The Brain Reacting to COVID-19: Analysis of the Cerebrospinal Fluid and Serum Proteome,Transcriptome and Inflammatory Proteins

Patients with COVID-19 can have a variety of neurological symptoms, but the pathomechanism of CNS involvement in COVD-19 remains unclear. While routine cerebrospinal fluid (CSF) analyses in patients with neurological manifestations of COVID-19 generally show no or only mild inflammation, more detailed data on inflammatory mediators in the CSF of patients with COVID-19 are scarce. Here, we used mass spectrometry to study the proteome, Enzym-linkend immunoassays, semiquantitative cytokine arrays, autoantibody screening, and RNA profiling to study the neuroinflammation. We study the inflammatory response in paired CSF and serum samples of patients with COVID-19 (n=38). Patients with herpes simplex virus encephalitis (HSVE, n=10) and patients with non-inflammatory, non-neurodegenerative neurological diseases (n=28) served as controls. Proteomics on single protein level and subsequent pathway analysis showed similar yet strongly attenuated inflammatory changes in the CSF of COVID-19 patients compared to HSVE patients. CSF/serum indices of interleukin-6, interleukin-16 and CXCL10 together point at an origin from these inflammatory proteins from outside the central nervous system. When stratifying COVID-19 patients into those with and without bacterial superinfection as indicated by elevated procalcitonin levels, inflammatory markers were significantly higher in those with concomitant bacterial superinfection. RNA sequencing in the CSF revealed 101 linear RNAs comprising messenger RNAs, micro RNAs and t-RNA fragments being significantly differentially expressed in COVID-19 than in HSVE or controls. Our findings may explain the absence of signs of intrathecal inflammation upon routine CSF testing despite the presence of SARS-CoV2 infection-associated neurological symptoms. The relevance of blood-derived mediators of inflammation in the CSF for neurological post-COVID-19 symptoms deserves further investigation. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study did not receive any funding ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Ethics committee of the Charite Univesitaetsmedizin Berlin, Germany gave ethical approval for this work (approval number: EA 176_20) I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors * AD : Alzheimer’s dementia ARHGAP26 : Rho GTPase-Activatin Protein 26 AMPAR : -Amino-3-hydroxy-5 methyl-4-isoazolepropionic acid receptor BSI : Bacterial Superinfection Caspr2 : Contactin-associated protein 2 CBA : Culture based assay CNS : Central Nervous System COVID-19 : Coronavirus Disease 2019 CSF : Cerebrospinal fluid CV2/CRMP5 : Cytoplasmatic protein 5 CXCL-10 : C-X-C motif chemokine 10 DPPX : Dipeptidyl-Peptidase-like Protein-6 EEG : Electroencephalogramm ELISA : Enzyme-linkend Immunfluorescene Assay GABAaR : Gamma-amino-butyrat-a-receptor GABAbR : Gamma-amino-butyrat-b-receptor GAD-65 : Glutamic Acid Decarboxylase 65 HSVE : Herpes-simplex virus meningoencephalitis IL-6 : Interleukine- 6 LGI-1 : Leucin-rich glioma inactivated Protein 1 mGluR1 : metabotropic Glutamat Receptor 1 mGluR5 : metabotropic Glutamta-receptor 5 MOG : Myelin-Oligodendrocyte Glycoprotein NMDAR : N-Methyl-D-Aspartate Receptor PCT : Procalcitonin PGRN : Progranulin SARS-CoV2 : Severe Acute Respiratory Syndrome Coronavirus 2 Tr/DNER : Delta/notch-like epidermal growth factor ITPR1/anti-Sj : Inositol 1,4,5-trisphosphate receptor type 1