Διερεύνηση του ρόλου του πυρηνικού υποδοχέα PPARβ στην καρδιά φυσιολογικών και διαβητικών επίμυων
Authors: Γαλάτου Ελευθερία 
Published: September 2021

Cardiovascular diseases are one of the major causes of morbidity and mortality in the modern world. They are characterized by molecular, cellular and pathophysiological changes in the myocardium, a condition known as cardiac remodeling. While short-term cardiac remodeling is an adaptive response that contributes to the maintenance of cardiac function the long term remodeling leads to contractile dysfunction and eventually heart failure while it is also associated with sudden death from arrhythmias. The energy metabolism of the heart and the utilization of various substrates are modified in various pathological conditions, including cardiac hypertrophy, which is associated with an increase in the catabolism of glucose and reduction of the oxidation of fatty acids, while diabetes mellitus is characterized by increased by enhanced fatty acid metabolism and reduced glucose and lactate metabolism. Given that peroxisome proliferator activated receptors (PPARs) are key transcriptional regulators of energy metabolism and lipid homeostasis, the aim of this thesis was to investigate the role of PPARα/δ activation in cardiac hypertrophy, diabetes mellitus and ischaemia.Primary cultures of cardiomyocytes were exposed to the specific PPARα/δ agonist, GW0742, and then they were treated with a1 adrenergic agonist, phenylephrine (PE). GW0742 inhibited PE- induced increase in cell area and expression of ANP and BNP. The inhibitory effect of GW0742 on cell growth and gene expression was abolished in the presence of GSK0660, a PPARα/δ antagonist. Furthermore, gene expression levels of PPARα/δ and the target genes of the receptor involved in the oxidation of fatty acids (mCPT-1, UCP3) and glucose metabolism (PDK4, GLUT4) were determined. PE- induced down- regulation of PPARα/δ and target genes, was reversed in the presence of GW0742. These results show that activation of PPARα/δ probably compensates for the metabolic dysfunction that characterizes cardiac hypertrophy, by adjusting fatty acids oxidation and glucose metabolism.The molecular mechanisms that contribute to the development of cardiac hypertrophy include, among others, kinase signaling pathways, (MAPK, PI3K/Akt), and reactive oxygen species (ROS). GW0742 inhibited PE -induced ROS production modulating signaling and redox mechanisms that are involved in cardiac hypertrophy. The non genomic role of GW0742 was confirmed by using the antagonist GSK0660. Furthermore, a second aim was to evaluate whether the administration of GW0742, improves cardiac dysfunction in diabetes and to explore the underlying molecular mechanisms of cardioprotection. For this purpose we used the experimental model of streptozotocin (65mg/kg) induced diabetes in rats with total duration of six weeks. GW0742 was found to reduce glucose, cholesterol and triglyceride levels in blood plasma, improve impairment of cardiac contractility, decrease the diabetes-induced fibrosis and inhibits hypertrophy. Additionally, in order to assess the changes in myocardial metabolism both in streptozotocin-induced diabetes and after administration of GW0742, we determined gene expression of PPARα/δ and of the target genes involved in glucose metabolism (GLUT4) and fatty acids (MCAD and mCPT-1). The results showed that PPARα/δ, MCAD and mCPT-1 expression increased in the diabetic myocardium and remained elevated in the presence of GW0742 but at lower levels. Furthermore, GW0742 administration in diabetic animals restored the decreased expression levels of GLUT4 in the control group. These results suggest that glucose metabolism could be compensated in these animals. In parallel, we investigated whether autophagy mechanisms are involved in this experimental model of diabetes mellitus and assessed the effect of GW0742 on them. For this purpose, expression levels of autophagy marker proteins LC3II, p62 and Beclin-1 were determined. We showed that autophagy levels were reduced by diabetes, but were restored to basal levels in the presence of GW0742. Finally, it was determined the infarct size and the effect of GW0742 on ischemia-induced ventricular arrhythmias and on physiological pressure parameters (LVDP) in normal and diabetic animals. The results indicate that GW0742 and WY14643 reduce infarct size and arrhythmias in both normal and diabetic model, via activation of transcription factors PPARα/δ and PPARα, respectively. Furthermore, expression of PPARα/δ and target gene GLUT4 was determined. GLUT4 expression levels are reduced after ischemia/ reperfusion (I/R) in both normal and diabetic myocardium, which is reversed in the presence of GW0742. In contrast, administration of WY14643 in normal animals restores expression of GLUT4 after I/ R. These results suggest that PPARα ηαζ PPARα/δ regulate the expression of GLUT4 differently, although the latter is a target gene of both.