Abstract Body (Do not enter title and authors here): Introduction: Preeclampsia (PE), a leading cause of maternal morbidity and mortality, is associated with diastolic dysfunction and increased long-term cardiovascular risk. Mice lacking S-nitrosoglutathione reductase (GSNOR^-/-) recapitulate the clinical and molecular features of PE, including nitroso-redox imbalance. However, the mechanisms by which redox dysregulation impairs myocardial relaxation during pregnancy remain poorly defined.
Hypothesis: GSNOR deficiency during pregnancy promotes oxidative stress-induced dysregulation of sarcomere protein phosphorylation, leading to altered Ca²⁺ sensitivity and impaired cardiomyocyte relaxation.
Methods: Ventricular cardiomyocytes were isolated from non-pregnant, late-pregnant (E17.5), and ascorbate-treated pregnant WT and GSNOR^-/- mice (N=3–4 mothers/group). Ascorbate, a potent antioxidant, was delivered in drinking water. Sarcomere shortening, relaxation time (tt50%), and resting length were measured using IonOptix. Sarcomere length (SL)-[Ca²⁺] hysteresis loops plotted SL vs. cytosolic [Ca²⁺]. Western blots of heart lysates were assessed for total and phosphorylated (p) cardiac Troponin I (cTnI) and Myosin binding protein C (cMyBPC), oxidized (ox) CaMKII, and redox regulatory proteins including Xanthine oxidoreductase (XOR), transcription factor Nrf2, Catalase, Superoxide dismutase (SOD1/2).
Results: In WT mice, pregnancy enhanced sarcomere relaxation (↓tt50% by ~18%), increased p-cTnI (1.8-fold), consistent with physiological adaptation. Pregnant GSNOR^-/- mice failed to show these changes, exhibiting blunted sarcomere relaxation (tt50% unchanged) and incomplete re-lengthening (↓6%), increased total cMyBPC and reduced p-cMyBPC (~45%), indicating impaired cross-bridge cycling. SL-[Ca²⁺] hysteresis was altered, suggesting disrupted Ca²⁺ responsiveness. GSNOR^-/- hearts also displayed reduced total CaMKII and higher ox-CaMKII level, and a 2.5-fold increase in XOR, a major ROS source, but suppressed antioxidant defenses (Nrf2, catalase, SOD 1/2). Ascorbate restored resting SL and contractile amplitude, but relaxation kinetics remained blunted.
Conclusion: GSNOR deficiency impairs sarcomere relaxation via redox-sensitive suppression of cMyBPC phosphorylation, driven by XOR-mediated ROS and impaired antioxidant defense. This study is the first to mechanistically link nitroso-redox imbalance to sarcomere dysfunction in a model of PE and identifies redox-sensitive therapeutic targets to improve maternal cardiac function.