SLAM- and Nectin-4-Independent Noncytolytic Spread of Canine Distemper Virus in Astrocytes

Abstract

Measles and canine distemper viruses (MeV and CDV, respectively) first replicate in lymphatic and epithelial tissues by using SLAM and nectin-4 as entry receptors, respectively. The viruses may also invade the brain to establish persistent infections, triggering fatal complications, such as subacute sclerosis pan-encephalitis (SSPE) in MeV infection or chronic, multiple sclerosislike, multifocal demyelinating lesions in the case of CDV infection. In both diseases, persistence is mediated by viral nucleocapsids that do not require packaging into particles for infectivity but are directly transmitted from cell to cell (neurons in SSPE or astrocytes in distemper encephalitis), presumably by relying on restricted microfusion events. Indeed, although morphological evidence of fusion remained undetectable, viral fusion machineries and, thus, a putative cellular receptor, were shown to contribute to persistent infections. Here, we first showed that nectin-4-dependent cell-cell fusion in Vero cells, triggered by a demyelinating CDV strain, remained extremely limited, thereby supporting a potential role of nectin-4 in mediating persistent infections in astrocytes. However, nectin-4 could not be detected in either primary cultured astrocytes or the white matter of tissue sections. In addition, a bioengineered "nectin-4-blind" recombinant CDV retained full cell-to-cell transmission efficacy in primary astrocytes. Combined with our previous report demonstrating the absence of SLAM expression in astrocytes, these findings are suggestive for the existence of a hitherto unrecognized third CDV receptor expressed by glial cells that contributes to the induction of noncytolytic cell-to-cell viral transmission in astrocytes. IMPORTANCE While persistent measles virus (MeV) infection induces SSPE in humans, persistent canine distemper virus (CDV) infectioncauses chronic progressive or relapsing demyelination in carnivores. Common to both central nervous system (CNS) infections is that persistence is based on noncytolytic cell-to-cell spread, which, in the case of CDV, was demonstrated to rely on functional membrane fusion machinery complexes. This inferred a mechanism where nucleocapsids are transmitted through macroscopically invisible microfusion events between infected and target cells. Here, we provide evidence that CDV induces such microfusions in a SLAM-and nectin-4-independent manner, thereby strongly suggesting the existence of a third receptor expressed in glial cells (referred to as GliaR). We propose that GliaR governs intercellular transfer of nucleocapsids and hence contributes to viral persistence in the brain and ensuing demyelinating lesions.

Infectious Progression of Canine Distemper Virus from Circulating Cerebrospinal Fluid into the Central Nervous System

“…Pratakpiriya et al detected nectin-4 in dog brain and postulated that CDV can infect the CNS through nectin-4 (14). Conversely, Alves et al did not detect nectin-4 in primary dog brain cell cultures or in the white matter of dog brain tissues (15). In our study, Vero and HEK293 cells were nectin-4 negative, which suggests that the H protein of CDV-OndMB likely uses an unidentified receptor for entry into these cells.…”

“…Nectin-4 has also been identified as a receptor for polarized epithelial cells (12)(13)(14). CDV also infects SLAM-and nectin-4-negative cell types in the central nervous system (CNS) (15), suggesting the existence of an unidentified third receptor.…”

Pathogenesis of canine distemper virus in experimentally infected raccoon dogs, foxes, and minks

“…The infection of other cells, i.e. epithelial cells and neurons, is most likely mediated by binding on a newly identified Nectin-4 receptor or to other yet unidentified receptors (Noyce et al, 2013;Pratakpiriya et al, 2012;Alves et al, 2015). SLAM-related immune cell infection induces CDV entry and immune suppression while Nectin-4-based epithelial cell infection is important for the development of clinical signs and efficient virus shedding (von Messling et al, 2004;Sawatsky et al, 2012).…”

Morbillivirus Experimental Animal Models: Measles Virus Pathogenesis Insights from Canine Distemper Virus

“…However, this model has not been further developed or used in recent years. Instead, an in vitro culture system of different CNS cell types is being increasingly used to study the mechanisms involved in morbillivirus CNS persistence and to explore therapeutic strategies [67,68,69]. …”