Sustained Increases in Cardiomyocyte Protein O-Linked β-N-Acetylglucosamine Levels Lead to Cardiac Hypertrophy and Reduced Mitochondrial Function Without Systolic Contractile Impairment

Deficiency in nucleoside diphosphate kinase B leads to endothelial activation of the hexosamine biosynthesis pathway and cardiac dysfunction

BACKGROUND

Nucleoside diphosphate kinase B (NDPKB) deficiency in endothelial cells (ECs) promotes the activation of the hexosamine biosynthesis pathway (HBP), leading to vascular damage in the retina. The aim of this study was to investigate the consequences of NDPKB deficiency in the mouse heart.

METHODS

NDPKB deficient mice were used in the study. Echocardiography was employed to assess cardiac function in vivo. Characterization of contractility in hiPSC-derived cardiomyocytes (hiPSC-CMs) was measured with the IonOptix contractility system. Immunoblotting and immunofluorescence were carried out to analyze the expression and localization of proteins in cultured cells and left ventricles (LVs).

RESULTS

NDPKB deficient mice displayed impaired glucose tolerance and increased heart weight compared to controls. Echocardiographic analysis revealed an increase in the diastolic diameter of the left ventricular posterior wall (LVPW), a decrease in the early diastolic mitral valve E and E' wave, and in the ratios of E/A and E'/A' in NDPKB deficient hearts, suggesting cardiac hypertrophy and diastolic dysfunction. In line with cardiac dysfunction, the phosphorylation of myocardial phospholamban (PLN) and the expression of sarcoplasmic/endoplasmic reticulum Ca2+-ATPase 2 (SERCA2) in the NDPKB deficient LVs were significantly reduced. Moreover, the accumulation of collagen, fibronectin as well as the upregulation of transforming growth factor β (TGF-β), were detected in NDPKB deficient LVs. In addition, activation of the HBP and its downstream O-GlcNAc cycle was observed in the LVs and cardiac ECs (CECs) isolated from the NDPKB-/- mice. Furthermore, a bipolar O-GlcNAc regulation was identified in CMs. O-GlcNAc was decreased in NDPKB-depleted CMs, while conditioned medium from NDPKB-depleted ECs significantly increased O-GlcNAc levels, along with contractile and relaxation dysfunction of the hiPSC-CMs, which was attenuated by inhibiting endothelial HBP activation.

CONCLUSIONS

Deficiency in NDPKB leads to endothelial activation of the HBP and cardiac dysfunction. Our findings may highlight the crucial role of proper endothelial HBP in maintaining cardiovascular homeostasis.

The role of protein O-GlcNAcylation in diabetic cardiomyopathy

It is well established that diabetes markedly increases the risk of multiple types of heart disease including heart failure. However, despite substantial improvements in the treatment of heart failure in recent decades the relative increased risk associated with diabetes remains unchanged. There is increasing appreciation of the importance of the post translational modification by O-linked-N-acetylglucosamine (O-GlcNAc) of serine and threonine residues on proteins in regulating cardiomyocyte function and mediating stress responses. In response to diabetes there is a sustained increase in cardiac O-GlcNAc levels, which has been attributed to many of the adverse effects of diabetes on the heart. Here we provide an overview of potential mechanisms by which increased cardiac O-GlcNAcylation contributes to the adverse effects on the heart and highlight some of the key gaps in our knowledge.

Opportunities for Therapeutic Modulation of O-GlcNAc

O-Linked β-N-acetylglucosamine (O-GlcNAc) is an essential, dynamic monosaccharide post-translational modification (PTM) found on serine and threonine residues of thousands of nucleocytoplasmic proteins. The installation and removal of O-GlcNAc is controlled by a single pair of enzymes, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), respectively. Since its discovery four decades ago, O-GlcNAc has been found on diverse classes of proteins, playing important functional roles in many cellular processes. Dysregulation of O-GlcNAc homeostasis has been implicated in the pathogenesis of disease, including neurodegeneration, X-linked intellectual disability (XLID), cancer, diabetes, and immunological disorders. These foundational studies of O-GlcNAc in disease biology have motivated efforts to target O-GlcNAc therapeutically, with multiple clinical candidates under evaluation. In this review, we describe the characterization and biochemistry of OGT and OGA, cellular O-GlcNAc regulation, development of OGT and OGA inhibitors, O-GlcNAc in pathophysiology, clinical progress of O-GlcNAc modulators, and emerging opportunities for targeting O-GlcNAc. This comprehensive resource should motivate further study into O-GlcNAc function and inspire strategies for therapeutic modulation of O-GlcNAc.

