Axonal Transport Enables Neuron-to-Neuron Propagation of Human Coronavirus OC43

Abstract

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.

Non-invasive bioluminescence imaging of HCoV-OC43 infection and therapy in the central nervous system of live mice

“…HCoV-OC43, a respiratory CoV, could be a powerful tool for gaining new insights into the neurological manifestations and neurotropic mechanisms of other respiratory viruses. In the present study, our data demonstrated that rOC43-ns2DelRluc levels reflected HCoV-OC43-WT replication in the brain and its spread to the spinal cord of living mice, with bioluminescence intensity directly correlating with viral loads as measured by IFA and western blot and consistent with previous studies (Dubé et al, 2018;Jacomy et al, 2006).…”

“…2A, upper), whereas low viral RNA levels were detected in the hearts and spleen, and extremely low levels were detected in the blood ( Fig. 2A, lower), consistent with previous reports on HCoV-OC43-WT (Dubé et al, 2018;Jacomy and Talbot, 2003). Immunostaining of brain and spinal cord sections from mice that underwent intracerebral infection confirmed the presence of rOC43-ns2DelRluc ( Fig.…”

Human Coronaviruses and Other Respiratory Viruses: Underestimated Opportunistic Pathogens of the Central Nervous System?

“…Furthermore, based on more recent work [269], Figure 1 illustrates the olfactory route, which is clearly the main route of neuroinvasion used by HCoV-OC43, as well as the early steps of subsequent neuropropagation within the CNS in susceptible mice and recapitulates the suggested equivalent pathway in humans. Nevertheless, our data suggest that HCoV-OC43 may also invade the CNS from the external environment through other pathways involving other cranial peripheral nerves [269], reminiscent of what was shown for other human respiratory viruses such as RSV and influenza virus [8]. Therefore, on the one hand, an apparently innocuous human respiratory pathogen such as the HCoV may reach the CNS by different routes and induce short-term illnesses, such as encephalitis.…”

“…Experimental intranasal infections of susceptible mice also indicate that, once it has invaded the CNS, the virus disseminated to several regions of the brain and the brainstem before it eventually reaches the spinal cord [266][267][268]. Furthermore, based on more recent work [269], Figure 1 illustrates the olfactory route, which is clearly the main route of neuroinvasion used by HCoV-OC43, as well as the early steps of subsequent neuropropagation within the CNS in susceptible mice and recapitulates the suggested equivalent pathway in humans. Nevertheless, our data suggest that HCoV-OC43 may also invade the CNS from the external environment through other pathways involving other cranial peripheral nerves [269], reminiscent of what was shown for other human respiratory viruses such as RSV and influenza virus [8].…”

“…In susceptible mice, HCoV-OC43 has a selective tropism for neurons in which it is able to use axonal transport as a way of neuron-to-neuron propagation [269]. These results, together with data harvested with the use of microfluidic devices (Xona microfluidic), helped to elaborate a putative model of propagation adapted from Tomishima and Enquist [291], in which infectious HCoV-OC43 could either be assembled in the cell body or at different points along the axon using the anterograde axonal transport to propagate between neurons or from neurons to glial cells surrounding neurons in the CNS (Figure 2).…”