Acid-sensing ion channel 1a regulates mitochondrial function and pulmonary arterial smooth muscle cell apoptosis

Pulmonary hypertension (PH) is a complex vascular disease that is characterized by prominent pulmonary arterial remodeling attributed to hyperproliferation, apoptosis resistance, and trans-differentiation of arterial cells. Our laboratory previously demonstrates that the proton-gated, cation channel acid-sensing ion channel 1a (ASIC1a) is required for the development of chronic hypoxia (CH)-induced pulmonary hypertension (PH) in rodents. Importantly, this prominent role involves hypoxia-dependent effects on the cellular localization of ASIC1a. Recent studies suggest that mitochondrial-localized ASIC1a (mtASIC1a) may be important for oxidative stress-induced mitochondrial membrane potential (ΔΨm) depolarization and subsequent apoptosis in cortical neurons. Interestingly, we show that mtASIC1a levels are decreased (p < 0.0001) in transiently cultured PASMC from male Wistar rats following hypobaric CH (4 wks @ 380 mmHg) compared to age-matched, normobaric (630 mmHg; Albuquerque, NM) control rats. Taken together, our study objective is to assess the functional role of mtASIC1a in PASMC, which may be important for our understanding of mitochondrial impairment and apoptosis resistance in PH. We hypothesize that the loss of mtASIC1a results in ΔΨm hyperpolarization and mitochondrial dysfunction leading to apoptosis resistance in PASMC following CH. To test this hypothesis, we first assessed mitochondrial bioenergetic processes in PASMC from control and CH rats. Interestingly, PASMC from CH rats exhibit increased (p < 0.0001) tetramethylrhodamine (TMRE) fluoresence indicating ΔΨm hyperpolarization. Consistent with these findings, the fluorescence of the mitochondrial Ca 2+ indicator, Rhod-2, AM, and the mitochondrial O 2 - indicator, MitoSOX, were also increased (p = 0.0059 and p = 0.0463, respectively) following CH. Using western blot analysis, we show that levels of LC3II/I and mitochondrial Parkin are decreased (p = 0.0004 and p = 0.0310, respectively) in PASMC from CH rats suggesting impaired mitophagy. Additionally, we found that immunofluoresence for cleaved caspase 3 is decreased (p = 0.0344) following CH indicating apoptosis resistance. Similarly, PASMC from global Asic1a knockout ( Asic1a -/- ) mice exhibit ∆Ψm hyperpolarization and apoptosis resistance. To determine the specific role of mtASIC1a in regulating mitochondrial function, we performed lentiviral transduction of mtASIC1a and found that ΔΨm hyperpolarization was prevented in PASMC from Asic1a -/- mice compared to the control vector group. Importantly, PASMC from control rats exhibit increased (p = 0.0060) TMRE fluoresence following in vitro hypoxia (5 d @ 2% O 2 , 5% CO 2 , balanced N 2 ) that tends to decrease following mtASIC1a transduction (p = 0.0640). Future studies will examine the pathophysiological effects of the loss of mtASIC1a in PH as well as the mechanisms regulating the cellular localization of ASIC1a in PASMC. This work was supported by NIH R01 HL111084 (N.L. Jernigan), NIH T32 HL007736 (T.C. Resta), AHA 24PRE1196925 (M.N. Tuineau), and NIH F31 HL170503 (M.N. Tuineau). This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.