Effects of overexpressing ASIC2a and ASIC3 in transgenic mice

Vivian Costa, University of Iowa

Abstract

Acid-sensing ion channels (ASICs) are proton-gated cation channels expressed throughout the nervous system. These channels are activated by acidic pH conditions within an attainable physiologic range. The specific function of these channels has proven to be elusive, but it is clear that they are involved in various neuronal processes, both in the central nervous system as well as in the periphery.In order to further study the functions of these channels in an animal model system, transgenic animals were generated that overexpress individual ASIC subunits: ASIC2a and ASIC3. Transgenic proteins were detectable in brain and peripheral nervous tissue, and each had differential effects on acid-gated current properties in cultured neurons.Transgenes included N-terminal epitope tags to distinguish from endogenous ASICs, and expression was driven by a pan-neuronal promoter. Mechanical thermal sensory behaviors were tested in the transgenic mice. However, no effect was observed in these behaviors. The most interesting effect of overexpressing ASIC3 was the resulting impairment of conditioned fear behaviors in the transgenic animals without effect on unconditioned fear. ASIC3 transgenic behave like ASIC1a knockout mice in conditioned fear behaviors. Transgenic ASIC3 interacts with endogenous ASIC1, and is likely altering subunit composition of ASIC channels in the brain without abolishing proton-gated currenst like in the ASIC1a knockout. Overexpressing these two ASIC subunits in transgenic animals has produced tools that may be used to further study the functions of these channels. While this still is an artificial setting for studying ASIC functions, it nonetheless provides an in vivo method to study the effects of altering subunit composition in a whole animal and its behavioral effects, as well as in vivo expression of transgenes that can be studies biochemically. It is hopeful that studying localization in the transgenic mice will afford a better understanding of the localization and function of endogenous channels without the limitations of generating antibodies against endogenous mouse ASIC proteins, which is still in progress.