Placental Growth Factor Expression is Inhibited by Hyperglycemia in Cardiac Cells

Cardiovascular disease (CVD) is the leading cause of death worldwide. Each year, 1 in every 6 US deaths is due to CVD, and around 84 million people are currently affected. Coronary artery disease (CAD), characterized by narrowing of coronary arteries due to plaque deposition, is the most common type of CVD. In CAD, localized narrowing reduces downstream blood and nutrient supply, resulting in ischemic tissue damage. Diabetics are predisposed to CAD development, as diabetes‐associated metabolic changes are major risk factors for CAD. When faced with vascular occlusion, the body attempts to preserve blood flow to regions downstream of the occluded vessel through a compensatory mechanism known as arteriogenesis. During this process, pre‐existing collateral arteries remodel and radially enlarge to meet the increased blood flow demand. Surgical interventions for reopening or replacing occluded blood vessels are not feasible for many people with CAD, due to age and physical condition. Stimulation of collateral artery growth would therefore be a desirable therapy. Placental growth factor (PLGF) is a secreted growth factor that enhances arteriogenesis through monocyte recruitment. The goal of this study was to investigate how PLGF expression in human cardiac cells is modulated by different metabolic features of diabetes‐associated metabolic dysfunction (such as hypercholesterolemia, hyperglycemia, or oxidative stress). Since the heart wall is comprised of cardiomyocytes, and the inner lining of the cardiac chambers and of blood vessels is made up of endothelial cells (EC), we focused on these two major cell types of the heart. Initially, human coronary artery EC (HCAEC) were exposed to each of the following for 24 h: low density lipoprotein (LDL, 0.05–0.2 μg/mL) or oxidized LDL to mimic hypercholesterolemia; glucose (5–20 mM) to mimic hyperglycemia; advanced glycation end products (AGE, either glucose or glyceraldehyde derived; 0.3–1 μg/mL), a byproduct formed during long term hyperglycemia; or hydrogen peroxide (H 2 O 2 , 0.05–0.3 mM) to mimic oxidative stress. Post‐treatment, media samples were collected at 4, 8, and 24 h for quantification of PLGF protein (ELISA). Data analysis of PLGF expression (normalized to total protein as determined by BCA assay) was conducted using ANOVA and the Student‐Newman‐Keuls post ho c method. In HCAEC, both glucose and AGE reduced PLGF expression by ~24–49% ( P <0.05), while 0.3 mM H 2 O 2 reduced PLGF by ~58% ( P <0.05). The most effective concentrations of the metabolic molecules tested were then used to treat cardiomyocytes (CM). In CM, 1 μg/mL AGE reduced PLGF expression by ~43–50% ( P <0.05); interestingly, 0.3 mM H 2 O 2 increased PLGF expression by ~66–133% ( P <0.05). Comparative analysis indicated that PLGF production by untreated HCAEC is ~10–15 times greater than in CM. These results suggest that long‐term hyperglycemia resulting in AGE formation is a major influence on PLGF expression in the heart, and identify HCAEC as the major source of PLGF in the heart. These findings provide insight into how diabetes‐associated metabolic dysfunction can modulate PLGF expression in cardiac cells and suggest a novel mechanism for the impairment of coronary arteriogenesis which is known to occur in diabetes. Support or Funding Information NIH R01 HL‐084494 (PL)