The long-term goal of this proposal is to elucidate the role of cilia on cells of the olfactory epithelium (OE) in the regulation and maintenance of olfactory function and their alterations in cilia-related disorders. Olfactory dysfunction in the general population is frequent, affecting at least 2.5 million people in the U.S. alone. In at leas 20% of the cases the etiology of the chemosensory disturbance cannot be identified. Recently, we were one of the first to demonstrate olfactory dysfunction as a clinical manifestation of an emerging class of human genetic disorders, termed ciliopathies. It is surprising that while many of the ascribed functions of cilia are reported to occur in the OE and cilia are abundant on OSNs, we have an incomplete understanding of the role of cilia in this sensory tissue. New data in this application show that horizontal basal cells (HBCs) possess cilia (previously thought to exist in the OE only on olfactory sensory neurons) that may regulate proliferation or differentiation of olfactory stem cells. Therefore, investigation into the possible pleotropic role of cilia in the OE is necessary. Importantly, despite significant progress identifying the genes underlying ciliopathies, curative therapies are not yet available to patients. Recently, we reported that odor detection can be restored to animals with a hypomorphic mutation in the gene encoding for the ciliary protein IFT88 that results in the loss of cilia on differentiated olfactory sensory neurons (OSNs)(ref). This suggests that ectopic gene delivery in vivo may provide a viable approach to treating olfactory dysfunction resulting from ciliopathies. We hypothesize that ciliopathy alleles and loss of cilia genes affect the function of both OSNs and HBCS to reduce olfactory function, which can be therapeutically rescued by ectopic, adenoviral-gene expression in vivo. Therefore, we will test the following Specific Aims: (1) Elucidate the effects of cilia loss from olfactory sensory neurons and the extent of functional rescue following ectopic adenoviral gene delivery in vivo; (2) Determine the effects of sensory depravation by cilia loss on olfactory bulb organization and function and its plasticity following restoration; (3 Establish the necessity of cilia for the regulation of HBC proliferation and differentiation in the developing, mature, and injured OE. Successful completion of this work will undoubtedly provide us important new information regarding the pathogenesis of human sensory perception diseases and paves the way for the development of treatments in humans, where no curative therapies for ciliopathic disease exist.
Although many of the causes of loss of smell have yet to be discovered, one known cause is a disruption of cilia, hair-like projections extending from neurons into the nasal cavity. Cilia contain proteins responsible for detecting odors, hence genetic diseases that disrupt the cilia have been tied to the loss of smell. The goal for this proposal is to better understand the function and mutations of cilia and to determine how to therapeutically treat such disorders.
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