Glucagon-Like Peptide-1 in the Regulation of PPARs and Calcium Handling in Hyperglycemia or Hypertensive HL-1 Cells

Background: Cardiovascular disease is the leading cause of diabetes-related morbidity and mortality. A high incidence of cardiomyopathy found in diabetes was described as a complex of impaired mechanical function and electrical abnormalities with increased tendencies for some cardiac arrhythmia. Hypertension may directly impair heart functions and induce Ca2+ dysregulation with arrhythmogenesis. The glucagon like peptide-1 (GLP-1) is an incretin rapidly released after meal intake that stimulates insulin output in a glucose-dependent manner from pancreatic β-cells. GLP-1 inhibits glucagon secretion and can effectively lower blood glucose level. The cardiovascular actions of GLP-1 receptor agonists include cardiovascular protection in preclinical studies and reductions in blood pressure, postprandial lipids, markers of inflammation, and oxidative stress in clinical studies. Peroxisome proliferator-activated receptors (PPARs)-, -, and - are nuclear transcription factors expressed in the heart that modulate myocardial lipid, glucose and energy homeostasis. Calcium (Ca2+) regulations play an important role in cardiac electrical activity, and hypertrophy. Our previous studies have shown that PPARs agonist significantly regulate cardiac inflammation and oxidative stress with calcium modulation. In addition, dipeptidylpeptidase-4 inhibitors can reduce blood glucose with several cardiac benefits. However, it is not clear whether GLP-1 can directly regulate cardiac PPARs and calcium modulations. Therefore. the purpose of this study will investigate whether GLP-1 can directly modulate myocardial expressions of PPAR isoforms under different conditions in cardiomyocytes, evaluate the effect of GLP-1 on the regulation of inflammation, oxidative stress, receptor advanced glycated end-products (RAGE) under hyperglycemic or hypertensive conditions, and explore the significant effect of GLP-1 in the regulation of Ca2+ under different conditions. Methods: Western blot will be used to proteins expressions of PPAR isoforms, tumor necrosis factor-, interleukin-6, NF-B p65, calcium regulation proteins (ryanodine receptor, sarcoplasmic reticulum Ca2+-ATPase, Na+-Ca2+exchanger, voltage-dependent Ca2+ CaV1.2, calmoduline kinase, phospholamban, phosphorylated phospholamban), angiotensin II receptors type 1 (ATR1), RAGE in HL-1 cells with or without hyperglycemia (20 mM) or angiotension II (1 M) with or without GLP-1 (1. 10 100 mM). Fluorimetric ratio technique will be used to detect the intracellular calcium in HL-1 myocytes. Nicotinamide adenine dinucleotide phosphate oxidase activity will be quantified through photometric measurements. Real time PCR will be used to measure the RNA expressions of PPARs. Expected Results: GLP-1 can reduce RAGE and increase sarcoplasmic reticulum Ca2+-ATPase, which may attenuate the adverse effects of hyperglycemia or angiotensin II.