Molecular Mechanism of Constitutive Endocytosis of Acid-Sensing Ion Channel la and Its Protective Function in Acidosis-Induced Neuronal Death.

Acid-sensing ion channels (ASICs) are protongated cation channels widely expressed in the peripheral and CNSs, which critically contribute to a variety of pathophysiological conditions that involve tissue acidosis, such as ischemic stroke and epileptic seizures. However, the trafficking mechanisms of ASICs and the related proteins remain largely unknown. Here, we demonstrate that ASIC la, the main ASICsubunit in the brain, undergoes constitutive endocytosis in a clathrin- and dynamin-dependent manner in both mouse cortical neurons and heterologous cell cultures. The endocytosis of ASIC1 a was inhibited by either the small molecular inhibitor tyrphostin A23 or knockdown of the core subunit of adaptor protein 2 ( AP2) μ2 using RNA interference, supporting a clathrin-dependent endocytosis of ASIC1 a. In addition, the internalization of ASIC1 a was blocked by dominant-negative dynamin 1 mutation K44A and the small molecular inhibitor dynasore, suggesting that it is also dynamin-dependent. We show that the membrane-proximal residues ⁴⁶⁵LCRRG⁴⁶⁹ at the cytoplasmic C terminus of ASIC la are critical for interaction with the endogenous adaptor protein complex and inhibition of ASIC I a internalization strongly exacerbated acidosis-induced death of cortical neurons from wild-type but not ASIC la knock-out mice. Together, these results reveal the molecular mechanism of ASIC la internalization and suggest the importance of endocytic pathway in functional regulation of ASICla channels as well as neuronal damages mediated by these channels during neurodegeneration. [ABSTRACT FROM AUTHOR]