P. Christian Schulze

Lipid Metabolism and Toxicity in the Heart

The heart has both the greatest caloric needs and the most robust oxidation of fatty acids (FAs). Under pathological conditions such as obesity and type 2 diabetes, cardiac uptake and oxidation are not balanced and hearts accumulate lipid potentially leading to cardiac lipotoxicity. We will first review the pathways utilized by the heart to acquire FAs from the circulation and to store triglyceride intracellularly. Then we will describe mouse models in which excess lipid accumulation causes heart dysfunction and experiments performed to alleviate this toxicity. Finally, the known relationships between heart lipid metabolism and dysfunction in humans will be summarized.

Ventricular Assist Device Implantation Corrects Myocardial Lipotoxicity, Reverses Insulin Resistance, and Normalizes Cardiac Metabolism in Patients With Advanced Heart Failure

Background— Heart failure is associated with impaired myocardial metabolism with a shift from fatty acids to glucose use for ATP generation. We hypothesized that cardiac accumulation of toxic lipid intermediates inhibits insulin signaling in advanced heart failure and that mechanical unloading of the failing myocardium corrects impaired cardiac metabolism. Methods and Results— We analyzed the myocardium and serum of 61 patients with heart failure (body mass index, 26.5±5.1 kg/m2; age, 51±12 years) obtained during left ventricular assist device implantation and at explantation (mean duration, 185±156 days) and from 9 control subjects. Systemic insulin resistance in heart failure was accompanied by decreased myocardial triglyceride and overall fatty acid content but increased toxic lipid intermediates, diacylglycerol, and ceramide. Increased membrane localization of protein kinase C isoforms, inhibitors of insulin signaling, and decreased activity of insulin signaling molecules Akt and Foxo were detectable in heart failure compared with control subjects. Left ventricular assist device implantation improved whole-body insulin resistance (homeostatic model of analysis–insulin resistance, 4.5±0.6–3.2±0.5; P<0.05) and decreased myocardial levels of diacylglycerol and ceramide, whereas triglyceride and fatty acid content remained unchanged. Improved activation of the insulin/phosphatidylinositol-3 kinase/Akt signaling cascade after left ventricular assist device implantation was confirmed by increased phosphorylation of Akt and Foxo, which was accompanied by decreased membrane localization of protein kinase C isoforms after left ventricular assist device implantation. Conclusions— Mechanical unloading after left ventricular assist device implantation corrects systemic and local metabolic derangements in advanced heart failure, leading to reduced myocardial levels of toxic lipid intermediates and improved cardiac insulin signaling.

Effects of Continuous-Flow Versus Pulsatile-Flow Left Ventricular Assist Devices on Myocardial Unloading and Remodeling

Background— Continuous-flow left ventricular assist devices (LVAD) are increasingly used for patients with end-stage heart failure (HF). We analyzed the effects of ventricular decompression by continuous-flow versus pulsatile-flow LVADs on myocardial structure and function in this population. Methods and Results— Sixty-one patients who underwent LVAD implantation as bridge-to-transplant were analyzed (pulsatile-flow LVAD: group P, n=31; continuous-flow LVAD: group C, n=30). Serial echocardiograms, serum levels of brain natriuretic peptide (BNP), and extracellular matrix biomarkers (ECM) were compared between the groups. Myocardial BNP and ECM gene expression were evaluated in a subset of 18 patients. Postoperative LV ejection fraction was greater (33.2±12.6% versus 17.6±8.8%, P<0.0001) and the mitral E/E′ was lower (9.9±2.6 versus 13.2±3.8, P=0.0002) in group P versus group C. Postoperative serum levels of BNP, metalloproteinases (MMP)-9, and tissue inhibitor of MMP (TIMP)-4 were significantly lower in group P compared with group C (BNP: 552.6±340.6 versus 965.4±805.7 pg/mL, P<0.01; MMP9: 309.0±220.2 versus 475.2±336.9 ng/dL, P<0.05; TIMP4: 1490.9±622.4 versus 2014.3±452.4 ng/dL, P<0.001). Myocardial gene expression of ECM markers and BNP decreased in both groups; however, expression of TIMP-4 decreased only in group P (P=0.024). Conclusions— Mechanical unloading of the failing myocardium using pulsatile devices is more effective as indicated by echocardiographic parameters of systolic and diastolic LV function as well as dynamics of BNP and ECM markers. Therefore, specific effects of pulsatile mechanical unloading on the failing myocardium may have important implications for device selection especially for the purpose of bridge-to-recovery in patients with advanced HF.

