Lysophosphatidylcholine Alters Valvular Interstitial Cell Mineralization

AbstractCalcific aortic valve disease (CAVD) is a condition of the heart characterized by thickening and calcification of the aortic valve and can lead to aortic stenosis, narrowing of the aortic valve that can obstruct left ventricular outflow. CAVD is thought to have similarities with atherosclerosis, in which the aortic wall demonstrates thickening due to plaque buildup. A notable similarity seen between CAVD and atherosclerosis is the accumulation of lipids in the tissues. One important chemical component involved in atherosclerosis is lysophosphatidylcholine (LPC), a phospholipid derived from phosphatidylcholine. LPC concentrations have been shown to increase in atherosclerotic conditions, and induce expression of osteogenic factors by vascular smooth muscle cells. The potential for LPC to affect valve cell calcification, however, has not been previously investigated. In addition, calcification of cells from different valves warrants investigation because the aortic valve becomes more bone-like and experiences onset of calcification sooner than the mitral valve during the calcification process. This study investigated the effect of LPC on the propensity for calcification by porcine valve interstitial cells (VICs) from aortic and mitral valves. On day 0 VICs were seeded at a density of 50 000 cells/cm2 in low serum media. On day 1, the media is changed to media containing LPC in concentrations ranging from 0 to 100 µM. The cells are cultured for 8 days and then assessed for mineralization using histological stains (Alizarin Red S for calcium deposition and Von Kossa for phosphate deposition) and biochemical assays (Alkaline phosphatase activity). Significance (p <0.05) was determined using Analysis of Variance followed by Tukey post-hoc testing. Interestingly, mineralization in the VIC cultures was decreased as LPC concentration increased from 0 to 1 µM. At 10 µM, however, an increase in mineralization was observed compared to the 1 µM cultures. VICs in 100 µM LPC media began to detach within 24 hours of LPC media application. Also, VICs from different valves displayed different levels of calcification at each condition. LPC alters mineralization in VIC cultures from both aortic and mitral valves, in a concentration dependent manner. Extremely high concentrations of LPC (at and above 100 µM) can be toxic to VICs. There is a unique behavior of VICs with addition of varying concentrations of LPC, most notably that low concentrations (below 10 µM) actually reduced mineralization. Other factors, such as effects of LPC on VIC proliferation and apoptosis, will be important to investigate in future work. This study demonstrates that LPC affects the mineralization potential of valvular cells in a way that is distinct from vascular cell types.