly in number and location. A reverse genetic approach was used to define the importance of particular N-glycosylation sites on H1 in determining sensitivity to innate immune defenses and virulence in mice. The HA of A/PR/8/34 (PR8, H1N1) and A/Brazil/11/78 (Brazil, H1N1) express zero and four glycosylation sites on the head of HA, respectively. Site-directed mutagenesis was used to add (PR8) or delete (Brazil) glycosylation sites, and IAV expressing wild-type or mutant HA were generated on a PR8 backbone. Addition or removal of particular glycans modulated sensitivity to mouse lung fluids but was not a major factor determining susceptibility of airway macrophages to infection. PR8 is a mouse-adapted virus, and mutations in multiple IAV genes have been shown to contribute to virulence, yet addition of glycosylation to PR8 HA was sufficient to attenuate disease. In contrast, removal of glycans from Brazil HA resulted in severe disease and death. These studies provide insight regarding the mechanisms by which IAV can induce disease in mice. Moreover, reduced glycosylation of HA is likely to be an important factor associated with adaptation of human IAV to growth in mouse lung.