Lamina-Associated Polypeptide-1 Interacts with the Muscular Dystrophy Protein Emerin and Is Essential for Skeletal Muscle Maintenance

X-linked Emery-Dreifuss muscular dystrophy is caused by loss of function of emerin, an integral protein of the inner nuclear membrane. Yet emerin null mice are essentially normal, suggesting the existence of a critical compensating factor. We show that the lamina-associated polypeptide1 (LAP1) interacts with emerin. Conditional deletion of LAP1 from striated muscle causes muscular dystrophy; this pathology is worsened in the absence of emerin. LAP1 levels are significantly higher in mouse than human skeletal muscle, and reducing LAP1 by approximately half in mice also induces muscle abnormalities in emerin null mice. Conditional deletion of LAP1 from hepatocytes yields mice that exhibit normal liver function and are indistinguishable from littermate controls. These results establish that LAP1 interacts physically and functionally with emerin and plays an essential and selective role in skeletal muscle maintenance. They also highlight how dissecting differences between mouse and human phenotypes can provide fundamental insights into disease mechanisms.

Kruppel-like Factor 15 Is a Critical Regulator of Cardiac Lipid Metabolism

Background: Metabolic homeostasis is central to normal cardiac function. The molecular mechanisms underlying metabolic plasticity in the heart remain poorly understood. Results: Kruppel-like factor 15 (KLF15) is a direct and independent regulator of myocardial lipid flux. Conclusion: KLF15 is a core component of the transcriptional circuitry that governs cardiac metabolism. Significance: This work is the first to implicate the KLF transcription factor family in cardiac metabolism. The mammalian heart, the bodys largest energy consumer, has evolved robust mechanisms to tightly couple fuel supply with energy demand across a wide range of physiologic and pathophysiologic states, yet, when compared with other organs, relatively little is known about the molecular machinery that directly governs metabolic plasticity in the heart. Although previous studies have defined Kruppel-like factor 15 (KLF15) as a transcriptional repressor of pathologic cardiac hypertrophy, a direct role for the KLF family in cardiac metabolism has not been previously established. We show in human heart samples that KLF15 is induced after birth and reduced in heart failure, a myocardial expression pattern that parallels reliance on lipid oxidation. Isolated working heart studies and unbiased transcriptomic profiling in Klf15-deficient hearts demonstrate that KLF15 is an essential regulator of lipid flux and metabolic homeostasis in the adult myocardium. An important mechanism by which KLF15 regulates its direct transcriptional targets is via interaction with p300 and recruitment of this critical co-activator to promoters. This study establishes KLF15 as a key regulator of myocardial lipid utilization and is the first to implicate the KLF transcription factor family in cardiac metabolism.

Peroxisome Proliferator–Activated Receptor-γ Activation Prevents Sepsis-Related Cardiac Dysfunction and Mortality In Mice

