COVID-19 Induces Neuroinflammation and Suppresses Peroxisomes in the Brain

OBJECTIVE

Peroxisome injury occurs in the central nervous system (CNS) during multiple virus infections that result in neurological disabilities. We investigated host neuroimmune responses and peroxisome biogenesis factors during severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection using a multiplatform strategy.

METHODS

Brain tissues from coronavirus disease 2019 (COVID-19) (n = 12) and other disease control (ODC) (n = 12) patients, as well as primary human neural cells and Syrian hamsters, infected with a clinical variant of SARS-CoV-2, were investigated by droplet digital polymerase chain reaction (ddPCR), quantitative reverse transcriptase PCR (RT-qPCR), and immunodetection methods.

RESULTS

SARS-CoV-2 RNA was detected in the CNS of 4 patients with COVID-19 with viral protein (NSP3 and spike) immunodetection in the brainstem. Olfactory bulb, brainstem, and cerebrum from patients with COVID-19 showed induction of pro-inflammatory transcripts (IL8, IL18, CXCL10, NOD2) and cytokines (GM-CSF and IL-18) compared to CNS tissues from ODC patients (p < 0.05). Peroxisome biogenesis factor transcripts (PEX3, PEX5L, PEX11β, and PEX14) and proteins (PEX3, PEX14, PMP70) were suppressed in the CNS of COVID-19 compared to ODC patients (p < 0.05). SARS-CoV-2 infection of hamsters revealed viral RNA detection in the olfactory bulb at days 4 and 7 post-infection while inflammatory gene expression was upregulated in the cerebrum of infected animals by day 14 post-infection (p < 0.05). Pex3 transcript levels together with catalase and PMP70 immunoreactivity were suppressed in the cerebrum of SARS-CoV-2 infected animals (p < 0.05).

INTERPRETATION

COVID-19 induced sustained neuroinflammatory responses with peroxisome biogenesis factor suppression despite limited brainstem SARS-CoV-2 neurotropism in humans. These observations offer insights into developing biomarkers and therapies, while also implicating persistent peroxisome dysfunction as a contributor to the neurological post-acute sequelae of COVID-19. ANN NEUROL 2023;94:531-546.

Upregulation of TRAIL expression on human T lymphocytes by interferon b and glatiramer acetate

We measured the in vivo and in vitro effects of interferon (IFN)b and glatiramer acetate (GA) on the expression of the regulatory molecule, tumor necrosis factor related apoptosis inducing ligand (TRAIL), in patients with multiple sclerosis (MS). We confirmed the prior observation that TRAIL is enhanced on anti-CD3 activated T cells by the in vitro addition of IFNβ. T cells from IFNβ-treated patients stimulated with anti-CD3 only, had higher levels of TRAIL than untreated patients, suggesting that in vivo IFNβ exposure has an effect on TRAIL expression in association with T cell activation. In vitro IFNβ-induced TRAIL upregulation on anti-CD3 or phytohemagglutinin-activated T cells was comparable for IFNβ-treated and non-treated MS patients and controls, indicating that IFN receptors were neither saturated nor down-regulated by current IFNβ therapy. Although GAin vivo orin vitro did not induce TRAIL, the IFNβ-GA combination in vitro enhanced TRAIL expression to higher levels than IFNβ alone on CD4+ T cells obtained from MS patients, regardless of GA treatment status, and healthy donors, and on GA reactive T cell lines derived from GA-treated patients or controls. Whether any observed therapeutic effects of GA/IFNβ combination therapy will correlate with TRAIL expression and function remains to be determined.

