Hypoxia Attenuates Pressure Overload-Induced Heart Failure

BACKGROUND

Alveolar hypoxia is protective in the context of cardiovascular and ischemic heart disease; however, the underlying mechanisms are incompletely understood. The present study sought to test the hypothesis that hypoxia is cardioprotective in left ventricular pressure overload (LVPO)-induced heart failure. We furthermore aimed to test that overlapping mechanisms promote cardiac recovery in heart failure patients following left ventricular assist device-mediated mechanical unloading and circulatory support.

METHODS AND RESULTS

We established a novel murine model of combined chronic alveolar hypoxia and LVPO following transverse aortic constriction (HxTAC). The HxTAC model is resistant to cardiac hypertrophy and the development of heart failure. The cardioprotective mechanisms identified in our HxTAC model include increased activation of HIF (hypoxia-inducible factor)-1α-mediated angiogenesis, attenuated induction of genes associated with pathological remodeling, and preserved metabolic gene expression as identified by RNA sequencing. Furthermore, LVPO decreased Tbx5 and increased Hsd11b1 mRNA expression under normoxic conditions, which was attenuated under hypoxic conditions and may induce additional hypoxia-mediated cardioprotective effects. Analysis of samples from patients with advanced heart failure that demonstrated left ventricular assist device-mediated myocardial recovery revealed a similar expression pattern for TBX5 and HSD11B1 as observed in HxTAC hearts.

CONCLUSIONS

Hypoxia attenuates LVPO-induced heart failure. Cardioprotective pathways identified in the HxTAC model might also contribute to cardiac recovery following left ventricular assist device support. These data highlight the potential of our novel HxTAC model to identify hypoxia-mediated cardioprotective mechanisms and therapeutic targets that attenuate LVPO-induced heart failure and mediate cardiac recovery following mechanical circulatory support.

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

Background Lifestyle and metabolic diseases influence the severity and pathogenesis of cardiovascular disease through numerous mechanisms, including regulation via posttranslational modifications. A specific posttranslational modification, the addition of O-linked β-N acetylglucosamine (O-GlcNAcylation), has been implicated in molecular mechanisms of both physiological and pathologic adaptations. The current study aimed to test the hypothesis that in cardiomyocytes, sustained protein O-GlcNAcylation contributes to cardiac adaptations, and its progression to pathophysiology. Methods and Results Using a naturally occurring dominant-negative O-GlcNAcase (dnOGA) inducible cardiomyocyte-specific overexpression transgenic mouse model, we induced dnOGA in 8- to 10-week-old mouse hearts. We examined the effects of 2-week and 24-week dnOGA overexpression, which progressed to a 1.8-fold increase in protein O-GlcNAcylation. Two-week increases in protein O-GlcNAc levels did not alter heart weight or function; however, 24-week increases in protein O-GlcNAcylation led to cardiac hypertrophy, mitochondrial dysfunction, fibrosis, and diastolic dysfunction. Interestingly, systolic function was maintained in 24-week dnOGA overexpression, despite several changes in gene expression associated with cardiovascular disease. Specifically, mRNA-sequencing analysis revealed several gene signatures, including reduction of mitochondrial oxidative phosphorylation, fatty acid, and glucose metabolism pathways, and antioxidant response pathways after 24-week dnOGA overexpression. Conclusions This study indicates that moderate increases in cardiomyocyte protein O-GlcNAcylation leads to a differential response with an initial reduction of metabolic pathways (2-week), which leads to cardiac remodeling (24-week). Moreover, the mouse model showed evidence of diastolic dysfunction consistent with a heart failure with preserved ejection fraction. These findings provide insight into the adaptive versus maladaptive responses to increased O-GlcNAcylation in heart.

Best practices in assessing cardiac protein O-GlcNAcylation by immunoblot

The modification of serine and threonine amino acids of proteins by O-linked N-acetylglucosamine (O-GlcNAc) regulates the activity, stability, function, and subcellular localization of proteins. Dysregulation of O-GlcNAc homeostasis is well established as a hallmark of various cardiac diseases, including cardiac hypertrophy, heart failure, complications associated with diabetes, and responses to acute injuries such as oxidative stress and ischemia-reperfusion. Given the limited availability of site-specific O-GlcNAc antibodies, studies of changes in O-GlcNAcylation in the heart frequently use pan-O-GlcNAc antibodies for semiquantitative evaluation of overall O-GlcNAc levels. However, there is a high degree of variability in many published cardiac O-GlcNAc blots. For example, many blots often have regions that lack O-GlcNAc positive staining of proteins either below 50 or above 100 kDa. In some O-GlcNAc blots, only a few protein bands are detected, while in others, intense bands around 75 kDa dominate the gel due to nonspecific IgM band staining, making it difficult to visualize less intense bands. Therefore, the goal of this study was to develop a modifiable protocol that optimizes O-GlcNAc positive banding of proteins in cardiac tissue extracts. We showed that O-GlcNAc blots using CTD110.6 antibody of proteins ranging from <30 to ∼450 kDa could be obtained while also limiting nonspecific staining. We also show that some myofilament proteins are recognized by the CTD110.6 antibody. Therefore, by protocol optimization using the widely available CTD110.6 antibody, we found that it is possible to obtain pan-O-GlcNAc blots of cardiac tissue, which minimizes common limitations associated with this technique.NEW & NOTEWORTHY The post-translational modification of proteins by O-linked N-acetylglucosamine (O-GlcNAc) is recognized as mediating cardiac pathophysiology. However, there is considerable variability in the quality of O-GlcNAc immunoblots used to evaluate changes in cardiac O-GlcNAc levels. Here we show that with relatively minor changes to a commonly used protocol it is possible to minimize the intensity of nonspecific bands while also reproducibly generating O-GlcNAc immunoblots covering a range of molecular weights from <30 to ∼450 kDa.

Metabolic adaptation to tyrosine kinase inhibition in leukemia stem cells

Tyrosine kinase inhibitors (TKIs) are very effective in treating chronic myelogenous leukemia (CML), but primitive, quiescent leukemia stem cells persist as a barrier to the cure. We performed a comprehensive evaluation of metabolic adaptation to TKI treatment and its role in CML hematopoietic stem and progenitor cell persistence. Using a CML mouse model, we found that glycolysis, glutaminolysis, the tricarboxylic acid cycle, and oxidative phosphorylation (OXPHOS) were initially inhibited by TKI treatment in CML-committed progenitors but were restored with continued treatment, reflecting both selection and metabolic reprogramming of specific subpopulations. TKI treatment selectively enriched primitive CML stem cells with reduced metabolic gene expression. Persistent CML stem cells also showed metabolic adaptation to TKI treatment through altered substrate use and mitochondrial respiration maintenance. Evaluation of transcription factors underlying these changes helped detect increased HIF-1 protein levels and activity in TKI-treated stem cells. Treatment with an HIF-1 inhibitor in combination with TKI treatment depleted murine and human CML stem cells. HIF-1 inhibition increased mitochondrial activity and reactive oxygen species (ROS) levels, reduced quiescence, increased cycling, and reduced the self-renewal and regenerating potential of dormant CML stem cells. We, therefore, identified the HIF-1-mediated inhibition of OXPHOS and ROS and maintenance of CML stem cell dormancy and repopulating potential as a key mechanism of CML stem cell adaptation to TKI treatment. Our results identify a key metabolic dependency in CML stem cells persisting after TKI treatment that can be targeted to enhance their elimination.

Enzyme-based assay for quantification of UDP-GlcNAc in cells and tissues

In this issue of Cell Reports Methods, Sunden et al. develop an enzymatic assay to measure UDP-GlcNAc levels from cells and tissue.1 By reporting on the level of the substrate itself, this approach can potentially enhance the fields' understanding of UDP-GlcNAc concentration under a variety of conditions.

