Analysis of a Subacute Sclerosing Panencephalitis Genotype B3 Virus from the 2009-2010 South African Measles Epidemic Shows That Hyperfusogenic F Proteins Contribute to Measles Virus Infection in the Brain.

During a measles virus (MeV) epidemic in 2009 in South Africa, measles inclusion body encephalitis (MIBE) was identified in several HIV-infected patients. Years later, children are presenting with subacute sclerosing panencephalitis (SSPE). To investigate the features of established MeV neuronal infections, viral sequences were analyzed from brain tissue samples of a single SSPE case and compared with MIBE sequences previously obtained from patients infected during the same epidemic. Both the SSPE and the MIBE viruses had amino acid substitutions in the ectodomain of the F protein that confer enhanced fusion properties. Functional analysis of the fusion complexes confirmed that both MIBE and SSPE F protein mutations promoted fusion with less dependence on interaction by the viral receptor-binding protein with known MeV receptors. While the SSPE F required the presence of a homotypic attachment protein, MeV H, in order to fuse, MIBE F did not. Both F proteins had decreased thermal stability compared to that of the corresponding wild-type F protein. Finally, recombinant viruses expressing MIBE or SSPE fusion complexes spread in the absence of known MeV receptors, with MIBE F-bearing viruses causing large syncytia in these cells. Our results suggest that alterations to the MeV fusion complex that promote fusion and cell-to-cell spread in the absence of known MeV receptors is a key property for infection of the brain.IMPORTANCE Measles virus can invade the central nervous system (CNS) and cause severe neurological complications, such as MIBE and SSPE. However, mechanisms by which MeV enters the CNS and triggers the disease remain unclear. We analyzed viruses from brain tissue of individuals with MIBE or SSPE, infected during the same epidemic, after the onset of neurological disease. Our findings indicate that the emergence of hyperfusogenic MeV F proteins is associated with infection of the brain. We also demonstrate that hyperfusogenic F proteins permit MeV to enter cells and spread without the need to engage nectin-4 or CD150, known receptors for MeV that are not present on neural cells.

The PACS-2 protein and trafficking motifs in CCHFV Gn and Gc cytoplasmic domains govern CCHFV assembly.

The Crimean-Congo hemorrhagic fever virus (CCHFV) is a tick-borne bunyavirus that causes high mortality in humans. This enveloped virus harbors two surface glycoproteins (GP), Gn and Gc, that are released by processing of a glycoprotein precursor complex whose maturation takes place in the ER and is completed through the secretion pathway. Here, we characterized the trafficking network exploited by CCHFV GPs during viral assembly, envelopment, and/or egress. We identified membrane trafficking motifs in the cytoplasmic domains (CD) of CCHFV GPs and addressed how they impact these late stages of the viral life cycle using infection and biochemical assays, and confocal microscopy in virus-producing cells. We found that several of the identified CD motifs modulate GP transport through the retrograde trafficking network, impacting envelopment and secretion of infectious particles. Finally, we identified PACS-2 as a crucial host factor contributing to CCHFV GPs trafficking required for assembly and release of viral particles.

The low-density lipoprotein receptor and apolipoprotein E associated with CCHFV particles mediate CCHFV entry into cells.

The Crimean-Congo hemorrhagic fever virus (CCHFV) is an emerging pathogen of the Orthonairovirus genus that can cause severe and often lethal hemorrhagic diseases in humans. CCHFV has a broad tropism and can infect a variety of species and tissues. Here, by using gene silencing, blocking antibodies or soluble receptor fragments, we identify the low-density lipoprotein receptor (LDL-R) as a CCHFV entry factor. The LDL-R facilitates binding of CCHFV particles but does not allow entry of Hazara virus (HAZV), another member of the genus. In addition, we show that apolipoprotein E (apoE), an exchangeable protein that mediates LDL/LDL-R interaction, is incorporated on CCHFV particles, though not on HAZV particles, and enhances their specific infectivity by promoting an LDL-R dependent entry. Finally, we show that molecules that decrease LDL-R from the surface of target cells could inhibit CCHFV infection. Our study highlights that CCHFV takes advantage of a lipoprotein receptor and recruits its natural ligand to promote entry into cells.

Host-Pathogen Interactions Influencing Zoonotic Spillover Potential and Transmission in Humans.

Emerging infectious diseases of zoonotic origin are an ever-increasing public health risk and economic burden. The factors that determine if and when an animal virus is able to spill over into the human population with sufficient success to achieve ongoing transmission in humans are complex and dynamic. We are currently unable to fully predict which pathogens may appear in humans, where and with what impact. In this review, we highlight current knowledge of the key host-pathogen interactions known to influence zoonotic spillover potential and transmission in humans, with a particular focus on two important human viruses of zoonotic origin, the Nipah virus and the Ebola virus. Namely, key factors determining spillover potential include cellular and tissue tropism, as well as the virulence and pathogenic characteristics of the pathogen and the capacity of the pathogen to adapt and evolve within a novel host environment. We also detail our emerging understanding of the importance of steric hindrance of host cell factors by viral proteins using a "flytrap"-type mechanism of protein amyloidogenesis that could be crucial in developing future antiviral therapies against emerging pathogens. Finally, we discuss strategies to prepare for and to reduce the frequency of zoonotic spillover occurrences in order to minimize the risk of new outbreaks.