TLR-mediated B cell activation results in ectopic CLIP expression that promotes B cell-dependent inflammation

Infectious pathogens produce compounds called Toll ligands that activate TLRs on lymphocytes. Acute activation triggered by certain TLRs appears to "jump start" the innate immune response, characterized by the release of inflammatory cytokines and cellular expansion. In some individuals, there is a failure to control acute inflammation, resulting in postinfectious, chronic inflammation. Susceptibility to chronic inflammation is strongly associated with an individual's MHC genes. Recent clinical trials for several autoimmune diseases characterized by chronic inflammation suggest that B lymphocyte depletion therapies dampen chronic immune activation. However, currently, there is no known mechanism that accounts for the correlation among TLR activation, MHC genetics, and a pathological role for B-lymphocytes. Our hypothesis is that TLR-activated B cells (B cells that have been polyclonally activated in the absence of antigen-specific signals) are not controlled properly by T cell-dependent B cell death, thereby causing B cell-dependent chronic inflammation. Here, we show that treatment with Toll ligands results in polyclonal B cell activation accompanied by ectopic expression of CLIP. Furthermore, by adoptively transferring purified CLIP+ B cells in syngeneic animals, we find that CLIP+ B cells induce production of TNF-α by host T cells. Finally, we demonstrate that CLIP-targeted peptide competition results in the death of polyclonally activated CLIP+ B cells.

Neuroinvasion by human respiratory coronaviruses

Human coronaviruses (HCoV) cause common colds but can also infect neural cell cultures. To provide definitive experimental evidence for the neurotropism and neuroinvasion of HCoV and its possible association with multiple sclerosis (MS), we have performed an extensive search and characterization of HCoV RNA in a large panel of human brain autopsy samples. Very stringent reverse transcription-PCR with two primer pairs for both viral strains (229E and OC43), combined with Southern hybridization, was performed on samples from 90 coded donors with various neurological diseases (39 with MS and 26 with other neurological diseases) or normal controls (25 patients). We report that 44% (40 of 90) of donors were positive for 229E and that 23% (21 of 90) were positive for OC43. A statistically significant higher prevalence of OC43 in MS patients (35.9%; 14 of 39) than in controls (13.7%; 7 of 51) was observed. Sequencing of nucleocapsid protein (N) gene amplicons revealed point mutations in OC43, some consistently found in three MS patient brains and one normal control but never observed in laboratory viruses. In situ hybridization confirmed the presence of viral RNA in brain parenchyma, outside blood vessels. The presence of HCoV in human brains is consistent with neuroinvasion by these respiratory pathogens. Further studies are needed to distinguish between opportunistic and disease-associated viral presence in human brains.

Persistent infection of human oligodendrocytic and neuroglial cell lines by human coronavirus 229E

Human coronaviruses (HuCV) cause common colds. Previous reports suggest that these infectious agents may be neurotropic in humans, as they are for some mammals. With the long-term aim of providing experimental evidence for the neurotropism of HuCV and the establishment of persistent infections in the nervous system, we have evaluated the susceptibility of various human neural cell lines to acute and persistent infection by HuCV-229E. Viral antigen, infectious virus progeny and viral RNA were monitored during both acute and persistent infections. The astrocytoma cell lines U-87 MG, U-373 MG, and GL-15, as well as neuroblastoma SK-N-SH, neuroglioma H4, and oligodendrocytic MO3.13 cell lines, were all susceptible to an acute infection by HuCV-229E. The CHME-5 immortalized fetal microglial cell line was not susceptible to infection by this virus. The MO3.13 and H4 cell lines also sustained a persistent viral infection, as monitored by detection of viral antigen and infectious virus progeny. Sequencing of the S1 gene from viral RNA after approximately 130 days of infection showed two point mutations, suggesting amino acid changes during persistent infection of MO3.13 cells but none for H4 cells. Thus, persistent in vitro infection did not generate important changes in the S1 portion of the viral spike protein, which was shown for murine coronaviruses to bear hypervariable domains and to interact with cellular receptor. These results are consistent with the potential persistence of HuCV-229E in cells of the human nervous system, such as oligodendrocytes and possibly neurons, and the virus's apparent genomic stability.