Cardiomyocyte ZKSCAN3 regulates remodeling following pressure-overload

Autophagy is important for protein and organelle quality control. Growing evidence demonstrates that autophagy is tightly controlled by transcriptional mechanisms, including repression by zinc finger containing KRAB and SCAN domains 3 (ZKSCAN3). We hypothesize that cardiomyocyte-specific ZKSCAN3 knockout (Z3K) disrupts autophagy activation and repression balance and exacerbates cardiac pressure-overload-induced remodeling following transverse aortic constriction (TAC). Indeed, Z3K mice had an enhanced mortality compared to control (Con) mice following TAC. Z3K-TAC mice that survived exhibited a lower body weight compared to Z3K-Sham. Although both Con and Z3K mice exhibited cardiac hypertrophy after TAC, Z3K mice exhibited TAC-induced increase of left ventricular posterior wall thickness at end diastole (LVPWd). Conversely, Con-TAC mice exhibited decreases in PWT%, fractional shortening (FS%), and ejection fraction (EF%). Autophagy genes (Tfeb, Lc3b, and Ctsd) were decreased by the loss of ZKSCAN3. TAC suppressed Zkscan3, Tfeb, Lc3b, and Ctsd in Con mice, but not in Z3K. The Myh6/Myh7 ratio, which is related to cardiac remodeling, was decreased by the loss of ZKSCAN3. Although Ppargc1a mRNA and citrate synthase activities were decreased by TAC in both genotypes, mitochondrial electron transport chain activity did not change. Bi-variant analyses show that while in Con-Sham, the levels of autophagy and cardiac remodeling mRNAs form a strong correlation network, such was disrupted in Con-TAC, Z3K-Sham, and Z3K-TAC. Ppargc1a also forms different links in Con-sham, Con-TAC, Z3K-Sham, and Z3K-TAC. We conclude that ZKSCAN3 in cardiomyocytes reprograms autophagy and cardiac remodeling gene transcription, and their relationships with mitochondrial activities in response to TAC-induced pressure overload.

Assessing the impact of boldine on the gastrocnemius using multiomic profiling at 7 and 28 days post-complete spinal cord injury in young male mice

Spinal cord injury (SCI) results in rapid muscle loss. Exogenous molecular interventions to slow muscle atrophy after SCI have been relatively ineffective and requires the search for novel therapeutic targets. Connexin hemichannels (CxHC) allow non-selective passage of small molecules into and out of the cell. Boldine, a CxHC-inhibiting aporphine found in the boldo tree (Peumus boldus), has shown promising pre-clinical results in slowing atrophy during sepsis and restoring muscle function in dysferlinopathy. We administered 50 mg/kg/d of boldine to spinal cord transected mice beginning 3 d post-injury. Tissue was collected 7 and 28 d post-SCI and the gastrocnemius was used for multiomics profiling. Boldine did not prevent body or muscle mass loss but attenuated SCI-induced changes in the abundance of the amino acids proline, phenylalanine, leucine and isoleucine, as well as glucose, 7 d post-SCI. SCI resulted in the differential expression of ~7,700 and ~2,000 genes at 7 and 28 d, respectively, compared to sham controls. Pathway enrichment of these genes highlighted ribosome biogenesis at 7 d and translation and oxidative phosphorylation at both timepoints. Boldine altered the expression of ~150 genes at 7 d and ~110 genes at 28 d post-SCI. Pathway enrichment of these genes indicated a potential role for boldine in suppressing protein ubiquitination and degradation at the 7 d timepoint. Methylation analyses showed minimal differences between groups. Taken together, boldine is not an efficacious therapy to preserve body and muscle mass after complete SCI, though it attenuated some SCI-induced changes across the metabolome and transcriptome.

Vitamin A regulates tissue-specific organ remodeling in diet-induced obesity independent of mitochondrial function

Background

Perturbed mitochondrial energetics and vitamin A (VitA) metabolism are associated with the pathogenesis of diet-induced obesity (DIO) and type 2 diabetes (T2D).

Methods

To test the hypothesis that VitA regulates tissue-specific mitochondrial energetics and adverse organ remodeling in DIO, we utilized a murine model of impaired VitA availability and high fat diet (HFD) feeding. Mitochondrial respiratory capacity and organ remodeling were assessed in liver, skeletal muscle, and kidney tissue, which are organs affected by T2D-associated complications and are critical for the pathogenesis of T2D.

Results

In liver, VitA had no impact on maximal ADP-stimulated mitochondrial respiratory capacity (VADP) following HFD feeding with palmitoyl-carnitine and pyruvate each combined with malate as substrates. Interestingly, histopathological and gene expression analyses revealed that VitA mediates steatosis and adverse remodeling in DIO. In skeletal muscle, VitA did not affect VADP following HFD feeding. No morphological differences were detected between groups. In kidney, VADP was not different between groups with both combinations of substrates and VitA transduced the pro-fibrotic transcriptional response following HFD feeding.

Conclusion

The present study identifies an unexpected and tissue-specific role for VitA in DIO that regulates the pro-fibrotic transcriptional response and that results in organ damage independent of changes in mitochondrial energetics.

Vitamin A preserves cardiac energetic gene expression in a murine model of diet-induced obesity

Perturbed vitamin-A metabolism is associated with type 2 diabetes and mitochondrial dysfunction that are pathophysiologically linked to the development of diabetic cardiomyopathy (DCM). However, the mechanism, by which vitamin A might regulate mitochondrial energetics in DCM has previously not been explored. To test the hypothesis that vitamin-A deficiency accelerates the onset of cardiomyopathy in diet-induced obesity (DIO), we subjected mice with lecithin retinol acyltransferase (Lrat) germline deletion, which exhibit impaired vitamin-A stores, to vitamin A-deficient high-fat diet (HFD) feeding. Wild-type mice fed with a vitamin A-sufficient HFD served as controls. Cardiac structure, contractile function, and mitochondrial respiratory capacity were preserved despite vitamin-A deficiency following 20 wk of HFD feeding. Gene profiling by RNA sequencing revealed that vitamin A is required for the expression of genes involved in cardiac fatty acid oxidation, glycolysis, tricarboxylic acid cycle, and mitochondrial oxidative phosphorylation in DIO as expression of these genes was relatively preserved under vitamin A-sufficient HFD conditions. Together, these data identify a transcriptional program, by which vitamin A preserves cardiac energetic gene expression in DIO that might attenuate subsequent onset of mitochondrial and contractile dysfunction.NEW & NOTEWORTHY The relationship between vitamin-A status and the pathogenesis of diabetic cardiomyopathy has not been studied in detail. We assessed cardiac mitochondrial respiratory capacity, contractile function, and gene expression by RNA sequencing in a murine model of combined vitamin-A deficiency and diet-induced obesity. Our study identifies a role for vitamin A in preserving cardiac energetic gene expression that might attenuate subsequent development of mitochondrial and contractile dysfunction in diet-induced obesity.

Transcriptomic and proteomic profiling of human diabetic heart disease

 

Studies in animal models demonstrated the capability of type 2 diabetes (T2D) to induce cardiac dysfunction in the absence of vascular disease. However, whether and how T2D also impairs structure and function in human hearts remains poorly understood. Here, we performed transcriptional and proteomic profiling of left ventricular samples of 8 subjects with T2D, preserved EF (63,5%) and no history of ischemic heart disease (= diabetic cardiomyopathy; DbCM), 7 subjects with T2D, reduced EF (26,9%) and ischemic heart disease (= diabetic heart failure; DbHF), and 15 non-diabetic individuals with normal EF (64,7%) serving as controls. Among 1168 proteins identified by LC-MS/MS, 146 proteins were differentially regulated in DbHF, but only 66 in DbCM. Pathway analysis revealed downregulation of energy metabolic proteins, but upregulation of proteins involved in oxidative stress and inflammatory response. In DbCM, pathways of structural remodeling, cardiomyocyte proliferation, and mechanotransduction were upregulated. Bulk RNA sequencing revealed 1795 differentially regulated genes in DbHF, and 527 in DbCM, with only 128 genes being commonly regulated. DbHF, but not DbCM, could be clearly discriminated from controls by hierarchical clustering. While inflammation/immunity were major regulated pathways in DbHF, extracellular matrix remodeling and cellular growth were the most regulated pathways in DbCM. Thus, the differential regulation of biological pathways in DbCM versus DbHF suggests the existence of two distinct disease entities rather than DbHF being an advanced disease stage of DbCM.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Austrian Diabetes Society

Abstract P3099: Identification Of Hub Genes And Construction Of Protein-protein Interaction (PPI) Network Clusters Define Racially Distinct Signatures Of Ischemic Heart Failure

Cardiovascular diseases, including ischemic heart failure (IHF), are the leading cause of mortality worldwide; furthermore, African Americans (AA) have 30% higher mortality than Caucasian Americans (CA). Our recent study correlates racial differences in socioeconomic status with DNA methylation (DNAm), altered gene expression, and mortality in HF independent of etiology.

