Publication Date
2025
Document Type
Dissertation
Committee Members
Eric S. Bennett, Ph.D. (Committee Co-Chair); Andrew R. Ednie, Ph.D. (Committee Co-Chair); Courtney E.W. Sulentic, Ph.D. (Committee Member); Hongmei Ren, Ph.D. (Committee Member); Mark M. Rich, M.D., Ph.D. (Committee Member)
Degree Name
Doctor of Philosophy (PhD)
Abstract
Cardiovascular disease is the leading cause of death and contributes to the increasing global prevalence of heart failure (HF). N-glycosylation is a common co-/post-translational modification where branching oligosaccharides are bound to the extracellular domain of membrane proteins. This creates a diverse range of glycan structures and requires the coordination of hundreds of regulated genes. Inherited mutations in glycan synthesis frequently present with cardiomyopathies leading to HF with reduced ejection fraction (HFrEF). Additionally, gene expression studies of HFrEF patients have shown altered expression of glycosylation-related genes, including alpha-1,3-mannosyl-glycoproten 2-beta-N acetlyglucosaminyltransferase (Mgat1). This gene encodes N-acetylglucosaminyl transferase 1 (GlcNAcT1) which is required for the synthesis of hybrid and complex N-glycans. N-glycans can directly impact voltage-gated ion channel gating and may contribute to progressive cardiac dysfunction. Prior studies utilized a constitutive, cardiomyocyte-specific knockout of Mgat1 in mice (cMgat1KO) to demonstrate that embryonic reductions in N glycosylation results in HFrEF, extensive cardiac remodeling, and premature death. Similar to other established HF models, which often decompensate too quickly to model human disease, it was difficult to determine whether the worsening CM functions were responsible for, contributed to, or resulted from HF onset. These limitations in current models warranted the creation of a new model to help expand our understanding of the pathophysiological onset and progression of HF and the role cardiac N-glycans. Therefore, we developed and characterized a novel, a tamoxifen-inducible, CM-specific Mgat1KO mouse model (iMgat1KO) to investigate the effects of reduced hybrid/complex N glycosylation in the developed heart. We demonstrated a successful reduction of GlcNAcT1 I activity and confirm that N-glycans modulate gating of CM voltage-gated calcium channels. A longitudinal echocardiographic and electrocardiogram study showed the development of cardiac dysfunction starting around 28 days post induction (dpi) that progresses into HFrEF without ventricular hypertrophy, dilation or fibrosis. Further, there was minimal, if any, physiologic or pathophysiologic CM electromechanical remodeling of action potentials, calcium transients or contractility observed before (10–21dpi) or after (90–130dpi) HFrEF development. These results suggested that the gross dysfunction could be caused by a disruption of CM-to-CM electromechanical coupling. We showed that vital intercalated disc proteins are GlcNAcT1 targets and investigated the functional consequences of these changes. Echocardiographic strain analysis showed there is an increase in the peak ventricular radial thickening and longitudinal shortening that occurs earlier in the cardiac cycle in the iMgat1KO hearts by 14dpi. Finally, pilot optical mapping investigations suggest there are minimal, if any, changes in action potential conduction across the epicardial surface at 60dpi. Overall, the novel iMgat1KO mice offers a unique model for the progressive development of HF that lacks significant remodeling at the individual CM or gross structural level. This work suggests hybrid/complex N-glycans could be playing an intricate role in the proper function of CM electromechanical coupling.
Page Count
141
Department or Program
Biomedical Sciences
Year Degree Awarded
2025
Copyright
Copyright 2025, all rights reserved. My ETD will be available under the "Fair Use" terms of copyright law.
ORCID ID
0000-0002-4593-7396
