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 β-protein precursor (AβPP), the β-amyloid (Aβ) peptide and apolipoprotein E (ApoE). Full length LRP consists of a 515 kDa extracellular ligand binding α-chain and an 85 kDa membrane spanning β-chain. A soluble form of LRP (sLRP) present in human plasma retains the ability to bind ligands, including Aβ. 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.