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Butowt R, Bilinska K, von Bartheld CS. Olfactory dysfunction in COVID-19: new insights into the underlying mechanisms. Trends Neurosci 2023; 46:75-90. [PMID: 36470705 PMCID: PMC9666374 DOI: 10.1016/j.tins.2022.11.003] [Citation(s) in RCA: 31] [Impact Index Per Article: 31.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2022] [Revised: 11/06/2022] [Accepted: 11/14/2022] [Indexed: 11/17/2022]
Abstract
The mechanisms of olfactory dysfunction in COVID-19 are still unclear. In this review, we examine potential mechanisms that may explain why the sense of smell is lost or altered. Among the current hypotheses, the most plausible is that death of infected support cells in the olfactory epithelium causes, besides altered composition of the mucus, retraction of the cilia on olfactory receptor neurons, possibly because of the lack of support cell-derived glucose in the mucus, which powers olfactory signal transduction within the cilia. This mechanism is consistent with the rapid loss of smell with COVID-19, and its rapid recovery after the regeneration of support cells. Host immune responses that cause downregulation of genes involved in olfactory signal transduction occur too late to trigger anosmia, but may contribute to the duration of the olfactory dysfunction.
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Affiliation(s)
- Rafal Butowt
- Global Consortium of Chemosensory Research - Poland, Przybory Str 3/2, 85-791 Bydgoszcz, Poland
| | - Katarzyna Bilinska
- Department of Molecular Cell Genetics, L. Rydygier Collegium Medicum, Nicolaus Copernicus University, uI. Curie Sklodowskiej 9, 85-94, Bydgoszcz, Poland.
| | - Christopher S. von Bartheld
- Center of Biomedical Research Excellence in Cell Biology, University of Nevada, Reno School of Medicine, Reno, NV 89557-0352, USA,Department of Physiology and Cell Biology, University of Nevada, Reno School of Medicine, Reno, NV 89557-0352, USA,Correspondence:
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Bryche B, Frétaud M, Saint-Albin Deliot A, Galloux M, Sedano L, Langevin C, Descamps D, Rameix-Welti MA, Eléouët JF, Le Goffic R, Meunier N. Respiratory syncytial virus tropism for olfactory sensory neurons in mice. J Neurochem 2020; 155:137-153. [PMID: 31811775 DOI: 10.1111/jnc.14936] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2019] [Revised: 11/29/2019] [Accepted: 12/01/2019] [Indexed: 01/08/2023]
Abstract
The olfactory mucosa, where the first step of odor detection occurs, is a privileged pathway for environmental toxicants and pathogens toward the central nervous system. Indeed, some pathogens can infect olfactory sensory neurons including their axons projecting to the olfactory bulb allowing them to bypass the blood-brain barrier and reach the central nervous system (CNS) through the so-called olfactory pathway. The respiratory syncytial virus (RSV) is a major respiratory tract pathogen but there is growing evidence that RSV may lead to CNS impairments. However, the mechanisms involved in RSV entering into the CNS have been poorly described. In this study, we wanted to explore the capacity of RSV to reach the CNS via the olfactory pathway and to better characterize RSV cellular tropism in the nasal cavity. We first explored the distribution of RSV infectious sites in the nasal cavity by in vivo bioluminescence imaging and a tissue clearing protocol combined with deep-tissue imaging and 3D image analyses. This whole tissue characterization was confirmed with immunohistochemistry and molecular biology approaches. Together, our results provide a novel 3D atlas of mouse nasal cavity anatomy and show that RSV can infect olfactory sensory neurons giving access to the central nervous system by entering the olfactory bulb. Cover Image for this issue: doi: 10.1111/jnc.14765.
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Affiliation(s)
- Bertrand Bryche
- NBO, INRA, Univ Paris-Saclay, Jouy-en-Josas, France.,Université de Versailles Saint-Quentin en Yvelines, Versailles, France
| | - Maxence Frétaud
- VIM, INRA, Univ Paris Saclay, Jouy-en-Josas, France.,INRA, EMERG'IN- Plateforme d'Infectiologie Expérimentale IERP- Domaine de Vilvert, Jouy-en-Josas, France
| | | | | | - Laura Sedano
- VIM, INRA, Univ Paris Saclay, Jouy-en-Josas, France
| | - Christelle Langevin
- VIM, INRA, Univ Paris Saclay, Jouy-en-Josas, France.,INRA, EMERG'IN- Plateforme d'Infectiologie Expérimentale IERP- Domaine de Vilvert, Jouy-en-Josas, France
| | | | - Marie-Anne Rameix-Welti
- UMR INSERM U1173 I2, UFR des Sciences de la Santé Simone Veil-UVSQ, Montigny-Le-Bretonneux, France.,Assistance Publique-Hôpitaux de Paris, Laboratoire de Microbiologie, Hôpital Ambroise Paré, Boulogne-Billancourt, France
| | | | | | - Nicolas Meunier
- NBO, INRA, Univ Paris-Saclay, Jouy-en-Josas, France.,Université de Versailles Saint-Quentin en Yvelines, Versailles, France
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Endothelin impacts on olfactory processing in rats. Behav Brain Res 2018; 362:1-6. [PMID: 30597250 DOI: 10.1016/j.bbr.2018.12.048] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2018] [Revised: 12/19/2018] [Accepted: 12/27/2018] [Indexed: 01/28/2023]
Abstract
In the olfactory epithelium, olfactory sensitive neurons and their axons are surrounded by glia-like cells called sustentacular cells, which maintain both the structural and ionic integrity of the olfactory mucosa. We have previously found that endothelin-1 (ET-1) can uncouple sustentacular cell gap junctions in vitro similarly as carbenoxolone, a known gap junction uncoupling agent. The role of gap junctions in odorant transduction remains controversial and we explored here if ET-1 naturally produced by the olfactory mucosa could impact odorant detection. Using calcium imaging on olfactory mucosa explant, we first confirmed that ET-1 uncouples gap junctions in an olfactory mucosa preparation preserving the tissue integrity. We next measured the olfactory epithelium responses to odorant stimulation using electro-olfactogram recordings. While the amplitude of the response was not modified by application of ET-1 and carbenoxolone, its repolarizing phase was slower after both treatments. We finally examined the behavioral performances of rat pups in an orientation test based on maternal odor recognition after intranasal instillations of ET-1 or carbenoxolone. While rat pups performances were decreased after ET-1 treatment, it was unchanged after carbenoxolone treatment. Overall, our results indicate that ET-1 modulates olfactory responses at least partly through gap junction uncoupling.
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