The capacity of the olfactory epithelium (OE) for replenishing the population of olfactory sensory neurons and for regenerating the epithelium after injury depends on the persistence and maintained function of stem cells within that adult epithelium. Decline in sensory function in the elderly is accompanied by pathological changes in the OE that emerge because the normally active olfactory stem and progenitor cells, namely globose basal cells (GBCs), become disordered and eventually depleted. At present, we can construct a flow diagram designed to encompass and sequence the various categories of GBCs, beginning with GBCs that function as multipotent progenitors, progressing through GBCs that act as transit amplifying progenitors, and reaching GBCs that give rise directly to neurons. We can also align those purported stages in the GBC hierarchy with the expression of various transcription factors. However, we lack a comprehensive understanding of this critical stem/progenitor cell population. Are these stages discrete or are they snapshots of a more fluid progression? How do we explain the plasticity in the progenitor capacity of some GBCs? How might aging disorder the progression? The current application proposes two specific aims designed to address the critical gaps in our knowledge of the active stem and progenitor cell population.
Specific Aim 1 will generate transcriptomic profiles of the various functional categories of GBCs using transgenic mouse strains that express a fluorescent marker in conjunction with the transcription factor(s) gene(s) ? Sox2, Ascl1, and Neurog1 ? used to define the stages in the hierarchy.
Specific Aim 2 will focus on and profile a specific kinetically- defined subset of GBCs that experience prolonged mitotic quiescence, as shown by the retention of the tagged histone fusion protein H2B/GFP, which is a feature common to many stem cell types. In both cases, cells labeled by expression of the fluorescent tags will be isolated by FACS, captured as single cells, and individually profiled. Analysis of the single cell expression libraries will be used for unbiased clustering of the cells and defining the genes whose expression differs across the clusters. The patterns of gene expression that differentiate the clusters will be validated by Q-PCR and either immunohistochemistry or in situ hybridization depending on antibody availability. At the conclusion of the analysis we will have achieved a comprehensive understanding of the GBC population and will clarify whether the existing flow diagram ? which envisions distinct stages and abrupt transitions ? is an accurate representation of the biology of this stem and progenitor cell-encompassing population. These advances, in turn, will inform our attempts to alleviate olfactory sensory dysfunction, particularly that which accompanies aging.

Public Health Relevance

Decline in the sense of smell is a very frequent accompaniment of aging and compromises quality of life, nutritional status, and personal safety. As we age, all too often the stem and progenitor cells that are responsible for renewing the olfactory tissue in the nose (and the population of neurons within it that are responsible for detecting odors in the environment) become disordered and then completely disappear. We need to understand those stem and progenitor cells ? who they are and how they do what they do ? much better, which is the purpose of this grant, if we are to learn how to treat the decline in olfactory function in the elderly; our goal is closely aligned with one of the mission areas of the National Institute on Deafness and Other Communication Disorders.

Agency
National Institute of Health (NIH)
Institute
National Institute on Deafness and Other Communication Disorders (NIDCD)
Type
Exploratory/Developmental Grants (R21)
Project #
5R21DC015889-02
Application #
9385296
Study Section
Somatosensory and Chemosensory Systems Study Section (SCS)
Program Officer
Sullivan, Susan L
Project Start
2016-12-01
Project End
2019-11-30
Budget Start
2017-12-01
Budget End
2019-11-30
Support Year
2
Fiscal Year
2018
Total Cost
Indirect Cost
Name
Tufts University
Department
Biochemistry
Type
Schools of Medicine
DUNS #
039318308
City
Boston
State
MA
Country
United States
Zip Code
Lin, Brian; Coleman, Julie H; Peterson, Jesse N et al. (2017) Injury Induces Endogenous Reprogramming and Dedifferentiation of Neuronal Progenitors to Multipotency. Cell Stem Cell 21:761-774.e5