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Background Anosmia/hyposmia affects 13.3 million people in the U.S. alone according to the recent U.S. National Health and Nutrition Examination Survey (NHANES). Hundreds of thousands more people with persistent olfactory dysfunction will be added to this number due to the COVID-19 pandemic. Patients with loss-of-function mutations in SCN9A, the gene encoding NaV1.7, experience anosmia in addition to congenital insensitivity to pain. Tsp1a is a recently discovered peptide that inhibits NaV1.7 with high potency and selectivity. In this study, we examined whether a fluorescently tagged version of Tsp1a could be used to visualize normal and damaged mouse olfactory nerves. Methods Athymic nude mice were intravenously injected with Tsp1a-IR800. As a control, mice were injected with PBS only, and as a blocking control were injected with combination of Tsp1a and Tsp1a-IR800. All mice were imaged in-vivo and epifluorescence images were acquired using an IVIS Spectrum animal imaging system. Semiquantitative analysis of the Tsp1a-IR800 signal was conducted by measuring the average radiant efficiency in the region of the olfactory epithelium/bulb (ROEB). Methimazole was used to chemically ablate the olfactory epithelium. We performed a food buried test to correlate the level of anosmia with the level of radiance efficiency. Results The area of olfactory epithelium/bulb was clearly visible in epifluorescence in-vivo images of mice receiving the imaging agent. The radiant efficiency was significantly less in both mice injected with PBS and in mice injected with the blocking formulation. The mice after olfactory ablation had a significantly reduced radiant efficiency compared with normal mice. Moreover, there was a statistically significant and inverse correlation between the time required for the mouse to find buried food and the radiant efficiency. We also performed immunohistochemistry using NaV1.7 antibody. Mice after olfactory ablation as well as COVID-19-infected mice had significantly lower expression of NaV1.7 on the level of olfactory epithelium/bulb. Conclusion We show that the fluorescent imaging of mouse olfactory epithelium/bulb is possible, suggesting that labeled Tsp1a tracers may serve as the first objective diagnostic tool of smell disorders, including those caused by COVID-19.

The process of apoptosis in epithelia involves activation of caspases, delamination of cells, and degradation of cellular components. Corpses and cellular debris are then rapidly cleared from the tissue by phagocytic blood cells. In studies of the Drosophila TNF, Eiger (Egr) and cell death in wing imaginal discs, the epithelial primordia of fly wings, we noticed that dying cells appeared to transiently accumulate in egr3 mutant wing discs, raising the possibility that their phagocytic engulfment by hemocytes was impaired. Further investigation revealed that lymph glands and circulating hemocytes from egr3 mutant larvae were completely devoid of NimC1 staining, a marker of phagocytic hemocytes. Genome sequencing uncovered mutations in the NimC1 coding region that are predicted to truncate the NimC1 protein before its transmembrane domain, and provide an explanation for the lack of NimC staining. The work that we report here demonstrates the presence of these NimC1 mutations in the widely used egr3 mutant, its sister allele, egr1, and its parental strain, Regg1GS9830. As the egr3 and egr1 alleles have been used in numerous studies of immunity and cell death, it may be advisable to re-evaluate their associated phenotypes.

SUMMARYSARS-CoV-2 has been found capable of inducing prolonged pathologies collectively referred to as Long-COVID. To better understand this biology, we compared the short- and long-term systemic responses in the golden hamster following either SARS-CoV-2 or influenza A virus (IAV) infection. While SARS-CoV-2 exceeded IAV in its capacity to cause injury to the lung and kidney, the most significant changes were observed in the olfactory bulb (OB) and olfactory epithelium (OE) where inflammation was visible beyond one month post SARS-CoV-2 infection. Despite a lack of detectable virus, OB/OE demonstrated microglial and T cell activation, proinflammatory cytokine production, and interferon responses that correlated with behavioral changes. These findings could be corroborated through sequencing of individuals who recovered from COVID-19, as sustained inflammation in OB/OE tissue remained evident months beyond disease resolution. These data highlight a molecular mechanism for persistent COVID-19 symptomology and characterize a small animal model to develop future therapeutics.