Acute and persistent infection of human neural cell lines by human coronavirus OC43

Human coronaviruses (HuCV) are recognized respiratory pathogens. Data accumulated by different laboratories suggest their neurotropic potential. For example, primary cultures of human astrocytes and microglia were shown to be susceptible to an infection by the OC43 strain of HuCV (A. Bonavia, N. Arbour, V. W. Yong, and P. J. Talbot, J. Virol. 71:800-806, 1997). We speculate that the neurotropism of HuCV will lead to persistence within the central nervous system, as was observed for murine coronaviruses. As a first step in the verification of our hypothesis, we have characterized the susceptibility of various human neural cell lines to infection by HuCV-OC43. Viral antigen, infectious virus progeny, and viral RNA were monitored during both acute and persistent infections. The astrocytoma cell lines U-87 MG, U-373 MG, and GL-15, as well as neuroblastoma SK-N-SH, neuroglioma H4, oligodendrocytic MO3.13, and the CHME-5 immortalized fetal microglial cell lines, were all susceptible to an acute infection by HuCV-OC43. Viral antigen and RNA and release of infectious virions were observed during persistent HuCV-OC43 infections ( approximately 130 days of culture) of U-87 MG, U-373 MG, MO3.13, and H4 cell lines. Nucleotide sequences of RNA encoding the putatively hypervariable viral S1 gene fragment obtained after 130 days of culture were compared to that of initial virus input. Point mutations leading to amino acid changes were observed in all persistently infected cell lines. Moreover, an in-frame deletion was also observed in persistently infected H4 cells. Some point mutations were observed in some molecular clones but not all, suggesting evolution of the viral population and the emergence of viral quasispecies during persistent infection of H4, U-87 MG, and MO3.13 cell lines. These results are consistent with the potential persistence of HuCV-OC43 in cells of the human nervous system, accompanied by the production of infectious virions and molecular variation of viral genomic RNA.

Persistent infection of neural cell lines by human coronaviruses

Human coronaviruses (HCV) have been associated mainly with infections of the respiratory tract. Accumulating evidence from in vitro and in vivo observations is consistent with the neurotropism of these viruses in humans. To verify the possibility of a persistent infection within the central nervous system (CNS), various human cell lines of neural origin were tested for their ability to maintain chronic infection by both known strains of HCV, OC43 and 229E. Production of infectious progeny virions was monitored by an immunoperoxydase assay on a susceptible cell line and viral RNA was observed after RT-PCR. Astrocytic cell lines U-373 MG and U-87 MG did not sustain a persistent HCV-229E infection, even though they were susceptible to an acute infection by this virus. On the other hand, these two cell lines could maintain a persistent infection by HCV-OC43 for as many as 25 cell passages (about 130 days of culture). Relatively stable titers of infectious viral particles, as well as apparently constant amounts of viral RNA were detected throughout the persistent infection of U-87 MG cells. However, persistent infection of U-373 MG cells was accompanied by the detection of infectious viral particles from passage 0 to passage 13 and then from passage 20 to the end of the experiment. This gap in the production of infectious virions was correlated by a drop in the apparent amount of viral RNA detected at passages 15 and 20. These results confirm the ability of HCV-OC43 to persistently infect cells of an astrocytic lineage and, together with our previous observations of HCV infection of primary cultures of human astrocytes and the detection of HCV RNA in human brains, are consistent with the possibility that this human coronavirus could persist in the human CNS by targeting astrocytes.