The current analysis focused on etiology-specific differences in DNAm with a specific focus on IHF, the related changes in gene expression, within self-reported race. RNA-seq expression ( P < 0.05, ±1.5-fold) and array-based methylation ( P < 0.05, ±5%) profiles were examined using cardiac biopsies from non-IHF (NIHF) and IHF AA (n = 9/5) and CA (n = 10/5) male patients. Network clusters were identified with MCODE (v2.0) and top hub genes identified via Cytohubba (v0.1). Both AA and CA patients showed similar numbers of IHF-specific differentially expressed genes (DEG) (591/365 AA; 439/486 CA; up/down). However, CA-specific methylation changes (29703/22703; up/down) were more abundant compared to AA (2904/2897; up/down). PPI network construction of these changes identified clusters unique to each group. The AA-specific upregulated cluster included AGPAT2, PPARG, and 10 other DEG associated with the fatty acid metabolism, while BMP2, SMAD6, and 4 other DEG that regulate BMP signaling and SMAD phosphorylation were downregulated. The CA-specific upregulated cluster included EZH2, CCNA1, and 18 other DEG that regulate mitotic sister chromatic separation, while EGFR, TNF, and 12 other DEG important for chronic inflammatory response formed the top downregulated cluster. Consistent with greater changes in DNAm the majority of DEGs in CA-specific clusters were also differentially methylated (58%) while fewer were in AA-specific clusters (17%). Within AA-specific PPI networks, PPARG/BMP2 (up/down) were the top ranked hub genes and KIF20A/KIT (up/down) in CA-specific networks. These racially distinct hub genes suggest altered regulatory mechanisms. Our analysis identified racially distinct clusters associated with specific pathways, which may connect the regulators of DNAm to gene expression and IHF, supporting the potential to use this information as prognostic biomarkers.

Soluble α-klotho and heparin modulate the pathologic cardiac actions of fibroblast growth factor 23 in chronic kidney disease

Fibroblast growth factor (FGF) 23 is a phosphate-regulating hormone that is elevated in patients with chronic kidney disease and associated with cardiovascular mortality. Experimental studies showed that elevated FGF23 levels induce cardiac hypertrophy by targeting cardiac myocytes via FGF receptor isoform 4 (FGFR4). A recent structural analysis revealed that the complex of FGF23 and FGFR1, the physiologic FGF23 receptor in the kidney, includes soluble α-klotho (klotho) and heparin, which both act as co-factors for FGF23/FGFR1 signaling. Here, we investigated whether soluble klotho, a circulating protein with cardio-protective properties, and heparin, a factor that is routinely infused into patients with kidney failure during the hemodialysis procedure, regulate FGF23/FGFR4 signaling and effects in cardiac myocytes. We developed a plate-based binding assay to quantify affinities of specific FGF23/FGFR interactions and found that soluble klotho and heparin mediate FGF23 binding to distinct FGFR isoforms. Heparin specifically mediated FGF23 binding to FGFR4 and increased FGF23 stimulatory effects on hypertrophic growth and contractility in isolated cardiac myocytes. When repetitively injected into two different mouse models with elevated serum FGF23 levels, heparin aggravated cardiac hypertrophy. We also developed a novel procedure for the synthesis and purification of recombinant soluble klotho, which showed anti-hypertrophic effects in FGF23-treated cardiac myocytes. Thus, soluble klotho and heparin act as independent FGF23 co-receptors with opposite effects on the pathologic actions of FGF23, with soluble klotho reducing and heparin increasing FGF23-induced cardiac hypertrophy. Hence, whether heparin injections during hemodialysis in patients with extremely high serum FGF23 levels contribute to their high rates of cardiovascular events and mortality remains to be studied.

Guidelines on Models of Diabetic Heart Disease

Diabetes is a major risk factor for cardiovascular diseases, including diabetic cardiomyopathy, atherosclerosis, myocardial infarction, and heart failure. As cardiovascular disease represents the number one cause of death in people with diabetes, there has been a major emphasis on understanding the mechanisms by which diabetes promotes cardiovascular disease, and how antidiabetic therapies impact diabetic heart disease. With a wide array of models to study diabetes (both type 1 and type 2), the field has made major progress in answering these questions. However, each model has its own inherent limitations. Therefore, the purpose of this guidelines document is to provide the field with information on which aspects of cardiovascular disease in the human diabetic population are most accurately reproduced by the available models. This review aims to emphasize the advantages and disadvantages of each model, and to highlight the practical challenges and technical considerations involved. We will review the preclinical animal models of diabetes (based on their method of induction), appraise models of diabetes-related atherosclerosis and heart failure, and discuss in vitro models of diabetic heart disease. These guidelines will allow researchers to select the appropriate model of diabetic heart disease, depending on the specific research question being addressed.

miRNA-200b—A Potential Biomarker Identified in a Porcine Model of Cardiogenic Shock and Mechanical Unloading

Background

Cardiogenic shock (CS) alters whole body metabolism and circulating biomarkers serve as prognostic markers in CS patients. Percutaneous ventricular assist devices (pVADs) unload the left ventricle by actively ejecting blood into the aorta. The goal of the present study was to identify alterations in circulating metabolites and transcripts in a large animal model that might serve as potential prognostic biomarkers in acute CS and additional left ventricular unloading by Impella ^® pVAD support.

Methods

CS was induced in a preclinical large animal model by injecting microspheres into the left coronary artery system in six pigs. After the induction of CS, mechanical pVAD support was implemented for 30 min total. Serum samples were collected under basal conditions, after the onset of CS, and following additional pVAD unloading. Circulating metabolites were determined by metabolomic analysis, circulating RNA entities by RNA sequencing.

Results

CS and additional pVAD support alter the abundance of circulating metabolites involved in Aminoacyl-tRNA biosynthesis and amino acid metabolism. RNA sequencing revealed decreased abundance of the hypoxia sensitive miRNA-200b following the induction of CS, which was reversed following pVAD support.

Conclusion

The hypoxamir miRNA-200b is a potential circulating marker that is repressed in CS and is restored following pVAD support. The early transcriptional response with increased miRNA-200b expression following only 30 min of pVAD support suggests that mechanical unloading alters whole body metabolism. Future studies are required to delineate the impact of serum miRNA-200b levels as a prognostic marker in patients with acute CS and pVAD unloading.

FGF21-FGFR4 signaling in cardiac myocytes promotes concentric cardiac hypertrophy in mouse models of diabetes

Fibroblast growth factor (FGF) 21, a hormone that increases insulin sensitivity, has shown promise as a therapeutic agent to improve metabolic dysregulation. Here we report that FGF21 directly targets cardiac myocytes by binding β-klotho and FGF receptor (FGFR) 4. In combination with high glucose, FGF21 induces cardiac myocyte growth in width mediated by extracellular signal-regulated kinase 1/2 (ERK1/2) signaling. While short-term FGF21 elevation can be cardio-protective, we find that in type 2 diabetes (T2D) in mice, where serum FGF21 levels are elevated, FGFR4 activation induces concentric cardiac hypertrophy. As T2D patients are at risk for heart failure with preserved ejection fraction (HFpEF), we propose that induction of concentric hypertrophy by elevated FGF21-FGFR4 signaling may constitute a novel mechanism promoting T2D-associated HFpEF such that FGFR4 blockade might serve as a cardio-protective therapy in T2D. In addition, potential adverse cardiac effects of FGF21 mimetics currently in clinical trials should be investigated.

Cardiomyocyte stromal interaction molecule 1 is a key regulator of Ca2+ -dependent kinase and phosphatase activity in the mouse heart

Stromal interaction molecule 1 (STIM1) is a major regulator of store-operated calcium entry in non-excitable cells. Recent studies have suggested that STIM1 plays a role in pathological hypertrophy; however, the physiological role of STIM1 in the heart is not well understood. We have shown that mice with a cardiomyocyte deletion of STIM1 (^cr STIM1^-/- ) develop ER stress, mitochondrial, and metabolic abnormalities, and dilated cardiomyopathy. However, the specific signaling pathways and kinases regulated by STIM1 are largely unknown. Therefore, we used a discovery-based kinomics approach to identify kinases differentially regulated by STIM1. Twelve-week male control and ^cr STIM1^-/- mice were injected with saline or phenylephrine (PE, 15 mg/kg, s.c, 15 min), and hearts obtained for analysis of the Serine/threonine kinome. Primary analysis was performed using BioNavigator 6.0 (PamGene), using scoring from the Kinexus PhosphoNET database and GeneGo network modeling, and confirmed using standard immunoblotting. Kinomics revealed significantly lower PKG and protein kinase C (PKC) signaling in the hearts of the ^cr STIM1^-/- in comparison to control hearts, confirmed by immunoblotting for the calcium-dependent PKC isoform PKCα and its downstream target MARCKS. Similar reductions in ^cr STIM1^-/- hearts were found for the kinases: MEK1/2, AMPK, and PDPK1, and in the activity of the Ca²⁺ -dependent phosphatase, calcineurin. Electrocardiogram analysis also revealed that ^cr STIM1^-/- mice have significantly lower HR and prolonged QT interval. In conclusion, we have shown several calcium-dependent kinases and phosphatases are regulated by STIM1 in the adult mouse heart. This has important implications in understanding how STIM1 contributes to the regulation of cardiac physiology and pathophysiology.

