Construction of an irreversible allergic rhinitis-induced olfactory loss mouse model

Highlights

• Constructed a persistent allergic rhinitis-induced olfactory loss mouse model.

• CD45⁺ Leukocytes accumulation may contribute to irreversible ORNs loss.

• Apoptotic neutrophils is positively correlated with olfactory loss.

Abstract

Clinical data show that part of patients with sinonasal diseases suffered from olfactory dysfunction, especially with allergic rhinitis (AR) and chronic rhinosinusitis (CRS). However, the mechanisms responsible for AR-induced olfactory loss are still largely unknown. Because of the difficulty to obtain human olfactory mucosa, an AR-induced olfactory loss animal model needs to be constructed to clarify the mechanism. The AR mouse model was induced by intraperitoneal sensitizing with ovalbumin (OVA) followed by intranasal challenge lasted from 1 to 12 weeks. For groups with recovery, mice were housed for another 4-week long without any treatment after the last intranasal challenge. Olfactory function, olfactory receptor neurons (ORNs) density and leukocytes infiltration were examined at different time points. Olfactory loss occurs immediately after 1-week intranasal challenge and deteriorates almost to anosmia after 8th week, and after that olfactory loss become irreversible. Nasal inflammation induces significant infiltration of leukocytes into olfactory epithelium (OE), which negatively correlated with the density of ORNs and mouse olfaction in a time dependent manner. The neutrophilic subtype dominates in number amongst the total infiltrated leukocytes, indicating its pivotal role in nasal inflammation-induced olfactory dysfunction. In this study, we constructed a persistent AR-induced olfactory loss mouse model, losing the ability to recover from dysfunction if the disease duration more than eight weeks, which implies that timely treatments are necessary. Meanwhile, this mouse model could provide an easy and reliable system to clarify the mechanisms of AR-induced irreversible olfactory dysfunction.

Introduction

Olfaction is an ancient and critical system in the evolution which plays important roles in safety, nutrition, sexuality, mood, etc [1]. Olfactory dysfunction impairs the ability to discriminate flavors, detect harmful odors from the environment, and decreases the quality of life [2,3]. Recent researches show the prevalence of olfactory dysfunction is 3–20% in the general population [4], which may be underestimated due to the lack of attention (as compared to blindness and deafness). Risks of olfactory dysfunction include age, chronic sinonasal diseases, upper airway infections, severe head trauma and neurodegenerative diseases [5]. Chronic sinonasal diseases, especially allergic rhinitis (AR) and chronic rhinosinusitis (CRS) account for the main causes of olfactory dysfunction [6]. Morbidity of olfactory dysfunction in AR patients ranges from 20% to 40%, with a mild-to-moderate severity [7], which increases to 61%–83% in CRS patients. Nowadays AR-induced olfactory loss has attracted much attention, while the mechanisms responsible for AR-induced olfactory loss are still largely unknown and need further investigation.

Because of the difficulty to obtain and analyze human olfactory mucosa, available animal model needs to be constructed. When odor molecules bind to the receptors on the olfactory cilia, they activate the ion channels of olfactory receptor neurons (ORNs), which transduce the signals through the cribriform plate into olfactory bulb and then transfer to the olfactory center, leading to sense of smell [8]. Several animal models of olfactory loss have been developed by damaging the olfactory pathways, including viruses, toxins, transection of the olfactory filaments, or use transgenic mouse that exhibits olfactory ciliary loss [[9], [10], [11], [12]]. It is considered that nasal obstruction prevents odor molecules from binding to the olfactory receptor, then causing olfactory loss. Recently, it is reported that loss of ORNs has been observed in CRS patients [13], which may be the main reasons for olfactory dysfunction. Despite the animal models of olfactory loss constructed by direct impairment of nasal mucosa, there are also limitations that they cannot reflect the main progress of olfactory dysfunction induced by allergic response, which is the main reason of olfactory loss in patients.

The classic animal model of AR was made by ovalbumin (OVA) sensitization and challenge [14]. After nasal challenge, this AR model can show typical symptoms of AR including sneezing and nasal rubbing, as well as increased serum IgE and eosinophil infiltration in the nasal mucosa [15]. Loss of ORNs can also be observed in an AR mouse model [16]. However, these animal studies did not show the dynamic changes of olfactory dysfunction and immunological profile within the olfactory epithelium (OE) in a long period of time. Therefore, the results of AR-induced olfactory loss in a long period of time are still unclear.

In the present study, we attempted to use the mouse model of OVA induced AR to study the olfactory changes, and then observe the dynamic changes of olfactory function in different period of time, using behavioral assessment of olfaction and histopathological analysis of olfactory epithelial, so as to construct a mouse model to mimic AR-induced olfactory loss in patients.