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Hedgehog signaling in taste cell maintenance and regeneration

Philip A Beachy

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National Institutes of Health (NIH)
The sensation of taste contributes centrally to discrimination of substances whose ingestion sustains us and others that are detrimental to our well-being. Taste sensation is thus a critical component of basic human survival. Even in modern times, with safe and abundant sources of nutrients all around us, taste sensation becomes a significant clinical issue when its loss, often associated with neuronal damage or the cytotoxic treatments and radiation employed in cancer therapy, causes unwanted weight reduction and a significant decrement in quality of life. A particularly acute manifestation of thi problem occurs in cancer patients treated with a Hedgehog (Hh) pathway antagonist who are forced or choose to discontinue therapy due to loss of taste sensation, a specific biological effect caused by this class of mechanism-based cancer therapeutic agent. Our proposal focuses on the role of Hh signaling in maintenance and regeneration of taste receptor cells (TRCs), which are housed within cup-shaped structures formed by invagination of the lingual epithelium (taste buds). We plan to determine the cellular source of the Hedgehog signal and the nature of its effects and, of particular significance; we will address the role of Shh ligand provided by sensory neurons that innervate TRCs. The Hh signal produced by these neurons may represent a cellular memory that specifies TRC regeneration within taste buds, as opposed to other parts of the lingual epithelium. Such memory may serve as a fundamental mechanism that coordinates the location of regenerative signaling with the presence of innervation that is able to receive and process sensory input, and may be relevant to the homeostasis and regeneration of other sensory organs. In addition, because Hh pathway manipulation provides a powerful tool to cause loss or gain of TRCs, we will be able to compare degenerating and regenerating states to identify other secreted factors that may play a role. These advances will expand our biological understanding of homeostasis and regeneration of sensory organs generally, and will improve our ability to prevent loss of taste or facilitate its recovery in patints undergoing cancer therapy. Our experimental aims are: Aim 1: Determine the cellular source of the Hh signal and its role in maintenance of TRCs. Conditional genetic approaches will be used to determine how Shh signaling functions in TRC maintenance. Aim 2: Define the role of Shh from gustatory sensory neurons in regeneration of TRCs. Surgical denervation, conditional genetic and pharmacological approaches, and organoid culture will be used to assess the role of neuronal Shh in TRC regeneration. Aim 3. Identify Hh-dependent factors required for maintenance and regeneration of TRCs. Gene expression profiling of FACS-sorted cells will be used to identify Hh-dependent factors that contribute to TRC maintenance and regeneration. Candidates will be tested in vitro in organoid culture and in vivo.

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