The lingual sense of taste is initially communicated by taste buds, clusters of sensory cells located in highly organized taste papillae, to chemosensory neurons whose cell bodies are located in the geniculate and petrosal ganglia. The chemosensory receptor cells in taste buds continuously turn over and are replaced throughout life. The molecular mechanisms that direct the developmental innervation of taste buds, and maintain these constantly renewing functional connections throughout life, are still being elucidated. Neurotrophic factors are essential for the development and lifelong maintenance of sensory systems. Two members of the neurotrophin family, BDNF and NT-4, are well established as being critical for the survival of geniculate chemosensory neurons, and for their innervation of fungiform taste buds. The members of a second important family of neurotrophic factors, the glial cell line-derived neurotrophic factor (GDNF) family ligands (GFLs), are expressed in the tongue during the period of chemosensory innervation. The GFLs, which consist of GDNF, neurturin, artemin and persephin, are potent neurotrophic factors for subpopulations of somatosensory neurons, spinal motor neurons and autonomic neurons. We recently discovered that the signal-transducing receptor for the GFLs, Ret, is widely expressed in Phox2B+ chemosensory geniculate neurons early in development prior to their innervation of the tongue (greater than 70% at E13.5) and then becomes restricted to a subset (approximately 15%) of Phox2B+ chemosensory neurons in adulthood. This expression profile suggests that the GFL/Ret pathway may have two distinct developmentally regulated functions in the differentiation and maintenance of geniculate chemosensory neurons, but their role in the peripheral taste system is unexplored. Based on preliminary data presented in this proposal, our overarching hypothesis is that the GFL/Ret receptor complex is critically important for the early cell fate determination of geniculate chemosensory neurons, as well as for the life-long maintenance and function of physiologically distinct subpopulations of these neurons.
In Specific Aim 1 we will test the hypothesis that GDNF, NRTN and Ret are critical for the developmental specification of chemosensory neurons of the geniculate ganglion, as well as their peripheral innervation of fungiform taste buds and central innervation of the nucleus of the solitary tract.
In Specific Aim 2 we will test the hypothesis that the GDNF/Ret receptor complex is necessary for the lifelong maintenance and physiology of a subset of lingual sensory neurons of the geniculate ganglion. The physiologic function of Ret+ lingual afferent neurons will be determined with chorda tympani nerve recordings in response to the various chemical stimuli and lingual modalities. The rationale for a mechanistic examination of the GFL/Ret pathway in geniculate neurons is that this may aid in the rational design of therapeutic interventions for diseases and injuries of peripheral neurons, and will bring novel insights to the development and maintenance of the peripheral taste system.

Public Health Relevance

The potent survival and growth effects of the GFL family of growth factors have led to their development as therapeutic agents for the treatment of diseases and injuries of the nervous system. Therefore, an understanding of the mechanisms of action of the GFLs will aid in improving the efficacy of treatment regimens that utilize the GFLs. Furthermore, an analysis of the function of GFLs in the peripheral taste system will shed light on the regenerative capacity of chemosensory neurons and taste buds and will inform further investigation of the potential therapeutic properties of the GFLs using the peripheral taste system as a model of neuron- target regeneration.

Agency
National Institute of Health (NIH)
Institute
National Institute on Deafness and Other Communication Disorders (NIDCD)
Type
Research Project (R01)
Project #
5R01DC015799-02
Application #
9495693
Study Section
Somatosensory and Chemosensory Systems Study Section (SCS)
Program Officer
Sullivan, Susan L
Project Start
2017-06-05
Project End
2022-05-31
Budget Start
2018-06-01
Budget End
2019-05-31
Support Year
2
Fiscal Year
2018
Total Cost
Indirect Cost
Name
University of Michigan Ann Arbor
Department
Dentistry
Type
Schools of Dentistry/Oral Hygn
DUNS #
073133571
City
Ann Arbor
State
MI
Country
United States
Zip Code
48109
Donnelly, Christopher R; Gabreski, Nicole A; Suh, Esther B et al. (2018) Non-canonical Ret signaling augments p75-mediated cell death in developing sympathetic neurons. J Cell Biol 217:3237-3253
Donnelly, Christopher R; Shah, Amol A; Mistretta, Charlotte M et al. (2018) Biphasic functions for the GDNF-Ret signaling pathway in chemosensory neuron development and diversification. Proc Natl Acad Sci U S A 115:E516-E525
Chen, Zhijiang; Donnelly, Christopher R; Dominguez, Bertha et al. (2017) p75 Is Required for the Establishment of Postnatal Sensory Neuron Diversity by Potentiating Ret Signaling. Cell Rep 21:707-720