FAR-INFRARED IRRADIATION INHIBITS CELL PROLIFERATION IN BASAL AND PDGF-STIMULATED RAT VASCULAR SMOOTH MUSCLE CELLS THROUGH REGULATION AMPK/MTOR/P70S6K SIGNALING AXIS

Abstract

Objective: Far-infrared (FIR) rays are invisible electromagnetic radiation with a wavelength of 3-1000 um, which elicits molecular vibrations in water and other organic molecules in cells and tissues, thereby FIR rays may have various biological effects. Aberrant proliferation of vascular smooth muscle cells (VSMCs) is associated with the development of diverse vascular diseases including atherosclerosis. Although FIR irradiation is reported to inhibit cell proliferation in various types of cells, effect of FIR irradiation on VSMC proliferation and the underlying mechanism remain elusive. Here, we investigated the molecular mechanism by which FIR irradiation inhibited VSMC proliferation. Design and method: We performed cell proliferation and viability assay, inhibitor studies, transfection of dominant negative (dn)-AMP-activated protein kinase (AMPK) alpha 1 gene, and western blot analyses. We also conducted confocal microscopic image analyses and ex vivo studies using isolated rat aortas. Results: FIR irradiation for 30 min decreased VSMC proliferation with no alteration in cell viability, which was accompanied by decreased phosphorylation of mammalian target of rapamycin (mTOR) at Ser2448 (p-mTOR-Ser2448) and p70 S6 kinase (p70S6K) at Thr389 (p-p70S6K-Thr389). Furthermore, FIR irradiation increased phosphorylation of AMP-activated protein kinase (AMPK) at Thr172 (p-AMPK-Thr172). Pre-treatment with compound C, a specific AMPK inhibitor, or ectopic expression of dn-AMPK alpha 1 gene, significantly reversed FIR irradiation-decreased VSMC proliferation, p-mTOR-Ser2448, and p-p70S6K-Thr389. However, hyperthermal stimulus (39 degrees) did not change VSMC proliferation and AMPK/mTOR/p70S6K phosphorylation. Similar to in vitro results, FIR irradiation increased p-AMPK-Thr172, and decreased p-mTOR-Ser2448 and p-p70S6K-Thr389 in isolated rat aortas. Finally, FIR irradiation attenuated platelet-derived growth factor (PDGF)-stimulated VSMC proliferation by increasing p-AMPK-Thr172, and decreasing p-mTOR-Ser2448 and p-p70S6K-Thr389 in PDGF-induced in vitro atherosclerosis model. Conclusions: We demonstrate that FIR irradiation decreases VSMC proliferation, at least in part, by regulating AMPK/mTOR/p70S6K signaling axis. These observations suggest that FIR ray therapy can be used to treat arterial narrowing diseases including atherosclerosis and in-stent restenosis.