Abstract 11625: Natural Killer T Cells are Involved in Aortic Valvular Calcification via Inhibiting Osteoclastic Differentiation in Uremic Apolipoprotein-E Deficient Mice
Objective: Tissue calcification is actively regulated by the balance of osteoblastic and osteoclastic differentiation. Osteoclasts arise from mononuclear precursors in the presence of receptor activator of nuclear factor κB ligand (RANKL) secreted from activated T lymphocytes. Natural killer T (NKT) cells, a unique subset of T lymphocytes, are known to be involved in atherogenesis. However, it remains unclear whether NKT cells are also involved in the osteoclastic differentiation and the development of valvular calcification.
Methods and Results: Female apolipoprotein-E deficient mice were subtotally nephrectomized and fed with a high-fat diet for 8 weeks and were divided into 2 groups according to the intraperitoneal injection of α-galactosylceramide (αGC, 0.1 μ g/g body weight; n=15), which specifically activates NKT cells, or phosphate-buffered saline (PBS; n=16). αGC significantly increased the calcified area in the aortic valve (3.5±0.2 vs. 2.5±0.2%, p<0.05). It significantly enhanced the expression of IFN-γ and IL-4 gene, both of which are known to inhibit osteoclastic differentiation, and inhibited the expression of calcitonin receptor gene, a marker of osteoclast, within the aorta, whereas it did not affect genes involved in osteoblastic differentiation such as BMP2 and Runx2. To further determine whether NKT cell activation by αGC can directly affect the osteoclastic differentiation, mouse splenocytes, including mononuclear precursors and NKT cells, were cultured with RANKL (100 ng/ml) and macrophage colony stimulating factor (M-CSF, 100 ng/ml) for 6 days with or without αGC (0, 0.1, 1, and 10 ng/mL) and estimated osteoclastic differentiation by tartrate-resistant acid phosphatase staining. αGC significantly increased IFN-γ and IL-4 levels in the culture media and inhibited the osteoclastic differentiation in a dose-dependent manner. The combined administration of anti-IFN-γ and anti-IL-4 neutralizing antibodies (10μ g/ml each) canceled the inhibitory effect of αGC on osteoclastic differentiation.
Conclusions: NKT cells are involved in aortic valvular calcification via inhibiting osteoclastic differentiation. The regulation of NKT cell activity may be a novel therapeutic strategy against aortic valvular stenosis.
- © 2011 by American Heart Association, Inc.