Oxygenized low density lipoprotein down-regulates the TRPV4 protein expression of macrophage through activation of...

TRPV4, a non-selective cation channel, is involved in lipometabolism and atherosclerosis. However, whether TRPV4 participates in oxygenized low density lipoprotein (oxLDL)-induced foam cell formation remains unknown. The present study investigates the effect of oxLDL on the expression of TRPV4 in macrophages and its underlying mechanisms.

The expression of TRPV4 in RAW264.7 and phorbol-12-myristate-13-acetate (PMA) induced U937, THP-1 cells was detected by immunofluorescence, and western blot was used to detect the TRPV4 expression before and after PMA induction. Each cell line was divided into three groups, including control group, native low-density lipoprotein (nLDL) (100 μg/mL) group and oxLDL (100μg/mL) group; the expression of TRPV4 in each group was measured using immunohistochemistry and western blot. TRPV4 protein expression was detected by western blot after RAW 264.7 cells were treated with 0, 0.01 μM, 0.1 μM and 1 μM T0070907 or preincubated with 0.1 μM T0070709 for 1 h before incubation with oxLDL for 24 h.

In all macrophage cell lines, TRPV4 was widely expressed. PMA increased TRPV4 expression in U937 and THP-1 cells. There was no significant difference in TRPV4 expression in the nLDL group compared to that in the control group; however a significant reduction in TRPV4 expression was detected in the oxLDL group compared to that in the control and nLDL groups using measurements obtained from both immunohistochemistry and western blot. The PPARγ inhibitor T0070907 enhanced the basal expression of TRPV4 and protected RAW264.7 cells from oxLDL-induced TRPV4 down-regulation.

This study revealed that TRPV4 was widely expressed in macrophages and that oxLDL could induce the down-regulation of TRPV4 expression through its actions on PPARγ. This study may serve as an important first step for further investigation into the roles of TRPV4 in macrophage-derived foam cell formation in atherosclerosis.