Early Permissiveness of Central Nervous System Cells to Measles Virus Infection Is Determined by Hyperfusogenicity and Interferon Pressure.

The cessation of measles virus (MeV) vaccination in more than 40 countries as a consequence of the COVID-19 pandemic is expected to significantly increase deaths due to measles. MeV can infect the central nervous system (CNS) and lead to lethal encephalitis. Substantial part of virus sequences recovered from patients' brain were mutated in the matrix and/or the fusion protein (F). Mutations of the heptad repeat domain located in the C terminal (HRC) part of the F protein were often observed and were associated to hyperfusogenicity. These mutations promote brain invasion as a hallmark of neuroadaptation. Wild-type F allows entry into the brain, followed by limited spreading compared with the massive invasion observed for hyperfusogenic MeV. Taking advantage of our ex vivo models of hamster organotypic brain cultures, we investigated how the hyperfusogenic mutations in the F HRC domain modulate virus distribution in CNS cells. In this study, we also identified the dependence of neural cells susceptibility on both their activation state and destabilization of the virus F protein. Type I interferon (IFN-I) impaired mainly astrocytes and microglial cells permissiveness contrarily to neurons, opening a new way of consideration on the development of treatments against viral encephalitis.

Molecular Features of the Measles Virus Viral Fusion Complex That Favor Infection and Spread in the Brain.

Measles virus (MeV) bearing a single amino acid change in the fusion protein (F)-L454W-was isolated from two patients who died of MeV central nervous system (CNS) infection. This mutation in F confers an advantage over wild-type virus in the CNS, contributing to disease in these patients. Using murine ex vivo organotypic brain cultures and human induced pluripotent stem cell-derived brain organoids, we show that CNS adaptive mutations in F enhance the spread of virus ex vivo. The spread of virus in human brain organoids is blocked by an inhibitory peptide that targets F, confirming that dissemination in the brain tissue is attributable to F. A single mutation in MeV F thus alters the fusion complex to render MeV more neuropathogenic. IMPORTANCE Measles virus (MeV) infection can cause serious complications in immunocompromised individuals, including measles inclusion body encephalitis (MIBE). In some cases, MeV persistence and subacute sclerosing panencephalitis (SSPE), another severe central nervous system (CNS) complication, develop even in the face of a systemic immune response. Both MIBE and SSPE are relatively rare but lethal. It is unclear how MeV causes CNS infection. We introduced specific mutations that are found in MIBE or SSPE cases into the MeV fusion protein to test the hypothesis that dysregulation of the viral fusion complex-comprising F and the receptor binding protein, H-allows virus to spread in the CNS. Using metagenomic, structural, and biochemical approaches, we demonstrate that altered fusion properties of the MeV H-F fusion complex permit MeV to spread in brain tissue.

Monoclonal therapy against calcitonin gene-related peptide lowers hyperglycemia and adiposity in type 2 diabetes mouse models.

OBJECTIVE: Calcitonin Gene-Related Peptide α (CGRPα) is a multifunctional neuropeptide found in the central and peripheral nervous system with cardiovascular, nociceptive, and gastrointestinal activities. CGRPα has been linked to obesity and insulin secretion but the role of this circulating peptide in energy metabolism remains unclear. Here, we thought to utilize a monoclonal antibody against circulating CGRPα to assess its ability to improve glucose homeostasis in mouse models of hyperglycemia and diabetes. METHODS: We examined the outcome of anti-CGRPα treatment in mouse models of diabetes and diet-induced obesity, using db/db mice, Streptozotocin (STZ) treatment to eliminate pancreatic islets, and high fat diet-fed mice. We also correlated these data with application of recombinant CGRPα peptide on cultured mature adipocytes to measure its impact on mitochondrial bioenergetics and fatty acid oxidation. Furthermore, we applied recombinant CGRPα to primary islets to measure glucose-stimulated insulin secretion (GSIS) and gene expression. RESULTS: BL6-db diabetic mice receiving anti-CGRPα treatment manifested weight loss, reduced adiposity, improved glucose tolerance, insulin sensitivity, GSIS and reduced pathology in adipose tissue and liver. Anti-CGRPα failed to modulate weight or glucose homeostasis in STZ-treated animals. High fat diet-fed mice showed reduced adiposity but no benefit on glucose homeostasis. Considering these findings, we postulated that CGRPα may have dual effects on adipocytes to promote lipid utilization while acting on pancreatic ß-cells to modulate insulin secretion. Analysis of CGRPα in the pancreas showed that the peptide localized to insulin-positive cells and perivascular nerves surrounding islets. Ex-vivo analysis of pancreatic islets determined that CGRPα blocked GSIS and reduced insulin-2 gene expression. Mechanistical analysis revealed that recombinant CGRPα was able to reduce glycolytic capacity as well as fatty acid oxidation in primary white adipocytes. CONCLUSIONS: These results establish a multifaceted role in energy metabolism for circulating CGRPα, with the ability to modulate thermogenic pathways in adipose tissue, as well as pancreatic ß-cell dependent insulin secretion. Reducing circulating CGRPα levels with monoclonal therapy presents therapeutic potential for type 2 diabetes as shown in BL6-db/db mice but has reduced potential for models of hyperglycemia resulting from loss of ß-cells (STZ treatment).