Soluble lipoprotein receptor-related protein immunoreactive species in cell culture media and serum replacement supplements

The low-density lipoprotein receptor-related protein (LRP) is a large multifunctional cell surface membrane receptor capable of binding over 50 ligands. These include molecules important in Alzheimer's disease such as the amyloid beta-protein precursor (A beta PP), the beta-amyloid (A beta) peptide and apolipoprotein E (ApoE). Full length LRP consists of a 515 kDa extracellular ligand binding alpha-chain and an 85 kDa membrane spanning beta-chain. A soluble form of LRP (sLRP) present in human plasma retains the ability to bind ligands, including A beta. This soluble form is an ectodomain fragment generated from the membrane bound form of the receptor by proteolytic cleavage. Here we report data demonstrating that some commercial 'serum-free' supplements and 'serum-free' media contain unlisted sLRP immunoreactive species that may reflect the presence of undefined serum protein extracts in these 'serum-free' preparations. This has the potential to interfere with experimental results and interpretation in a range of cell culture studies involving LRP or any of its ligands and possibly also other serum proteins.