Abstract
BackgroundUnderstanding viral infection of the olfactory epithelium is essential because the olfactory nerve is an important route of entry for viruses to the central nervous system. Specialized chemosensory epithelial cells that express the transient receptor potential cation channel subfamily M member 5 (TRPM5) are found throughout the airways and intestinal epithelium and are involved in responses to viral infection.ResultsHerein we performed deep transcriptional profiling of olfactory epithelial cells sorted by flow cytometry based on the expression of mCherry as a marker for olfactory sensory neurons and for eGFP in OMP-H2B::mCherry/TRPM5-eGFP transgenic mice (Mus musculus). We find profuse expression of transcripts involved in inflammation, immunity and viral infection in TRPM5-expressing microvillous cells compared to olfactory sensory neurons.ConclusionOur study provides new insights into a potential role for TRPM5-expressing microvillous cells in viral infection of the olfactory epithelium. We find that, as found for solitary chemosensory cells (SCCs) and brush cells in the airway epithelium, and for tuft cells in the intestine, the transcriptome of TRPM5-expressing microvillous cells indicates that they are likely involved in the inflammatory response elicited by viral infection of the olfactory epithelium.
Highlights
Understanding viral infection of the olfactory epithelium is essential because the olfactory nerve is an important route of entry for viruses to the central nervous system
Fluorescence-activated cell sorting of cells isolated from the main olfactory epithelium The olfactory epithelium of Olfactory marker protein (OMP)-H2B::mCherry/ TRPM5-Enhanced green fluorescent protein (eGFP) mice expressed nuclear mCherry driven by the OMP promoter in the intermediate layer of the olfactory epithelium (Fig. 1a), as expected for the location of nuclei of mature olfactory sensory neurons (OSNs) [22]. eGFP expression driven by the TRPM5 promoter was found in microvillous cells (MVCs), with cell bodies located mostly in the apical layer of the epithelium, and at lower expression levels in a subset of OSNs double-labeled with mCherry (Fig. 1a), consistent with earlier publications [48, 49]
Compared to OSN_eGFP- cells both the MVC_eGFP cells and OSN_eGFP+ cells expressed higher levels of TRPM5 transcript (Fig. 1e,iii) and choline acetyl transferase (ChAT)(Fig. 1e,iv), a protein involved in acetylcholine neurotransmission that is expressed in MVCs [63]
Summary
Understanding viral infection of the olfactory epithelium is essential because the olfactory nerve is an important route of entry for viruses to the central nervous system. Specialized chemosensory epithelial cells that express the transient receptor potential cation channel subfamily M member 5 (TRPM5) are found throughout the airways and intestinal epithelium and are involved in responses to viral infection. Chemosensory cells found in the airway (SCCs/brush cells) and intestinal epithelium (tuft cells) express the transient receptor potential cation channel subfamily M member 5 (TRPM5) and other elements of the taste transduction pathway and have been implicated in immune and inflammatory responses to bacterial, viral and parasitic infection [53, 54, 62, 68, 73, 75, 85]. We performed transcriptional profiling of MVCs and a subset of olfactory sensory neurons (OSNs) expressing eGFP under control of a fragment of the TRPM5 promoter (OSN_eGFP+ cells) [49, 50]. We isolated cells from the olfactory epithelium and used FACS to sort MVC_eGFP cells (mCherry negative and eGFP positive) and cells labeled by OMP-driven mCherry that did or did not express eGFP (OSN_eGFP+ and OSN_eGFPcells) followed by transcriptional profiling by RNA sequencing (RNAseq)
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