The Identification of a Novel Calcium-Dependent Link Between NAD+ and Glucose Deprivation-Induced Increases in Protein O-GlcNAcylation and ER Stress

The modification of proteins by O-linked β-N-acetylglucosamine (O-GlcNAc) is associated with the regulation of numerous cellular processes. Despite the importance of O-GlcNAc in mediating cellular function our understanding of the mechanisms that regulate O-GlcNAc levels is limited. One factor known to regulate protein O-GlcNAc levels is nutrient availability; however, the fact that nutrient deficient states such as ischemia increase O-GlcNAc levels suggests that other factors also contribute to regulating O-GlcNAc levels. We have previously reported that in unstressed cardiomyocytes exogenous NAD⁺ resulted in a time and dose dependent decrease in O-GlcNAc levels. Therefore, we postulated that NAD⁺ and cellular O-GlcNAc levels may be coordinately regulated. Using glucose deprivation as a model system in an immortalized human ventricular cell line, we examined the influence of extracellular NAD⁺ on cellular O-GlcNAc levels and ER stress in the presence and absence of glucose. We found that NAD⁺ completely blocked the increase in O-GlcNAc induced by glucose deprivation and suppressed the activation of ER stress. The NAD⁺ metabolite cyclic ADP-ribose (cADPR) had similar effects on O-GlcNAc and ER stress suggesting a common underlying mechanism. cADPR is a ryanodine receptor (RyR) agonist and like caffeine, which also activates the RyR, both mimicked the effects of NAD⁺. SERCA inhibition, which also reduces ER/SR Ca²⁺ levels had similar effects to both NAD⁺ and cADPR on O-GlcNAc and ER stress responses to glucose deprivation. The observation that NAD⁺, cADPR, and caffeine all attenuated the increase in O-GlcNAc and ER stress in response to glucose deprivation, suggests a potential common mechanism, linked to ER/SR Ca²⁺ levels, underlying their activation. Moreover, we showed that TRPM2, a plasma membrane cation channel was necessary for the cellular responses to glucose deprivation. Collectively, these findings support a novel Ca²⁺-dependent mechanism underlying glucose deprivation induced increase in O-GlcNAc and ER stress.

Abstract MP204: Pyruvate Dehydrogenase Kinase Isozyme Specific Regulation Of Protein Acetylation In Cardiac Tissue

Heart disease is the number one cause of death in developed countries. Metabolic diseases influence the severity of heart disease linked to risk factors which are thought to alter epigenetic mechanisms. Pyruvate dehydrogenase (PDH) kinases (PDK), which phosphorylate and reduce the activity of PDH the nexus of glucose oxidation and fatty acid oxidation are sensitive to metabolic status. Four isozymes of PDK (PDK1-4) exist with PDK2 and PDK4 as the major regulators in cardiac tissue. Owing to the role of PDH in regulating pyruvate to acetyl-CoA, we hypothesized that PDK inhibition may regulate protein acetylation through increasing acetyl-CoA because of PDH activation leading to post-translational modifications both directly to proteins in metabolic pathways as well as to histones associated with the genes encoding them. To test this, we utilized PDK2 germline knockout mice (P2KO), PDK4 germline knockout mice (P4KO), and PDK2 and PDK4 double knockout (DKO) mice for molecular analysis. Our results identify a novel increase in whole-cell protein acetylation in P2KO left ventricle tissue (LV). However, protein acetylation in P4KO LV was not changed compared to WT mice. The most robust protein acetylation was observed in the DKO LV. Furthermore, when we explored sub-cellular distribution of protein acetylation, the greatest increases were found on cytoplasmic proteins, with moderate changes in mitochondrial proteins. We also found PDK2 ablation induces histone H3 acetylation, which may also lead to changes in gene expression. Moreover, this protein acetylation in P2KO and DKO was not seen in other tissues examined (e.g., liver, skeletal muscle). The hyperacetylation is robust in male LV compared to female LV. In conclusion, our study supports a novel protein acetylation mechanism that is both tissue and PDK isozyme specific highlighting the role of PDK2, which is relatively understudied compared to PDK4 in heart disease. Further study will evaluate if the hyperacetylation has a beneficial effect in various heart disease settings as well as identify the impact on changes in gene expression. This study supports PDK isozyme-specific inhibition strategies will be required to develop therapeutic targets of cardiovascular disease with metabolic inflexibility.

Branched chain amino acids selectively promote cardiac growth at the end of the awake period

Essentially all biological processes fluctuate over the course of the day, manifesting as time-of-day-dependent variations with regards to the way in which organ systems respond to normal behaviors. For example, basic, translational, and epidemiologic studies indicate that temporal partitioning of metabolic processes governs the fate of dietary nutrients, in a manner in which concentrating caloric intake towards the end of the day is detrimental to both cardiometabolic and cardiovascular parameters. Despite appreciation that branched chain amino acids impact risk for obesity, diabetes mellitus, and heart failure, it is currently unknown whether the time-of-day at which dietary BCAAs are consumed influence cardiometabolic/cardiovascular outcomes. Here, we report that feeding mice a BCAA-enriched meal at the end of the active period (i.e., last 4 h of the dark phase) rapidly increases cardiac protein synthesis and mass, as well as cardiomyocyte size; consumption of the same meal at the beginning of the active period (i.e., first 4 h of the dark phase) is without effect. This was associated with a greater BCAA-induced activation of mTOR signaling in the heart at the end of the active period; pharmacological inhibition of mTOR (through rapamycin) blocked BCAA-induced augmentation of cardiac mass and cardiomyocyte size. Moreover, genetic disruption of the cardiomyocyte circadian clock abolished time-of-day-dependent fluctuations in BCAA-responsiveness. Finally, we report that repetitive consumption of BCAA-enriched meals at the end of the active period accelerated adverse cardiac remodeling and contractile dysfunction in mice subjected to transverse aortic constriction. Thus, our data demonstrate that the timing of BCAA consumption has significant implications for cardiac health and disease.

Identification of Nrf2-responsive microRNA networks as putative mediators of myocardial reductive stress

Although recent advances in the treatment of acute coronary heart disease have reduced mortality rates, few therapeutic strategies exist to mitigate the progressive loss of cardiac function that manifests as heart failure. Nuclear factor, erythroid 2 like 2 (Nfe2l2, Nrf2) is a transcriptional regulator that is known to confer transient myocardial cytoprotection following acute ischemic insult; however, its sustained activation paradoxically causes a reductive environment characterized by excessive antioxidant activity. We previously identified a subset of 16 microRNAs (miRNA) significantly diminished in Nrf2-ablated (Nrf2^−/−) mouse hearts, leading to the hypothesis that increasing levels of Nrf2 activation augments miRNA induction and post-transcriptional dysregulation. Here, we report the identification of distinct miRNA signatures (i.e. “reductomiRs”) associated with Nrf2 overexpression in a cardiac-specific and constitutively active Nrf2 transgenic (caNrf2-Tg) mice expressing low (TgL) and high (TgH) levels. We also found several Nrf2 dose-responsive miRNAs harboring proximal antioxidant response elements (AREs), implicating these “reductomiRs” as putative meditators of Nrf2-dependent post-transcriptional regulation. Analysis of mRNA-sequencing identified a complex network of miRNAs and effector mRNAs encoding known pathological hallmarks of cardiac stress-response. Altogether, these data support Nrf2 as a putative regulator of cardiac miRNA expression and provide novel candidates for future mechanistic investigation to understand the relationship between myocardial reductive stress and cardiac pathophysiology.

