Abstract 1471: Vascular-protective Effects of High Density Lipoprotein Include the Down-regulation of the AT1 Receptor
Introduction: Angiotensin II exerts via stimulation of the AT1 receptor (AT1R) inflammatory and apoptotic stimuli which are involved in the induction of endothelial dysfunction. Given the known endothelial-protective effects of high density lipoprotein (HDL), we hypothesized that increases of HDL via gene transfer (GT) with human apolipoprotein (apo) A-I would reduce AT1 receptor associated vascular damage in an animal model of experimental diabetes mellitus.
Methods: Intravenous GT was performed 5 days after streptozotocin (STZ) injection with 3 x 1012 total particles/kg of the adenoviral vector Ad.hapoA-I or of Ad.Null, containing no expression cassette. Age-matched non-diabetic SD rats injected with the same dose of Ad.Null were used as controls. Six weeks after GT, thoracic aortic rings were isolated. Endothelial function was analyzed in an organ chamber bath by using endothelial-dependent vasodilator acetylcholine (Ach). Aortic mRNA expression of AT1R, extracellular (ec)-superoxide dismutase (SOD), Bcl-2 and Bax was determined by real-time PCR. Aortic phosphorylated (p) and total (tot.) Erk1/2 and eNOS protein levels were analyzed by Western Blot.
Results: Ad.hapo A-I induced sustained human apo A-I expression and increased HDL cholesterol (C) for the entire duration of the experiment, 6w, without affecting increased blood glucose and LDL-C levels. Human apo A-I peak expression was associated with a 1.7-fold (p<0.05) increase of HDL-C levels in STZ rats. In the Ad.hapo A-I STZ group, Ach-dependent vasodilatation was significantly improved in a dose-dependent manner compared to the Ad.Null STZ group: maximum relaxation for Ad.hapo A-I STZ was 57± 2% versus 42± 3% for Ad.Null STZ (p<0.05). This was associated with a 8.0-fold decrease in AT1R, a 1.6-fold increase in ec-SOD and a 2.0-fold increase in Bcl-2/Bax ratio vs. STZ Ad.Null (p<0.05). Ratio of p to tot. Erk 1/2 was 1.8-fold decreased, whereas p to tot. eNOS ratio was 1.7-fold higher vs. STZ Ad.Null rats (p<0.05).
Conclusion: Induced HDL-C by human apo A-I GT improves endothelial dysfunction via down-regulation of AT1R expression and downstream signalling despite hyperglycemia and unaltered LDL-C levels.