Impaired cardiac contractility contributes to the hypotension and increased mortality that occur with sepsis1. A possible cause of sepsis-mediated cardiac dysfunction is reduced energy production due in part to compromised fatty acid oxidation (FAO)2-5 and glucose catabolism3, 6. Thus, it is likely that sepsis compromises cardiac energy production, which might be the major cause of cardiac dysfunction. Alternatively, sepsis induces the production of inflammatory cytokines, such as tumor necrosis factor (TNF) α, interleukin (IL)-1 and IL-6, and these might directly alter heart function7-9. n nIntraperitoneal (i.p.) injection of lipopolysaccharide (LPS) has been extensively used to model many of the clinical features of sepsis, including elevated inflammation and cardiac dysfunction10. LPS leads to production of inflammatory cytokines7-9, 11 and also reduces cardiac energy utilization2, 3, 12. n nNuclear receptors, particularly peroxisomal proliferator-activated receptors (PPARs), regulate cardiac FAO. The PPAR family consists of three members, PPARα, PPARδ and PPARγ. PPARα increases FA storage in triglycerides13 and FAO in heart14 and induces expression of peroxisomal and mitochondrial enzymes. Besides PPARα, cardiac FAO can be increased by activation of PPARγ15 or PPARδ16. Cardiomyocyte-specific overexpression of PPARα14 or PPARγ17 leads to cardiac lipid accumulation, an indication that lipid uptake exceeds FAO. PPARγ-coactivator-1 (PGC-1) α and β18 enhance FAO and mitochondrial biogenesis19. Both PPARα and PGC-1 mRNA levels are markedly reduced in the heart by LPS administration2, 3, 12, 20, while PPARγ is not affected2. n nOur group showed that maintenance of normal cardiac FAO via c-Jun-N-terminal kinase (JNK) inhibitor-mediated prevention of PPARα downregulation rescued cardiac function in septic mice despite elevated expression of cardiac inflammatory markers. In a similar context constitutive cardiac expression of PGC-1β prevented cardiac dysfunction that was caused by LPS-mediated sepsis3, an observation that was proposed to be due to improvement in cardiac FAO and attenuation of reactive oxygen species production. In the current study we show that constitutive cardiomyocyte-specific expression of PPARγ or systemic administration of the PPARγ agonist, rosiglitazone, increased cardiac FAO and prevented cardiac dysfunction in mice with LPS-induced sepsis, despite increased expression of cardiac inflammatory markers. In addition, we show that rosiglitazone-mediated activation of PPARγ prevents the loss of cardiac mitochondria that occurs in sepsis. Moreover, we show that restoration of cardiac FAO by rosiglitazone not only prevents but also treats LPS-induced heart dysfunction and improves survival. Thus the use of rosiglitazone is proposed as a potential treatment for septic cardiac dysfunction.Background—Cardiac dysfunction with sepsis is associated with both inflammation and reduced fatty acid oxidation. We hypothesized that energy deprivation accounts for sepsis-related cardiac dysfunction. Methods and Results—Escherichia coli lipopolysaccharide (LPS) administered to C57BL/6 mice (wild type) induced cardiac dysfunction and reduced fatty acid oxidation and mRNA levels of peroxisome proliferator–activated receptor (PPAR)-&agr; and its downstream targets within 6–8 hours. Transgenic mice in which cardiomyocyte-specific expression of PPAR&ggr; is driven by the &agr;-myosin heavy chain promoter (&agr;MHC-PPAR&ggr;) were protected from LPS-induced cardiac dysfunction. Despite a reduction in PPAR&agr;, fatty acid oxidation and associated genes were not decreased in hearts of LPS-treated &agr;MHC-PPAR&ggr; mice. LPS treatment, however, continued to induce inflammation-related genes, such as interleukin-1&agr;, interleukin-1&bgr;, interleukin-6, and tumor necrosis factor-&agr; in hearts of &agr;MHC-PPAR&ggr; mice. Treatment of wild-type mice with LPS and the PPAR&ggr; agonist, rosiglitazone, but not the PPAR&agr; agonist (WY-14643), increased fatty acid oxidation, prevented LPS-mediated reduction of mitochondria, and treated cardiac dysfunction, as well as it improved survival, despite continued increases in the expression of cardiac inflammatory markers. Conclusions—Activation of PPAR&ggr; in LPS-treated mice prevented cardiac dysfunction and mortality, despite development of cardiac inflammation and PPAR&agr; downregulation.

Kruppel-like factor 4 is critical for transcriptional control of cardiac mitochondrial homeostasis

Mitochondrial homeostasis is critical for tissue health, and mitochondrial dysfunction contributes to numerous diseases, including heart failure. Here, we have shown that the transcription factor Kruppel-like factor 4 (KLF4) governs mitochondrial biogenesis, metabolic function, dynamics, and autophagic clearance. Adult mice with cardiac-specific Klf4 deficiency developed cardiac dysfunction with aging or in response to pressure overload that was characterized by reduced myocardial ATP levels, elevated ROS, and marked alterations in mitochondrial shape, size, ultrastructure, and alignment. Evaluation of mitochondria isolated from KLF4-deficient hearts revealed a reduced respiration rate that is likely due to defects in electron transport chain complex I. Further, cardiac-specific, embryonic Klf4 deletion resulted in postnatal premature mortality, impaired mitochondrial biogenesis, and altered mitochondrial maturation. We determined that KLF4 binds to, cooperates with, and is requisite for optimal function of the estrogen-related receptor/PPARγ coactivator 1 (ERR/PGC-1) transcriptional regulatory module on metabolic and mitochondrial targets. Finally, we found that KLF4 regulates autophagy flux through transcriptional regulation of a broad array of autophagy genes in cardiomyocytes. Collectively, these findings identify KLF4 as a nodal transcriptional regulator of mitochondrial homeostasis.

