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Apoptosis in Pulmonary Hypertension is Regulated by the Sodium‐Hydrogen Exchanger
Author(s) -
Huetsch John,
Yun Xin,
Suresh Karthik,
Jiang Haiyang,
Shimoda Larissa
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.1073.3
Subject(s) - unfolded protein response , amiloride , sodium–hydrogen antiporter , apoptosis , endoplasmic reticulum , chemistry , pulmonary hypertension , microbiology and biotechnology , intracellular ph , endocrinology , medicine , pharmacology , biology , biochemistry , sodium , intracellular , organic chemistry
Objective Remodeling of the pulmonary vasculature, involving resistance to apoptosis by pulmonary arterial smooth muscle cells (PASMCs) and lung microvascular endothelial cells (LMVECs), is a key component of the pathology underlying pulmonary hypertension (PH). To better understand the mechanisms contributing to apoptotic resistance in PH, we studied endoplasmic reticulum (ER) stress signaling in PASMCs and LMVECs isolated from the SU5416‐hypoxia (SuHx) rat model of PH. Methods PH was induced in male Wistar rats via exposure to the vascular endothelial growth factor receptor inhibitor SU5416 plus 3 wk of 10% oxygen followed by 2 wk of normoxia (SuHx model), while control rats were exposed to vehicle and 5 wk of normoxia. PASMCs and LMVECs were isolated from SuHx and control rats and expanded in culture. Apoptosis was measured using Hoechst stain. Thioflavin fluorescence was quantified as a measure of ER stress. Protein levels of the ER stress‐induced transcription factor, CCAAT/enhancer‐binding protein homologous protein (CHOP), were measured via immunoblot. To measure activity of the sodium‐hydrogen exchanger (NHE), cells were incubated with pH‐sensitive fluorescent dye and the Na + ‐dependent recovery of intracellular pH following acidification by ammonium pulse challenge was measured via fluorescence microscopy. Cell stress was induced with H 2 O 2 (250 μM for PASMC; 100 μM for LMVEC). NHE was pharmacologically inhibited with 10 μM ethyl‐isopropyl amiloride. Results ER stress, which often induces apoptosis, was increased at baseline in PASMCs/LMVECs from SuHx rats. In control cells, H 2 O 2 increased ER stress. Paradoxically, PASMCs and LMVECs from SuHx rats were protected from apoptosis both at baseline and following exposure to H 2 O 2 . The expression of CHOP, which is induced by ER stress and mediates apoptosis, was induced by H 2 O 2 in control cells, but remained low in SuHx PASMCs/LMVECs. NHE activity was increased in PASMCs/LMVECs from SuHx rats, and NHE inhibition increased both basal and H 2 O 2 ‐induced CHOP expression and apoptosis in SuHx PASMCs/LMVECs. Conclusions Decreased CHOP expression in the pulmonary vasculature during PH prevents ER stress‐induced apoptosis. Increasing CHOP expression via NHE‐inhibition restores stress‐induced apoptosis in PH vascular cells, suggesting a novel mechanism to control vascular remodeling in PH. Support or Funding Information NIH K08HL133475, F32HL124727, & R01HL073859