Current Molecular Pharmacology - Volume 4, Issue 3, 2011

The main goal of this review is to provide more specific and effective targets for prevention and treatment of insulin resistance and associated atherosclerosis. Modern technologies and medicine have vastly improved human health and prolonged the average life span of humans primarily by eliminating various premature deaths and infectious diseases. The modern technologies have also provided us abundant food and convenient transportation tools such as cars. As a result, more people are becoming overfed and sedentary. People are generally ingesting more calories than their bodies' need, leading to the so-called “positive energy imbalance”, which is inseparable from the development of insulin resistance and its associated atherosclerosis. A direct consequence of insulin resistance is hyperinsulinemia. The current general view is that insulin is not functional properly in the presence of insulin resistance. Thus, the role of insulin itself in the development of insulin resistance and associated atherosclerosis has not been recognized. We have recently observed that the basal level of insulin signaling is increased in the presence of insulin resistance and hyperinsulinemia. In this review, we will explain how the increased basal insulin signaling contributes to the development of insulin resistance and associated atherosclerosis. We will first explain how insulin causes insulin resistance through two arbitrary stages (before and after the presence of obvious insulin resistance), and, then, explain how the excess exposure to insulin and the relative insulin insufficiency contributes to the atherosclerotic diseases. We propose that blockade of the excess insulin signaling is a viable approach to prevent and/or reverse insulin resistance and its associated atherosclerosis.

Tumor cells display progressive changes in metabolism that correlate with malignancy, including development of a lipogenic phenotype. Highly proliferating cancer cells need to synthesise fatty acids de novo to continually provide glycerophospholipids particularly for membrane production. The synthesised fatty acids are also used for energy production through β-oxidation and lipid modification of proteins. In addition, deregulated lipogenesis plays an important role in tumor cell survival and affects fundamental cellular processes, including signal transduction and gene expression. These observations suggest that enzymes involved in the pathways of lipid synthesis would be rational therapeutic targets in cancer. Over the past few decades, many substantial discoveries regarding enzymes and proteins acting in lipid synthesis have led to the current understanding of the complex signalling network implicated in the metabolic transduction pathways. This review presents an overview of mammalian glycerophospholipid synthesis, signal transduction and cellular distribution of the biochemical activities that produce distinct membrane lipid molecular species.

Endothelin (ET) is one of the most investigated molecules in vascular biology. Since its discovery two decades ago, several ET isoforms, receptors, signaling pathways, agonists and antagonists have been identified. ET functions as a potent endothelium-derived vasoconstrictor, but could also play a role in vascular relaxation. In endothelial cells, preproET and big ET are cleaved by ET converting enzymes into ET-1, -2, -3 and -4. These ET isoforms bind with different affinities to ETA and ETB receptors in vascular smooth muscle (VSM), and in turn increase [Ca2+]i, protein kinase C and mitogen-activated protein kinase and other signaling pathways of VSM contraction and cell proliferation. ET also binds to endothelial ETB receptors and stimulates the release of nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor. ET, via endothelial ETB receptor, could also promote ET re-uptake and clearance. While the effects of ET on vascular reactivity and growth have been thoroughly examined, its role in the regulation of blood pressure and the pathogenesis of hypertension is not clearly established. Elevated plasma and vascular tissue levels of ET have been identified in saltsensitive hypertension and in moderate to severe hypertension, and ET receptor antagonists have been shown to reduce blood pressure to variable extents in these forms of hypertension. The development of new pharmacological and genetic tools could lead to more effective and specific modulators of the vascular ET system for treatment of hypertension and related cardiovascular disease.

The preservation of a functional pancreatic β-cell mass has become a major point of research in type 2 diabetes (T2D) and the future therapies of T2D notably aim at protecting the β-cell from dysfunction and apoptotic death. β-cell proliferation, survival and insulin secretion are regulated by crucial transcription factors which are activated by signalling pathways engaged by nutrients, G-protein coupled receptors or tyrosine kinase receptors. Among these factors, the cAMPresponsive element-binding protein (CREB) has emerged as a key transcriptional element for the maintenance of an efficient glucose sensing, insulin exocytosis, insulin gene transcription and β-cell survival. CREB activates the transcription of target genes within the β-cells in response to a diverse array of stimuli including glucose, incretin hormones such as the glucagon-like peptide-1 (GLP-1) or the gastric inhibitory polypeptide (GIP), the pituitary adenylate cyclase-activating polypeptide (PACAP), or growth factors such as the insulin like growth factor-1 (IGF-1). All these stimuli phosphorylate CREB at a particular residue, serine 133, which is required for CREB-mediated transcription. However, the molecular mechanisms by which CREB activates gene transcription in β-cells vary according to the nature of the stimulus. These mechanisms involve different protein kinases, scaffold proteins and cofactors which allow CREB to specifically regulate the expression of crucial genes such as insulin, BCL-2, cyclin D1, cyclin A2 or IRS-2. In this review, we summarize the signalling pathways that lead to CREB phosphorylation in β-cells and the molecular features of each signalling pathway that rise specificity at the level of CREB activation and regulation.

Age-related macular degeneration (AMD) is a progressive retinal degenerative disease and a common cause of blindness. In AMD, there are two phenotypes; “atrophic (dry)” and “neovascular (wet)”. The former is characterized by the geographic atrophy due to death of retinal pigment epithelium, and the latter is developed due to choroidal neovascularization. While wet AMD can be treated by the inhibition of vascular endothelial growth factor or photodynamic therapy, so far there are no available treatments for dry AMD. Fortunately, understanding of pathogenesis in dry AMD has significantly been progressed and many candidates for the treatment of dry AMD have been introduced in clinical trials as well as preclinical stages. In this article, the progress of therapeutic approaches for dry AMD is reviewed.