Deafferentation of Olfactory Bulb in Subjects Dying with COVID-19

  1. Cécilia Tremblay
  2. Thomas G. Beach
  3. Anthony J. Intorcia
  4. Jessica E. Walker
  5. Richard A. Arce
  6. Lucia I. Sue
  7. Courtney M. Nelson
  8. Claryssa I. Borja
  9. Katsuko E. Suszczewicz
  10. Madison P. Cline
  11. Spencer J. Hemmingsen
  12. Sanaria H. Qiji
  13. Marc Desforges
  14. Geidy E. Serrano

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Abstract

There have been clinical descriptions of diverse neurological effects in COVID-19 disease, involving up to 36% of patients. It appears likely that most of these are not caused by viral brain invasion but by systemic accompaniments of critical illness such as coagulopathy, deleteriously upregulated immune response, autoimmune mechanisms, hypoxia or multiorgan failure. Anosmia or hyposmia is present in a majority of COVID-19 patients, and there is early and severe involvement of the nasopharyngeal mucosa and olfactory epithelium. Preliminary studies by our group have found massive gene expression changes in olfactory bulb, but the magnitude of these changes are not different between subjects with detectable versus non-detectable olfactory bulb SARS-CoV-2 RNA. As spontaneous discharge of olfactory epithelial afferents dictates intra-olfactory bulb neurophysiological activity and connectivity, we hypothesized that olfactory bulb deafferentation during COVID-19 is responsible for a large fraction of our observed olfactory bulb transcriptional changes. As the olfactory marker protein (OMP-1) is a specific marker of olfactory epithelial afferents to the olfactory bulb and is severely depleted in animal model lesions of olfactory epithelium, we quantified OMP-1-immunoreactivity in the olfactory bulb of subjects dying with or without COVID-19. Additionally, we quantified olfactory bulb tyrosine hydroxylase (TH), which is often also reduced after olfactory epithelium lesions, and SNAP-25, a pan-synaptic marker. COVID-19 cases (n = 18) were generally elderly and were not significantly different in age or gender distribution from the non-COVID-19 cases (n = 28). Both COVID-19 and non-COVID-19 cases had a wide range of neuropathological diagnoses. The area occupied by OMP-1 immunoreactivity in COVID-19 cases was significantly less, about 60% of that in control cases but amongst subjects with COVID-19, there was no significant difference between OBT-SARS-CoV-2-PCR-positive and negative cases. There were no significant group differences for TH or SNAP-25, supporting a selective effect for OMP-1. We suggest that olfactory dysfunction, and some of the COVID-19-associated transcriptional changes that we have reported for the olfactory bulb and amygdala, may be due to olfactory bulb deafferentation and subsequent transsynaptic effects. Additionally, animal models of olfactory bulb deafferentation or bulbectomy indicate a possibility for widespread changes in interconnected brain regions, providing a possible substrate for diverse post-acute COVID-19 neurological sequelae.

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  1. ScreenIT

    SciScore for 10.1101/2021.12.21.21268119: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    EthicsIRB: Ethical approval for autopsy and subsequent research was obtained for all subjects through Institutional Review Board-approved protocols and informed consent documents (Western IRB, Puyallup, WA; protocols 1132516 and 20201852).
    Consent: Ethical approval for autopsy and subsequent research was obtained for all subjects through Institutional Review Board-approved protocols and informed consent documents (Western IRB, Puyallup, WA; protocols 1132516 and 20201852).
    Sex as a biological variablenot detected.
    Randomizationnot detected.
    BlindingImage capture and analyses were done while blinded to subject clinical or autopsy information.
    Power Analysisnot detected.

    Table 2: Resources

    Antibodies
    SentencesResources
    Primary antibody concentrations used were 1;2,000 for OMP-1, 1:3,000 for TH and 1:5,000 for SNAP-25.
    SNAP-25
    suggested: None
    Software and Algorithms
    SentencesResources
    TH Sigma Aldrich
    TH Sigma Aldrich
    suggested: None
    The area occupied by stained tissue elements within the olfactory bulb nerve fiber layer and adjacent glomerular layer was determined with digital image analysis (Image J software with image processing and analysis in Java: https://imagej.nih.gov/ij/).
    Image J
    suggested: (ImageJ, RRID:SCR_003070)
    The means of the areas occupied by staining in the 4 images were used for statistical analyses, performed using SPSS software (IBM SPSS Statistics 23.0).
    SPSS
    suggested: (SPSS, RRID:SCR_002865)

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    Limitations of our study include relatively small subject numbers, especially for subgroups, and inclusion of only COVID-19 subjects with severe illness.

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    Results from scite Reference Check: We found no unreliable references.

    About SciScore

    SciScore is an automated tool that is designed to assist expert reviewers by finding and presenting formulaic information scattered throughout a paper in a standard, easy to digest format. SciScore checks for the presence and correctness of RRIDs (research resource identifiers), and for rigor criteria such as sex and investigator blinding. For details on the theoretical underpinning of rigor criteria and the tools shown here, including references cited, please follow this link.

  2. Version published to 10.1101/2021.12.21.21268119v1 on medRxiv