Immunohistochemical and biochemical detection of low density lipoprotein receptors in cultured rat mesangial cells

The expression of low density lipoprotein (LDL) receptors by cultured rat mesangial cells was demonstrated using immunohistochemical and biochemical methods. Using a mouse monoclonal anti-human LDL receptor antibody, the immunofluorescence technique was applied to cultured mesangial cells and showed granular staining. Immunoblotting analysis of the membrane fraction of cultured mesangial cells showed a single band with a protein of approximately 130,000 molecular weight. In addition, [¹²⁵I]LDL binding and the uptake of [¹²⁵I]LDL by cultured mesangial cells were studied. Binding and uptake both reached an equilibrium after about 30 min of incubation. A 50% reduction in [¹²⁵I]LDL (20 μg protein/ml) binding and uptake occurred when unlabelled LDL was added to cultures at 20-40μg protein/ml. Addition of high density lipoprotein without apoE to the culture medium did not induce competitive inhibition of [¹²⁵I]LDL binding and uptake by mesangial cells. These findings suggest that cultured mesangial cells have the capacity to express an LDL receptor that regulates the cellular uptake of LDL.