Showing papers by "Adam R. Wende published in 2020"

Maintaining Myocardial Glucose Utilization in Diabetic Cardiomyopathy Accelerates Mitochondrial Dysfunction

Abstract: Cardiac glucose uptake and oxidation are reduced in diabetes despite hyperglycemia. Mitochondrial dysfunction contributes to heart failure in diabetes. It is unclear if these changes are adaptive or maladaptive. To directly evaluate the relationship between glucose delivery and mitochondrial dysfunction in diabetic cardiomyopathy we generated transgenic mice with inducible cardiomyocyte-specific expression of the glucose transporter (GLUT4). We examined mice rendered hyperglycemic following low-dose streptozotocin prior to increasing cardiomyocyte glucose uptake by transgene induction. Enhanced myocardial glucose in non-diabetic mice decreased mitochondrial ATP generation and was associated with echocardiographic evidence of diastolic dysfunction. Increasing myocardial glucose delivery after short-term diabetes onset, exacerbated mitochondrial oxidative dysfunction. Transcriptomic analysis revealed that the largest changes, driven by glucose and diabetes, were in genes involved in mitochondrial function. This glucose-dependent transcriptional repression was in part mediated by O-GlcNAcylation of the transcription factor Sp1. Increased glucose uptake induced direct O-GlcNAcylation of many electron transport chain subunits and other mitochondrial proteins. These findings identify mitochondria as a major target of glucotoxicity. They also suggest reduced glucose utilization in diabetic cardiomyopathy might defend against glucotoxicity and caution that restoring glucose delivery to the heart in the context of diabetes could accelerate mitochondrial dysfunction by disrupting protective metabolic adaptations.

Increased Glucose Availability Attenuates Myocardial Ketone Body Utilization

Abstract: Background Perturbations in myocardial substrate utilization have been proposed to contribute to the pathogenesis of cardiac dysfunction in diabetic subjects. The failing heart in nondiabetics tends to decrease reliance on fatty acid and glucose oxidation, and increases reliance on ketone body oxidation. In contrast, little is known regarding the mechanisms mediating this shift among all 3 substrates in diabetes mellitus. Therefore, we tested the hypothesis that changes in myocardial glucose utilization directly influence ketone body catabolism. Methods and Results We examined ventricular-cardiac tissue from the following murine models: (1) streptozotocin-induced type 1 diabetes mellitus; (2) high-fat-diet-induced glucose intolerance; and transgenic inducible cardiac-restricted expression of (3) glucose transporter 4 (transgenic inducible cardiac restricted expression of glucose transporter 4); or (4) dominant negative O-GlcNAcase. Elevated blood glucose (type 1 diabetes mellitus and high-fat diet mice) was associated with reduced cardiac expression of β-hydroxybutyrate-dehydrogenase and succinyl-CoA:3-oxoacid CoA transferase. Increased myocardial β-hydroxybutyrate levels were also observed in type 1 diabetes mellitus mice, suggesting a mismatch between ketone body availability and utilization. Increased cellular glucose delivery in transgenic inducible cardiac restricted expression of glucose transporter 4 mice attenuated cardiac expression of both Bdh1 and Oxct1 and reduced rates of myocardial BDH1 activity and β-hydroxybutyrate oxidation. Moreover, elevated cardiac protein O-GlcNAcylation (a glucose-derived posttranslational modification) by dominant negative O-GlcNAcase suppressed β-hydroxybutyrate dehydrogenase expression. Consistent with the mouse models, transcriptomic analysis confirmed suppression of BDH1 and OXCT1 in patients with type 2 diabetes mellitus and heart failure compared with nondiabetic patients. Conclusions Our results provide evidence that increased glucose leads to suppression of cardiac ketolytic capacity through multiple mechanisms and identifies a potential crosstalk between glucose and ketone body metabolism in the diabetic myocardium.

MitoQ regulates redox-related noncoding RNAs to preserve mitochondrial network integrity in pressure-overload heart failure.

