Dysfunction of cholesterol sensor SCAP under high phosphate condition promotes cholesterol accumulation in macrophage
10.16781/j.0258-879x.2017.12.1514
- Author:
Qiao LIU
1
Author Information
1. Department of Cardiology, The First Affiliated Hospital of Chongqing Medical University
- Publication Type:Journal Article
- Keywords:
Atherosclerosis;
Cholesterosis;
Hyperphosphatemia;
Macrophage
- From:
Academic Journal of Second Military Medical University
2017;38(12):1514-1520
- CountryChina
- Language:Chinese
-
Abstract:
Objective To explore the effects of high phosphate (Pi) condition on the cholesterol accumulation in macrophage and its underlying mechanisms. Methods The human monocytic cell line THP-1 derived macrophages were divided into control group (concentration of Pi being 1.0 mmol/L), high Pi exposure group (concentration of Pi being 3.0 mmol/L), phosphonoformic acid (PFA) treatment group (concentration of Pi and PFA being 1.0 mmol/L) and high phosphate plus PFA treatment group (concentration of Pi and PFA being 3.0 mmol/L and 1.0 mmol/L, respectively). Intracellular neutral lipids were observed by Oil Red O staining. Cholesterol contents were quantified by enzyme catalyzed colorimetry. qPCR was used to dectect the relative mRNA expressions of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase(HMGCoAR), low density lipoprotein receptor (LDLR) and sterol regulatory element binding protein (SREBP) cleavage activating protein (SCAP), and their proteins and nuclear SREBP 2 (N-SREBP2) protein expressions were assessed by Western blotting. The translocation of SCAP from endoplasmic reticulum (ER) to Golgi body was observed by laser confocal microscope. Results Compared with the control group, the macrophages in the high Pi exposure group showed an obvious aggregation of neutral lipids and significantly increased contents intracellular cholesterol ester and total cholesterol (P<005). The mRNA and protein expressions of LDLR and HMGCoAR, and protein level of N-SREBP2 in macrophage nucleus in the high Pi exposure group were increased significantly in comparison to the control group (P<0.05, P<0.01). The SCAP translocated obviously from ER to Golgi body. However, above-mentioned changes were significantly suppressed by PFA treatment (high Pi plus PFA treatment group) (P<0.05, P<0.01). Furthermore, the significant increase of protein level of SCAP induced by high Pi treatment (P<0.05) was suppressed by PFA treatment, but there were no differences in SCAP mRNA expressions in each group (P>0.05). Conclusion Under high Pi condition, sodium-phosphate transporter Pit-1 mediates the entry of phosphorus ions into the macrophages. High Pi concentration in macrophages up-regulates the protein level via an post transcriptional pathway and induces the dysfunction of SCAP, which facilitates the transport of SREBP2 from ER to Golgi body. SREBP2 in Golgi body is splitted, activited and releases N-SREBP2. The N-SREBP2 translocates into the nucleus and promotes the expressions of LDLR and HMGCoAR, increasing exogenous LDL uptake and endogenous cholesterol synthesis leading abnormal accumulation of intracellular cholesterol.
