Evidence that acetyl-CoA carboxylase isoforms play different biological roles in H9c2 cardiomyocyte

Progress of potential drugs targeted in lipid metabolism research

Lipids are a class of complex hydrophobic molecules derived from fatty acids that not only form the structural basis of biological membranes but also regulate metabolism and maintain energy balance. The role of lipids in obesity and other metabolic diseases has recently received much attention, making lipid metabolism one of the attractive research areas. Several metabolic diseases are linked to lipid metabolism, including diabetes, obesity, and atherosclerosis. Additionally, lipid metabolism contributes to the rapid growth of cancer cells as abnormal lipid synthesis or uptake enhances the growth of cancer cells. This review introduces the potential drug targets in lipid metabolism and summarizes the important potential drug targets with recent research progress on the corresponding small molecule inhibitor drugs. The significance of this review is to provide a reference for the clinical treatment of metabolic diseases related to lipid metabolism and the treatment of tumors, hoping to deepen the understanding of lipid metabolism and health.

Mechanisms of myocyte cytotoxicity induced by the multiple receptor tyrosine kinase inhibitor sunitinib

The anticancer tyrosine kinase inhibitor sunitinib has been shown recently to be cardiotoxic. Using a neonatal rat myocyte model, we investigated various mechanisms that might be responsible for its cardiotoxicity. Sunitinib potently inhibited the enzyme activity of both AMP-activated protein kinase (AMPK) and the ribosomal S6 kinase RSK1 at therapeutically relevant concentrations. Heart tissue with its high energy needs might be particularly sensitive to inhibition of AMPK because of its role as an energy sensor regulating ATP levels. As measured by lactate dehydrogenase release, sunitinib treatment of myocytes caused dose-dependent damage at therapeutic levels. Sunitinib treatment also caused a dose-dependent reduction in myocyte protein levels of the phosphorylated alpha and beta isoforms of the AMPK phosphorylation target acetyl-Coenzyme A carboxylase. However, myocytes were not protected from sunitinib treatment by pretreating them with the AMPK-activating antidiabetic drug metformin. Sunitinib treatment of myocytes also did not affect cellular ATP levels. Together, these last two results do not suggest a major role for inhibition of AMPK in sunitinib-induced myocyte damage. Dexrazoxane, which is a clinically approved doxorubicin cardioprotective agent, also did not protect myocytes from damage, which suggests that sunitinib did not induce oxidative damage. In conclusion, even though sunitinib potently inhibits AMPK and RSK1, given the extreme lack of kinase selectivity that sunitinib exhibits, it is likely that inhibition of other kinases or combinations of kinases are responsible for the cardiotoxic effects of sunitinib.

AMP-activated protein kinase--the fat controller of the energy railroad

AMP-activated protein kinase plays an important role in the regulation of lipid metabolism in response to metabolic stress and energy demand. It is also under endocrine control. AMPK acts at multiple steps and has a central role controlling fatty acid, triglyceride, and cholesterol synthesis, as well as the oxidation of fatty acids through direct phosphorylation effects and the control of gene transcription. As such, it can be considered to be the fat controller of the energy railroad. It is thought that AMPK may be a major mediator of the health benefits of exercise in mitigating the development of obesity and age-onset diseases.

AMP-activated protein kinase (AMPK) control of fatty acid and glucose metabolism in the ischemic heart

Myocardial ischemia is the leading cause of all cardiovascular deaths in North America. Myocardial ischemia is accompanied by profound changes in metabolism including alterations in glucose and fatty acid metabolism, increased uncoupling of glucose oxidation from glycolysis and accumulation of protons within the myocardium. These changes can contribute to a poor functional recovery of the heart. One key player in the ischemia-induced alteration in fatty acid and glucose metabolism is 5'AMP-activated protein kinase (AMPK). Accumulating evidence suggest that activation of AMPK during myocardial ischemia both increases glucose uptake and glycolysis while also increasing fatty acid oxidation during reperfusion. Gain-of-function mutations of AMPK in cardiac muscle may also be causally related to the development of hypertrophic cardiomyopathies. Therefore, a better understanding of role of AMPK in cardiac metabolism is necessary to appropriately modulate its activity as a potential therapeutic target in treating ischemia reperfusion injuries. This review attempts to update some of the recent findings that delineate various pathways through which AMPK regulates glucose and fatty acid metabolism in the ischemic myocardium.

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).

The regulation of acetyl-CoA carboxylase--a potential target for the action of hypolipidemic agents

ACC exists as two major isoforms ACC1 or ACC alpha, and ACC2 or ACC beta, and there is evidence that they play separate roles in the production of malonyl-CoA for fatty acid synthesis and the control of mitochondrial beta-oxidation, respectively. ACC alpha can be regulated at the level of gene expression, allosteric regulation of the enzyme, and reversible phosphorylation by AMP-PK. Emerging lines of research suggest that similar mechanisms of regulation exist for ACC beta. Its inactivation in heart and skeletal muscle through phosphorylation by AMP-PK is becoming well-established. ACC is an important target of certain hypolipidemic drugs such as the fibrates. This is not simply because ACC alpha inhibition decreases the synthesis of a lipid component of VLDL because fatty acids synthesized de novo in liver are not always major contributors to VLDL lipid (158); it is also because ACC beta inhibition leads to a decrease in malonyl-CoA levels and the disinhibition of fatty acid oxidation. Partitioning fatty acids towards oxidation and away from esterification is an important aspect of the lipid-lowering effects of fibrates. Fibrates could use any of the mechanisms of ACC regulation to decrease activity. They could repress ACC gene expression through the activation of PPAR alpha, and fibroyl-CoA esters could inhibit ACC allosterically just as TOFyl-CoA does. However, we have demonstrated a rapid inactivation of ACC in cultured rat hepatocytes by gemfibrozil that is mediated by activation of AMP-PK and the subsequent phosphorylation of ACC. The end result is the inhibition of hepatic fatty acid synthesis and a possible activation of beta-oxidation as evidenced by the increased production of ketone bodies. The mechanism through which fibrates activate the AMP-PK cascade, the role of PPAR alpha, the physiological responses of biosynthesis and oxidation and the use of these mechanisms by other hypolipidemic agents are areas of ongoing investigation.

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

Acetyl-CoA carboxylase beta is expressed primarily in heart and skeletal muscle, where it may play a role in the control of mitochondrial fatty acid uptake and oxidation by controlling carnitine-palmitoyl-CoA transferase 1. To investigate the relationship between ACC-beta expression and myoblast differentiation, we specifically blocked ACC-beta production by expressing an antisense gene to the specific N-terminal region of ACC-beta in H9c2 cells. The expression of the antisense ACC-beta mRNA retarded cell fusion, myosin formation, and creatine kinase induction; all of these parameters are hallmarks of muscle cell differentiation. On the other hand, the rate of fatty acid oxidation was not affected by the presence or absence of ACC-beta in the cells.