Normalizing glucose levels reconfigures the mammary tumor immune and metabolic microenvironment and decreases metastatic seeding

Obesity and diabetes cumulatively create a distinct systemic metabolic pathophysiological syndrome that predisposes patients to several diseases including breast cancer. Moreover, diabetic and obese women with breast cancer show a significant increase in mortality compared to non-obese and/or non-diabetic women. We hypothesized that these metabolic conditions incite an aggressive tumor phenotype by way of impacting tumor cell-autonomous and tumor cell non-autonomous events. In this study, we established a type 2 diabetic mouse model of triple-negative mammary carcinoma and investigated the effect of a glucose lowering therapy, metformin, on the overall tumor characteristics and immune/metabolic microenvironment. Diabetic mice exhibited larger mammary tumors that had increased adiposity with high levels of O-GlcNAc protein post-translational modification. These tumors also presented with a distinct stromal profile characterized by altered collagen architecture, increased infiltration by tumor-permissive M2 macrophages, and early metastatic seeding compared to non-diabetic/lean mice. Metformin treatment of the diabetic/obese mice effectively normalized glucose levels, reconfigured the mammary tumor milieu, and decreased metastatic seeding. Our results highlight the impact of two metabolic complications of obesity and diabetes on tumor cell attributes and showcase metformin's ability to revert tumor cell and stromal changes induced by an obese and diabetic host environment.

Cardiac Energy Metabolism in Heart Failure

Alterations in cardiac energy metabolism contribute to the severity of heart failure. However, the energy metabolic changes that occur in heart failure are complex and are dependent not only on the severity and type of heart failure present but also on the co-existence of common comorbidities such as obesity and type 2 diabetes. The failing heart faces an energy deficit, primarily because of a decrease in mitochondrial oxidative capacity. This is partly compensated for by an increase in ATP production from glycolysis. The relative contribution of the different fuels for mitochondrial ATP production also changes, including a decrease in glucose and amino acid oxidation, and an increase in ketone oxidation. The oxidation of fatty acids by the heart increases or decreases, depending on the type of heart failure. For instance, in heart failure associated with diabetes and obesity, myocardial fatty acid oxidation increases, while in heart failure associated with hypertension or ischemia, myocardial fatty acid oxidation decreases. Combined, these energy metabolic changes result in the failing heart becoming less efficient (ie, a decrease in cardiac work/O₂ consumed). The alterations in both glycolysis and mitochondrial oxidative metabolism in the failing heart are due to both transcriptional changes in key enzymes involved in these metabolic pathways, as well as alterations in NAD redox state (NAD⁺ and nicotinamide adenine dinucleotide levels) and metabolite signaling that contribute to posttranslational epigenetic changes in the control of expression of genes encoding energy metabolic enzymes. Alterations in the fate of glucose, beyond flux through glycolysis or glucose oxidation, also contribute to the pathology of heart failure. Of importance, pharmacological targeting of the energy metabolic pathways has emerged as a novel therapeutic approach to improving cardiac efficiency, decreasing the energy deficit and improving cardiac function in the failing heart.

Racial and socioeconomic disparity associates with differences in cardiac DNA methylation among men with end-stage heart failure

Heart failure (HF) is a multifactorial syndrome that remains a leading cause of worldwide morbidity. Despite its high prevalence, only half of patients with HF respond to guideline-directed medical management, prompting therapeutic efforts to confront the molecular underpinnings of its heterogeneity. In the current study, we examined epigenetics as a yet unexplored source of heterogeneity among patients with end-stage HF. Specifically, a multicohort-based study was designed to quantify cardiac genome-wide cytosine-p-guanine (CpG) methylation of cardiac biopsies from male patients undergoing left ventricular assist device (LVAD) implantation. In both pilot (n = 11) and testing (n = 31) cohorts, unsupervised multidimensional scaling of genome-wide myocardial DNA methylation exhibited a bimodal distribution of CpG methylation found largely to occur in the promoter regions of metabolic genes. Among the available patient attributes, only categorical self-identified patient race could delineate this methylation signature, with African American (AA) and Caucasian American (CA) samples clustering separately. Because race is a social construct, and thus a poor proxy of human physiology, extensive review of medical records was conducted, but ultimately failed to identify covariates of race at the time of LVAD surgery. By contrast, retrospective analysis exposed a higher all-cause mortality among AA (56.3%) relative to CA (16.7%) patients at 2 yr following LVAD placement (P = 0.03). Geocoding-based approximation of patient demographics uncovered disparities in income levels among AA relative to CA patients. Although additional studies are needed, the current analysis implicates cardiac DNA methylation as a previously unrecognized indicator of socioeconomic disparity in human heart failure outcomes.

NEW & NOTEWORTHY A bimodal signature of cardiac DNA methylation in heart failure corresponds with racial differences in all-cause mortality following mechanical circulatory support. Racial differences in promoter methylation disproportionately affect metabolic signaling pathways. Socioeconomic factors are associated with racial differences in the cardiac methylome among men with end-stage heart failure.

Listen to this article’s corresponding podcast at https://ajpheart.podbean.com/e/racial-socioeconomic-determinants-of-the-cardiac-epigenome/.

The human aortic endothelium undergoes dose-dependent DNA methylation in response to transient hyperglycemia

BACKGROUND

Glycemic control is a strong predictor of long-term cardiovascular risk in patients with diabetes mellitus, and poor glycemic control influences long-term risk of cardiovascular disease even decades after optimal medical management. This phenomenon, termed glycemic memory, has been proposed to occur due to stable programs of cardiac and endothelial cell gene expression. This transcriptional remodeling has been shown to occur in the vascular endothelium through a yet undefined mechanism of cellular reprogramming.

METHODS

In the current study, we quantified genome-wide DNA methylation of cultured human endothelial aortic cells (HAECs) via reduced-representation bisulfite sequencing (RRBS) following exposure to diabetic (250 mg/dL), pre-diabetic (125 mg/dL), or euglycemic (100 mg/dL) glucose concentrations for 72 h (n = 2).

RESULTS

We discovered glucose-dependent methylation of genomic regions (DMRs) encompassing 2199 genes, with a disproportionate number found among genes associated with angiogenesis and nitric oxide (NO) signaling-related pathways. Multi-omics analysis revealed differential methylation and gene expression of VEGF (↑5.6% DMR, ↑3.6-fold expression), and NOS3 (↓20.3% DMR, ↓1.6-fold expression), nodal regulators of angiogenesis and NO signaling, respectively.

CONCLUSION

In the current exploratory study, we examine glucose-dependent and dose-responsive alterations in endothelial DNA methylation to examine a putative epigenetic mechanism underlying diabetic vasculopathy. Specifically, we uncover the disproportionate glucose-dependent methylation and gene expression of VEGF and NO signaling cascades, a physiologic imbalance known to cause endothelial dysfunction in diabetes. We therefore hypothesize that epigenetic mechanisms encode a glycemic memory within endothelial cells.

Maintaining Myocardial Glucose Utilization in Diabetic Cardiomyopathy Accelerates Mitochondrial Dysfunction

Cardiac glucose uptake and oxidation are reduced in diabetes despite hyperglycemia. Mitochondrial dysfunction contributes to heart failure in diabetes. It is unclear whether 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 GLUT4. We examined mice rendered hyperglycemic following low-dose streptozotocin prior to increasing cardiomyocyte glucose uptake by transgene induction. Enhanced myocardial glucose in nondiabetic 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 that 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.

