Taste is a vital sense that depends on taste bud receptor complexes in the gustatory epithelia to direct eating and food choices. Taste bud cells and supporting epithelia turn over, are renewed throughout life, and are susceptible to environmental and pharmacological agents. Taste organs therefore depend on tightly regulated proliferation and differentiation. The Hedgehog (HH) pathway regulates maintenance of adult stem and progenitor cells in many tissues. Our data implicate HH signaling as a principal regulator of maintenance and renewal of taste receptor organs. However, HH activity not only regulates tissue maintenance, but also uncontrolled HH signaling is the cause of basal cell carcinoma (BCC), a common skin tumor. Therefore, HH Pathway Inhibitors (HPIs) that block signaling by affecting the HH pathway effector, Smoothened, have been developed as targeted therapeutics for BCC. HPIs lead to regression of BCCs, but patients often discontinue treatment due to adverse effects including severe taste disturbances. Our preliminary data suggest that the taste alterations are an on-target effect reflecting a strict requirement for HH signaling in taste function. We hypothesize that HH signaling functions to control renewal of taste organs and that pharmacological disruption of this control is responsible for chemosensory disturbances in patients treated with HPIs. We use genetic models (mouse) and pharmacological treatment (mouse and human cancer patients) to study the taste system with altered HH signaling. Our Multi PI approach includes chemosensory and HH signaling biologists, and a clinician/scientist treating BCC patients with HPIs.
In Aim 1 we hypothesize that HH signaling regulates taste bud and/or papilla maintenance and function through an essential role in epithelial tissue renewal. In mouse we analyze: Hh pathway gene expression pattern and signaling in taste organs throughout the oral cavity; taste bud receptor cell maintenance, renewal and function, during and after treatment with HPIs that target the signal transduction component Smoothened; and, in genetic models, effects of targeted deletion of Smoothened on taste organs. We study cell and tissue effects, and behavioral and neurophysiological taste function.
In Aim 2 we propose that HH signaling acts to control taste organ maintenance and function in BCC patients, explaining why pharmacological inhibition of this pathway causes chemosensory disturbance. In patients receiving HPIs, we test predictions about the extent and time course of chemosensory disruption, before, during and after HPI treatment, with questionnaires and NIH Toolbox tests of taste and smell sensory function; and, we quantify the number and distribution of fungiform papillae to correlate with taste sensation tests. The project addresses mechanisms of HH signaling inhibition in altering taste organ dynamics and function. This knowledge contributes to explaining the poorly understood, taste disturbances in patients treated with HPIs, and could ultimately lead to dietary modifications or other approaches to ameliorate chemosensory disruption and improve quality of life.
Taste is an essential sensory system that directs eating and food choices. The taste bud receptor complexes and their supporting epithelia are distributed throughout the tongue and soft palate, in lingual papillae and mucosal locations respectively. Because the taste bud cells turn over in renewing cycles throughout adult life, gustatory organ homeostasis and maintenance require highly regulated differentiation and proliferation. Knowledge about the regulatory controls for taste bud renewal is necessary to understand how adult food choices are susceptible to change, or not, with diet, metabolic and environmental agents. A principal regulator of cell and tissue renewal is the Hedgehog (HH) pathway and this proposal addresses basic mechanisms of this key pathway in taste bud and/papilla maintenance and function. The project can fill a major gap in knowledge about how taste bud cells throughout the oral cavity are maintained and renewed. Importantly, the knowledge is needed to comprehend the severe taste deficits reported by patients with basal cell carcinoma (BCC), treated with HH Pathway Inhibitors. Understanding the basic mechanisms of HH in taste organ maintenance and renewal, and how inhibiting the pathway treats BCC but leads to taste disruption could lead to ways to inform patients and propose possible diet modifications to ameliorate chemosensory disturbances. This can improve quality of life for these patients.
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