Effects of Serum Amyloid A and Lysophosphatidylcholine on Human Coronary Artery Smooth Muscle Cells : Roles of Transient Receptor Potential Channels

Abstract

Background: Serum amyloid A (SAA) and lysophosphatidylcholine (LPC) contribute to physiological processes of atherosclerosis and cardiovascular disease. However, the effects of SAA/LPC on human coronary artery smooth muscle cells (hCASMCs) have not been investigated. Therefore, I examined the effects of SAA/LPC on Ca2+/Mg2+ mobilization and its underlying mechanisms in hCASMCs. Methods: Intracellular Ca2+/Mg2+ concentration ([Ca2+]i/[Mg2+]i) was measured with fura-2 AM/mag-fura-2 AM. The conventional/real-time quantitative RT-PCR, Western blot and immunocytochemistry were applied. Small interfering RNA (siRNA) for TRPC4 was used to knock down TRPC4. Result: SAA/LPC increased [Ca2+]i by Ca2+ entry. The SAA-induced Ca2+ entry was inhibited by Gd3+, SKF96365 and 2-aminoethoxydiphenyl borate (2-APB), but not nifedipine. The LPC-induced Ca2+ entry was blocked by Gd3+, but not nifedipine, SKF96365 and 2-APB. U73122 and PTX prevented the activation of SAA-, but not LPC-induced Ca2+ influx. LPC, but not SAA, increased [Mg2+]i. The RT-PCR, Western blot and immunocytochemistry of TRP channels revealed the expression of TRPC1/4, TRPV1/2/4 and TRPM7. In siRNA treated cells, the level of TRPC4 mRNA was reduced, and Ca2+ response for SAA was attenuated, compared with control cells. Conclusion: These results suggest that SAA/LPC activate Ca2+ influx in hCASMCs; SAA activates it via PTX-sensitive G-protein, PLC and TRPC pathways, where TRPC4 may be involved. On the other hand, LPC may activate it independently of these pathways. TRP protein may be a target molecule of Ca2+ signaling in hCASMCs elicited by SAA/LPC, which may play roles in coronary muscle remodeling under the pathophysiological conditions such as atherosclerosis.