ATO decreases serum lipid levels in ApoE-/-mice and CD36-mediated ox-LDL uptake in macrophages
Excessive cholesterol accumulation in macrophages results in the
transformation of macrophages into foam cells, which eventually causes
atherosclerosis (Akıl et al. , 2014;
Kavurma et al. , 2017). Preventing
excessive cholesterol accumulation in macrophages is one
atheroprotective strategy. Indeed, high CD36 expression can facilitate
foam cell formation (Zhao et al. ,
2016). To investigate whether ATO regulates lipid metabolism by
regulating CD36 expression in macrophages, we first determined the serum
lipid levels of ApoE-/- mice treated with ATO and
those left untreated (Figure 2A-E). After 4 weeks of ATO therapy, serum
total cholesterol (TC), triglyceride (TG), low-density lipoprotein
(LDL), and ox-LDL levels decreased significantly compared with those in
the controls. However, high-density lipoprotein (HDL) levels were
slightly, but not significantly, lower in the ATO group (Figure 2A-E).
These data indicate that the protective effect of ATO against
atherosclerosis in ApoE-/- mice may be attributed to
altered serum lipid metabolism. Compared with those in the untreated
model group, CD36 mRNA and protein levels in the aortic tissue were
significantly decreased by ATO treatment (Figure 2F, I, L). When we
determined the CD36 expression in lesion areas by immunofluorescence
staining, we observed that CD36 expression in macrophages
(CD68+) was substantially reduced by ATO treatment
(Figure 2G, H).
We also evaluated the ATO-mediated
promotion of CD36-mediated ox-LDL internalization in vitro .
Peritoneal macrophages of ApoE-/- mice were treated
with ox-LDL (50 μg mL-1), and either 2.5 or 5.0 μΜ ATO
for 24 h. Oil red O staining showed that both ATO doses significantly
decreased ox-LDL uptake by peritoneal macrophages (Figure 2M, N).
Moreover, both ATO doses significantly reduced CD36 protein and mRNA
levels in RAW264.7 cells (Figure 2J, K, O). Taken together, these data
suggest that ATO protects against foam cell formation by decreasing
CD36-mediated cholesterol uptake in vivo and in vitro ,
which may be the mechanism by which ATO regulates blood lipid
metabolism.