Neuropathic pain is a prevalent disorder that accompanies a wide spectrum of diseases including cancer, diabetes, traumatic injuries and AIDS. It is a significant clinical problem because the pain is severe and known analgesics have limited clinical efficacy. One of the important discoveries in pain research in the last few years has been the role of ATP activated P2X4 receptors (P2X4Rs) and microglia-neuron interactions in neuropathic pain. During neuropathic pain P2X4R expression is upregulated in microglia located in the dorsal horn of the pain pathway, and reducing P2X4R function alleviates symptoms of neuropathic pain in rodent models of the disorder. However, many fundamental aspects remain unexplored and there is only a rudimentary understanding of microglial P2X4R properties or the mechanisms involved in their upregulation in neuropathic pain. Progress has been hindered because it is not possible to identify and record from P2X4R expressing cells in tissue slices. A method for identifying P2X4R expressing cells in slices and in vivo would enable the rigorous testing of mechanistic hypotheses regarding microglial P2X4Rs in the healthy CNS and during disease processes. Here we seek to generate and thoroughly characterize an optical reporter mouse using the red fluorescent protein tdTomato. The availability of this mouse will allow researchers to directly visualize and record from P2X4R expressing cells within tissue slices and thus explore the cellular mechanisms that determine P2X4R upregulation and thus contribute significantly to the understanding of mechanisms and plasticity changes in the pain pathway during neuropathic pain. Within the scope of two aims we will generate and fully characterize the reporter mouse and exploit it to measure P2X4 responses using fluorescence guided patch-clamp recordings from microglia and neurons.
In Aim 1 we will generate P2X4R reporter mice expressing tdTomato fluorescent proteins as well as establish and characterize different founder lines of transgenic mice to map the location and identity of P2X4R expressing cells.
In Aim 2 we will study P2X4R expressing cells using patch-clamp electrophysiology in tissue slices from reporter mice. We will directly test the hypothesis that P2X4R upregulation is specific to activated microglia in the dorsal horn pain pathway. Overall, our approach will provide novel, well characterized optical reporter mice that will allow us and other researchers to identify and record from P2X4R expressing cells within intact tissue structures such as slices of CNS. These new reporter mice will be valuable general tools for the P2X, microglia and pain research communities.

Public Health Relevance

We will develop mouse models that will allow us and other researchers to identify and record from cells in the brain that express P2X4 receptors. The availability of these mice would constitute exceptional tools with which to study the role of P2X4 receptors in the normal healthy brain and in diseases of the nervous system, including the processes that lead to the development of neuropathic pain states.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Exploratory/Developmental Grants (R21)
Project #
5R21NS073980-02
Application #
8269867
Study Section
Cellular and Molecular Biology of Glia Study Section (CMBG)
Program Officer
Morris, Jill A
Project Start
2011-06-01
Project End
2014-05-31
Budget Start
2012-06-01
Budget End
2014-05-31
Support Year
2
Fiscal Year
2012
Total Cost
$192,500
Indirect Cost
$67,500
Name
University of California Los Angeles
Department
Physiology
Type
Schools of Medicine
DUNS #
092530369
City
Los Angeles
State
CA
Country
United States
Zip Code
90095
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Xu, Ji; Khakh, Baljit S (2014) Slow neuromodulation mediated by ATP P2X receptors. Neuron 83:257-9
Samways, Damien S K; Khakh, Baljit S; Egan, Terrance M (2012) Allosteric modulation of Ca2+ flux in ligand-gated cation channel (P2X4) by actions on lateral portals. J Biol Chem 287:7594-602
Toulme, Estelle; Khakh, Baljit S (2012) Imaging P2X4 receptor lateral mobility in microglia: regulation by calcium and p38 MAPK. J Biol Chem 287:14734-48