Involvement of aminopeptidase N (CD13) in infection of human neural cells by human coronavirus 229E

Attachment to a cell surface receptor can be a major determinant of virus tropism. Previous studies have shown that human respiratory coronavirus HCV-229E uses human aminopeptidase N (hAPN [CD13]) as its cellular receptor for infection of lung fibroblasts. Although human coronaviruses are recognized respiratory pathogens, occasional reports have suggested their possible neurotropism. We have previously shown that human neural cells, including glial cells in primary cultures, are susceptible to human coronavirus infection in vitro (A. Bonavia, N. Arbour, V. W. Yong, and P. J. Talbot, J. Virol. 71:800-806, 1997). However, the only reported expression of hAPN in the nervous system is at the level of nerve synapses. Therefore, we asked whether hAPN is utilized as a cellular receptor for infection of these human neural cell lines. Using flow cytometry, we were able to show the expression of hAPN on the surfaces of various human neuronal and glial cell lines that are susceptible to HCV-229E infection. An hAPN-specific monoclonal antibody (WM15), but not control antibody, inhibited the attachment of radiolabeled HCV-229E to astrocytic, neuronal, and oligodendrocytic cell lines. A correlation between the apparent amount of cell surface hAPN and the level of virus attachment was observed. Furthermore, the presence of WM15 inhibited virus infection of these cell lines, as detected by indirect immunofluorescence. These results indicate that hAPN (CD13) is expressed on neuronal and glial cell lines in vitro and serves as the receptor for infection by HCV-229E. This further strengthens the neurotropic potential of this human respiratory virus.

Infection of primary cultures of human neural cells by human coronaviruses 229E and OC43

We evaluated the ability of human coronaviruses to infect primary cultures of human neural cells. Double immunofluorescence with antibodies to virus and cell markers showed infection of fetal astrocytes and of adult microglia and astrocytes by strain OC43. RNA amplification revealed infection of fetal astrocytes, adult microglia, and a mixed culture of adult oligodendrocytes and astrocytes by strain 229E. Infectious virus was released only from fetal astrocytes, with higher titers for OC43. Human coronaviruses have the capacity to infect some cells of the central nervous system, although infection of adult cells appears abortive.

N-formyl-methionyl-leucyl-phenylalanine induces and modulates IL-1 and IL-6 in human PBMC

N-formyl-methionyl-leucyl-phenylalanine (fMLP), a bacterial derivative, induces and modulates various cellular responses linked to inflammation. In this work we evaluated the impact of fMLP stimulation on three pro-inflammatory cytokines: IL-1 alpha, IL-1 beta and IL-6. We found that fMLP induces the secretion of IL-1 alpha, IL-1 beta and IL-6 in human peripheral blood mononuclear cells (PBMC). It also increased LPS-induced secretion of these three cytokines. Northern blot analysis demonstrated that fMLP induced IL-1 alpha, IL-1 beta and IL-6 gene expression by human PBMC. The fMLP-induced IL-1 alpha and IL-1 beta gene expression and IL-6 secretion were abolished by pertussis toxin pretreatment, which suggests that the fMLP induction of cytokine was also mediated via a Gi protein. The concentration range of fMLP used to obtain these effects, in a dose dependent fashion, was 20 microM to 1100 microM. The mechanism by which fMLP modulates cytokine secretion is still not characterized. fMLP seems to share similar biological activities with other chemotactic factors (C5a, MCP-1, PAF, IL-8) that are able to modulate cytokines, and whose receptors belong to the same superfamily as the fMLP receptor(s).

Differential effects of PKC inhibitors on gelatinase B and interleukin 6 production in the mouse macrophage

Pretreatment of LPS-induced RAW 264.7 cells with three PKC inhibitors suggests that induction of TNF-alpha, nitric oxide (NO), gelatinase B (Gel B) and IL-6 involves at least three distinct signalling pathways. We confirmed the PKC dependence of TNF-alpha and NO productions and found that Gel B was inhibited by Calphostin C (CAL), but potentiated by staurosporine (STAR) and CGP 41 251. IL-6 production was stimulated by the three inhibitors. Our results indicate that up-regulation of Gel B, TNF-alpha and NO seems to involve PKC at different levels, whereas up-regulation of IL-6 production appears to be PKC-independent. However, IL-6 production in RAW 264.7 cells seems to be down-regulated by a PKC-dependent feedback mechanism.