Abstract: Evidence suggests that mitochondrial network integrity is impaired in cardiomyocytes from failing hearts. While oxidative stress has been implicated in heart failure (HF)-associated mitochondrial remodeling, the effect of mitochondrial-targeted antioxidants, such as mitoquinone (MitoQ), on the mitochondrial network in a model of HF (e.g., pressure overload) has not been demonstrated. Furthermore, the mechanism of this regulation is not completely understood with an emerging role for posttranscriptional regulation via long noncoding RNAs (lncRNAs). We hypothesized that MitoQ preserves mitochondrial fusion proteins (i.e., mitofusin), likely through redox-sensitive lncRNAs, leading to improved mitochondrial network integrity in failing hearts. To test this hypothesis, 8-wk-old C57BL/6J mice were subjected to ascending aortic constriction (AAC), which caused substantial left ventricular (LV) chamber remodeling and remarkable contractile dysfunction in 1 wk. Transmission electron microscopy and immunostaining revealed defective intermitochondrial and mitochondrial-sarcoplasmic reticulum ultrastructure in AAC mice compared with sham-operated animals, which was accompanied by elevated oxidative stress and suppressed mitofusin (i.e., Mfn1 and Mfn2) expression. MitoQ (1.36 mg·day-1·mouse-1, 7 consecutive days) significantly ameliorated LV dysfunction, attenuated Mfn2 downregulation, improved interorganellar contact, and increased metabolism-related gene expression. Moreover, our data revealed that MitoQ alleviated the dysregulation of an Mfn2-associated lncRNA (i.e., Plscr4). In summary, the present study supports a unique mechanism by which MitoQ improves myocardial intermitochondrial and mitochondrial-sarcoplasmic reticulum (SR) ultrastructural remodeling in HF by maintaining Mfn2 expression via regulation by an lncRNA. These findings underscore the important role of lncRNAs in the pathogenesis of HF and the potential of targeting them for effective HF treatment.NEW & NOTEWORTHY We have shown that MitoQ improves cardiac mitochondrial network integrity and mitochondrial-SR alignment in a pressure-overload mouse heart-failure model. This may be occurring partly through preventing the dysregulation of a redox-sensitive lncRNA-microRNA pair (i.e., Plscr4-miR-214) that results in an increase in mitofusin-2 expression.

Insulin receptor substrates differentially exacerbate insulin-mediated left ventricular remodeling

Abstract: Pressure overload (PO) cardiac hypertrophy and heart failure are associated with generalized insulin resistance and hyperinsulinemia, which may exacerbate left ventricular (LV) remodeling. While PO activates insulin receptor tyrosine kinase activity that is transduced by insulin receptor substrate 1 (IRS1), the present study tested the hypothesis that IRS1 and IRS2 have divergent effects on PO-induced LV remodeling. We therefore subjected mice with cardiomyocyte-restricted deficiency of IRS1 (CIRS1KO) or IRS2 (CIRS2KO) to PO induced by transverse aortic constriction (TAC). In WT mice, TAC-induced LV hypertrophy was associated with hyperactivation of IRS1 and Akt1, but not IRS2 and Akt2. CIRS1KO hearts were resistant to cardiac hypertrophy and heart failure in concert with attenuated Akt1 activation. In contrast, CIRS2KO hearts following TAC developed more severe LV dysfunction than WT controls, and this was prevented by haploinsufficiency of Akt1. Failing human hearts exhibited isoform-specific IRS1 and Akt1 activation, while IRS2 and Akt2 activation were unchanged. Kinomic profiling identified IRS1 as a potential regulator of cardioprotective protein kinase G-mediated signaling. In addition, gene expression profiling revealed that IRS1 signaling may promote a proinflammatory response following PO. Together, these data identify IRS1 and Akt1 as critical signaling nodes that mediate LV remodeling in both mice and humans.

Differential DNA Methylation Encodes Proliferation and Senescence Programs in Human Adipose-Derived Mesenchymal Stem Cells.

Abstract: Adult adipose tissue-derived mesenchymal stem cells (ASCs) constitute a vital population of multipotent cells capable of differentiating into numerous end-organ phenotypes. However, scientific and translational endeavors to harness the regenerative potential of ASCs are currently limited by an incomplete understanding of the mechanisms that determine cell-lineage commitment and stemness. In the current study, we used reduced representation bisulfite sequencing (RRBS) analysis to identify epigenetic gene targets and cellular processes that are responsive to 5'-azacitidine (5'-AZA). We describe specific changes to DNA methylation of ASCs, uncovering pathways likely associated with the enhancement of their proliferative capacity. We identified 4,797 differentially methylated regions (FDR < 0.05) associated with 3,625 genes, of which 1,584 DMRs annotated to the promoter region. Gene set enrichment of differentially methylated promoters identified "phagocytosis," "type 2 diabetes," and "metabolic pathways" as disproportionately hypomethylated, whereas "adipocyte differentiation" was the most-enriched pathway among hyper-methylated gene promoters. Weighted coexpression network analysis of DMRs identified clusters associated with cellular proliferation and other developmental programs. Furthermore, the ELK4 binding site was disproportionately hyper-methylated within the promoters of genes associated with AKT signaling. Overall, this study offers numerous preliminary insights into the epigenetic landscape that influences the regenerative capacity of human ASCs.