Single or Repeated Ablation of Mouse Olfactory Epithelium by Methimazole

Noninvasive Diagnostic Method to Objectively Measure Olfaction and Diagnose Smell Disorders by a Molecularly Targeted Fluorescence Imaging Agent

Despite the recent advances in understanding the mechanisms of olfaction, no tools are currently available to noninvasively identify loss of smell. Because of the substantial increase in patients presenting with coronavirus disease 2019-related loss of smell, the pandemic has highlighted the urgent need to develop quantitative methods. Methods: Our group investigated the use of a novel fluorescent probe named Tsp1a-IR800P as a tool to diagnose loss of smell. Tsp1a-IR800P targets sodium channel 1.7, which plays a critical role in olfaction by aiding the signal propagation to the olfactory bulb. Results: Intuitively, we have identified that conditions leading to loss of smell, including chronic inflammation and coronavirus disease 2019, correlate with the downregulation of sodium channel 1.7 expression in the olfactory epithelium, both at the transcript and at the protein levels. We demonstrated that lower Tsp1a-IR800P fluorescence emissions significantly correlate with loss of smell in live animals-thus representing a potential tool for its semiquantitative assessment. Currently available methods rely on delayed subjective behavioral studies. Conclusion: This method could aid in significantly improving preclinical and clinical studies by providing a way to objectively diagnose loss of smell and therefore aid the development of therapeutic interventions.

The functional role of the visual and olfactory modalities in the development of socially transferred mechanical hypersensitivity in male C57BL/6J mice

An increasing body of evidence suggests that the state of hyperalgesia could be socially transferred from one individual to another through a brief empathetic social contact. However, how the social transfer of pain develops during social contact is not well-known. Utilizing a well-established mouse model, the present study aims to study the functional role of visual and olfactory cues in the development of socially-transferred mechanical hypersensitivity. Behavioral tests demonstrated that one hour of brief social contact with a conspecific mouse injected with complete Freund's adjuvant (CFA) was both sufficient and necessary for developing socially-transferred mechanical hypersensitivity. One hour of social contact with visual deprivation could not prevent the development of socially-transferred mechanical hypersensitivity, and screen observation of a CFA cagemate was not sufficient to develop socially-transferred mechanical hypersensitivity in bystanders. Methimazole-induced olfactory deprivation, a compound with reversible toxicity on the nasal olfactory epithelium, was sufficient to prevent the development of socially-transferred mechanical hypersensitivity. Intriguingly, repeated but not acute olfactory exposure to the CFA mouse bedding induced a robust decrease in 50 % paw withdrawal thresholds (50 %PWTs) to mechanical stimuli, an effect returned to the baseline level after two days of washout with clean bedding. The findings strongly indicate that the normal olfactory function is crucial for the induction of mechanical hypersensitivity through brief empathetic contact, offering valuable insights for animal housing in future pain research.

An in vitro model of acute horizontal basal cell activation reveals dynamic gene regulatory networks underlying the acute activation phase

Horizontal basal cells (HBCs) activate only in response to severe olfactory epithelium (OE) injury. This activation is mediated by the loss of the transcription factor TP63. Using the compound phorbol 12-myristate 13-acetate (PMA), we find that we can model the process of acute HBC activation. First, we find that PMA treatment induces a rapid loss in TP63 protein and induces the expression of HOPX and the nuclear translocation of RELA, previously identified to mediate HBC activation. Using bulk RNA sequencing, we find that PMA-treated HBCs pass through various stages of acute activation identifiable by transcriptional regulatory signatures that mimic stages identified in vivo . These temporal stages are associated with varying degrees of engraftment and differentiation potential in transplantation assays. Together, this data shows that our model can model physiologically relevant features of HBC activation and identifies new candidates for mechanistic testing.

Pcdh19 mediates olfactory sensory neuron coalescence during postnatal stages and regeneration

The mouse olfactory system regenerates constantly throughout life. While genes critical for the initial projection of olfactory sensory neurons (OSNs) to the olfactory bulb have been identified, what genes are important for maintaining the olfactory map during regeneration are still unknown. Here we show a mutation in Protocadherin 19 (Pcdh19), a cell adhesion molecule and member of the cadherin superfamily, leads to defects in OSN coalescence during regeneration. Surprisingly, lateral glomeruli were more affected and males in particular showed a more severe phenotype. Single cell analysis unexpectedly showed OSNs expressing the MOR28 odorant receptor could be subdivided into two major clusters. We showed that at least one protocadherin is differentially expressed between OSNs coalescing on the medial and lateral glomeruli. Moreover, females expressed a slightly different complement of genes from males. These features may explain the differential effects of mutating Pcdh19 on medial and lateral glomeruli in males and females.

Zika virus leads to olfactory disorders in mice by targeting olfactory ensheathing cells

BACKGROUND

Zika virus (ZIKV) is an emerging arbovirus of the genus flavivirus that is associated with congenital Zika syndrome (CZS) in newborns. A wide range of clinical symptoms including intellectual disability, speech delay, coordination or movement problems, and hearing and vision loss, have been well documented in children with CZS. However, whether ZIKV can invade the olfactory system and lead to post-viral olfactory dysfunction (PVOD) remains unknown.

METHODS

We investigated the susceptibility and biological responses of the olfactory system to ZIKV infection using mouse models and human olfactory organoids derived from patient olfactory mucosa.

FINDINGS

We demonstrate that neonatal mice infected with ZIKV suffer from transient olfactory dysfunction when they reach to puberty. Moreover, ZIKV mainly targets olfactory ensheathing cells (OECs) and exhibits broad cellular tropism colocalizing with small populations of mature/immature olfactory sensory neurons (mOSNs/iOSNs), sustentacular cells and horizontal basal cells in the olfactory mucosa (OM) of immunodeficient AG6 mice. ZIKV infection induces strong antiviral immune responses in both the olfactory mucosa and olfactory bulb tissues, resulting in the upregulation of proinflammatory cytokines/chemokines and genes related to the antiviral response. Histopathology and transcriptomic analysis showed typical tissue damage in the olfactory system. Finally, by using an air-liquid culture system, we showed that ZIKV mainly targets sustentacular cells and OECs and support robust ZIKV replication.

INTERPRETATION

Our results demonstrate that olfactory system represents as significant target for ZIKV infection, and that PVOD may be neglected in CZS patients.

FUNDING

Stated in the acknowledgment.

Immune responses in the injured olfactory and gustatory systems: a role in olfactory receptor neuron and taste bud regeneration?

Sensory cells that specialize in transducing olfactory and gustatory stimuli are renewed throughout life and can regenerate after injury unlike their counterparts in the mammalian retina and auditory epithelium. This uncommon capacity for regeneration offers an opportunity to understand mechanisms that promote the recovery of sensory function after taste and smell loss. Immune responses appear to influence degeneration and later regeneration of olfactory sensory neurons and taste receptor cells. Here we review surgical, chemical, and inflammatory injury models and evidence that immune responses promote or deter chemosensory cell regeneration. Macrophage and neutrophil responses to chemosensory receptor injury have been the most widely studied without consensus on their net effects on regeneration. We discuss possible technical and biological reasons for the discrepancy, such as the difference between peripheral and central structures, and suggest directions for progress in understanding immune regulation of chemosensory regeneration. Our mechanistic understanding of immune-chemosensory cell interactions must be expanded before therapies can be developed for recovering the sensation of taste and smell after head injury from traumatic nerve damage and infection. Chemosensory loss leads to decreased quality of life, depression, nutritional challenges, and exposure to environmental dangers highlighting the need for further studies in this area.