Acid-sensing ion channel 1a regulates mitochondrial membrane potential and pulmonary arterial smooth muscle cell apoptosis
Authors: Tuineau Megan , Herbert Lindsay , Yellowhair Tracylyn , Resta Thomas , Jernigan Nikki 
Published: May 2023

Acid-sensing ion channel 1a (ASIC1a) is a proton-gated cation channel that contributes to the development of chronic hypoxia (CH)-induced pulmonary hypertension (PH). Our prior studies demonstrate that ASIC1a is expressed in pulmonary arterial smooth muscle cells (PASMCs) and contributes to plasmalemmal membrane potential ( E m) depolarization and augmented intracellular Ca2+ signaling leading to enhanced vasoconstrictor reactivity and vascular remodeling. During PH, mitochondrial dysfunction associated with mitochondrial membrane potential (Δψm) hyperpolarization can inhibit opening of the mitochondrial permeability transition pore (mPTP), thereby repressing apoptosis and promoting the hyperproliferative and apoptosis-resistant PASMC phenotype. Recent evidence suggests that ASIC1a is localized to mitochondria and regulates the mPTP. However, it is unknown if mitochondrial-localized ASIC1a (mtASIC1a) contributes to the pathogenesis of PH. Therefore, the overall objective of this study is to determine the functional role of mtASIC1a in the apoptosis-resistant PASMC phenotype associated with PH. We hypothesized that CH causes Δψm hyperpolarization and apoptosis-resistance in PASMCs due to loss of mtASIC1a localization. To test this hypothesis, we housed Asic1a knockout ( Asic1a-/- ) and wild-type ( Asic1a+/+ ) mice in a hypobaric chamber (barometric pressure: ~380 mmHg) for 4 weeks to induce PH. Following CH, we found increased expression of ASIC1a at the plasma membrane and decreased expression in mitochondria, which were associated with PASMC E m depolarization and Δψm hyperpolarization. Using tetramethylrhodamine (TMRE) fluorescence to measure Δψm, we found that TMRE fluorescence was significantly increased (p=0.02) in PASMCs from normoxic Asic1a-/- mice compared to Asic1a+/+ mice, indicating that deletion of Asic1a leads to Δψm hyperpolarization. We utilized a lentiviral vector encoding mitochondrial-targeted human ASIC1a (mtASIC1a LV) to overexpress mtASIC1a in PASMCs (p=0.003) and found that transduction with mtASIC1a LV in PASMCs from Asic1a-/- mice significantly decreased TMRE fluorescence (p=0.004), further supporting the functional role of mtASIC1a to regulate Δψm. To assess apoptosis, we measured levels of active caspase-3 by western blot analysis in intrapulmonary arteries (PAs) from Asic1a+/+ and Asic1a-/- mice following CH. CH decreased levels of active caspase-3 in PAs from Asic1a+/+ (p=0.032), but not Asic1a-/- mice. Under normoxic conditions, active caspase-3 was lower in PAs from Asic1a-/- compared to Asic1a+/+ mice (p=0.044). These data suggest mtASIC1a plays an important role in the regulation of Δψm and that the loss of mtASIC1a contributes to Δψm hyperpolarization and apoptosis resistance in PASMCs following CH. Future studies will examine the contributions of mtASIC1a to the pathogenesis of PH through the regulation of mitochondrial reactive oxygen species, mitochondrial Ca2+ levels, mPTP sensitivity, and mitochondrial dynamics. NIH R01 HL111084 to N.L. Jernigan and NIH T32 HL007736 to T.C. Resta This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.