Roles of acetyl-CoA carboxylase beta in muscle cell differentiation and in mitochondrial fatty acid oxidation

Gene Expression Profiling of H9c2 Myoblast Differentiation towards a Cardiac-Like Phenotype

H9c2 myoblasts are a cell model used as an alternative for cardiomyocytes. H9c2 cells have the ability to differentiate towards a cardiac phenotype when the media serum is reduced in the presence of all-trans-retinoic acid (RA), creating multinucleated cells with low proliferative capacity. In the present study, we performed for the first time a transcriptional analysis of the H9c2 cell line in two differentiation states, i.e. embryonic cells and differentiated cardiac-like cells. The results show that RA-induced H9c2 differentiation increased the expression of genes encoding for cardiac sarcomeric proteins such as troponin T, or calcium transporters and associated machinery, including SERCA2, ryanodine receptor and phospholamban as well as genes associated with mitochondrial energy production including respiratory chain complexes subunits, mitochondrial creatine kinase, carnitine palmitoyltransferase I and uncoupling proteins. Undifferentiated myoblasts showed increased gene expression of pro-survival proteins such as Bcl-2 as well as cell cycle-regulating proteins. The results indicate that the differentiation of H9c2 cells lead to an increase of transcripts and protein levels involved in calcium handling, glycolytic and mitochondrial metabolism, confirming that H9c2 cell differentiation induced by RA towards a more cardiac-like phenotype involves remodeled mitochondrial function. PI3K, PDK1 and p-CREB also appear to be involved on H9c2 differentiation. Furthermore, complex analysis of differently expressed transcripts revealed significant up-regulation of gene expression related to cardiac muscle contraction, dilated cardiomyopathy and other pathways specific for the cardiac tissue. Metabolic and gene expression remodeling impacts cell responses to different stimuli and determine how these cells are used for biochemical assays.

Malonyl-CoA decarboxylase is a major regulator of myocardial fatty acid oxidation

The energy demands of the heart are normally met by oxidation of both glucose and fatty acids. Fatty acid oxidation is limited by the uptake of fatty acyl coenzyme A (CoA) into the mitochondria, a process regulated by carnitine palmitoyltransferase (CPT)1. Malonyl CoA is a potent endogenous inhibitor of CPT1, and therefore plays an integral role in the control of myocardial fatty acid oxidation. Malonyl-CoA decarboxylase (MCD) is responsible for the removal of malonyl CoA and may control myocardial fatty acid oxidation. Indeed, strategies using MCD inhibitors and MCD knockout mice have provided the first evidence for a direct role of MCD in the control of myocardial fatty acid oxidation. Based on these studies, pharmacologic inhibition of MCD has been proposed to be a viable approach for the treatment of ischemic heart disease resulting from a variety of pathologic conditions, including coronary artery diseases, pathologic hypertrophy, and hypertension.

Structure and regulation of acetyl-CoA carboxylase genes of metazoa

Acetyl-CoA carboxylase (ACC) plays a fundamental role in fatty acid metabolism. The reaction product, malonyl-CoA, is both an intermediate in the de novo synthesis of long-chain fatty acids and also a substrate for distinct fatty acyl-CoA elongation enzymes. In metazoans, which have evolved energy storage tissues to fuel locomotion and to survive periods of starvation, energy charge sensing at the level of the individual cell plays a role in fuel selection and metabolic orchestration between tissues. In mammals, and probably other metazoans, ACC forms a component of an energy sensor with malonyl-CoA, acting as a signal to reciprocally control the mitochondrial transport step of long-chain fatty acid oxidation through the inhibition of carnitine palmitoyltransferase I (CPT I). To reflect this pivotal role in cell function, ACC is subject to complex regulation. Higher metazoan evolution is associated with the duplication of an ancestral ACC gene, and with organismal complexity, there is an increasing diversity of transcripts from the ACC paraloges with the potential for the existence of several isozymes. This review focuses on the structure of ACC genes and the putative individual roles of their gene products in fatty acid metabolism, taking an evolutionary viewpoint provided by data in genome databases.

Acetyl-CoA carboxylase and SREBP expression during peripheral nervous system myelination

The expression of acetyl-CoA carboxylase (ACC) in mouse peripheral nervous system (PNS) was investigated. Both ACC 265 and ACC 280 isoforms were expressed in the sciatic nerve, although ACC 265 was predominant. ACC 265 transcripts originating from promoters P1 and P2 could be detected in the developing nerve, as well as the two splice products, which are characterized by the presence or the absence of a 24-base sequence before the codon serine-1200. The mRNA levels for ACC 265 parallel those of other lipogenic genes whose expression is linked to the myelination process. In addition, ACC 265 mRNA and protein levels in the nerves of the trembler mutant, which is a mouse model of PNS dysmyelination, represented around 30% of the normal values. The expression of the sterol regulatory element-binding proteins (SREBPs) was also studied. SREBP 1 mRNAs were expressed at a constant level during nerve development, and their quantities were normal in trembler. On the contrary, SREBP 2 mRNA quantities varied during the myelination period similarly to the lipogenic gene mRNAs, and the levels measured in trembler represented only 10% of the normal values. Taken together, these results suggest that the coordinate expression of several lipogenic genes, which occurs during PNS myelination, could possibly be regulated by SREBP 2.

Preclinical developments in type 2 diabetes

Type 2 diabetes is associated with insulin resistance in peripheral tissues, such as muscle and fat, impaired glucose-stimulated insulin secretion from pancreatic beta-cells and elevated hepatic gluconeogenesis. Current pharmacotherapy does not adequately address the metabolic defects underlying this disease. Thus, novel targets are being explored that enhance insulin action at target tissues, stimulate carbohydrate and fat catabolism, decrease endogenous glucose production and increase pancreatic beta-cell neogenesis and glucose-dependent insulin secretion. This article reviews recent developments in research on several of these targets, namely acetyl-CoA carboxylase 2 (ACC2), I kappa kinase (IKK) beta, dipeptidyl peptidase IV (DPP-IV) and glucagon-like peptide-1 receptor (GLP-1R).

Malonyl CoA control of fatty acid oxidation in the ischemic heart

Abnormally high rates of fatty acid metabolism is an important contributor to the severity of ischemic heart disease. During and following myocardial ischemia a number of alterations in fatty acid oxidation occur that result in an excessive amount of fatty acids being used as a fuel source by the heart. This contributes to a decrease in cardiac efficiency both during and following the ischemic episode. Central to the regulation of fatty acid oxidation in the heart is malonyl CoA, which is a potent endogenous inhibitor of mitochondrial fatty acid uptake. The levels of malonyl CoA are regulated both by its synthesis by acetyl CoA carboxylase (ACC) and its degradation by malonyl CoA decarboxylase (MCD). ACC is in turn controlled by AMP-activated protein kinase (AMPK), which acts as a fuel gauge in the heart. The control of these enzymes are altered during ischemia, such that malonyl CoA levels in the heart decrease, resulting in an increased relative contribution of fatty acids to oxidative metabolism. Activation of AMPK during and following ischemia appears to be centrally involved in this decrease in malonyl CoA. Clinical evidence is now accumulating that show that inhibition of fatty acid oxidation is an effective approach to treating ischemic heart disease. As a result, modulation of fatty acid oxidation by targeting the enzymes controlling malonyl CoA may be a novel approach to treating angina pectoris and acute myocardial infarction. This paper will discuss some of the molecular changes that occur in fatty acid oxidation in the ischemic heart and will include a discussion of the important role of malonyl CoA in this process.