Pathophysiology of Sepsis-Related Cardiac Dysfunction: Driven by Inflammation, Energy Mismanagement, or Both?

Sepsis is a systemic inflammatory response that follows bacterial infection. Cardiac dysfunction is an important consequence of sepsis that affects mortality and has been attributed to either elevated inflammation or suppression of both fatty acid and glucose oxidation and eventual ATP depletion. Moreover, cardiac adrenergic signaling is compromised in septic patients and this aggravates further heart function. While anti-inflammatory therapies are important for the treatment of the disease, administration of anti-inflammatory drugs did not improve survival in septic patients. This review article summarizes findings on inflammatory and other mechanisms that are triggered in sepsis and affect cardiac function and mortality. Particularly, it focuses on the effects of the disease in metabolic pathways, as well as in adrenergic signaling and the potential interplay of the latter with inflammation. It is suggested that therapeutic approaches should include combination of anti-inflammatory treatments, stimulation of energy production, and restoration of adrenergic signaling in the heart.

Palmitic Acid and DGAT1 Deficiency Enhance Osteoclastogenesis, while Oleic Acid‐Induced Triglyceride Formation Prevents It

Both obesity and diabetes mellitus are associated with alterations in lipid metabolism as well as a change in bone homeostasis and osteoclastogenesis. We hypothesized that increased fatty acid levels affect bone health by altering precursor cell differentiation and osteoclast activation. Here we show that palmitic acid (PA, 16:0) enhances receptor activator of NF‐κB ligand (RANKL)‐stimulated osteoclastogenesis and is sufficient to induce osteoclast differentiation even in the absence of RANKL. TNFα expression is crucial for PA‐induced osteoclastogenesis, as shown by increased TNFα mRNA levels in PA‐treated cells and abrogation of PA‐stimulated osteoclastogenesis by TNFα neutralizing antibodies. In contrast, oleic acid (OA, 18:1) does not enhance osteoclast differentiation, leads to increased intracellular triglyceride accumulation, and inhibits PA‐induced osteoclastogenesis. Adenovirus‐mediated expression of diacylglycerol acyl transferase 1 (DGAT1), a gene involved in triglyceride synthesis, also inhibits PA‐induced osteoclastogenesis, suggesting a protective role of DGAT1 for bone health. Accordingly, Dgat1 knockout mice have larger bone marrow‐derived osteoclasts and decreased bone mass indices. In line with these findings, mice on a high‐fat PA‐enriched diet have a greater reduction in bone mass and structure than mice on a high‐fat OA‐enriched diet. Thus, we propose that TNFα mediates saturated fatty acid‐induced osteoclastogenesis that can be prevented by DGAT activation or supplementation with OA.

Preoperative Serum Albumin Levels Predict 1-Year Postoperative Survival of Patients Undergoing Heart Transplantation

Background—Serum albumin concentration has been recognized as a marker of nutrition, severity of inflammation, and hepatic function in patients with various chronic diseases. The purpose of this study was to investigate the impact of pretransplant serum albumin concentration on post-transplant outcome in heart transplant recipients. Methods and Results—Preoperative laboratory variables, including albumin concentration and donor-related information, were obtained from 822 consecutive patients undergoing heart transplant at Columbia University Medical Center between 1999 and 2010. The association between pretransplant albumin concentration and post-transplant 1-year survival was analyzed. Available data from the United Network for Organ Sharing (n=13u2009671) were also analyzed to evaluate the impact of preoperative albumin levels on post-transplant outcome. In our cohort, multivariable analysis revealed that preoperative albumin (mg/dL; hazard ratio, 0.46; P<0.0001) and preoperative total bilirubin (mg/dL; hazard ratio, 1.26; P=0.0002) were associated with post-transplant 1-year mortality. This implied that for every 1 mg/dL increase in albumin concentration, the post-transplant 1-year mortality rate decreased by 54%. The Kaplan–Meier analysis based on our patients cohort and the United Network for Organ Sharing dataset showed lower survival rate at 1-year post-transplant in patients with albumin levels ⩽3.5 mg/dL compared with those with >3.5 mg/dL (our patients, 91.3 versus 72.4%; P<0.0001; United Network for Organ Sharing, 88.4 versus 84.8%; P<0.0001). Conclusions—Pretransplant serum albumin concentration is a strong prognostic marker for post-transplant survival in heart transplant recipients.