ASIC subunit ratio and differential surface trafficking in the brain.

Junjun Wu,Youjia Hu,Yuanyuan Xu,Jiangping Xu,Yu-Qing Jiang,Xiang-Ming Zha

doi:10.1186/s13041-016-0185-7

Abstract

BackgroundAcid-sensing ion channels (ASICs) are key mediators of acidosis-induced responses in neurons. However, little is known about the relative abundance of different ASIC subunits in the brain. Such data are fundamental for interpreting the relative contribution of ASIC1a homomers and 1a/2 heteromers to acid signaling, and essential for designing therapeutic interventions to target these channels. We used a simple biochemical approach and semi-quantitatively determined the molar ratio of ASIC1a and 2 subunits in mouse brain. Further, we investigated differential surface trafficking of ASIC1a, ASIC2a, and ASIC2b.Results and conclusionsASIC1a subunits outnumber the sum of ASIC2a and ASIC2b. There is a region-specific variation in ASIC2a and 2b expression, with cerebellum and striatum expressing predominantly 2b and 2a, respectively. Further, we performed surface biotinylation and found that surface ASIC1a and ASIC2a ratio correlates with their total expression. In contrast, ASIC2b exhibits little surface presence in the brain. This result is consistent with increased co-localization of ASIC2b with an ER marker in 3T3 cells. Our data are the first semi-quantitative determination of relative subunit ratio of various ASICs in the brain. The differential surface trafficking of ASICs suggests that the main functional ASICs in the brain are ASIC1a homomers and 1a/2a heteromers. This finding provides important insights into the relative contribution of various ASIC complexes to acid signaling in neurons.

Highlights

Acid-sensing ion channels (ASICs) are key mediators of acidosis-induced responses in neurons
A method to semi-quantitatively assess ASIC subunit ratio in the brain To quantitatively compare the molar ratio of two proteins, we presented here a biochemical calibration method (Fig. 1)
In summary, with a simple biochemical approach, we performed a semi-quantitative quantification of relative ASIC1a and 2 subunits in the brain

Summary

Introduction

Acid-sensing ion channels (ASICs) are key mediators of acidosis-induced responses in neurons. Little is known about the relative abundance of different ASIC subunits in the brain Such data are fundamental for interpreting the relative contribution of ASIC1a homomers and 1a/2 heteromers to acid signaling, and essential for designing therapeutic interventions to target these channels. Protons are recognized to function as neurotransmitters [1,2,3,4] In neurological diseases such as ischemia, brain acidosis is an important contributor to neuronal injury [5,6,7]. The main neuronal proton receptor is the acidsensing ion channel (ASIC) [8,9,10] In the brain, both in situ hybridization and immunostaining data show that ASIC1a, 2a and 2b subunits are predominantly expressed in neurons [9, 11,12,13,14]. Acid-activated currents in multiple neurons show components from both ASIC1a homomers and 1a/2 heteromers [17,18,19,20,21,22,23,24], the relative contribution of

Methods

Results

Discussion

Conclusion