Abstract 511: Transcriptomic Analysis of End-stage Human Heart Failure Highlights Strong Interaction Effect Between Race and Diabetes

African Americans (AA) have an elevated risk for cardiovascular diseases compared to Caucasian Americans (CA), including heart failure (HF). Type 2 diabetes (T2D) is a major risk factor for HF that also disproportionately affects AA. These health disparities and others reduce life expectancy ~3.5 y for AA compared to CA. While prior studies have explored the connection between diabetes and heart failure, the current understanding of HF pathogenesis is based almost exclusively from studies of CA, whereas those considering race have been either epidemiologic or narrow in focus. The purpose of this study was to examine things from a different angle through the use of genome-wide RNA-sequencing to uncover how diabetes differentially or similarly affects end-stage heart failure in AA vs CA. To accomplish this, human biopsy samples were obtained from 32 age and diabetes status (T2D or non-diabetic (ND)) matched male patients undergoing left ventricle assist device surgeries (n = 8: CA-ND, CA-T2D, AA-ND, AA-T2D). Differential expression analysis was then performed using generalized linear modeling to control for clinical covariates including hypertension and coronary artery disease. Results of T2D vs ND in AA patients showed a greater number of differentially expressed genes (DEGs, P < 0.05,

Role of O-Linked N-Acetylglucosamine Protein Modification in Cellular (Patho)Physiology

In the mid-1980s, the identification of serine and threonine residues on nuclear and cytoplasmic proteins modified by a N-acetylglucosamine moiety (O-GlcNAc) via an O-linkage overturned the widely held assumption that glycosylation only occurred in the endoplasmic reticulum, Golgi apparatus, and secretory pathways. In contrast to traditional glycosylation, the O-GlcNAc modification does not lead to complex, branched glycan structures and is rapidly cycled on and off proteins by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), respectively. Since its discovery, O-GlcNAcylation has been shown to contribute to numerous cellular functions, including signaling, protein localization and stability, transcription, chromatin remodeling, mitochondrial function, and cell survival. Dysregulation in O-GlcNAc cycling has been implicated in the progression of a wide range of diseases, such as diabetes, diabetic complications, cancer, cardiovascular, and neurodegenerative diseases. This review will outline our current understanding of the processes involved in regulating O-GlcNAc turnover, the role of O-GlcNAcylation in regulating cellular physiology, and how dysregulation in O-GlcNAc cycling contributes to pathophysiological processes.

Increased Glucose Availability Attenuates Myocardial Ketone Body Utilization

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.

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

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.

Insulin receptor substrates differentially exacerbate insulin-mediated left ventricular remodeling

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.

The SETD6 Methyltransferase Plays an Essential Role in Hippocampus-Dependent Memory Formation

BACKGROUND

Epigenetic mechanisms are critical for hippocampus-dependent memory formation. Building on previous studies that implicate the N-lysine methyltransferase SETD6 in the activation of nuclear factor-κB RELA (also known as transcription factor p65) as an epigenetic recruiter, we hypothesized that SETD6 is a key player in the epigenetic control of long-term memory.

METHODS

Using a series of molecular, biochemical, imaging, electrophysiological, and behavioral experiments, we interrogated the effects of short interfering RNA-mediated knockdown of Setd6 in the rat dorsal hippocampus during memory consolidation.

RESULTS

Our findings demonstrate that SETD6 is necessary for memory-related nuclear factor-κB RELA methylation at lysine 310 and associated increases in H3K9me2 (histone H3 lysine 9 dimethylation) in the dorsal hippocampus and that SETD6 knockdown interferes with memory consolidation, alters gene expression patterns, and disrupts spine morphology.

CONCLUSIONS

Together, these findings suggest that SETD6 plays a critical role in memory formation and may act as an upstream initiator of H3K9me2 changes in the hippocampus during memory consolidation.

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

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.

DNA methylation reprograms cardiac metabolic gene expression in end-stage human heart failure

Heart failure (HF) is a leading cause of morbidity and mortality in the United States and worldwide. As a multifactorial syndrome with unpredictable clinical outcomes, identifying the common molecular underpinnings that drive HF pathogenesis remains a major focus of investigation. Disruption of cardiac gene expression has been shown to mediate a common final cascade of pathological hallmarks wherein the heart reactivates numerous developmental pathways. Although the central regulatory mechanisms that drive this cardiac transcriptional reprogramming remain unknown, epigenetic contributions are likely. In the current study, we examined whether the epigenome, specifically DNA methylation, is reprogrammed in HF to potentiate a pathological shift in cardiac gene expression. To accomplish this, we used paired-end whole genome bisulfite sequencing and next-generation RNA sequencing of left ventricle tissue obtained from seven patients with end-stage HF and three nonfailing donor hearts. We found that differential methylation was localized to promoter-associated cytosine-phosphate-guanine islands, which are established regulatory regions of downstream genes. Hypermethylated promoters were associated with genes involved in oxidative metabolism, whereas promoter hypomethylation enriched glycolytic pathways. Overexpression of plasmid-derived DNA methyltransferase 3A in vitro was sufficient to lower the expression of numerous oxidative metabolic genes in H9c2 rat cardiomyoblasts, further supporting the importance of epigenetic factors in the regulation of cardiac metabolism. Last, we identified binding-site competition via hypermethylation of the nuclear respiratory factor 1 (NRF1) motif, an established upstream regulator of mitochondrial biogenesis. These preliminary observations are the first to uncover an etiology-independent shift in cardiac DNA methylation that corresponds with altered metabolic gene expression in HF.NEW & NOTEWORTHY The failing heart undergoes profound metabolic changes because of alterations in cardiac gene expression, reactivating glycolytic genes and suppressing oxidative metabolic genes. In the current study, we discover that alterations to cardiac DNA methylation encode this fetal-like metabolic gene reprogramming. We also identify novel epigenetic interference of nuclear respiratory factor 1 via hypermethylation of its downstream promoter targets, further supporting a novel contribution of DNA methylation in the metabolic remodeling of heart failure.

P3480Tissue-specific regulation of the mitochondrial proteome by adiponectin receptor 1

Lack of the adiponectin target receptor adiponectin receptor 1 (AdipoR1) impairs gene expression of mitochondrial OXPHOS proteins due to impaired AMPK-SIRT1-PGC-1α signaling. Since decreased adiponectin serum levels in diabetes mellitus should thus compromise AdipoR1 signaling, we hypothesized that impaired AdipoR1 signaling may causally contribute to typically observed mitochondrial defects in diabetes complications. Thus, we performed comparative proteomics in cardiac, renal and hepatic tissue of AdipoR1−/− mice using LC-MS/MS. Using principal component analysis, heatmapping and hierarchical clustering, a significant separation of genotypes was observed across tissues. Enrichment analysis of differentially expressed proteins revealed disproportionate representation of proteins involved in oxidative phosphorylation, TCA cycle and fatty acid oxidation in all tissues. While 121 or 98 or 78 proteins were differentially regulated in cardiac or renal or hepatic tissue, respectively, only 15 proteins were regulated in the same direction across all tissues. Pathway analysis identified HNF4, NRF1, LONP, RICTOR, SURF1, insulin receptor and PGC-1α as most likely upstream regulators. Importantly, we found a dramatic downregulation of AdipoR1 expression in heart (−70%), liver (−90%) and kidney (−80%; all p<0.05) of high fat-fed and prediabetic non-transgenic mice compared to low fat-fed mice. In addition and beyond diabetes, AdipoR1 expression was also decreased in endstage failing hearts of non-diabetic human subjects compared to non-failing donor hearts. Thus, we conclude that AdipoR1 signaling regulates mitochondrial protein composition across all tissues in a functionally conserved, yet molecularly distinct, manner. Impaired AdipoR1 signaling may causally contribute to mitochondrial defects in diabetic complications and even human heart failure.

Abstract 288: Mitoq Regulates Redox-related Non-coding Rnas to Improve Mitochondrial Network in Pressure Overload Heart Failure

Background: Previous studies show that mitochondrial network excitability, or the propagation of ROS signals, is impaired in cardiomyocytes from failing hearts. While oxidative stress has been implicated in heart failure (HF)-associated mitochondrial network abnormality, the effect of mitochondrial-targeted antioxidant, such as mitoquinone (MitoQ), on mitochondrial network in pressure overload hearts has not been demonstrated. We hypothesize that MitoQ improves mitochondrial networks in HF via regulation of redox-related cardiac remodeling-associated non-coding RNAs.

Methods and results: To test the hypothesis, C57BL/6J mice were subjected to ascending aortic constriction (AAC) to induce left ventricular (LV) pressure overload, followed by 7 days of MitoQ treatment (2 μmol). Doppler echocardiography revealed severe LV dilation and decreased ejection fraction following AAC, which were attenuated by MitoQ. Electron microscopy and immunostaining showed that inter-mitochondrial and mitochondria-sarcoplasmic reticulum (SR) network structure were altered in HF myocardium, in parallel with reduced expression of mitofusin proteins (e.g., MFN1 and MFN2) compared to sham-operated animals. MitoQ blunted mitofusin protein downregulation and improved mitochondrial networks. Our data also identified a MitoQ-mediated mechanism of mitofusin expression in HF by ameliorating the dysregulation of redox-related cardiac remodeling-associated long non-coding RNAs and microRNAs (i.e. Plscr4-miR-214 axis).

