The broad goal of our proposed studies is to exploit our new insights into the identity of CALHM1 as a founding member of a novel ion channel family. CALHM1, a gene of unknown function, was identified as a susceptibility factor for late-onset Alzheimer's disease that influences the age of onset. CALHM1 encodes a membrane protein expressed throughout the brain and in taste buds that lacks significant homology to other functionally characterized proteins, although five human homologs have been identified, and CALHM1 is conserved across species. We recently identified CALHM1 as the pore-forming subunit of Ca2+ permeable ion channel with unusual permeation properties and gating regulation by both voltage and extracellular Ca2+ concentration (Ca2+o). We have discovered that CALHM1 is essential for the perceptions of sweet, bitter and umami tastes, since CALHM1 knockout mice cannot perceive these tastants. Furthermore, we have identified the molecular mechanism that links CALHM1 expression to taste perception by discovering that CALHM1 is an ATP permeable channel, and that tastants activate ATP release as a neurotransmitter through CALHM1 channels by a voltage dependent mechanism that transduces taste in the periphery to the central nervous system. We will employ a combination of biophysical (electrophysiology, optical imaging), biochemical and cell biological approaches to define the molecular physiology of CALHM1 in taste perception. We will record the electrical properties of taste cells from wild-type mice and mice with CALHM1 genetically deleted and fully characterize the properties of CALHM channels in taste cells. We will define the role of CALHM1 in taste cell signal transduction by single cell imaging of intracellular Ca2+ and whole cell electrophysiology. Because a CALHM1 channel is multimeric, type II taste cells also express CALHM2 and CALHM3, and co-expression of CALHMs 1 and 3 generates a novel ATP-permeable channel, we will determine the biochemical and functional interactions and roles of all three CALHMs to define their channel properties with the goal to reconstitute the ATP release channel currents in taste cells. Finally we will use electrophysiological recordings of heterologous cells and taste cells to understand the mechanisms by which taste cell electrical responses activate CALHM channels and are in turn modified by CALHM channel activation. The results of these studies will provide new insights into the properties and regulation of this unique voltage-gated Ca2+ and ATP permeable ion channel and its essential role in taste sensory perception.

Public Health Relevance

The sense of taste plays an important role in the quality of human life. Identification of a mechanism that is essential for perception of sweet, bitter and fa tastes may provide new targets for pharmacological manipulation of these appetitive and aversive taste sensations, which may be important in obesity, diabetes and formulations of medicines.

Agency
National Institute of Health (NIH)
Institute
National Institute on Deafness and Other Communication Disorders (NIDCD)
Type
Research Project (R01)
Project #
5R01DC012538-03
Application #
8819530
Study Section
Neurotransporters, Receptors, and Calcium Signaling Study Section (NTRC)
Program Officer
Sullivan, Susan L
Project Start
2013-04-10
Project End
2016-03-31
Budget Start
2015-04-01
Budget End
2016-03-31
Support Year
3
Fiscal Year
2015
Total Cost
Indirect Cost
Name
University of Pennsylvania
Department
Physiology
Type
Schools of Medicine
DUNS #
042250712
City
Philadelphia
State
PA
Country
United States
Zip Code
19104
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Arduino, Daniela M; Wettmarshausen, Jennifer; Vais, Horia et al. (2017) Systematic Identification of MCU Modulators by Orthogonal Interspecies Chemical Screening. Mol Cell 67:711-723.e7
Ma, Zhongming; Saung, Wint Thu; Foskett, J Kevin (2017) Action potentials and ion conductances in wild-type and CALHM1-knockout type II taste cells. J Neurophysiol 117:1865-1876
Ma, Zhongming; Tanis, Jessica E; Taruno, Akiyuki et al. (2016) Calcium homeostasis modulator (CALHM) ion channels. Pflugers Arch 468:395-403
Tordoff, Michael G; Aleman, Tiffany R; Ellis, Hillary T et al. (2015) Normal Taste Acceptance and Preference of PANX1 Knockout Mice. Chem Senses 40:453-9
Vingtdeux, Valérie; Tanis, Jessica E; Chandakkar, Pallavi et al. (2014) Effect of the CALHM1 G330D and R154H human variants on the control of cytosolic Ca2+ and A? levels. PLoS One 9:e112484
Tordoff, Michael G; Ellis, Hillary T; Aleman, Tiffany R et al. (2014) Salty taste deficits in CALHM1 knockout mice. Chem Senses 39:515-28
Taruno, Akiyuki; Matsumoto, Ichiro; Ma, Zhongming et al. (2013) How do taste cells lacking synapses mediate neurotransmission? CALHM1, a voltage-gated ATP channel. Bioessays 35:1111-8
Tanis, Jessica E; Ma, Zhongming; Krajacic, Predrag et al. (2013) CLHM-1 is a functionally conserved and conditionally toxic Ca2+-permeable ion channel in Caenorhabditis elegans. J Neurosci 33:12275-86