Infectability of human BrainSphere neurons suggests neurotropism of SARS-CoV-2

C Korin Bullen

doi:10.14573/altex.2006111

Abstract

Reports from Wuhan suggest that 36% of COVID-19 patients show neurological symptoms, and cases of viral encephalitis have been reported, suggesting that the virus is neurotropic under unknown circumstances. This is well established for other coronaviruses. In order to understand why some patients develop such symptoms and others do not, we address herein the infectability of the central nervous system (CNS). Reports that the ACE2 receptor – critical for virus entry into lung cells – is found in different neurons support this expectation. We employed a human induced pluripotent stem cell (iPSC)- derived BrainSphere model, which we used earlier for Zika, Dengue, HIV and John Cunningham virus infection studies. We detected the expression of the ACE2 receptor, but not TMPRSS2, in the model. Incubating the BrainSpheres for 6 hours with SARS-CoV-2 at a multiplicity of infection (MOI) of 0.1 led to infection of a fraction of neural cells with replication of the virus evident at 72 hpi. Virus particles were found in the neuronal cell body extending into apparent neurite structures. PCR measurements corroborated the replication of the virus, suggesting at least a tenfold increase in virus copies per total RNA. Leveraging state-of-the-art 3D organotypic cell culture, which has been shown to allow both virus infection and modeling of (developmental) neurotoxicity but is at the same time simple enough to be transferred and used in a BSL-3 environment, we demonstrate, for the first time, the potential critically important neurotropism of SARS-CoV-2.

Highlights

The question whether severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infects brain cells and induces neuropathology or derails neural physiology is of critical importance for the understanding of this disease and its potential long-term sequelae
3.1 ACE2 but not TMPRSS2 is expressed in neuroprogenitor cells (NPC) and mature BrainSpheres It has been shown that SARS-CoV-2 utilizes angiotensin-converting enzyme 2 (ACE2) receptors to enter cells and transmembrane serine protease 2 (TMPRSS2) for S protein priming (Hoffmann et al, 2020)
The relatively frequent neurological symptoms in COVID-19 patients (Mao et al, 2020; Helms et al, 2020) prompted us to investigate whether SARS-CoV-2 can infect BrainSpheres directly

Summary

Introduction

The question whether severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infects brain cells and induces neuropathology or derails neural physiology is of critical importance for the understanding of this disease and its potential long-term sequelae. Initial reports from Wuhan, China, where the virus first emerged, indicate that 36% of COVID-19 patients have neurological symptoms (Mao et al, 2020), in the meantime confirmed by a European collective (Helms et al, 2020), and a case of acute hemorrhagic necrotizing encephalopathy, a rare encephalopathy that has been associated with other viral infections, has been reported in a COVID-19 patient (Poyiadji et al, 2020). The availability of experimental models to study SARS-CoV-2 is critical for drug development (Busquet et al, 2020) and to understand environmental cofactors for public health measures. Viral infections are the prototypic species-specific dis-

Methods

Results

Conclusion