Taxonomy: 2014

AMPK-Dependent Inhibitory Phosphorylation of ACC is not Essential for Maintaining Myocardial Fatty Acid Oxidation. Zordoky BN, Nagendran J, Pulinilkunnil T, Kienesberger PC, Masson G, Waller TJ, Kemp BE, Steinberg GR, Dyck JR. Circ Res. 2014 Aug 15;115(5):518-24.

Rationale: The energy sensor AMP-activated protein kinases (AMPK) is thought to play an important role in regulating myocardial fatty acid oxidation (FAO) via its phosphorylation and inactivation of acetyl coenzyme A carboxylase (ACC). However, studies supporting this have not directly assessed whether the maintenance of FAO rates and subsequent cardiac function requires AMPK-dependent inhibitory phosphorylation of ACC.

Objective: To determine whether preventing AMPK-mediated inactivation of ACC influences myocardial FAO or function.

Methods and Results: A double knock-in (DKI) mouse (ACC-DKI) model was generated in which the AMPK phosphorylation sites Ser79 on ACC1 and Ser221 (Ser212 mouse) on ACC2 were mutated to prevent AMPK-dependent inhibitory phosphorylation of ACC. Hearts from ACC-DKI mice displayed a complete loss of ACC phosphorylation at the AMPK phosphorylation sites. Despite the inability of AMPK to regulate ACC activity, hearts from ACC-DKI mice displayed normal basal AMPK activation and cardiac function at both standard and elevated workloads. In agreement with the inability of AMPK in hearts from ACC-DKI mice to phosphorylate and inhibit ACC, there was a significant increase in cardiac malonyl-CoA content compared with wild-type mice. However, cardiac FAO rates were comparable between wild-type and ACC-DKI mice at baseline, during elevated workloads, and after a more stressful condition of myocardial ischemia that is known to robustly activate AMPK.

Conclusions: Our findings show AMPK-dependent inactivation of ACC is not essential for the control of myocardial FAO and subsequent cardiac function during a variety of conditions involving AMPK-independent and AMPK-dependent metabolic adaptations.

Read more – http://circres.ahajournals.org/content/115/5/518.long

Nicotinamide N-methyltransferase knockdown protects against diet-induced obesity. Kraus D, Yang Q, Kong D, Banks AS, Zhang L, Rodgers JT, Pirinen E, Pulinilkunnil TC, Gong F, Wang YC, Cen Y, Sauve AA, Asara JM, Peroni OD, Monia BP, Bhanot S, Alhonen L, Puigserver P, Kahn BB. Nature. 2014 Apr 10;508(7495):258-62.

In obesity and type 2 diabetes, Glut4 glucose transporter expression is decreased selectively in adipocytes. Adipose-specific knockout or overexpression of Glut4 alters systemic insulin sensitivity. Here we show, using DNA array analyses, that nicotinamide N-methyltransferase (Nnmt) is the most strongly reciprocally regulated gene when comparing gene expression in white adipose tissue (WAT) from adipose-specific Glut4-knockout or adipose-specific Glut4-overexpressing mice with their respective controls. NNMT methylates nicotinamide (vitamin B3) using S-adenosylmethionine (SAM) as a methyl donor,. Nicotinamide is a precursor of NAD+, an important cofactor linking cellular redox states with energy metabolism. SAM provides propylamine for polyamine biosynthesis and donates a methyl group for histone methylation. Polyamine flux including synthesis, catabolism and excretion, is controlled by the rate-limiting enzymes ornithine decarboxylase (ODC) and spermidine–spermine N1-acetyltransferase (SSAT; encoded by Sat1) and by polyamine oxidase (PAO), and has a major role in energy metabolism,. We report that NNMT expression is increased in WAT and liver of obese and diabetic mice. Nnmtknockdown in WAT and liver protects against diet-induced obesity by augmenting cellular energy expenditure. NNMT inhibition increases adipose SAM and NAD+ levels and upregulates ODC and SSAT activity as well as expression, owing to the effects of NNMT on histone H3 lysine 4 methylation in adipose tissue. Direct evidence for increased polyamine flux resulting from NNMT inhibition includes elevated urinary excretion and adipocyte secretion of diacetylspermine, a product of polyamine metabolism. NNMT inhibition in adipocytes increases oxygen consumption in an ODC-, SSAT- and PAO-dependent manner. Thus, NNMT is a novel regulator of histone methylation, polyamine flux and NAD+-dependent SIRT1 signalling, and is a unique and attractive target for treating obesity and type 2 diabetes.

Read online- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4107212/

The role of ubiquitin ligases in cardiac disease. Willis MS, Bevilacqua A, Pulinilkunnil T, Kienesberger P, Tannu M, Patterson C. J Mol Cell Cardiol. 2014 Jun;71:43-53.

Rigorous surveillance of protein quality control is essential for the maintenance of normal cardiac function, while the dysregulation of protein turnover is present in a diverse array of common cardiac diseases. Central to the protein quality control found in all cells is the ubiquitin proteasome system (UPS). The UPS plays a critical role in protein trafficking, cellular signaling, and most prominently, protein degradation. As ubiquitin ligases (E3s) control the specificity of the UPS, their description in the cardiomyocyte has highlighted how ubiquitin ligases are critical to the turnover and function of the sarcomere complex, responsible for the heart’s required continuous contraction. In this review, we provide an overview of the UPS, highlighting a comprehensive overview of the cardiac ubiquitin ligases identified to date. We then focus on recent studies of new cardiac ubiquitin ligases outlining their novel roles in protein turnover, cellular signaling, and the regulation of mitochondrial dynamics and receptor turnover in the pathophysiology of cardiac hypertrophy, cardiac atrophy, myocardial infarction, and heart failure. This article is part of a Special Issue entitled “Protein Quality Control, the Ubiquitin Proteasome System, and Autophagy”.

Read online – https://www.jmmc-online.com/article/S0022-2828(13)00340-4/fulltext?code=yjmcc-site

The Pathophysiology of Cardiac Hypertrophy and Heart Failure. Stansfield WE, Ranek M, Pendse A, Schisler JC, Wang S, Pulinilkunnil T, Willis MS. Cellular and Molecular Pathobiology of Cardiovascular Disease, Chapter 4, 2014, Pages 51-78

Left ventricular hypertrophy (LVH) is one of the most common cardiovascular diseases; the estimated prevalence is 20{8617e24ab0b76aabcd10cf8004a7bdc562123dc1ea8adc37299158a7c05423e6} in the general population. In spite of being one of the greatest independent risk factors for cardiovascular morbidity and mortality, it remains essentially untreated. In this chapter, we review the complex interplay of physiologic systems that give rise to pathologic hypertrophy and heart failure. We explore the hierarchy of intra- and intercellular signaling systems that converge to produce the hypertrophic phenotype. Lastly, we consider novel access points within these systems that may represent new therapeutic windows for pharmacologic intervention.

Read online – https://www.sciencedirect.com/science/article/pii/B9780124052062000041