Chronic Reductive Stress Impairs Endoplasmic Reticulum Function and Cause Proteotoxic Cardiac Disease

Abstract

BackgroundHeart failure (HF) is a growing cause of global human morbidity and mortality and elevated ROS are generalized as drivers of HF pathology. However, antioxidant treatments have failed to offer sufficient therapeutic benefits; the underlying mechanisms remain largely unknown. Here, we hypothesized that chronic reductive stress (cRS) induces endoplasmic reticulum (ER) dysfunction, which leads to proteotoxicity and pathological cardiac remodeling.MethodsTransgenic mice expressing cardiac specific, constitutively active Nrf2 (caNrf2‐TG) and their non‐transgenic (NTG) littermates at the age of 3 and ~6 months (n=6–8/group) were used to determine ER redox states and protein aggregation levels. Diastolic function was measured by echocardiography.ResultscRS substantially increased ER glutathione levels and suppressed protein oxidation (DMPO‐adducts) in TG vs. NTG mouse hearts. The co‐localization of KDEL (ER‐marker) with GSH or DMPO, showed by immunofluorescent imaging, indicates a hyper‐reductive redox milieu in the ER. Immunoblotting revealed a dose‐dependent induction of ER‐proteins (CHOP, GRP78, GRP94 and PDI) in TG hearts at 3‐months‐old. However, at 6‐months of age, this response was significantly repressed along with impaired protein folding response in TG mice, evidencing that progressive cRS is associated with a transition from adaptive ER stress‐response to ER dysfunction. Notably, electron micrograph and Proteostat® staining showed a dose‐ and age‐dependent augmentation of misfolded/aggregated proteins in TG hearts; these aggregates were highly ubiquitinated as demonstrated. Patterns of Mitral valve movement showed that ≥6 month‐old TG mice developed overt LV diastolic dysfunction as evidenced by increased mitral inflow velocity (MV E/A ratio).ConclusionER dysfunction and proteotoxic insults triggered pathological cardiac remodeling and diastolic dysfunction in the TG hearts experiencing cRS. The heterogeneity of redox profiles in HF subjects demands further investigation into the potential impact of RS in cardiovascular pathology. Research focusing on correlations between redox stress intensity, redox imbalance and disease progression may offer insights into redox‐based therapies.Support or Funding InformationThis study was supported by funding from NHLBI (HL118067), NIA (AG042860), the AHA (BGIA 0865015F), University of Utah Center for Aging Pilot grant (2009), the Division of Cardiovascular Medicine/Department of Medicine, University of Utah and the start‐up funds (for NSR) by Department of Pathology, the University of Alabama at Birmingham, AL and UABAMC21 grant by the University of Alabama at Birmingham, AL.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.