Human coronaviruses (HCoV) are recognized respiratory pathogens for which accumulating evidence indicates that in vulnerable patients, the infection can cause more severe pathologies. HCoVs are not always confined to the upper respiratory tract and can invade the CNS upon still unclear circumstances. HCoV-induced neuropathologies in human are difficult to diagnose early enough to allow therapeutic interventions. Making use of our already described animal model of HCoV neuropathogenesis, we describe the route of neuropropagation from the nasal cavity to the olfactory bulb, piriform cortex then brainstem. We identified neuron-to-neuron propagation as one underlying mode of virus spreading in cell culture. Our data demonstrate that both passive diffusion of released viral particles and axonal transport are valid propagation strategies used by the virus. We describe for the first time the presence along axons of viral platforms whose static dynamism are reminiscent of viral assembly sites. We further revealed that HCoV-OC43 modes of propagation could be modulated by selected HCoV-OC43 proteins and axonal transport. Our work, therefore, identifies processes that may govern the severity and nature of HCoV-OC43 neuropathogenesis and will make possible the development of therapeutic strategies to prevent occurrences. Coronaviruses may invade the CNS, disseminate and participate in the induction of neurological diseases. Their neuropathogenicity is being increasingly recognized in humans, and the presence and persistence of human coronaviruses (HCoV) in human brains was proposed to cause long-term sequelae. Using our mouse model relying on natural susceptibility to HCoV-OC43 and neuronal cell cultures, we have defined the most relevant path taken by HCoV-OC43 to access and spread to and within the CNS toward the brainstem and spinal cord and studied in cell culture the underlying modes of intercellular propagation to better understand its neuropathogenesis. Our data suggest that the axonal transport governs HCoV-OC43 egress in the CNS leading to exacerbate neuropathogenesis. Exploiting knowledge on neuroinvasion and dissemination will enhance our ability to control viral infection within the CNS as it will shed light on underlying mechanisms of neuropathogenesis and uncover potential "druggable" molecular virus-host interfaces.

Background: Human aminopeptidase N (hAPN) is a dimeric cell surface protease involved in peptide processing, cell adhesion, endocytosis, and signal transduction. Results: Crystal structures of peptide and inhibitor complexes were determined. Conclusion: Unlike other family members, hAPN shows substrate-dependent loop ordering and a novel dimer structure. Significance: A model for catalysis and conformational changes provides mechanistic insights into how hAPN mediates its functional roles.

The coronavirus S-protein mediates receptor binding and fusion of the viral and host cell membranes. In HCoV-229E, its receptor binding domain (RBD) shows extensive sequence variation but how S-protein function is maintained is not understood. Reported are the X-ray crystal structures of Class III-V RBDs in complex with human aminopeptidase N (hAPN), as well as the electron cryomicroscopy structure of the 229E S-protein. The structures show that common core interactions define the specificity for hAPN and that the peripheral RBD sequence variation is accommodated by loop plasticity. The results provide insight into immune evasion and the crossspecies transmission of 229E and related coronaviruses. We also find that the 229E S-protein can expose a portion of its helical core to solvent. This is undoubtedly facilitated by hydrophilic subunit interfaces that we show are conserved among coronaviruses. These interfaces likely play a role in the S-protein conformational changes associated with membrane fusion.Li et al. eLife 2019;8:e51230.

RNA viruses are characterized by a high mutation rate, a buffer against environmental change. Nevertheless, the means by which random mutation improves viral fitness is not well characterized. Here we report the X-ray crystal structure of the receptor-binding domain (RBD) of the human coronavirus, HCoV-229E, in complex with the ectodomain of its receptor, aminopeptidase N (APN). Three extended loops are solely responsible for receptor binding and the evolution of HCoV-229E and its close relatives is accompanied by changing loop–receptor interactions. Phylogenetic analysis shows that the natural HCoV-229E receptor-binding loop variation observed defines six RBD classes whose viruses have successively replaced each other in the human population over the past 50 years. These RBD classes differ in their affinity for APN and their ability to bind an HCoV-229E neutralizing antibody. Together, our results provide a model for alphacoronavirus adaptation and evolution based on the use of extended loops for receptor binding.

The role of dolichol phosphate in the synthesis of N-glycosidically linked oligosaccharides of glycoproteins is well documented (see Refs. 1 and 2 for recent reviews). These glycoproteins possess a common core region ( 2 N-acetylglucosamine and at least 3 mannose residues) synthesized via the dolichol phosphate pathway. An oligosaccharide is preformed on dolichol phosphate, transferred to an asparagine residue in the protein, and then extensively modified to yield a heterogeneous population of N-linked oligosaccharides.Another class of glycoconjugates, composed of most of the proteoglycans, also contains a core oligosaccharide structure. This core is a tetrasaccharide (glucuronic acid-galactose-gaGrants 5R01 NS15775-02 and AM-05816. This paper is part of the

Pg has distinct immunomodulatory properties involved in poorly understood immune phenomena, including maternal tolerance of the fetus, increased risk of certain infections during pregnancy or after Pg birth control, and pregnancy-associated remission of autoimmune disease. Several potential mechanisms have been identified, including alteration of Th1 and Treg activity, but the precise cellular and molecular targets of Pg immunomodulation in vivo remain obscure, partly because Pg can signal through several different receptor types. One such receptor, the iPR, encoded by the pgr gene, is essential for reproduction in female mice and is expressed in the thymus and CD4(+) T cells. We hypothesized that iPR regulates CD4(+) T cell activity and adaptive immune responses in vivo. With the use of iPR KO mice, we demonstrate that iPR specifically suppresses TD antibody responses, primarily by dampening CD4(+) Teff activity, likely via transcriptional repression of the IFN-γ gene and modulation of other programs regulating CD4(+) T cells. Our results highlight a novel mechanism linking the endocrine and immune systems, and they offer insight into important but poorly understood phenomena in women's health and autoimmunity.

Important interactions between female reproduction and autoimmunity are suggested by the female-predominance of systemic lupus erythematosus (SLE) and other autoimmune diseases and the amelioration of certain autoimmune diseases during pregnancy. Sexually dimorphic risk of developing SLE involves modulation of genetic risk by environmental factors, sex hormones and non-hormonal factors encoded on the sex chromosomes. In some lupus models, estrogen, via estrogen receptor alpha (ER-α), enhances production of highly pathogenic IgG2a/c autoantibodies (autoAbs). Some studies indicate that treatment with progesterone, a chief female reproductive steroid, can suppress IgG2a/2c autoAb production. Little is known about how endogenous progesterone impacts lupus autoimmunity. To investigate this, we introduced a disruptive progesterone receptor (PR) gene mutation into lupus-prone mice and tracked the development of spontaneous IgG autoAbs. Here, we present evidence that PR can suppress the emergence of class-switched IgG2c autoAbs, suggesting that PR and ER-α counter-regulate a critical step in lupus autoimmunity. PR's control of IgG2c autoAb production correlates with alterations in the relative abundance of splenic T follicular helper (TFH) cells and non-TFH CD4+ T cells, especially regulatory T cells (TREGS). Surprisingly, PR also appears to help maintain sexually dimorphic abundance of splenic leukocytes, a feature common to many mouse models of SLE. Together our results identify a novel molecular link between female reproduction and lupus autoimmunity. Further investigation into the immunomodulatory functions of PR promises to inform reproductive health care in women and offer mechanistic insight into important immunologic phenomena of pregnancy.

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