Conclusion: The present study indicates that MitoQ improves inter-mitochondrial and mitochondrial-SR structural organization in pressure overload hearts by attenuating the dysregulation of cardiac remodeling-associated non-coding RNAs.

Abstract 945: A Novel Role of Cardiac DNA Methylation as a Regulator of Fibrosis in Human Diabetic Heart Failure

Human heart failure (HF) is accompanied by changes in cardiac gene expression; however, the impact of diabetes mellitus on this transcriptional regulation remains unclear. Our laboratory studies the role of epigenetics in HF and focuses on DNA methylation, commonly accepted as a negative regulator of gene expression when present in a gene’s promoter. In the current study, we hypothesized that diabetes alters cardiac DNA methylation and the transcriptome. We performed an integrated analysis of RNA-sequencing and DNA methylation using human left ventricle biopsies from HF patients to determine the effect of diabetes on this reprogramming. Our analysis identified global changes in cardiac DNA methylation as well as mRNA expression sufficient to distinguish diabetic from non-diabetic patients. Specifically, we identified significant regulation of 1,133 genes (|1.5| fold-change, P<0.05) and 9,302 methylation sites (|5%| methylation, P<0.05). Within the 391 co-regulated genes, only 174 genes had altered promoter-associated methylation. Consistent with the accepted dogma that promoter methylation inversely regulates gene expression, we found that 119 of those 174 genes displayed this inverse relationship; of these, an overwhelming majority (102) were hypomethylated in diabetic relative to non-diabetic hearts. These findings contrast the cardiac hypermethylation we have reported for ischemic HF. Gene set enrichment of the 119 inversely-regulated genes identified numerous pathways involved in fibrosis, including extracellular matrix organization (FDR<0.05, 3.9% enriched) and collagen biosynthesis (FDR<0.05, 6.3% enriched), which suggest that DNA methylation contributes to the adverse cardiac remodeling associated with diabetic heart failure. To identify putative regulators of these transcriptional and epigenetic differences, a candidate gene approach was used to reveal induction (2.5-fold, Q<0.05) and demethylation (20.5%, P<0.05) of EGR2, a known regulator of fibrosis. Furthermore, we found induction of GADD45beta (2.6-fold, Q < 0.05) a known regulator of DNA demethylation. Taken together, these observations suggest that epigenetic mechanisms underlie an etiology-specific reprogramming of cardiac fibrosis in diabetic HF.

Prolactin Receptor Signaling Regulates a Pregnancy-Specific Transcriptional Program in Mouse Islets

Pancreatic β-cells undergo profound hyperplasia during pregnancy to maintain maternal euglycemia. Failure to reprogram β-cells into a more replicative state has been found to underlie susceptibility to gestational diabetes mellitus (GDM). We recently identified a requirement for prolactin receptor (PRLR) signaling in the metabolic adaptations to pregnancy, where β-cell-specific PRLR knockout (βPRLRKO) mice exhibit a metabolic phenotype consistent with GDM. However, the underlying transcriptional program that is responsible for the PRLR-dependent metabolic adaptations during gestation remains incompletely understood. To identify PRLR signaling gene regulatory networks and target genes within β-cells during pregnancy, we performed a transcriptomic analysis of pancreatic islets isolated from either βPRLRKO mice or littermate controls in late gestation. Gene set enrichment analysis identified forkhead box protein M1 and polycomb repressor complex 2 subunits, Suz12 and enhancer of zeste homolog 2 (Ezh2), as novel candidate regulators of PRLR-dependent β-cell adaptation. Gene ontology term pathway enrichment revealed both established and novel PRLR signaling target genes that together promote a state of increased cellular metabolism and/or proliferation. In contrast to the requirement for β-cell PRLR signaling in maintaining euglycemia during pregnancy, PRLR target genes were not induced following high-fat diet feeding. Collectively, the current study expands our understanding of which transcriptional regulators and networks mediate gene expression required for islet adaptation during pregnancy. The current work also supports the presence of pregnancy-specific adaptive mechanisms distinct from those activated by nutritional stress.

Resident macrophages reprogram toward a developmental state after acute kidney injury

Acute kidney injury (AKI) is a devastating clinical condition affecting at least two-thirds of critically ill patients, and, among these patients, it is associated with a greater than 60% risk of mortality. Kidney mononuclear phagocytes (MPs) are implicated in pathogenesis and healing in mouse models of AKI and, thus, have been the subject of investigation as potential targets for clinical intervention. We have determined that, after injury, F4/80hi-expressing kidney-resident macrophages (KRMs) are a distinct cellular subpopulation that does not differentiate from nonresident infiltrating MPs. However, if KRMs are depleted using polyinosinic/polycytidylic acid (poly I:C), they can be reconstituted from bone marrow-derived precursors. Further, KRMs lack major histocompatibility complex class II (MHCII) expression before P7 but upregulate it over the next 14 days. This MHCII- KRM phenotype reappears after injury. RNA sequencing shows that injury causes transcriptional reprogramming of KRMs such that they more closely resemble that found at P7. KRMs after injury are also enriched in Wingless-type MMTV integration site family (Wnt) signaling, indicating that a pathway vital for mouse and human kidney development is active. These data indicate that mechanisms involved in kidney development may be functioning after injury in KRMs.

Mitoquinone ameliorates pressure overload-induced cardiac fibrosis and left ventricular dysfunction in mice

Increasing evidence indicates that mitochondrial-associated redox signaling contributes to the pathophysiology of heart failure (HF). The mitochondrial-targeted antioxidant, mitoquinone (MitoQ), is capable of modifying mitochondrial signaling and has shown beneficial effects on HF-dependent mitochondrial dysfunction. However, the potential therapeutic impact of MitoQ-based mitochondrial therapies for HF in response to pressure overload is reliant upon demonstration of improved cardiac contractile function and suppression of deleterious cardiac remodeling. Using a new (patho)physiologically relevant model of pressure overload-induced HF we tested the hypothesis that MitoQ is capable of ameliorating cardiac contractile dysfunction and suppressing fibrosis. To test this C57BL/6J mice were subjected to left ventricular (LV) pressure overload by ascending aortic constriction (AAC) followed by MitoQ treatment (2 µmol) for 7 consecutive days. Doppler echocardiography showed that AAC caused severe LV dysfunction and hypertrophic remodeling. MitoQ attenuated pressure overload-induced apoptosis, hypertrophic remodeling, fibrosis and LV dysfunction. Profibrogenic transforming growth factor-β1 (TGF-β1) and NADPH oxidase 4 (NOX4, a major modulator of fibrosis related redox signaling) expression increased markedly after AAC. MitoQ blunted TGF-β1 and NOX4 upregulation and the downstream ACC-dependent fibrotic gene expressions. In addition, MitoQ prevented Nrf2 downregulation and activation of TGF-β1-mediated profibrogenic signaling in cardiac fibroblasts (CF). Finally, MitoQ ameliorated the dysregulation of cardiac remodeling-associated long noncoding RNAs (lncRNAs) in AAC myocardium, phenylephrine-treated cardiomyocytes, and TGF-β1-treated CF. The present study demonstrates for the first time that MitoQ improves cardiac hypertrophic remodeling, fibrosis, LV dysfunction and dysregulation of lncRNAs in pressure overload hearts, by inhibiting the interplay between TGF-β1 and mitochondrial associated redox signaling.

Dysregulation of the Mitochondrial Proteome Occurs in Mice Lacking Adiponectin Receptor 1

Decreased serum adiponectin levels in type 2 diabetes has been linked to the onset of mitochondrial dysfunction in diabetic complications by impairing AMPK-SIRT1-PGC-1α signaling via impaired adiponectin receptor 1 (AdipoR1) signaling. Here, we aimed to characterize the previously undefined role of disrupted AdipoR1 signaling on the mitochondrial protein composition of cardiac, renal, and hepatic tissues as three organs principally associated with diabetic complications. Comparative proteomics were performed in mitochondria isolated from the heart, kidneys and liver of Adipor1 ^-/- mice. A total of 790, 1,573, and 1,833 proteins were identified in cardiac, renal and hepatic mitochondria, respectively. While 121, 98, and 78 proteins were differentially regulated in cardiac, renal, and hepatic tissue of Adipor1^-/- mice, respectively; only 15 proteins were regulated in the same direction across all investigated tissues. Enrichment analysis of differentially expressed proteins revealed disproportionate representation of proteins involved in oxidative phosphorylation conserved across tissue types. Curated pathway analysis identified HNF4, NRF1, LONP, RICTOR, SURF1, insulin receptor, and PGC-1α as candidate upstream regulators. In high fat-fed non-transgenic mice with obesity and insulin resistance, AdipoR1 gene expression was markedly reduced in heart (-70%), kidney (-80%), and liver (-90%) (all P < 0.05) as compared to low fat-fed mice. NRF1 was the only upstream regulator downregulated both in Adipor1^-/- mice and in high fat-fed mice, suggesting common mechanisms of regulation. Thus, AdipoR1 signaling regulates mitochondrial protein composition across all investigated tissues in a functionally conserved, yet molecularly distinct, manner. The biological significance and potential implications of impaired AdipoR1 signaling are discussed.