Protein glycosylation in cardiovascular health and disease

Protein glycosylation, which involves the attachment of carbohydrates to proteins, is one of the most abundant protein co-translational and post-translational modifications. Advances in technology have substantially increased our knowledge of the biosynthetic pathways involved in protein glycosylation, as well as how changes in glycosylation can affect cell function. In addition, our understanding of the role of protein glycosylation in disease processes is growing, particularly in the context of immune system function, infectious diseases, neurodegeneration and cancer. Several decades ago, cell surface glycoproteins were found to have an important role in regulating ion transport across the cardiac sarcolemma. However, with very few exceptions, our understanding of how changes in protein glycosylation influence cardiovascular (patho)physiology remains remarkably limited. Therefore, in this Review, we aim to provide an overview of N-linked and O-linked protein glycosylation, including intracellular O-linked N-acetylglucosamine protein modification. We discuss our current understanding of how all forms of protein glycosylation contribute to normal cardiovascular function and their roles in cardiovascular disease. Finally, we highlight potential gaps in our knowledge about the effects of protein glycosylation on the heart and vascular system, highlighting areas for future research.

O-GlcNAcylation in ischemic diseases

Protein glycosylation is an extensively studied field, with the most studied forms being oxygen or nitrogen-linked N-acetylglucosamine (O-GlcNAc or N-GlcNAc) glycosylation. Particular residues on proteins are targeted by O-GlcNAcylation, which is among the most intricate post-translational modifications. Significantly contributing to an organism's proteome, it influences numerous factors affecting protein stability, function, and subcellular localization. It also modifies the cellular function of target proteins that have crucial responsibilities in controlling pathways related to the central nervous system, cardiovascular homeostasis, and other organ functions. Under conditions of acute stress, changes in the levels of O-GlcNAcylation of these proteins may have a defensive function. Nevertheless, deviant O-GlcNAcylation nullifies this safeguard and stimulates the advancement of several ailments, the prognosis of which relies on the cellular milieu. Hence, this review provides a concise overview of the function and comprehension of O-GlcNAcylation in ischemia diseases, aiming to facilitate the discovery of new therapeutic targets for efficient treatment, particularly in patients with diabetes.

Roles of O-GlcNAcylation in Mitochondrial Homeostasis and Cardiovascular Diseases

Protein posttranslational modifications are important factors that mediate the fine regulation of signaling molecules. O-linked β-N-acetylglucosamine-modification (O-GlcNAcylation) is a monosaccharide modification on N-acetylglucosamine linked to the hydroxyl terminus of serine and threonine of proteins. O-GlcNAcylation is responsive to cellular stress as a reversible and posttranslational modification of nuclear, mitochondrial and cytoplasmic proteins. Mitochondrial proteins are the main targets of O-GlcNAcylation and O-GlcNAcylation is a key regulator of mitochondrial homeostasis by directly regulating the mitochondrial proteome or protein activity and function. Disruption of O-GlcNAcylation is closely related to mitochondrial dysfunction. More importantly, the O-GlcNAcylation of cardiac proteins has been proven to be protective or harmful to cardiac function. Mitochondrial homeostasis is crucial for cardiac contractile function and myocardial cell metabolism, and the imbalance of mitochondrial homeostasis plays a crucial role in the pathogenesis of cardiovascular diseases (CVDs). In this review, we will focus on the interactions between protein O-GlcNAcylation and mitochondrial homeostasis and provide insights on the role of mitochondrial protein O-GlcNAcylation in CVDs.

ROCK Inhibitor Fasudil Attenuates Neuroinflammation and Associated Metabolic Dysregulation in the Tau Transgenic Mouse Model of Alzheimer's Disease

BACKGROUND

The pathological manifestations of Alzheimer's disease (AD) include not only brain amyloid β protein (Aβ) containing neuritic plaques and hyperphosphorylated tau (p-- tau) containing neurofibrillary tangles but also microgliosis, astrocytosis, and neurodegeneration mediated by metabolic dysregulation and neuroinflammation.

METHODS

While antibody-based therapies targeting Aβ have shown clinical promise, effective therapies targeting metabolism, neuroinflammation, and p-tau are still an urgent need. Based on the observation that Ras homolog (Rho)-associated kinases (ROCK) activities are elevated in AD, ROCK inhibitors have been explored as therapies in AD models. This study determines the effects of fasudil, a ROCK inhibitor, on neuroinflammation and metabolic regulation in the P301S tau transgenic mouse line PS19 that models neurodegenerative tauopathy and AD. Using daily intraperitoneal (i.p.) delivery of fasudil in PS19 mice, we observed a significant hippocampal-specific decrease of the levels of phosphorylated tau (pTau Ser202/Thr205), a decrease of GFAP+ cells and glycolytic enzyme Pkm1 in broad regions of the brain, and a decrease in mitochondrial complex IV subunit I in the striatum and thalamic regions.

RESULTS

Although no overt detrimental phenotype was observed, mice dosed with 100 mg/kg/day for 2 weeks exhibited significantly decreased mitochondrial outer membrane and electron transport chain (ETC) protein abundance, as well as ETC activities.

CONCLUSION

Our results provide insights into dose-dependent neuroinflammatory and metabolic responses to fasudil and support further refinement of ROCK inhibitors for the treatment of AD.