Overexpression of lipoprotein lipase in mesangial cells enhances VLDL-induced cellular lipid accmnulation and MCP-1 secretion / 中华肾脏病杂志

ABSTRACT

Objective To investigate the role of LPL in enhancing VLDL uptake in mesangial cells and modulating VLDL-mesangial interaction. Methods Human wild type LPL (LPLwt), catalytically inactive LPL (LPL194) or control alkaline phosphatase (AP) were expressed in human mesangiai cell line (HMCL) via adenoviral vectors. The expression of LPL mRNA and protein was detected by RT-PCR and immunoehemistry staining, respectively. LPL activity was assayed by radioisotope labeled liposome substrate. Cellular lipid deposition was visualized by oil red O staining and analyzed quantitatively by standard enzymatic procedures. Effect of LPL on HMCL proliferation was evaluated by colorimetric assay using MTr. MCP-1 mRNA and protein levels in treated HMCLs were determined by real-time quantitative BT-PCB and enzyme-linked immunosorbent assay respectively. For adhesion study, HMCLs were treated with VLDL for six hours, followed by one-hour incubation with Tamm-Horsfall protein-1 (THP-1) cells. Results Compared with HMCLs transfected by Ad-AP, the lever of cellular triglyceride content was sharply increased in Ad-LPLwt Wansfected HMCLs [(109.11±5.01) mg/g protein vs (23.98±3.23) mg/g protein,P<0.01] and was slightly increased in Ad-LPL194 transfected HMCLs [(36.33±2.64) mg/g protein vs (23.98±3.23) mg/g protein, P<0.05]. LPLwt amplified VLDL-driven mesangial cells proliferation. Compared to the HMCL-Ad-AP, MCP-1 mRNA and protein expression increasd by 39% (P<0.05) and 171% (P<0.01) in HMCL-Ad-LPLwt, and the amount of THP-1 cells adhering to HMCL-Ad-LPLwt was increased by 1.69-fold (P<0.05), without significant difference between HMCL-Ad-LPLI94 and HMCL-Ad-AP. Conclusions Overexpression of either active or inactive LPL in HMCLs accelerates VLDL-induced triglyceride accumulation, and enzymolysis action of LPL may be the major factor in this process. Active LPL significantly amplifies VLDL-induced proliferative effect on mesangial cells and enhances monocyte adhesion to mesangial cells through up-regulation of MCP-1. Hence, LPL may be an important contribution to initiation and progression of renal injury mediated by triglyceride-rich lipoproteins.