SARS-CoV-2 infects less than 1% of cells in the human body, yet it can cause severe damage in a variety of organs. Thus, deciphering the non-cell autonomous effects of SARS-CoV-2 infection is imperative for understanding the cellular and molecular disruption it elicits. Neurological and cognitive defects are among the least understood symptoms of COVID-19 patients, with olfactory dysfunction being their most common sensory deficit. Here, we show that both in humans and hamsters SARS-CoV-2 infection causes widespread downregulation of olfactory receptors (OR) and of their signaling components. This non-cell autonomous effect is preceded by a dramatic reorganization of the neuronal nuclear architecture, which results in dissipation of genomic compartments harboring OR genes. Our data provide a potential mechanism by which SARS-CoV-2 infection alters the cellular morphology and the transcriptome of cells it cannot infect, offering insight to its systemic effects in olfaction and beyond., Graphical Abstract, SARS-CoV-2 induces non-cell autonomous effects in olfactory epithelium that disrupts nuclear architecture and downregulates olfactory receptor expression in olfactory sensory neurons.

Numerous signaling pathways have been implicated in the elimination of cells in cell competition. Here we explore the relative contributions of two of them, the recently discovered CCSM and the conserved JNK stress pathway, using a series of genetic interactions tests. We demonstrate that the expression of the TNF Eiger (Egr), and the TNFR adaptor protein Traf4, are specifically up-regulated in the wild-type “loser” cell population during Myc-mediated cell competition. We find that the absence of Egr or its receptor Grindelwald (grnd) robustly prevents elimination of the loser cells in genetic cell competition assays. In contrast, although canonical JNK signaling is activated downstream of these adaptors, loss of either of the JNK effectors Tak1/JNKK or Hemipterous/JNK is not sufficient to prevent loser cell elimination in the competitive context. Our results instead suggest that Egr/Grnd influences the Rel activator Dredd in carrying out the cells’ competitive death and elimination. Our experiments thus provide evidence that although Egr/Grnd signaling activates two parallel pathways in Myc cell competition, only the CCSM is sufficient to remove the wild-type loser cells from the tissue.

Olfaction relies on a coordinated partnership between odorant flow and neuronal communication. Disruption in our ability to detect odors, or anosmia, has emerged as a hallmark symptom of infection with SARS-CoV-2, yet the mechanism behind this abrupt sensory deficit remains elusive. Here, using molecular evaluation of human olfactory epithelium (OE) from subjects succumbing to COVID-19 and a hamster model of SARS-CoV-2 infection, we discovered widespread downregulation of olfactory receptors (ORs) as well as key components of their signaling pathway. OR downregulation likely represents a non-cell autonomous effect, since SARS-CoV-2 detection in OSNs is extremely rare both in human and hamster OEs. A likely explanation for the reduction of OR transcription is the striking reorganization of nuclear architecture observed in the OSN lineage, which disrupts multi-chromosomal compartments regulating OR expression in humans and hamsters. Our experiments uncover a novel molecular mechanism by which a virus with a very selective tropism can elicit persistent transcriptional changes in cells that evade it, contributing to the severity of COVID-19.

SARS-CoV-2 infects less than 1% of cells in the human body, yet it can cause severe damage in a variety of organs. Thus, deciphering the non-cell autonomous effects of SARS-CoV-2 infection is imperative for understanding the cellular and molecular disruption it elicits. Neurological and cognitive defects are among the least understood symptoms of COVID-19 patients, with olfactory dysfunction being their most common sensory deficit. Here, we show that both in humans and hamsters SARS-CoV-2 infection causes widespread downregulation of olfactory receptors (OR) and of their signaling components. This non-cell autonomous effect coincides with a dramatic reorganization of the neuronal nuclear architecture, which results in dissipation of genomic OR compartments and elimination of genomic contact domains genomewide. Our data provide a novel mechanism by which SARS-CoV-2 infection alters the cellular morphology and the transcriptome of cells it cannot infect, providing insight to its systemic effects in the nervous system and beyond. Funding Information: NIDCD 3R01DC018744-01S1 (SL, JO) National Institutes of Health grant, 4D Nucleome Consortium U01DA052783 (SL) Howard Hughes Medical Institute Faculty Scholar Award (SL), Zegar Family Foundation (SL). Ethics Approval Statement: The study was approved by the ethics and Institutional Review Board of Columbia University Medical Center (IRB AAAT0689, AAAS7370). LVG Golden Syrian hamsters (Mesocricetus auratus) were treated in compliance with the rules and regulations of IACUC under protocol number PROTO202000113-20-0743.