Genome-wide DNA methylation encodes cardiac transcriptional reprogramming in human ischemic heart failure

Ischemic cardiomyopathy (ICM) is the clinical endpoint of coronary heart disease and a leading cause of heart failure. Despite growing demands to develop personalized approaches to treat ICM, progress is limited by inadequate knowledge of its pathogenesis. Since epigenetics has been implicated in the development of other chronic diseases, the current study was designed to determine whether transcriptional and/or epigenetic changes are sufficient to distinguish ICM from other etiologies of heart failure. Specifically, we hypothesize that genome-wide DNA methylation encodes transcriptional reprogramming in ICM. RNA-sequencing analysis was performed on human ischemic left ventricular tissue obtained from patients with end-stage heart failure, which enriched known targets of the polycomb methyltransferase EZH2 compared to non-ischemic hearts. Combined RNA sequencing and genome-wide DNA methylation analysis revealed a robust gene expression pattern consistent with suppression of oxidative metabolism, induced anaerobic glycolysis, and altered cellular remodeling. Lastly, KLF15 was identified as a putative upstream regulator of metabolic gene expression that was itself regulated by EZH2 in a SET domain-dependent manner. Our observations therefore define a novel role of DNA methylation in the metabolic reprogramming of ICM. Furthermore, we identify EZH2 as an epigenetic regulator of KLF15 along with DNA hypermethylation, and we propose a novel mechanism through which coronary heart disease reprograms the expression of both intermediate enzymes and upstream regulators of cardiac metabolism such as KLF15.

Novel role of the ER/SR Ca2+ sensor STIM1 in the regulation of cardiac metabolism

The endoplasmic reticulum/sarcoplasmic reticulum Ca²⁺ sensor stromal interaction molecule 1 (STIM1), a key mediator of store-operated Ca²⁺ entry, is expressed in cardiomyocytes and has been implicated in regulating multiple cardiac processes, including hypertrophic signaling. Interestingly, cardiomyocyte-restricted deletion of STIM1 (^crSTIM1-KO) results in age-dependent endoplasmic reticulum stress, altered mitochondrial morphology, and dilated cardiomyopathy in mice. Here, we tested the hypothesis that STIM1 deficiency may also impact cardiac metabolism. Hearts isolated from 20-wk-old ^crSTIM1-KO mice exhibited a significant reduction in both oxidative and nonoxidative glucose utilization. Consistent with the reduction in glucose utilization, expression of glucose transporter 4 and AMP-activated protein kinase phosphorylation were all reduced, whereas pyruvate dehydrogenase kinase 4 and pyruvate dehydrogenase phosphorylation were increased, in ^crSTIM1-KO hearts. Despite similar rates of fatty acid oxidation in control and ^crSTIM1-KO hearts ex vivo, ^crSTIM1-KO hearts contained increased lipid/triglyceride content as well as increased fatty acid-binding protein 4, fatty acid synthase, acyl-CoA thioesterase 1, hormone-sensitive lipase, and adipose triglyceride lipase expression compared with control hearts, suggestive of a possible imbalance between fatty acid uptake and oxidation. Insulin-mediated alterations in AKT phosphorylation were observed in ^crSTIM1-KO hearts, consistent with cardiac insulin resistance. Interestingly, we observed abnormal mitochondria and increased lipid accumulation in 12-wk ^crSTIM1-KO hearts, suggesting that these changes may initiate the subsequent metabolic dysfunction. These results demonstrate, for the first time, that cardiomyocyte STIM1 may play a key role in regulating cardiac metabolism. NEW & NOTEWORTHY Little is known of the physiological role of stromal interaction molecule 1 (STIM1) in the heart. Here, we demonstrate, for the first time, that hearts lacking cardiomyocyte STIM1 exhibit dysregulation of both cardiac glucose and lipid metabolism. Consequently, these results suggest a potentially novel role for STIM1 in regulating cardiac metabolism.

Glucagon Receptor Signaling Regulates Energy Metabolism via Hepatic Farnesoid X Receptor and Fibroblast Growth Factor 21

Glucagon, an essential regulator of glucose and lipid metabolism, also promotes weight loss, in part through potentiation of fibroblast growth factor 21 (FGF21) secretion. However, FGF21 is only a partial mediator of metabolic actions ensuing from glucagon receptor (GCGR) activation, prompting us to search for additional pathways. Intriguingly, chronic GCGR agonism increases plasma bile acid levels. We hypothesized that GCGR agonism regulates energy metabolism, at least in part, through farnesoid X receptor (FXR). To test this hypothesis, we studied whole-body and liver-specific FXR-knockout (Fxr∆liver) mice. Chronic GCGR agonist (IUB288) administration in diet-induced obese (DIO) Gcgr, Fgf21, and Fxr whole-body or liver-specific knockout (∆liver) mice failed to reduce body weight when compared with wild-type (WT) mice. IUB288 increased energy expenditure and respiration in DIO WT mice, but not Fxr∆liver mice. GCGR agonism increased [14C]palmitate oxidation in hepatocytes isolated from WT mice in a dose-dependent manner, an effect blunted in hepatocytes from Fxr∆liver mice. Our data clearly demonstrate that control of whole-body energy expenditure by GCGR agonism requires intact FXR signaling in the liver. This heretofore-unappreciated aspect of glucagon biology has implications for the use of GCGR agonism in the therapy of metabolic disorders.

Abstract 234: Nrf2-Dependent Transcriptional and Post-Transcriptional Regulatory Responses in Reductive Stress Myocardium

Background: Transient activation of nuclear factor, erythroid 2 like 2 (Nfe2l2/Nrf2), a master regulator of antioxidant transcription, protects from oxidative insult. However, sustained Nrf2 signaling causes proteotoxic reductive stress (RS). Using Nrf2 - / - mice, we recently uncovered several cardiac microRNAs (miRNAs) potentially expressed in an Nrf2-dependent manner. Here, we utilized cardiac-specific constitutively active Nrf2 transgenic (caNrf2-Tg) mice to elucidate necessary and sufficient miRNAs, and hypothesized that miRNA dysregulation underlies RS.

Methods: Next-generation RNA sequencing (RNAseq) was used to compare mRNA and miRNA transcriptomes of 6-month low (TgL) and high (TgH) transgene-expressing caNrf2-Tg mice to non-transgenic (NTg) controls (n=3-4/group). Differentially expressed genes (DEGs) were run through Ingenuity Pathway Analysis (IPA). Real-time qPCR validated RNAseq results (n=4-6/group). In silico target prediction correlated miRNA changes with corresponding mRNA levels.

Results: Principal component and hierarchal clustering analyses revealed distinct TgL and TgH transcriptomes. Relative to NTg, TgL mice exhibited 246 DEGs, 214 of which were consistent in TgH hearts. Strikingly, TgH mice displayed 1031 DEGs. As expected, IPA of DEGs indicated enhanced free radical scavenging; however, caNrf2 expression also dose-dependently enriched hypertrophic signaling, protein ubiquitination and the unfolded protein response. While 16 miRNAs were significantly altered in TgL hearts, a total of 101 miRNAs were detected TgH mice, several of which were predicted to account for mRNA changes in RS pathways. Notably, miR-671-3p and miR-455-5p, two miRNAs decreased in Nrf2 - / - mice, were reciprocally increased in caNrf2-Tg mice suggesting that Nrf2 is necessary and sufficient for their function in the heart.

Conclusion: While RS underlies human mutant protein aggregation cardiomyopathy, molecular determinants of pathogenesis downstream of Nrf2 remain unknown. Here, we identified key transcriptional responses and pathways associated with RS. These results link post-transcriptional regulation with redox imbalances in the heart, and highlight novel miRNAs for future mechanistic studies.