Abstract 17330: The Intermediate-conductance Ca2+ -activated K+ Channel KCa3.1 Regulates Monocyte Adhesiveness to VCAM-1 and Macrophage Cholesterol Efflux
Introduction: The intermediate-conductance Ca2+ -activated K+ channel KCa3.1 is upregulated in many types of activated, non-excitable cells, and regulates Ca2+-dependent signaling via maintaining Ca2+ influx. We have previously discovered that KCa3.1 is expressed in plaque macrophages (MØ), and the blockade or deficiency results in smaller lesions by reducing the infiltration of plaques by cholesterol-rich MØ in apoE -/- mice. Since Ca2+ influx plays a crucial role in monocyte recruitment processes and monocyte-derived MØ cholesterol metabolism, we investigated the role of KCa3.1 in monocyte adhesiveness and MØ cholesterol efflux; key events in the development of atherosclerosis.
Methods and Results: KCa3.1 mRNA expression was increased in circulating CD14+ monocytes harvested from whole blood samples of apoE knockout mice compared to those from wildtype mice (WT). Consistently, the adhesion to E-selectin or VCAM-1-coated surface also increased KCa3.1 expression in human U937 monocytes, which was confirmed by patch-clamp recording of the strong K+ current sensitive to 10 μ M TRAM-34, a specific blocker of KCa3.1. Adhesion assay showed that KCa3.1 blockade significantly reduced the number of U937 cells adherent to VCAM-1 (59±6% vs. 109±11% TRAM-7, an inactive analog of TRAM-34; p<0.05, n=13) but not to collagen (type I), fibronectin, ICAM-1, PECAM-1, and E- and P-selectins (p=ns). The mRNA expression of CD29 and CD49d, integrins forming VLA-4 (the ligand for VCAM-1), remained unchanged after 2h or 6h of treatment with TRAM-34. Moreover, compared to MØ from WT mice, peritoneal MØ from KCa3.1 knockout mice (KO) showed a marked increase in cholesterol efflux to HDL (KO 46±3% vs WT 36±3%, p<0.05, n=8) and ApoAI (KO 27±4% vs. WT 18±1%, p=0.05).
Conclusions: Activation of monocytes upregulates KCa3.1 which regulates VLA-4-mediated adhesion of monocytes and MØ cholesterol efflux, implying its regulatory roles in VLA-4-mediated outside-in signaling of monocyte adhesion to VCAM-1 and in the membranous expression and/or activity of the ATP-binding cassette transporters ABCA1 and ABCG1 in MØ. Therefore, KCa3.1 could be a promising new therapeutic target for the prevention of atherosclerosis.
- © 2012 by American Heart Association, Inc.