Mitochondrial acid-sensing ion channel 1a deficiency induces mitochondrial dysfunction in pulmonary arterial smooth muscle cells

Pulmonary hypertension (PH) is a progressive vascular disease driven by pulmonary arterial remodeling, characterized by cellular hyperproliferation, resistance to apoptosis, and phenotypic plasticity. Our laboratory has shown that the proton-gated cation channel, acid-sensing ion channel 1a (ASIC1a), is essential for the development of chronic hypoxia (CH)-induced PH in rodents. Importantly, ASIC1a activation occurs without changes in total ASIC1a levels but reflects a hypoxia-dependent redistribution to the plasma membrane in pulmonary arterial smooth muscle cells (PASMCs). In neurons, mitochondrial-localized ASIC1a (mtASIC1a) contributes to oxidative stress-induced mitochondrial membrane potential (ΔΨm) depolarization and apoptosis. Although mtASIC1a has not been described in vascular cells, its role in PASMCs may be relevant to mitochondrial dysfunction and apoptosis resistance in PH. We hypothesize that mtASIC1a is a crucial regulator of PASMC mitochondrial homeostasis, and its loss following CH promotes mitochondrial dysfunction and apoptosis resistance. Consistent with this, mtASIC1a localization was decreased in PASMCs and intrapulmonary arteries from CH rats compared to controls. Functionally, PASMCs from CH rats or Asic1a knockout mice exhibited ΔΨm hyperpolarization, elevated mitochondrial Ca 2+ and superoxide, impaired mitophagy, and reduced cleaved caspase-3. Transmission electron microscopy revealed mitochondrial morphological changes, including increased size and circularity, decreased aspect ratio, and reduced mitochondrial number per cell, while fusion/fission proteins remained largely unchanged. Lentiviral restoration of mtASIC1a prevented ΔΨm hyperpolarization and restored caspase-3 cleavage. These findings identify mtASIC1a as a novel regulator of mitochondrial function in PASMCs, where its loss following CH promotes ΔΨm hyperpolarization, impaired mitophagy, and resistance to apoptosis.