Biology subjects

Niedermeyer, S.

Publications and source records attributed to Niedermeyer, S..

3 recordsLinked to original sources

bioRxiv2025

Na+/H+ Exchanger Isoform 1 Regulates Apoptosis Susceptibility in Pulmonary Arterial Smooth Muscle from the Sugen/Hypoxia model of Pulmonary Hypertension

Pulmonary hypertension (PH) is characterized by vascular remodeling driven in part by apoptosis-resistant pulmonary arterial smooth muscle cells (PASMCs). Na/H exchanger isoform 1 (NHE1) regulates intracellular pH and plasma membrane cytoskeleton anchoring, influencing PASMC migration and proliferation, but the role of NHE1 in apoptosis remains unclear. NHE activity and NHE1 surface expression were increased in PASMCs from the Sugen/Hypoxia (SuHx) rat model compared to controls. Despite increased endoplasmic reticulum (ER) stress at baseline, SuHx PASMCs were resistant to apoptosis following H2O2 challenge. Pharmacological inhibition of NHE activity with ethyl-isopropyl amiloride (EIPA) and silencing with siRNA restored apoptosis in SuHx PASMCs. Conversely, NHE1 overexpression in control PASMCs conferred apoptosis resistance. Expression of mutant NHE1 constructs lacking ion translocation or binding to the adaptor protein, ezrin, also reduced H2O2-induced apoptosis. Mechanistically, apoptotic stimulation with H2O2 increased p38 phosphorylation in PASMCs from control, but not SuHx, rats, indicating impaired activation of this pro-apoptotic pathway. NHE1 suppression via EIPA or siRNA restored p38 phosphorylation in SuHx PASMCs, while overexpression of NHE1 (wild-type or mutants) suppressed p38 activation following apoptotic stimulation. Inhibition of p38 with SB203580 prevented the pro-apoptotic effect of EIPA, validating a role for p38 signaling in NHE1-mediated apoptosis resistance in SuHx PASMCs. These findings identify NHE1 as necessary and sufficient for PASMC apoptosis resistance in PH, by a mechanism independent of ion transport or ezrin-binding functions but involving suppression of p38 phosphorylation. Targeting NHE1-dependent pathways may restore PASMC apoptosis and offer a novel therapeutic strategy to reverse pulmonary vascular remodeling in PH.

physiology↗

bioRxiv2023

Aquaporin 1 confers apoptosis resistance in pulmonary arterial smooth muscle cells from the SU5416 hypoxia rat model

Pulmonary arterial hypertension (PAH) is a deadly condition that arises from increased pulmonary vascular resistance due to contraction and remodeling of the pulmonary arteries. The structural changes that occur in the pulmonary arteries include thickening of the medial (smooth muscle) layer resulting from increased proliferation and resistance to apoptosis. The mechanisms underlying apoptosis resistance in PAH are not fully understood. In cancer cells, high expression of aquaporin 1 (AQP1), a water channel, is associated with apoptosis resistance. We previously showed functional AQP1 protein was expressed in pulmonary arterial smooth muscle cells (PASMCs) and was upregulated in pre-clinical models of pulmonary hypertension. Whether AQP1 controls susceptibility of PASMCs to apoptosis in pre-clinical models of PAH is unknown. In this study, we used PASMCs isolated from control rats and rats exposed to SU5416 plus hypoxia (SuHx) to test the role of AQP1 in modulating apoptosis in PASMCs. We found that elevated levels of AQP1 in PASMCs from pulmonary hypertensive rats were necessary for resistance to apoptosis, and that apoptosis resistance could be conferred by increasing expression of AQP1 in PASMCs from control rats. Moreover, in exploring the downstream pathways involved, we found AQP1 levels influence the expression of Bcl-2, with enhanced AQP1 levels corresponding to increased Bcl-2 expression, resulting in reductions in the ratio of BAX to Bcl-2 as are typically associated with apoptosis resistance. These early results provide a mechanism by which AQP1 can regulate PASMC fate and suggest further investigation could provide additional clues regarding whether AQP1-mediated apoptosis resistance contributes to PAH development or progression and whether AQP1 might be a suitable target for therapy.

cell biology↗

bioRxiv2023

A Novel Interaction Between Aquaporin 1 and Caspase-3 in Pulmonary Arterial Smooth Muscle Cells

Pulmonary arterial hypertension (PAH) is a disease in which remodeling of the precapillary pulmonary vasculature leads to hyperplasia and hypertrophy of the muscular vascular wall, and the formation of vaso-occlusive lesions. These pathologic changes are predominantly due to abnormal proliferation and migration of pulmonary arterial smooth muscle cells (PASMCs), enhanced cellular functions that have been linked to increases in the cell membrane protein aquaporin-1 (AQP1). However, the mechanisms underlying increased AQP1 abundance have not been fully elucidated. Here we present data that establishes a novel interaction between AQP1 and the proteolytic enzyme caspase-3. In silico analysis of the AQP1 protein reveals two caspase-3 cleavage sites on its c-terminal tail, proximal to known ubiquitin sites. Using biotin proximity ligase techniques, we establish that AQP1 and caspase-3 interact in both HEK293A cells and rat PASMCs. Furthermore, we demonstrate that AQP1 levels increase and decrease with enhanced caspase-3 activity and inhibition respectively. Ultimately, further work characterizing this interaction could provide the foundation for novel PAH therapeutics.

cell biology↗