Roles of Two Major Domains of the Porcine Deltacoronavirus S1 Subunit in Receptor Binding and Neutralization.

Determination of the mechanisms of interspecies transmission is of great significance for the prevention of epidemic diseases caused by emerging coronaviruses (CoVs). Recently, porcine deltacoronavirus (PDCoV) was shown to exhibit broad host cell range mediated by surface expression of aminopeptidase N (APN), and humans have been reported to be at risk of PDCoV infection. In the present study, we first demonstrated overexpression of APN orthologues from various species, including mice and felines, in the APN-deficient swine small intestine epithelial cells permitted PDCoV infection, confirming that APN broadly facilitates PDCoV cellular entry and perhaps subsequent interspecies transmission. PDCoV was able to limitedly infect mice in vivo, distributing mainly in enteric and lymphoid tissues, suggesting that mice may serve as a susceptible reservoir of PDCoV. Furthermore, elements (two glycosylation sites and four aromatic amino acids) on the surface of domain B (S1B) of the PDCoV spike glycoprotein S1 subunit were identified to be critical for cellular surface binding of APN orthologues. However, both domain A (S1A) and domain B (S1B) were able to elicit potent neutralizing antibodies against PDCoV infection. The antibodies against S1A inhibited the hemagglutination activity of PDCoV using erythrocytes from various species, which might account for the neutralizing capacity of S1A antibodies partially through a blockage of sialic acid binding. The study reveals the tremendous potential of PDCoV for interspecies transmission and the role of two major PDCoV S1 domains in receptor binding and neutralization, providing a theoretical basis for development of intervention strategies. IMPORTANCE Coronaviruses exhibit a tendency for recombination and mutation, which enables them to quickly adapt to various novel hosts. Previously, orthologues of aminopeptidase N (APN) from mammalian and avian species were found to be associated with porcine deltacoronavirus (PDCoV) cellular entry in vitro. Here, we provide in vivo evidence that mice are susceptible to PDCoV limited infection. We also show that two major domains (S1A and S1B) of the PDCoV spike glycoprotein involved in APN receptor binding can elicit neutralizing antibodies, identifying two glycosylation sites and four aromatic amino acids on the surface of the S1B domain critical for APN binding and demonstrating that the neutralization activity of S1A antibodies is partially attributed to blockage of sugar binding activity. Our findings further implicate PDCoV's great potential for interspecies transmission, and the data of receptor binding and neutralization may provide a basis for development of future intervention strategies.

GC-MS-Based Serum Metabolomic Investigations on the Ameliorative Effects of Polysaccharide from Turpiniae folium in Hyperlipidemia Rats.

Hyperlipidemia, a typical metabolic disorder syndrome, can cause various cardiovascular diseases. The polysaccharides were found to have enormous potential in the therapy of hyperlipidemia. This study was aimed at evaluating the ameliorative effects of polysaccharide from Turpiniae folium (TFP) in rats with hyperlipidemia. A serum metabolomic method based on gas chromatography-mass spectrometry (GC-MS) was used to explore the detailed mechanism of TFP in rats with hyperlipidemia. The oxidative stress indicators, biochemical indexes, and inflammatory factors in serum and histopathological changes in the liver were also evaluated after 10-week oral administration of TFP in rats with high-fat diet-induced hyperlipidemia. TFP significantly relieved oxidative stress, inflammation, and liver histopathology and reduced blood lipid levels. Multivariate statistical approaches such as principal component analysis and orthogonal projection to latent structure square-discriminant analysis revealed clear separations of metabolic profiles among the control, HFD, and HFD+TFP groups, indicating a moderating effect of TFP on the metabolic disorders in rats with hyperlipidemia. Seven metabolites in serum, involved in glycine, serine, and threonine metabolism and aminoacyl-tRNA biosynthesis, were selected as potential biomarkers in rats with hyperlipidemia and regulated by TFP administration. It was concluded that TFP had remarkable potential for treating hyperlipidemia. These findings provided evidence for further understanding of the mechanism of action of TFP on hyperlipidemia.

The Intestinal Microbiome Primes Host Innate Immunity against Enteric Virus Systemic Infection through Type I Interferon.

Intestinal microbiomes are of vital importance in antagonizing systemic viral infection. However, very little literature has shown whether commensal bacteria play a crucial role in protecting against enteric virus systemic infection from the aspect of modulating host innate immunity. In the present study, we utilized an enteric virus, encephalomyocarditis virus (EMCV), to inoculate mice treated with phosphate-buffered saline (PBS) or given an antibiotic cocktail (Abx) orally or intraperitoneally to examine the impact of microbiota depletion on virulence and viral replication in vivo Microbiota depletion exacerbated the mortality, neuropathogenesis, viremia, and viral burden in brains following EMCV infection. Furthermore, Abx-treated mice exhibited severely diminished mononuclear phagocyte activation and impaired type I interferon (IFN) production and expression of IFN-stimulated genes (ISG) in peripheral blood mononuclear cells (PBMC), spleens, and brains. With the help of fecal bacterial 16S rRNA sequencing of PBS- and Abx-treated mice, we identified a single commensal bacterium, Blautia coccoides, that can restore mononuclear phagocyte- and IFNAR (IFN-α/ß receptor)-dependent type I IFN responses to restrict systemic enteric virus infection. These findings may provide insight into the development of novel therapeutics for preventing enteric virus infection or possibly alleviating clinical diseases by activating host systemic innate immune responses via respective probiotic treatment using B. coccoidesIMPORTANCE While cumulative data indicate that indigenous commensal bacteria can facilitate enteric virus infection, little is known regarding whether intestinal microbes have a protective role in antagonizing enteric systemic infection by modulating host innate immunity. Although accumulating literature has pointed out that the microbiota has a fundamental impact on host systemic antiviral innate immune responses mediated by type I interferon (IFN), only a few specific commensal bacteria species have been revealed to be capable of regulating IFN-I and ISG expression, not to mention the underlying mechanisms. Thus, it is important to understand the cross talk between microbiota and host anti-enteric virus innate immune responses and characterize the specific bacterial species that possess protective functions. Our study demonstrates how fundamental innate immune mediators such as mononuclear phagocytes and type I IFN are regulated by commensal bacteria to antagonize enteric virus systemic infection. In particular, we have identified a novel commensal bacterium, Blautia coccoides, that can restrict enteric virus replication and neuropathogenesis by activating IFN-I and ISG responses in mononuclear phagocytes via an IFNAR- and STAT1-mediated signaling pathway.